Taysha Gene Therapies (TSHA) 10-Q 11 May 21 2021 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2021	May 11, 2021
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2021
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q1
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	No
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		37,917,473
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

Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 228,684	$ 251,253
Prepaid expenses and other current assets	10,817	6,626
Deferred offering costs	128
Total current assets	239,629	257,879
Deferred lease asset	703	715
Property, plant and equipment, net	2,497	287
Total assets	242,829	258,881
Current liabilities
Accounts payable	4,083	1,994
Accrued expenses and other current liabilities	14,875	5,135
Total current liabilities	18,958	7,129
Other non-current liabilities	999	450
Total liabilities	19,957	7,579
Commitments and contingencies - Note 10
Stockholders' equity
Preferred stock, $0.00001 par value per share; 10,000,000 shares authorized and no shares issued and outstanding as of March 31, 2021 and December 31, 2020
Common stock, $0.00001 par value per share; 200,000,000 shares authorized and 37,761,435 issued and outstanding as of March 31, 2021 and December 31, 2020
Additional paid-in capital	316,022	312,428
Accumulated deficit	(93,150)	(61,126)
Total stockholders’ equity	222,872	251,302
Total liabilities and stockholders' equity	$ 242,829	$ 258,881

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical) - $ / shares	Mar. 31, 2021	Dec. 31, 2020
Statement Of Financial Position [Abstract]
Preferred stock, par value per share	$ 0.00001	$ 0.00001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value per share	$ 0.00001	$ 0.00001
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	37,761,435	37,761,435
Common stock, shares outstanding	37,761,435	37,761,435

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Operating expenses:
Research and development	$ 23,854	$ 5,514
General and administrative	8,236	70
Total operating expenses	32,090	5,584
Loss from operations	(32,090)	(5,584)
Other income (expense):
Change in fair value of preferred stock tranche liability	200	180
Interest income	66
Interest expense		(27)
Total other income, net	66	153
Net loss	$ (32,024)	$ (5,431)
Net loss per common share, basic and diluted	$ (0.87)	$ (0.50)
Weighted average common shares outstanding, basic and diluted	36,992,377	10,894,999

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) (Unaudited) - USD ($) $ in Thousands	Total	Series A 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		$ 16,520
Issuance of convertible preferred stock, shares		6,000,000
Net loss	(5,431)				(5,431)
Balance at Mar. 31, 2020	(5,566)			980	(6,546)
Balance, shares at Mar. 31, 2020			10,894,999
Convertible preferred stock balance, shares at Mar. 31, 2020		6,000,000
Convertible preferred stock balance at Mar. 31, 2020		$ 16,520
Balance at Dec. 31, 2020	$ 251,302			312,428	(61,126)
Balance, shares at Dec. 31, 2020	37,761,435		37,761,435
Stock-based compensation	$ 3,594			3,594
Net loss	(32,024)				(32,024)
Balance at Mar. 31, 2021	$ 222,872			$ 316,022	$ (93,150)
Balance, shares at Mar. 31, 2021	37,761,435		37,761,435

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) (Parenthetical) (Unaudited) $ in Thousands	3 Months Ended
	Mar. 31, 2020USD ($)
Issuance of preferred stock tranche liability	$ 1,050
Series A Convertible Preferred Stock
Issuance of convertible preferred stock, offering costs	$ 430

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Cash flows from operating activities
Net loss	$ (32,024,000)	$ (5,431,000)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation expense	32,000	0
Change in fair value of preferred stock tranche liability	(200,000)	(180,000)
Research and development license expense	5,500,000	3,000,000
Stock-based compensation	3,594,000	0
Changes in operating assets and liabilities:
Prepaid expenses and other assets	(4,184,000)	0
Accounts payable	1,872,000	0
Accrued expenses and other liabilities	3,183,000	907,000
Due to related party	(8,000)	5,000
Net cash used in operating activities	(22,035,000)	(1,699,000)
Cash flows from investing activities
Purchase of property, plant and equipment	(534,000)	0
Net cash used in investing activities	(534,000)	0
Cash flows from financing activities
Proceeds from issuances of Series A convertible preferred stock		18,000,000
Proceeds from note payable to related party		1,673,000
Repayment of note payable to related party		(1,646,000)
Net cash provided by financing activities		18,027,000
Net (decrease) increase in cash and cash equivalents	(22,569,000)	16,328,000
Cash at the beginning of the period	251,253,000	0
Cash at the end of the period	228,684,000	16,328,000
Supplemental disclosure of noncash investing and financing activities:
Purchase of research and development license not yet paid	5,500,000	3,000,000
Property, plant and equipment in accounts payable and accrued expenses	1,101,000	0
Acquisition of property, plant and equipment funded by landlord	607,000	0
Deferred offering costs not yet paid	$ 128,000	0
Allocation of preferred stock tranche liability		1,050,000
Series A issuance costs not yet paid		$ 430,000

