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CONSOLIDATED STATEMENTS OF REDEEMABLE CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS' EQUITY (DEFICIT) (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Statement Of Stockholders Equity [Abstract]
Issuance of common stock upon public offering, net of issuance costs	$ 560	$ 2,373

Stock-Based Compensation - Summary of Assumptions used in Black-Scholes Option Pricing Model (Details) - Service-Based Awards - $ / shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate	0.83%	0.68%
Expected term (in years)	6 years 2 months 12 days	6 years 2 months 4 days
Expected volatility	68.21%	68.75%
Expected dividend yield	0.00%	0.00%
Fair value per share of common stock	$ 14.37	$ 13.52

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Income Taxes [Line Items]
Income tax benefits for net operating losses	$ 0	$ 0
Changes in valuation allowance for deferred tax assets	12,300,000	27,500,000
Unrecognized tax benefits	$ 0	0
Operating loss carryforwards, limitations on use	Net operating loss carryforwards may become subject to an annual limitation in the event of certain cumulative changes in the ownership interest of significant shareholders over a three-year period in excess of 50%, as defined under Sections 382 and 383 of the Internal Revenue Code, respectively, as well as similar state provisions.
Accrued interest related to uncertain tax positions	$ 0	0
Accrued penalties related to uncertain tax positions	0	0
Interest amounts recognized	0	0
Penalty amounts recognized	0	$ 0
Domestic Tax Authority
Income Taxes [Line Items]
Net operating loss carryforwards	189,400,000
Deferred tax assets, operating loss carryforwards, not subject to expiration	152,900,000
Deferred tax assets, operating loss carryforwards, subject to expiration	36,400,000
Domestic Tax Authority \| Research Tax Credit Carryforward
Income Taxes [Line Items]
Tax credit carryforward	$ 10,500,000
Tax credit carryforward, expiration year	2035
State
Income Taxes [Line Items]
Net operating loss carryforwards	$ 188,700,000
Operating loss carryforwards, expiration year	2035
State \| Research Tax Credit Carryforward
Income Taxes [Line Items]
Tax credit carryforward	$ 5,000,000.0
Tax credit carryforward, expiration year	2031

CONSOLIDATED STATEMENTS OF REDEEMABLE CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS' EQUITY (DEFICIT) - USD ($) $ in Thousands	Total	Series A Redeemable Convertible Preferred Stock	Series B Redeemable Convertible Preferred Stock	Series C Redeemable Convertible Preferred Stock	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive (Loss) Income	Accumulated Deficit
Beginning balance at Dec. 31, 2019	$ (192,833)					$ 2	$ 43	$ (192,878)
Temporary equity, Beginning balance, shares at Dec. 31, 2019		33,200,000	20,520,828	20,204,079
Temporary equity, Beginning balance at Dec. 31, 2019		$ 44,169	$ 81,108	$ 89,507
Beginning balance, shares at Dec. 31, 2019					2,997,040
Issuance of Series B redeemable convertible preferred stock in conjunction with sponsored research agreement, shares			62,500
Exercise of options to purchase common stock	232					232
Exercise of options to purchase common stock, shares					47,592
Issuance of common stock in connection with license agreement	2,660					2,660
Issuance of common stock in connection with license agreement, shares					177,318
Accretion of redeemable convertible preferred stock to redemption value	(10,784)					(7,237)		(3,547)
Temporary equity, Accretion of preferred stock to redemption value		$ 2,097	$ 3,853	$ 4,834
Stock-based compensation	7,080					7,080
Unrealized loss on investments	(43)						$ (43)
Temporary Equity, Conversion of redeemable convertible preferred stock into common stock upon initial public offering, shares		(33,200,000)	(20,583,328)	(20,204,079)
Temporary Equity, Conversion of redeemable convertible preferred stock into common stock upon initial public offering		$ (46,266)	$ (84,961)	$ (94,341)
Conversion of redeemable convertible preferred stock into common stock upon initial public offering	225,568				$ 1	225,567
Conversion of redeemable convertible preferred stock into common stock upon initial public offering, shares					10,065,629
Issuance of common stock upon initial public offering/public offering, net of issuance costs	74,352				$ 1	74,351
Issuance of common stock upon initial public offering/public offering, net of issuance costs, shares					5,500,000
Net loss	(91,665)							(91,665)
Ending balance at Dec. 31, 2020	$ 14,567				$ 2	302,655		(288,090)
Temporary equity, Ending balance, shares at Dec. 31, 2020	0
Ending balance, shares at Dec. 31, 2020					18,787,579
Exercise of options to purchase common stock	$ 3,737					3,737
Exercise of options to purchase common stock, shares	433,751				433,751
Stock-based compensation	$ 10,677					10,677
Issuance of common stock upon initial public offering/public offering, net of issuance costs	61,681					61,681
Issuance of common stock upon initial public offering/public offering, net of issuance costs, shares					3,162,500
Net loss	(37,157)							(37,157)
Ending balance at Dec. 31, 2021	$ 53,505				$ 2	$ 378,750		$ (325,247)
Temporary equity, Ending balance, shares at Dec. 31, 2021	0
Ending balance, shares at Dec. 31, 2021					22,383,830

Income Taxes - Summary of Significant Components of Company's Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Deferred tax assets:
Net operating loss carryforwards	$ 51,672	$ 37,609
Capitalized license and research and development payments	7,786	8,393
Research and development credits	15,062	11,910
Deferred revenue	11,919	17,117
Lease liabilities	10,105	10,519
Accrued bonus	1,085	1,053
Stock compensation	4,344	3,335
Other temporary differences	289	349
Total deferred tax assets	102,262	90,285
Valuation allowance	(93,091)	(80,758)
Deferred tax assets	9,171	9,527
Deferred tax liabilities:
Right-of-use asset	(5,996)	(6,007)
Depreciation	$ (3,175)	$ (3,520)

Net Loss Per Share

12 Months Ended

Dec. 31, 2021

Earnings Per Share [Abstract]

Net Loss Per Share

18. Net loss per share

Basic and diluted net loss per share attributable to common stockholders was calculated as follows (in thousands, except share and per share data):


	YEAR ENDED DECEMBER 31,
	2021			2020
Numerator:
Net loss	$	(37,157	)	$	(91,665	)
Cumulative dividends on redeemable convertible preferred stock		—			(10,831	)
Net loss attributable to common stockholders	$	(37,157	)	$	(102,496	)
Denominator:
Weighted average common shares outstanding, basic and diluted		21,794,546			6,332,841
Net loss per share attributable to common stockholders, basic and diluted	$	(1.70	)	$	(16.18	)

As of December 31, 2021 and 2020, we had 4,763,489 and 4,543,318 outstanding stock options, respectively, representing potential common shares, presented based on amounts outstanding at each period end, were excluded from the calculation of diluted net loss per share attributable to common stockholders for the periods indicated because including them would have been anti-dilutive.

