0001564590-22-012782 | 10-K | XBRL Viewer | Taysha Gene Therapies INC

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 149,103	$ 251,253
Prepaid expenses and other current assets	10,499	6,626
Total current assets	159,602	257,879
Restricted cash	2,637
Deferred lease asset	667	715
Property, plant and equipment, net	50,610	287
Other non-current assets	440
Total assets	213,956	258,881
Current liabilities
Accounts payable	21,763	1,994
Accrued expenses and other current liabilities	29,983	5,135
Total current liabilities	51,746	7,129
Build-to-suit lease liability	25,900
Term loan, net	37,192
Other non-current liabilities	3,735	450
Total liabilities	118,573	7,579
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, 2021 and December 31, 2020
Common stock, $0.00001 par value per share; 200,000,000 shares authorized and 38,473,945 and 37,761,435 issued and outstanding as of December 31, 2021 and December 31, 2020
Additional paid-in capital	331,032	312,428
Accumulated deficit	(235,649)	(61,126)
Total stockholders’ equity	95,383	251,302
Total liabilities and stockholders' equity	$ 213,956	$ 258,881

Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Operating expenses:
Research and development	$ 131,943	$ 31,893
General and administrative	41,324	11,109
Total operating expenses	173,267	43,002
Loss from operations	(173,267)	(43,002)
Other income (expense):
Change in fair value of preferred stock tranche liability		(17,030)
Interest income	172	49
Interest expense	(1,428)	(28)
Total other expense, net	(1,256)	(17,009)
Net loss	$ (174,523)	$ (60,011)
Net loss per common share, basic and diluted	$ (4.64)	$ (3.40)
Weighted average common shares outstanding, basic and diluted	37,650,566	17,665,683

Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($)	Total	Series A Convertible Preferred Stock	Series B Convertible Preferred Stock	Common Stock	Additional Paid-in Capital	Accumulated Deficit
Balance at Dec. 31, 2019	$ (135,000)				$ 980,000	$ (1,115,000)
Balance, shares at Dec. 31, 2019				10,894,999
Issuance of convertible preferred stock		$ 28,345,000	$ 95,815,000
Issuance of convertible preferred stock, shares		10,000,000	5,647,048
Reclassification of preferred stock tranche liability upon issuance of Series A milestone shares		$ 18,080,000
Conversion of Series A and Series B convertible preferred stock to common stock		$ (46,425,000)	$ (95,815,000)
Conversion of Series A and Series B convertible preferred stock to common stock, shares		(10,000,000)	(5,647,048)
Conversion of Series A and Series B convertible preferred stock to common stock	142,240,000				142,240,000
Conversion of convertible to common stock, shares				17,047,378
Issuance of restricted stock award, shares				769,058
Stock-based compensation	3,354,000				3,354,000
Issuance of shares of common stock	165,854,000				165,854,000
Issuance of shares of common stock, shares				9,050,000
Net loss	(60,011,000)					(60,011,000)
Balance at Dec. 31, 2020	$ 251,302,000				312,428,000	(61,126,000)
Balance, shares at Dec. 31, 2020	37,761,435			37,761,435
Stock-based compensation	$ 18,604,000				18,604,000
Issuance of common stock, upon vesting and settlement of restricted stock units				$ 712,510
Net loss	(174,523,000)					(174,523,000)
Balance at Dec. 31, 2021	$ 95,383,000				$ 331,032,000	$ (235,649,000)
Balance, shares at Dec. 31, 2021	38,473,945			38,473,945

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Cash flows from operating activities
Net loss	$ (174,523)	$ (60,011)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation expense	492	9
Change in fair value of preferred stock tranche liability		17,030
Research and development license expense	9,750	9,000
Stock-based compensation	18,184	3,354
Other	388
Changes in operating assets and liabilities:
Prepaid expenses and other assets	(3,361)	(6,585)
Accounts payable	14,494	1,961
Accrued expenses and other liabilities	17,542	4,512
Due to related party	(8)	1
Net cash used in operating activities	(117,042)	(30,729)
Cash flows from investing activities
Purchase of research and development license	(6,250)	(9,000)
Purchase of property, plant and equipment	(15,304)	(82)
Net cash used in investing activities	(21,554)	(9,082)
Cash flows from financing activities
Proceeds from Term Loan, net	39,957
Proceeds from initial public offering, net of underwriting discounts and commission and other offering costs		165,854
Payment of shelf registration costs	(360)
Other	(514)
Proceeds from note payable to related party		1,673
Repayment of note payable to related party		(1,673)
Net cash provided by financing activities	39,083	291,064
Net (decrease) increase in cash, cash equivalents and restricted cash	(99,513)	251,253
Cash, cash equivalents and restricted cash at the beginning of the period	251,253
Cash, cash equivalents and restricted cash at the end of the period	151,740	251,253
Cash and cash equivalents	149,103	251,253
Restricted cash	2,637
Supplemental disclosure of cash flow information:
Cash paid for interest	641	28
Supplemental disclosure of noncash investing and financing activities:
Property, plant and equipment in accounts payable and accrued expenses	8,282	214
Acquisition of property, plant and equipment funded by landlord	606
Build-to-suit lease liability	26,250
Deferred offering costs not yet paid	141
Reclassification of preferred stock tranche liability		18,080
Allocation of preferred stock tranche liability		1,050
Conversion of Series A and Series B convertible preferred stock to common stock		142,240
Purchase of research and development license not yet paid	$ 3,500
Series A Convertible Preferred Stock
Cash flows from financing activities
Proceeds from convertible preferred stock, net of issuance costs		29,395
Series B Convertible Preferred Stock
Cash flows from financing activities
Proceeds from convertible preferred stock, net of issuance costs		$ 95,815

Significant Accounting Policies

12 Months Ended

Dec. 31, 2021

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 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, and the valuation of the preferred stock tranche liability. 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. In response to the ongoing and rapidly evolving COVID-19 pandemic, management considered the impact of the estimated economic implications on the Company’s critical and significant accounting estimates, including assessment of impairment of long-lived assets.

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 CNS.

As of December 31, 2021 and 2020, the Company did not have any long-lived assets located outside of the United States.

Cash and Cash Equivalents

Cash and cash equivalents consist of funds held in a standard checking account and a 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, 2021 and 2020, 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. Management believes that the Company is not exposed to significant credit risk as the Company’s deposits are held at financial institutions that management believes 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. As of December 31, 2021 and 2020, there was $0.5 million and 0, respectively, of such deferred costs included in prepaid expenses and other current assets on the consolidated balance sheets.

Deferred offering costs, consisting of legal, accounting, and filing fees directly relating to the IPO and the Company’s Series A and Series B preferred stock financings, were capitalized and offset against the related proceeds upon the completion of the offerings in 2020. Upon completion of the IPO in September 2020, approximately $2.5 million of deferred offering costs were offset against the IPO proceeds in additional paid-in capital.

Property, Plant and Equipment, net

Property, plant and equipment, net are stated at cost less accumulated depreciation and consist solely of computer equipment and laboratory equipment. Directly identifiable payroll and payroll-related costs incurred in connection with the build-out of the Company’s cGMP manufacturing facility are capitalized into the cost basis of the asset to the extent that such costs are 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 five 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.

Build-to-Suit Lease

In the Company’s lease arrangement in Durham, North Carolina (as described in Note 11), 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 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. Upon completion of construction, the Company will consider the requirements for sale-leaseback accounting treatment, including evaluating whether all risks of ownership have been transferred back to the landlord.

Impairment of Long-Lived Assets

The Company evaluates its long-lived assets, which consist of property and equipment, 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 exceeds the fair value of the asset. There were no impairment losses recognized during the years ended December 31, 2021 and 2020.

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.

Convertible Preferred Stock

The Company recorded shares of its convertible preferred stock at their respective fair values on the dates of issuance, net of issuance costs. The Company applied the guidance in ASC 480-10-S99-3A, SEC Staff Announcement: Classification and Measurement of Redeemable Securities and therefore classified the Series A convertible preferred stock as mezzanine equity. The convertible preferred stock was recorded outside of stockholders’ deficit because, in the event of certain deemed liquidation events considered not solely within the Company’s control, such as a merger, acquisition and sale of all or substantially all of the Company’s assets (a “Deemed Liquidation Event”), the convertible preferred stock would become redeemable at the option of the holders. In the event of a change of control of the Company, proceeds received from the sale of such shares would have been distributed in accordance with the liquidation preferences set forth in the Company’s Amended and Restated Certificate of Incorporation. The Company determined not to adjust the carrying values of the convertible preferred stock to the liquidation preferences of such shares because of the uncertainty of whether or when such an event would occur. All shares of the Company’s previously issued and outstanding convertible preferred stock were converted into shares of common stock upon the closing of the IPO (see Note 7).