Organization and Description of

Organization and Description of Business Operations	3 Months Ended
	Mar. 31, 2021
Organization Consolidation And Presentation Of Financial Statements [Abstract]
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 5. 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 March 31, 2021, the Company had an accumulated deficit of $93.2 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 March 31, 2021, the Company had cash of 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 (“COVID-19”) emerged and has subsequently spread worldwide. The World Health Organization has declared COVID-19 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, and advisories and quarantining 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 three months ended March 31, 2021 were not significantly impacted by COVID-19. 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 three months ended March 31, 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 as a result of new information that may emerge concerning COVID-19 and the actions taken to contain it or treat COVID-19.

Summary of Significant Accounti

Summary of Significant Accounting Policies	3 Months Ended
	Mar. 31, 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. 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. 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. 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 consolidated financial statements.

Balance Sheet Components

Balance Sheet Components	3 Months Ended
	Mar. 31, 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): March 31, 2021 December 31, 2020 Prepaid research and development $ 6,281 $ 2,462 Prepaid insurance 1,654 2,480 Prepaid bonus 1,115 409 Prepaid clinical trial 928 944 Other 839 331 Total prepaid expenses and other current assets $ 10,817 $ 6,626 Property, plant and equipment consisted of the following (in thousands): March 31, 2021 December 31, 2020 Computer equipment $ 242 $ 95 Laboratory equipment 407 — Construction in progress 1,889 201 2,538 296 Accumulated depreciation (41 ) (9 ) Property, plant and equipment, net $ 2,497 $ 287 Depreciation expense was $32,000 for the three months ended March 31, 2021. There was no depreciation expense for the three months ended March 31, 2020. Accrued expenses and other current liabilities consisted of the following (in thousands): March 31, 2021 December 31, 2020 Accrued research and development $ 5,672 $ 2,106 Accrued license fees 5,500 — Accrued compensation 1,427 1,766 Accrued professional and consulting fees 1,119 999 Accrued construction in progress 1,029 173 Other 128 91 Total accrued expenses and other current liabilities $ 14,875 $ 5,135

Research, Collaboration and Lic

Research, Collaboration and License Agreements	3 Months Ended
	Mar. 31, 2021
Research Collaboration And License Agreements [Abstract]
Research, Collaboration and License Agreements	Note 4—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 8). 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 for the three months ended March 31, 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. 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 three months ended March 31, 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 three months ended March 31, 2021. Acquisition of Worldwide Rights for TSHA-120 for the treatment of GAN In March 2021, the Company acquired the exclusive worldwide rights to a clinical-stage AAV9 gene therapy program, now known as TSHA-120, for the treatment of Giant Axonal Neuropathy (“GAN”). 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 was acquired through a license agreement, effective March 29, 2021, between Hannah’s Hope Fund for Giant Axonal Neuropathy, Inc. (“HHF”). Under the terms of the agreement, in exchange for granting the Company the exclusive worldwide rights to TSHA-120, HHF will receive 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 not paid as of March 31, 2021 and has been recorded in accrued expenses and other current liabilities.

Stockholders' Equity (Deficit),

Stockholders' Equity (Deficit), Convertible Preferred Stock and Tranche Liability	3 Months Ended
	Mar. 31, 2021
Equity [Abstract]
Stockholders' Equity (Deficit), Convertible Preferred Stock and Tranche Liability	Note 5—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 March 31, 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 tranche liability at March 31, 2020, resulting in a gain of $0.2 million that was recorded in other income, net in the condensed consolidated statements of operations. The tranche liability was again later remeasured to fair value and reclassified to convertible preferred stock when the remaining Milestone Shares were sold to the investors.