Prepaids and Other Current Assets - Components of Prepaid and Other Current Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Prepaid Expense and Other Assets, Current [Abstract]
Clinical trial costs	$ 1,053	$ 805
Prepaid Insurance	2,593	2,598
Other receivables	1,289	31
Other prepaid expenses and other current assets	983	1,308
Prepaid Expense and Other Assets, Current	$ 5,918	$ 4,742

Collaboration Agreements - Summary of Total Consolidated Net Revenue from Strategic Collaborators (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Collaboration Agreements [Line Items]
Total collaboration revenue	$ 22,935	$ 2,915
Jazz
Collaboration Agreements [Line Items]
Total collaboration revenue	11,322	641
Sarepta
Collaboration Agreements [Line Items]
Total collaboration revenue	$ 11,613	$ 2,274

- Definition

Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

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+ Details

Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2021

Accounting Policies [Abstract]

Property and Equipment Estimated Useful Lives

Property and equipment is stated at cost, net of accumulated depreciation and amortization. Depreciation and amortization is calculated using the straight-line method over the estimated useful lives of the assets, which are as follows:


		Estimated useful life
Computer equipment and software		3 years
Furniture and fixtures		5 years
Laboratory and manufacturing equipment		5 years
Leasehold improvements		Shorter of useful life or remaining lease term

Net Loss Per Share (Tables)

12 Months Ended

Dec. 31, 2021

Earnings Per Share [Abstract]

Basic and Diluted Net Loss Per Share Attributable to Common Stockholders

Basic and diluted net loss per share attributable to common stockholders was calculated as follows (in thousands, except share and per share data):


	YEAR ENDED DECEMBER 31,
	2021			2020
Numerator:
Net loss	$	(37,157	)	$	(91,665	)
Cumulative dividends on redeemable convertible preferred stock		—			(10,831	)
Net loss attributable to common stockholders	$	(37,157	)	$	(102,496	)
Denominator:
Weighted average common shares outstanding, basic and diluted		21,794,546			6,332,841
Net loss per share attributable to common stockholders, basic and diluted	$	(1.70	)	$	(16.18	)

Stock-Based Compensation - Summary of Stock Option Activity (Details) - USD ($)
$ / shares in Units, $ in Thousands

12 Months Ended

Dec. 31, 2021

Dec. 31, 2020

4,543,318

1,449,400

(433,751)

(795,478)

4,763,489

4,543,318

Exercisable

2,688,532

Vested and expected to vest

4,763,489

Weighted Average Exercise Price Per Share

$ 8.52

23.26

8.62

11.10

12.56

$ 8.52

Exercisable

8.02

Vested and expected to vest

$ 12.56

Weighted Average Remaining Contractual Term

Outstanding

6 years 5 months 8 days

7 years 2 months 19 days

Exercisable

5 years 4 months 28 days

Vested and expected to vest

6 years 5 months 8 days

Outstanding

^[1]

$ 10,370

$ 108,048

Exercisable

^[1]

9,372

Vested and expected to vest

^[1]

$ 10,370

[1]	Aggregate intrinsic value is calculated as the difference between the exercise price of the underlying options and the fair value of common stock for those stock options that had exercise prices lower than the fair value of the Company’s common stock as of December 31, 2021 and 2020

Net Loss Per Share - Basic and Diluted Net Loss Per Share Attributable to Common Stockholders (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Numerator:
Net loss	$ (37,157)	$ (91,665)
Cumulative dividends on redeemable convertible preferred stock		(10,831)
Net loss attributable to common stockholders	$ (37,157)	$ (102,496)
Denominator:
Weighted average common shares outstanding, basic and diluted	21,794,546	6,332,841
Net loss per share attributable to common stockholders, basic and diluted	$ (1.70)	$ (16.18)

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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+ Details

- Definition

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

+ References

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+ Details

Other Significant Agreements

12 Months Ended

Dec. 31, 2021

Significant Agreements [Abstract]

Other Significant Agreements

16. Other significant agreements

MDACC sponsored research agreement

In November 2015, the Company entered into the MDACC Research Agreement with MDACC. Under the MDACC Research Agreement, the Company engaged MDACC to perform research and development services relating to its technology on patients suffering with cancer (the Research Program). MDACC was obligated to use reasonable efforts to conduct the Research Program and furnish the facilities necessary to carry out the program. The Research Program allowed for amendments from time to time during the term, by agreement of the parties, to modify the current Research Program or to add additional research projects for inclusion as part of the Research Program. The MDACC Research Agreement provided the Company with an option to negotiate a license to certain other technology derived from the program in the field of exosome technology. The term of the MDACC Research Agreement was originally scheduled to expire in November 2018. The MDACC Research Agreement was subsequently amended in February 2017 and in April 2018 to extend the term of the MDACC Research Agreement to February 2021 and to modify the payment terms of the MDACC Research Agreement. The MDACC Research Agreement was further amended in September 2019 to terminate the agreement, effective as of December 31, 2019.

Under the terms of the MDACC Research Agreement, the Company was obligated to pay fixed tiered quarterly cash payments (the Quarterly Payments) and to issue a fixed number of shares of its Series A Preferred Stock or Series B Preferred Stock to MDACC in consideration for the research services. The Quarterly Payments consisted of the following: (i) direct expenses comprising $1.0 million payable to MDACC in the first year and $1.25 million payable in years two through five, and (ii) overhead charges of 25% of the direct expenses. In addition to the Quarterly Payments, the Company was also obligated to issue an aggregate of 200,000 shares of Series A Preferred Stock in the first year of the arrangement and 20,833 shares of Series B Preferred Stock, quarterly, in years two through five of the MDACC Research Agreement. The Company recognized the payments made to MDACC as research and development expense as incurred. The shares to be issued were expensed on the date the associated Quarterly Payment was due based on the estimated fair value of the underlying series of Redeemable Convertible Preferred Stock on such date. Subsequent to issuance, the Series A Preferred Stock and Series B Preferred Stock issued to MDACC was accounted for consistent with all other outstanding shares of the respective series of Redeemable Convertible Preferred Stock. As noted above, the agreement was terminated as of December 31, 2019. As of December 31, 2019, the Company accrued the final $1.2 million cash payment and 62,500 shares of Series B Preferred Stock related to services provided in 2019. The Company made the final cash payment and issued the remaining shares of Series B Preferred Stock to MDACC in January 2020. There are no further payments or share issuances owed to MDACC pursuant to the MDACC Research Agreement.

There was no expense recognized during the year ended December 31, 2021 or 2020 related to the MDACC Research Agreement.

MDACC in-license agreement

In November 2015, the Company entered into a Patent and Technology License Agreement with MDACC, as amended in April 2018 (the MDACC License Agreement). Pursuant to the MDACC License Agreement, the Company holds exclusive worldwide license rights to certain intellectual property relating to the use of exosomes for diagnostic and therapeutic applications and a non-exclusive worldwide license under certain related technologies, with the right to grant sublicenses. The Company also obtained the exclusive right of first negotiation, for a specified time period, for a license to certain of MDACC’s rights in future exosome technology.

Under the terms of the MDACC License Agreement, the Company is responsible for all patent costs incurred by MDACC for the underlying licensed technology in excess of $1.5 million from the effective date of the agreement through February 1, 2021, and for all patent costs incurred or invoiced after this date. As of December 31, 2021, there was no remaining funding provided by MDACC for patent-related costs under the MDACC License Agreement.

Pursuant to the MDACC License Agreement, the Company is also required to make future payments to MDACC upon the occurrence of events related to the development of products and upon the achievement of certain development and regulatory approval milestones up to an aggregate of $11.9 million, comprising up to $2.4 million for diagnostic products and up to $9.5 million for therapeutic products. The Company may at its discretion pay up to $4.4 million in such contingent payments in cash or through the issuance of equity in the form of redeemable convertible preferred stock or common stock, as applicable. Such payments will be expensed or capitalized based on the nature of the associated asset at the date the related contingency is resolved. In addition, the Company is obligated to pay certain payments upon the execution of sublicenses for qualifying products, as well as single digit percentage royalty payments on net sales from a licensed product.

The MDACC License Agreement will continue until the last to occur of: (i) the expiration of all patents issued underlying the licenses conveyed, (ii) the cancellation, withdrawal or express abandonment of all patent rights underlying the licenses conveyed or (iii) the fifteenth anniversary of the effective date of the agreement. Upon expiration of the MDACC License Agreement, the licenses granted will automatically convert to a fully-paid irrevocable and perpetual license. The Company may terminate the license for convenience upon 180 days prior written notice to MDACC. The license automatically terminates upon the Company’s bankruptcy, if the Company challenges the validity or enforceability of any of the licensed patent rights, or if the Company fails to make a number of payments in a timely manner over a specified period of time. Additionally, MDACC may terminate the license for the Company’s breach subject to certain specified cure periods.