Preferred Stock Tranche Liability

The Company determined that its obligation to issue, and the Company’s investors’ right to purchase, additional shares of Series A convertible preferred stock pursuant to the milestone closings (see Note 7) represented a freestanding financial instrument (the “tranche liability”). The tranche liability was initially recorded at fair value. The proceeds from the sale of the convertible preferred stock were first allocated to the fair value of the tranche liability with the remaining proceeds from the sale of the convertible preferred stock allocated to the Series A convertible preferred stock. The tranche liability was remeasured at each reporting period and upon the exercise or expiration of the obligation, with gains and losses arising from subsequent changes in its fair value recognized in other expense in the consolidated statements of operations. At the time of the exercise or expiration of the tranche liability, any remaining value of the tranche liability was reclassified to convertible preferred stock on the consolidated balance sheets.

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 on the Nasdaq Global Select Market 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 are directly involved in the buildout of the Company’s cGMP manufacturing facility are capitalized into the cost basis of that asset to the extent that such costs are 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 year ended December 31, 2021, the Company recorded an increase in the amount of gross unrecognized tax benefits by $4.7 million. 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, 2021 and 2020.

Comprehensive Loss

Comprehensive loss is equal to net loss as presented in the accompanying consolidated statements of operations, as the Company did not have any other comprehensive income or loss for the periods presented.

Recently Adopted Accounting Pronouncements

In August 2018, the FASB issued Accounting Standards Update (“ASU”) No. 2018-13, Fair Value Measurement (ASC Topic 820) (“ASU 2018-13”), which modifies, removes and adds certain disclosure requirements on fair value measurements based on the FASB Concepts Statement, Conceptual Framework for Financial Reporting—Chapter 8: Notes to Financial Statements. The amendments on changes in unrealized gains and losses, the range and weighted-average of significant unobservable inputs used to develop Level 3 fair value measurements and the narrative description of measurement uncertainty should be applied prospectively for only the most recent

interim or annual period presented in the initial fiscal year of adoption. All other amendments should be applied retrospectively to all periods presented upon their effective date. The Company adopted ASU 2018-13 as of January 1, 2020 for the annual period. The adoption of the guidance did not have a material impact on the Company’s consolidated financial statements.

In November 2018, the FASB issued ASU No. 2018-18 – Collaborative Arrangements, which clarifies that certain transactions between collaborative arrangement participants should be accounted for as revenue when the collaborative arrangement participant is a customer in the context of a unit of account and precludes recognizing as revenue consideration received from a collaborative arrangement participant if the participant is not a customer. The Company early adopted this standard as of January 1, 2020. This ASU requires retrospective adoption to the date the Company adopted ASC 606, which was early adopted upon the Company’s Inception, by recognizing a cumulative-effect adjustment to the opening balance of retained earnings of the earliest annual period presented. As the Company does not have any contracts with customers or collaborative arrangements, the adoption of this guidance did not have any impact on the Company’s consolidated financial statements.

Recently Issued 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. This guidance will become effective for the Company for annual reporting periods beginning after December 15, 2021 and interim periods within fiscal years beginning after December 15, 2022. The Company is currently evaluating the impact of this standard on its consolidated financial statements.

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 is currently evaluating the impact of this standard on its consolidated financial statements.

Supplemental Financial Information

12 Months Ended

Dec. 31, 2021

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, 2021			December 31, 2020
Leasehold improvements	$	2,067		$	—
Furniture and fixtures		845			—
Computer equipment		1,098			95
Laboratory equipment		1,095			—
Construction in progress		46,004			201
		51,109			296
Accumulated depreciation		(499	)		(9	)
Property, plant and equipment, net	$	50,610		$	287

Included in construction in progress at December 31, 2021 was $45.8 million of costs associated with the Build-to-Suit lease (see Note 11), which includes $2.0 million of capitalized payroll and payroll-related costs.

Depreciation expense was $0.5 million and an immaterial amount for the years ended December 31, 2021 and 2020 respectively.

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

	December 31, 2021		December 31, 2020
Accrued research and development	$	11,895	$	2,106
Accrued compensation		7,703		1,766
Accrued license fees		3,500		—
Accrued property, plant, and equipment		2,644		173
Accrued clinical trials		1,659		—
Accrued professional and consulting fees		1,091		999
Other		1,491		91
Total accrued expenses and other current liabilities	$	29,983	$	5,135

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

	December 31, 2021		December 31, 2020
Prepaid research and development	$	5,218	$	2,462
Prepaid clinical trial		3,298		944
Deferred offering costs		545		—
Prepaid bonus		427		409
Prepaid insurance		148		2,480
Other		863		331
Total prepaid expenses and other current assets	$	10,499	$	6,626

Loan with Silicon Valley Bank

12 Months Ended

Dec. 31, 2021

Debt Disclosure [Abstract]

Loan with Silicon Valley Bank

Note 4 – 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 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. 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 may be 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, 2021. 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, 2021. 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, 2021, the Company recognized interest expense related to the Term Loan of $1.1 million.

Future principal debt payments on the Term Loan Agreement as of December 31, 2021 are as follows (in thousands):

Year Ending December 31,
2022		-
2023		-
2024		6,667
2025		20,000
2026		13,333
Total principal payments		40,000
Unamortized debt discount		(2,808	)
Term Loan, net	$	37,192

- 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.

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+ Details

Research, Collaboration, Grant and License Agreements

12 Months Ended

Dec. 31, 2021

Research Collaboration And License Agreements [Abstract]

Research, Collaboration, Grant and License Agreements

Note 5—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 (“UT 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.

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. As additional consideration, UT Southwestern was entitled to receive additional shares if their holdings fell below 10% on a fully-diluted basis before or as a result of the completion of a qualified financing. In March 2020, following the initial closing of the Series A convertible preferred stock agreement, which met the definition of such qualified financing, the anti-dilution feature expired and no additional shares were issued. 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

In late December 2019, the Company entered into a research grant agreement (“RGA”) with Queen’s University at Kingston (“Queen’s”), for certain research and development activities related to the generation of AAV9 vector. The Company committed to fund $3.8 million under the RGA with Queen’s, all of which was paid during the year ended December 31, 2020.

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 year ended December 31, 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.

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.

No additional milestone payments were made in connection with the Abeona Rett Agreement during the year ended December 31, 2021.

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 for Giant Axonal Neuropathy, Inc. (“HHF”). 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 since the acquired license does not have an alternative future use. No additional milestone payments were made in connection with this agreement during the year ended December 31, 2021.

Stockholders' Equity (Deficit), Convertible Preferred Stock and Tranche Liability

12 Months Ended

Dec. 31, 2021

Equity [Abstract]

Stockholders' Equity (Deficit), Convertible Preferred Stock and Tranche Liability

Note 7— Stockholders’ Equity (Deficit), Convertible Preferred Stock and Tranche Liability

Authorized shares

The Company amended its certificate of incorporation on March 4, 2020, July 2, 2020 and again on July 28, 2020 such that the total number of shares of common stock authorized to be issued was increased to 32,685,000, and the total number of shares of preferred stock authorized to be issued was increased to 15,647,052, of which 10,000,000 preferred shares were designated Series A convertible preferred stock and 5,647,052 were designated Series B convertible preferred stock. On September 28, 2020, the Company amended its certificate of incorporation such that the total number of shares of common stock authorized to be issued was increased to 200,000,000, and the total number of shares of new preferred stock authorized to be issued was 10,000,000. As of December 31, 2021, no shares of preferred stock were issued or outstanding.

IPO

On September 28, 2020, the Company issued an aggregate of 7,869,566 shares of common stock in the IPO, and on September 29, 2020, the Company issued an aggregate of 1,180,434 shares of common stock upon the underwriters’ exercise in full of their option to purchase additional shares, each at the public offering price of $20.00 per share less underwriting discounts and commissions. In connection with the IPO, the Company received gross proceeds of $181.0 million, which was offset by issuance costs, including underwriters’ discounts and commissions, of approximately $15.1 million.

In connection with the closing of the IPO, 10,000,000 shares of Series A convertible preferred stock and 5,647,048 shares of Series B convertible preferred stock automatically converted into an aggregate of 17,047,378 shares of common stock with a conversion ratio of 1.0895 shares of common stock for each share of Series A and Series B convertible preferred stock then outstanding.

As a result of the IPO, the underwriters’ exercise of their option, and the conversions of the Series A and B convertible preferred stock, the Company’s total number of outstanding shares increased by 26,097,378 immediately following the closing of the IPO.

Series A and B convertible preferred stock

On March 4, 2020, the Company entered into a purchase agreement (the “Series A Purchase Agreement”) providing for a private placement of up to 10,000,000 shares of Series A convertible preferred stock at an original issuance price of $3.00 per share, subject to separate closings, including: (1) 6,000,000 shares at the initial closing on March 4, 2020, and (2) 2,000,000 shares at each of two subsequent closings triggered by the achievement of specific clinical milestones. The Series A Purchase Agreement obligated the Company to issue and sell and the Series A investors to purchase up to a total of 4,000,000 additional shares of Series A convertible preferred stock (the “Milestone Shares”) at the same price per share upon the achievement of certain defined clinical milestones (the “tranche liability”). The determination as to whether the milestone events had been met was subject to certification by the Board of Directors. Each Series A investor had the right, but not the obligation, to purchase all or any portion of the Milestone Shares at any time in its sole option and in its sole and absolute discretion, whether or not the Company had achieved the applicable clinical milestone.