Stock-Based Compensation

Stock-Based Compensation	3 Months Ended
	Mar. 31, 2021
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Compensation	Note 6—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 March 31, 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 March 31, 2021, 1,621,900 shares of common stock under the New Plan were awarded with a weighted-average grant date fair value per share of $18.75. The stock options vest over 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 months ended March 31, 2021: Risk-free interest rate 0.64 % Expected dividend yield — Expected term in years 6.1 Expected volatility 75 % The following table summarizes stock option activity, during the three months ended March 31, 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 1,621,900 28.81 Options cancelled or forfeited (10,600 ) 26.87 Outstanding at March 31, 2021 2,286,142 $ 26.42 9.8 $ 213 Vested and expected to vest at March 31, 2021 2,286,142 $ 26.42 9.8 $ 213 Options exercisable at March 31, 2021 27,552 $ 20.44 9.5 $ 6 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 March 31, 2021 and the exercise price of the stock options. As of March 31, 2021, the total unrecognized compensation related to unvested stock option awards granted was $37.0 million, which the Company expects to recognize over a weighted-average period of approximately 3.7 years. 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 March 31, 2021, the total unrecognized compensation related to unvested RSUs granted, including the remaining compensation cost associated with the RSUs granted on September 2, 2020 in exchange for the Cancelled Options, was $15.4 million which is expected to be amortized on a straight-line basis over the weighted-average remaining vesting period of approximately 1.7 years. 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 — — Nonvested at March 31, 2021 2,850,053 $ 6.37 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 March 31, 2021, the total unrecognized compensation related to unvested RSAs granted was $3.0 million which is expected to be amortized on a straight-line basis over the weighted-average remaining vesting period of approximately 2.0 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 three months ended March 31, 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 — — Nonvested at March 31, 2021 769,058 $ 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 months ended March 31, 2021 (in thousands): For the Three Months Ended March 31, 2021 Research and development expense $ 1,579 General and administrative expense 2,015 Total $ 3,594

Net Loss Per Common Share

Net Loss Per Common Share	3 Months Ended
	Mar. 31, 2021
Earnings Per Share [Abstract]
Net Loss Per Common Share	Note 7—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 March 31, 2021 2020 Net loss $ (32,024 ) $ (5,431 ) Weighted-average shares of common stock outstanding used to compute net loss per common share, basic and diluted 36,992,377 10,894,999 Net loss per common share, basic and diluted $ (0.87 ) $ (0.50 ) The following common stock equivalents outstanding as of March 31, 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: March 31, 2021 March 31, 2020 Unvested RSUs 2,850,053 — Unvested RSAs 769,058 — Stock options 2,286,142 — Series A convertible preferred stock — 6,000,000 Total 5,905,253 6,000,000

Related Party Transactions

Related Party Transactions	3 Months Ended
	Mar. 31, 2021
Related Party Transactions [Abstract]
Related Party Transactions	Note 8—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 provides 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. As of March 31, 2021, and December 31, 2020, the Company had recorded an immaterial amount due to PBM in the consolidated balance sheets.

Income Taxes

Income Taxes	3 Months Ended
	Mar. 31, 2021
Income Tax Disclosure [Abstract]
Income Taxes	Note 9—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 March 31, 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.