As of December 31, 2021, no milestones had been achieved, nor had any royalties, sublicensing fees or other contingent payments been incurred under the MDACC License Agreement. The Company did not make any payments to MDACC for the years ended December 31, 2021 or 2020, with respect to the MDACC License Agreement.

Kayla Therapeutics S.A.S license agreement

On November 6, 2018, the Company entered into a License Agreement with Kayla, pursuant to which it obtained a co-exclusive worldwide, sublicensable license under certain patent rights and to related know-how and methods to research, develop, manufacture and commercialize compounds and products covered by such patent rights in all diagnostic, prophylactic and therapeutic uses (the Kayla License Agreement). The foregoing license is co-exclusive with Kayla, but Kayla’s retained rights are subject to certain restrictions.

During the first six years following the effective date of the Kayla License Agreement, Kayla and its affiliates may not research, develop, manufacture or commercialize anywhere in the world any product containing a small molecule STING agonist and an exosome. In addition, during the term of the Kayla License Agreement, Kayla and its affiliates may not grant a license to any third party under the licensed patent rights to, develop, manufacture or commercialize anywhere in the world a product containing certain STING compounds for therapeutic or veterinary purpose. The Kayla License Agreement also restricts the Company from developing any competing product containing a small molecule STING agonist and an exosome until the expiration of a non-compete period determined by the achievement of clinical milestones.

Pursuant to ASC 730, the Company determined that the assets acquired represent in-process research and development with no alternative future use. Therefore, the value of the consideration given for the licenses was expensed to acquired in-process research and development in the period in which it was incurred.

In consideration for entering into the Kayla License Agreement, the Company paid an up-front payment of $6.5 million in cash and issued 118,212 shares of common stock. The Company recorded an aggregate of $8.1 million to acquired in-process research and development expense during the year ended December 31, 2018 comprising: (i) $6.5 million related to the cash payment and (ii) $1.6 million related to the issuance of its common stock based on the fair value of the Company’s common stock at the effective date of the Kayla License Agreement.

The Company has certain diligence obligations under the Kayla License Agreement, which include using commercially reasonable efforts to develop, commercialize and market the products developed under the licensed patent rights, including using commercially reasonable efforts to initiate a cohort extension of a Phase 1/2 trial after obtaining IND approval. The Company is also obligated to pay up to $100.0 million in cash payments and up to $13.0 million payable in shares of the Company’s common stock upon the achievement of specified clinical and regulatory milestones, including approvals in the US, the EU and Japan. Such payments will be expensed or capitalized based on the nature of the associated asset at the date the related contingency is resolved. Additionally, the Company is obligated to pay to Kayla a percentage of the payments that the Company receives from sublicensees of the rights licensed to it by Kayla, excluding any royalties. This percentage varies from single digits to low double digits. The first milestone was achieved upon the dosing of the first subject in the Company’s exoSTING Phase 1/2 clinical trial in September 2020. Upon achievement of the milestone, the Company was obligated to make a nonrefundable payment of $15.0 million in cash and issue 177,318 shares of common stock to Kayla. The common stock was issued as of the date of dosing, and the cash payment of $15.0 million was paid as of December 31, 2020. As of December 31, 2021, no other milestones had been achieved.

The Company is obligated to pay to Kayla tiered royalties ranging from low single-digits to mid-single-digits based on annual net sales by the Company, its affiliates and its sublicensees of licensed products. The royalty term is determined on a product-by-product and country-by-country basis and continues until the later of (i) the expiration of the last valid claim of the licensed patent rights that covers such product in such country, (ii) the loss or expiration of any period of marketing exclusivity for such product in such country, or (iii) ten years after the first commercial sale of such product in such country; provided that if the royalty is payable when no valid claim covers a given product in a given country, the royalty rate for sales of such product in such country is decreased. The Company may terminate the Kayla License Agreement on a licensed compound-by-licensed compound basis and on a region-by region basis for any reason upon 30 days prior written notice to Kayla. The Company or Kayla may terminate the Kayla License Agreement for the other’s material breach that remains uncured for 60 days after receiving notice thereof. As of December 31, 2021, no royalties, or other contingent payments had been incurred under the Kayla License Agreement.

Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2021

Summary of Stock Option Activity

The following table summarizes the Company’s stock option activity during the twelve months ended December 31, 2021:


	NUMBER OF SHARES			WEIGHTED AVERAGE EXERCISE PRICE PER SHARE		WEIGHTED AVERAGE REMAINING CONTRACTUAL TERM		AGGREGATE INTRINSIC VALUE (1)
						(In years)		(In thousands)
Outstanding as of December 31, 2020		4,543,318		$	8.52		7.22	$	108,048
Granted		1,449,400			23.26
Exercised		(433,751	)		8.62
Forfeited/Cancelled		(795,478	)		11.10
Outstanding as of December 31, 2021		4,763,489			12.56		6.44		10,370
Exercisable as of December 31, 2021		2,688,532			8.02		5.41		9,372
Vested and expected to vest as of December 31, 2021		4,763,489			12.56		6.44		10,370

(1)

Aggregate intrinsic value is calculated as the difference between the exercise price of the underlying options and the fair value of common stock for those stock options that had exercise prices lower than the fair value of the Company’s common stock as of December 31, 2021 and 2020.

Schedule of Components and Classification of Stock-Based Compensation Expense

The following table presents the components and classification of stock-based compensation expense (in thousands):


	YEAR ENDED DECEMBER 31,
	2021		2020
Research and development	$	4,733	$	3,563
General and administrative		5,409		3,517
Gain on disposition		535		-
	$	10,677	$	7,080

Employee	$	9,862	$	6,547
Non-employee		815		533
	$	10,677	$	7,080

Service-Based Awards

Summary of Key Assumptions Used for Stock Option Valuation

The key assumptions used in the Black-Scholes option pricing model on the date of grant for options with service-based vesting conditions granted to employees, directors and non-employees, were as follows, presented on a weighted average basis:


	YEAR ENDED DECEMBER 31,
	2021			2020
Risk-free interest rate		0.83	%		0.68	%
Expected term (in years)		6.20		6.18
Expected volatility		68.21	%		68.75	%
Expected dividend yield		0.00	%		0.00	%
Fair value per share of common stock	$	14.37		$	13.52

Leases (Tables)

12 Months Ended

Dec. 31, 2021

Leases [Abstract]

Components of Operating Lease Costs

The components of operating lease costs were as follows (in thousands):


	FOR THE YEAR ENDED DECEMBER 31,
	2021			2020
Operating lease costs	$	4,882		$	4,836
Short-term lease costs		27			19
Variable lease costs		2,582			2,222
Sublease income		(1,850	)		(861	)
	$	5,641		$	6,216

Summary of Additional Lease Information

Additional lease information is summarized in the following table (in millions, except lease term and discount rate):


	FOR THE YEAR ENDED DECEMBER 31,
	2021			2020
Cash paid for amounts included in the measurement of operating lease liabilities	$	6.0		$	6.0
Weighted-average remaining lease term - operating leases (years)		7.9			8.9
Weighted-average discount rate - operating leases		10.1	%		10.3	%

Schedule of Undiscounted Cash Flows Used in Calculating the Operating Lease Liabilities and Amounts to be Received under the Sublease

Undiscounted cash flows used in calculating the Company’s operating lease liabilities and amounts to be received under the sublease at 35 CambridgePark Drive and 4 Hartwell Place as of December 31, 2021 are as follows (in thousands):


