0001564590-21-056225 | 10-Q | XBRL Viewer | Taysha Gene Therapies INC

Print Document View Excel Document

Document and Entity Information - shares	9 Months Ended
Document and Entity Information - shares	Sep. 30, 2021	Nov. 10, 2021
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2021
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q3
Trading Symbol	TSHA
Entity Registrant Name	Taysha Gene Therapies, Inc.
Entity Central Index Key	0001806310
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Shell Company	false
Entity File Number	001-39536
Entity Tax Identification Number	84-3199512
Entity Address, Address Line One	3000 Pegasus Park Drive
Entity Address, Address Line Two	Ste 1430
Entity Address, City or Town	Dallas
Entity Address, State or Province	TX
Entity Address, Postal Zip Code	75247
City Area Code	214
Local Phone Number	612-0000
Entity Common Stock, Shares Outstanding		38,473,945
Title of 12(b) Security	Common stock, par value $0.00001 per share
Security Exchange Name	NASDAQ
Entity Incorporation, State or Country Code	DE
Entity Interactive Data Current	Yes
Document Quarterly Report	true
Document Transition Report	false

Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 188,785	$ 251,253
Prepaid expenses and other current assets	8,385	6,626
Total current assets	197,170	257,879
Restricted cash	2,628
Deferred lease asset	691	715
Property, plant and equipment, net	40,553	287
Total assets	241,042	258,881
Current liabilities:
Accounts payable	22,051	1,994
Accrued expenses and other current liabilities	21,163	5,135
Total current liabilities	43,214	7,129
Build-to-suit lease liability	26,607
Term loan	27,812
Other non-current liabilities	3,015	450
Total liabilities	100,648	7,579
Commitments and contingencies - Note 11
Stockholders' equity
Preferred stock, $0.00001 par value per share; 10,000,000 shares authorized and no shares issued and outstanding as of September 30, 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 September 30, 2021 and December 31, 2020
Additional paid-in capital	325,657	312,428
Accumulated deficit	(185,263)	(61,126)
Total stockholders’ equity	140,394	251,302
Total liabilities and stockholders' equity	$ 241,042	$ 258,881

Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical) - $ / shares	Sep. 30, 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

Condensed Consolidated Statements of Operations (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Operating expenses:
Research and development	$ 39,528	$ 11,057	$ 94,025	$ 19,633
General and administrative	11,153	3,984	29,518	5,002
Total operating expenses	50,681	15,041	123,543	24,635
Loss from operations	(50,681)	(15,041)	(123,543)	(24,635)
Other income (expense):
Change in fair value of preferred stock tranche liability				(17,030)
Interest income	37		143
Interest expense	(543)	(1)	(737)	(28)
Total other expense, net	(506)	(1)	(594)	(17,058)
Net loss	$ (51,187)	$ (15,042)	$ (124,137)	$ (41,693)
Net loss per common share, basic and diluted	$ (1.35)	$ (1.28)	$ (3.31)	$ (3.73)
Weighted average common shares outstanding, basic and diluted	38,003,954	11,733,170	37,495,537	11,176,429

Condensed Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) (Unaudited) - USD ($) $ in Thousands	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)				$ 980	$ (1,115)
Balance, shares at Dec. 31, 2019				10,894,999
Issuance of convertible preferred stock		$ 28,345	$ 95,815
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
Conversion of Series A and Series B convertible preferred stock to common stock		$ (46,425)	$ (95,815)
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				142,240
Conversion of convertible to common stock, shares				17,047,378
Issuance of shares of common stock	165,889				165,889
Issuance of shares of common stock, shares				9,050,000
Issuance of restricted stock award, shares				769,058
Stock-based compensation	1,341				1,341
Net loss	(41,693)					(41,693)
Balance at Sep. 30, 2020	267,642				310,450	(42,808)
Balance, shares at Sep. 30, 2020				37,761,435
Balance at Jun. 30, 2020	(26,786)				980	(27,766)
Convertible preferred stock balance, shares at Jun. 30, 2020		6,200,000
Convertible preferred stock balance at Jun. 30, 2020		$ 18,014
Balance, shares at Jun. 30, 2020				10,894,999
Issuance of convertible preferred stock		$ 11,235	$ 95,815
Issuance of convertible preferred stock, shares		3,800,000	5,647,048
Reclassification of preferred stock tranche liability upon issuance of Series A milestone shares		$ 17,176
Conversion of Series A and Series B convertible preferred stock to common stock		$ (46,425)	$ (95,815)
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				142,240
Conversion of convertible to common stock, shares				17,047,378
Issuance of shares of common stock	165,889				165,889
Issuance of shares of common stock, shares				9,050,000
Issuance of restricted stock award, shares				769,058
Stock-based compensation	1,341				1,341
Net loss	(15,042)					(15,042)
Balance at Sep. 30, 2020	267,642				310,450	(42,808)
Balance, shares at Sep. 30, 2020				37,761,435
Balance at Dec. 31, 2020	$ 251,302				312,428	(61,126)
Balance, shares at Dec. 31, 2020	37,761,435			37,761,435
Issuance of shares of common stock, shares				712,510
Stock-based compensation	$ 13,229				13,229
Net loss	(124,137)					(124,137)
Balance at Sep. 30, 2021	$ 140,394				325,657	(185,263)
Balance, shares at Sep. 30, 2021	38,473,945			38,473,945
Balance at Jun. 30, 2021	$ 186,495				320,571	(134,076)
Balance, shares at Jun. 30, 2021				38,391,165
Issuance of shares of common stock, shares				82,780
Stock-based compensation	5,086				5,086
Net loss	(51,187)					(51,187)
Balance at Sep. 30, 2021	$ 140,394				$ 325,657	$ (185,263)
Balance, shares at Sep. 30, 2021	38,473,945			38,473,945

Condensed Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) (Parenthetical) (Unaudited) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2020
Issuance of preferred stock tranche liability		$ 1,050
Adjustments to Additional Paid in Capital, Stock Issued, Issuance Costs	$ 15,111	15,111
Series A Convertible Preferred Stock
Issuance of convertible preferred stock, offering costs	165	605
Series B Convertible Preferred Stock
Issuance of convertible preferred stock, offering costs	$ 185	$ 185