On June 30, 2020, several affiliated Series A investors elected to exercise in full their options to purchase 200,000 shares, representing all of their remaining pro-rata portion of the Milestone Shares, prior to the Company’s achievement of the clinical milestones for gross proceeds of $0.6 million. The remainder of the Series A investors exercised in full their options to purchase 3,800,000 shares, representing all of their remaining pro-rata portion of the Milestone Shares, prior to the Company’s achievement of the clinical milestones, for gross proceeds of $11.4 million between July 1, 2020 and July 2, 2020. As part of this issuance, the Company issued and sold 3,266,667 shares to PBM TGT Holdings, LLC and 400,000 shares to Nolan Capital, LLC, which stockholders are controlled by certain members of the Company’s board of directors.

On July 2, 2020, the Company entered into a purchase agreement (the “Series B Purchase Agreement”), as later amended on July 28, 2020, providing for a private placement of up to 5,647,052 shares of Series B convertible preferred stock. The Company sold 5,647,048 shares of Series B convertible preferred stock at a price of $17.00 per share in multiple closings in July and August 2020 for gross proceeds of $96.0 million. The majority of investors that participated in the Series B Purchase Agreement were new investors.

As described above, in connection with the closing of the IPO, all shares of Series A and Series B convertible preferred stock were automatically converted into an aggregate of 17,047,378 shares of common stock with a conversion ratio, which was adjusted for the stock split, of 1.0895 shares of common stock for each share of Series A and Series B convertible preferred stock then outstanding.

Series A convertible preferred stock tranche liability

The Company concluded that the tranche liability met the definition of a freestanding financial instrument, as it was legally detachable and separately exercisable from the initial closing of the Series A convertible preferred stock.

The estimated fair value of the tranche liability was determined using a Monte Carlo simulation at the initial issuance date. As of March 4, 2020, the simulations occurred based on the implied aggregate equity value of the Company derived from the Series A convertible preferred stock offering price of $3.00 per share, along with, in part, the following subjective assumptions: risk-free rate of 0.59%, an expected volatility of 80%, the expected term to a liquidity event of 1 year, and a 60% probability of achieving the clinical milestones and timing thereof. Subsequently, the estimated fair value of the tranche liability was determined using a backsolve approach at June 30, 2020, immediately prior to the issuance of the Milestone Shares, which was calculated based on the aggregate equity value of the Company

derived from the Series B convertible preferred stock offering price of $17.00 per share. The subsequent remeasurement also considered, in part, a risk-free rate of 0.17%, an expected volatility of 80%, and the expected term to a liquidity event of 0.5 years.

Based on the analysis, the Company recorded a preferred stock tranche liability of $1.1 million at the issue date to account for the obligation to issue the Milestone Shares at a predetermined fixed price at a future settlement date.

At June 30, 2020, ahead of the anticipated closing of the Series B Purchase Agreement for $17.00 per share that occurred on July 2, 2020, certain investors elected to exercise in full their options to their pro-rata portion of the Milestone Shares prior to the Company’s achievement of the clinical milestones and purchased 200,000 shares of Series A convertible preferred stock. The Company remeasured the fair value of the entire tranche liability at June 30, 2020 and recognized a non-cash expense of $17.0 million in the consolidated statements of operations. Between June 30, 2020 and July 2, 2020, all of the 4,000,000 Milestone Shares were issued and the related tranche liability was extinguished in its entirety, and the Company reclassified the entire tranche liability of $18.1 million to convertible preferred stock on the consolidated balance sheets.

The Company concluded that no beneficial conversion feature (“BCF”) existed as the effective conversion price of the Series A convertible preferred stock exceeded the fair value of the Company’s common stock at each of the commitment dates. Specifically, at the commitment date of June 30, 2020, when 200,000 Milestone Shares were issued, the deemed proceeds were equal to the cash proceeds received for the shares of Series A convertible preferred stock and the fair value of the tranche liability that related to the Milestone Shares, or $7.52 per share. As the effective conversion price exceeded the fair value of the Company’s common stock at the commitment date, no BCF existed.

The following table provides a reconciliation of the preferred stock tranche liability measured at fair value using Level 3 significant unobservable inputs (in thousands):

Balance at December 31, 2019	$	—
Fair value at issuance of Series A convertible preferred stock		1,050
Change in fair value		17,030
Settlement of preferred stock tranche liability due to issuance of Milestone Shares		(18,080	)
Balance at December 31, 2020	$	—

- Definition

The entire disclosure for shareholders' equity comprised of portions attributable to the parent entity and noncontrolling interest, including other comprehensive income. Includes, but is not limited to, balances of common stock, preferred stock, additional paid-in capital, other capital and retained earnings, accumulated balance for each classification of other comprehensive income and amount of comprehensive income.

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+ Details

Stock-Based Compensation

12 Months Ended

Dec. 31, 2021

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock-Based Compensation

Note 8—Stock-Based Compensation

On July 1, 2020, the Company’s board of directors approved the 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 July 1, 2020, 3,529,412 shares of common stock were authorized for issuance under the Existing Plan. On September 16, 2020, the Company increased the number of shares of common stock authorized for issuance under the Existing Plan to 3,845,294.

On September 16, 2020, the Company’s stockholders approved the New Plan, which became effective upon the execution of the underwriting agreement in connection with the IPO. The number of shares available for future issuance under the New Plan is the sum of (1) 3,390,168 new shares of common stock, (2) 209,841 remaining shares of common stock reserved under the Existing Plan that became available for issuance upon the effectiveness of the New Plan and (3) the number of shares of common stock subject to outstanding awards under the Existing Plan when the New Plan became effective that thereafter expire or are forfeited, canceled, withheld to satisfy tax withholding or to purchase or exercise an award, repurchased by the Company or are otherwise terminated. The number of shares of common stock reserved for issuance under the New Plan will automatically increase 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, 2021 the board of directors increased the number of common stock reserved for issuance under the New Plan by 1,434,934 shares. On January 1, 2022 the board of directors increased the number of common stock reserved for issuance under the New Plan by 1,923,697 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 1st of each year for a period of up to ten years, commencing on the first January 1 following the IPO Date and ending on (and including) January 1, 2030, in an amount equal to the lesser of (i) one percent (1.0%) of the total number of shares of capital stock outstanding on December 31st of the preceding calendar year, and (ii) 724,000 shares of common stock. No shares were added to the ESPP in 2021, and no issuances have been made under the ESPP as of December 31, 2021. On January 1, 2022, the board of directors increased the number of common stock reserved for issuance under the ESPP by 384,739.

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.

The estimated fair value of the Company’s common stock at July 1, 2020 was $5.28 per share, as determined using information derived from the issuance price of the Company’s Series B convertible preferred stock of $17.00 per share on July 2, 2020. The valuation of the common stock was determined using an option-pricing model under which shares are valued by creating a series of call options with exercise prices based on the liquidation preferences and conversion terms of each equity class, adjusted for a discount for the lack of marketability to account for a lack of access to an active public market.

The following assumptions were used to estimate the fair value of the Cancelled Options that were granted on July 1, 2020:

Risk-free interest rate	0.31	%
Expected dividend yield	—
Expected term in years	6.3
Expected volatility	80	%

During the year ended December 31, 2020, excluding the Cancelled Options, options to purchase 674,842 shares of common stock were granted with a weighted-average exercise price per share of $20.68. On September 2, 2020, options to purchase 16,342 shares of common stock under the Existing Plan were awarded to certain directors of the Company with an exercise price per share of $14.90, and on various dates beginning at the closing of the IPO through December 31, 2020, 658,500 shares of common stock under the New Plan were awarded with a weighted-average exercise price per share of $20.83. The stock options generally vest over three or four years and have a ten-year contractual term.