Fiscal Year	OPERATING LEASE PAYMENTS			SUBLEASE RECEIPTS		NET OPERATING LEASE PAYMENTS
2022	$	6,252		$	2,821	$	3,431
2023		6,436			1,962		4,474
2024		6,625			936		5,689
2025		6,820					6,820
2026		7,020					7,020
Thereafter		21,779					21,779
Total undiscounted cash flows	$	54,932		$	5,719	$	49,213
Less: Amounts representing interest		(17,387	)
Present value of lease liabilities	$	37,545

Income Taxes - Summary of Reconciliation of US Statutory Income Tax Rate to the Company's Effective Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Federal statutory income tax rate%	21.00%	21.00%
State taxes, net of federal benefit	8.50%	7.40%
Federal and state research and development credits	5.90%	2.70%
Executive Compensation	(0.70%)	(0.30%)
Non-deductible items	(0.10%)	(0.10%)
Stock Compensation	(1.50%)	(0.80%)
Change in valuation allowance	(33.20%)	(30.00%)
Other	0.10%	0.10%

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2021

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2. Summary of significant accounting policies

Basis of presentation and principles of consolidation

The Company's consolidated financial statements are prepared in accordance with U.S. generally accepted accounting principles (GAAP). Any reference in these notes to applicable guidance is meant to refer to the authoritative accounting principles generally accepted in the United States as found in the Accounting Standard Codification (ASC) and Accounting Standards Update (ASU) of the Financial Accounting Standards Board (FASB).

The accompanying consolidated financial statements include the accounts of the Company and its wholly-owned subsidiary, Codiak Securities Corporation. All intercompany balances and transactions have been eliminated in consolidation.

Use of estimates

We have made estimates and judgments affecting the amounts reported in our consolidated financial statements and the accompanying notes. On an ongoing basis, we evaluate our estimates, including critical accounting policies or estimates related to revenue recognition, stock-based compensation, accrued expenses, leases, gain upon derecognition, contingent consideration and the long-lived lives of useful assets. We base our estimates on historical experience and various relevant assumptions that we believe to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities that are not readily apparent from other sources. The actual results that we experience may differ materially from our estimates. Significant estimates relied upon in preparing these financial statements include, among others, those related to the fair value of equity awards, revenue recognition, accrued expenses, leases, gain upon derecognition, contingent consideration, income taxes, and long-lived lives of useful assets.

Segments

The Company has one operating segment. The Company’s chief operating decision maker, its Chief Executive Officer, manages the Company’s operations on a consolidated basis for the purposes of assessing performance and allocating resources. All of the Company’s long-lived assets are held in the United States.

Disposition of Business

The Company accounts for the derecognition of a group of assets that is a business in transactions with noncustomers in accordance with ASC 810-10-40. The Company measures the gain or loss upon derecognition as the difference between: (i) aggregate fair value of any consideration received and (ii) carrying amount of the group of assets, net of transaction and other costs directly attributable to the transaction. Gains and losses are recognized as of the date the Company ceases to have a controlling financial interest in the associated group of assets. Consideration received, including contingent consideration, is initially measured at fair value. Contingent consideration is subsequently remeasured by recognizing increases using a gain contingency approach and impairments based on the loss contingency model. Both the fair value of the consideration received and any potential future contingent gains contain unobservable inputs, whereby expected future cash flows are discounted using a rate that includes assumptions regarding an entity’s average cost of debt and equity, incorporates expected future cash flows based on internal business plans, and applies certain assumptions about risk and uncertainties.

Cash, cash equivalents and restricted cash

The Company considers all highly liquid investments purchased with original final maturities of three months or less from the date of purchase to be cash equivalents. Cash equivalents comprises money market accounts invested in US Treasury securities. Restricted cash is composed of letters of credit held as collateral related to the Company’s lease arrangements. Restricted cash is classified as either current or non-current based on the term of the underlying lease agreement.

Investments

The Company classifies all of its investments as available-for-sale securities. The Company’s investments are measured and reported at fair value using quoted prices in active markets for similar securities. Unrealized gains and losses on available-for-sale securities are reported as accumulated other comprehensive (loss) income, which is a separate component of stockholders’ equity (deficit). The cost of securities sold is determined on a specific identification basis, and realized gains and losses are included in other income (expense), net within the consolidated statements of operations and comprehensive loss. If any adjustment to fair value reflects a decline in the value of the investment that the Company considers to be “other than temporary”, the Company reduces the investment to fair value through a charge to the consolidated statements of operations and comprehensive loss. No such adjustments were necessary during the periods presented. The Company classifies its available-for-sale investments as current assets on the consolidated balance sheets if they mature within one year from the balance sheet date. Those investments with maturities greater than 12 months would be considered non-current. Investments with original maturities of less than 90 days are included in cash and cash equivalents on the condensed consolidated balance sheets.

Deferred offering costs

The Company capitalizes certain legal, accounting and other third-party fees that are directly associated with in-process equity financings as deferred offering costs until such financings are consummated. Such costs are classified in prepaid expenses and other current assets in the accompanying consolidated balance sheets. After the consummation of the equity financing, these costs are recorded in stockholders’ equity (deficit) as a reduction of additional paid-in capital or the associated preferred stock account, as applicable. In the event the offering is terminated, all capitalized deferred offering costs are expensed. Deferred offering costs as of December 31, 2021 were $0.2 million in connection with the Company's shelf registration and “at-the-market” offering facility. Deferred offering costs as of December 31, 2020 were $0.2 million in connection with the follow-on equity funding completed in February 2021.

Concentrations of credit risk and significant suppliers and license agreements

Financial instruments that potentially expose the Company to credit risk primarily consist of cash, cash equivalents, restricted cash and investments. The Company maintains its cash, cash equivalent, restricted cash and investment balances with accredited financial institutions and, consequently, the Company does not believe it is subject to unusual credit risk beyond the normal credit risk associated with commercial banking relationships.

The Company’s cash management and investment policy limits investment instruments to investment-grade securities with the objective to preserve capital and to maintain liquidity until the funds can be used in business operations. Bank accounts in the United States are insured by the Federal Deposit Insurance Corporation (FDIC) up to $250,000. As of December 31, 2021 and 2020, the Company’s primary operating accounts significantly exceeded the FDIC limits.

The Company is presently dependent on third-party manufacturers to supply materials for research and development activities of its programs, including clinical and preclinical testing. The Company’s development programs could be adversely affected by a significant interruption in the supply of the necessary materials. The Company is also dependent on third parties who provide license rights used in the development of certain programs. The Company could experience delays in the development of its programs if any of these license agreements are terminated, if the Company fails to meet the obligations required under its arrangements, or if the Company is unable to successfully secure new strategic alliances or licensing agreements.

For the year ended December 31, 2021, Jazz accounted for 49% of total collaboration revenue and Sarepta accounted for 51% of total collaboration revenue. For the year ended December 31, 2020, Jazz accounted for 22% of total collaboration revenue and Sarepta accounted for 78% of total collaboration revenue.

Off-balance sheet risk

As of December 31, 2021 and 2020, the Company had no off-balance sheet risks such as foreign exchange contracts, option contracts or other foreign hedging arrangements.

Fair value of financial instruments

The Company is required to disclose information on all assets and liabilities reported at fair value that enables an assessment of the inputs used in determining the reported fair values. FASB ASC Topic 820, Fair Value Measurements and Disclosures (ASC 820), establishes a hierarchy of inputs used in measuring fair value that maximizes the use of observable inputs and minimizes the use of unobservable inputs by requiring that the observable inputs be used when available. Observable inputs are inputs that market participants would use in pricing the asset or liability based on market data obtained from sources independent of the Company. Unobservable inputs are inputs that reflect the Company’s assumptions about the inputs that market participants would use in pricing the asset or liability and are developed based on the best information available in the circumstances. The fair value hierarchy applies only to the valuation inputs used in determining the reported fair value of the investments and is not a measure of the investment credit quality.