Condensed Consolidated Statements of Cash Flows (Unaudited)	9 Months Ended
	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)
Cash flows from operating activities
Net loss	$ (124,137,000)	$ (41,693,000)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation expense	283,000	3,000
Change in fair value of preferred stock tranche liability		17,030,000
Research and development license expense	6,750,000	6,000,000
Stock-based compensation	13,229,000	1,341,000
Build-to-suit lease	357,000
Other	93,000
Changes in operating assets and liabilities:
Prepaid expenses and other assets	(1,530,000)	(604,000)
Accounts payable	16,000,000	5,403,000
Accrued expenses and other liabilities	12,179,000	1,579,000
Due to related party	(8,000)	60,000
Net cash used in operating activities	(76,784,000)	(10,881,000)
Cash flows from investing activities
Purchase of research and development license	(6,000,000)	(3,000,000)
Purchase of property, plant and equipment	(7,034,000)	(31,000)
Net cash used in investing activities	(13,034,000)	(3,031,000)
Cash flows from financing activities
Proceeds from Term Loan, net	29,978,000
Proceeds from initial public offering, net of underwriting discounts and commission and other offering costs		167,162,000
Proceeds from note payable to related party		1,673,000
Repayment of note payable to related party		(1,673,000)
Net cash provided by financing activities	29,978,000	292,546,000
Net (decrease) increase in cash, cash equivalents and restricted cash	(59,840,000)	278,634,000
Cash, cash equivalents and restricted cash at the beginning of the period	251,253,000
Cash, cash equivalents and restricted cash at the end of the period	191,413,000	278,634,000
Cash and cash equivalents	188,785,000	278,634,000
Restricted cash	2,628,000
Supplemental disclosure of cash flow information:
Cash paid for interest	110,000	28,000
Supplemental disclosure of noncash investing and financing activities:
Property, plant and equipment in accounts payable and accrued expenses	6,658,000
Acquisition of property, plant and equipment funded by landlord	606,000
Build-to-suit lease liability	26,607,000
Deferred offering costs not yet paid	204,000
Reclassification of preferred stock tranche liability		18,080,000
Allocation of preferred stock tranche liability		1,050,000
Conversion of Series A and Series B convertible preferred stock to common stock		142,240,000
Purchase of research and development license not yet paid	$ 750,000	3,000,000
Common Stock
Supplemental disclosure of noncash investing and financing activities:
Issuance costs for issuances of stock not yet paid		1,273,000
Series A Convertible Preferred Stock
Cash flows from financing activities
Proceeds from convertible preferred stock, net of issuance costs		29,569,000
Supplemental disclosure of noncash investing and financing activities:
Issuance costs for issuances of stock not yet paid		174,000
Series B Convertible Preferred Stock
Cash flows from financing activities
Proceeds from convertible preferred stock, net of issuance costs		$ 95,815,000

Organization and Description of Business Operations

9 Months Ended

Sep. 30, 2021

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Organization and Description of Business Operations

Note 1—Organization and Description of Business Operations

Taysha Gene Therapies, Inc. (the “Company” or “Taysha”) was originally formed under the laws of the State of Texas on September 20, 2019 (“Inception”). Taysha converted to a Delaware corporation on February 13, 2020, which had no impact to the Company’s par value or issued and authorized capital structure.

Taysha is a patient-centric gene therapy company focused on developing and commercializing AAV-based gene therapies for the treatment of monogenic diseases of the central nervous system in both rare and large patient populations.

Stock Split

On September 16, 2020, the Company effected a 1.0895-for-one stock split of its authorized, issued and outstanding shares of common stock and a proportional adjustment to the existing conversion ratios for each series of the Company’s convertible preferred stock as discussed in Note 6. Accordingly, all share and per share amounts for the periods presented in the accompanying condensed consolidated financial statements and notes thereto have been adjusted retroactively, where applicable, to reflect this stock split and adjustment of the convertible preferred stock conversion ratios. On September 16, 2020, the Company also increased the number of shares of common stock authorized for issuance under the 2020 Equity Incentive Plan (the “Existing Plan”) to 3,845,294.

Initial Public Offering

On September 23, 2020, the Company’s registration statement on Form S-1 (File No. 333-248559) related to the initial public offering (“IPO”) of its common stock became effective and on September 28, 2020, the IPO closed. Pursuant to the IPO, the Company issued and sold 9,050,000 shares of common stock at a public offering price of $20.00 per share, which included 1,180,434 shares of common stock issued upon the exercise in full of the underwriters’ option to purchase additional shares. The Company received net proceeds of $165.9 million after deducting underwriting discounts and commissions and other offering costs of $2.5 million. The shares began trading on the Nasdaq Global Select Market on September 24, 2020.

On September 28, 2020, in connection with the closing of the IPO, 10,000,000 shares of Series A 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.

As a result of the IPO, including the underwriters’ exercise in full of their option to purchase additional shares, 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.

Upon the effectiveness of the Company’s registration statement related to the IPO, the Company’s 2020 Stock Incentive Plan (the “New Plan”) and 2020 Employee Stock Purchase Plan became effective. At that time, all shares reserved for issuance under the Existing Plan ceased to be available for issuance under such plan and became available for issuance under the New Plan.

Liquidity and Capital Resources

The Company has incurred operating losses since inception and expects to continue to incur significant operating losses for the foreseeable future and may never become profitable. As of September 30, 2021, the Company had an accumulated deficit of $185.3 million.

Prior to the closing of the Company’s IPO, between March and July 2020, the Company closed on the sale of an aggregate of 10,000,000 shares of Series A convertible preferred stock for gross proceeds of $30.0 million. Between July and August 2020, the Company closed on the sale of an aggregate of 5,647,048 shares of Series B convertible preferred stock for gross proceeds of $96.0 million.

Future capital requirements will depend on many factors, including the timing and extent of spending on research and development and the market acceptance of the Company’s products. The Company will need to obtain additional financing in order to complete clinical studies and launch and commercialize any product candidates for which it receives regulatory approval. There can be no assurance that such financing will be available or will be on terms acceptable to the Company. As of September 30, 2021, the Company had cash and cash equivalents of $188.8 million which the Company believes will be sufficient to fund its planned operations for a period of at least twelve months from the date of issuance of these condensed consolidated financial statements.

In December 2019, the novel coronavirus that causes the disease COVID-19 emerged and has subsequently spread worldwide. The World Health Organization has declared the COVID-19 outbreak a global pandemic, resulting in federal, state and

local governments and private entities implementing various restrictions including travel restrictions, restrictions on public gatherings, stay at home orders, other advisories and quarantines of people who may have been exposed to the virus. The Company has been actively monitoring COVID-19 and its impact globally. Management believes the financial results for the nine months ended September 30, 2021 were not significantly impacted by the COVID-19 pandemic. In addition, management believes the remote working arrangements and travel restrictions imposed by various governmental jurisdictions have had limited impact on the Company’s ability to maintain internal operations during the nine months ended September 30, 2021. The full extent to which the COVID-19 pandemic will directly or indirectly impact the Company’s business, results of operations and financial condition will depend on future developments that are highly uncertain, including new information that may emerge concerning COVID-19 and the actions taken to contain it or treat COVID-19.

Summary of Significant Accounting Policies

9 Months Ended

Sep. 30, 2021

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

Note 2—Summary of Significant Accounting Policies

Basis of Presentation

The unaudited condensed consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States ("GAAP") as determined by the Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“ASC”) for interim financial information and the instructions to Form 10-Q and Article 10 of Regulation S-X and are consistent in all material respects with those included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2020, filed with the Securities and Exchange Commission ("SEC") on March 3, 2021 (the “2020 Annual Report”). In the opinion of management, the unaudited condensed consolidated financial statements reflect all adjustments, which include only normal recurring adjustments necessary for the fair statement of the balances and results for the periods presented. The consolidated balance sheet as of December 31, 2020 is derived from audited financial statements, however, it does not include all of the information and footnotes required by GAAP for complete financial statements. These unaudited condensed consolidated financial statements should be read in conjunction with the consolidated financial statements and related notes in the Company’s 2020 Annual Report on Form 10-K for the year ended December 31, 2020, filed with the SEC on March 3, 2021.