During the year ended December 31, 2021, option to purchase 3,192,600 shares of common stock under the New Plan were awarded with a weighted-average grant date fair value per share of $16.33. 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, excluding the Cancelled Options, for the years ended December 31, 2021 and 2020:

	Year Ended December 31,
	2021			2020
Risk-free interest rate		0.84	%		0.54	%
Expected dividend yield		—			—
Expected term in years		6.0			6.2
Expected volatility		75	%		77	%

The following table summarizes stock option activity during the year ended December 31, 2021:

						Weighted
				Weighted		Average		Aggregate
				Average		Remaining		Intrinsic
	Stock			Exercise		Contractual		Value
	Options			Price		Life (in years)		(in thousands)
Outstanding at December 31, 2019		—		$	—		—	$	—
Options granted		674,842			20.68
Outstanding at December 31, 2020		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 exercisable at December 31, 2021		243,722		$	21.30		8.7	$	—

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, 2021 and the exercise price of the stock options. As of December 31, 2021, the total unrecognized compensation related to unvested stock option awards granted was $44.7 million, which the Company expects to recognize over a weighted-average period of approximately 3.1 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 RSUs were also subject to a liquidity-based performance vesting condition that was met upon the closing of the IPO. 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, 2021, 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 $10.7 million which is expected to be amortized on a straight-line basis over the weighted- average remaining vesting 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, 2021 and 2020 was as follows:

				Weighted
				Average
				Grant Date
	Number			Fair Value
	of Shares			per Share
Nonvested at January 1, 2020		—		$	—
Replacement restricted units granted		2,518,932			5.25
Restricted units granted		331,121			14.90
Vested		—			—
Nonvested at December 31, 2020		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 Stock Awards

RA Session II, the Company’s 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, 2021, the total unrecognized compensation related to unvested RSAs granted was $1.8 million which is expected to be amortized on a straight-line basis

over the weighted average remaining vesting period of approximately 0.6 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, 2021 and 2020 was as follows:

				Weighted
				Average
				Grant Date
	Number			Fair Value
	of Shares			per Share
Nonvested at December 31, 2019		—		$	—
Restricted stock granted		769,058			5.28
Vested		—			—
Nonvested at December 31, 2020		769,058		$	5.28
Restricted stock granted		—			—
Vested		(427,083	)		5.28
Nonvested at December 31, 2021		341,975		$	5.28

During the year ended December 31, 2021, $0.4 million of stock-based compensation expense was capitalized as part of construction in process (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, 2021 and 2020 (in thousands):

	For the Year Ended December 31,
	2021		2020
Research and development expense	$	8,286	$	1,167
General and administrative expense		9,898		2,187
Total	$	18,184	$	3,354

Income Taxes

12 Months Ended

Dec. 31, 2021

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 2021 or 2020.

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,
	2021			2020
Statutory rate		21.00	%		21.00	%
State tax		0.20	%		0.06	%
Research and development tax credits		7.68	%		1.06	%
Other permanent differences		(1.12	)%		(0.25	)%
Change in valuation allowance		(27.76	)%		(15.91	)%
Change in fair value of tranche liability		(0.00	)%		(5.96	)%
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, 2021 and 2020, the significant components of the Company’s net deferred tax asset are as follows (in thousands):

	For the Year Ended December 31,
	2021			2020
Net operating loss carryforwards	$	37,005		$	5,810
Tax credit carryforwards		14,813			672
Accruals and reserves		1,467			334
Other		103			21
Intangibles		4,169			2,390
Non-qualified stock options		674			555
Total deferred tax assets		58,231			9,782
Valuation allowance		(58,231	)		(9,782	)
Deferred tax asset, net of allowance	$	—		$	—

There are no deferred tax liabilities as of December 31, 2021 and 2020, respectively. The valuation allowance is equal to the total deferred tax asset amounts as of December 31, 2021 and 2020 as there are no deferred tax liabilities in the respective periods. 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 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 $48.4 million during the year ended December 31, 2021 and by $9.5 million during the year ended December 31, 2020.

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 $1.0 million. The net operating losses and state tax credit carryforward do not expire. As of December 31, 2020, there were net federal operating losses of $27.7 million, federal tax credit carryforward of $0.9 million, and state tax credit carryforward of less than $0.1 million. The federal tax credit carryforward will expire in 2040. The Company files federal 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 not completed a study to assess whether an ownership change has occurred, or whether there have been multiple ownership changes since its formation. There could also be additional ownership changes in the future 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 http://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 http://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 http://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 http://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 http://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 http://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 http://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 http://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 http://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690

+ Details

Commitments and Contingencies

12 Months Ended

Dec. 31, 2021

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

Note 11—Commitments and Contingencies

Litigation

The Company is not a party to any material legal proceedings and is not aware of any pending or threatened claims. From time to time, the Company may be subject to various legal proceedings and claims that arise in the ordinary course of its business activities.

Commitments

In the normal course of business, the Company enters into contracts that contain a variety of indemnifications with its employees, licensors, suppliers and service providers. The Company’s maximum exposure under these arrangements is unknown at December 31, 2021. The Company does not anticipate recognizing any significant losses relating to these arrangements.

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, 2021 and are expected to be released in 2023. 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.

The Company incurred initial direct costs to enter into the Durham Lease of approximately $0.8 million. The costs have been recorded on the consolidated balance sheets as a deferred lease asset and are being amortized into earnings over the term of the Durham Lease.

In accordance with ASC Topic 840, Leases, the Company is 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 are also capitalized within property, plant and equipment, net. Costs of approximately $45.8 million have been capitalized during the year ended December 31, 2021, related to both equipment purchases and the build-out of the leased Facility. The Company will assess and determine if the build-to-suit asset and corresponding liability should be derecognized upon completion of construction.

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’s obligation for the payment of base rent for the Office Space is initially approximately $32,500 per month and will increase annually, up to an estimated monthly base rent of $50,000 during the term of the Dallas Lease. The Company is obligated to pay operating costs and utilities applicable to the Office Space. Total future minimum lease payments under the Dallas Lease over the initial 10 year term are approximately $4.9 million. The Company is responsible for costs of constructing interior improvements within the Office Space that exceed $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 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.

As of December 31, 2021, the Company recognized approximately $0.6 million of lease construction incentive based on the construction allowance provided. The construction incentive has been recorded on the consolidated balance sheets as a deferred lease incentive obligation and is being amortized into earnings as a deduction of rent expense over the term of the Dallas Lease.

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 commences on the date on which certain improvements to the Expansion Premises have been made and the Expansion Premises is tendered to the Company for possession, which the Company and the Dallas Landlord presently anticipate to be delivered on or about June 1, 2022, and will have a term of approximately ten years. The Company’s obligation for the payment of base rent for the Expansion Premises will initially be approximately $40,000 per month and will increase annually, up to an estimated monthly base rent of $62,000 during the term of the Dallas Lease Expansion.

The Company is obligated to pay operating costs and utilities applicable to the Expansion Premises. Total future minimum lease payments under the Dallas Lease 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 15^th floor at 3000 Pegasus Park Drive, Dallas, Texas 75247 before the Dallas Landlord accepts any offer for such space.

On-site Generation Lease

On June 30, 2021, the Company entered into a lease agreement (the “On-site Generation Lease”) with an Electricity Utility Company (the “On-site Generation Landlord”), pursuant to which the Company will lease equipment to generate its supply of electricity (the “Leased Equipment”).

The On-site Generation Lease has not commenced as of December 31, 2021, as the Company does not have the right to operate nor control the leased equipment. The On-site Generation Lease will have an initial term of ten years, and will automatically renew annually thereafter until terminated. The Company’s obligation for the payment of fees for the Leased Equipment and monthly maintenance and fuel acquisition costs (the “Monthly Rate”) is $29,465 per month and eight advanced monthly payments of $126,500. Total future minimum lease payments under the On-site Generation Lease over the initial ten-year term, including the advanced payments, are approximately $4.5 million.

The On-site Generation Landlord has the right to terminate the lease upon breach of a material provision of the On-site Generation Lease, including the Company’s failure to pay financial obligations in a timely manner.

Central Utilities Building

On December 21, 2021, the Company entered into a lease agreement for a Central Utilities Building (the “CUB Lease”) with an Electricity Utility Company (the “CUB Landlord”), pursuant to which the Company will lease equipment to maintain and distribute its supply of electricity (the “Leased CUB”).

The CUB Lease has not commenced as of December 31, 2021, as the Company does not have the right to operate nor control the leased equipment. The CUB Lease will have an initial term of ten years. After the initial term CUB Lease will renew on an annual basis until terminated. The Company’s obligation for the payment of fees (the “Monthly Fees”) for the CUB Lease is $82,700 per month and ten advanced monthly payments of $169,753. Total future minimum lease payments under the CUB Lease over the initial ten-year term, including advanced payments, are approximately $11.6 million.

The CUB Landlord has the right to terminate the lease upon breach of a material provision of the CUB Lease, including the Company’s failure to pay financial obligations in a timely manner.

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

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

Significant Accounting Policies (Policies)	12 Months Ended
Significant Accounting Policies (Policies)	Dec. 31, 2021
Accounting Policies [Abstract]
Property Plant and Equipment, net	Property, Plant and Equipment, net Property, plant and equipment, net are stated at cost less accumulated depreciation and consist solely of computer equipment and laboratory equipment. Directly identifiable payroll and payroll-related costs incurred in connection with the build-out of the Company’s cGMP manufacturing facility are capitalized into the cost basis of the asset to the extent that such costs are 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 five 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.
Build-to-Suit Lease	Build-to-Suit Lease In the Company’s lease arrangement in Durham, North Carolina (as described in Note 11), 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 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. Upon completion of construction, the Company will consider the requirements for sale-leaseback accounting treatment, including evaluating whether all risks of ownership have been transferred back to the landlord.
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 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, and the valuation of the preferred stock tranche liability. 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. In response to the ongoing and rapidly evolving COVID-19 pandemic, management considered the impact of the estimated economic implications on the Company’s critical and significant accounting estimates, including assessment of impairment of long-lived assets.
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 CNS. As of December 31, 2021 and 2020, the Company did not have any long-lived assets located outside of the United States.
Cash and Cash Equivalents	Cash and Cash Equivalents Cash and cash equivalents consist of funds held in a standard checking account and a 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, 2021 and 2020, 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. Management believes that the Company is not exposed to significant credit risk as the Company’s deposits are held at financial institutions that management believes 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. As of December 31, 2021 and 2020, there was $0.5 million and 0, respectively, of such deferred costs included in prepaid expenses and other current assets on the consolidated balance sheets. Deferred offering costs, consisting of legal, accounting, and filing fees directly relating to the IPO and the Company’s Series A and Series B preferred stock financings, were capitalized and offset against the related proceeds upon the completion of the offerings in 2020. Upon completion of the IPO in September 2020, approximately $2.5 million of deferred offering costs were offset against the IPO proceeds in additional paid-in capital.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets The Company evaluates its long-lived assets, which consist of property and equipment, 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 exceeds the fair value of the asset. There were no impairment losses recognized during the years ended December 31, 2021 and 2020.
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.
Convertible Preferred Stock	Convertible Preferred Stock The Company recorded shares of its convertible preferred stock at their respective fair values on the dates of issuance, net of issuance costs. The Company applied the guidance in ASC 480-10-S99-3A, SEC Staff Announcement: Classification and Measurement of Redeemable Securities and therefore classified the Series A convertible preferred stock as mezzanine equity. The convertible preferred stock was recorded outside of stockholders’ deficit because, in the event of certain deemed liquidation events considered not solely within the Company’s control, such as a merger, acquisition and sale of all or substantially all of the Company’s assets (a “Deemed Liquidation Event”), the convertible preferred stock would become redeemable at the option of the holders. In the event of a change of control of the Company, proceeds received from the sale of such shares would have been distributed in accordance with the liquidation preferences set forth in the Company’s Amended and Restated Certificate of Incorporation. The Company determined not to adjust the carrying values of the convertible preferred stock to the liquidation preferences of such shares because of the uncertainty of whether or when such an event would occur. All shares of the Company’s previously issued and outstanding convertible preferred stock were converted into shares of common stock upon the closing of the IPO (see Note 7).
Preferred Stock Tranche Liability	Preferred Stock Tranche Liability The Company determined that its obligation to issue, and the Company’s investors’ right to purchase, additional shares of Series A convertible preferred stock pursuant to the milestone closings (see Note 7) represented a freestanding financial instrument (the “tranche liability”). The tranche liability was initially recorded at fair value. The proceeds from the sale of the convertible preferred stock were first allocated to the fair value of the tranche liability with the remaining proceeds from the sale of the convertible preferred stock allocated to the Series A convertible preferred stock. The tranche liability was remeasured at each reporting period and upon the exercise or expiration of the obligation, with gains and losses arising from subsequent changes in its fair value recognized in other expense in the consolidated statements of operations. At the time of the exercise or expiration of the tranche liability, any remaining value of the tranche liability was reclassified to convertible preferred stock on the consolidated balance sheets.
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 on the Nasdaq Global Select Market 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 are directly involved in the buildout of the Company’s cGMP manufacturing facility are capitalized into the cost basis of that asset to the extent that such costs are 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 year ended December 31, 2021, the Company recorded an increase in the amount of gross unrecognized tax benefits by $4.7 million. 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, 2021 and 2020.
Comprehensive Loss	Comprehensive Loss Comprehensive loss is equal to net loss as presented in the accompanying consolidated statements of operations, as the Company did not have any other comprehensive income or loss for the periods presented.
Recently Adopted Accounting Pronouncements	Recently Adopted Accounting Pronouncements In August 2018, the FASB issued Accounting Standards Update (“ASU”) No. 2018-13, Fair Value Measurement (ASC Topic 820) (“ASU 2018-13”), which modifies, removes and adds certain disclosure requirements on fair value measurements based on the FASB Concepts Statement, Conceptual Framework for Financial Reporting—Chapter 8: Notes to Financial Statements. The amendments on changes in unrealized gains and losses, the range and weighted-average of significant unobservable inputs used to develop Level 3 fair value measurements and the narrative description of measurement uncertainty should be applied prospectively for only the most recent interim or annual period presented in the initial fiscal year of adoption. All other amendments should be applied retrospectively to all periods presented upon their effective date. The Company adopted ASU 2018-13 as of January 1, 2020 for the annual period. The adoption of the guidance did not have a material impact on the Company’s consolidated financial statements. In November 2018, the FASB issued ASU No. 2018-18 – Collaborative Arrangements, which clarifies that certain transactions between collaborative arrangement participants should be accounted for as revenue when the collaborative arrangement participant is a customer in the context of a unit of account and precludes recognizing as revenue consideration received from a collaborative arrangement participant if the participant is not a customer. The Company early adopted this standard as of January 1, 2020. This ASU requires retrospective adoption to the date the Company adopted ASC 606, which was early adopted upon the Company’s Inception, by recognizing a cumulative-effect adjustment to the opening balance of retained earnings of the earliest annual period presented. As the Company does not have any contracts with customers or collaborative arrangements, the adoption of this guidance did not have any impact on the Company’s consolidated financial statements.
Recently Issued Accounting Pronouncements	Recently Issued 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. This guidance will become effective for the Company for annual reporting periods beginning after December 15, 2021 and interim periods within fiscal years beginning after December 15, 2022. The Company is currently evaluating the impact of this standard on its consolidated financial statements. 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 is currently evaluating the impact of this standard on its consolidated financial statements.

Supplemental Financial Information (Tables)

12 Months Ended

Dec. 31, 2021

Balance Sheet Related Disclosures [Abstract]

Schedule of Property, Plant and Equipment

Property, Plant and Equipment, net consisted of the following (in thousands):

	December 31, 2021			December 31, 2020
Leasehold improvements	$	2,067		$	—
Furniture and fixtures		845			—
Computer equipment		1,098			95
Laboratory equipment		1,095			—
Construction in progress		46,004			201
		51,109			296
Accumulated depreciation		(499	)		(9	)
Property, plant and equipment, net	$	50,610		$	287

Schedule of Accrued Expenses and Other Current Labilities

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

	December 31, 2021		December 31, 2020
Accrued research and development	$	11,895	$	2,106
Accrued compensation		7,703		1,766
Accrued license fees		3,500		—
Accrued property, plant, and equipment		2,644		173
Accrued clinical trials		1,659		—
Accrued professional and consulting fees		1,091		999
Other		1,491		91
Total accrued expenses and other current liabilities	$	29,983	$	5,135

Schedule of Prepaid Expenses and Other Current Assets

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

	December 31, 2021		December 31, 2020
Prepaid research and development	$	5,218	$	2,462
Prepaid clinical trial		3,298		944
Deferred offering costs		545		—
Prepaid bonus		427		409
Prepaid insurance		148		2,480
Other		863		331
Total prepaid expenses and other current assets	$	10,499	$	6,626

Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2021

Schedule of Restricted Stock Units Activity

The Company’s RSU activity for the year ended December 31, 2021 and 2020 was as follows:

				Weighted
				Average
				Grant Date
	Number			Fair Value
	of Shares			per Share
Nonvested at January 1, 2020		—		$	—
Replacement restricted units granted		2,518,932			5.25
Restricted units granted		331,121			14.90
Vested		—			—
Nonvested at December 31, 2020		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

Schedule of Restricted Stock Awards Activity

The Company’s RSA activity for the year ended December 31, 2021 and 2020 was as follows:

				Weighted
				Average
				Grant Date
	Number			Fair Value
	of Shares			per Share
Nonvested at December 31, 2019		—		$	—
Restricted stock granted		769,058			5.28
Vested		—			—
Nonvested at December 31, 2020		769,058		$	5.28
Restricted stock granted		—			—
Vested		(427,083	)		5.28
Nonvested at December 31, 2021		341,975		$	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, 2021 and 2020 (in thousands):

	For the Year Ended December 31,
	2021		2020
Research and development expense	$	8,286	$	1,167
General and administrative expense		9,898		2,187
Total	$	18,184	$	3,354

Cancelled Options

Schedule of Assumptions Used to Estimate Fair Value of Stock Options and Cancelled Options

The following assumptions were used to estimate the fair value of the Cancelled Options that were granted on July 1, 2020:

Risk-free interest rate	0.31	%
Expected dividend yield	—
Expected term in years	6.3
Expected volatility	80	%

Stock Options

Schedule of Assumptions Used to Estimate Fair Value of Stock Options and Cancelled Options

The following weighted-average assumptions were used to estimate the fair value of stock options, excluding the Cancelled Options, for the years ended December 31, 2021 and 2020:

	Year Ended December 31,
	2021			2020
Risk-free interest rate		0.84	%		0.54	%
Expected dividend yield		—			—
Expected term in years		6.0			6.2
Expected volatility		75	%		77	%

Schedule of Stock Option Activity

The following table summarizes stock option activity during the year ended December 31, 2021:

						Weighted
				Weighted		Average		Aggregate
				Average		Remaining		Intrinsic
	Stock			Exercise		Contractual		Value
	Options			Price		Life (in years)		(in thousands)
Outstanding at December 31, 2019		—		$	—		—	$	—
Options granted		674,842			20.68
Outstanding at December 31, 2020		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 exercisable at December 31, 2021		243,722		$	21.30		8.7	$	—

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2021

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,
	2021			2020
Statutory rate		21.00	%		21.00	%
State tax		0.20	%		0.06	%
Research and development tax credits		7.68	%		1.06	%
Other permanent differences		(1.12	)%		(0.25	)%
Change in valuation allowance		(27.76	)%		(15.91	)%
Change in fair value of tranche liability		(0.00	)%		(5.96	)%
Income tax provision (benefit)		0.00	%		0.00	%

Schedule of Significant Components of Net Deferred Tax Asset

At December 31, 2021 and 2020, the significant components of the Company’s net deferred tax asset are as follows (in thousands):

	For the Year Ended December 31,
	2021			2020
Net operating loss carryforwards	$	37,005		$	5,810
Tax credit carryforwards		14,813			672
Accruals and reserves		1,467			334
Other		103			21
Intangibles		4,169			2,390
Non-qualified stock options		674			555
Total deferred tax assets		58,231			9,782
Valuation allowance		(58,231	)		(9,782	)
Deferred tax asset, net of allowance	$	—		$	—

Organization and Description of Business Operations - Additional Information (Details)					2 Months Ended	5 Months Ended	12 Months Ended
	Oct. 05, 2021 USD ($)	Sep. 29, 2020 shares	Sep. 28, 2020 USD ($) $ / shares shares	Sep. 16, 2020	Aug. 31, 2020 USD ($) shares	Jul. 31, 2020 USD ($) shares	Dec. 31, 2021 USD ($) $ / shares shares	Dec. 31, 2020 USD ($) shares	Jun. 30, 2020 $ / shares
Organization and Description of Business Operations [Line Items]
Share issue price per share \| $ / shares									$ 7.52
Accumulated deficit \| $							$ (235,649,000)	$ (61,126,000)
Cash and cash equivalents \| $							$ 149,103,000	$ 251,253,000
Sales Agreement
Organization and Description of Business Operations [Line Items]
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
Series A Convertible Preferred Stock
Organization and Description of Business Operations [Line Items]
Conversion of convertible preferred stock to common stock, shares			10,000,000					10,000,000
Aggregate shares sold						10,000,000
Proceeds from issuances of convertible preferred stock, net of issuance costs \| $						$ 30,000,000.0		$ 29,395,000
Series B Convertible Preferred Stock
Organization and Description of Business Operations [Line Items]
Conversion of convertible preferred stock to common stock, shares			5,647,048					5,647,048
Aggregate shares sold					5,647,048
Proceeds from issuances of convertible preferred stock, net of issuance costs \| $					$ 96,000,000.0			$ 95,815,000
IPO
Organization and Description of Business Operations [Line Items]
Issuance of shares of common stock, shares			7,869,566				9,050,000
Share issue price per share \| $ / shares			$ 20.00				$ 20.00
Net proceeds from issuance of common stock \| $			$ 165,900,000
Increase in outstanding shares			26,097,378
Underwriters’ Option to Purchase Additional Shares
Organization and Description of Business Operations [Line Items]
Issuance of shares of common stock, shares		1,180,434	1,180,434
Common Stock
Organization and Description of Business Operations [Line Items]
Conversion ratio			1.0895	1.0895
Issuance of shares of common stock, shares								9,050,000
Conversion of convertible to common stock, shares			17,047,378					17,047,378

Significant Accounting Policies - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Sep. 30, 2020
Significant Accounting Policies [Line Items]
Cash equivalents	$ 0	$ 0
Shelf Registration,term	3 years
Deferred offering costs	$ 545,000
Impairment losses	0	0
Increase in the amount of gross unrecognized tax benefits	4,700,000
Unrecognized tax benefits to change significantly over next 12 months	0
Interest and penalties associated with income tax positions	$ 0	0
ASU 2018-13
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, 2020
Change in Accounting Principle, Accounting Standards Update, Immaterial Effect [true false]	true
ASU No. 2018-18
Significant Accounting Policies [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adoption Date	Jan. 01, 2020
Change in Accounting Principle, Accounting Standards Update, Immaterial Effect [true false]	true
Change in Accounting Principle, Accounting Standards Update, Early Adoption [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	5 years
Prepaid Expenses and Other Current Assets
Significant Accounting Policies [Line Items]
Deferred offering costs	$ 500,000	0
IPO
Significant Accounting Policies [Line Items]
Deferred offering costs			$ 2,500,000
United States
Significant Accounting Policies [Line Items]
Long-lived assets	$ 0	$ 0

Loan with Silicon Valley Bank - Additional Information (Details) $ in Thousands		12 Months Ended
	Aug. 12, 2021 USD ($) Program	Dec. 31, 2021 USD ($)
Debt Instrument [Line Items]
Debt instrument, maturity date	Aug. 01, 2026
Percentage of interest rate	7.00%
Percentage of prepayment of facility	7.50%
Warrants associated with loan facility	$ 0
Exit fee recorded as debt discount		$ 3,000
Percentage of annual default interest rate	5.00%
Interest expense related to term loan		1,100
Prime Rate
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate	3.75%
Term Loan
Debt Instrument [Line Items]
Current borrowing capacity	$ 30,000	$ 10,000
Through December 31, 2021 \| Term Loan
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 40,000
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
Debt instrument, maturity start date	Jan. 01, 2022
Debt instrument, maturity end date	Sep. 30, 2022
October 1, 2022 until March 31, 2023 \| Term Loan
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 20,000
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
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%

Research, Collaboration, Grant and License Agreements - Additional Information (Details)	1 Months Ended					12 Months Ended
	Mar. 31, 2021 USD ($)	Oct. 31, 2020 USD ($)	Aug. 31, 2020 USD ($)	Apr. 30, 2020 USD ($) Product	Dec. 31, 2019 USD ($)	Dec. 31, 2021 USD ($) shares	Dec. 31, 2020 USD ($) shares	Oct. 29, 2020 USD ($)	Mar. 31, 2020 shares	Feb. 21, 2020 USD ($)	Nov. 30, 2019 shares
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Common stock, shares issued \| shares						38,473,945	37,761,435
Research and development						$ 131,943,000	$ 31,893,000
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
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									0		2,179,000
Percentage of fully diluted common stock shares outstanding											20.00%
Percentage of entitled to receive additional shares on fully diluted basis											10.00%
Queen's Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Research grant of committed fund amount					$ 3,800,000
Additional milestone payments						0
Queen's Agreement \| Research and Development Expense
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Cash payment to acquire license agreement				$ 3,000,000.0
Queen's 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]
Additional milestone payments						$ 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

Stockholders' Equity (Deficit), Convertible Preferred Stock and Tranche Liability - Additional Information (Details) $ / shares in Units, $ in Thousands									2 Months Ended	5 Months Ended	12 Months Ended
	Sep. 29, 2020 shares	Sep. 28, 2020 USD ($) $ / shares shares	Sep. 16, 2020	Jul. 28, 2020 $ / shares shares	Jul. 02, 2020 USD ($) $ / shares shares	Jun. 30, 2020 USD ($) $ / shares shares	Mar. 05, 2020 shares	Mar. 04, 2020 USD ($) $ / shares shares	Aug. 31, 2020 USD ($)	Jul. 31, 2020 USD ($)	Dec. 31, 2021 $ / shares shares	Dec. 31, 2020 USD ($) shares
Class Of Stock [Line Items]
Common stock, shares authorized		200,000,000		32,685,000							200,000,000	200,000,000
Convertible preferred stock, shares authorized				15,647,052
Convertible preferred stock, shares authorized		10,000,000									10,000,000	10,000,000
Preferred stock, shares issued											0	0
Preferred stock, shares outstanding											0	0
Share issue price per share \| $ / shares						$ 7.52
Preferred stock tranche liability \| $								$ 1,100
Non cash expenses due to remeasured fair value of tranche liability \| $						$ 17,000						$ (17,030)
Mile stone shares issued during the period					4,000,000	200,000
Tranche liability amount reclassified to convertible preferred stock \| $					$ 18,100
Common Stock
Class Of Stock [Line Items]
Shares issued during period												9,050,000
Conversion of stock, shares issued		17,047,378										17,047,378
Conversion ratio		1.0895	1.0895
IPO
Class Of Stock [Line Items]
Shares issued during period		7,869,566									9,050,000
Share issue price per share \| $ / shares		$ 20.00									$ 20.00
Gross proceeds from issuance of common stock \| $		$ 181,000
Stock issuance costs, including underwriters' discounts and commissions \| $		$ 15,100
Increase in outstanding shares		26,097,378
Underwriters’ Option to Purchase Additional Shares
Class Of Stock [Line Items]
Shares issued during period	1,180,434	1,180,434
Series A Convertible Preferred Stock
Class Of Stock [Line Items]
Convertible preferred stock, shares authorized				10,000,000
Conversion of convertible preferred stock to common stock, shares		10,000,000										10,000,000
Number of share options exercised					3,800,000	200,000
Clinical milestones for gross proceeds \| $					$ 11,400	$ 600
Proceeds from issuances of convertible preferred stock, net of issuance costs \| $										$ 30,000		$ 29,395
Convertible preferred stock tranche liability, offering price \| $ / shares								$ 3.00
Convertible preferred stock tranche liability, term								1 year
Milestone pro-rate shares issued during the period						200,000
Series A Convertible Preferred Stock \| Risk Free Rate
Class Of Stock [Line Items]
Convertible preferred stock tranche liability, measurement input								0.0059
Series A Convertible Preferred Stock \| Expected Volatility
Class Of Stock [Line Items]
Convertible preferred stock tranche liability, measurement input								0.80
Series A Convertible Preferred Stock \| Probability of Achieving Clinical Milestones and Timing
Class Of Stock [Line Items]
Convertible preferred stock tranche liability, measurement input								0.60
Series A Convertible Preferred Stock \| PBM TGT Holdings, LLC
Class Of Stock [Line Items]
Shares issued during period						3,266,667
Series A Convertible Preferred Stock \| Nolan Capital, LLC
Class Of Stock [Line Items]
Shares issued during period						400,000
Series A Convertible Preferred Stock \| Private Placement \| Series A Purchase Agreement
Class Of Stock [Line Items]
Share issue price per share \| $ / shares								$ 3.00
Series A Convertible Preferred Stock \| Private Placement \| Series A Purchase Agreement \| Maximum
Class Of Stock [Line Items]
Shares issued during period								10,000,000
Series A Convertible Preferred Stock \| Private Placement \| Initial Closing
Class Of Stock [Line Items]
Shares issued during period								6,000,000
Series A Convertible Preferred Stock \| Private Placement \| Achievement of Specific Clinical Milestone One
Class Of Stock [Line Items]
Shares issued during period							2,000,000
Series A Convertible Preferred Stock \| Private Placement \| Achievement of Specific Clinical Milestone Two
Class Of Stock [Line Items]
Shares issued during period							2,000,000
Series A Convertible Preferred Stock \| Private Placement \| Upon Achievement of Certain Defined Clinical Milestones
Class Of Stock [Line Items]
Shares issued during period								4,000,000
Series B Convertible Preferred Stock
Class Of Stock [Line Items]
Convertible preferred stock, shares authorized				5,647,052
Conversion of convertible preferred stock to common stock, shares		5,647,048										5,647,048
Proceeds from issuances of convertible preferred stock, net of issuance costs \| $									$ 96,000			$ 95,815
Convertible preferred stock tranche liability, offering price \| $ / shares						$ 17.00
Convertible preferred stock tranche liability, term						6 months
Series B Convertible Preferred Stock \| Risk Free Rate
Class Of Stock [Line Items]
Convertible preferred stock tranche liability, measurement input						0.0017
Series B Convertible Preferred Stock \| Expected Volatility
Class Of Stock [Line Items]
Convertible preferred stock tranche liability, measurement input						0.80
Series B Convertible Preferred Stock \| Series B Purchase Agreement
Class Of Stock [Line Items]
Share issue price per share \| $ / shares					$ 17.00
Series B Convertible Preferred Stock \| Private Placement \| Series B Purchase Agreement
Class Of Stock [Line Items]
Shares issued during period				5,647,048
Share issue price per share \| $ / shares				$ 17.00
Proceeds from issuances of convertible preferred stock, net of issuance costs \| $									$ 96,000
Series B Convertible Preferred Stock \| Private Placement \| Series B Purchase Agreement \| Maximum
Class Of Stock [Line Items]
Shares issued during period				5,647,052

Stock-Based Compensation - Additional Information (Details) - USD ($)				3 Months Ended	4 Months Ended	12 Months Ended
	Sep. 16, 2020	Sep. 02, 2020	Jul. 01, 2020	Mar. 31, 2021	Dec. 31, 2020	Dec. 31, 2021	Dec. 31, 2020	Jan. 01, 2022	Jan. 01, 2021	Jul. 02, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Fair value of common stock per share			$ 5.28
Stock-based compensation expense						$ 18,184,000	$ 3,354,000
Construction in Progress
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense						$ 400,000
Series B Convertible Preferred Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Preferred stock, issuing price per share										$ 17.00
Employee Stock Purchase Plan (ESPP)
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance	724,000							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 1st of each year for a period of up to ten years, commencing on the first January 1 following the IPO Date and ending on (and including) January 1, 2030, in an amount equal to the lesser of (i) one percent (1.0%) of the total number of shares of capital stock outstanding on December 31st of the preceding calendar year, and (ii) 724,000 shares of common stock.
Number of shares of common stock issued under ESPP	0					0
Restricted Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares awarded							2,518,932
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							331,121
Share-based payment award, unvested RSU/RSA granted, compensation cost not yet recognized						$ 10,700,000
Share-based payment award, RSU/RSA granted, weighted average grant date fair value							$ 14.90
Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based payment award, expiration period						10 years	10 years
Share-based payment award, options granted						3,192,600	674,842
Share-based payment award, options granted, exercise price per share						$ 24.99	$ 20.68
Stock options were exercised during the period						$ 0
Share-based payment award, options, compensation cost not yet recognized						$ 44,700,000
Share-based payment award, compensation cost not yet recognized, weighted-average period of recognition						3 years 1 month 6 days
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						7 months 6 days
Share-based payment award, RSU/RSA granted							769,058
Share-based payment award, unvested RSU/RSA granted, compensation cost not yet recognized						$ 1,800,000
Share-based payment award, RSU/RSA granted, weighted average grant date fair value			$ 5.28				$ 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
Maximum \| Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Award vesting period						4 years	4 years
Minimum [Member] \| Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Award vesting period						1 year	3 years
2020 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance	209,841
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 \| Stock Options \| Directors
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based payment award, options granted		16,342
Share-based payment award, options granted, exercise price per share		$ 14.90
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
2020 Equity Incentive Plan \| Common Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares authorized for issuance	3,845,294		3,529,412
New Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance	3,390,168							1,923,697	1,434,934
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 will automatically increase 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, options granted					658,500	3,192,600
Share-based payment award, options granted, exercise price per share					$ 20.83
Share-based payment award, options, weighted-average grant date fair value						$ 16.33

Stock-Based Compensation - Schedule of Stock Option Activity (Details) - Stock Options - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Outstanding. Stock Options, Beginning Balance	674,842
Options granted, Stock Options	3,192,600	674,842
Options cancelled or forfeited, Stock Options	(217,480)
Outstanding. Stock Options, Ending Balance	3,649,962	674,842
Options exercisable at December 31, 2021, Stock Options	243,722
Outstanding, Weighted Average Exercise Price, Beginning balance	$ 20.68
Options granted, Weighted Average Exercise Price	24.99	$ 20.68
Options cancelled or forfeited, Weighted Average Exercise Price	26.07
Outstanding, Weighted Average Exercise Price, Ending balance	24.13	$ 20.68
Options exercisable at December 31, 2021, Weighted Average Exercise Price	$ 21.30
Outstanding, Weighted Average Remaining Contractual Life	9 years 2 months 12 days	9 years 9 months 18 days
Weighted Average Remaining Contractual Life, Options exercisable at December 31, 2021	8 years 8 months 12 days
Outstanding, Aggregate Intrinsic Value, Beginning Balance	$ 3,953
Outstanding, Aggregate Intrinsic Value, Ending Balance		$ 3,953

Commitments and Contingencies - Additional Information (Details)						12 Months Ended
	Dec. 21, 2021 USD ($)	Dec. 14, 2021 USD ($) ft²	Jun. 30, 2021 USD ($)	Jan. 11, 2021 USD ($) ft²	Dec. 17, 2020 ft²	Dec. 31, 2021 USD ($)
Loss Contingencies [Line Items]
Future minimum lease payments						$ 52,153,000
Durham Lease
Loss Contingencies [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
Operating lease extend term of contract					5 years
Amount required to place in escrow account						2,600,000
Operating leases initial direct costs						800,000
Build-to-suit asset						26,300,000
Build-to-suit lease liability						26,300,000
Equipment purchases and build-out of leased Facility						45,800,000
Dallas Lease
Loss Contingencies [Line Items]
Lease construction incentive						$ 600,000
Dallas Lease \| Pegasus Park L L C
Loss Contingencies [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
Operating lease extend term of contract				5 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.
Lease, option to extend				true
Obligation for payment of initial base rent for office space				$ 32,500,000
Maximum estimated monthly base rent increase annually during term of lease				50,000,000
Future minimum lease payments				$ 4,900,000
Dallas Lease \| Pegasus Park L L C \| Minimum [Member]
Loss Contingencies [Line Items]
Maximum construction allowance provided by landlord per rentable square foot \| ft²				40.00
Dallas Lease Amendment \| Pegasus Park L L C
Loss Contingencies [Line Items]
Number of operating lease landlord square feet manufacturing facility \| ft²		18,000
Operating lease term of contract		10 years
Obligation for payment of initial base rent for office space		$ 40,000,000
Maximum estimated monthly base rent increase annually during term of lease		62,000,000
Future minimum lease payments		$ 6,000,000.0
Dallas Lease Amendment \| Pegasus Park L L C \| Minimum [Member]
Loss Contingencies [Line Items]
Maximum construction allowance provided by landlord per rentable square foot \| ft²		40.00
On Site Generation Lease
Loss Contingencies [Line Items]
Operating lease term of contract			10 years
Future minimum lease payments			$ 4,500,000
Obligation for payment of fees for leased equipment and monthly maintenance and fuel acquisition costs			29,465,000
Advanced monthly prepayment			$ 126,500,000
Central Utilities Building
Loss Contingencies [Line Items]
Operating lease term of contract	10 years
Future minimum lease payments	$ 11,600,000
Obligation for payment of fees for leased equipment and monthly maintenance and fuel acquisition costs	82,700,000
Advanced monthly prepayment	$ 169,753,000

Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) (Parenthetical) $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($)
Issuance of shares of common stock in initial public offering, net of offering costs and underwriting discounts and commissions	$ 15,145
Issuance of preferred stock tranche liability	1,050
Series A Convertible Preferred Stock
Issuance of convertible preferred stock, offering costs	605
Series B Convertible Preferred Stock
Issuance of convertible preferred stock, offering costs	$ 185

Supplemental Financial Information - Schedule of Property, Plant and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 51,109	$ 296
Accumulated depreciation	(499)	(9)
Property, plant and equipment, net	50,610	287
Leasehold Improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross	2,067
Furniture and Fixtures
Property, Plant and Equipment [Line Items]
Property and equipment, gross	845
Computer Equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	1,098	95
Construction in Progress
Property, Plant and Equipment [Line Items]
Property and equipment, gross	46,004	$ 201
Laboratory Equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 1,095

Related Party Transactions - Additional Information (Details)	1 Months Ended	12 Months Ended
	Jan. 31, 2020 USD ($) PromissoryNote	Dec. 31, 2020 USD ($)	Aug. 12, 2021
Related Party Transaction [Line Items]
Percentage of interest rate			7.00%
RA Session II
Related Party Transaction [Line Items]
Number of secured promissory notes \| PromissoryNote	2
Secured Promissory Notes \| RA Session II
Related Party Transaction [Line Items]
Aggregate amount, related party transaction	$ 1,670,000
Percentage of interest rate	10.00%
Interest expense related party		$ 28,000

Stock-Based Compensation - Schedule of Restricted Stock Units Activity (Details) - Restricted Stock Units - $ / shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Nonvested, Number of Shares, Beginning Balance	2,850,053
Replacement restricted units granted, Number of Shares		2,518,932
Restricted units/stock granted, Number of Shares		331,121
Vested, Number of Shares	(712,510)
Cancelled or forfeited, Number of Shares	(250,778)
Nonvested, Number of Shares, Ending Balance	1,886,765	2,850,053
Nonvested, Weighted Average Grant Date Fair Value per Share, Beginning Balance	$ 6.37
Replacement restricted units granted, Weighted Average Grant Date Fair Value per Share		$ 5.25
Restricted units/stock granted, Weighted Average Grant Date Fair Value per Share		14.90
Vested, Weighted Average Grant Date Fair Value per Share	6.37
Cancelled or forfeited, Weighted Average Grant Date Fair Value per Share	5.25
Nonvested, Weighted Average Grant Date Fair Value per Share, Ending Balance	$ 6.52	$ 6.37

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, 2021	Dec. 31, 2020
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per share	5,878,702	4,293,953
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	1,886,765	2,850,053
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	341,975	769,058
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	3,649,962	674,842

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2021	Dec. 31, 2020
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	38,473,945	37,761,435
Common stock, shares outstanding	38,473,945	37,761,435

Supplemental Financial Information - Schedule of Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Balance Sheet Related Disclosures [Abstract]
Accrued research and development	$ 11,895	$ 2,106
Accrued compensation	7,703	1,766
Accrued license fees	3,500
Accrued property, plant, and equipment	2,644	173
Accrued clinical trials	1,659
Accrued professional and consulting fees	1,091	999
Other	1,491	91
Total accrued expenses and other current liabilities	$ 29,983	$ 5,135

Supplemental Financial Information - Schedule of Prepaid Expenses and Other Current Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Balance Sheet Related Disclosures [Abstract]
Prepaid research and development	$ 5,218	$ 2,462
Prepaid clinical trial	3,298	944
Deferred offering costs	545
Prepaid bonus	427	409
Prepaid insurance	148	2,480
Other	863	331
Total prepaid expenses and other current assets	$ 10,499	$ 6,626

Loan with Silicon Valley Bank - Schedule of Future Principal Debt Payments on Term Loan Agreement (Details) $ in Thousands	Dec. 31, 2021 USD ($)
Debt Disclosure [Abstract]
2024	$ 6,667
2025	20,000
2026	13,333
Total principal payments	40,000
Unamortized debt discount	(2,808)
Term Loan, net	$ 37,192

Stockholders' Equity (Deficit), Convertible Preferred Stock and Tranche Liability - Reconciliation of Preferred Stock Tranche Liability Measured at Fair Value (Details) - Preferred Stock Tranche Liability $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($)
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair value at issuance of Series A convertible preferred stock	$ 1,050
Change in fair value	17,030
Settlement of preferred stock tranche liability due to issuance of Milestone Shares	$ (18,080)

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, 2021	Dec. 31, 2020
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 18,184	$ 3,354
Research and Development Expense
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	8,286	1,167
General and Administrative Expense
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 9,898	$ 2,187

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, 2021	Dec. 31, 2020
Earnings Per Share [Abstract]
Net loss	$ (174,523)	$ (60,011)
Weighted average common shares outstanding, basic and diluted	37,650,566	17,665,683
Net loss per common share, basic and diluted	$ (4.64)	$ (3.40)

Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Line Items]
Provision for income taxes		$ 0
Net operating loss carryforward percentage		80.00%	80.00%	80.00%
Deferred tax liabilities	$ 0	$ 0
Valuation allowance increased	48,400,000	9,500,000
Tax credit carryforwards	14,813,000	672,000
Federal
Income Tax Disclosure [Line Items]
Net operating loss carryforward	175,600,000	27,700,000
Tax credit carryforwards	19,000,000.0	$ 900,000
Tax credit carryforward expiration or due date year		2040
State
Income Tax Disclosure [Line Items]
Net operating loss carryforward	4,100,000
Tax credit carryforwards	$ 1,000,000.0
Minimum [Member]
Income Tax Disclosure [Line Items]
Tax Cuts and Jobs Act, adjusted taxable income limitation percentage		0.30	0.30
Maximum
Income Tax Disclosure [Line Items]
Tax Cuts and Jobs Act, adjusted taxable income limitation percentage		0.50	0.50
Maximum \| State
Income Tax Disclosure [Line Items]
Tax credit carryforwards		$ 100,000

Income Taxes - Schedule of Significant Components of Net Deferred Tax Asset (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Components Of Deferred Tax Assets [Abstract]
Net operating loss carryforwards	$ 37,005	$ 5,810
Tax credit carryforwards	14,813	672
Accruals and reserves	1,467	334
Other	103	21
Intangibles	4,169	2,390
Non-qualified stock options	674	555
Total deferred tax assets	58,231	9,782
Valuation allowance	$ (58,231)	$ (9,782)

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

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

Subsequent Events - Additional Information (Details) - Subsequent Event	1 Months Ended	3 Months Ended
	Mar. 31, 2022 USD ($)	Mar. 31, 2022 USD ($) $ / shares shares
Subsequent Event [Line Items]
Percentage of headcount reduced	35.00%
Severance and termination-related costs		$ 1,400,000
Options granted for purchase an aggregate share of common stock \| shares		1,874,100
Weighted-average exercise price \| $ / shares		$ 6.23
License Agreement for CLN7
Subsequent Event [Line Items]
Payment of one-time upfront license fee	$ 300,000
License agreement regulatory related milestones maximum amount payable	7,700,000	$ 7,700,000
License agreement sales-related milestones maximum amount payable	$ 7,500,000	$ 7,500,000