The three levels of the fair value hierarchy are described below:

Level 1 — Valuations based on quoted prices in active markets for identical assets or liabilities that the Company has the ability to access at the measurement date.

Level 2 — Valuations based on quoted prices for similar assets or liabilities in markets that are not active or for which all significant inputs are observable, either directly or indirectly.

Level 3 —Valuations that require inputs that reflect the Company’s own assumptions that are both significant to the fair value measurement and unobservable.

To the extent that valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair value requires more judgment. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement.

Items measured at fair value on a recurring basis include cash equivalents as of December 31, 2021 and 2020. Certain cash equivalents that are measured at fair value using the net asset value per share (or its equivalent) practical expedient have not been classified in the fair value hierarchy. The carrying amounts reflected in the consolidated balance sheets for prepaid expenses and other current assets, accounts payable and accrued expenses approximate their fair values due to their short-term maturities.

Property and equipment


		Estimated useful life
Computer equipment and software		3 years
Furniture and fixtures		5 years
Laboratory and manufacturing equipment		5 years
Leasehold improvements		Shorter of useful life or remaining lease term

Purchased assets that are not yet in service are recorded to construction-in-progress and no depreciation expense is recorded. Once they are placed in service they are reclassified to the appropriate asset class and depreciated over their respective estimated useful lives. Upon the retirement or sale of an asset, the related cost and accumulated depreciation or amortization is removed from the accounts and any resulting gain or loss is recorded to other income (expense), net. Expenditures for maintenance and repairs are expensed as incurred.

Impairment of long-lived assets

The Company periodically evaluates its long-lived assets, which consist of property and equipment, prepaid manufacturing services and right-of-use-assets, for impairment whenever events or changes in circumstances indicate that a potential impairment may have occurred. If such events or changes in circumstances arise, the Company compares the carrying amount of the long-lived assets to the estimated future undiscounted cash flows expected to be generated by the long-lived assets. If the estimated aggregate undiscounted cash flows are less than the carrying amount of the long-lived assets, an impairment charge, calculated as the amount by which the carrying amount of the assets exceeds the fair value of the assets, is recorded. The fair value of the long-lived assets is determined based on the estimated discounted cash flows expected to be generated from the long-lived assets. The Company has not recorded any such impairment charges during the years ended December 31, 2021 or 2020.

Term loan

The Company accounts for its Loan and Security Agreement with Hercules as a liability measured at net proceeds less debt discount and is accreted to the associated face value of the term loan over its respective expected term using the effective interest method. The Company considers whether there are any embedded features in its debt instruments that require bifurcation and separate accounting as derivative financial instruments pursuant to FASB ASC Topic 815, Derivatives and Hedging.

The Company capitalizes certain legal and other third-party fees that are directly associated with obtaining access to capital under credit facilities. Deferred financing costs related to a recognized debt liability are recorded as a reduction of the carrying amount of the debt liability and amortized to interest expense using the effective interest rate method. Deferred financing costs related to the term loan were less than $0.1 million for the years ended December 31, 2021 and 2020, respectively.

Leases

The Company accounts for leases in accordance with ASC 842, Leases. Leases are classified at their commencement date, which is defined as the date on which the lessor makes the underlying asset available for use by the lessee, as either operating or finance leases based on the economic substance of the agreement. Lease liabilities are measured at the lease commencement date as the present value of the future lease payments using the interest rate implicit in the lease. If the rate implicit is not readily determinable, the Company will utilize their incremental borrowing rate as of the lease commencement date. If the rate implicit is not readily determinable, the Company will utilize their incremental borrowing rate as of the lease commencement date.

Lease right-of-use assets are measured as the lease liability plus initial direct costs and prepaid lease payments less lease incentives. The lease term is the non-cancelable period of the lease, adjusted for any options to extend or terminate when it is reasonably certain the Company will exercise such options. The Company does not recognize leases with an initial term of 12 months or less.

The Company’s operating leases are presented in the consolidated balance sheets as operating lease right-of-use assets, classified as noncurrent assets, and operating lease liabilities, classified as current and noncurrent liabilities based on the portion of the lease liability that will mature within the proceeding twelve months. Operating lease expense for the minimum lease payments is recognized on a straight-line basis over the lease term. The Company assesses its right-of-use assets for impairment consistent with the assessment performed for long-lived assets used in operations.

The Company evaluates its subleases in which it is the sublessor to determine whether it is relieved of the primary obligation under the original lease. If it remains the primary obligor, the Company continues to account for the original lease as it did before the commencement of the sublease and reports the sublease income on a gross basis in other income in the consolidated statements of operations and comprehensive loss.

Redeemable convertible preferred stock

Prior to the automatic conversion of all outstanding shares of the Company’s redeemable convertible preferred stock upon the closing of the IPO, the Company recorded all redeemable convertible preferred stock upon issuance at its respective fair value or original issuance price less issuance costs. The Company classified its redeemable convertible preferred stock outside of stockholders’ equity (deficit) as the redemption of such shares was outside the Company’s control. The Company adjusted the carrying values of the redeemable convertible preferred stock to redemption value when the redemption value exceeded the carrying value. As of December 31, 2021 and 2020, the Company did not have any convertible preferred stock issued or outstanding.

Revenue recognition

The Company recognizes revenue in accordance with FASB ASC Topic 606, Revenue from Contracts with Customers (ASC 606). The core principle of ASC 606 is that an entity should recognize revenue to depict the transfer of promised goods and/or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods and/or services. To determine the appropriate amount of revenue to be recognized, the Company performs the following steps: (i) identify the contract(s) with the customer, (ii) identify the performance obligations in the contract, (iii) determine the transaction price, (iv) allocate the transaction price to the performance obligations in the contract and (v) recognize revenue when (or as) each performance obligation is satisfied.

Pursuant to the guidance in ASC 606, the Company accounts for a contract with a customer that is within the scope of ASC 606 when all of the following criteria are met: (i) the arrangement has been approved by the parties and the parties are committed to perform their respective obligations, (ii) each party’s rights regarding the goods and/or services to be transferred can be identified, (iii) the payment terms for the goods and/or services to be transferred can be identified, (iv) the arrangement has commercial substance and (v) collection of substantially all of the consideration to which the Company will be entitled in exchange for the goods and/or services that will be transferred to the customer is probable.

The Company assesses the goods and/or services promised within a contract which contains multiple promises to evaluate which promises are distinct. Promises are considered to be distinct and therefore, accounted for as separate performance obligations, provided that: (i) the customer can benefit from the good or service either on its own or together with other resources that are readily available to the customer and (ii) the promise to transfer the good or service to the customer is separately identifiable from other promises in the contract. The Company determines that a customer can benefit from a good or service if it could be used, consumed, sold for an amount that is greater than scrap value, or otherwise held in a way that generates economic benefits. Factors that are considered in determining whether or not two or more promises are not separately identifiable include, but are not limited to, the following: (i) the Company provides a significant service of integrating goods and/or services with other goods and/or services promised in the contract, (ii) one or more of the goods and/or services significantly modifies or customizes, or are significantly modified or customized by, one or more of the other goods and/or services promised in the contract and (iii) the goods and/or services are highly interdependent or highly interrelated. Individual goods or services (or bundles of goods and/or services) that meet both criteria for being distinct are accounted for as separate performance obligations. Promises that are not distinct at contract inception are combined into a single performance obligation. Options to acquire additional goods and/or services are evaluated to determine if such option provides a material right to the customer that it would not have received without entering into the contract. If so, the option is accounted for as a separate performance obligation. If not, the option is considered a marketing offer which would be accounted for as a separate contract upon the customer’s election.