Principles of Consolidation

The accompanying interim condensed consolidated financial statements include the accounts of Taysha and its inactive wholly owned U.S. subsidiaries that were incorporated during 2020, and two inactive foreign subsidiaries incorporated during 2021. All intercompany transactions and balances have been eliminated in consolidation.

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 preclinical 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.

Significant Accounting Policies

There have been no changes in the Company’s significant accounting policies as disclosed in Note 2 to the audited consolidated financial statements included in the 2020 Annual Report, except as described below:

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.

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 September 30, 2021, $0.2 million of such deferred costs are included in prepaid expenses and other current assets on the condensed consolidated balance sheet.

Build-to-Suit Lease

In the Company’s recent lease arrangement (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.

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 new standard requires the use of one of the following two approaches, either (1) retrospectively to each prior reporting period presented in the financial statements with the cumulative effect recognized at the beginning of the earliest comparative period presented, or (2) retrospectively at the beginning of the period of adoption through a cumulative-effect adjustment. The Company has not yet concluded which approach will be utilized to adopt the new standard and is currently evaluating the impact of this standard on its condensed consolidated financial statements.

Balance Sheet Components

9 Months Ended

Sep. 30, 2021

Balance Sheet Related Disclosures [Abstract]

Balance Sheet Components

Note 3—Balance Sheet Components

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

	September 30, 2021		December 31, 2020
Prepaid research and development	$	5,500	$	2,462
Prepaid bonus		800		409
Prepaid clinical trial		779		944
Prepaid insurance		144		2,480
Other		1,162		331
Total prepaid expenses and other current assets	$	8,385	$	6,626

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

	September 30, 2021			December 31, 2020
Leasehold improvements	$	1,876		$	—
Furniture and fixtures		759			—
Computer equipment		818			95
Laboratory equipment		476			—
Construction in progress		36,916			201
		40,845			296
Accumulated depreciation		(292	)		(9	)
Property, plant and equipment, net	$	40,553		$	287

Included in construction in progress at September 30, 2021 was $36.7 million of costs associated with the Build-to-Suit lease (see Note 11).

Depreciation expense was $166,000 and $283,000 for the three and nine months ended September 30, 2021, respectively. Depreciation expense was not significant for the three and nine months ended September 30, 2020.

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

	September 30, 2021		December 31, 2020
Accrued research and development	$	9,330	$	2,106
Accrued compensation		5,752		1,766
Accrued professional and consulting fees		1,386		999
Accrued property, plant, and equipment		2,774		173
Accrued clinical trial		1,142		—
Other		779		91
Total accrued expenses and other current liabilities	$	21,163	$	5,135

Loan with Silicon Valley Bank

9 Months Ended

Sep. 30, 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 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 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.

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 $2.3 million was recorded as debt discount and has also been fully accrued within non-current liabilities as of September 30, 2021. The debt discount is being accreted using the effective interest method over the term of the Term Loans within interest expense in the condensed 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 September 30, 2021. Upon the occurrence of an event of default, a default interest rate of an addition 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.

Future principal debt payments on the loan payable as of September 30, 2021 are as follows (in thousands):

Year Ending December 31,
2021	$	—
2022		—
2023		—
2024		5,000
2025		15,000
2026		10,000
Total principal payments		30,000
Less: Unamortized debt discount		(2,188	)
Term loan, net	$	27,812

- Definition

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-URI http://asc.fasb.org/topic&trid=2208564

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 1B
-Subparagraph (h)
-URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495323-112611

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 1C
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495334-112611

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 1I
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495371-112611

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 1I
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495371-112611

Reference 6: 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(c))
-URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 1B
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495323-112611

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 1C
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495334-112611

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 1C
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495334-112611

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 1E
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495348-112611

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495323-112611

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 1I
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495371-112611

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 1B
-Subparagraph (i)
-URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495323-112611

+ Details

Research, Collaboration and License Agreements

9 Months Ended

Sep. 30, 2021

Research Collaboration And License Agreements [Abstract]

Research, Collaboration and License Agreements

Note 5—Research, Collaboration and License Agreements

UT Southwestern Agreement

On November 19, 2019, the Company entered into a research, collaboration and license agreement (“UT Southwestern Agreement”) with the Board of Regents of the University of Texas System on behalf of The University of Texas 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 investigational new drug application-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. The Company issued Queen’s a promise-to-pay note whereby any amounts paid directly by Queen’s for the manufacture of the vector for use in the funded research activities, to the extent such amounts had not already been funded by the Company to Queen’s, would become a loan obligation for the Company (the “Note”), subject to an interest rate of 6%. Any amounts outstanding under the Note were required to be repaid, along with any accrued interest, by or before June 30, 2020. In the event of default, any amount outstanding was deemed immediately payable by RA Session II, the Company’s President and Chief Executive Officer, as a personal guarantor (see Note 9). For the period from Inception through December 31, 2019, the Company did not incur any expenses associated with the Queen’s RGA, and no amounts were due or outstanding under the Note as of December 31, 2019. For the year ended December 31, 2020, the Company paid all expenses associated with the Queen’s RGA, thus no amounts were due or outstanding under the Note as of December 31, 2020, and the promise-to-pay has therefore expired.

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 condensed consolidated statements of operations and included as an investing cash outflow in the condensed consolidated statements of cash flows since the acquired license does not have an alternative future use for the nine months ended September 30, 2020. 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 nine months ended September 30, 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.

No additional milestone payments were made in connection with this agreement during the nine months ended September 30, 2021.

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 nine months ended September 30, 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”). TSHA-120 is an intrathecally dosed AAV9 gene therapy currently being evaluated in a clinical trial for the treatment of GAN. The trial is being conducted by the National Institutes of Health in close collaboration with a leading patient advocacy group focused on finding treatments and cures for GAN. TSHA-120 has received rare pediatric disease and orphan drug designations from the U.S. Food and Drug Administration for the treatment of GAN. The worldwide rights were acquired through a license agreement, effective March 29, 2021, between Hannah’s Hope Fund for Giant Axonal Neuropathy, Inc. (“HHF”) and the Company.

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 condensed consolidated statements of operations since the acquired license does not have an alternative future use. This license fee was paid in April 2021 and has been classified as an investing outflow in the condensed consolidated statements of cash flows for the nine months ended September 30, 2021. No additional milestone payments were made in connection with this agreement during the nine months ended September 30, 2021.

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

9 Months Ended

Sep. 30, 2021

Equity [Abstract]

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

Note 6—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 September 30, 2021 and December 31, 2020, 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.

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. 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 condensed consolidated statement 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 $18.1 million to convertible preferred stock on the condensed consolidated balance sheet.

- 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.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 13
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123467817&loc=SL123496158-112644

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 13
-URI http://asc.fasb.org/extlink&oid=123467817&loc=SL123496158-112644

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 14
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=123467817&loc=SL123496171-112644

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 14
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123467817&loc=SL123496171-112644

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI http://asc.fasb.org/extlink&oid=120397183&loc=d3e187085-122770

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 18
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=123467817&loc=SL123496189-112644

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 13
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=123467817&loc=SL123496158-112644

Reference 8: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-URI http://asc.fasb.org/topic&trid=2208762

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 18
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=123467817&loc=SL123496189-112644

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 13
-Subparagraph (h)
-URI http://asc.fasb.org/extlink&oid=123467817&loc=SL123496158-112644

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 14
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=123467817&loc=SL123496171-112644

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 18
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123467817&loc=SL123496189-112644

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 16
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123467817&loc=SL123496180-112644

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 13
-Subparagraph (i)
-URI http://asc.fasb.org/extlink&oid=123467817&loc=SL123496158-112644

Reference 15: 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(e)(1))
-URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690

+ Details

Stock-Based Compensation

9 Months Ended

Sep. 30, 2021

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock-Based Compensation

Note 7—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. At December 31, 2020, there were 2,941,509 shares available for future grant under the New Plan. 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.

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 have been added to the ESPP as of January 1, 2021 and no issuances have been made under the ESPP as of September 30, 2021.

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.

For the three months ended September 30, 2021, 415,100 shares of common stock under the New Plan were awarded with a weighted-average grant date fair value per share of $12.83. For the nine months ended September 30, 2021, 3,001,750 shares of common stock under the New Plan were awarded with a weighted-average grant date fair value per share of $16.64. 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 that were granted during the three and nine months ended September 30, 2021 and 2020:

	Three months ended September 30,						Nine months ended September 30,
	2021			2020			2021			2020
Risk-free interest rate		1.02	%		0.46	%		0.83	%		0.46	%
Expected dividend yield	—				—		—				—
Expected term in years		6.1			6.7			6.0			6.7
Expected volatility		75	%		80	%		75	%		80	%

The following table summarizes stock option activity, during the nine months ended September 30, 2021:

						Weighted
				Weighted		Average		Aggregate
				Average		Remaining		Intrinsic
	Stock			Exercise		Contractual		Value
	Options			Price		Life (in years)		(in thousands)
Outstanding at December 31, 2020		674,842			20.68		9.8	$	3,953
Options granted		3,001,750			25.46
Options cancelled or forfeited		(159,600	)		27.14
Outstanding at September 30, 2021		3,516,992		$	24.47		9.4	$	175
Vested and expected to vest at September 30, 2021		3,516,992		$	24.47		9.4	$	175
Options exercisable at September 30, 2021		84,349		$	20.08		9.0	$	17

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 September 30, 2021 and the exercise price of the stock options. As of September 30, 2021, the total unrecognized compensation related to unvested stock option awards granted was $47.3 million, which the Company expects to recognize over a weighted-average period of approximately 3.3 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 September 30, 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 $11.8 million which is expected to be amortized on a straight-line basis over the weighted-average remaining vesting period of approximately 1.3 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 nine months ended September 30, 2021 was as follows:

				Weighted
				Average
				Grant Date
	Number			Fair Value
	of Shares			per Share
Nonvested at January 1, 2021		2,850,053		$	6.37
Restricted units granted		—			—
Vested		(712,510	)		6.37
Cancelled or forfeited		(250,778	)		5.25
Nonvested at September 30, 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 September 30, 2021, the total unrecognized compensation related to unvested RSAs granted was $2.2 million which is expected to be amortized on a straight-line basis over the weighted-average remaining vesting period of approximately 0.8 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 nine months ended September 30, 2021 was as follows:

				Weighted
				Average
				Grant Date
	Number			Fair Value
	of Shares			per Share
Nonvested at December 31, 2020		769,058		$	5.28
Restricted stock granted		—			—
Vested		(362,963	)		5.28
Nonvested at September 30, 2021		406,095		$	5.28

The following table summarizes the total stock-based compensation expense for the stock options, RSAs and RSUs recorded in the condensed consolidated statements of operations for the three and nine months ended September 30, 2021 and 2020 (in thousands):

	For the Three Months Ended September 30,				For the Nine Months Ended September 30,
	2021		2020		2021		2020
Research and development expense	$	2,305	$	399	$	6,098	$	399
General and administrative expense		2,781		942		7,131		942
Total	$	5,086	$	1,341	$	13,229	$	1,341

Net Loss Per Common Share

9 Months Ended

Sep. 30, 2021

Earnings Per Share [Abstract]

Net Loss Per Common Share

Note 8—Net Loss Per Common Share

Basic net loss per common share is computed by dividing net loss attributable to common stockholders by the weighted-average number of shares of common stock outstanding for the period. Since the Company had a net loss in all periods presented, basic and diluted net loss per common share are the same.

The following table represents the calculation of basic and diluted net loss per common share (in thousands, except share and per share data):

	For the Three Months Ended September 30,						For the Nine Months Ended September 30,
	2021			2020			2021			2020
Net loss	$	(51,187	)	$	(15,042	)	$	(124,137	)	$	(41,693	)
Weighted-average shares of common stock outstanding used to compute net loss per common share, basic and diluted		38,003,954			11,733,170			37,495,537			11,176,429
Net loss per common share, basic and diluted	$	(1.35	)	$	(1.28	)	$	(3.31	)	$	(3.73	)

The following common stock equivalents outstanding as of September 30, 2021 and 2020 were excluded from the computation of diluted net loss per share attributable to common stockholders for the periods presented because including them would have been anti‑dilutive:

	September 30, 2021		September 30, 2020
Unvested RSUs		1,886,765		2,850,053
Unvested RSAs		406,095		769,058
Stock options		3,516,992		185,342
Total		5,809,852		3,804,453

Related Party Transactions

9 Months Ended

Sep. 30, 2021

Related Party Transactions

Note 9—Related Party Transactions

RA Session II, President and Chief Executive Officer and a member of the Company’s board of directors, was a guarantor under the Guaranty and Security Agreement between himself, Queen’s and the Company, and in the event of the Company’s failure to fund its obligations under the RGA with Queen’s, had personally guaranteed payments due by the Company to Queen’s. In addition, the Company entered into two secured promissory notes with Mr. Session in January 2020 for an aggregate of $1.67 million, with 10% interest. The Company secured the notes with a first priority security interest in certain assets of the Company. During March 2020, the Company repaid $1.65 million of the notes, and the remaining balance was repaid in July 2020.

In March 2020, the Company entered into a services agreement with PBM Capital Group, LLC (“PBM”), an affiliate of PBM TGT Holdings, LLC whereby PBM provided accounting and other administrative and management services related to payroll administration, human resources, bookkeeping, preparation of financial statements and tax returns, accounts payable and receivable, and other similar functions for a fee of $2,500 per month. Paul B. Manning, a member of the Company’s board of directors and a holder of more than 5% of the Company’s capital stock, is the Chief Executive Officer of PBM Capital Group, LLC and has sole voting and investment power with respect to the shares held by PBM TGT Holdings, LLC. In September 2020, PBM TGT Holdings, LLC distributed all of the shares of Series A convertible preferred stock it previously held to its beneficial owners, including Mr. Manning and entities controlled by Mr. Manning, for no additional consideration in accordance with the terms of its operating agreement. In April 2021, the PBM services agreement was terminated and all outstanding amounts due have been paid.

Income Taxes

9 Months Ended

Sep. 30, 2021

Income Tax Disclosure [Abstract]

Income Taxes

Note 10—Income Taxes

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. 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 evaluated the positive and negative evidence bearing upon the realizability of its deferred tax assets. 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.

As of September 30, 2021, there were no material changes to either the nature or the amounts of the uncertain tax positions previously determined for the year ended December 31, 2020.

- 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

9 Months Ended

Sep. 30, 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 September 30, 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 condensed consolidated balance sheet as of September 30, 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 condensed 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 expected 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 condensed 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 $10.5 million have been capitalized during the nine months ended September 30, 2021, related to both equipment purchases and the build-out of the leased Facility. Construction is expected to be completed in 2023, upon which time the Company will assess and determine if the build-to-suit asset and corresponding liability should be de-recognized.

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. The Company was required to provide a security deposit of $32,500 in connection with its entry into the Dallas Lease. 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 a construction allowance provided by the Dallas Landlord not to exceed $40.00 per rentable square foot.

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 September 30, 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 condensed 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.

Subsequent Events

9 Months Ended

Sep. 30, 2021

Subsequent Events [Abstract]

Subsequent Events

Note 12 — Subsequent Events

Acquisition of Option to License Worldwide Rights to Clinical-Stage AAV9 Gene Therapy Program for CLN7 Disease

In October 2021, the Company announced its exclusive option to license the worldwide rights to a clinical-stage AAV9 gene therapy program for the treatment of CLN7, a form of Batten disease. The first-generation construct for the CLN7 program was developed in the laboratory of Steven Gray, Ph.D., Associate Professor at UT Southwestern Chief Scientific Advisor for the Company. The CLN7 program is currently in a Phase 1 clinical proof-of-concept trial run by UT Southwestern, and the Company expects the availability of preliminary human proof-of-concept clinical safety and efficacy data from the first-generation construct by year-end 2021. The Company also entered into a research collaboration with UT Southwestern to develop a next-generation construct for the treatment of CLN7 disease, which is expected to improve potency, safety profile, packaging efficiency and manufacturability over the first-generation construct. Completion of the next-generation construct design is anticipated by year-end 2021 with commercial-grade GMP material expected in 2022. The Company intends to initiate a planned pivotal trial using the next-generation construct in 2022, with reference to the human proof-of-concept clinical data being generated from the first generation construct.

Sales Agreement

On October 5, 2021, the Company entered into a Sales Agreement (the “Sales Agreement”) with SVB Leerink LLC and Wells Fargo Securities, LLC (collectively, the “Sales Agents”), pursuant to which the Company may issue and sell, from time to time, shares of its common stock having an aggregate offering price of up to $150.0 million through the Sales Agents. The Sales Agents may sell common stock by any method permitted by law deemed to be an “at the market offering” as defined in Rule 415(a)(4) of the Securities Act, including sales made directly on or through the Nasdaq Global Select Market or any other existing trade market for the common stock, in negotiated transactions at market prices prevailing at the time of sale or at prices related to prevailing market prices, or any other method permitted by law. The Sales Agents will be entitled to receive 3.0% of the gross sales price per share of common stock sold under the Sales Agreement. As of the date of these financial statements, no shares of common stock have been issued and sold pursuant to the Sales Agreement.

Summary of Significant Accounting Policies (Policies)	9 Months Ended
Summary of Significant Accounting Policies (Policies)	Sep. 30, 2021
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The unaudited condensed consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States ("GAAP") as determined by the Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“ASC”) for interim financial information and the instructions to Form 10-Q and Article 10 of Regulation S-X and are consistent in all material respects with those included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2020, filed with the Securities and Exchange Commission ("SEC") on March 3, 2021 (the “2020 Annual Report”). In the opinion of management, the unaudited condensed consolidated financial statements reflect all adjustments, which include only normal recurring adjustments necessary for the fair statement of the balances and results for the periods presented. The consolidated balance sheet as of December 31, 2020 is derived from audited financial statements, however, it does not include all of the information and footnotes required by GAAP for complete financial statements. These unaudited condensed consolidated financial statements should be read in conjunction with the consolidated financial statements and related notes in the Company’s 2020 Annual Report on Form 10-K for the year ended December 31, 2020, filed with the SEC on March 3, 2021.
Principles of Consolidation	Principles of Consolidation The accompanying interim condensed consolidated financial statements include the accounts of Taysha and its inactive wholly owned U.S. subsidiaries that were incorporated during 2020, and two inactive foreign subsidiaries incorporated during 2021. All intercompany transactions and balances have been eliminated in consolidation.
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 preclinical 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.
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.
Offering Costs	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 September 30, 2021, $0.2 million of such deferred costs are included in prepaid expenses and other current assets on the condensed consolidated balance sheet.
Build-to-Suit Lease	Build-to-Suit Lease In the Company’s recent lease arrangement (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.
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 new standard requires the use of one of the following two approaches, either (1) retrospectively to each prior reporting period presented in the financial statements with the cumulative effect recognized at the beginning of the earliest comparative period presented, or (2) retrospectively at the beginning of the period of adoption through a cumulative-effect adjustment. The Company has not yet concluded which approach will be utilized to adopt the new standard and is currently evaluating the impact of this standard on its condensed consolidated financial statements.

Balance Sheet Components (Tables)

9 Months Ended

Sep. 30, 2021

Balance Sheet Related Disclosures [Abstract]

Schedule of Prepaid Expenses and Other Current Assets

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

	September 30, 2021		December 31, 2020
Prepaid research and development	$	5,500	$	2,462
Prepaid bonus		800		409
Prepaid clinical trial		779		944
Prepaid insurance		144		2,480
Other		1,162		331
Total prepaid expenses and other current assets	$	8,385	$	6,626

Schedule of Property Plant and Equipment

	September 30, 2021			December 31, 2020
Leasehold improvements	$	1,876		$	—
Furniture and fixtures		759			—
Computer equipment		818			95
Laboratory equipment		476			—
Construction in progress		36,916			201
		40,845			296
Accumulated depreciation		(292	)		(9	)
Property, plant and equipment, net	$	40,553		$	287

Schedule of Accrued Expense and Other Current Labilities

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

	September 30, 2021		December 31, 2020
Accrued research and development	$	9,330	$	2,106
Accrued compensation		5,752		1,766
Accrued professional and consulting fees		1,386		999
Accrued property, plant, and equipment		2,774		173
Accrued clinical trial		1,142		—
Other		779		91
Total accrued expenses and other current liabilities	$	21,163	$	5,135

Loan with Silicon Valley Bank (Tables)

9 Months Ended

Sep. 30, 2021

Debt Disclosure [Abstract]

Schedule of Future Principal Debt Payments on Loan Payable

Future principal debt payments on the loan payable as of September 30, 2021 are as follows (in thousands):

Year Ending December 31,
2021	$	—
2022		—
2023		—
2024		5,000
2025		15,000
2026		10,000
Total principal payments		30,000
Less: Unamortized debt discount		(2,188	)
Term loan, net	$	27,812

Stock-Based Compensation (Tables)

9 Months Ended

Sep. 30, 2021

Schedule of Restricted Stock Units Activity

The Company’s RSU activity for the nine months ended September 30, 2021 was as follows:

				Weighted
				Average
				Grant Date
	Number			Fair Value
	of Shares			per Share
Nonvested at January 1, 2021		2,850,053		$	6.37
Restricted units granted		—			—
Vested		(712,510	)		6.37
Cancelled or forfeited		(250,778	)		5.25
Nonvested at September 30, 2021		1,886,765		$	6.52

Schedule of Restricted Stock Awards Activity

The Company’s RSA activity for the nine months ended September 30, 2021 was as follows:

				Weighted
				Average
				Grant Date
	Number			Fair Value
	of Shares			per Share
Nonvested at December 31, 2020		769,058		$	5.28
Restricted stock granted		—			—
Vested		(362,963	)		5.28
Nonvested at September 30, 2021		406,095		$	5.28

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

	For the Three Months Ended September 30,				For the Nine Months Ended September 30,
	2021		2020		2021		2020
Research and development expense	$	2,305	$	399	$	6,098	$	399
General and administrative expense		2,781		942		7,131		942
Total	$	5,086	$	1,341	$	13,229	$	1,341

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 that were granted during the three and nine months ended September 30, 2021 and 2020:

	Three months ended September 30,						Nine months ended September 30,
	2021			2020			2021			2020
Risk-free interest rate		1.02	%		0.46	%		0.83	%		0.46	%
Expected dividend yield	—				—		—				—
Expected term in years		6.1			6.7			6.0			6.7
Expected volatility		75	%		80	%		75	%		80	%

Schedule of Stock Option Activity

The following table summarizes stock option activity, during the nine months ended September 30, 2021:

						Weighted
				Weighted		Average		Aggregate
				Average		Remaining		Intrinsic
	Stock			Exercise		Contractual		Value
	Options			Price		Life (in years)		(in thousands)
Outstanding at December 31, 2020		674,842			20.68		9.8	$	3,953
Options granted		3,001,750			25.46
Options cancelled or forfeited		(159,600	)		27.14
Outstanding at September 30, 2021		3,516,992		$	24.47		9.4	$	175
Vested and expected to vest at September 30, 2021		3,516,992		$	24.47		9.4	$	175
Options exercisable at September 30, 2021		84,349		$	20.08		9.0	$	17

Net Loss Per Common Share (Tables)

9 Months Ended

Sep. 30, 2021

Earnings Per Share [Abstract]

Schedule of Calculation of Basic and Diluted Net Loss Per Common Share

The following table represents the calculation of basic and diluted net loss per common share (in thousands, except share and per share data):

	For the Three Months Ended September 30,						For the Nine Months Ended September 30,
	2021			2020			2021			2020
Net loss	$	(51,187	)	$	(15,042	)	$	(124,137	)	$	(41,693	)
Weighted-average shares of common stock outstanding used to compute net loss per common share, basic and diluted		38,003,954			11,733,170			37,495,537			11,176,429
Net loss per common share, basic and diluted	$	(1.35	)	$	(1.28	)	$	(3.31	)	$	(3.73	)

Schedule of Common Stock Equivalents Outstanding Excluded from Computation of Diluted Net Loss Per Share Attributable to Common Stockholders

	September 30, 2021		September 30, 2020
Unvested RSUs		1,886,765		2,850,053
Unvested RSAs		406,095		769,058
Stock options		3,516,992		185,342
Total		5,809,852		3,804,453

Organization and Description of Business Operations - Additional Information (Details) $ / shares in Units, $ in Thousands				2 Months Ended	3 Months Ended		5 Months Ended	9 Months Ended
	Sep. 29, 2020 shares	Sep. 28, 2020 USD ($) $ / shares shares	Sep. 16, 2020 shares	Aug. 31, 2020 USD ($) shares	Sep. 30, 2021 USD ($) $ / shares shares	Sep. 30, 2020 shares	Jul. 31, 2020 USD ($) shares	Sep. 30, 2021 USD ($) $ / shares shares	Sep. 30, 2020 USD ($) shares	Dec. 31, 2020 USD ($)	Jul. 01, 2020 shares
Organization and Description of Business Operations [Line Items]
Date of incorporation								Feb. 13, 2020
Accumulated deficit \| $					$ (185,263)			$ (185,263)		$ (61,126)
Cash, cash equivalents and restricted cash \| $					$ 188,800			$ 188,800
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			10,000,000
Aggregate shares sold							10,000,000
Gross proceeds from sale of convertible preferred stock \| $							$ 30,000		$ 29,569
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			5,647,048
Aggregate shares sold				5,647,048
Gross proceeds from sale of convertible preferred stock \| $				$ 96,000					$ 95,815
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
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			$ 20.00
Net proceeds from issuance of common stock \| $		$ 165,900
Underwriting discounts and commissions and other offering costs \| $		$ 2,500
Increase in outstanding shares		26,097,378
2020 Equity Incentive Plan
Organization and Description of Business Operations [Line Items]
Number of common stock authorized for issuance			3,845,294
Common Stock
Organization and Description of Business Operations [Line Items]
Conversion ratio		1.0895	1.0895
Issuance of shares of common stock, shares					82,780	9,050,000		712,510	9,050,000
Conversion of stock, shares issued		17,047,378				17,047,378			17,047,378
Common Stock \| 2020 Equity Incentive Plan
Organization and Description of Business Operations [Line Items]
Number of common stock authorized for issuance			3,845,294								3,529,412

Summary of Significant Accounting Policies - Additional Information (Details) $ in Millions	9 Months Ended
	Sep. 30, 2021 USD ($)
Significant Accounting Policies [Line Items]
Shelf Registration,term	3 years
Prepaid expenses and other current assets
Significant Accounting Policies [Line Items]
Deferred offering costs	$ 0.2

Balance Sheet Components - Schedule of Prepaid Expenses and Other Current Assets (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Balance Sheet Related Disclosures [Abstract]
Prepaid research and development	$ 5,500	$ 2,462
Prepaid bonus	800	409
Prepaid clinical trial	779	944
Prepaid insurance	144	2,480
Other	1,162	331
Total prepaid expenses and other current assets	$ 8,385	$ 6,626

Balance Sheet Components - Schedule of Property, Plant and Equipment (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Property Plant And Equipment [Line Items]
Property, plant and equipment, gross	$ 40,845	$ 296
Accumulated depreciation	(292)	(9)
Property, plant and equipment, net	40,553	287
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property, plant and equipment, gross	1,876
Furniture and Fixtures
Property Plant And Equipment [Line Items]
Property, plant and equipment, gross	759
Computer Equipment
Property Plant And Equipment [Line Items]
Property, plant and equipment, gross	818	95
Laboratory Equipment
Property Plant And Equipment [Line Items]
Property, plant and equipment, gross	476
Construction in Progress
Property Plant And Equipment [Line Items]
Property, plant and equipment, gross	$ 36,916	$ 201

Balance Sheet Components - Additional Information (Details) - USD ($)	3 Months Ended	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2021	Sep. 30, 2020
Property Plant And Equipment [Line Items]
Depreciation expense	$ 166,000	$ 283,000	$ 3,000
Build-to-Suit Lease
Property Plant And Equipment [Line Items]
Construction in progress	$ 36,700	$ 36,700

Balance Sheet Components - Schedule of Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Balance Sheet Related Disclosures [Abstract]
Accrued research and development	$ 9,330	$ 2,106
Accrued compensation	5,752	1,766
Accrued professional and consulting fees	1,386	999
Accrued property, plant, and equipment	2,774	173
Accrued clinical trial	1,142
Other	779	91
Total accrued expenses and other current liabilities	$ 21,163	$ 5,135

Loan with Silicon Valley Bank - Additional Information (Details) $ in Thousands	Aug. 12, 2021 USD ($) Program	Sep. 30, 2021 USD ($)
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		$ 2,300
Percentage of annual default interest rate	5.00%
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
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%

Loan with Silicon Valley Bank - Schedule of Future Principal Debt Payments on Loan Payable (Details) $ in Thousands	Sep. 30, 2021 USD ($)
Debt Disclosure [Abstract]
2024	$ 5,000
2025	15,000
2026	10,000
Total principal payments	30,000
Less: Unamortized debt discount	(2,188)
Term loan, net	$ 27,812

- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References + Details

Research, Collaboration and License Agreements - Additional Information (Details)	1 Months Ended					3 Months Ended			9 Months Ended		12 Months Ended
	Mar. 31, 2021 USD ($)	Oct. 31, 2020 USD ($)	Aug. 31, 2020 USD ($)	Apr. 30, 2020 Product	Dec. 31, 2019 USD ($)	Sep. 30, 2021 USD ($) shares	Sep. 30, 2020 USD ($)	Mar. 31, 2020 USD ($) shares	Sep. 30, 2021 USD ($) shares	Sep. 30, 2020 USD ($)	Dec. 31, 2020 USD ($) shares	Aug. 12, 2021	Oct. 29, 2020 USD ($)	Feb. 21, 2020 USD ($)	Nov. 30, 2019 shares
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Common stock, shares issued \| shares						38,473,945			38,473,945		37,761,435
Percentage of interest rate												7.00%
Research and development						$ 39,528,000	$ 11,057,000		$ 94,025,000	$ 19,633,000
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
Percentage of interest rate					6.00%
Research grant outstanding fund amount											$ 0
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]
Additional milestone payments									0
License fee payment			$ 3,000,000.0
Purchase of clinical materials and reimbursement incurred development costs		$ 4,000,000.0
Research and development											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)									2 Months Ended	3 Months Ended		5 Months Ended	9 Months Ended
	Sep. 29, 2020 shares	Sep. 28, 2020 USD ($) $ / shares shares	Sep. 16, 2020	Jul. 28, 2020 $ / shares shares	Jul. 02, 2020 USD ($) shares	Jun. 30, 2020 USD ($) $ / shares shares	Mar. 05, 2020 shares	Mar. 04, 2020 USD ($) $ / shares shares	Aug. 31, 2020 USD ($)	Sep. 30, 2021 $ / shares shares	Sep. 30, 2020 shares	Jul. 31, 2020 USD ($)	Sep. 30, 2021 $ / shares shares	Sep. 30, 2020 USD ($) shares	Dec. 31, 2020 shares
Class Of Stock [Line Items]
Common stock, shares authorized		200,000,000		32,685,000						200,000,000			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		10,000,000
Preferred stock, shares issued										0			0		0
Preferred stock, shares outstanding										0			0		0
Preferred stock tranche liability \| $								$ 1,100,000
Non cash expenses due to remeasured fair value of tranche liability \| $						$ 17,000,000.0								$ (17,030,000)
Mile stone shares issued during the period					4,000,000
Tranche liability amount reclassified to convertible preferred stock \| $						$ 18,100
Common Stock
Class Of Stock [Line Items]
Shares issued during period										82,780	9,050,000		712,510	9,050,000
Conversion of stock, shares issued		17,047,378									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			$ 20.00
Gross proceeds from issuance of common stock \| $		$ 181,000,000.0
Stock issuance costs, including underwriters’ discounts and commissions \| $		$ 15,100,000
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
Number of share options exercised					3,800,000	200,000
Clinical milestones for gross proceeds \| $					$ 11,400,000	$ 600,000
Gross proceeds from sale of convertible preferred stock \| $												$ 30,000,000.0		$ 29,569,000
Convertible preferred stock tranche liability, offering price \| $ / shares								$ 3.00
Convertible preferred stock tranche liability, term								1 year
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
Gross proceeds from sale of convertible preferred stock \| $									$ 96,000,000.0					$ 95,815,000
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 \| 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
Gross proceeds from sale of convertible preferred stock \| $									$ 96,000,000.0
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		9 Months Ended
	Jan. 01, 2021	Sep. 16, 2020	Sep. 02, 2020	Jul. 01, 2020	Sep. 30, 2021	Mar. 31, 2021	Sep. 30, 2021
Employee Stock Purchase Plan (ESPP)
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance		724,000
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.
Share-based payment award, options granted	0
Number of shares of common stock issued under ESPP							0
Employee Stock Purchase Plan (ESPP) \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares authorized for issuance		362,000
Restricted Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based payment award, compensation cost not yet recognized, weighted-average period of recognition							1 year 3 months 18 days
Share-based payment award, unvested RSU/RSA granted, compensation cost not yet recognized					$ 11,800,000		$ 11,800,000
Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based payment award, options granted							3,001,750
Share-based payment award, options granted, exercise price per share							$ 25.46
Share-based payment award, options, compensation cost not yet recognized					47,300,000		$ 47,300,000
Share-based payment award, compensation cost not yet recognized, weighted-average period of recognition							3 years 3 months 18 days
Stock options were exercised during the period							$ 0
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							9 months 18 days
Share-based payment award, unvested RSU/RSA granted, compensation cost not yet recognized					$ 2,200,000		$ 2,200,000
Share-based payment award, RSU/RSA granted, weighted average grant date fair value				$ 5.28
2020 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares authorized for issuance		3,845,294
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 \| 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	1,434,934	3,390,168
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							At December 31, 2020, there were 2,941,509 shares available for future grant under the New Plan. 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.
New Plan \| Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based payment award, expiration period							10 years
Share-based payment award, options granted					415,100		3,001,750
Share-based payment award, options, weighted-average grant date fair value					$ 12.83		$ 16.64
New Plan \| Stock Options \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Award vesting period							4 years
New Plan \| Stock Options \| Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Award vesting period							1 year

Stock-Based Compensation - Schedule of Assumptions Used to Estimate Fair Value of Stock Options and Cancelled Options (Details) - Stock Options	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate	1.02%	0.46%	0.83%	0.46%
Expected term in years	6 years 1 month 6 days	6 years 8 months 12 days	6 years	6 years 8 months 12 days
Expected volatility	75.00%	80.00%	75.00%	80.00%

Stock-Based Compensation - Schedule of Stock Option Activity (Details) - Stock Options $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021 USD ($) $ / shares shares	Dec. 31, 2020 USD ($) $ / shares shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Outstanding. Stock Options, Beginning Balance \| shares	674,842
Options granted, Stock Options \| shares	3,001,750
Options cancelled or forfeited, Stock Options \| shares	(159,600)
Outstanding. Stock Options, Ending Balance \| shares	3,516,992	674,842
Vested and expected to vest at September 30, 2021, Stock Options \| shares	3,516,992
Options exercisable at September 30, 2021, Stock Options \| shares	84,349
Outstanding, Weighted Average Exercise Price, Beginning balance \| $ / shares	$ 20.68
Options granted, Weighted Average Exercise Price \| $ / shares	25.46
Options cancelled or forfeited, Weighted Average Exercise Price \| $ / shares	27.14
Outstanding, Weighted Average Exercise Price, Ending balance \| $ / shares	24.47	$ 20.68
Vested and expected to vest at September 30, 2021, Weighted Average Exercise Price \| $ / shares	24.47
Options exercisable at September 30, 2021, Weighted Average Exercise Price \| $ / shares	$ 20.08
Outstanding, Weighted Average Remaining Contractual Life	9 years 4 months 24 days	9 years 9 months 18 days
Vested and expected to vest at September 30, 2021, Weighted Average Remaining Contractual Life	9 years 4 months 24 days
Options exercisable at September 30, 2021, Weighted Average Remaining Contractual Life	9 years
Outstanding, Aggregate Intrinsic Value, Beginning Balance \| $	$ 3,953
Outstanding, Aggregate Intrinsic Value, Ending Balance \| $	175	$ 3,953
Vested and expected to vest at September 30, 2021, Aggregate Intrinsic Value \| $	175
Options exercisable at September 30, 2021, Aggregate Intrinsic Value \| $	$ 17

Stock-Based Compensation - Schedule of Restricted Stock Units Activity (Details) - Restricted Stock Units	9 Months Ended
	Sep. 30, 2021 $ / shares shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Nonvested, Number of Shares, Beginning Balance \| shares	2,850,053
Vested, Number of Shares \| shares	(712,510)
Cancelled or forfeited, Number of Shares \| shares	(250,778)
Nonvested, Number of Shares, Ending Balance \| shares	1,886,765
Nonvested, Weighted Average Grant Date Fair Value per Share, Beginning Balance \| $ / shares	$ 6.37
Vested, Weighted Average Grant Date Fair Value per Share \| $ / shares	6.37
Cancelled or forfeited, Weighted Average Grant Date Fair Value per Share \| $ / shares	5.25
Nonvested, Weighted Average Grant Date Fair Value per Share, Ending Balance \| $ / shares	$ 6.52

Stock-Based Compensation - Schedule of Restricted Stock Awards Activity (Details) - Restricted Stock Awards - $ / shares		9 Months Ended
	Jul. 01, 2020	Sep. 30, 2021
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Nonvested, Number of Shares, Beginning Balance		769,058
Vested, Number of Shares		(362,963)
Nonvested, Number of Shares, Ending Balance		406,095
Nonvested, Weighted Average Grant Date Fair Value per Share, Beginning Balance		$ 5.28
Restricted units/stock granted, Weighted Average Grant Date Fair Value per Share	$ 5.28
Vested, Weighted Average Grant Date Fair Value per Share		5.28
Nonvested, Weighted Average Grant Date Fair Value per Share, Ending Balance		$ 5.28

Stock-Based Compensation - Schedule of Total Stock-Based Compensation Expense for Stock Options, RSAs and RSUs (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 5,086	$ 1,341	$ 13,229	$ 1,341
Research and Development Expense
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	2,305	399	6,098	399
General and Administrative Expense
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 2,781	$ 942	$ 7,131	$ 942

Net Loss Per Common Share - Schedule of Calculation of Basic and Diluted Net Loss Per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Earnings Per Share [Abstract]
Net loss	$ (51,187)	$ (15,042)	$ (124,137)	$ (41,693)
Weighted average common shares outstanding, basic and diluted	38,003,954	11,733,170	37,495,537	11,176,429
Net loss per common share, basic and diluted	$ (1.35)	$ (1.28)	$ (3.31)	$ (3.73)

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=124431687&loc=d3e22595-107794

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=125511455&loc=d3e1448-109256

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 11
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=124431687&loc=d3e22694-107794

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=125511455&loc=d3e1377-109256

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=124432515&loc=d3e3550-109257

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 22
-URI http://asc.fasb.org/extlink&oid=123359005&loc=d3e8736-108599

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 11
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=124431687&loc=d3e22694-107794

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 60B
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=125511455&loc=SL5780133-109256

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 32
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=123359005&loc=d3e8933-108599

Reference 10: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 31
-URI http://asc.fasb.org/extlink&oid=123359005&loc=d3e8924-108599

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 30
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123359005&loc=d3e8906-108599

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=124431687&loc=d3e22583-107794

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 32
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=123359005&loc=d3e8933-108599

+ Details

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	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per share	5,809,852	3,804,453
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	406,095	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	3,516,992	185,342

Related Party Transactions - Additional Information (Details)	1 Months Ended
	Mar. 31, 2020 USD ($)	Jan. 31, 2020 USD ($) PromissoryNote	Aug. 12, 2021	Sep. 30, 2020 USD ($)
Related Party Transaction [Line Items]
Percentage of interest rate			7.00%
PBM Capital Group, LLC \| Services Agreement
Related Party Transaction [Line Items]
Accounting and other administrative and management services fee per month	$ 2,500
PBM TGT Holdings, LLC
Related Party Transaction [Line Items]
Additional consideration payable under operating agreement				$ 0
RA Session II
Related Party Transaction [Line Items]
Number of secured promissory notes \| PromissoryNote		2
Paul B. Manning \| Services Agreement
Related Party Transaction [Line Items]
Ownership percentage more than capital stock	5.00%
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%
Repayments of debt	$ 1,650,000

Income Taxes - Additional Information (Details)	9 Months Ended
Income Taxes - Additional Information (Details)	Sep. 30, 2021 USD ($)
Income Tax Disclosure [Abstract]
Provision for income taxes	$ 0

- Definition

Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

+ References + Details

Commitments and Contingencies - Additional Information (Details)			9 Months Ended
	Jan. 11, 2021 USD ($) ft²	Dec. 17, 2020 ft²	Sep. 30, 2021 USD ($)
Dallas Lease
Loss Contingencies [Line Items]
Lease construction incentive			$ 600,000
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			$ 10,500,000
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
Security deposit	$ 32,500,000
Maximum construction allowance provided by landlord per rentable square foot \| ft²	40.00
Future minimum lease payments	$ 4,900,000

Subsequent Events - Additional Information (Details) - Sales Agreement - USD ($)	Oct. 05, 2021	Sep. 30, 2021
Subsequent Event [Line Items]
Common stock shares issued and sold		0
Sales Agents \| Subsequent Event
Subsequent Event [Line Items]
Percentage of gross sales price per share of common stock	3.00%
Sales Agents \| Subsequent Event \| Maximum
Subsequent Event [Line Items]
Aggregate offering price from sale of common stock	$ 150,000,000.0