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2021
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	Note 10—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 March 31, 2021. The Company does not anticipate recognizing any significant losses relating to these arrangements. Durham Lease On December 17, 2020, the Company entered into a lease agreement (the “Durham Lease”) with Patriot Park Partners II, LLC, a Delaware limited liability company (the “Durham Landlord”), pursuant to which the Company agreed to lease approximately 187,500 square feet of a manufacturing facility located at 5 National Way, Durham, North Carolina (the “Facility”). The Durham Lease commenced on April 1, 2021 and is expected to have a term of approximately fifteen years and six months. The Company has two options to extend the term of the Durham Lease, each for a period of an additional five years. The Company was not required to provide a security deposit in connection with its entry into the Durham Lease. The Company will be responsible for constructing interior improvements within the Facility. The 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 may terminate the Durham Lease if construction of the base building shell of the Facility is not complete by May 16, 2021. The Company incurred initial direct costs to enter into the Durham Lease of approximately $0.8 million. The costs have been recorded on the consolidated balance sheets as a deferred lease asset and will be amortized into earnings over the term of the Durham Lease. 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 Lease commences on the date on which certain improvements to the Office Space have been made and the Office Space is tendered to the Company for possession, which the Company and the Dallas Landlord presently anticipate to be delivered on or about May 15, 2021, and will have a term of approximately ten years. The Company has an option to extend the term of the Lease for one additional period of five years. The Company’s obligation for the payment of base rent for the Office Space will initially be approximately $32,500 per month and will increase annually, up to an estimated monthly base rent of $50,000 during the term of the 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 Lease. Total future minimum lease payments under the Dallas Lease over the initial 10 year term are approximately $4.9 million. 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 Landlord has the right to terminate the Lease, or the Company’s right to possess the Office Space without terminating the 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 may terminate the Lease if the Office Space is not delivered will all improvements to be made by the Landlord pursuant to the Lease substantially completed by May 31, 2021. As of March 31, 2021, the Company recognized approximately $0.6 million of lease construction incentive based on the construction allowance provided. The construction incentive has been recorded on the consolidated balance sheets as a deferred lease incentive obligation and will be amortized into earnings as a deduction of rent expense over the term of the Dallas Lease.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 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.
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. 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.
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 consolidated financial statements.

Balance Sheet Components (Table

Balance Sheet Components (Tables)	3 Months Ended
	Mar. 31, 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): March 31, 2021 December 31, 2020 Prepaid research and development $ 6,281 $ 2,462 Prepaid insurance 1,654 2,480 Prepaid bonus 1,115 409 Prepaid clinical trial 928 944 Other 839 331 Total prepaid expenses and other current assets $ 10,817 $ 6,626
Schedule of Property Plant and Equipment	March 31, 2021 December 31, 2020 Computer equipment $ 242 $ 95 Laboratory equipment 407 — Construction in progress 1,889 201 2,538 296 Accumulated depreciation (41 ) (9 ) Property, plant and equipment, net $ 2,497 $ 287
Schedule Of Accrued Expense And Other Current Labilities	Accrued expenses and other current liabilities consisted of the following (in thousands): March 31, 2021 December 31, 2020 Accrued research and development $ 5,672 $ 2,106 Accrued license fees 5,500 — Accrued compensation 1,427 1,766 Accrued professional and consulting fees 1,119 999 Accrued construction in progress 1,029 173 Other 128 91 Total accrued expenses and other current liabilities $ 14,875 $ 5,135

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	3 Months Ended
	Mar. 31, 2021
Schedule of Restricted Stock Units Activity	The Company’s RSU activity for the three months ended March 31, 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 — — Nonvested at March 31, 2021 2,850,053 $ 6.37
Schedule of Restricted Stock Awards Activity	The Company’s RSA activity for the three months ended March 31, 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 — — Nonvested at March 31, 2021 769,058 $ 5.28
Schedule of Total Stock-Based Compensation Expense for Stock Options, RSAs and RSUs (Detail)	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 months ended March 31, 2021 (in thousands): For the Three Months Ended March 31, 2021 Research and development expense $ 1,579 General and administrative expense 2,015 Total $ 3,594
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 months ended March 31, 2021: Risk-free interest rate 0.64 % Expected dividend yield — Expected term in years 6.1 Expected volatility 75 %
Schedule of Stock Option Activity	The following table summarizes stock option activity, during the three months ended March 31, 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 1,621,900 28.81 Options cancelled or forfeited (10,600 ) 26.87 Outstanding at March 31, 2021 2,286,142 $ 26.42 9.8 $ 213 Vested and expected to vest at March 31, 2021 2,286,142 $ 26.42 9.8 $ 213 Options exercisable at March 31, 2021 27,552 $ 20.44 9.5 $ 6

Net Loss Per Common Share (Tabl

Net Loss Per Common Share (Tables)	3 Months Ended
	Mar. 31, 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 March 31, 2021 2020 Net loss $ (32,024 ) $ (5,431 ) Weighted-average shares of common stock outstanding used to compute net loss per common share, basic and diluted 36,992,377 10,894,999 Net loss per common share, basic and diluted $ (0.87 ) $ (0.50 )
Schedule of Common Stock Equivalents Outstanding Excluded from Computation of Diluted Net Loss Per Share Attributable to Common Stockholders	The following common stock equivalents outstanding as of March 31, 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: March 31, 2021 March 31, 2020 Unvested RSUs 2,850,053 — Unvested RSAs 769,058 — Stock options 2,286,142 — Series A convertible preferred stock — 6,000,000 Total 5,905,253 6,000,000

Organization and Description _2

Organization and Description of Business Operations - Additional Information (Details) $ / shares in Units, $ in Thousands	Sep. 29, 2020shares	Sep. 28, 2020USD ($)$ / sharesshares	Sep. 16, 2020shares	Aug. 31, 2020USD ($)shares	Mar. 31, 2021USD ($)$ / sharesshares	Mar. 31, 2020USD ($)	Jul. 31, 2020USD ($)shares	Dec. 31, 2020USD ($)	Jul. 01, 2020shares
Organization and Description of Business Operations [Line Items]
Date of incorporation					Feb. 13, 2020
Accumulated deficit | $					$ (93,150)			$ (61,126)
Gross proceeds from sale of convertible preferred stock | $						$ 18,000
Cash | $					$ 228,700
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
Aggregate shares sold							10,000,000
Gross proceeds from sale of convertible preferred stock | $							$ 30,000
Series B Convertible Preferred Stock
Organization and Description of Business Operations [Line Items]
Conversion of convertible preferred stock to common stock, shares		5,647,048
Aggregate shares sold				5,647,048
Gross proceeds from sale of convertible preferred stock | $				$ 96,000
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			$ 20
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
Conversion of stock, shares issued		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

Balance Sheet Components - Sche

Balance Sheet Components - Schedule of Prepaid Expenses and Other Current Assets (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Balance Sheet Related Disclosures [Abstract]
Prepaid research and development	$ 6,281	$ 2,462
Prepaid insurance	1,654	2,480
Prepaid bonus	1,115	409
Prepaid clinical trial	928	944
Other	839	331
Total prepaid expenses and other current assets	$ 10,817	$ 6,626

Balance Sheet Components - Sc_2

Balance Sheet Components - Schedule of Property Plant and Equipment (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Property Plant And Equipment [Line Items]
Property, plant and equipment, gross	$ 2,538	$ 296
Accumulated depreciation	(41)	(9)
Property, plant and equipment, net	2,497	287
Computer Equipment
Property Plant And Equipment [Line Items]
Property, plant and equipment, gross	242	95
Laboratory Equipment
Property Plant And Equipment [Line Items]
Property, plant and equipment, gross	407
Construction in Progress
Property Plant And Equipment [Line Items]
Property, plant and equipment, gross	$ 1,889	$ 201

Balance Sheet Components - Addi

Balance Sheet Components - Additional Information (Details) - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Balance Sheet Related Disclosures [Abstract]
Depreciation expense	$ 32,000	$ 0

Balance Sheet Components - Sc_3

Balance Sheet Components - Schedule of Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Balance Sheet Related Disclosures [Abstract]
Accrued research and development	$ 5,672	$ 2,106
Accrued license fees	5,500
Accrued compensation	1,427	1,766
Accrued professional and consulting fees	1,119	999
Accrued construction in progress	1,029	173
Other	128	91
Total accrued expenses and other current liabilities	$ 14,875	$ 5,135

Research, Collaboration and L_2

Research, Collaboration and License Agreements - Additional Information (Details)	1 Months Ended					3 Months Ended		12 Months Ended
	Mar. 31, 2021USD ($)shares	Oct. 31, 2020USD ($)	Aug. 31, 2020USD ($)	Apr. 30, 2020Product	Dec. 31, 2019USD ($)	Mar. 31, 2021USD ($)shares	Mar. 31, 2020USD ($)shares	Dec. 31, 2020USD ($)shares	Oct. 29, 2020USD ($)	Feb. 21, 2020USD ($)	Nov. 30, 2019shares
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Common stock, shares issued | shares	37,761,435					37,761,435		37,761,435
Research and development						$ 23,854,000	$ 5,514,000
TSHA-120
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Research and development	$ 5,500,000
Upfront payment	5,500,000
Clinical, regulatory and commercial milestones to be received	$ 19,300,000					19,300,000
UT Southwestern Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Preclinical activities period under sponsored research agreements				2 years
Minimum licensed product to develop obtain regulatory approval for and commercialize | Product				1
Common stock, shares issued | shares							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
Queen's Agreement | Research and Development Expense
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Cash payment to acquire license agreement							$ 3,000,000
Queen's Agreement | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
License agreement regulatory milestones payment										$ 10,000,000
License agreement commercial milestones payment										$ 10,000,000
Abeona CLN1 Agreements
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
License fee payment			$ 3,000,000
Purchase of clinical materials and reimbursement incurred development costs		$ 4,000,000
Research and development								7,000,000
Additional milestone payments						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
License and inventory purchase agreement sales related milestones payment			$ 30,000,000
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
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

Stockholders' Equity (Deficit_2

Stockholders' Equity (Deficit), Convertible Preferred Stock and Tranche Liability - Additional Information (Details) $ / shares in Units, $ in Thousands

Sep. 29, 2020shares

Sep. 28, 2020USD ($)$ / sharesshares

Sep. 16, 2020

Jul. 28, 2020$ / sharesshares

Jul. 02, 2020USD ($)shares

Jun. 30, 2020USD ($)$ / sharesshares

Mar. 05, 2020shares

Mar. 04, 2020USD ($)$ / sharesshares

Aug. 31, 2020USD ($)

Mar. 31, 2021USD ($)$ / sharesshares

Mar. 31, 2020USD ($)

Jul. 31, 2020USD ($)

Dec. 31, 2020shares

Class Of Stock [Line Items]

Common stock, shares authorized

200,000,000

32,685,000

200,000,000

200,000,000

Convertible preferred stock, shares authorized

15,647,052

Convertible preferred stock, shares authorized

10,000,000

10,000,000

10,000,000

Preferred stock, shares issued

0

0

Preferred stock, shares outstanding

0

0

Proceeds from issuances of Series A convertible preferred stock | $

$ 18,000

Preferred stock tranche liability | $

$ 1,100

Change in fair value of preferred stock tranche liability | $

$ 200

$ 180

Common Stock

Class Of Stock [Line Items]

Conversion of stock, shares issued

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

$ 20

Gross proceeds from issuance of common stock | $

$ 181,000

Stock issuance costs, including underwriters’ discounts and commissions | $

$ 15,100

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

$ 600

Proceeds from issuances of Series A convertible preferred stock | $

$ 30,000

Convertible preferred stock tranche liability, offering price | $ / shares

$ 3

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

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

Proceeds from issuances of Series A convertible preferred stock | $

$ 96,000

Convertible preferred stock tranche liability, offering price | $ / shares

$ 17

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

Proceeds from issuances of Series A convertible preferred stock | $

$ 96,000

Series B Convertible Preferred Stock | Private Placement | Series B Purchase Agreement | Maximum

Class Of Stock [Line Items]

Shares issued during period

5,647,052

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Details) - USD ($)	Jan. 01, 2021	Sep. 16, 2020	Sep. 02, 2020	Jul. 01, 2020	Mar. 31, 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. 1, 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 8 months 12 days
Share-based payment award, unvested RSU/RSA granted, compensation cost not yet recognized					$ 15,400,000
Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based payment award, options granted					1,621,900
Share-based payment award, options granted, exercise price per share					$ 28.81
Share-based payment award, options, compensation cost not yet recognized					$ 37,000,000
Share-based payment award, compensation cost not yet recognized, weighted-average period of recognition					3 years 8 months 12 days
Restricted Stock Awards
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based payment award, compensation cost not yet recognized, weighted-average period of recognition					2 years
Share-based payment award, unvested RSU/RSA granted, compensation cost not yet recognized					$ 3,000,000
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. 1, 2021
Share-based payment award, expiration date		Jan. 1, 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					1,621,900
Award vesting period					4 years
Share-based payment award, options, weighted-average grant date fair value					$ 18.75

Stock-Based Compensation - Sche

Stock-Based Compensation - Schedule of Assumptions Used to Estimate Fair Value of Stock Options and Cancelled Options (Details) - Stock Options	3 Months Ended
	Mar. 31, 2021
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate	0.64%
Expected term in years	6 years 1 month 6 days
Expected volatility	75.00%

Stock-Based Compensation - Sc_2

Stock-Based Compensation - Schedule of Stock Option Activity (Details) - Stock Options - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Outstanding. Stock Options, Beginning Balance	674,842
Options granted, Stock Options	1,621,900
Options cancelled or forfeited, Stock Options	(10,600)
Outstanding. Stock Options, Ending Balance	2,286,142	674,842
Vested and expected to vest at March 31, 2021, Stock Options	2,286,142
Options exercisable at March 31, 2021, Stock Options	27,552
Outstanding, Weighted Average Exercise Price, Beginning balance	$ 20.68
Options granted, Weighted Average Exercise Price	28.81
Options cancelled or forfeited, Weighted Average Exercise Price	26.87
Outstanding, Weighted Average Exercise Price, Ending balance	26.42	$ 20.68
Vested and expected to vest at March 31, 2021, Weighted Average Exercise Price	26.42
Options exercisable at March 31, 2021, Weighted Average Exercise Price	$ 20.44
Outstanding, Weighted Average Remaining Contractual Life	9 years 9 months 18 days	9 years 9 months 18 days
Vested and expected to vest at March 31, 2021, Weighted Average Remaining Contractual Life	9 years 9 months 18 days
Weighted Average Remaining Contractual Life, Options exercisable at March 31, 2021	9 years 6 months
Outstanding, Aggregate Intrinsic Value, Beginning Balance	$ 3,953
Outstanding, Aggregate Intrinsic Value, Ending Balance	213	$ 3,953
Vested and expected to vest at March 31, 2021, Aggregate Intrinsic Value	213
Options exercisable at March 31, 2021, Aggregate Intrinsic Value	$ 6

Stock-Based Compensation - Sc_3

Stock-Based Compensation - Schedule of Restricted Stock Awards Activity (Details)	Jul. 01, 2020$ / shares
Restricted Stock Awards
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Restricted units/stock granted, Weighted Average Grant Date Fair Value per Share	$ 5.28

Stock-Based Compensation - Sc_4

Stock-Based Compensation - Schedule of Total Stock-Based Compensation Expense for Stock Options, RSAs and RSUs (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2021USD ($)
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 3,594
Research and Development Expense
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	1,579
General and Administrative Expense
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 2,015

Net Loss Per Common Share - Sch

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
	Mar. 31, 2021	Mar. 31, 2020
Earnings Per Share [Abstract]
Net loss	$ (32,024)	$ (5,431)
Weighted average common shares outstanding, basic and diluted	36,992,377	10,894,999
Net loss per common share, basic and diluted	$ (0.87)	$ (0.50)

Net Loss Per Common Share - S_2

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	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per share	5,905,253	6,000,000
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	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	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	2,286,142
Series A Convertible Preferred Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per share		6,000,000

Related Party Transactions - Ad

Related Party Transactions - Additional Information (Details)	1 Months Ended
	Mar. 31, 2020USD ($)	Jan. 31, 2020USD ($)PromissoryNote	Sep. 30, 2020USD ($)
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 Infor

Income Taxes - Additional Information (Details)	3 Months Ended
	Mar. 31, 2021USD ($)
Income Tax Disclosure [Abstract]
Provision for income taxes	$ 0

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details)	Jan. 11, 2021USD ($)ft²	Dec. 17, 2020ft²	Mar. 31, 2021USD ($)
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. 1, 2021
Operating lease term of contract		15 years 6 months
Operating lease extend term of contract		5 years
Operating leases initial direct costs			$ 800,000
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 15, 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 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
Future minimum lease payments	$ 4,900,000

Uncategorized Items - tsha-2021

Label	Element	Value
Restricted Stock Units R S U [Member]
Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nonvested Number	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber	2,850,053
Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nonvested Number	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber	2,850,053
Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nonvested Weighted Average Grant Date Fair Value	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue	$ 6.37
Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nonvested Weighted Average Grant Date Fair Value	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue	$ 6.37
Restricted Stock [Member]
Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nonvested Number	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber	769,058
Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nonvested Number	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber	769,058
Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nonvested Weighted Average Grant Date Fair Value	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue	$ 5.28
Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nonvested Weighted Average Grant Date Fair Value	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue	$ 5.28