The terms of the Company’s arrangements include the payment of one or more of the following: (i) non-refundable, up-front fees, (ii) cost reimbursements, (iii) development, regulatory and commercial milestone payments, (iv) royalties on net sales of licensed products and (v) profit share for co-commercialized products. The transaction price generally comprises of fixed fees due at contract inception and an estimate of variable consideration for cost reimbursements and milestone payments due upon the achievement of specified events. Additionally, the Company may earn sales milestones, tiered royalties earned when the licensee recognizes net sales of licensed products and potentially profit share related to co-commercialized products. The Company measures the transaction price based on the amount of consideration to which it expects to be entitled in exchange for transferring the promised goods and/or services to the customer. The Company utilizes either the expected value method or the most likely amount method to estimate the amount of variable consideration, depending on which method is expected to better predict the amount of consideration to which it will be entitled. Amounts of variable consideration are included in the transaction price to the extent that it is probable that a significant reversal in the amount of cumulative revenue recognized will not occur when the uncertainty associated with the variable consideration is subsequently resolved. With respect to development and regulatory milestone payments, at the inception of the arrangement, the Company evaluates whether the associated event is considered probable of achievement and estimates the amount to be included in the transaction price using the most likely amount method. As part of the evaluation for development milestone payments, the Company considers several factors, including the stage of development of the targets included in the arrangement, the risk associated with the remaining development work required to achieve the milestone and whether or not the achievement of the milestone is within the Company’s control. Milestone payments that are not within the control of the Company or the licensee, such as those dependent upon receipt of regulatory approval, are not considered to be probable of achievement until the triggering event occurs. With respect to sales-based royalties and profit share payments, including milestone payments based upon the achievement of a certain level of product sales, wherein the license is deemed to be the sole or predominant item to which the payments relate, the Company recognizes revenue upon the later of: (i) when the related sales occur or (ii) when the performance obligation to which some or all of the payment has been allocated has been satisfied (or partially satisfied). To date, the Company has not recognized any development, regulatory or commercial milestones, royalty or profit share revenue resulting from its arrangements with customers. The Company considered the existence of a significant financing component in its arrangements and has determined that a significant financing component does not exist due to the applicability of available practical expedients, existence of substantive business purposes and/or presence of other compelling factors. The Company updates its assessment of the estimated transaction price, including the constraint on variable consideration, at the end of each reporting period and as uncertain events are

resolved or other changes in circumstances occur. Any adjustments to the transaction price are recorded on a cumulative catch-up basis, which would affect revenue and net loss in the period of adjustment.

The Company generally allocates the transaction price to each performance obligation identified in the contract on a relative standalone selling price basis. However, certain components of variable consideration are allocated specifically to one or more particular performance obligations to the extent both of the following criteria are met: (i) the terms of the payment relate specifically to the efforts to satisfy the performance obligation or transfer the distinct good or service and (ii) allocating the variable amount of consideration entirely to the performance obligation or the distinct good or service is consistent with the allocation objective of the standard whereby the amount allocated depicts the amount of consideration to which the entity expects to be entitled in exchange for transferring the promised goods or services. The Company develops assumptions that require judgment to determine the standalone selling price for each performance obligation identified in the contract. The key assumptions utilized in determining the standalone selling price for the performance obligations may include forecasted revenues, development timelines, estimated research and development costs, discount rates, other comparable transactions, likelihood of exercise and probabilities of technical and regulatory success.

Revenue is recognized based on the amount of the transaction price that is allocated to each respective performance obligation when or as the performance obligation is satisfied by transferring a promised good and/or service to the customer. For performance obligations that are satisfied at a point in time, the Company recognizes revenue when control of the goods and/or services is transferred to the customer. For performance obligations that are satisfied over time, the Company recognizes revenue by measuring the progress toward complete satisfaction of the performance obligation using a single method of measuring progress which depicts the performance in transferring control of the associated goods and/or services to the customer. The Company generally uses input methods to measure the progress toward the complete satisfaction of performance obligations satisfied over time. With respect to promises related to licenses to intellectual property that is determined to be distinct from the other performance obligations identified in the arrangement, the Company recognizes revenue from amounts allocated to the license when the license is transferred to the licensee and the licensee is able to use and benefit from the license. For licenses that are bundled with other promises, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. Any such adjustments are recorded on a cumulative catch-up basis, which would affect revenue and net loss in the period of adjustment.

The Company receives payments from its licensees in accordance with the terms of the contracts. Up-front payments and fees are recorded as contract liabilities upon receipt or when due and may require deferral of revenue recognition to a future period until the Company performs its obligations under the arrangement. Amounts expected to be recognized as revenue within the 12 months following the balance sheet date are classified in current liabilities. Amounts not expected to be recognized as revenue within the 12 months following the balance sheet date are classified as contract liabilities, net of current portion. Amounts payable to the Company are recorded as accounts receivable when the Company’s right to consideration is unconditional.

Research and development expense

Research and development costs are expensed as incurred. Research and development expenses consist of costs incurred in performing research and development activities, including salaries and benefits, overhead costs, contract services and other related costs. The value of goods and services received from contract research organizations and contract manufacturing organizations in the reporting period are estimated based on the level of services performed, and progress in the period in cases when the Company has not received an invoice from the supplier. In circumstances where amounts have been paid in excess of costs incurred, the Company records a prepaid expense.

Patent costs

Costs to secure, defend and maintain patents are expensed as incurred due to the uncertainty of future benefits and are classified as general and administrative expenses.

Stock-based compensation

The Company issues stock-based awards to employees and non-employees, generally in the form of stock options and restricted stock units (RSUs). The Company accounts for stock-based compensation awards in accordance with ASC 718, Compensation—Stock Compensation. Most of its stock-based awards have been made to employees. The Company measures compensation cost for equity awards at their grant-date fair value and recognize compensation expense over the requisite service period, which is generally the vesting period, on a straight-line basis. The grant date fair value of stock options is estimated using the Black-Scholes option pricing model, which requires management to make assumptions with respect to the fair value of the common stock on the grant date, including the expected term of the award, the expected volatility of the stock, calculated based on a period of time generally commensurate with the expected term of the award, risk-free interest rates and expected dividend yields of the stock. Historically, for periods prior to the IPO, the fair value of the shares of common stock and common units underlying our stock-based awards were determined on each grant date by the board of directors based on valuation estimates from management considering our most recently available independent third-party valuation of the common stock. The board of directors also assessed and considered, with input from management, additional objective and subjective factors that it believed were relevant and which may have changed from the date of the most recent valuation through the grant date. The grant date fair value of RSUs is estimated based on the fair value of the underlying common stock. For performance-based stock awards, The Company recognizes stock-based compensation expense over the requisite service period using the accelerated attribution method when achievement is probable. The Company classifies stock-based compensation expense in its consolidated statement of operations in the same manner in which the award recipient’s salary and related costs are classified or in which the award recipient’s service payments are classified.

The Company uses the simplified method prescribed by Securities and Exchange Commission Staff Accounting Bulletin No. 107, Share-Based Payment, to calculate the expected term of options granted to employees, non-employees and directors. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods approximately equal to the expected term of the award. Expected dividend yield is based on the fact that the Company has never paid cash dividends and does not expect to pay any cash dividends in the foreseeable future.

Income taxes

Income taxes are recorded in accordance with FASB ASC Topic 740, Income Taxes (ASC 740), which provides for deferred taxes using an asset and liability approach. The Company recognizes deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the financial statements or tax returns. Deferred tax assets and liabilities are determined based on the difference between the financial statement and tax basis 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 makes estimates and judgments about future taxable income based on assumptions that are consistent with the Company’s plans and estimates. Should the actual amounts differ from these estimates, the amount of the Company’s valuation allowance could be materially impacted. Changes in these estimates may result in significant increases or decreases to the tax provision in a period in which such estimates are changed, which in turn would affect net income or loss.

