0000950170-23-010343 | 10-K | XBRL Viewer | Taysha Gene Therapies INC

Document and Entity Information - USD ($)	12 Months Ended
Document and Entity Information - USD ($)	Dec. 31, 2022	Mar. 28, 2023	Jun. 30, 2022
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2022
Document Fiscal Year Focus	2022
Document Fiscal Period Focus	FY
Trading Symbol	TSHA
Entity Registrant Name	Taysha Gene Therapies, Inc.
Entity Central Index Key	0001806310
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Shell Company	false
Entity File Number	001-39536
Entity Tax Identification Number	84-3199512
Entity Address, Address Line One	3000 Pegasus Park Dr
Entity Address Address Line2	Ste 1430
Entity Address, City or Town	Dallas
Entity Address, State or Province	TX
Entity Address, Postal Zip Code	75247
City Area Code	214
Local Phone Number	612-0000
Entity Common Stock, Shares Outstanding		63,473,349
Title of 12(b) Security	Common stock, par value $0.00001 per share
Security Exchange Name	NASDAQ
Entity Incorporation, State or Country Code	DE
Entity Interactive Data Current	Yes
Document Annual Report	true
Document Transition Report	false
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
ICFR Auditor Attestation Flag	false
Entity Public Float			$ 91,978,421
Auditor Name	Deloitte & Touche LLP
Auditor Location	Dallas, Texas
Auditor Firm ID	34
Documents Incorporated by Reference	DOCUMENTS INCORPORATED BY REFERENCE Portions of the registrant’s definitive Proxy Statement relating to the 2023 Annual Meeting of Stockholders are incorporated herein by reference in Part III of this Annual Report on Form 10-K. The Proxy Statement will be filed with the Securities and Exchange Commission within 120 days after the year ended December 31, 2022.

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Current assets:
Cash and cash equivalents	$ 87,880	$ 149,103
Prepaid expenses and other current assets	8,537	10,499
Total current assets	96,417	159,602
Restricted cash	2,637	2,637
Property, plant and equipment, net	14,963	50,610
Operating lease right-of-use assets	10,943
Other non-current assets	1,316	1,107
Total assets	126,276	213,956
Current liabilities
Accounts payable	10,946	21,763
Accrued expenses and other current liabilities	18,287	29,983
Deferred revenue	33,557
Total current liabilities	62,790	51,746
Build-to-suit lease liability		25,900
Term loan, net	37,967	37,192
Operating lease liability, net of current portion	20,440
Other non-current liabilities	4,130	3,735
Total liabilities	125,327	118,573
Commitments and contingencies - Note 11
Stockholders' equity
Preferred stock, $0.00001 par value per share; 10,000,000 shares authorized and no shares issued and outstanding as of December 31, 2022 and December 31, 2021
Common stock, $0.00001 par value per share; 200,000,000 shares authorized and 63,207,507 and 38,473,945 issued and outstanding as of December 31, 2022 and December 31, 2021 respectively	1
Additional paid-in capital	402,389	331,032
Accumulated deficit	(401,441)	(235,649)
Total stockholders’ equity	949	95,383
Total liabilities and stockholders' equity	$ 126,276	$ 213,956

Consolidated Statements of Operations - USD ($)	12 Months Ended
Consolidated Statements of Operations - USD ($)	Dec. 31, 2022	Dec. 31, 2021
Income Statement [Abstract]
Revenues	$ 2,502,000
Operating expenses:
Research and development	91,169,000	$ 131,943,000
General and administrative	37,360,000	41,324,000
Impairment of long-lived assets	36,420,000	0
Total operating expenses	164,949,000	173,267,000
Loss from operations	(162,447,000)	(173,267,000)
Other income (expense):
Interest income	249,000	172,000
Interest expense	(3,798,000)	(1,428,000)
Other expense	(18,000)
Total other expense, net	(3,567,000)	(1,256,000)
Net loss	$ (166,014,000)	$ (174,523,000)
Net loss per common share, basic	$ (3.78)	$ (4.64)
Net loss per common share, diluted	$ (3.78)	$ (4.64)
Weighted average common shares outstanding, basic	43,952,015	37,650,566
Weighted average common shares outstanding, diluted	43,952,015	37,650,566

Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Cumulative Effect, Period of Adoption, Adjustment	Offering to Astellas	Public Offering	At-the-Market Offering	Common Stock	Common Stock Offering to Astellas	Common Stock Public Offering	Common Stock At-the-Market Offering	Additional Paid-in Capital	Additional Paid-in Capital Offering to Astellas	Additional Paid-in Capital Public Offering	Additional Paid-in Capital At-the-Market Offering	Accumulated Deficit	Accumulated Deficit Cumulative Effect, Period of Adoption, Adjustment
Balance at Dec. 31, 2020	$ 251,302									$ 312,428				$ (61,126)
Balance, shares at Dec. 31, 2020						37,761,435
Stock-based compensation	18,604									18,604
Issuance of common stock, upon vesting and settlement of restricted stock units, shares						712,510
Net loss	(174,523)													(174,523)
Balance at Dec. 31, 2021	$ 95,383	$ 222								331,032				(235,649)	$ 222
Balance, shares at Dec. 31, 2021	38,473,945					38,473,945
Accounting Standards Update [Extensible Enumeration]	Accounting Standards Update 2016-02 [Member]
Stock-based compensation	$ 18,275									18,275
Issuance of common stock			$ 13,764	$ 27,457	$ 11,609				$ 1		$ 13,764	$ 27,457	$ 11,608
Issuance of common stock, shares							7,266,342	14,765,226	2,000,000
Issuance of common stock, upon vesting and settlement of restricted stock units, shares						628,921
Issuance of common stock under ESPP	253									253
Issuance of common stock under ESPP, shares						73,073
Net loss	(166,014)													(166,014)
Balance at Dec. 31, 2022	$ 949					$ 1				$ 402,389				$ (401,441)
Balance, shares at Dec. 31, 2022	63,207,507					63,207,507

Consolidated Statements of Cash Flows - USD ($)	12 Months Ended
Consolidated Statements of Cash Flows - USD ($)	Dec. 31, 2022	Dec. 31, 2021
Cash flows from operating activities
Net loss	$ (166,014,000)	$ (174,523,000)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation expense	1,172,000	492,000
Research and development license expense	1,250,000	9,750,000
Stock-based compensation	18,043,000	18,184,000
Impairment of long-lived assets	36,420,000	0
Non-cash lease expense	1,315,000
Other	906,000	388,000
Changes in operating assets and liabilities:
Prepaid expenses and other assets	2,088,000	(3,361,000)
Accounts payable	(7,804,000)	14,494,000
Accrued expenses and other liabilities	(9,323,000)	17,542,000
Deferred revenue	33,557,000
Due to related party		(8,000)
Net cash used in operating activities	(88,390,000)	(117,042,000)
Cash flows from investing activities
Purchase of research and development license	(4,250,000)	(6,250,000)
Purchase of property, plant and equipment	(20,619,000)	(15,304,000)
Other	(61,000)
Net cash used in investing activities	(24,930,000)	(21,554,000)
Cash flows from financing activities
Proceeds from Term Loan, net		39,957,000
Payment of shelf registration costs	(358,000)	(360,000)
Proceeds from common stock issuances under ESPP	253,000
Other	(1,042,000)	(514,000)
Net cash provided by financing activities	52,097,000	39,083,000
Net decrease in cash, cash equivalents and restricted cash	(61,223,000)	(99,513,000)
Cash, cash equivalents and restricted cash at the beginning of the period	151,740,000	251,253,000
Cash, cash equivalents and restricted cash at the end of the period	90,517,000	151,740,000
Cash and cash equivalents	87,880,000	149,103,000
Restricted cash	2,637,000	2,637,000
Supplemental disclosure of cash flow information:
Cash paid for interest	2,775,000	641,000
Supplemental disclosure of noncash investing and financing activities:
Property, plant and equipment in accounts payable and accrued expenses	4,002,000	8,282,000
Acquisition of property, plant and equipment funded by landlord		606,000
Right-of-use assets obtained in exchange for lease liabilities	23,432,000
Offering costs not yet paid	387,000	141,000
Purchase of research and development license not yet paid		3,500,000
Build-to-suit lease liability		$ 26,250,000
Public Offering
Cash flows from financing activities
Net proceeds from issuance of common stock	27,717,000
Offering to Astellas
Cash flows from financing activities
Net proceeds from issuance of common stock	13,887,000
At-the-Market Offering
Cash flows from financing activities
Net proceeds from issuance of common stock	$ 11,640,000

Significant Accounting Policies	12 Months Ended
Significant Accounting Policies	Dec. 31, 2022
Accounting Policies [Abstract]
Significant Accounting Policies	Note 2—Significant Accounting Policies Basis of Presentation The Company’s financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“U.S. GAAP”) as determined by the Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“ASC”) and include all adjustments necessary for the fair presentation of the Company’s financial position for the periods presented. Principles of Consolidation The accompanying consolidated financial statements include the accounts of Taysha and its wholly owned subsidiaries. All intercompany transactions and balances have been eliminated in consolidation. Emerging Growth Company From time to time, new accounting pronouncements are issued by the FASB, or other standard setting bodies and adopted by the Company as of the specified effective date. Unless otherwise discussed, the impact of recently issued standards that are not yet effective will not have a material impact on the Company’s financial statements upon adoption. Under the Jumpstart Our Business Startups Act of 2012, as amended, the Company meets the definition of an emerging growth company and has elected the extended transition period for complying with new or revised accounting standards, which delays the adoption of these accounting standards until they would apply to private companies. Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of expenses during the reporting period. The most significant estimates and assumptions in the Company’s financial statements relate to the determination of the fair value of the common stock prior to the IPO (as an input into stock-based compensation), estimating manufacturing accruals and accrued or prepaid research and development expenses, the measurement of impairment of long-lived assets, and the allocation of consideration received in connection with the Astellas Transactions. These estimates and assumptions are based on current facts, historical experience and various other factors believed to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities and the recording of expenses that are not readily apparent from other sources. Actual results may differ materially from these estimates. To the extent there are material differences between the estimates and actual results, the Company’s future results of operations will be affected. Risks and Uncertainties The Company is subject to risks common to companies in the biotechnology industry, including, but not limited to, development by the Company or its competitors of technological innovations, risks of failure of clinical studies, dependence on key personnel, protection of proprietary technology, compliance with government regulations, and ability to transition from preclinical manufacturing to commercial production of products. The Company’s product candidates require approvals from the FDA and comparable foreign regulatory agencies prior to commercial sales in their respective jurisdictions. There can be no assurance that any product candidates will receive the necessary approvals. If the Company was denied approval, approval was delayed or the Company was unable to maintain approval for any product candidate, it could have a materially adverse impact on the Company. Segments Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision-maker in making decisions regarding resource allocation and assessing performance. The Company views its operations and manages its business as a single operating segment, which is the business of developing AAV-based gene therapies for the treatment of rare monogenic diseases of the central nervous system. As of December 31, 2022 and 2021, the Company did not have any significant long-lived assets located outside of the United States. Revenue Recognition The Company recognizes revenue in accordance with ASC 606, Revenue from Contracts with Customers. Revenues consist of activities in connection with the Astellas Transactions, including the exclusive option to license intellectual property and the performance of research and development activities. See Note 6 for additional information. The Company evaluates the agreement to determine if the other party is a customer, and then determines the units of account within the agreement to determine which promised goods or services are distinct. In order for a promised good or service to be considered "distinct” under ASC 606, the customer can benefit from the good or service either on its own or together with other resources that are readily available to the customer (i.e., the good or service is capable of being distinct), and the entity’s promise to transfer the good or service to the customer is separately identifiable from other promises in the contract (i.e., the promise to transfer the good or service is distinct within the context of the contract). For any units of account, that fall within the scope of ASC 606, where the other party is a customer, the Company (i) evaluates the separate performance obligation(s) under each contract, (ii) determines the transaction price, (iii) allocates the transaction price to each performance obligation considering the estimated standalone selling prices of the services and (iv) recognizes revenue when, or as, the Company satisfies the performance obligation(s). At the inception of an arrangement that includes options for a customer to purchase additional services or products at agreed upon prices in the future, the Company evaluates whether each option provides a material right. An option that provides a material right will be accounted for as a separate performance obligation. As part of the accounting for arrangements under ASC 606, the Company must use significant judgment to determine the performance obligations, the transaction price, and the standalone selling price (“SSP”) for each performance obligation identified in the contract for the allocation of the transaction price. The SSP is the price at which an entity would sell a promised good or service separately to a customer. Management estimates the SSP of each of the identified performance obligations, maximizing the use of observable inputs. Because the Company has not sold the same goods or services in its contracts separately to any customers on a standalone basis, the Company utilizes similar observable transactions in the marketplace or estimates the SSP of each performance obligation in its customer arrangements at contract inception based on either (1) its estimate of costs to be incurred to fulfill its obligations associated with the performance obligation, plus a reasonable margin, or (2) an estimate that reflects the discount that the customer would obtain when exercising its option adjusted for (i) any discount that the customer could receive without exercising the option and (ii) the likelihood that the option will be exercised. The Company allocates the transaction price to each performance obligation in proportion to its SSP. A performance obligation is satisfied and revenue is recognized when “control” of the promised good or service is transferred, either over time or at a point in time, to the customer. A customer obtains control of a good or service if it has the ability to (1) direct its use and (2) obtain substantially all of the remaining benefits from it. Amounts received prior to satisfying the revenue recognition criteria listed above are recorded as deferred revenue in the accompanying consolidated balance sheets. Amounts expected to be recognized as revenue within 12 months of the balance sheet date are classified as current deferred revenue. Amounts not expected to be recognized as revenue within the following 12 months of the balance sheet date are classified as deferred revenue, net of current portion. The Company does not incur commission or other costs to fulfill customer contracts and as such, no capitalized contract costs are recorded on the consolidated balance sheets. Cash and Cash Equivalents Cash and cash equivalents consist of funds held in a standard checking account and standard savings account. The Company considers all highly liquid investments with an original maturity of three months or less at the date of purchase to be cash equivalents. As of December 31, 2022 and 2021, respectively, the Company had no cash equivalents. Restricted Cash Restricted cash consists of cash that the Company has placed in an escrow account which is pledged as collateral under certain lease agreements and letters of credit. Concentrations of Credit Risk Financial instruments that potentially subject the Company to significant concentration of credit risk consist primarily of cash and cash equivalents. Periodically, the Company may maintain deposits in financial institutions in excess of government insured limits. On March 10, 2023, the California Department of Financial Protection and Innovation closed the Silicon Valley Bank, Santa Clara, California (“SVB”), and appointed the FDIC as receiver. On March 12, 2023, the Treasury Department announced that depositors of SVB will have access to all of their money starting March 13, 2023. On March 14, 2023, the Company regained access to the full amount of its cash that was deposited with SVB. Management believes that the Company is not exposed to significant credit risk as the Company’s deposits are held at financial institutions that management continues to believe to be of high credit quality. The Company has not experienced any losses on these deposits. Fair Value of Financial Instruments The Company’s financial assets and liabilities are accounted for in accordance with ASC 820, Fair Value Measurements and Disclosures which defines fair value as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. The fair value hierarchy requires an entity to maximize the use of observable inputs when measuring fair value and classifies those inputs into three levels: Level 1—Observable inputs, such as quoted prices in active markets for identical assets or liabilities. Level 2—Inputs other than Level 1 inputs that are either directly or indirectly observable, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the instrument’s anticipated life. Level 3—Unobservable inputs in which there is little or no market data, which require the reporting entity to develop its own assumptions. To the extent the valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair values requires more judgement. Accordingly, the degree of judgement exercised by the Company in determining fair value is greatest for instruments categorized as Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. The carrying values reported in the Company’s consolidated balance sheets for cash and cash equivalents, prepaid expenses and other current assets, accounts payable, accrued expenses and other current liabilities are reasonable estimates of their fair values due to the short-term nature of these items. Deferred Offering Costs The Company capitalizes costs directly associated with equity financings until such financings are consummated, at which time such costs are recorded in additional paid-in capital against the gross proceeds of the equity financings. Costs associated with the shelf registration statement on Form S-3, filed with the SEC on October 5, 2021 have been capitalized and will be reclassified to additional paid-in capital on a pro rata basis when the Company completes offerings under the shelf registration. At the end of the three-year term of the shelf registration, the remaining deferred offering costs, if any, will be charged to operations. Property, Plant and Equipment, net Property, plant and equipment, net are stated at cost less accumulated depreciation and consist of computer equipment, laboratory equipment and leasehold improvements. Directly identifiable payroll and payroll-related costs incurred in connection with the build-out of the Company’s cGMP manufacturing facility were capitalized into the cost basis of the asset to the extent that such costs had been incurred to bring the asset to the condition and location for its intended use. Depreciation expense is recognized using the straight-line method over its estimated useful life of three to seven years. Upon retirement or sale, the cost of assets disposed of and the related accumulated depreciation are removed from the accounts and any resulting gain or loss is included in loss from operations. Expenditures for repairs and maintenance are charged to expense as incurred. Leases Effective January 1, 2022, the Company adopted ASC 842, Leases using the modified retrospective approach and utilizing the effective dates as its date of initial application. As a result, prior periods are presented in accordance with the previous guidance in ASC 840, Leases. At the inception of an arrangement, the Company determines whether the arrangement is or contains a lease based on the unique facts and circumstances present in the arrangement. Leases with a term greater than one year are recognized on the balance sheet as right-of-use assets and short-term and long-term lease liabilities, as applicable. Operating lease liabilities and their corresponding right-of-use assets are initially recorded based on the present value of lease payments over the expected remaining lease term. Certain adjustments to the right-of-use asset may be required for items such as incentives received. The interest rate implicit in lease contracts is typically not readily determinable. As a result, the Company utilizes its incremental borrowing rate to discount lease payments, which reflects the fixed rate at which the Company could borrow on a collateralized basis the amount of the lease payments in the same currency, for a similar term, in a similar economic environment. To estimate its incremental borrowing rate, a credit rating applicable to the Company is estimated using a synthetic credit rating analysis since the Company does not currently have a rating agency-based credit rating. The Company has elected not to recognize leases with an original term of one year or less on the balance sheet. The Company typically only includes an initial lease term in its assessment of a lease arrangement. Options to renew a lease are not included in the Company’s assessment unless there is reasonable certainty that the Company will renew. Assumptions made by the Company at the commencement date are re-evaluated upon occurrence of certain events, including a lease modification. A lease modification results in a separate contract when the modification grants the lessee an additional right of use not included in the original lease and when lease payments increase commensurate with the standalone price for the additional right of use. When a lease modification results in a separate contract, it is accounted for in the same manner as a new lease. The Company has elected to account for lease and non-lease components together as a single lease component for all underlying assets. Build-to-Suit Lease In the Company’s lease arrangement in Durham, North Carolina (as described in Note 4), the Company was involved in the construction of the build-out. To the extent the Company is involved with the structural improvements of the construction project or takes construction risk prior to the commencement of a lease, accounting guidance ASC Topic 840, Leases, requires the Company to be considered the owner for accounting purposes of these types of projects during the construction period. In such cases, the Company records an asset in property, plant and equipment on its consolidated balance sheet equal to the fair value of the building shell, and a corresponding build-to-suit lease obligation on its consolidated balance sheet representing the amounts paid by the lessor. As part of its adoption of ASC 842, the Company de-recognized the building asset and corresponding financing obligation recorded on the Company’s consolidated balance sheets as of January 1, 2022, in accordance with the ASC 842 transition guidance. Impairment of Long-Lived Assets The Company evaluates its long-lived assets, which consist of property, plant and equipment as well as right-of-use assets, for impairment whenever events or changes in circumstances indicate that the carrying amount of such assets may not be recoverable. Recoverability of assets to be held and used is measured by a comparison of the carrying amount of an asset to the future undiscounted net cash flows expected to be generated by the asset. If such assets are considered to be impaired, the impairment to be recognized is measured by the amount by which the carrying amount of the asset group exceeds the fair value of the asset group. In November 2022, the Company decided not to continue the build-out of the North Carolina manufacturing facility, resulting in a change in use of this asset group. The Company performed an undiscounted cash flow analysis over the long-lived assets associated with the manufacturing facility and determined that the carrying value of the asset group is not recoverable. Significant assumptions used to determine this non-recurring fair value measurement include the time to sublease the facility, the amount of sublease income expected to be generated over the remaining lease term, and the discount rate used to measure the present value of the net cash flows associated with this asset group. The impairment charge represented the entire amount of the asset group’s carrying amount as of the date of impairment. The Company recorded a non-cash impairment charge of $36.4 million (see Note 3) in connection with the North Carolina manufacturing facility which was allocated on a pro rata basis across the assets within the asset group. No impairment losses were recorded for the year ended December 31, 2021. Debt Issuance Costs Debt issuance costs are deferred and presented as a reduction to long-term debt. Debt issuance costs are amortized using the effective interest rate method over the term of the loan. Amortization of deferred debt issuance costs are included in interest expense in the consolidated statements of operations. Research and Development The Company has entered into research and development contracts with research institutions and other companies. These agreements are generally cancelable, and related payments are recorded as research and development expenses as incurred. Payments for these activities are based on the terms of the individual agreements, which may differ from the pattern of costs incurred, and are reflected on the consolidated balance sheets as prepaid or accrued expenses. The Company records accruals for estimated ongoing research costs. When evaluating the adequacy of the accrued liabilities, the Company analyzes progress of the studies, including the phase or completion of events, invoices received and contracted costs. Research and development costs primarily consist of payroll, stock-based compensation, certain manufacturing costs, laboratory costs and other supplies, and the cost to acquire license. Costs incurred in obtaining technology licenses through asset acquisitions are charged to research and development expense if the licensed technology has not reached technological feasibility and has no alternative future use. Payments of such upfront license fees and subsequent development milestones are included as investing cash outflows in the consolidated statements of cash flows. Stock-Based Compensation The Company accounts for all stock-based payments to employees and non-employees, including grants of stock options, restricted stock awards, or RSAs, and restricted stock units, or RSUs, based on their respective grant date fair values. The Company estimates the fair value of stock option grants using the Black-Scholes option pricing model, which is affected principally by the estimated fair value of shares of the Company’s common stock and requires management to make a number of other assumptions, including the expected life of the option, the volatility of the underlying shares, the risk-free interest rate and expected dividends. Expected volatility is based on the historical share volatility of a set of comparable publicly traded companies over a period of time equal to the expected term of the options. Due to the lack of historical exercise history, the expected term of the Company’s stock options is determined using the “simplified” method. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods approximately equal to the expected term of the award. Expected dividend yield is zero based on the fact that the Company has never paid cash dividends and does not expect to pay any cash dividends in the foreseeable future. Prior to September 23, 2020, the fair value of common stock underlying the Company’s stock options, RSAs and RSUs was estimated by the Company’s board of directors considering, among other things, contemporaneous valuations of the Company’s common stock prepared by unrelated third-party valuation firms. After the IPO, the fair value of common stock is based on the closing price of the Company’s common stock as reported on the date of the grant. The RSAs and RSUs are valued based on the fair value of the Company’s common stock on the date of grant. The Company expenses stock-based compensation related to stock options, RSAs and RSUs over the requisite service period using the straight-line method. Stock-based compensation costs are initially recorded in research and development expense or general and administrative expense in the consolidated statements of operations in a manner consistent with the classification of the respective employee’s payroll costs. A portion of stock-based compensation expense that relates to employees who were directly involved in the buildout of the Company’s cGMP manufacturing facility have been capitalized into the cost basis of that asset to the extent that such costs were incurred to bring the asset to the condition and location for its intended use. Forfeitures are recorded as they occur. Income Taxes Income taxes are recorded in accordance with ASC 740, Income Taxes (“ASC 740”), which provides for deferred taxes using an asset and liability approach. The Company recognizes deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the financial statements or tax returns. Deferred tax assets and liabilities are determined based on the difference between the financial statement and tax bases of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse, and net operating loss (“NOL”) carryforwards and research and development tax credit (“R&D Credit”) carryforwards. Valuation allowances are provided, if based upon the weight of available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized. The Company has recorded a full valuation allowance to reduce its net deferred income tax assets to zero. In the event the Company were to determine that it would be able to realize some or all of its deferred income tax assets in the future, an adjustment to the deferred income tax asset valuation allowance would increase income in the period such determination was made. The Company accounts for uncertain tax positions in accordance with the provisions of ASC 740. When uncertain tax positions exist, the Company recognizes the tax benefit of tax positions to the extent that the benefit would more likely than not be realized assuming examination by the taxing authority. The determination as to whether the tax benefit will more likely than not be realized is based upon the technical merits of the tax position as well as consideration of the available facts and circumstances. During the years ended December 31, 2022 and 2021, the Company recorded increases in the amount of gross unrecognized tax benefits of $3.1 million and $4.7 million, respectively. The unrecognized tax benefits, if recognized, would not affect the effective income tax rate due to the valuation allowance that currently offsets deferred tax assets. The Company does not expect the unrecognized tax benefits to change significantly over the next 12 months. The Company would recognize any corresponding interest and penalties associated with its income tax positions in income tax expense. There was no income tax interest or penalties incurred for the years ended December 31, 2022 and 2021. Comprehensive Loss Comprehensive loss is equal to net loss as presented in the accompanying consolidated statements of operations. Recently Adopted Accounting Pronouncements In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842), as amended, with guidance regarding the accounting for and disclosure of leases. This update requires lessees to recognize the liabilities related to all leases, including operating leases, with a term greater than 12 months on the balance sheets. This update also requires lessees and lessors to disclose key information about their leasing transactions. Effective January 1, 2022, the Company adopted ASU 2016-02 using the modified retrospective approach and utilizing the effective date as its date of initial application. As a result, prior periods are presented in accordance with the previous guidance in ASC 840. The Company elected the following practical expedients, which must be elected as a package and applied consistently to all of its leases at the transition date (including those for which the entity is a lessee or a lessor): i) the Company did not reassess whether any expired or existing contracts are or contain leases; ii) the Company did not reassess the lease classification for any expired or existing leases (that is, all existing leases that were classified as operating leases in accordance with ASC 840 are classified as operating leases, and all existing leases that were classified as capital leases in accordance with ASC 840 are classified as finance leases); and iii) the Company did not reassess initial direct costs for any existing leases. For leases that existed prior to the date of initial application of ASC 842 (which were previously classified as operating leases), a lessee may elect to use either the total lease term measured at lease inception under ASC 840 or the remaining lease term as of the date of initial application of ASC 842 in determining the period for which to measure its incremental borrowing rate. In transition to ASC 842, the Company utilized the remaining lease term of its leases in determining the appropriate incremental borrowing rates. The adoption of this standard resulted in the recognition of operating lease right-of-use assets and operating lease liabilities of $18.4 million and $19.1 million, respectively, on the Company’s consolidated balance sheet at adoption relating to its operating leases. The lease liabilities were determined based on the present value of the remaining minimum lease payments. Upon adoption of ASC 842, the Company also (i) derecognized the build-to-suit lease asset of $26.3 million previously presented in property, plant and equipment, (ii) derecognized the build-to-suit lease liability of $26.5 million, and (iii) eliminated $0.7 million of deferred rent liabilities and tenant improvement allowances as of January 1, 2022 as these liabilities are reflected in the operating lease right-of-use assets. In adopting ASU 2016-02, the Company recorded a total one-time adjustment of $0.2 million to the opening balance of accumulated deficit as of January 1, 2022 related to the de-recognition of the build-to-suit lease asset and related build-to-suit lease obligation. The adoption did not have a material impact on accumulated deficit and on the consolidated statements of operations and cash flows. In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes (“ASU 2019-12”), which is intended to simplify various aspects related to accounting for income taxes. ASU 2019-12 removes certain exceptions to the general principles in ASC 740 and also clarifies and amends existing guidance to improve consistent application. This guidance is effective for fiscal years beginning after December 15, 2021, and interim periods within fiscal years beginning after December 15, 2022, with early adoption permitted. The Company adopted this guidance on January 1, 2022. There is no impact to the consolidated balance sheets as of December 31, 2022 because of the full valuation allowance position taken for deferred taxes.

Supplemental Financial Information

12 Months Ended

Dec. 31, 2022

Balance Sheet Related Disclosures [Abstract]

Supplemental Financial Information

Note 3—Supplemental Financial Information

Property, plant and equipment, net consisted of the following (in thousands):


	December 31, 2022			December 31, 2021
Leasehold improvements	$	2,091		$	2,067
Laboratory equipment		2,868			1,095
Computer equipment		1,115			1,098
Furniture and fixtures		898			845
Construction in progress		9,633			46,004
		16,605			51,109
Accumulated depreciation		(1,642	)		(499	)
Property, plant and equipment, net	$	14,963		$	50,610

In November 2022, the Company recognized a non-cash impairment charge of $36.4 million for the manufacturing facility asset group, of which $26.3 million relates to construction in progress and finance lease right-of-use assets. The impairment charge was estimated using a discounted cash flow model and recorded in the consolidated statements of operations for the year ended December 31, 2022. Included in construction in progress at December 31, 2021 was $45.8 million of costs associated with the Build-to-Suit lease (see Note 4),

which included $2.0 million of capitalized payroll and payroll-related costs. Property, plant and equipment, net includes $1.3 million of assets capitalized as finance leases as of December 31, 2022.

Depreciation expense was $1.2 million and $0.5 million for the years ended December 31, 2022 and 2021, respectively.

Accrued expenses and other current liabilities consisted of the following (in thousands):


	December 31, 2022		December 31, 2021
Accrued research and development	$	8,190	$	11,895
Accrued compensation		2,519		7,703
Accrued property, plant and equipment		2,081		2,644
Accrued clinical trial		1,473		1,659
Accrued severance		1,463		—
Lease liabilities, current portion		1,521		—
Accrued professional and consulting fees		390		1,091
Accrued license fees		—		3,500
Other		650		1,491
Total accrued expenses and other current liabilities	$	18,287	$	29,983

Prepaid expenses and other current assets consisted of the following (in thousands):


	December 31, 2022		December 31, 2021
Prepaid research and development	$	4,840	$	5,218
Prepaid clinical trial		2,119		3,298
Deferred offering costs		724		545
Prepaid insurance		388		148
Prepaid bonus		18		427
Other		448		863
Total prepaid expenses and other current assets	$	8,537	$	10,499

Leases

12 Months Ended

Dec. 31, 2022

Leases [Abstract]

Leases

Note 4— Leases

The Company leases certain office, laboratory, and manufacturing space.

Dallas Lease

On January 11, 2021, the Company entered into a lease agreement (the “Dallas Lease”) with Pegasus Park, LLC, a Delaware limited liability company (the “Dallas Landlord”), pursuant to which the Company will lease approximately 15,000 square feet of office space at 3000 Pegasus Park Drive, Dallas, Texas 75247 (the “Office Space”).

The Dallas Lease commenced on May 27, 2021, and has a term of approximately ten years. The Company has an option to extend the term of the Dallas Lease for one additional period of five years.

The Company has a right of first refusal with respect to certain additional adjacent office space before the Dallas Landlord accepts any offer for such space.

The Dallas Landlord has the right to terminate the Dallas Lease, or the Company’s right to possess the Office Space without terminating the Dallas Lease, upon specified events of default, including the Company’s failure to pay rent in a timely manner and upon the occurrence of certain events of insolvency with respect to the Company.

Dallas Lease Expansion

On December 14, 2021, the Company amended the Dallas Lease (the “Dallas Lease Amendment”) with the Dallas Landlord, pursuant to which the Company will lease approximately 18,000 square feet of office space adjacent to the Office Space at 3000 Pegasus Park Drive, Dallas, Texas 75247 (the “Expansion Premises”).

The Dallas Lease Amendment commenced on July 1, 2022, and has a term of approximately ten years.

The Company is obligated to pay operating costs and utilities applicable to the Expansion Premises. Total future minimum lease payments under the Dallas Lease Amendment over the initial 10 year term are approximately $6.0 million. The Company will be responsible for costs of constructing interior improvements within the Expansion Premises that exceed a $40.00 per rentable square foot construction allowance provided by the Dallas Landlord.

The Company has a right of first refusal with respect to certain additional office space on the 15th floor at 3000 Pegasus Park Drive, Dallas, Texas 75247 before the Dallas Landlord accepts any offer for such space.

Durham Lease

On December 17, 2020, the Company entered into a lease agreement (the “Durham Lease”) with Patriot Park Partners II, LLC, a Delaware limited liability company (the “Durham Landlord”), pursuant to which the Company agreed to lease approximately 187,500 square feet of a manufacturing facility located at 5 National Way, Durham, North Carolina (the “Facility”). The Durham Lease commenced on April 1, 2021 and is expected to have a term of approximately fifteen years and six months. The Company has two options to extend the term of the Durham Lease, each for a period of an additional five years.

The Company was not required to provide a security deposit in connection with its entry into the Durham Lease. The Company will be responsible for constructing interior improvements within the Facility. The Company was required to place $2.6 million in an escrow account which will be released when the improvements are substantially complete. The escrow funds are recorded as restricted cash on the consolidated balance sheet as of December 31, 2022. The Durham Landlord has the right to terminate the Durham Lease upon specified events of default, including the Company’s failure to pay rent in a timely manner and upon the occurrence of certain events of insolvency with respect to the Company.

In accordance with ASC Topic 840, Leases, the Company was deemed, for accounting purposes only, to be the owner of the entire leased Facility, including the building shell, during the construction period because of the Company’s level of direct financial and operational involvement in the substantial tenant improvements, including structural improvements, required to build out the Facility. As a result, the Company capitalized approximately $26.3 million as a build-to-suit asset within property, plant and equipment, net and recognized a corresponding build-to-suit lease financing obligation as a liability on its consolidated balance sheets equal to the fair value of the existing building shell using comparable market prices per square foot for similar space for public real estate transactions in the surrounding area at commencement of construction. Additionally, construction costs incurred as part of the build-out and tenant improvements were also capitalized within property, plant and equipment, net. Costs of approximately $45.8 million were capitalized during the year ended December 31, 2021, related to both equipment purchases and the build-out of the leased Facility. As part of its adoption of ASC 842, the Company de-recognized the building asset and corresponding financing obligation recorded on the Company’s consolidated balance sheets as of January 1, 2022, in accordance with the ASC 842 transition guidance.

Summary of all lease costs recognized under ASC 842

The following table summarizes the lease costs recognized under ASC 842 and other information pertaining to the Company's operating leases for the year ended December 31, 2022 (in thousands):


	For the Year Ended December 31, 2022

Operating lease cost	$	2,873
Variable lease cost		452
Total lease cost	$	3,325

Supplemental information related to the remaining lease term and discount rate are as follows:


	December 31, 2022
Weighted average remaining lease term (in years) - Finance leases		3.88
Weighted average remaining lease term (in years) - Operating leases		11.45

Weighted average discount rate - Finance leases		10.51	%
Weighted average discount rate - Operating leases		7.72	%

Supplemental cash flow information related to the Company's operating leases are as follows (in thousands):


	For the year ended December 31, 2022
Operating cash flows for operating leases	$	2,486

As of December 31, 2022, future minimum commitments under ASC 842 under the Company's operating and finance leases were as follows (in thousands):


Year Ending December 31,	Operating			Finance
2023	$	2,819		$	454
2024		2,918			454
2025		3,021			454
2026		2,485			325
2027		2,577			73
Thereafter		19,721			—
Total lease payments		33,541			1,760
Less: imputed interest		(11,900	)		(308	)
Total lease liabilities	$	21,641		$	1,452
Lease liabilities, current		1,201			320
Lease liabilities, non-current		20,440			1,132
Total lease liabilities	$	21,641		$	1,452

In 2021, the Company signed a lease agreement pursuant to which the Company will lease equipment to generate its supply of electricity, which has not yet commenced for accounting purposes as of December 31, 2022. This lease agreement provides for total remaining lease payments of $3.5 million over the 10-year lease term, which is not included in the maturity table above.

The following table summarizes aggregate lease commitments as of December 31, 2021 (in thousands) under ASC 840:


Year Ending December 31,
2022	$	4,848
2023		4,201
2024		4,301
2025		4,372
2026		3,868
Thereafter		30,563
Total Lease Commitments	$	52,153

Loan with Silicon Valley Bank

12 Months Ended

Dec. 31, 2022

Debt Disclosure [Abstract]

Loan with Silicon Valley Bank

Note 5 – Loan with Silicon Valley Bank

On August 12, 2021 (the “Closing Date”), the Company entered into a Loan and Security Agreement (the “Term Loan Agreement”), by and among the Company, the lenders party thereto from time to time (the “Lenders”) and Silicon Valley Bank, as administrative agent and collateral agent for the Lenders (“Agent”). The Term Loan Agreement provides for (i) on the Closing Date, $40.0 million aggregate principal amount of term loans available through December 31, 2021, (ii) from January 1, 2022 until September 30, 2022, an additional $20.0 million term loan facility available at the Company’s option upon having three distinct and active clinical stage programs, determined at the discretion of the Agent, at the time of draw, (iii) from October 1, 2022 until March 31, 2023, an additional $20.0 million term loan facility available at the Company’s option upon having three distinct and active clinical stage programs, determined at the discretion of the Agent, at the time of draw and (iv) from April 1, 2023 until December 31, 2023, an additional $20.0 million term loan facility available upon approval by the Agent and the Lenders (collectively, the “Term Loans”). The Company drew $30.0 million in term loans on the Closing Date and $10.0 million in term loans in December 2021. The Company did not draw on the additional $20.0 million tranche prior to its expiration on September 30, 2022.

The interest rate applicable to the Term Loans is the greater of (a) the WSJ Prime Rate plus 3.75% or (b) 7.00% per annum. As of December 31, 2022, the interest rate was 11.25%. The Term Loans are interest only from the Closing Date through August 31, 2024, after which the Company is required to pay equal monthly installments of principal through August 1, 2026, the maturity date.

The Term Loans could have been prepaid in full through August 12, 2022 with payment of a 2.00% prepayment premium, after which they may be prepaid in full through August 12, 2023 with payment of a 1.00% prepayment premium, after which they may be prepaid in full with no prepayment premium. An additional final payment of 7.5% of the amount of Terms Loans advanced by the Lenders (“Exit Fee”) will be due upon prepayment or repayment of the Term Loans in full. The Exit Fee of $3.0 million was recorded as debt discount and has also been fully accrued within non-current liabilities as of December 31, 2022. The debt discount is being accreted using the effective interest method over the term of the Term Loans within interest expense in the consolidated statements of operations.

The obligations under the Term Loan Agreement are secured by a perfected security interest in all of the Company’s assets except for intellectual property and certain other customarily excluded property pursuant to the terms of the Term Loan Agreement. There are no financial covenants and no warrants associated with the Term Loan Agreement. The Term Loan Agreement contains various covenants that limit the Company’s ability to engage in specified types of transactions without the consent of the Lenders which include, among others, incurring or assuming certain debt; merging, consolidating or acquiring all or substantially all of the capital stock or property of another entity; changing the nature of the Company’s business; changing the Company’s organizational structure or type; licensing, transferring or disposing of certain assets; granting certain types of liens on the Company’s assets; making certain investments; and paying cash dividends.

The Term Loan Agreement also contains customary representations and warranties, and also includes customary events of default, including payment default, breach of covenants, change of control, and material adverse effects. The Company was in compliance with all covenants under the Term Loan Agreement as of December 31, 2022. Upon the occurrence of an event of default, a default interest rate of an additional 5% per annum may be applied to the outstanding loan balances, and the Lenders may declare all outstanding obligations immediately due and payable and exercise all of its rights and remedies as set forth in the Term Loan Agreement and under applicable law.

During the year ended December 31, 2022, the Company recognized interest expense related to the Term Loan of $3.7 million.

Future principal debt payments on the Term Loan Agreement as of December 31, 2022 are as follows (in thousands):


Year Ending December 31,
2023	$	—
2024		6,667
2025		20,000
2026		13,333
Total principal payments		40,000
Unamortized debt discount		(2,033	)
Term Loan, net	$	37,967

- Definition

The entire disclosure for information about short-term and long-term debt arrangements, which includes amounts of borrowings under each line of credit, note payable, commercial paper issue, bonds indenture, debenture issue, own-share lending arrangements and any other contractual agreement to repay funds, and about the underlying arrangements, rationale for a classification as long-term, including repayment terms, interest rates, collateral provided, restrictions on use of assets and activities, whether or not in compliance with debt covenants, and other matters important to users of the financial statements, such as the effects of refinancing and noncompliance with debt covenants.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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Reference 6: http://www.xbrl.org/2003/role/disclosureRef
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-Paragraph 1
-Subparagraph (SX 210.4-08(c))
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Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
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Reference 9: http://www.xbrl.org/2003/role/disclosureRef
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-URI https://asc.fasb.org/extlink&oid=123466505&loc=SL123495334-112611

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
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Reference 12: http://www.xbrl.org/2003/role/disclosureRef
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Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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-URI https://asc.fasb.org/extlink&oid=123466505&loc=SL123495323-112611

+ Details

Astellas Agreements

12 Months Ended

Dec. 31, 2022

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Astellas Agreements

Note 7—Research, Collaboration, Grant and License Agreements

UT Southwestern Agreement

On November 19, 2019, the Company entered into a research, collaboration and license agreement (“UT Southwestern Agreement”) with the Board of Regents of the University of Texas System on behalf of The University of Southwestern Medical Center (“UT Southwestern”). Under the UT Southwestern Agreement, UT Southwestern is primarily responsible for preclinical development activities with respect to licensed products for use in certain specified indications (up to IND-enabling studies), and the Company is responsible for all subsequent clinical development and commercialization activities with respect to the licensed products. UT Southwestern will conduct such preclinical activities for a two-year period under mutually agreed upon sponsored research agreements that were entered into beginning in April 2020. During the initial research phase, the Company has the right to expand the scope of specified indications under the UT Southwestern Agreement.

In connection with the UT Southwestern Agreement, the Company obtained an exclusive, worldwide, royalty-free license under certain patent rights of UT Southwestern and a non-exclusive, worldwide, royalty-free license under certain know-how of UT Southwestern, in each case to make, have made, use, sell, offer for sale and import licensed products for use in certain specified indications. Additionally, the Company obtained a non-exclusive, worldwide, royalty-free license under certain patents and know-how of UT Southwestern for use in all human uses, with a right of first refusal to obtain an exclusive license under certain of such patent rights and an option to negotiate an exclusive license under other of such patent rights. The Company is required to use commercially reasonable efforts to develop, obtain regulatory approval for, and commercialize at least one licensed product.

On April 2, 2020, the Company amended the UT Southwestern Agreement to include the addition of another licensed product and certain indications, and a right of first refusal to the Company over certain patient dosing patents. No additional consideration was transferred in connection with this amendment. In March 2022, the Company and UT Southwestern mutually agreed to revise the payment schedules and current performance expectations of the current sponsored research agreements under the UT Southwestern Agreement and defer payments by fifteen months.

The UT Southwestern Agreement expires on a country-by-country and licensed product-by-licensed product basis upon the expiration of the last valid claim of a licensed patent in such country for such licensed product. After the initial research term, the Company may terminate the agreement, on an indication-by-indication and licensed product-by-licensed product basis, at any time upon specified written notice to UT Southwestern. Either party may terminate the agreement upon an uncured material breach of the agreement or insolvency of the other party.

In November 2019, as partial consideration for the license rights granted under the UT Southwestern Agreement, the Company issued 2,179,000 shares of its common stock, or 20% of its then outstanding fully-diluted common stock, to UT Southwestern. The Company does not have any future milestone or royalty obligations to UT Southwestern under the UT Southwestern Agreement other than costs related to maintenance of patents.

Queen’s Agreement

On February 21, 2020, the Company entered into a license agreement with Queen’s (the “Queen’s Agreement”) to obtain the exclusive perpetual, royalty-bearing license, with the right to sublicense through multiple tiers, under certain patent rights and know-how of Queen’s, including certain improvements to such patent rights and know-how, to develop products in any field which use one or more valid claims of the patents licensed under the Queen’s Agreement (the “Licensed Patents”), or the technology, information and intellectual property related to the patents licensed under the Queen’s Agreement (together with the Licensed Patents, the “Licensed Products”), and to make, have made, use, sell, offer for sale, import and export Licensed Products and otherwise exploit such patents and know-how for use in certain specified indications. In exchange for the rights granted to the Company, the Company made a cash payment of $3.0 million in April 2020 which is recorded in research and development expenses in the consolidated statements of operations since the acquired license does not have an alternative future use. The Company is obligated to make aggregate cash payments of up to $10.0 million upon the completion of a combination of regulatory milestones and up to $10.0 million upon the completion of a combination of commercial milestones. In further consideration of the rights granted, beginning with the Company’s first commercial sale of the Licensed Products, the Company will also pay an annual earned royalty in the low single digits on net sales of Licensed Products, subject to certain customary reductions, and a percentage of non-royalty sublicensing revenue ranging in the low double digits. Royalties are payable, on a Licensed Products-by-Licensed Products and a country-by-country basis, until expiration of the last valid claim of a Licensed Patent covering such Licensed Products in such country and the expiration of any regulatory exclusivity for such Licensed Products in such country.

No additional milestone payments were made in connection with the Queen’s Agreement during the years ended December 31, 2022 and 2021.

Abeona CLN1 Agreements

In August 2020, the Company entered into license and inventory purchase agreements with Abeona Therapeutics Inc. (“Abeona”) for worldwide exclusive rights to certain intellectual property rights and know-how relating to the research, development and manufacture of ABO-202, an AAV-based gene therapy for CLN1 disease (also known as infantile Batten disease). Under the terms of the agreements, the Company made initial cash payments to Abeona of $3.0 million for the license fee and $4.0 million for purchase of clinical materials and reimbursement for previously incurred development costs in October 2020. In exchange for the license rights, the Company recorded an aggregate of $7.0 million within research and development expenses in the consolidated statements of operations for the year ended December 31, 2020 since the acquired license or acquired inventory do not have an alternative future use. The Company is obligated to make up to $26.0 million in regulatory-related milestones and up to $30.0 million in sales-related milestones per licensed CLN1 product. The Company will also pay an annual earned royalty in the high single digits on net sales of any licensed CLN1 products. The license agreement expires on a country-by-country and licensed product-by-licensed product basis upon the expiration of the last royalty term of a licensed product. Either party may terminate the agreement upon an uncured material breach of the agreement or insolvency of the other party. The Company may terminate the license agreement for convenience upon specified prior written notice to Abeona.

In December 2021, a regulatory milestone was triggered in connection with this agreement and therefore the Company recorded $3.0 million within research and development expenses in the consolidated statements of operations for the year ended December 31, 2021. The milestone fee was paid in January 2022 and classified as an investing cash outflow in the consolidated statements of cash flows for the year ended December 31, 2022. No additional milestone payments were triggered in connection with this agreement during the year ended December 31, 2022.

Abeona Rett Agreement

On October 29, 2020, the Company entered into a license agreement (the “Abeona Rett Agreement”) with Abeona pursuant to which the Company obtained an exclusive, worldwide, royalty-bearing license, with the right to grant sublicenses under certain patents, know-how and materials originally developed by the University of North Carolina at Chapel Hill, the University of Edinburgh and Abeona to research, develop, manufacture, have manufactured, use, and commercialize licensed products for gene therapy and the use of related transgenes for Rett syndrome.

Subject to certain obligations of Abeona, the Company is required to use commercially reasonable efforts to develop at least one licensed product and commercialize at least one licensed product in the United States.

In connection with the Abeona Rett Agreement, the Company paid Abeona a one-time upfront license fee of $3.0 million which is recorded in research and development expenses in the consolidated statements of operations for the year ended December 31, 2020 since the acquired license does not have an alternative future use. The Company is obligated to pay Abeona up to $26.5 million in regulatory-related milestones and up to $30.0 million in sales-related milestones per licensed Rett product and high single-digit royalties on net sales of licensed Rett products. Royalties are payable on a licensed product-by-licensed product and country-by-country basis until the latest of the expiration or revocation or complete rejection of the last licensed patent covering such licensed product in the country where the licensed

product is sold, the loss of market exclusivity in such country where the product is sold, or, if no licensed product exists in such country and no market exclusivity exists in such country, ten years from first commercial sale of such licensed product in such country.

The Abeona Rett Agreement expires on a country-by-country and licensed product-by-licensed product basis upon the expiration of the last royalty term of a licensed product. Either party may terminate the agreement upon an uncured material breach of the agreement or insolvency of the other party. The Company may terminate the agreement for convenience upon specified prior written notice to Abeona.

In March 2022, the Company’s CTA filing for TSHA-102 for the treatment of Rett Syndrome was approved by Health Canada and therefore triggered a regulatory milestone payment in connection with this agreement. The Company recorded $1.0 million within research and development expenses in the consolidated statements of operations for the year ended December 31, 2022. The $1.0 million regulatory milestone fee was paid in July 2022 and classified as an investing cash outflow in the consolidated statements of cash flows for the year ended December 31, 2022.

Acquisition of Worldwide Rights for TSHA-120 for the treatment of GAN

In March 2021, the Company acquired the exclusive worldwide rights to a clinical-stage AAV9 gene therapy program, now known as TSHA-120, for the treatment of Giant Axonal Neuropathy (“GAN”) pursuant to a license agreement with Hannah’s Hope Fund (“HHF”) for Giant Axonal Neuropathy, Inc. TSHA-120 is an intrathecally dosed AAV9 gene therapy currently being evaluated in a clinical trial for the treatment of GAN. Under the terms of the agreement, in exchange for granting the Company the exclusive worldwide rights to TSHA-120, HHF received an upfront payment of $5.5 million and will be eligible to receive clinical, regulatory and commercial milestones totaling up to $19.3 million, as well as a low, single-digit royalty on net sales upon commercialization of the product.

In exchange for the license rights, the Company recorded an aggregate of $5.5 million within research and development expenses in the consolidated statements of operations for the year ended March 31, 2021, since the acquired license does not have an alternative future use. This license fee was paid in April 2021 and has been classified as an investing outflow in the consolidated statements of cash flows for the year ended December 30, 2021. No additional milestone payments were made in connection with this agreement during the year ended December 31, 2022.

License Agreement for CLN7

In March 2022, the Company entered into a license agreement with UT Southwestern (the “CLN7 Agreement”) pursuant to which the Company obtained an exclusive worldwide, royalty-bearing license with right to grant sublicenses to develop, manufacture, use, and commercialize licensed products for gene therapy for CLN7, a form of Batten Disease. In connection with the CLN7 Agreement, the Company paid a one-time upfront license fee of $0.3 million. The Company recorded the upfront license fee in research and development expense in the consolidated statements of operations since the acquired license does not have an alternative future use. The upfront license fee was classified as an investing cash outflow in the consolidated statements of cash flows for the year ended December 31, 2022. The Company is obligated to pay UT Southwestern up to $7.7 million in regulatory-related milestones and up to $7.5 million in sales-related milestones, as well as a low, single-digit royalty on net sales upon commercialization of the product. No additional milestone payments were made in connection with this agreement during the year ended December 31, 2022.

Astellas

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Astellas Agreements

Note 6—Astellas Agreements

On October 21, 2022 (the “Effective Date”), the Company entered into the Option Agreement with Astellas, pursuant to which the Company granted to Astellas an exclusive option to obtain an exclusive, worldwide, royalty and milestone-bearing right and license (A) to research, develop, make, have made, use, sell, offer for sale, have sold, import, export and otherwise exploit, or, collectively, exploit, the product known, as of the Effective Date, as TSHA-120 (the “120 GAN Product”), and any backup products with respect thereto for use in the treatment of GAN or any other gene therapy product for use in the treatment of GAN that is controlled by Taysha or any of its affiliates or with respect to which the Company or any of its affiliates controls intellectual property rights covering the exploitation thereof, or a GAN Product, and (B) under any intellectual property rights controlled by Taysha or any of its affiliates with respect to such exploitation (the “GAN Option”). Subject to certain extensions, the GAN Option is exercisable from the Effective Date through a specified period of time following Astellas’ receipt of (i) the formal minutes from the Type B end-of-Phase 2 meeting between Taysha and the FDA in response to the Company’s meeting request sent to the FDA on September 19, 2022 for the 120 GAN Product (the “Type B end-of-Phase 2 Meeting”), (ii) all written feedback from the FDA with respect to the Type B end-of-Phase 2 Meeting, and (iii) all briefing documents sent by Taysha to the FDA with respect to the Type B end-of-Phase 2 Meeting.

Under the Option Agreement, the Company also granted to Astellas an exclusive option to obtain an exclusive, worldwide, royalty and milestone-bearing right and license (A) to exploit any Rett Product (as defined below), and (B) under any intellectual property rights controlled by Taysha or any of its affiliates with respect to such exploitation (the “Rett Option,” and together with the GAN Option, each, an “Option”). Subject to certain extensions, the Rett Option is exercisable from the Effective Date through a specified period of time following Astellas’ receipt of (i) certain clinical data from the female pediatric trial and (ii) certain specified data with respect to TSHA-102, such period, the Rett Option Period, related to (i) the product known, as of the Effective Date, as TSHA-102 and any backup products with respect thereto for use in the treatment of Rett syndrome, and (ii) any other gene therapy product for use in the treatment of Rett syndrome that is controlled by Taysha or any of its affiliates or with respect to which the Company or any of its affiliates controls intellectual property rights covering the exploitation thereof (a “Rett Product”).

The parties have agreed that, if Astellas exercises an Option, the parties will, for a specified period, negotiate a license agreement in good faith on the terms and conditions outlined in the Option Agreement, including payments by Astellas of a to be determined upfront payment, certain to be determined milestone payments, and certain to be determined royalties on net sales of GAN Products and/or Rett Products, as applicable.

During the Rett Option Period, the Company has agreed to (A) not solicit or encourage any inquiries, offers or proposals for, or that could reasonably be expected to lead to, a Change of Control (as defined in the Option Agreement), or (B) otherwise initiate a process for a potential Change of Control, in each case, without first notifying Astellas and offering Astellas the opportunity to submit an offer or proposal to the Company for a transaction that would result in a Change of Control. If Astellas fails or declines to submit any such offer within a specified period after the receipt of such notice, the Company will have the ability to solicit third party bids for a Change of Control transaction. If Astellas delivers an offer to the Company for a transaction that would result in a Change of Control, the Company and Astellas will attempt to negotiate in good faith the potential terms and conditions for such potential transaction that would result in a Change of Control for a specified period, which period may be shortened or extended by mutual agreement.

As partial consideration for the rights granted to Astellas under the Option Agreement, Astellas paid the Company the Upfront Payment, which is $20.0 million. Astellas or any of its affiliates shall have the right, in its or their discretion and upon written notice to the Company, to offset the amount of the Upfront Payment (in whole or in part, until the full amount of the Upfront Payment has been offset) against (a) any payment(s) owed to Taysha or any of its affiliates (or to any third party on behalf of the Company) under or in connection with any license agreement entered into with respect to any GAN Product or Rett Product, including, any upfront payment, milestone payment or royalties owed to Taysha or any of its affiliates (or to any third party on behalf of the Company) under or in connection with any such license agreement or (b) any amount owed to Taysha or any of its affiliates in connection with a Change of Control transaction with Astellas or any of its affiliates. As further consideration for the rights granted to Astellas under the Option Agreement, the Company and Astellas also entered into the Securities Purchase Agreement.

Securities Purchase Agreement

On October 21, 2022, the Company entered into the Securities Purchase Agreement with Astellas, pursuant to which the Company agreed to issue and sell to Astellas in a private placement (the “Private Placement”), an aggregate of 7,266,342 shares (the “Private Placement Shares”), of its common stock, for aggregate gross proceeds of $30.0 million. The Private Placement closed on October 24, 2022. Pursuant to the Securities Purchase Agreement, in connection with the Private Placement, Astellas has the right to designate one individual to attend all meetings of the Board in a non-voting observer capacity. The Company also granted Astellas certain registration rights with respect to the Private Placement Shares.

Accounting Treatment

In October 2022, upon closing of the Private Placement and transferring the 7,266,342 shares to Astellas, the Company recorded the issuance of shares at fair value. Fair value of the shares transferred to Astellas was calculated in accordance with ASC 820, Fair Value Measurement by analyzing the Company's stock price for a short period of time prior to and after the transaction date as traded on the NASDAQ. The NASDAQ trading data is considered an active market and a Level 1 measurement under ASC 820. The fair value was determined to be approximately $13.95 million or $1.92 per share. The $16.1 million difference between the $30.0 million paid by Astellas and the fair market value of shares issued was allocated to the transaction price of the Option Agreement.

The Company determined that the Option Agreement falls within the scope of ASC 606, Revenue from Contracts with Customers as the development of TSHA-102 for the treatment of Rett Syndrome and TSHA-120 for the treatment of GAN are considered ordinary activities for the Company. In accordance with ASC 606, the Company evaluated the Option Agreement and identified three separate performance obligations: (1) option to obtain licensing right to GAN, (2) option to obtain licensing right to Rett and (3) performance of research and development activities in the Rett development plan. The transaction price is determined to be $36.1 million which is comprised of the $20.0 million Upfront Payment and the $16.1 million allocated from the Private Placement.

To determine the standalone selling price ("SSP") of the Rett and GAN options, which the Company concluded to be material rights, the Company utilized the probability-weighted expected return (PWERM) method. The PWERM method contemplates the probability and timing of an option exercise. At contract inception, the Company estimated that the probability of exercise was 50% for each of the GAN and Rett options. The SSP of the Rett research and development activities was estimated using an expected cost plus margin approach. The standalone selling prices of the material rights and Rett research and development activities were then used to proportionately allocate the $36.1 million transaction price to the three performance obligations. The $36.1 million transaction price was recorded as deferred revenue on the consolidated balance sheet at the inception of the Astellas Transactions.

The following table summarizes the allocation of the transaction price to the three performance obligations at contract inception:


	Transaction Price Allocation
Option to obtain license for Rett	$	5,485
Option to obtain license for GAN		2,317
Rett research and development activities		28,257
Total	$	36,059

Revenue allocated to the material rights will be recognized at a point in time when each option period expires or when a decision is made by Astellas to exercise or not exercise each option. Revenue from the Rett research and development activities will be recognized as activities are performed using an input method, according to the costs incurred as related to the total costs expected to be incurred to satisfy the performance obligation. The transfer of control occurs over this time period and is a reliable measure of progress towards satisfying the performance obligation. Research and development services related to this performance obligation are expected to be completed by the end of 2023.

During the year ended December 31, 2022, there were no significant changes to the total estimated costs to be incurred to satisfy the performance obligation associated with the Rett research and development activities.

The Company recognized revenue of $2.5 million from Rett research and development activities for the year ended December 31, 2022. The Company had $33.6 million of deferred revenue on the consolidated balance sheet as of December 31, 2022. The Company will recognize revenues for these performance obligations as they are satisfied, which for the Rett research and development activities is expected to occur over a period of 1.0 year from December 31, 2022.

Research, Collaboration, Grant and License Agreements

12 Months Ended

Dec. 31, 2022

Research Collaboration And License Agreements [Abstract]

Research, Collaboration, Grant and License Agreements

Note 7—Research, Collaboration, Grant and License Agreements

UT Southwestern Agreement

Queen’s Agreement

No additional milestone payments were made in connection with the Queen’s Agreement during the years ended December 31, 2022 and 2021.

Abeona CLN1 Agreements

Abeona Rett Agreement

Acquisition of Worldwide Rights for TSHA-120 for the treatment of GAN

License Agreement for CLN7

Stock-Based Compensation

12 Months Ended

Dec. 31, 2022

Share-Based Payment Arrangement [Abstract]

Stock-Based Compensation

Note 8—Stock-Based Compensation

On July 1, 2020, the Company’s board of directors approved the 2020 Equity Incentive Plan (“Existing Plan”) which permits the granting of incentive stock options, non-statutory stock options, stock appreciation rights, RSAs, RSUs and other stock-based awards to employees, directors, officers and consultants. On September 16, 2020, the approval date of the New Plan (as defined below), no additional awards will be granted under the Existing Plan. The terms of the Existing Plan will continue to govern the terms of outstanding equity awards that were granted prior to approval of the New Plan.

On September 16, 2020, the Company’s stockholders approved the 2020 Stock Incentive Plan (“New Plan”), which became effective upon the execution of the underwriting agreement in connection with the IPO. The number of shares of common stock reserved for issuance under the New Plan automatically increases on January 1 of each year, for a period of ten years, from January 1, 2021 continuing through January 1, 2030, by 5% of the total number of shares of common stock outstanding on December 31 of the preceding calendar year, or a lesser number of shares as may be determined by the Company’s board of directors. On January 1, 2023, the Company’s board of directors increased the number of shares of common stock reserved for issuance under the New Plan by 3,160,375 shares.

Furthermore, on September 16, 2020, the Company’s stockholders approved the Employee Stock Purchase Plan (“ESPP”), which became effective upon the execution of the underwriting agreement in connection with the IPO. The maximum number of shares of common stock that may be issued under the ESPP will not exceed 362,000 shares of common stock, plus the number of shares of common stock that are automatically added on January 1 of each year for a period of up to ten years, commencing on the first January 1 following the IPO and ending on (and including) January 1, 2030, in an amount equal to the lesser of (i) 1.0% of the total number of shares of capital stock outstanding on December 31 of the preceding calendar year, and (ii) 724,000 shares of common stock. No shares were added to the

ESPP in 2021. On January 1, 2022 and 2023, the Company’s board of directors increased the number of shares of common stock reserved for issuance under the ESPP by 384,739 and 632,075 respectively. The Company has issued 73,073 shares of common stock under the ESPP as of December 31, 2022.

The number of shares available for grant under the Company's incentive plans were as follows:


	Existing			New
	Plan			Plan			Total
Available for grant - January 1, 2021		—			2,941,509			2,941,509
Plan adjustments and amendments		(250,778	)		1,685,712			1,434,934
Grants		—			(3,192,600	)		(3,192,600	)
Forfeitures		250,778			217,480			468,258
Available for grant - December 31, 2021		—			1,652,101			1,652,101
Plan adjustments and amendments		—			1,923,697			1,923,697
Grants		—			(4,775,676	)		(4,775,676	)
Forfeitures		—			2,267,560			2,267,560
Available for grant - December 31, 2022		—			1,067,682			1,067,682

Stock Options

On July 1, 2020, options to purchase 2,896,782 shares of common stock under the Existing Plan were awarded to certain employees and consultants of the Company with an exercise price per share of $0.80, which were expected to vest over a four-year period, all of which were subsequently cancelled (the “Cancelled Options”). The grant date fair value of the Cancelled Options was $13.8 million at the original grant date. In exchange, the Company awarded 2,518,932 RSUs on September 2, 2020, which are expected to vest over a four-year term. The Company accounted for the changes in award terms as a modification in accordance with ASC 718 Compensation – Stock Compensation. The modification was accounted for as an exchange of the original award for a new award with total compensation cost equal to the grant-date fair value of the original award plus any incremental value measured on the modification date. The Company determined that there was no incremental value as the fair value of the original award immediately before the modification was greater than the fair value of the new award immediately after the modification. Accordingly, the Company continues to recognize the remaining compensation cost of the Cancelled Options over the vesting period of the RSUs.

During the year ended December 31, 2022, options to purchase 4,775,676 shares of common stock under the New Plan were awarded with a weighted-average grant date fair value per share of $3.07. The stock options vest over one to four years and have a ten-year contractual term.

The following weighted-average assumptions were used to estimate the fair value of stock options granted during the years ended December 31, 2022 and 2021:


	Year Ended December 31,
	2022			2021
Risk-free interest rate		2.95	%		0.84	%
Expected dividend yield		—			—
Expected term (in years)		6.1			6.0
Expected volatility		78	%		75	%

The following table summarizes stock option activity during the years ended December 31, 2022 and 2021:


						Weighted
				Weighted		Average		Aggregate
				Average		Remaining		Intrinsic
	Stock			Exercise		Contractual		Value
	Options			Price		Life (in years)		(in thousands)
Outstanding at January 1, 2021		674,842		$	20.68		9.8	$	3,953
Options granted		3,192,600			24.99		—		—
Options cancelled or forfeited		(217,480	)		26.07		—		—
Outstanding at December 31, 2021		3,649,962		$	24.13		9.2	$	—
Options granted		4,775,676			4.48		—		—
Options cancelled or forfeited		(2,048,192	)		15.25		—		—
Options expired		(219,368	)		24.36		—		—
Outstanding at December 31, 2022		6,158,078		$	11.84		8.9	$	62
Options exercisable at December 31, 2022		1,225,613		$	24.88		7.3	$	—

The aggregate intrinsic value in the above table is calculated as the difference between the fair value of the Company’s common stock as of December 31, 2022 and the exercise price of the stock options. As of December 31, 2022, the total unrecognized compensation related to unvested stock option awards granted was $26.4 million, which the Company expects to recognize over a weighted-average period of approximately 2.5 years. No stock options were exercised during the period.

Restricted Stock Units

On September 2, 2020, the Company issued 331,121 RSUs to an employee under the Existing Plan; 25% of the shares of common stock underlying the RSUs vest at each anniversary over a four-year period. The RSUs are subject to a service-based vesting condition. The Company at any time may accelerate the vesting of the RSUs. Such shares are not accounted for as outstanding until they vest. As of December 31, 2022, the total unrecognized compensation related to unvested RSUs granted, including the remaining compensation cost associated with the RSUs granted on September 2, 2020 in exchange for the Cancelled Options, was $6.4 million which is expected to be amortized on a straight-line basis over a weighted-average period of approximately 1.5 years.

The Company's default tax withholding method for RSUs is the sell-to-cover method, in which shares with a market value equivalent to the tax withholding obligation are sold on behalf of the holder of the RSUs upon vesting and settlement to cover the tax withholding liability and the cash proceeds from such sales are remitted by the Company to taxing authorities.

The Company’s RSU activity for the year ended December 31, 2022 and 2021 was as follows:


				Weighted
				Average
				Grant Date
	Number			Fair Value
	of Shares			per Share
Nonvested at January 1, 2021		2,850,053		$	6.37
Restricted units granted		—			—
Vested		(712,510	)		6.37
Cancelled or forfeited		(250,778	)		5.25
Nonvested at December 31, 2021		1,886,765		$	6.52
Restricted units granted		—			—
Vested		(628,921	)		6.52
Cancelled or forfeited		—			—
Nonvested at December 31, 2022		1,257,844		$	6.52

Restricted Stock Awards

RA Session II, the Company’s former President and Chief Executive Officer, was awarded 769,058 RSAs under the Existing Plan on July 1, 2020, which are expected to vest over a three-year term, subject to continuous employment. As of December 31, 2022, the total unrecognized compensation related to unvested RSAs granted was $0.4 million which is expected to be amortized on a straight-line basis over a weighted average period of approximately 0.2 years. The fair value of these RSAs at the grant date of July 1, 2020 was $5.28 per share.

The Company’s RSA activity for the year ended December 31, 2022 and 2021 was as follows:


				Weighted
				Average
				Grant Date
	Number			Fair Value
	of Shares			per Share
Nonvested at January 1, 2021		769,058		$	5.28
Restricted stock granted		—			—
Vested		(427,083	)		5.28
Nonvested at December 31, 2021		341,975		$	5.28
Restricted stock granted		—			—
Vested		(256,481	)		5.28
Nonvested at December 31, 2022		85,494		$	5.28

Employee Stock Purchase Plan

In February 2022, the Company’s board of directors authorized the first offering under the ESPP. Under the ESPP, eligible employees may purchase shares of Taysha common stock through payroll deductions at a price equal to 85% of the lower of the fair market values of the stock as of the beginning or the end of six-month offering periods. An employee’s payroll deductions under the ESPP are limited to 15% of the employee’s compensation and employees may not purchase more than 1,800 of shares of Taysha common stock during any offering period. During the year ended December 31, 2022, stock-based compensation expense related to the ESPP was not material.

During the year ended December 31, 2022, $0.2 million of stock-based compensation expense was capitalized as part of construction in progress (see Note 3). The following table summarizes the total remaining stock-based compensation expense for the stock options, RSAs and RSUs recorded in the consolidated statements of operations for the years ended December 31, 2022 and 2021 (in thousands):


	For the Year Ended December 31,
	2022		2021
Research and development expense	$	7,608	$	8,286
General and administrative expense		10,435		9,898
Total	$	18,043	$	18,184

Income Taxes

12 Months Ended

Dec. 31, 2022

Income Tax Disclosure [Abstract]

Income Taxes

Note 10—Income Taxes

Provision for income taxes

There is no provision for income taxes because the Company has incurred operating losses and capitalized certain items for income tax purposes since its inception and maintains a full valuation allowance against its net deferred tax assets. The reported amount of income tax expense for the period differs from the amount that would result from applying the federal statutory tax rate to net loss before taxes primarily because of the change in valuation allowance.

On March 27, 2020, the CARES Act, an economic relief package in response to the COVID-19 pandemic, was signed into law. The CARES Act contains several corporate income tax provisions, including making remaining alternative minimum tax credits immediately refundable; providing a 5-year carryback of NOL carryforwards generated in tax years 2018, 2019, and 2020, and removing the 80% taxable income limitation on utilization of those NOLs if carried back to prior tax years or utilized in tax years beginning before 2021; and temporarily liberalizing the interest deductibility rules under Section 163(j) of the Tax Cuts and Jobs Act, by raising the adjusted taxable income limitation from 30% to 50% for tax years 2019 and 2020 and giving taxpayers the election of using 2019 adjusted taxable income for purposes of computing 2020 interest deductibility. The CARES Act did not have a material effect on the realizability of deferred income tax assets or tax expense in 2022 or 2021.

Beginning in 2022, the 2017 Tax Cuts and Jobs Act amended Section 174 to eliminate current-year deductibility of research and experimentation (R&E) expenditures and software development costs (collectively, R&E expenditures) and instead require taxpayers to charge their R&E expenditures to a capital account amortized over five years (15 years for expenditures attributable to R&E activity performed outside the United States). The Company generated a deferred tax asset for capitalized R&E expenditures for the year ended December 31, 2022 which is fully offset by a valuation allowance.

On August 16, 2022, President Biden signed the Inflation Reduction Act of 2022, or the Inflation Act, into law. The Inflation Act contains certain tax measures, including a corporate alternative minimum tax of 15% on some large corporations and an excise tax of 1% on corporate stock buy-backs. The various provisions of the Inflation Act do not have a material impact on the Company’s consolidated financial statements.

The effective tax rate of the Company's provision (benefit) for income taxes differs from the federal statutory rate as follows:


	For the Year Ended December 31,
	2022			2021
Statutory rate		21.00	%		21.00	%
State tax		0.25	%		0.20	%
Research and development tax credits		4.91	%		7.68	%
Other permanent differences		(0.55	)%		(1.12	)%
Change in valuation allowance		(25.61	)%		(27.76	)%
Income tax provision (benefit)		0.00	%		0.00	%

Deferred tax assets and valuation allowance

Deferred tax assets reflect the tax effects of NOLs, tax credit carryovers, and temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. At December 31, 2022 and 2021, the significant components of the Company’s net deferred tax assets and liabilities are as follows (in thousands):


	For the Year Ended December 31,
	2022			2021
Deferred tax assets:
Net operating loss carryforwards	$	45,609		$	37,005
Tax credit carryforwards		23,216			14,813
Accruals and reserves		689			1,467
Other		1			103
Intangibles		4,607			4,169
Non-qualified stock options		3,647			674
R&E expenditures		15,563			—
Lease liabilities		4,574			—
Right-of-use asset impairments		5,525			—
Total deferred tax assets		103,431			58,231
Deferred tax liabilities
Right-of-use assets		(2,308	)		—
Fixed assets		(47	)		—
Total deferred tax liabilities		(2,355	)		—
Valuation allowance		(101,076	)		(58,231	)
Net deferred taxes	$	—		$	—

The valuation allowance is equal to the total net deferred tax asset amounts as of December 31, 2022 and 2021. ASC 740 requires that the tax benefit of net operating losses, temporary differences and credit carryforwards be recorded as an asset to the extent that management assesses that realization is "more likely than not." Realization of the future tax benefits is dependent on the Company's ability to generate sufficient taxable income within the carryforward period. Because of the Company's recent history of operating losses, management believes that recognition of the deferred tax assets net of liabilities arising from the above-mentioned future tax benefits is currently not likely to be realized and, accordingly, has provided a valuation allowance.

The valuation allowance increased by $42.8 million during the year ended December 31, 2022 and by $48.4 million during the year ended December 31, 2021.

As of December 31, 2022, there were net federal operating losses of $216.3 million, state operating losses of $4.5 million, federal tax credit carryforward of $30.2 million, and state tax credit carryforward of $1.3 million. The net operating losses and state tax credit carryforward do not expire. As of December 31, 2021, there were net federal operating losses of $175.6 million, state operating losses of $4.1 million, federal tax credit carryforward of $19.0 million, and state tax credit carryforward of less than $1.0 million. The federal tax credit carryforward will expire in 2040. The Company files federal, foreign and state income tax returns and, in the normal course of business, the Company is subject to examination by these taxing authorities. All periods since Inception are subject to examination by these taxing authorities, where applicable. There are currently no pending income tax examinations.

Pursuant to Section 382 of the Internal Revenue Code, certain substantial changes in the Company's ownership may result in a limitation on the amount of NOL carryforwards and tax credit carryforwards that may be used in future years. Utilization of the NOL and tax credit carryforwards may be subject to a substantial annual limitation under Section 382 of the Internal Revenue Code of 1986 due to ownership change limitations that have occurred previously or that could occur in the future. These ownership changes may limit the amount of NOL and tax credit carryforwards that can be utilized annually to offset future taxable income and tax, respectively. The Company has completed a study to assess whether an ownership change has occurred through December 31, 2022. Based on this analysis, several ownership changes were identified in 2020. As a result of the ownership changes, there were no NOLs or research credits being permanently limited. As of December 31, 2022, there are $2.9 million of gross NOLs that are however subject to an annual limitation. The Company could experience additional ownership changes subsequent to December 31, 2022, which may result in additional limitations on the utilization of NOL carryforwards and credits.

- Definition

The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 21
-URI https://asc.fasb.org/extlink&oid=121826272&loc=d3e32857-109319

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SAB Topic 11.C)
-URI https://asc.fasb.org/extlink&oid=122134291&loc=d3e330215-122817

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 17
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=121826272&loc=d3e32809-109319

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB TOPIC 6.I.5.Q1)
-URI https://asc.fasb.org/extlink&oid=122134291&loc=d3e330036-122817

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 14
-URI https://asc.fasb.org/extlink&oid=121826272&loc=d3e32705-109319

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 270
-Section 50
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=6424409&loc=d3e44925-109338

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-URI https://asc.fasb.org/topic&trid=2144680

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=6424122&loc=d3e41874-109331

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(h)(2))
-URI https://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690

+ Details

Significant Accounting Policies (Policies)	12 Months Ended
Significant Accounting Policies (Policies)	Dec. 31, 2022
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The Company’s financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“U.S. GAAP”) as determined by the Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“ASC”) and include all adjustments necessary for the fair presentation of the Company’s financial position for the periods presented.
Principles of Consolidation	Principles of Consolidation The accompanying consolidated financial statements include the accounts of Taysha and its wholly owned subsidiaries. All intercompany transactions and balances have been eliminated in consolidation.
Emerging Growth Company	Emerging Growth Company From time to time, new accounting pronouncements are issued by the FASB, or other standard setting bodies and adopted by the Company as of the specified effective date. Unless otherwise discussed, the impact of recently issued standards that are not yet effective will not have a material impact on the Company’s financial statements upon adoption. Under the Jumpstart Our Business Startups Act of 2012, as amended, the Company meets the definition of an emerging growth company and has elected the extended transition period for complying with new or revised accounting standards, which delays the adoption of these accounting standards until they would apply to private companies.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of expenses during the reporting period. The most significant estimates and assumptions in the Company’s financial statements relate to the determination of the fair value of the common stock prior to the IPO (as an input into stock-based compensation), estimating manufacturing accruals and accrued or prepaid research and development expenses, the measurement of impairment of long-lived assets, and the allocation of consideration received in connection with the Astellas Transactions. These estimates and assumptions are based on current facts, historical experience and various other factors believed to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities and the recording of expenses that are not readily apparent from other sources. Actual results may differ materially from these estimates. To the extent there are material differences between the estimates and actual results, the Company’s future results of operations will be affected.
Risks and Uncertainties	Risks and Uncertainties The Company is subject to risks common to companies in the biotechnology industry, including, but not limited to, development by the Company or its competitors of technological innovations, risks of failure of clinical studies, dependence on key personnel, protection of proprietary technology, compliance with government regulations, and ability to transition from preclinical manufacturing to commercial production of products. The Company’s product candidates require approvals from the FDA and comparable foreign regulatory agencies prior to commercial sales in their respective jurisdictions. There can be no assurance that any product candidates will receive the necessary approvals. If the Company was denied approval, approval was delayed or the Company was unable to maintain approval for any product candidate, it could have a materially adverse impact on the Company.
Segments	Segments Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision-maker in making decisions regarding resource allocation and assessing performance. The Company views its operations and manages its business as a single operating segment, which is the business of developing AAV-based gene therapies for the treatment of rare monogenic diseases of the central nervous system. As of December 31, 2022 and 2021, the Company did not have any significant long-lived assets located outside of the United States.
Revenue Recognition	Revenue Recognition The Company recognizes revenue in accordance with ASC 606, Revenue from Contracts with Customers. Revenues consist of activities in connection with the Astellas Transactions, including the exclusive option to license intellectual property and the performance of research and development activities. See Note 6 for additional information. The Company evaluates the agreement to determine if the other party is a customer, and then determines the units of account within the agreement to determine which promised goods or services are distinct. In order for a promised good or service to be considered "distinct” under ASC 606, the customer can benefit from the good or service either on its own or together with other resources that are readily available to the customer (i.e., the good or service is capable of being distinct), and the entity’s promise to transfer the good or service to the customer is separately identifiable from other promises in the contract (i.e., the promise to transfer the good or service is distinct within the context of the contract). For any units of account, that fall within the scope of ASC 606, where the other party is a customer, the Company (i) evaluates the separate performance obligation(s) under each contract, (ii) determines the transaction price, (iii) allocates the transaction price to each performance obligation considering the estimated standalone selling prices of the services and (iv) recognizes revenue when, or as, the Company satisfies the performance obligation(s). At the inception of an arrangement that includes options for a customer to purchase additional services or products at agreed upon prices in the future, the Company evaluates whether each option provides a material right. An option that provides a material right will be accounted for as a separate performance obligation. As part of the accounting for arrangements under ASC 606, the Company must use significant judgment to determine the performance obligations, the transaction price, and the standalone selling price (“SSP”) for each performance obligation identified in the contract for the allocation of the transaction price. The SSP is the price at which an entity would sell a promised good or service separately to a customer. Management estimates the SSP of each of the identified performance obligations, maximizing the use of observable inputs. Because the Company has not sold the same goods or services in its contracts separately to any customers on a standalone basis, the Company utilizes similar observable transactions in the marketplace or estimates the SSP of each performance obligation in its customer arrangements at contract inception based on either (1) its estimate of costs to be incurred to fulfill its obligations associated with the performance obligation, plus a reasonable margin, or (2) an estimate that reflects the discount that the customer would obtain when exercising its option adjusted for (i) any discount that the customer could receive without exercising the option and (ii) the likelihood that the option will be exercised. The Company allocates the transaction price to each performance obligation in proportion to its SSP. A performance obligation is satisfied and revenue is recognized when “control” of the promised good or service is transferred, either over time or at a point in time, to the customer. A customer obtains control of a good or service if it has the ability to (1) direct its use and (2) obtain substantially all of the remaining benefits from it. Amounts received prior to satisfying the revenue recognition criteria listed above are recorded as deferred revenue in the accompanying consolidated balance sheets. Amounts expected to be recognized as revenue within 12 months of the balance sheet date are classified as current deferred revenue. Amounts not expected to be recognized as revenue within the following 12 months of the balance sheet date are classified as deferred revenue, net of current portion. The Company does not incur commission or other costs to fulfill customer contracts and as such, no capitalized contract costs are recorded on the consolidated balance sheets.
Cash and Cash Equivalents	Cash and Cash Equivalents Cash and cash equivalents consist of funds held in a standard checking account and standard savings account. The Company considers all highly liquid investments with an original maturity of three months or less at the date of purchase to be cash equivalents. As of December 31, 2022 and 2021, respectively, the Company had no cash equivalents.
Restricted Cash	Restricted Cash Restricted cash consists of cash that the Company has placed in an escrow account which is pledged as collateral under certain lease agreements and letters of credit.
Concentrations of Credit Risk	Concentrations of Credit Risk Financial instruments that potentially subject the Company to significant concentration of credit risk consist primarily of cash and cash equivalents. Periodically, the Company may maintain deposits in financial institutions in excess of government insured limits. On March 10, 2023, the California Department of Financial Protection and Innovation closed the Silicon Valley Bank, Santa Clara, California (“SVB”), and appointed the FDIC as receiver. On March 12, 2023, the Treasury Department announced that depositors of SVB will have access to all of their money starting March 13, 2023. On March 14, 2023, the Company regained access to the full amount of its cash that was deposited with SVB. Management believes that the Company is not exposed to significant credit risk as the Company’s deposits are held at financial institutions that management continues to believe to be of high credit quality. The Company has not experienced any losses on these deposits.
Fair Value of Financial Instruments	Fair Value of Financial Instruments The Company’s financial assets and liabilities are accounted for in accordance with ASC 820, Fair Value Measurements and Disclosures which defines fair value as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. The fair value hierarchy requires an entity to maximize the use of observable inputs when measuring fair value and classifies those inputs into three levels: Level 1—Observable inputs, such as quoted prices in active markets for identical assets or liabilities. Level 2—Inputs other than Level 1 inputs that are either directly or indirectly observable, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the instrument’s anticipated life. Level 3—Unobservable inputs in which there is little or no market data, which require the reporting entity to develop its own assumptions. To the extent the valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair values requires more judgement. Accordingly, the degree of judgement exercised by the Company in determining fair value is greatest for instruments categorized as Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. The carrying values reported in the Company’s consolidated balance sheets for cash and cash equivalents, prepaid expenses and other current assets, accounts payable, accrued expenses and other current liabilities are reasonable estimates of their fair values due to the short-term nature of these items.
Deferred Offering Costs	Deferred Offering Costs The Company capitalizes costs directly associated with equity financings until such financings are consummated, at which time such costs are recorded in additional paid-in capital against the gross proceeds of the equity financings. Costs associated with the shelf registration statement on Form S-3, filed with the SEC on October 5, 2021 have been capitalized and will be reclassified to additional paid-in capital on a pro rata basis when the Company completes offerings under the shelf registration. At the end of the three-year term of the shelf registration, the remaining deferred offering costs, if any, will be charged to operations.
Property Plant and Equipment, net	Property, Plant and Equipment, net Property, plant and equipment, net are stated at cost less accumulated depreciation and consist of computer equipment, laboratory equipment and leasehold improvements. Directly identifiable payroll and payroll-related costs incurred in connection with the build-out of the Company’s cGMP manufacturing facility were capitalized into the cost basis of the asset to the extent that such costs had been incurred to bring the asset to the condition and location for its intended use. Depreciation expense is recognized using the straight-line method over its estimated useful life of three to seven years. Upon retirement or sale, the cost of assets disposed of and the related accumulated depreciation are removed from the accounts and any resulting gain or loss is included in loss from operations. Expenditures for repairs and maintenance are charged to expense as incurred.
Leases	Leases Effective January 1, 2022, the Company adopted ASC 842, Leases using the modified retrospective approach and utilizing the effective dates as its date of initial application. As a result, prior periods are presented in accordance with the previous guidance in ASC 840, Leases. At the inception of an arrangement, the Company determines whether the arrangement is or contains a lease based on the unique facts and circumstances present in the arrangement. Leases with a term greater than one year are recognized on the balance sheet as right-of-use assets and short-term and long-term lease liabilities, as applicable. Operating lease liabilities and their corresponding right-of-use assets are initially recorded based on the present value of lease payments over the expected remaining lease term. Certain adjustments to the right-of-use asset may be required for items such as incentives received. The interest rate implicit in lease contracts is typically not readily determinable. As a result, the Company utilizes its incremental borrowing rate to discount lease payments, which reflects the fixed rate at which the Company could borrow on a collateralized basis the amount of the lease payments in the same currency, for a similar term, in a similar economic environment. To estimate its incremental borrowing rate, a credit rating applicable to the Company is estimated using a synthetic credit rating analysis since the Company does not currently have a rating agency-based credit rating. The Company has elected not to recognize leases with an original term of one year or less on the balance sheet. The Company typically only includes an initial lease term in its assessment of a lease arrangement. Options to renew a lease are not included in the Company’s assessment unless there is reasonable certainty that the Company will renew. Assumptions made by the Company at the commencement date are re-evaluated upon occurrence of certain events, including a lease modification. A lease modification results in a separate contract when the modification grants the lessee an additional right of use not included in the original lease and when lease payments increase commensurate with the standalone price for the additional right of use. When a lease modification results in a separate contract, it is accounted for in the same manner as a new lease. The Company has elected to account for lease and non-lease components together as a single lease component for all underlying assets.
Build-to-Suit Lease	Build-to-Suit Lease In the Company’s lease arrangement in Durham, North Carolina (as described in Note 4), the Company was involved in the construction of the build-out. To the extent the Company is involved with the structural improvements of the construction project or takes construction risk prior to the commencement of a lease, accounting guidance ASC Topic 840, Leases, requires the Company to be considered the owner for accounting purposes of these types of projects during the construction period. In such cases, the Company records an asset in property, plant and equipment on its consolidated balance sheet equal to the fair value of the building shell, and a corresponding build-to-suit lease obligation on its consolidated balance sheet representing the amounts paid by the lessor. As part of its adoption of ASC 842, the Company de-recognized the building asset and corresponding financing obligation recorded on the Company’s consolidated balance sheets as of January 1, 2022, in accordance with the ASC 842 transition guidance.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets The Company evaluates its long-lived assets, which consist of property, plant and equipment as well as right-of-use assets, for impairment whenever events or changes in circumstances indicate that the carrying amount of such assets may not be recoverable. Recoverability of assets to be held and used is measured by a comparison of the carrying amount of an asset to the future undiscounted net cash flows expected to be generated by the asset. If such assets are considered to be impaired, the impairment to be recognized is measured by the amount by which the carrying amount of the asset group exceeds the fair value of the asset group. In November 2022, the Company decided not to continue the build-out of the North Carolina manufacturing facility, resulting in a change in use of this asset group. The Company performed an undiscounted cash flow analysis over the long-lived assets associated with the manufacturing facility and determined that the carrying value of the asset group is not recoverable. Significant assumptions used to determine this non-recurring fair value measurement include the time to sublease the facility, the amount of sublease income expected to be generated over the remaining lease term, and the discount rate used to measure the present value of the net cash flows associated with this asset group. The impairment charge represented the entire amount of the asset group’s carrying amount as of the date of impairment. The Company recorded a non-cash impairment charge of $36.4 million (see Note 3) in connection with the North Carolina manufacturing facility which was allocated on a pro rata basis across the assets within the asset group. No impairment losses were recorded for the year ended December 31, 2021.
Debt Issuance Costs	Debt Issuance Costs Debt issuance costs are deferred and presented as a reduction to long-term debt. Debt issuance costs are amortized using the effective interest rate method over the term of the loan. Amortization of deferred debt issuance costs are included in interest expense in the consolidated statements of operations.
Research and Development	Research and Development The Company has entered into research and development contracts with research institutions and other companies. These agreements are generally cancelable, and related payments are recorded as research and development expenses as incurred. Payments for these activities are based on the terms of the individual agreements, which may differ from the pattern of costs incurred, and are reflected on the consolidated balance sheets as prepaid or accrued expenses. The Company records accruals for estimated ongoing research costs. When evaluating the adequacy of the accrued liabilities, the Company analyzes progress of the studies, including the phase or completion of events, invoices received and contracted costs. Research and development costs primarily consist of payroll, stock-based compensation, certain manufacturing costs, laboratory costs and other supplies, and the cost to acquire license. Costs incurred in obtaining technology licenses through asset acquisitions are charged to research and development expense if the licensed technology has not reached technological feasibility and has no alternative future use. Payments of such upfront license fees and subsequent development milestones are included as investing cash outflows in the consolidated statements of cash flows.
Stock-Based Compensation	Stock-Based Compensation The Company accounts for all stock-based payments to employees and non-employees, including grants of stock options, restricted stock awards, or RSAs, and restricted stock units, or RSUs, based on their respective grant date fair values. The Company estimates the fair value of stock option grants using the Black-Scholes option pricing model, which is affected principally by the estimated fair value of shares of the Company’s common stock and requires management to make a number of other assumptions, including the expected life of the option, the volatility of the underlying shares, the risk-free interest rate and expected dividends. Expected volatility is based on the historical share volatility of a set of comparable publicly traded companies over a period of time equal to the expected term of the options. Due to the lack of historical exercise history, the expected term of the Company’s stock options is determined using the “simplified” method. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods approximately equal to the expected term of the award. Expected dividend yield is zero based on the fact that the Company has never paid cash dividends and does not expect to pay any cash dividends in the foreseeable future. Prior to September 23, 2020, the fair value of common stock underlying the Company’s stock options, RSAs and RSUs was estimated by the Company’s board of directors considering, among other things, contemporaneous valuations of the Company’s common stock prepared by unrelated third-party valuation firms. After the IPO, the fair value of common stock is based on the closing price of the Company’s common stock as reported on the date of the grant. The RSAs and RSUs are valued based on the fair value of the Company’s common stock on the date of grant. The Company expenses stock-based compensation related to stock options, RSAs and RSUs over the requisite service period using the straight-line method. Stock-based compensation costs are initially recorded in research and development expense or general and administrative expense in the consolidated statements of operations in a manner consistent with the classification of the respective employee’s payroll costs. A portion of stock-based compensation expense that relates to employees who were directly involved in the buildout of the Company’s cGMP manufacturing facility have been capitalized into the cost basis of that asset to the extent that such costs were incurred to bring the asset to the condition and location for its intended use. Forfeitures are recorded as they occur.
Income Taxes	Income Taxes Income taxes are recorded in accordance with ASC 740, Income Taxes (“ASC 740”), which provides for deferred taxes using an asset and liability approach. The Company recognizes deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the financial statements or tax returns. Deferred tax assets and liabilities are determined based on the difference between the financial statement and tax bases of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse, and net operating loss (“NOL”) carryforwards and research and development tax credit (“R&D Credit”) carryforwards. Valuation allowances are provided, if based upon the weight of available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized. The Company has recorded a full valuation allowance to reduce its net deferred income tax assets to zero. In the event the Company were to determine that it would be able to realize some or all of its deferred income tax assets in the future, an adjustment to the deferred income tax asset valuation allowance would increase income in the period such determination was made. The Company accounts for uncertain tax positions in accordance with the provisions of ASC 740. When uncertain tax positions exist, the Company recognizes the tax benefit of tax positions to the extent that the benefit would more likely than not be realized assuming examination by the taxing authority. The determination as to whether the tax benefit will more likely than not be realized is based upon the technical merits of the tax position as well as consideration of the available facts and circumstances. During the years ended December 31, 2022 and 2021, the Company recorded increases in the amount of gross unrecognized tax benefits of $3.1 million and $4.7 million, respectively. The unrecognized tax benefits, if recognized, would not affect the effective income tax rate due to the valuation allowance that currently offsets deferred tax assets. The Company does not expect the unrecognized tax benefits to change significantly over the next 12 months. The Company would recognize any corresponding interest and penalties associated with its income tax positions in income tax expense. There was no income tax interest or penalties incurred for the years ended December 31, 2022 and 2021.
Comprehensive Loss	Comprehensive Loss Comprehensive loss is equal to net loss as presented in the accompanying consolidated statements of operations.
Recently Adopted Accounting Pronouncements	Recently Adopted Accounting Pronouncements In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842), as amended, with guidance regarding the accounting for and disclosure of leases. This update requires lessees to recognize the liabilities related to all leases, including operating leases, with a term greater than 12 months on the balance sheets. This update also requires lessees and lessors to disclose key information about their leasing transactions. Effective January 1, 2022, the Company adopted ASU 2016-02 using the modified retrospective approach and utilizing the effective date as its date of initial application. As a result, prior periods are presented in accordance with the previous guidance in ASC 840. The Company elected the following practical expedients, which must be elected as a package and applied consistently to all of its leases at the transition date (including those for which the entity is a lessee or a lessor): i) the Company did not reassess whether any expired or existing contracts are or contain leases; ii) the Company did not reassess the lease classification for any expired or existing leases (that is, all existing leases that were classified as operating leases in accordance with ASC 840 are classified as operating leases, and all existing leases that were classified as capital leases in accordance with ASC 840 are classified as finance leases); and iii) the Company did not reassess initial direct costs for any existing leases. For leases that existed prior to the date of initial application of ASC 842 (which were previously classified as operating leases), a lessee may elect to use either the total lease term measured at lease inception under ASC 840 or the remaining lease term as of the date of initial application of ASC 842 in determining the period for which to measure its incremental borrowing rate. In transition to ASC 842, the Company utilized the remaining lease term of its leases in determining the appropriate incremental borrowing rates. The adoption of this standard resulted in the recognition of operating lease right-of-use assets and operating lease liabilities of $18.4 million and $19.1 million, respectively, on the Company’s consolidated balance sheet at adoption relating to its operating leases. The lease liabilities were determined based on the present value of the remaining minimum lease payments. Upon adoption of ASC 842, the Company also (i) derecognized the build-to-suit lease asset of $26.3 million previously presented in property, plant and equipment, (ii) derecognized the build-to-suit lease liability of $26.5 million, and (iii) eliminated $0.7 million of deferred rent liabilities and tenant improvement allowances as of January 1, 2022 as these liabilities are reflected in the operating lease right-of-use assets. In adopting ASU 2016-02, the Company recorded a total one-time adjustment of $0.2 million to the opening balance of accumulated deficit as of January 1, 2022 related to the de-recognition of the build-to-suit lease asset and related build-to-suit lease obligation. The adoption did not have a material impact on accumulated deficit and on the consolidated statements of operations and cash flows. In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes (“ASU 2019-12”), which is intended to simplify various aspects related to accounting for income taxes. ASU 2019-12 removes certain exceptions to the general principles in ASC 740 and also clarifies and amends existing guidance to improve consistent application. This guidance is effective for fiscal years beginning after December 15, 2021, and interim periods within fiscal years beginning after December 15, 2022, with early adoption permitted. The Company adopted this guidance on January 1, 2022. There is no impact to the consolidated balance sheets as of December 31, 2022 because of the full valuation allowance position taken for deferred taxes.

Supplemental Financial Information (Tables)

12 Months Ended

Dec. 31, 2022

Balance Sheet Related Disclosures [Abstract]

Schedule of Property, Plant and Equipment

Property, plant and equipment, net consisted of the following (in thousands):


	December 31, 2022			December 31, 2021
Leasehold improvements	$	2,091		$	2,067
Laboratory equipment		2,868			1,095
Computer equipment		1,115			1,098
Furniture and fixtures		898			845
Construction in progress		9,633			46,004
		16,605			51,109
Accumulated depreciation		(1,642	)		(499	)
Property, plant and equipment, net	$	14,963		$	50,610

Schedule of Accrued Expenses and Other Current Labilities

Accrued expenses and other current liabilities consisted of the following (in thousands):


	December 31, 2022		December 31, 2021
Accrued research and development	$	8,190	$	11,895
Accrued compensation		2,519		7,703
Accrued property, plant and equipment		2,081		2,644
Accrued clinical trial		1,473		1,659
Accrued severance		1,463		—
Lease liabilities, current portion		1,521		—
Accrued professional and consulting fees		390		1,091
Accrued license fees		—		3,500
Other		650		1,491
Total accrued expenses and other current liabilities	$	18,287	$	29,983

Schedule of Prepaid Expenses and Other Current Assets

Prepaid expenses and other current assets consisted of the following (in thousands):


	December 31, 2022		December 31, 2021
Prepaid research and development	$	4,840	$	5,218
Prepaid clinical trial		2,119		3,298
Deferred offering costs		724		545
Prepaid insurance		388		148
Prepaid bonus		18		427
Other		448		863
Total prepaid expenses and other current assets	$	8,537	$	10,499

Leases (Tables)

12 Months Ended

Dec. 31, 2022

Leases [Abstract]

Schedule of Lease Cost

The following table summarizes the lease costs recognized under ASC 842 and other information pertaining to the Company's operating leases for the year ended December 31, 2022 (in thousands):


	For the Year Ended December 31, 2022

Operating lease cost	$	2,873
Variable lease cost		452
Total lease cost	$	3,325

Schedule of Supplemental Information Related to Remaining Lease Term and Discount Rate

Supplemental information related to the remaining lease term and discount rate are as follows:


	December 31, 2022
Weighted average remaining lease term (in years) - Finance leases		3.88
Weighted average remaining lease term (in years) - Operating leases		11.45

Weighted average discount rate - Finance leases		10.51	%
Weighted average discount rate - Operating leases		7.72	%

Schedule of Supplemental Cash Flow Information Related to Operating Leases

Supplemental cash flow information related to the Company's operating leases are as follows (in thousands):


	For the year ended December 31, 2022
Operating cash flows for operating leases	$	2,486

Schedule of Future Minimum Commitments Under Company's Operating and Finance Leases

As of December 31, 2022, future minimum commitments under ASC 842 under the Company's operating and finance leases were as follows (in thousands):


Year Ending December 31,	Operating			Finance
2023	$	2,819		$	454
2024		2,918			454
2025		3,021			454
2026		2,485			325
2027		2,577			73
Thereafter		19,721			—
Total lease payments		33,541			1,760
Less: imputed interest		(11,900	)		(308	)
Total lease liabilities	$	21,641		$	1,452
Lease liabilities, current		1,201			320
Lease liabilities, non-current		20,440			1,132
Total lease liabilities	$	21,641		$	1,452

Schedule of Aggregate Lease Commitments

The following table summarizes aggregate lease commitments as of December 31, 2021 (in thousands) under ASC 840:


Year Ending December 31,
2022	$	4,848
2023		4,201
2024		4,301
2025		4,372
2026		3,868
Thereafter		30,563
Total Lease Commitments	$	52,153

Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2022

Schedule of Share Based Compensation Available for Grant under Incentive Plans

The number of shares available for grant under the Company's incentive plans were as follows:


	Existing			New
	Plan			Plan			Total
Available for grant - January 1, 2021		—			2,941,509			2,941,509
Plan adjustments and amendments		(250,778	)		1,685,712			1,434,934
Grants		—			(3,192,600	)		(3,192,600	)
Forfeitures		250,778			217,480			468,258
Available for grant - December 31, 2021		—			1,652,101			1,652,101
Plan adjustments and amendments		—			1,923,697			1,923,697
Grants		—			(4,775,676	)		(4,775,676	)
Forfeitures		—			2,267,560			2,267,560
Available for grant - December 31, 2022		—			1,067,682			1,067,682

Schedule of Restricted Stock Units Activity

The Company’s RSU activity for the year ended December 31, 2022 and 2021 was as follows:


				Weighted
				Average
				Grant Date
	Number			Fair Value
	of Shares			per Share
Nonvested at January 1, 2021		2,850,053		$	6.37
Restricted units granted		—			—
Vested		(712,510	)		6.37
Cancelled or forfeited		(250,778	)		5.25
Nonvested at December 31, 2021		1,886,765		$	6.52
Restricted units granted		—			—
Vested		(628,921	)		6.52
Cancelled or forfeited		—			—
Nonvested at December 31, 2022		1,257,844		$	6.52

Schedule of Restricted Stock Awards Activity

The Company’s RSA activity for the year ended December 31, 2022 and 2021 was as follows:


				Weighted
				Average
				Grant Date
	Number			Fair Value
	of Shares			per Share
Nonvested at January 1, 2021		769,058		$	5.28
Restricted stock granted		—			—
Vested		(427,083	)		5.28
Nonvested at December 31, 2021		341,975		$	5.28
Restricted stock granted		—			—
Vested		(256,481	)		5.28
Nonvested at December 31, 2022		85,494		$	5.28

Schedule of Total Remaining Stock-Based Compensation Expense for Stock Options, RSAs and RSUs (Detail)

The following table summarizes the total remaining stock-based compensation expense for the stock options, RSAs and RSUs recorded in the consolidated statements of operations for the years ended December 31, 2022 and 2021 (in thousands):


	For the Year Ended December 31,
	2022		2021
Research and development expense	$	7,608	$	8,286
General and administrative expense		10,435		9,898
Total	$	18,043	$	18,184

Stock Options

Schedule of Assumptions Used to Estimate Fair Value of Stock Options

The following weighted-average assumptions were used to estimate the fair value of stock options granted during the years ended December 31, 2022 and 2021:


	Year Ended December 31,
	2022			2021
Risk-free interest rate		2.95	%		0.84	%
Expected dividend yield		—			—
Expected term (in years)		6.1			6.0
Expected volatility		78	%		75	%

Schedule of Stock Option Activity

The following table summarizes stock option activity during the years ended December 31, 2022 and 2021:


						Weighted
				Weighted		Average		Aggregate
				Average		Remaining		Intrinsic
	Stock			Exercise		Contractual		Value
	Options			Price		Life (in years)		(in thousands)
Outstanding at January 1, 2021		674,842		$	20.68		9.8	$	3,953
Options granted		3,192,600			24.99		—		—
Options cancelled or forfeited		(217,480	)		26.07		—		—
Outstanding at December 31, 2021		3,649,962		$	24.13		9.2	$	—
Options granted		4,775,676			4.48		—		—
Options cancelled or forfeited		(2,048,192	)		15.25		—		—
Options expired		(219,368	)		24.36		—		—
Outstanding at December 31, 2022		6,158,078		$	11.84		8.9	$	62
Options exercisable at December 31, 2022		1,225,613		$	24.88		7.3	$	—

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2022

Income Tax Disclosure [Abstract]

Schedule of Reconciliation of Federal Statutory Income Tax Rate

The effective tax rate of the Company's provision (benefit) for income taxes differs from the federal statutory rate as follows:


	For the Year Ended December 31,
	2022			2021
Statutory rate		21.00	%		21.00	%
State tax		0.25	%		0.20	%
Research and development tax credits		4.91	%		7.68	%
Other permanent differences		(0.55	)%		(1.12	)%
Change in valuation allowance		(25.61	)%		(27.76	)%
Income tax provision (benefit)		0.00	%		0.00	%

Schedule of Significant Components of Net Deferred Tax Asset

At December 31, 2022 and 2021, the significant components of the Company’s net deferred tax assets and liabilities are as follows (in thousands):


	For the Year Ended December 31,
	2022			2021
Deferred tax assets:
Net operating loss carryforwards	$	45,609		$	37,005
Tax credit carryforwards		23,216			14,813
Accruals and reserves		689			1,467
Other		1			103
Intangibles		4,607			4,169
Non-qualified stock options		3,647			674
R&E expenditures		15,563			—
Lease liabilities		4,574			—
Right-of-use asset impairments		5,525			—
Total deferred tax assets		103,431			58,231
Deferred tax liabilities
Right-of-use assets		(2,308	)		—
Fixed assets		(47	)		—
Total deferred tax liabilities		(2,355	)		—
Valuation allowance		(101,076	)		(58,231	)
Net deferred taxes	$	—		$	—

Organization and Description of Business Operations - Additional Information (Details) - USD ($)			1 Months Ended		12 Months Ended
	Oct. 21, 2022	Oct. 05, 2021	Oct. 31, 2022	Apr. 30, 2022	Dec. 31, 2022	Dec. 31, 2021
Organization and Description of Business Operations [Line Items]
Date of incorporation					Feb. 13, 2020
Common stock, shares issued					63,207,507	38,473,945
Common stock, par value per share					$ 0.00001	$ 0.00001
Accumulated deficit					$ (401,441,000)	$ (235,649,000)
Cash and cash equivalents					$ 87,880,000	$ 149,103,000
Astellas
Organization and Description of Business Operations [Line Items]
Upfront payment	$ 20,000,000.0		$ 20,000,000.0
Gross proceeds including upfront payments			$ 50,000,000.0
Sales Agreement
Organization and Description of Business Operations [Line Items]
Number of shares issued				2,000,000
Net proceeds from issuance of common stock				$ 11,600,000
Common stock shares issued and sold					0
Sales Agreement \| Sales Agents
Organization and Description of Business Operations [Line Items]
Percentage of gross sales price per share of common stock		3.00%
Sales Agreement \| Sales Agents \| Maximum
Organization and Description of Business Operations [Line Items]
Aggregate offering price from sale of common stock		$ 150,000,000.0
Underwriting Agreement
Organization and Description of Business Operations [Line Items]
Common stock, shares issued			14,000,000
Common stock, par value per share			$ 2.00
Option to purchase additional number of shares			765,226
Underwriter agreed to purchase share price of per share			$ 1.88
Net proceeds from issuance of common stock			$ 27,700,000
Private Placement \| Securities Purchase Agreement \| Astellas
Organization and Description of Business Operations [Line Items]
Common stock, shares issued	7,266,342		7,266,342
Net proceeds from issuance of common stock			$ 30,000,000.0

Significant Accounting Policies - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Significant Accounting Policies [Line Items]
Cash equivalents	$ 0	$ 0
Shelf Registration,term	3 years
Impairment losses	$ 36,420,000	0
Accumulated Deficit	200,000
Increase in the amount of gross unrecognized tax benefits	3,100,000	4,700,000
Unrecognized tax benefits to change significantly over next 12 months	0
Interest and penalties associated with income tax positions	0	0
Derecognized build to suite lease asset	26,300,000
Deferred rent liabiilities and tenant improvement allowances	700,000
Operating Lease, Right-of-Use Asset	10,943,000
Operating Lease, Liability	21,641,000
Derecognized build to suit lease liablility	$ 26,500,000
ASU 2016-02
Significant Accounting Policies [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted [true false]	true
Change in Accounting Principle, Accounting Standards Update, Adoption Date	Jan. 01, 2022
Change in Accounting Principle, Accounting Standards Update, Immaterial Effect [true false]	false
Operating Lease, Right-of-Use Asset	$ 18,400,000
Operating Lease, Liability	$ 19,100,000
ASU 2019-12
Significant Accounting Policies [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted [true false]	true
Change in Accounting Principle, Accounting Standards Update, Adoption Date	Jan. 01, 2022
Change in Accounting Principle, Accounting Standards Update, Immaterial Effect [true false]	true
Minimum
Significant Accounting Policies [Line Items]
Property and equipment, useful life	3 years
Maximum
Significant Accounting Policies [Line Items]
Property and equipment, useful life	7 years
United States
Significant Accounting Policies [Line Items]
Long-lived assets	$ 0	$ 0

Leases - Schedule of Future Minimum Commitments Under Company's Operating and Finance Leases (Details) $ in Thousands	Dec. 31, 2022 USD ($)
Operating Lease
2023	$ 2,819
2024	2,918
2025	3,021
2026	2,485
2027	2,577
Thereafter	19,721
Total lease payments	33,541
Less: imputed interest	(11,900)
Total lease liabilities	21,641
Operating lease liabilities, current	$ 1,201
Operating Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration]	Accrued Liabilities and Other Liabilities
Operating lease liabilities, non-current	$ 20,440
Total lease liabilities	21,641
Finance Lease
2023	454
2024	454
2025	454
2026	325
2027	73
Total lease payments	1,760
Less: imputed interest	(308)
Total lease liabilities	1,452
Finance lease liabilities, current	$ 320
Finance Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration]	Accrued Liabilities and Other Liabilities
Finance, lease liabilities, non-current	$ 1,132
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration]	Other Liabilities, Noncurrent
Total lease liabilities	$ 1,452
Finance Lease, Liability, Statement of Financial Position [Extensible Enumeration]	Liabilities

Loan with Silicon Valley Bank - Additional Information (Details)		1 Months Ended	12 Months Ended
	Aug. 12, 2021 USD ($) Program	Dec. 31, 2021 USD ($)	Dec. 31, 2022 USD ($)
Debt Instrument [Line Items]
Debt instrument, maturity date	Aug. 01, 2026
Percentage of interest rate	7.00%		11.25%
Percentage of prepayment of facility	7.50%
Warrants associated with loan facility	$ 0
Exit fee recorded as debt discount			$ 3,000,000.0
Percentage of annual default interest rate	5.00%
Interest expense related to term loan			3,700,000
Prime Rate
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate	3.75%
Term Loan
Debt Instrument [Line Items]
Proceeds from term loan	$ 30,000,000.0	$ 10,000,000.0
Through December 31, 2021 \| Term Loan
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 40,000,000.0
Debt instrument, maturity date	Dec. 31, 2021
January 1, 2022 until September 30, 2022 \| Term Loan
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 20,000,000.0		$ 20,000,000.0
Debt instrument, maturity start date	Jan. 01, 2022
Debt instrument, maturity end date	Sep. 30, 2022		Sep. 30, 2022
Number of distinct and active clinical stage \| Program	3
Proceeds from term loan			$ 0
October 1, 2022 until March 31, 2023 \| Term Loan
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 20,000,000.0
Debt instrument, maturity start date	Oct. 01, 2022
Debt instrument, maturity end date	Mar. 31, 2023
Number of distinct and active clinical stage \| Program	3
April 1, 2023 until December 31, 2023 \| Term Loan
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 20,000,000.0
Debt instrument, maturity start date	Apr. 01, 2023
Debt instrument, maturity end date	Dec. 31, 2023
Through August 13, 2022
Debt Instrument [Line Items]
Percentage of prepayment premium	2.00%
Through August 13, 2023
Debt Instrument [Line Items]
Percentage of prepayment premium	1.00%

Astellas Agreements - Additional Information (Details) - USD ($)		1 Months Ended		12 Months Ended
	Oct. 21, 2022	Oct. 31, 2022	Mar. 31, 2021	Dec. 31, 2022	Dec. 31, 2021
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Common stock, shares issued				63,207,507	38,473,945
Probability of option exercise		50.00%
Deferred revenue				$ 33,600,000
Revenues				2,502,000
TSHA-120
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront Payment			$ 5,500,000
Astellas
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront Payment	$ 20,000,000.0	$ 20,000,000.0
Transaction price		36,100,000		36,059
Deferred revenue		$ 36,100,000
Astellas \| Securities Purchase Agreement \| Private Placement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Common stock, shares issued	7,266,342	7,266,342
Aggregate gross proceeds	$ 30,000,000.0
Fair value of shares transferred, Value		$ 13,950,000
Share price		$ 1.92
Difference of market value paid		$ 30,000,000.0
Transaction price		$ 16,100,000
Astellas \| TSHA-120
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront Payment				20,000,000.0
Transaction price				36,100,000
Astellas \| TSHA-120 \| Private Placement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Transaction price				$ 16,100,000

Research, Collaboration, Grant and License Agreements - Additional Information (Details)	1 Months Ended						12 Months Ended
	Jul. 31, 2022 USD ($)	Mar. 31, 2022 USD ($)	Mar. 31, 2021 USD ($)	Oct. 31, 2020 USD ($)	Aug. 31, 2020 USD ($)	Apr. 30, 2020 USD ($) Product	Dec. 31, 2022 USD ($) shares	Dec. 31, 2021 USD ($) shares	Mar. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Oct. 29, 2020 USD ($)	Feb. 21, 2020 USD ($)	Nov. 30, 2019 shares
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Common stock, shares issued \| shares							63,207,507	38,473,945
Research and development							$ 91,169,000	$ 131,943,000
License Agreement for CLN7
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Additional milestone payments							0
Payment of one-time upfront license fee		$ 300,000
License agreement regulatory related milestones maximum amount payable		7,700,000
License agreement sales-related milestones maximum amount payable		$ 7,500,000
TSHA-120
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Additional milestone payments							0
Research and development									$ 5,500,000
Upfront payment			$ 5,500,000
Clinical, regulatory and commercial milestones to be received			$ 19,300,000						$ 19,300,000
UT Southwestern Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Preclinical activities period under sponsored research agreements						2 years
Minimum licensed product to develop obtain regulatory approval for and commercialize \| Product						1
Common stock, shares issued \| shares													2,179,000
Percentage of fully diluted common stock shares outstanding													20.00%
Queens Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Additional milestone payments							0	0
Queens Agreement \| Research and Development Expense
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Cash payment to acquire license agreement						$ 3,000,000.0
Queens Agreement \| Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
License agreement regulatory milestones payment												$ 10,000,000.0
License agreement commercial milestones payment												$ 10,000,000.0
Abeona CLN1 Agreements
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
License fee payment					$ 3,000,000.0
Purchase of clinical materials and reimbursement incurred development costs				$ 4,000,000.0
Research and development								$ 3,000,000.0		$ 7,000,000.0
Abeona CLN1 Agreements \| Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
License and inventory purchase agreement regulatory related milestones payment					26,000,000.0
License and inventory purchase agreement sales related milestones payment					$ 30,000,000.0
Abeona \| Abeona Rett Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Research and development							$ 1,000,000.0
Regulatory milestone fee paid	$ 1,000,000.0
Payment of one-time upfront license fee										$ 3,000,000.0
Abeona \| Maximum \| Abeona Rett Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Regulatory related milestones obligation payable											$ 26,500,000
Sale-related milestones per licensed product and royalties on net sales of licensed products payable											$ 30,000,000.0

Stock-Based Compensation - Additional Information (Details) - USD ($)				1 Months Ended	12 Months Ended
	Sep. 16, 2020	Sep. 02, 2020	Jul. 01, 2020	Feb. 28, 2022	Dec. 31, 2022	Dec. 31, 2021	Jan. 01, 2023	Jan. 01, 2022
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense					$ 18,043,000	$ 18,184,000
Percentage of common stock price purchased through payroll deductions				85.00%
Percentage of payroll deductions of employee's compensation during offering period				15.00%
Maximum number of shares employees may purchase during offering period				1,800
Construction in Progress
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense					$ 200,000
Employee Stock Purchase Plan (ESPP)
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance	724,000						632,075	384,739
Share-based payment award, expiration period	10 years
Share-based payment award, expiration date	Jan. 01, 2030
Percentage of automatic increase every year in common stock shares reserved for future issuance	1.00%
Share-based payment award, terms of award issuance					the number of shares of common stock that are automatically added on January 1 of each year for a period of up to ten years, commencing on the first January 1 following the IPO and ending on (and including) January 1, 2030, in an amount equal to the lesser of (i) 1.0% of the total number of shares of capital stock outstanding on December 31 of the preceding calendar year, and (ii) 724,000 shares of common stock.
Number of shares of common stock issued under ESPP	0				73,073
Restricted Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based payment award, compensation cost not yet recognized, weighted-average period of recognition					1 year 6 months
Share-based payment award, RSU/RSA granted
Share-based payment award, unvested RSU/RSA granted, compensation cost not yet recognized					$ 6,400,000
Share-based payment award, RSU/RSA granted, weighted average grant date fair value
Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based payment award, options granted					4,775,676	3,192,600
Share-based payment award, options granted, exercise price per share					$ 4.48	$ 24.99
Stock options were exercised during the period					$ 0
Share-based payment award, options, compensation cost not yet recognized					$ 26,400,000
Share-based payment award, compensation cost not yet recognized, weighted-average period of recognition					2 years 6 months
Restricted Stock Awards
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based payment award, compensation cost not yet recognized, weighted-average period of recognition					2 months 12 days
Share-based payment award, unvested RSU/RSA granted, compensation cost not yet recognized					$ 400,000
Share-based payment award, RSU/RSA granted, weighted average grant date fair value			$ 5.28
Maximum \| Employee Stock Purchase Plan (ESPP)
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares authorized for issuance	362,000
2020 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based payment award, plan modification, incremental cost					$ 0
2020 Equity Incentive Plan \| Cancelled Options \| Certain Employees and Consultants
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based payment award, options granted			2,896,782
Share-based payment award, options granted, exercise price per share			$ 0.80
Award vesting period			4 years
Share-based payment award, options grant date fair value			$ 13,800,000
2020 Equity Incentive Plan \| Restricted Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Award vesting period		4 years
Number of shares awarded		2,518,932
Share-based payment award, RSU/RSA granted		331,121
2020 Equity Incentive Plan \| Restricted Stock Units \| Share-based Payment Arrangement, Tranche One
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based payment award, vesting rights percentage		25.00%
2020 Equity Incentive Plan \| Restricted Stock Units \| Share-based Payment Arrangement, Tranche Two
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based payment award, vesting rights percentage		25.00%
2020 Equity Incentive Plan \| Restricted Stock Units \| Share-based Payment Arrangement, Tranche Three
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based payment award, vesting rights percentage		25.00%
2020 Equity Incentive Plan \| Restricted Stock Units \| Share-based Payment Arrangement, Tranche Four
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based payment award, vesting rights percentage		25.00%
2020 Equity Incentive Plan \| Restricted Stock Awards \| RA Session II
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based payment award, RSU/RSA granted			769,058
Award requisite service vesting period			3 years
New Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance							3,160,375
Share-based payment award, expiration period	10 years
Share-based payment award, commencement date	Jan. 01, 2021
Share-based payment award, expiration date	Jan. 01, 2030
Percentage of automatic increase every year in common stock shares reserved for future issuance	5.00%
Share-based payment award, terms of award issuance					The number of shares of common stock reserved for issuance under the New Plan automatically increases on January 1 of each year, for a period of ten years, from January 1, 2021 continuing through January 1, 2030, by 5% of the total number of shares of common stock outstanding on December 31 of the preceding calendar year, or a lesser number of shares as may be determined by the Company’s board of directors.
New Plan \| Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based payment award, expiration period					10 years
Share-based payment award, options granted					4,775,676
Share-based payment award, options, weighted-average grant date fair value					$ 3.07
New Plan \| Maximum \| Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Award vesting period					4 years
New Plan \| Minimum [Member] \| Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Award vesting period					1 year

Stock-Based Compensation - Schedule of Stock Option Activity (Details) - Stock Options - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Outstanding. Stock Options, Beginning Balance	3,649,962		674,842
Options granted, Stock Options	4,775,676	3,192,600
Options cancelled or forfeited, Stock Options	(2,048,192)	(217,480)
Options expired, Stock Options	(219,368)
Outstanding. Stock Options, Ending Balance	6,158,078	3,649,962
Options exercisable at December 31, 2022	1,225,613
Outstanding, Weighted Average Exercise Price, Beginning balance	$ 24.13		$ 20.68
Options granted, Weighted Average Exercise Price	4.48	$ 24.99
Options cancelled or forfeited, Weighted Average Exercise Price	15.25	26.07
Options expired, Weighted Average Exercise Price	24.36
Outstanding, Weighted Average Exercise Price, Ending balance	11.84	$ 24.13
Options exercisable at December 31, 2021, Weighted Average Exercise Price	$ 24.88
Outstanding, Weighted Average Remaining Contractual Life	8 years 10 months 24 days	9 years 2 months 12 days	9 years 9 months 18 days
Weighted Average Remaining Contractual Life, Options exercisable at December 31, 2021	7 years 3 months 18 days
Outstanding, Aggregate Intrinsic Value, Beginning Balance			$ 3,953
Outstanding, Aggregate Intrinsic Value, Ending Balance	$ 62

Net Loss Per Common Share - Schedule of Calculation of Basic and Diluted Net Loss Per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Earnings Per Share [Abstract]
Net loss	$ (166,014)	$ (174,523)
Weighted average common shares outstanding, basic	43,952,015	37,650,566
Weighted average common shares outstanding, diluted	43,952,015	37,650,566
Net loss per common share, basic	$ (3.78)	$ (4.64)
Net loss per common share, diluted	$ (3.78)	$ (4.64)

- Definition

The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 40
-Section 65
-Paragraph 1
-Subparagraph (e)(4)
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
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-URI https://asc.fasb.org/extlink&oid=124431687&loc=d3e22583-107794

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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-URI https://asc.fasb.org/extlink&oid=124431687&loc=d3e22595-107794

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
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Reference 7: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 9: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 10: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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-Section S99
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-Subparagraph (SX 210.7-04(23))
-URI https://asc.fasb.org/extlink&oid=120400993&loc=SL114874131-224263

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
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Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
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Reference 15: http://www.xbrl.org/2003/role/disclosureRef
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- Definition

The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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Amount, after deduction of tax, noncontrolling interests, dividends on preferred stock and participating securities; of income (loss) available to common shareholders.

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+ Details

Income Taxes - Schedule of Significant Components of Net Deferred Tax Asset (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Components of Deferred Tax Assets [Abstract]
Net operating loss carryforwards	$ 45,609	$ 37,005
Tax credit carryforwards	23,216	14,813
Accruals and reserves	689	1,467
Other	1	103
Intangibles	4,607	4,169
Non-qualified stock options	3,647	674
R&E expenditures	15,563
Lease liabilities	4,574
Right-of-use asset impairments	5,525
Total deferred tax assets	103,431	58,231
Right-of-use assets	(2,308)
Fixed assets	(47)
Total deferred tax liabilities	(2,355)
Valuation allowance	(101,076)	(58,231)
Net deferred taxes	$ 0	$ 0

Supplemental Financial Information - Schedule of Property, Plant and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 16,605	$ 51,109
Accumulated depreciation	(1,642)	(499)
Property, plant and equipment, net	14,963	50,610
Leasehold Improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross	2,091	2,067
Laboratory Equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	2,868	1,095
Computer Equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	1,115	1,098
Furniture and Fixtures
Property, Plant and Equipment [Line Items]
Property and equipment, gross	898	845
Construction in Progress
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 9,633	$ 46,004

Supplemental Financial Information - Additional Information (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Nov. 30, 2022	Dec. 31, 2022	Dec. 31, 2021
Property, Plant and Equipment [Line Items]
Non-cash impairment charge	$ 36,400
Impairment charges to construction in process and finance lease right of use assets	$ 26,300
Depreciation expense		$ 1,172	$ 492
Property, plant and equipment, net		14,963	50,610
Build-to-Suit Lease
Property, Plant and Equipment [Line Items]
Construction in progress			45,800
Payroll and Payroll Related Costs
Property, Plant and Equipment [Line Items]
Construction in progress			$ 2,000
Assets Capitalized as Finance Leases
Property, Plant and Equipment [Line Items]
Property, plant and equipment, net		$ 1,300

Leases - Additional Information (Details)				12 Months Ended
Leases - Additional Information (Details)	Dec. 14, 2021 USD ($) ft²	Jan. 11, 2021 ft²	Dec. 17, 2020 ft²	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Lessee, Lease, Description [Line Items]
Future minimum remianing lease payments				$ 33,541,000
Build-to-suit lease liability					$ 26,300,000
Durham Lease
Lessee, Lease, Description [Line Items]
Number of operating lease landlord square feet manufacturing facility \| ft²			187,500
Operating lease commencement date			Apr. 01, 2021
Operating lease term of contract			15 years 6 months
Lease, option to extend description				The Company has two options to extend the term of the Durham Lease, each for a period of an additional five years.
Operating lease extend term of contract			5 years
Amount required to place in escrow account				$ 2,600,000
Equipment purchases and build-out of leased Facility					$ 45,800,000
On Site Generation Lease
Lessee, Lease, Description [Line Items]
Operating lease term of contract				10 years
Future minimum remianing lease payments				$ 3,500,000
Pegasus Park L L C \| Dallas Lease
Lessee, Lease, Description [Line Items]
Number of operating lease landlord square feet manufacturing facility \| ft²		15,000
Operating lease commencement date		May 27, 2021
Operating lease term of contract		10 years
Lease, option to extend description		Company has an option to extend the term of the Dallas Lease for one additional period of five years
Operating lease extend term of contract		5 years
Pegasus Park L L C \| Dallas Lease Amendment
Lessee, Lease, Description [Line Items]
Number of operating lease landlord square feet manufacturing facility \| ft²	18,000
Operating lease term of contract	10 years
Future minimum remianing lease payments	$ 6.0
Pegasus Park L L C \| Dallas Lease Amendment \| Minimum
Lessee, Lease, Description [Line Items]
Maximum construction allowance provided by landlord per rentable square foot \| ft²	40.00

Stock-Based Compensation - Schedule of Assumptions Used to Estimate Fair Value of Stock Options (Details) - Stock Options	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate	2.95%	0.84%
Expected term in years	6 years 1 month 6 days	6 years
Expected volatility	78.00%	75.00%

Net Loss Per Common Share - Schedule of Common Stock Equivalents Outstanding Excluded from Computation of Diluted Net Loss Per Share Attributable to Common Stockholders (Details) - shares	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per share	7,501,416	5,878,702
Unvested RSUs
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per share	1,257,844	1,886,765
Unvested RSAs
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per share	85,494	341,975
Stock Options
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per share	6,158,078	3,649,962

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2022	Dec. 31, 2021
Statement of Financial Position [Abstract]
Preferred stock, par value per share	$ 0.00001	$ 0.00001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value per share	$ 0.00001	$ 0.00001
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	63,207,507	38,473,945
Common stock, shares outstanding	63,207,507	38,473,945

Consolidated Statements of Stockholders' Equity (Parenthetical) $ in Thousands	12 Months Ended
	Dec. 31, 2022 USD ($)
Offering to Astellas
Offering costs	$ 187
Public Offering
Underwriting discount and other offering costs	2,072
At-the-Market Offering
Payment of sales commissions and other offering costs	$ 392

Supplemental Financial Information - Schedule of Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Balance Sheet Related Disclosures [Abstract]
Accrued research and development	$ 8,190	$ 11,895
Accrued compensation	2,519	7,703
Accrued property, plant, and equipment	2,081	2,644
Accrued clinical trial	1,473	1,659
Accrued severance	1,463
Lease liabilities, current portion	1,521
Accrued professional and consulting fees	390	1,091
Accrued license fees		3,500
Other	650	1,491
Total accrued expenses and other current liabilities	$ 18,287	$ 29,983

Supplemental Financial Information - Schedule of Prepaid Expenses and Other Current Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Balance Sheet Related Disclosures [Abstract]
Prepaid research and development	$ 4,840	$ 5,218
Prepaid clinical trial	2,119	3,298
Deferred offering costs	724	545
Prepaid insurance	388	148
Prepaid bonus	18	427
Other	448	863
Total prepaid expenses and other current assets	$ 8,537	$ 10,499

Leases - Schedule of Lease Cost (Details) $ in Thousands	12 Months Ended
Leases - Schedule of Lease Cost (Details) $ in Thousands	Dec. 31, 2022 USD ($)
Lease, Cost [Abstract]
Operating lease cost	$ 2,873
Variable lease cost	452
Total lease cost	$ 3,325

Leases - Supplemental Information Related to Remaining Lease Term and Discount Rate (Details)	Dec. 31, 2022
Leases [Abstract]
Weighted average remaining lease term (in years) - Finance leases	3 years 10 months 17 days
Weighted average remaining lease term (in years) - Operating leases	11 years 5 months 12 days
Weighted average discount rate - Finance leases	10.51%
Weighted average discount rate - Operating leases	7.72%

Leases - Schedule of Supplemental Cash Flow Information Related to Operating Leases (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2022 USD ($)
Cash Flow, Operating Activities, Lessee [Abstract]
Operating cash flows for operating leases	$ 2,486

Leases - Schedule of Aggregate Lease Commitments (Details) $ in Thousands	Dec. 31, 2021 USD ($)
Leases [Abstract]
2022	$ 4,848
2023	4,201
2024	4,301
2025	4,372
2026	3,868
Thereafter	30,563
Total Lease Commitments	$ 52,153

Loan with Silicon Valley Bank - Schedule of Future Principal Debt Payments on Term Loan Agreement (Details) $ in Thousands	Dec. 31, 2022 USD ($)
Debt Disclosure [Abstract]
2024	$ 6,667
2025	20,000
2026	13,333
Total principal payments	40,000
Unamortized debt discount	(2,033)
Term Loan, net	$ 37,967

Astellas Agreements - Additional Information 1 (Details)	Dec. 31, 2022
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-12-31
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	1 year

Stock-Based Compensation - Schedule of Total Remaining Stock-Based Compensation Expense for Stock Options, RSAs and RSUs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 18,043	$ 18,184
Research and Development Expense
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	7,608	8,286
General and Administrative Expense
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 10,435	$ 9,898

Strategic Reprioritization - Additional Information (Details) - Exit and Disposal Activities - USD ($) $ in Millions	1 Months Ended	3 Months Ended	12 Months Ended
	Dec. 31, 2022	Mar. 31, 2022	Dec. 31, 2022
Restructuring Cost and Reserve [Line Items]
Percentage of headcount reduced		35.00%
Severance and termination-related costs	$ 1.5		$ 2.6

Strategic Reprioritization - Summary of Accrued Severance Activity Recorded (Details) - Employee Severance $ in Thousands	12 Months Ended
	Dec. 31, 2022 USD ($)
Restructuring Cost and Reserve [Line Items]
Accrued severance recorded	$ 4,035
Severance paid	(2,572)
Accrued severance balance	$ 1,463

Retirement Plan - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Retirement Benefits [Abstract]
Contribution to retirement savings plan	$ 0.7	$ 0.4

Subsequent Events - Additional Information (Details) - $ / shares		1 Months Ended	12 Months Ended
	Mar. 07, 2023	Feb. 28, 2023	Dec. 31, 2022	Dec. 31, 2021
Restricted Stock Units
Subsequent Event [Line Items]
Restricted units/stock granted, Number of Shares
Subsequent Event
Subsequent Event [Line Items]
Options granted for purchase an aggregate share of common stock		1,200,000
Weighted-average exercise price		$ 1.18
Award vesting period		4 years
Option award, canceled	199,500
Subsequent Event \| Restricted Stock Units
Subsequent Event [Line Items]
Restricted units/stock granted, Number of Shares		200,000
Issuance of common stock, upon vesting and settlement of restricted stock units, shares	251,296