The Company accounts for uncertain tax positions in accordance with the provisions of ASC 740. When uncertain tax positions exist, the Company recognizes the tax benefit to the extent that the position is more likely than not to be sustained on examination by the taxing authorities based on the technical merits of the position as well as consideration of the available facts and circumstances. The Company records interest and penalties related to uncertain tax positions, if applicable, as a component of income tax expense.

Comprehensive loss

Comprehensive loss includes net loss as well as other changes in stockholders’ equity (deficit) that result from transactions and economic events other than those with stockholders. For the year ended December 31, 2020, other comprehensive (loss) income included unrealized gains and losses on investments. The Company did not have any other comprehensive (loss) income for the year ended December 31, 2021.

Net loss per share

The Company follows the two-class method when computing net loss per share attributable to common stockholders as the Company has issued shares that meet the definition of participating securities. The two-class method determines net loss per share for each class of common and participating securities according to dividends declared or accumulated and participation rights in undistributed earnings. The two-class method requires losses for the period to be allocated between common and participating securities based upon their respective rights to share in the earnings as if all losses for the period had been distributed. During periods of loss, there is no allocation required under the two-class method since the participating securities do not have a contractual obligation to fund the losses of the Company.

Basic net loss per share attributable to common stockholders is computed by dividing the net loss attributable to common stockholders by the weighted average number of common shares outstanding for the period, which excludes shares of restricted common stock that are not vested. Diluted net loss per share attributable to common stockholders is computed by dividing the net loss attributable to common stockholders by the weighted average number of common shares outstanding for the period, including the effect of potentially dilutive common shares. For purpose of this calculation, outstanding options to purchase shares of common stock, unvested shares of restricted common stock and shares of redeemable convertible preferred stock are considered potentially dilutive common shares. The Company has generated a net loss in all periods presented so the basic and diluted net loss per share attributable to common stockholders are the same, as the inclusion of the potentially dilutive securities would be anti-dilutive.

Emerging growth company status

The Company is an “emerging growth company”, or EGC, as defined in the Jumpstart Our Business Startups Act (JOBS Act), and may take advantage of certain exemptions from various reporting requirements that are applicable to other public companies that are not EGCs. The Company may take advantage of these exemptions until it is no longer an EGC under Section 107 of the JOBS Act, which provides that an EGC can take advantage of the extended transition period afforded by the JOBS Act for the implementation of new or revised accounting standards. The Company has elected to use the extended transition period for complying with new or revised accounting standards, and as a result of this election, the consolidated financial statements may not be comparable to companies that comply with public company FASB standards’ effective dates. The Company may take advantage of these exemptions up until the last day of the fiscal year following the fifth anniversary of an offering or such earlier time that it is no longer an EGC.

Recent accounting pronouncements

Recently issued accounting pronouncements not yet adopted

From time to time, new accounting pronouncements are issued by the FASB or other standard setting bodies and adopted by the Company as of the specified effective date. Unless otherwise discussed, the Company believes that the impact of recently issued standards that are not yet effective will not have a material impact on its financial position or results of operations upon adoption.

In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments - Credit Losses: Measurement of Credit Losses on Financial Instruments. The new standard amends the current financial instrument impairment model by requiring entities to use a forward-looking approach based on expected losses to estimate credit losses on certain types of financial instruments, including trade receivables. The new standard will be effective for the Company on January 1, 2023. The adoption of this standard is not expected to have a material impact on the Company’s financial position or results of operations.

In December 2019, the FASB issued ASU No. 2019-12 Income Taxes (Topic 740)-Simplifying the Accounting for Income Taxes (ASU 2019-12), as part of its initiative to reduce complexity in the accounting standards. The amendments in ASU 2019-12 eliminates certain exceptions related to the approach for intraperiod tax allocation, the methodology for calculating income taxes in an interim period and the recognition of deferred tax liabilities for outside basis differences. ASU 2019-12 also clarifies and simplifies other aspects of the accounting for income taxes. ASU 2019-12 is effective for the Company on January 1, 2022. The Company is currently evaluating the potential impact that this standard may have on its financial position and results of operations.

Fair Value Measurements - Assets Measured at Fair Value on a Recurring Basis (Details) - Recurring Basis - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Assets:
Assets	$ 67,603	$ 81,601
Money Market Funds
Assets:
Cash equivalents	67,603	81,601
Not Subject to Netting
Assets:
Assets	67,603	81,601
Not Subject to Netting \| Money Market Funds
Assets:
Cash equivalents	$ 67,603	$ 81,601

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS (Unaudited) (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Income Statement [Abstract]
Unrealized loss on investments, tax	$ 0	$ 0

Accrued Expenses (Tables)

12 Months Ended

Dec. 31, 2021

Payables And Accruals [Abstract]

Schedule of Accrued Expenses

Accrued expenses consisted of the following (in thousands):


	DECEMBER 31, 2021		DECEMBER 31, 2020
Accrued employee compensation	$	5,142	$	5,040
Accrued external research and development costs		2,420		1,475
Accrued professional services and consulting		1,523		902
Accrued facilities costs		190		846
Other expenditures		428		607
	$	9,703	$	8,870

Leases - Additional Information (Details)							12 Months Ended
Leases - Additional Information (Details)	Nov. 15, 2021 USD ($) Renewal	Jul. 01, 2021	Apr. 27, 2020 USD ($) ft²	Aug. 26, 2019	Mar. 22, 2019 USD ($) ft²	Mar. 05, 2019 USD ($) ft²	Dec. 31, 2021 USD ($) ft² Office	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Lessee Lease Description [Line Items]
Lease expiration year							2029
Number of location \| Office							2
Operating right-of-use assets obtained in exchange for operating lease liabilities							$ 1,034,000	$ 23,186,000
Sublease income							$ 1,850,000	861,000
500 Technology Square
Lessee Lease Description [Line Items]
Area of lease \| ft²							19,823
Lease, base rent per year							$ 1,500,000
Increase in annual rent percentage							2.50%
Lease commencement date							Dec. 28, 2016
Original lease expiration date							Dec. 31, 2021
Accelerated lease expiration date				Feb. 28, 2020
4 Hartwell Place
Lessee Lease Description [Line Items]
Area of lease \| ft²						18,707
Lease, base rent per year						$ 900,000
Increase in annual rent percentage						2.60%
Lease expiration month and year						2029-12
Lease commencement month and year						2019-07
Lessee, operating lease, existence of option to extend [true false]						true
Lessee, operating lease, option to extend							The Company has the option to extend the lease twice, each for a five-year period, on the same terms and conditions as the current lease, subject to a change in base rent based on market rates.
Lessee, operating lease, option to extend term						5 years
Tenant improvement allowance, received							$ 1,300,000
Increase in base rent	$ 100,000
Initial direct cost	0
Operating right-of-use assets obtained in exchange for operating lease liabilities	1,000,000.0
Sublease payments to be received annually	$ 1,000,000.0
Sublease income, increase in annual percentage	2.80%
Sublease commencement date	Nov. 15, 2021
Sublease income expiration date	Nov. 30, 2024
Lessee, operating sublease, existence of option to extend	true
Lessee, operating sublease, option to extend							Lonza has the option to extend the sublease term for five 12-month periods on the same terms and conditions as the current sublease, subject to an increase of 2.8% in the annual fixed rent charges.
Number of operating sublease renewal term \| Renewal	5
Lessee, operating sublease, option to extend term	12 months
Percentage of annual increase in fixed rent charges	2.80%
4 Hartwell Place \| Maximum
Lessee Lease Description [Line Items]
Tenant improvement allowance						$ 1,300,000
4 Hartwell Place \| Letter of Credit
Lessee Lease Description [Line Items]
Security deposit							$ 400,000	400,000
35 Cambridge Park Drive
Lessee Lease Description [Line Items]
Area of lease \| ft²					68,258
Lease, base rent per year					$ 4,900,000
Increase in annual rent percentage					3.00%
Lease commencement date					Mar. 26, 2019
Lease expiration month and year					2029-11
Lessee, operating lease, existence of option to extend [true false]					true
Lessee, operating lease, option to extend							The Company has the option to extend the lease for a 10-year period on the same terms and conditions as the current lease, subject to a change in base rent based on market rates.
Lessee, operating lease, option to extend term					10 years
Tenant improvement allowance					$ 12,300,000
Tenant improvement allowance, received								12,300,000
Construction oversight fee					2.00%
Area of space for sublease \| ft²			23,280
Sublease payments to be received annually			$ 1,300,000
Sublease income, increase in annual percentage			3.00%
Sublease commencement date			May 18, 2020
Sublease expiration month and year		2023-05	2022-05				2023-05
Lessee, operating sublease, existence of option to extend		true	true
Lessee, operating sublease, option to extend							The sublessee had the option to extend the sublease for a one-year period on the same terms and conditions as the current sublease, subject to a change in base rent based on the greater of (i) an increase of 3% of the annual rent owed by the sublessee in year two, and (ii) market rent for the subleased premises.
Lessee, operating sublease, option to extend term		1 year	1 year
35 Cambridge Park Drive \| Letter of Credit
Lessee Lease Description [Line Items]
Security deposit								$ 3,700,000	$ 3,700,000
Security deposit in connection with sublease			$ 300,000

Income Taxes

12 Months Ended

Dec. 31, 2021

Income Tax Disclosure [Abstract]

Income Taxes

19. Income taxes

During the years ended December 31, 2021 and 2020, the Company recorded no income tax benefits for the net operating losses incurred and research and development tax credits earned in each year or interim period due to its uncertainty of realizing a benefit from those items.

The reconciliation of the US statutory income tax rate to the Company’s effective tax rate for the years ended December 31, 2021 and 2020 is as follows:


	YEAR ENDED DECEMBER 31,
	2021			2020
Federal statutory income tax rate		21.0	%		21.0	%
State taxes, net of federal benefit		8.5			7.4
Federal and state research and development credits		5.9			2.7
Executive Compensation		(0.7	)		(0.3	)
Non-deductible items		(0.1	)		(0.1	)
Stock Compensation		(1.5	)		(0.8	)
Change in valuation allowance		(33.2	)		(30.0	)
Other		0.1			0.1
Effective income tax rate		—	%		—	%

Deferred taxes are recognized for temporary differences between the basis of assets and liabilities for financial statement and income tax purposes. The significant components of the Company’s deferred tax assets and liabilities consisted of the following (in thousands):


	YEAR ENDED DECEMBER 31,
	2021			2020
Deferred tax assets:
Net operating loss carryforwards	$	51,672		$	37,609
Capitalized license and research and development payments		7,786			8,393
Research and development credits		15,062			11,910
Deferred revenue		11,919			17,117
Lease Liabilities		10,105			10,519
Accrued bonus		1,085			1,053
Stock compensation		4,344			3,335
Other temporary differences		289			349
Total deferred tax assets		102,262			90,285
Valuation allowance		(93,091	)		(80,758	)
Deferred tax assets		9,171			9,527
Deferred tax liabilities:
Right of use asset		(5,996	)		(6,007	)
Depreciation		(3,175	)		(3,520	)
Net deferred taxes	$	—		$	—

As of December 31, 2021, the Company had federal and state net operating loss carryforwards of $189.4 million and $188.7 million, respectively, which may be available to offset future taxable income. The Company has generated federal net operating losses of $152.9 million which have an indefinite carryforward period. The remaining $36.4 million of federal net operating loss carryforwards and the Company’s state net operating loss carryforwards would begin to expire in 2035. As of December 31, 2021, the Company had federal and state research and development credit carryforwards of $10.5 million and $5.0 million, respectively, which may be available to offset future income tax liabilities and which would begin to expire in 2035 and 2031, respectively. The federal and state income tax returns are generally subject to tax examinations for the tax years ending December 31, 2018 through 2021. To the extent the Company has tax attribute carryforwards, the tax years in which the attribute was generated may still be adjusted upon examination by the Internal Revenue Service, state or foreign tax authorities to the extent utilized in a future period.

The Company has evaluated the positive and negative evidence bearing upon its ability to realize the deferred tax assets. Management has considered the Company’s cumulative net losses and its lack of commercialization of any products or generation of any revenue from product sales since inception and has concluded that it is more likely than not that the Company will not realize the benefits of the deferred tax assets. Accordingly, a full valuation allowance has been established against the net deferred tax assets as of December 31, 2021 and 2020. Management reevaluates the positive and negative evidence at each reporting period. Changes in the valuation allowance for deferred tax assets during the years ended December 31, 2021 and 2020 were primarily due to the increases in net operating loss and tax credit carryforwards and totaled $12.3 million and $27.5 million, respectively.

The Company has not recorded any amounts for unrecognized tax benefits as of December 31, 2021 or 2020.

The Company does not have any uncertain tax positions. The Company has not conducted a study of its research and development credit carryforwards. This study may result in an adjustment to research and development credit carryforwards; however, until a study is completed and any adjustment is known, no amounts are being presented as an uncertain tax position. A full valuation allowance has been provided against the Company’s research and development credits and, if an adjustment is required, this adjustment would be offset by an adjustment to the valuation allowance. Thus, there would be no impact to the consolidated balance sheet or statement of operations if an adjustment were required.

The Company files tax returns as prescribed by the tax laws of the jurisdictions in which it operates. Net operating losses are subject to review and possible adjustment by the Internal Revenue Service and state tax authorities. Net operating loss carryforwards may become subject to an annual limitation in the event of certain cumulative changes in the ownership interest of significant shareholders over a three-year period in excess of 50%, as defined under Sections 382 and 383 of the Internal Revenue Code, respectively, as well as similar state provisions. This could limit the amount of tax attributes that can be utilized annually to offset future taxable income or tax liabilities. The amount of the annual limitation is determined based on the value of the company immediately prior to the ownership change. Subsequent ownership changes may further affect the limitation in future years. The Company has not yet conducted a study to determine if any such changes have occurred that could limit its ability to use the net operating losses and tax credit carryforwards.

It is the Company’s policy to include penalties and interest expense related to income taxes as a component of income tax expense, as necessary. As of December 31, 2021 or 2020, the Company had no accrued interest or penalties related to uncertain tax positions and no amounts have been recognized in the Company’s consolidated statements of operations and comprehensive loss.

- Definition

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

+ References

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

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

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

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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+ Details

Collaborative Arrangements

12 Months Ended

Dec. 31, 2021

Collaboration Agreements [Abstract]

Collaborative Arrangements

15. Collaboration agreements

The following table summarizes the total consolidated net revenue from the strategic collaborators for the periods presented (in thousands):


	YEAR ENDED DECEMBER 31,
Collaboration Revenue by Strategic Collaborator:	2021		2020
Jazz	$	11,322	$	641
Sarepta		11,613		2,274
Total collaboration revenue	$	22,935	$	2,915

The following tables present changes in the Company’s contract assets and liabilities for the year ended December 31, 2021 (in thousands):


	YEAR ENDED DECEMBER 31, 2021
	BALANCE BEGINNING OF PERIOD		ADDITIONS		DEDUCTIONS			BALANCE END OF PERIOD
Contract assets:
Account receivable (1)	$	—	$	3,914	$	(3,286	)	$	628
Contract liabilities: