0000950170-22-021603 | 10-Q | XBRL Viewer

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Cover Page - shares	9 Months Ended
Cover Page - shares	Sep. 30, 2022	Oct. 31, 2022
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Quarterly Report	true
Document Transition Report	false
Document Period End Date	Sep. 30, 2022
Document Fiscal Year Focus	2022
Document Fiscal Period Focus	Q3
Entity Registrant Name	Magenta Therapeutics, Inc.
Trading Symbol	MGTA
Entity Central Index Key	0001690585
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Filer Category	Non-accelerated Filer
Entity Ex Transition Period	false
Entity Emerging Growth Company	true
Entity Small Business	true
Entity Shell Company	false
Entity Tax Identification Number	81-0724163
Title of 12(b) Security	Common Stock
Entity Interactive Data Current	Yes
Security Exchange Name	NASDAQ
Entity Incorporation, State or Country Code	DE
Entity Address, Address Line One	100 Technology Square
Entity Address, City or Town	Cambridge
Entity Address, Postal Zip Code	02139
Entity Address, State or Province	MA
Entity File Number	001-38541
City Area Code	857
Local Phone Number	242-0170
Entity Common Stock, Shares Outstanding		60,555,520

Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Current assets:
Cash and cash equivalents	$ 59,028	$ 131,650
Marketable securities	69,256	45,276
Prepaid expenses and other current assets	3,813	3,767
Total current assets	132,097	180,693
Restricted cash	1,780	1,780
Operating lease, right-of-use asset	23,930	0
Property and equipment, net	6,316	7,461
Total assets	164,123	189,934
Current liabilities:
Accounts payable	2,578	3,040
Accrued expenses and other current liabilities	6,722	7,823
Operating lease liability, current portion	3,621	0
Total current liabilities	12,921	10,863
Operating lease liability, net of current portion	27,177	0
Deferred rent	0	6,399
Total liabilities	40,098	17,262
Commitments and contingencies (Note 7)
Stockholders' Equity:
Preferred stock, $0.001 par value; 10,000,000 shares authorized; no shares issued or outstanding	0	0
Common stock, $0.001 par value; 150,000,000 shares authorized; 60,555,520 and 58,799,157 shares issued and outstanding as of September 30, 2022 and December 31, 2021, respectively	61	59
Additional paid-in capital	506,277	498,210
Accumulated other comprehensive loss	(462)	(30)
Accumulated deficit	(381,851)	(325,567)
Total stockholders' equity	124,025	172,672
Total liabilities and stockholders' equity	$ 164,123	$ 189,934

Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2022	Dec. 31, 2021
Preferred stock, par value	$ 0.001	$ 0.001
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	$ 0.001	$ 0.001
Common stock, shares authorized	150,000,000	150,000,000
Common stock, Shares issued	60,555,520	58,799,157
Common stock, Shares outstanding	60,555,520	58,799,157

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Operating expenses:
Research and development	$ 11,201	$ 10,795	$ 39,351	$ 33,652
General and administrative	6,052	7,450	19,819	20,900
Total operating expenses	17,253	18,245	59,170	54,552
Loss from operations	(17,253)	(18,245)	(59,170)	(54,552)
Interest and other income, net	1,190	818	2,886	2,708
Net loss	$ (16,063)	$ (17,427)	$ (56,284)	$ (51,844)
Net loss per share, basic	$ (0.27)	$ (0.30)	$ (0.95)	$ (0.97)
Net loss per share, diluted	$ (0.27)	$ (0.30)	$ (0.95)	$ (0.97)
Weighted average common shares outstanding, basic	59,269,965	58,583,476	58,963,280	53,655,314
Weighted average common shares outstanding, diluted	59,269,965	58,583,476	58,963,280	53,655,314
Comprehensive loss:
Net loss	$ (16,063)	$ (17,427)	$ (56,284)	$ (51,844)
Other comprehensive income (loss):
Unrealized gains (losses) on marketable securities	140	(1)	(432)	24
Total other comprehensive income (loss)	140	(1)	(432)	24
Total comprehensive loss	$ (15,923)	$ (17,428)	$ (56,716)	$ (51,820)

Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Accumulated Deficit [Member]
Beginning balance at Dec. 31, 2020	$ 143,906	$ 49	$ 398,311	$ (23)	$ (254,431)
Beginning balance, shares at Dec. 31, 2020		48,533,135
Issuance of common stock upon private investment, net of offering costs	86,097	$ 10	86,087
Issuance of common stock upon private investment, net of offering costs, shares		9,599,998
Vesting of restricted stock, shares		218,464
Issuance of common stock upon exercise of stock options	3,294		3,294
Issuance of common stock upon exercise of stock options, shares		411,685
Issuance of common stock under Employee Stock Purchase Plan	86		86
Issuance of common stock under Employee Stock Purchase Plan, shares		13,989
Stock-based compensation expense	8,125		8,125
Unrealized gains (losses) on marketable securities	24			24
Net loss	(51,844)				(51,844)
Ending balance at Sep. 30, 2021	189,688	$ 59	495,903	1	(306,275)
Ending balance, shares at Sep. 30, 2021		58,777,271
Beginning balance at Dec. 31, 2020	143,906	$ 49	398,311	(23)	(254,431)
Beginning balance, shares at Dec. 31, 2020		48,533,135
Net loss	(71,100)
Ending balance at Dec. 31, 2021	172,672	$ 59	498,210	(30)	(325,567)
Ending balance, shares at Dec. 31, 2021		58,799,157
Beginning balance at Jun. 30, 2021	202,892	$ 59	491,679	2	(288,848)
Beginning balance, shares at Jun. 30, 2021		58,508,735
Vesting of restricted stock, shares		209,998
Issuance of common stock upon exercise of stock options	425		425
Issuance of common stock upon exercise of stock options, shares		58,538
Stock-based compensation expense	3,799		3,799
Unrealized gains (losses) on marketable securities	(1)			(1)
Net loss	(17,427)				(17,427)
Ending balance at Sep. 30, 2021	189,688	$ 59	495,903	1	(306,275)
Ending balance, shares at Sep. 30, 2021		58,777,271
Beginning balance at Dec. 31, 2021	172,672	$ 59	498,210	(30)	(325,567)
Beginning balance, shares at Dec. 31, 2021		58,799,157
Issuance of common stock	2,763	$ 2	2,761
Issuance of common stock, shares		1,644,200
Vesting of restricted stock, shares		62,459
Issuance of common stock under Employee Stock Purchase Plan	49		49
Issuance of common stock under Employee Stock Purchase Plan, shares		49,704
Stock-based compensation expense	5,257		5,257
Unrealized gains (losses) on marketable securities	(432)			(432)
Net loss	(56,284)				(56,284)
Ending balance at Sep. 30, 2022	124,025	$ 61	506,277	(462)	(381,851)
Ending balance, shares at Sep. 30, 2022		60,555,520
Beginning balance at Jun. 30, 2022	135,678	$ 59	502,009	(602)	(365,788)
Beginning balance, shares at Jun. 30, 2022		58,848,861
Issuance of common stock	2,763	$ 2	2,761
Issuance of common stock, shares		1,644,200
Vesting of restricted stock, shares		62,459
Stock-based compensation expense	1,507		1,507
Unrealized gains (losses) on marketable securities	140			140
Net loss	(16,063)				(16,063)
Ending balance at Sep. 30, 2022	$ 124,025	$ 61	$ 506,277	$ (462)	$ (381,851)
Ending balance, shares at Sep. 30, 2022		60,555,520

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021
Cash flows from operating activities:
Net loss	$ (56,284)	$ (51,844)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	5,257	8,125
Depreciation and amortization expense	1,459	1,485
Loss on disposal of property and equipment	0	95
Noncash lease expense	2,158	0
Net amortization of premiums on marketable securities	306	630
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(46)	(1,167)
Accounts payable	(462)	(1,874)
Accrued expenses and other current liabilities	(546)	591
Operating lease liabilities	(2,244)	0
Deferred rent	0	118
Net cash used in operating activities	(50,402)	(43,841)
Cash flows from investing activities:
Purchases of property and equipment	(314)	(1,249)
Purchases of marketable securities	(59,718)	0
Maturities of marketable securities	35,000	55,000
Net cash provided by (used in) investing activities	(25,032)	53,751
Cash flows from financing activities:
Proceeds from private investment	0	86,400
Proceeds from issuance of common stock under the ATM Program, net of commissions	2,904	0
Payments of offering costs	(141)	(303)
Proceeds from exercise of common stock options	0	3,294
Proceeds from issuance of common stock under Employee Stock Purchase Plan	49	86
Net cash provided by financing activities	2,812	89,477
Net increase (decrease) in cash, cash equivalents and restricted cash	(72,622)	99,387
Cash, cash equivalents and restricted cash at beginning of period	133,430	59,932
Cash, cash equivalents and restricted cash at end of period	$ 60,808	$ 159,319

Nature of the Business and Basis of Presentation

9 Months Ended

Sep. 30, 2022

Nature of the Business and Basis of Presentation

1. Nature of the Business and Basis of Presentation

Magenta Therapeutics, Inc. (the “Company”) is a clinical-stage biotechnology company developing novel medicines designed to bring the curative power of stem cell transplant to more patients with blood cancers, genetic diseases and autoimmune diseases. The Company was incorporated under the laws of the State of Delaware in June 2015 as HSCTCo Therapeutics, Inc. In February 2016, the Company changed its name to Magenta Therapeutics, Inc. and in June 2018 the Company completed an initial public offering of its common stock.

The Company is subject to risks and uncertainties common to early-stage companies in the biotechnology industry, including, but not limited to, development by competitors of new technological innovations, dependence on key personnel, protection of proprietary technology, compliance with government regulations, the continuing impact of the ongoing coronavirus (“COVID-19”) pandemic and the ability to secure additional capital to fund operations. Product candidates currently under development will require significant additional research and development efforts, including extensive preclinical and clinical testing and regulatory approval prior to commercialization. These efforts require significant amounts of additional capital, adequate personnel and infrastructure and extensive compliance-reporting capabilities. Even if the Company’s development efforts are successful, it is uncertain when, if ever, the Company will realize significant revenue from product sales.

The Company has a shelf registration statement on Form S-3 (the “Shelf”) on file with the SEC, which covers the offering, issuance and sale of up to an aggregate of $250.0 million of common stock, preferred stock, debt securities, warrants and/or units of any combination thereof. The Company also entered into a sales agreement, as amended, with Cowen and Company, LLC, as sales agent to provide for the issuance and sale by the Company of up to $50.0 million of common stock from time to time in “at-the-market” offerings under the Shelf (the “ATM Program”). The Shelf was declared effective by the SEC on August 12, 2022. During the nine months ended September 30, 2022, the Company sold 1,644,200 shares of its common stock under the ATM program at a weighted average price per share of $1.82 resulting in net proceeds of $2.8 million after commissions and offering costs. As of September 30, 2022, $247.0 million remained available under the Shelf, including up to $47.0 million available for sale under the ATM Program.

The Company has incurred recurring losses since inception, including net losses of $56.3 million for the nine months ended September 30, 2022 and $71.1 million the year ended December 31, 2021. As of September 30, 2022, the Company had an accumulated deficit of $381.9 million. The Company expects to continue to generate operating losses for the foreseeable future. The Company expects that its cash, cash equivalents and marketable securities will be sufficient to fund its operating expenses and capital expenditure requirements through at least 12 months from the issuance date of these consolidated financial statements. The future viability of the Company beyond that point is dependent on its ability to raise additional capital to fund its operations.

The Company will need to obtain substantial additional funding in connection with continuing operations, particularly as the Company advances its preclinical activities and clinical trials for its product candidates in development. If the Company is unable to raise capital when needed, or on attractive terms, it could be forced to delay, reduce or eliminate its research or drug development programs or any future commercialization efforts. Although management continues to pursue these plans, there is no assurance that the Company will be successful in obtaining sufficient funding on terms acceptable to the Company to fund continuing operations, if at all.

The consolidated financial statements include the accounts of the Company and its wholly owned subsidiary. All intercompany balances and transactions have been eliminated. The consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”). Any reference in these notes to applicable guidance is meant to refer to the authoritative GAAP as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Update (“ASU”) of the Financial Accounting Standards Board (“FASB”).

Summary of Significant Accounting Policies

9 Months Ended

Sep. 30, 2022

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

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, the disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of expenses during the reporting periods. Significant estimates and assumptions reflected in these

financial statements include, but are not limited to, the accrual for research and development expenses and the valuation of stock-based awards. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Changes in estimates are recorded in the period in which they become known. Actual results could differ from those estimates.

Unaudited Interim Financial Information

The consolidated balance sheet at December 31, 2021 was derived from audited financial statements but does not include all disclosures required by GAAP. The accompanying unaudited consolidated financial statements as of September 30, 2022 and for the three and nine months ended September 30, 2022 and 2021 have been prepared by the Company pursuant to the rules and regulations of the SEC for interim financial statements. Certain information and footnote disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations. The Company believes, however, that the disclosures are adequate to make the information presented not misleading. These consolidated financial statements should be read in conjunction with the Company’s audited financial statements for the year ended December 31, 2021 included in the Company’s Annual Report on Form 10-K, on file with SEC. In the opinion of management, all adjustments, consisting only of normal recurring adjustments necessary for a fair statement of the Company’s consolidated financial position as of September 30, 2022 and consolidated results of operations for the three and nine months ended September 30, 2022 and 2021 and consolidated cash flows for the nine months ended September 30, 2022 and 2021 have been made. The results of operations for the nine months ended September 30, 2022 are not necessarily indicative of the results of operations that may be expected for the year ending December 31, 2022 or any other interim period.

Fair Value Measurements

Certain assets and liabilities are carried at fair value under GAAP. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. Financial assets and liabilities carried at fair value are to be classified and disclosed in one of the following three levels of the fair value hierarchy, of which the first two are considered observable and the last is considered unobservable:

•

Level 1—Quoted prices in active markets for identical assets or liabilities.

•

Level 2—Observable inputs (other than Level 1 quoted prices), such as quoted prices in active markets for similar assets or liabilities, quoted prices in markets that are not active for identical or similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data.

•

Level 3—Unobservable inputs that are supported by little or no market activity and that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques.

The Company’s cash equivalents and marketable securities are carried at fair value, determined according to the fair value hierarchy described above (see Note 3). The carrying values of the Company’s accounts payable and accrued expenses approximate their fair values due to the short-term nature of these assets and liabilities.

Income Taxes

The Company accounts for income taxes using the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been recognized in the consolidated financial statements or in the Company’s tax returns. Deferred taxes are determined based on the difference between the financial statement and tax basis of assets and liabilities using enacted tax rates in effect in the years in which the differences are expected to reverse. Changes in deferred tax assets and liabilities are recorded in the provision for income taxes. The Company assesses the likelihood that its deferred tax assets will be recovered from future taxable income and, to the extent it believes, based upon the weight of available evidence, that it is more likely than not that all or a portion of deferred tax assets will not be realized, a valuation allowance is established through a charge to income tax expense. Potential for recovery of deferred tax assets is evaluated by estimating the future taxable profits expected and considering prudent and feasible tax planning strategies.

The Company accounts for uncertainty in income taxes recognized in its consolidated financial statements by applying a two-step process to determine the amount of tax benefit to be recognized. First, the tax position must be evaluated to determine the likelihood that it will be sustained upon external examination by the taxing authorities. If the tax position is deemed more-likely-than-not to be sustained, the tax position is then assessed to determine the amount of benefit to recognize in the consolidated financial statements. The amount of the benefit that may be recognized is the largest amount that has a greater than 50% likelihood of being realized upon ultimate settlement. The provision for income taxes includes the effects of any resulting tax reserves, or unrecognized tax benefits, that are considered appropriate as well as the related net interest and penalties.

Leases

Prior to January 1, 2022, the Company accounted for leases under ASC 840, Leases (“ASC 840”). Effective January 1, 2022, the Company accounts for leases under ASC 842, Leases (“ASC 842”). Therefore, as of December 31, 2021 and for the three and nine months ended September 30, 2021, the Company’s consolidated financial statements continue to be presented in accordance with ASC 840, the accounting standard originally in effect for such periods. As of and for the three and nine months ended September 30, 2022, the Company’s consolidated financial statements are presented in accordance with ASC 842.

In accordance with ASC 842, the Company accounts for a contract as a lease when it has the right to control the asset for a period of time while obtaining substantially all of the asset’s economic benefits. The Company determines if an arrangement is a lease or contains an embedded lease at inception. For arrangements that meet the definition of a lease, the Company determines the initial classification and measurement of its right-of-use asset and lease liability at the lease commencement date and thereafter if modified. The lease term includes any renewal options that the Company is reasonably assured to exercise. The present value of lease payments is determined by using the interest rate implicit in the lease, if that rate is readily determinable; otherwise, the Company uses its estimated secured incremental borrowing rate for that lease term. The Company’s policy is to not record leases with an original term of twelve months or less on its consolidated balance sheets and recognizes those lease payments in the income statement on a straight-line basis over the lease term. The Company’s existing leases are for office and laboratory space.

In addition to rent, the leases may require the Company to pay additional costs, such as utilities, maintenance and other operating costs, which are generally referred to as non-lease components. The Company has elected to not separate lease and non-lease components. Only the fixed costs for lease components and their associated non-lease components are accounted for as a single lease component and recognized as part of a right-of-use asset and lease liability. Rent expense for operating leases is recognized on a straight-line basis over the reasonably assured lease term based on the total lease payments and is included in operating expense in the consolidated statements of operations and comprehensive loss.

Comprehensive Loss

Comprehensive loss includes net loss as well as other changes in stockholders’ equity that result from transactions and economic events other than those with stockholders. For the three and nine months ended September 30, 2022 and 2021, the Company’s only element of other comprehensive income (loss) was unrealized gains (losses) on marketable securities.

Net Loss per Share

Basic net income (loss) per share is computed by dividing the net income (loss) by the weighted average number of shares of common stock outstanding for the period. Diluted net income (loss) per share is computed by dividing net income (loss) by the weighted average number of common shares outstanding for the period, including potential dilutive common shares assuming the dilutive effect of outstanding stock options. For periods in which the Company has reported net losses, diluted net loss per common share is the same as basic net loss per common share, since dilutive common shares are not assumed to have been issued if their effect is anti-dilutive.

The Company reported a net loss for the three and nine months ended September 30, 2022 and 2021. The following potential dilutive securities, presented based on amounts outstanding at each period end, have been excluded from the calculation of diluted net loss per share because including them would have had an anti-dilutive impact:


	As of September 30,
	2022		2021
Stock options to purchase common stock		8,601,539		6,091,220
Unvested restricted common stock units		416,967		497,418
Shares of common stock issuable under Employee Stock Purchase Plan		76,086		8,843
		9,094,592		6,597,481

Recently Issued Accounting Pronouncements

In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments – Credit Losses (Topic 326). The new standard adjusts the accounting for assets held at amortized costs basis, including marketable securities accounted for as available for sale. The standard eliminates the probable initial recognition threshold and requires an entity to reflect its current estimate of all expected credit losses. The allowance for credit losses is a valuation account that is deducted from the amortized cost basis of the financial assets to present the net amount expected to be collected. For public entities, the guidance was effective for annual reporting periods beginning after December 15, 2019 and for interim periods within those fiscal years. For nonpublic entities and emerging growth companies that choose to take advantage of the extended transition period, the guidance is effective for annual reporting periods beginning after December 15, 2020. Early adoption is permitted for all entities. In November 2019, the FASB issued ASU No. 2019-10, which deferred the effective date for nonpublic entities to annual reporting periods beginning after December 15, 2022, including interim periods within those fiscal years. The Company does not believe the guidance will have a material impact on its consolidated financial statements.

Recently Adopted Accounting Pronouncements

In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) (“ASU 2016-02”), which require lessees to recognize most leases on their balance sheet as a right-of-use asset and a lease liability. In general, lease arrangements exceeding a twelve-month term must be recognized as assets and liabilities on the balance sheet. Under ASU 2016-02, a right-of-use asset and lease obligation is recorded for all leases, whether operating or financing, while the income statement reflects lease expense for operating leases and amortization and interest expense for financing leases. The FASB also issued ASU 2018-10, Codification Improvements to Topic 842 Leases, and ASU 2018-11, Targeted Improvements to Topic 842 Leases, which allows the new lease standard to be applied as of the adoption date with a cumulative-effect adjustment to the opening balance of retained earnings rather than retroactive restatement of all periods presented. The Company adopted the new leasing standards on January 1, 2022 using a modified retrospective approach applied at the beginning of the period of adoption.

The Company elected the “package of practical expedients,” which permits the Company not to reassess under the new standards for prior conclusions about lease identification, lease classification and initial direct costs. The Company did not apply the hindsight practical expedient when determining the lease term for existing leases and assessing impairment of expired or existing leases. The Company elected to utilize its incremental borrowing rate based on the remaining lease term as of the date of adoption. In connection with the adoption of ASU 2016-02, the Company recognized a right-of-use asset of $26.1 million and lease liabilities of $33.0 million on its consolidated balance sheet. The deferred rent balance of $7.0 million as of January 1, 2022 was recorded as an offset to the Company’s right-of-use asset. The adoption of the standard did not have a material impact on the Company’s results of operations or cash flows.

Fair Value of Financial Assets

9 Months Ended

Sep. 30, 2022

Fair Value of Financial Assets

3. Fair Value of Financial Assets

As of September 30, 2022, marketable securities by security type consisted of (in thousands):


			Gross		Gross			Estimated
	Amortized		Unrealized		Unrealized			Fair
	Cost		Gains		Losses			Value
U.S. treasury notes (due within one year)	$	69,718	$	—	$	(462	)	$	69,256
Total	$	69,718	$	—	$	(462	)	$	69,256

As of December 31, 2021, marketable securities by security type consisted of (in thousands):


			Gross		Gross			Estimated
	Amortized		Unrealized		Unrealized			Fair
	Cost		Gains		Losses			Value
U.S. treasury notes (due within one year)	$	30,213	$	—	$	(20	)	$	30,193
U.S. treasury notes (due after one year through two years)		15,093		—		(10	)		15,083
Total	$	45,306	$	—	$	(30	)	$	45,276

The following tables present information about the Company’s financial assets measured at fair value on a recurring basis and indicate the level of the fair value hierarchy utilized to determine such fair values (in thousands):


	Fair Value Measurements at September 30, 2022 Using:
	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	58,026	$	—	$	—	$	58,026
Marketable securities:
U.S. treasury notes		—		69,256		—		69,256
Total	$	58,026	$	69,256	$	—	$	127,282


	Fair Value Measurements at December 31, 2021 Using:
	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	131,542	$	—	$	—	$	131,542
Marketable securities:
U.S. treasury notes		—		45,276		—		45,276
Total	$	131,542	$	45,276	$	—	$	176,818

Accrued Expenses and Other Current Liabilities

9 Months Ended

Sep. 30, 2022

Accrued Expenses and Other Current Liabilities

4. Accrued Expenses and Other Current Liabilities

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



	September 30, 2022		December 31, 2021
Accrued payroll and related expenses	$	3,284	$	3,346
Accrued external research and development expenses		2,617		2,813
Deferred rent, current portion		—		555
Accrued other		821		1,109
	$	6,722	$	7,823

Stock-Based Awards

9 Months Ended

Sep. 30, 2022

Stock-Based Awards

5. Stock-Based Awards

2018 Stock Option and Incentive Plan

The Company grants stock-based awards under the Magenta Therapeutics, Inc. 2018 Stock Option and Incentive Plan (the “2018 Plan”). The Company also has outstanding stock options under the Magenta Therapeutics, Inc. 2016 Stock Option and Grant Plan, as amended (the “2016 Plan”), but is no longer granting awards under the 2016 Plan. As of September 30, 2022, 3,000,865 shares of common stock were available for issuance under the 2018 Plan.

Grant of Stock Options

During the nine months ended September 30, 2022, the Company granted options to certain employees, directors and consultants with service-based vesting conditions for the purchase of 4,357,798 shares of common stock with a weighted average grant date fair value of $1.51 per share. Stock-based compensation expense is being recognized over the requisite service period of 18 months to four years.

Grant of Restricted Stock Units

During the nine months ended September 30, 2022, the Company granted 160,558 restricted stock units to certain employees with a weighted average grant date fair value of $2.01 per share. Stock-based compensation expense is being recognized over the requisite service period of 18 months to four years.

2019 Employee Stock Purchase Plan

Employees may elect to participate in The Magenta Therapeutics, Inc. 2019 Employee Stock Purchase Plan (the “ESPP”). The purchase price of common stock under the ESPP is equal to 85% of the lower of the fair market value of the common stock on the offering date or the exercise date. The six-month offering periods begin in December and June of each year. During the nine months ended September 30, 2022, 49,704 shares of common stock were purchased under the ESPP at a purchase price per share of $0.99. During the nine months ended September 30, 2021, 13,989 shares of common stock were purchased under the ESPP at a purchase price per share of $6.15. As of September 30, 2022, 663,548 shares remained available for issuance under the ESPP.

Stock-Based Compensation

Stock-based compensation expense was classified in the statements of operations and comprehensive loss as follows (in thousands):


	Three Months Ended September 30,				Nine Months Ended September 30,
	2022		2021		2022		2021
Research and development expenses	$	315	$	1,335	$	1,304	$	3,276
General and administrative expenses		1,192		2,464		3,953		4,849
	$	1,507	$	3,799	$	5,257	$	8,125

As of September 30, 2022, unrecognized compensation expense related to unvested share-based awards with service-based vesting conditions was $15.5 million, which is expected to be recognized over a weighted average period of 2.4 years. Additionally, the Company had unrecognized compensation cost of $1.7 million related to the unvested performance restricted stock units for which the performance conditions were not considered probable of achievement as of September 30, 2022.

Leases

9 Months Ended

Sep. 30, 2022

Leases [Abstract]

Leases

6. Leases

The Company has a sublease, as amended, for up to approximately 69,000 square feet of office and laboratory space in Cambridge, Massachusetts. The sublease is subject and subordinate to a prime lease between the sublandlord and the prime landlord. The term of the sublease commenced in June 2018 and expires in February 2028. The sublandlord has the right to terminate the sublease after five years. The Company classified this sublease as an operating lease under ASC 842. The Company is obligated to pay real estate taxes and other costs related to the premises, including costs of operations and management of the leased premises. To the extent these costs are variable, they were not included in the measurement of the right-of-use asset and lease liability. In

connection with the sublease, as amended, the sublandlord funded $5.2 million in tenant improvements to the leased facility during 2019. The Company is required to maintain a cash balance of $1.8 million to secure a letter of credit associated with the sublease. This amount was classified as noncurrent restricted cash in the consolidated balance sheets at September 30, 2022 and December 31, 2021.

As of December 31, 2021, the Company had long-term deferred rent of $6.4 million related to lease incentives and payment escalations. As of December 31, 2021, the short-term portion of deferred rent of $0.6 million was included in accrued expenses and other current liabilities. In connection with the adoption of ASC 842 on January 1, 2022, these amounts were recorded as a reduction to the operating lease, right-of-use asset.

The components of the Company’s lease expense under ASC 842 were as follows (in thousands):


	Three Months Ended		Nine Months Ended
	September 30, 2022		September 30, 2022
Operating lease cost	$	1,602	$	4,805
Short-term lease cost		—		—
Variable lease cost		441		951
	$	2,043	$	5,756

Supplemental disclosure of cash flow information related to the lease was as follows (in thousands):


	Three Months Ended		Nine Months Ended
	September 30, 2022		September 30, 2022
Cash paid for amounts included in the measurement of operating lease liabilities	$	1,674	$	4,891
Operating lease liabilities arising from obtaining right-of-use asset	$	—	$	—

The weighted average remaining lease term and discount rate were as follows:


	September 30, 2022
Weighted-average remaining lease term - operating lease (in years)		5.42
Weighted-average discount rate - operating lease		11.00	%

Because the interest rate implicit in the lease was not readily determinable, the Company’s estimated incremental borrowing rate was used to calculate the present value of the lease.

As of September 30, 2022, the future minimum lease payments due under the noncancelable operating lease was as follows (in thousands):


2022 (three months)	$	1,675
2023		6,936
2024		7,313
2025		7,679
2026		8,062
Thereafter		9,905
Total future minimum lease payments		41,570
Less: imputed interest		(10,772	)
Total operating lease liabilities	$	30,798

The following table represents the lease liabilities on the consolidated balance sheet (in thousands):


	September 30, 2022
Current operating lease liability	$	3,621
Operating lease liability, net of current portion		27,177
Total operating lease liabilities	$	30,798

As previously disclosed in the Company’s Annual Report on Form 10-K and under the previous lease accounting standard, ASC 840, Leases, the following table summarizes the future minimum lease payments due under the operating lease as of December 31, 2021 (in thousands):


2022	$	6,375
2023		6,734
2024		7,100
2025		7,455
2026		7,828
Thereafter		9,617
	$	45,109

Rent expense for the three and nine months ended September 30, 2021 was $1.5 million and $4.6 million, respectively.

In 2018, the Company entered into two sub-subleases of approximately 27,000 square feet of office space in Cambridge, Massachusetts. One of the sub-subleases, as amended, expired in December 2021. The remaining sub-sublease, as amended, was set to expire in April 2022 but was further amended in January 2022 to increase the square footage from 13,643 square feet to 26,114 square feet and to extend the expiration to April 2023. As of September 30, 2022, the remaining base rent payments due to the Company under the amended sub-sublease was $1.5 million. The Company recorded other income of $0.8 million during each of the three months ended September 30, 2022 and 2021, respectively, related to these sub-subleases. The Company recorded other income of $2.2 million and $2.7 million during the nine months ended September 30, 2022 and 2021, respectively, related to these sub-subleases.

Commitments and Contingencies

9 Months Ended

Sep. 30, 2022

Commitments and Contingencies

7. Commitments and Contingencies

Leases

The Company’s commitments under its leases are described in Note 6.

Collaboration Agreement

In March 2018, the Company entered into a collaboration agreement with Heidelberg Pharma Research GmbH (“HDPR”) whereby the parties agreed to combine the Company’s stem cell platform with proprietary antibodies across up to four exclusive targets with HDPR’s proprietary Antibody Targeted Amanitin Conjugates platform. Under the agreement, the Company may pay upfront technology access fees, research exclusivity fees and payment for research support. Additionally, upon the exercise of certain license rights, the Company may be obligated to pay HDPR development, regulatory and commercial milestone payments of up to $83.5 million per target as well as royalties on net sales of products licensed under the agreement. During the three months ended September 30, 2022, the Company did not incur any research and development expenses related to this agreement. During the three months ended September 30, 2021, the Company recorded less than $0.1 million of research and development expense related to this agreement for upfront technology access fees, research exclusivity fees and research support. During each of the nine months ended September 30, 2022 and 2021, the Company recorded $0.4 million of research and development expense related to this agreement for upfront technology access fees, research exclusivity fees and research support. During the nine months ended September 30, 2022, the Company recorded $2.0 million of research and development expense related to the achievement of a development milestone. During the three and nine months ended September 30, 2021, the Company did not incur any expense related to the achievement of these milestones.

Intellectual Property Licenses

The Company has a license agreement with the President and Fellows of Harvard College (“Harvard”), entered into in November 2016, for an exclusive, worldwide, royalty-bearing license for certain technologies related to conditioning and mobilization. The Company is obligated to pay Harvard maintenance fees of $0.1 million annually and to reimburse qualified expenses related to the patents. The Company is also obligated to pay milestone payments of up to $7.4 million for the first two licensed products upon the achievement of certain development and regulatory milestones and to pay royalties on a product-by-product and country-by-country basis on net sales of products licensed under the agreement. During the three months ended September 30, 2022 and 2021 and the nine months ended September 30, 2022, the Company did not incur any expense related to the achievement of these milestones. During the nine months ended September 30, 2021, the Company recorded $0.1 million of expense related to the achievement of one of these milestones.

The Company has agreements with third parties in the normal course of business, under which it can license certain developed technologies. If the Company exercises its rights to license the respective technologies, it may be subject to additional fees and milestone payments. During the nine months ended September 30, 2022, the Company recorded research and development expense of $0.1 million related to the license of certain developed technologies under these agreements. During the three months ended September 30, 2022 and 2021 and the nine months ended September 30, 2021, the Company did not incur any expense related to these licenses.

Indemnification Agreements

In the ordinary course of business, the Company may provide indemnification of varying scope and terms to vendors, lessors, business partners and other parties with respect to certain matters including, but not limited to, losses arising out of breach of such agreements or from intellectual property infringement claims made by third parties. In addition, the Company has entered into indemnification agreements with members of its board of directors and senior management that will require the Company, among other things, to indemnify them against certain liabilities that may arise by reason of their status or service as directors or officers. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is, in many cases, unlimited. To date, the Company has not incurred any material costs as a result of such indemnifications. The Company is not aware of any claims under indemnification arrangements, and it has not accrued any liabilities related to such obligations in its consolidated financial statements as of September 30, 2022.

Legal Proceedings

The Company is not currently a party to any material legal proceedings. At each reporting date, the Company evaluates whether or not a potential loss amount or a potential range of loss is probable and reasonably estimable under the provisions of the authoritative guidance that addresses accounting for contingencies. The Company expenses the costs related to its legal proceedings as they are incurred.

401(k) Savings Plan

9 Months Ended

Sep. 30, 2022

401(k) Savings Plan

8. 401(k) Savings Plan

The Company has a 401(k) available for participating employees who meet certain eligibility requirements. Eligible employees may defer a portion of their salary as defined by the plan. Company contributions to the plan may be made at the discretion of the board of directors of the Company. Effective August 2021, the Company began making matching contributions of up to 2% of eligible wages. During the three and nine months ended September 30, 2022, the Company recorded $0.1 million and $0.2 million of expense, respectively, related to this matching contribution. During the three and nine months ended September 30, 2021, the Company recorded less than $0.1 million of expense related to this matching contribution.

- Definition

The entire disclosure for retirement benefits.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 55
-Paragraph 17
-URI https://asc.fasb.org/extlink&oid=123450688&loc=d3e4179-114921

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section S99
-Paragraph 2
-URI https://asc.fasb.org/extlink&oid=21916913&loc=d3e273930-122802

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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-Paragraph 1
-Subparagraph (d)(i)
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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Reference 6: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=49170846&loc=d3e28014-114942

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-URI https://asc.fasb.org/topic&trid=2235017

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 60
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-Paragraph 3
-Subparagraph (c)
-URI https://asc.fasb.org/extlink&oid=6414203&loc=d3e39689-114964

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
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-Subparagraph (d)(iv)(03)
-URI https://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 20
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-URI https://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 12: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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-Paragraph 1
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Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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-Paragraph 1
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-URI https://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
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-URI https://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920

+ Details

Related Parties

9 Months Ended

Sep. 30, 2022

Related Parties

9. Related Parties

Effective March 2018, Amy Lynn Ronneberg, the then serving President of Be The Match BioTherapies, LLC, became a member of the Company’s board of directors and subsequently was appointed Chief Executive Officer of the National Marrow Donor Program/Be The Match, or NMDP/Be The Match, organization in June 2020. The Company has collaboration agreements with the National Marrow Donor Program (as successor in interest to Be The Match BioTherapies Collection Services, LLC (formerly known as Be The Match BioTherapies, LLC)) and a research agreement with an affiliated organization, Center for International Blood and Marrow Transplant Research. In addition, in June 2020, the Company entered into a clinical collaboration agreement with NMDP/Be

The Match to evaluate the potential utility of MGTA-145 for mobilizing and collecting hematopoietic stem cells from donors in a single day and then using them for allogeneic transplant in patients. Under the terms of this agreement, the Company shall fund up to fifty percent of NMDP/Be The Match clinical trial costs and provide the trial drugs which will be included in research and development expense.

During the three months ended September 30, 2022 and 2021, the Company recorded expense of $0.1 million and $0.2 million, respectively, related to these agreements. During the nine months ended September 30, 2022 and 2021, the Company recorded expense of $0.2 million and $0.5 million, respectively, related to these agreements. As of September 30, 2022 and December 31, 2021, amounts on the consolidated balance sheets related to these agreements were less than $0.1 million and $0.2 million, respectively, which amounts were included in accounts payable and accrued expenses and other current liabilities and less than $0.1 million which amounts were included in prepaid expenses and other current assets.

Summary of Significant Accounting Policies (Policies)

9 Months Ended

Sep. 30, 2022

Use of Estimates

Unaudited Interim Financial Information

Fair Value Measurements

•

Level 1—Quoted prices in active markets for identical assets or liabilities.

•


	As of September 30,
	2022		2021
Stock options to purchase common stock		8,601,539		6,091,220
Unvested restricted common stock units		416,967		497,418
Shares of common stock issuable under Employee Stock Purchase Plan		76,086		8,843
		9,094,592		6,597,481

Recently Issued Accounting Pronouncements

Recently Adopted Accounting Pronouncements

- Definition

Disclosure of accounting policy for income taxes, which may include its accounting policies for recognizing and measuring deferred tax assets and liabilities and related valuation allowances, recognizing investment tax credits, operating loss carryforwards, tax credit carryforwards, and other carryforwards, methodologies for determining its effective income tax rate and the characterization of interest and penalties in the financial statements.

+ References + Details

Summary of Significant Accounting Policies (Tables)

9 Months Ended

Sep. 30, 2022

Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share

The following potential dilutive securities, presented based on amounts outstanding at each period end, have been excluded from the calculation of diluted net loss per share because including them would have had an anti-dilutive impact:


	As of September 30,
	2022		2021
Stock options to purchase common stock		8,601,539		6,091,220
Unvested restricted common stock units		416,967		497,418
Shares of common stock issuable under Employee Stock Purchase Plan		76,086		8,843
		9,094,592		6,597,481

Fair Value of Financial Assets (Tables)

9 Months Ended

Sep. 30, 2022

Schedule of Marketable Securities by Security Type

As of September 30, 2022, marketable securities by security type consisted of (in thousands):


			Gross		Gross			Estimated
	Amortized		Unrealized		Unrealized			Fair
	Cost		Gains		Losses			Value
U.S. treasury notes (due within one year)	$	69,718	$	—	$	(462	)	$	69,256
Total	$	69,718	$	—	$	(462	)	$	69,256

As of December 31, 2021, marketable securities by security type consisted of (in thousands):


			Gross		Gross			Estimated
	Amortized		Unrealized		Unrealized			Fair
	Cost		Gains		Losses			Value
U.S. treasury notes (due within one year)	$	30,213	$	—	$	(20	)	$	30,193
U.S. treasury notes (due after one year through two years)		15,093		—		(10	)		15,083
Total	$	45,306	$	—	$	(30	)	$	45,276

Schedule of Financial Assets Measured at Fair Value on Recurring Basis


	Fair Value Measurements at September 30, 2022 Using:
	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	58,026	$	—	$	—	$	58,026
Marketable securities:
U.S. treasury notes		—		69,256		—		69,256
Total	$	58,026	$	69,256	$	—	$	127,282


	Fair Value Measurements at December 31, 2021 Using:
	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	131,542	$	—	$	—	$	131,542
Marketable securities:
U.S. treasury notes		—		45,276		—		45,276
Total	$	131,542	$	45,276	$	—	$	176,818

Accrued Expenses and Other Current Liabilities (Tables)

9 Months Ended

Sep. 30, 2022

Schedule of Accrued Expenses and Other Current Liabilities

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



	September 30, 2022		December 31, 2021
Accrued payroll and related expenses	$	3,284	$	3,346
Accrued external research and development expenses		2,617		2,813
Deferred rent, current portion		—		555
Accrued other		821		1,109
	$	6,722	$	7,823

Stock-Based Awards (Tables)

9 Months Ended

Sep. 30, 2022

Schedule of Stock Based Compensation Expense

Stock-based compensation expense was classified in the statements of operations and comprehensive loss as follows (in thousands):


	Three Months Ended September 30,				Nine Months Ended September 30,
	2022		2021		2022		2021
Research and development expenses	$	315	$	1,335	$	1,304	$	3,276
General and administrative expenses		1,192		2,464		3,953		4,849
	$	1,507	$	3,799	$	5,257	$	8,125

Leases (Tables)

9 Months Ended

Sep. 30, 2022

Leases [Abstract]

Schedule of Components of the Company's Lease Expense

The components of the Company’s lease expense under ASC 842 were as follows (in thousands):


	Three Months Ended		Nine Months Ended
	September 30, 2022		September 30, 2022
Operating lease cost	$	1,602	$	4,805
Short-term lease cost		—		—
Variable lease cost		441		951
	$	2,043	$	5,756

Schedule of Supplemental Disclosure Of Cash Flow Information Related To The Lease

Supplemental disclosure of cash flow information related to the lease was as follows (in thousands):


	Three Months Ended		Nine Months Ended
	September 30, 2022		September 30, 2022
Cash paid for amounts included in the measurement of operating lease liabilities	$	1,674	$	4,891
Operating lease liabilities arising from obtaining right-of-use asset	$	—	$	—

Schedule of Weighted Average Remaining Lease Term And Discount Rate

The weighted average remaining lease term and discount rate were as follows:


	September 30, 2022
Weighted-average remaining lease term - operating lease (in years)		5.42
Weighted-average discount rate - operating lease		11.00	%

Schedule of Future Minimum Lease Payments Due Under Noncancelable Operating Lease

As of September 30, 2022, the future minimum lease payments due under the noncancelable operating lease was as follows (in thousands):


2022 (three months)	$	1,675
2023		6,936
2024		7,313
2025		7,679
2026		8,062
Thereafter		9,905
Total future minimum lease payments		41,570
Less: imputed interest		(10,772	)
Total operating lease liabilities	$	30,798


2022	$	6,375
2023		6,734
2024		7,100
2025		7,455
2026		7,828
Thereafter		9,617
	$	45,109

Schedule of Lease Liabilities

The following table represents the lease liabilities on the consolidated balance sheet (in thousands):


	September 30, 2022
Current operating lease liability	$	3,621
Operating lease liability, net of current portion		27,177
Total operating lease liabilities	$	30,798

Nature of the Business and Basis of Presentation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended		9 Months Ended		12 Months Ended
	Aug. 12, 2022	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021	Dec. 31, 2021
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Entity incorporation date				Jun. 01, 2015
Entity incorporation state code				DE
Net loss		$ (16,063)	$ (17,427)	$ (56,284)	$ (51,844)	$ (71,100)
Accumulated deficit		$ (381,851)		(381,851)		$ (325,567)
Net proceeds from common stock				2,904	$ 0
Maximum [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Shelf offering value	$ 250,000
Atm Program [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Net proceeds from common stock				$ 2,800
Issuance of common stock, shares				1,644,200
Atm Program [Member] \| WeightedAverageMember
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Stock issued, price per shares		$ 1.82		$ 1.82
Shelf [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Remaining value of securities available under the shelf		$ 247,000		$ 247,000
Cowen and Company LLC [Member] \| Maximum [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
ATM offering value	$ 50,000
Cowen and Company LLC [Member] \| Atm Program [Member] \| Maximum [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Remaining value of securities available under the shelf		$ 47,000		$ 47,000

Summary of Significant Accounting Policies - Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share (Detail) - shares	9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share, amount	9,094,592	6,597,481
Stock Option [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share, amount	8,601,539	6,091,220
Restricted Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share, amount	416,967	497,418
Employee Stock Purchase Plan [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share, amount	76,086	8,843

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands	Sep. 30, 2022	Jan. 01, 2022	Dec. 31, 2021
Summary Of Significant Accounting Policies [Line Items]
Operating Lease, Right-of-Use Asset	$ 23,930		$ 0
Operating Lease, Liability	30,798
Accounting Standards Update 2016-02 [Member]
Summary Of Significant Accounting Policies [Line Items]
Operating Lease, Right-of-Use Asset	26,100
Operating Lease, Liability	$ 33,000
Deferred rent balance		$ 7,000

Fair Value of Financial Assets - Schedule of Marketable Securities by Security Type (Detail) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Marketable Securities [Line Items]
Amortized Cost	$ 69,718	$ 45,306
Gross Unrealized Gains
Gross Unrealized Losses	(462)	(30)
Estimated Fair Value	69,256	45,276
US Treasury Notes [Member] \| Due With In One Year [Member]
Marketable Securities [Line Items]
Amortized Cost	69,718	30,213
Gross Unrealized Gains
Gross Unrealized Losses	(462)	(20)
Estimated Fair Value	$ 69,256	30,193
US Treasury Notes [Member] \| Due After One Year Through Two Years [Member]
Marketable Securities [Line Items]
Amortized Cost		15,093
Gross Unrealized Gains
Gross Unrealized Losses		(10)
Estimated Fair Value		$ 15,083

Fair Value of Financial Assets - Schedule of Financial Assets Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	$ 69,256	$ 45,276
Fair Value on Recurring Basis [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total	127,282	176,818
Level 1 [Member] \| Fair Value on Recurring Basis [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total	58,026	131,542
Level 2 [Member] \| Fair Value on Recurring Basis [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total	69,256	45,276
Money Market Funds [Member] \| Fair Value on Recurring Basis [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	58,026	131,542
Money Market Funds [Member] \| Level 1 [Member] \| Fair Value on Recurring Basis [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	58,026	131,542
US Treasury Notes [Member] \| Fair Value on Recurring Basis [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	69,256	45,276
US Treasury Notes [Member] \| Level 1 [Member] \| Fair Value on Recurring Basis [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities
US Treasury Notes [Member] \| Level 2 [Member] \| Fair Value on Recurring Basis [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	$ 69,256	$ 45,276

Accrued Expenses and Other Current Liabilities - Schedule of Accrued Expenses and Other Current Liabilities (Detail) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Payables and Accruals [Abstract]
Accrued payroll and related expenses	$ 3,284	$ 3,346
Accrued external research and development expenses	2,617	2,813
Deferred rent, current portion		555
Accrued other	821	1,109
Total	$ 6,722	$ 7,823

Stock-Based Awards - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized stock-based compensation expense related to unvested share-based awards	$ 15.5
Period for recognition of unrecognized expense	2 years 4 months 24 days
Employees, Directors and Consultants [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, options, grants in period, gross	4,357,798
Minimum [Member] \| Employees, Directors and Consultants [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation arrangement , requisite service period	18 months
Maximum [Member] \| Employees, Directors and Consultants [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation arrangement , requisite service period	4 years
Performance Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized stock-based compensation expense	$ 1.7
Restricted Stock Units (RSUs) [Member] \| Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant of restricted stock	160,558
Grant weighted average grant date fair value per share	$ 2.01
Restricted Stock Units (RSUs) [Member] \| Minimum [Member] \| Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation arrangement , requisite service period	18 months
Restricted Stock Units (RSUs) [Member] \| Maximum [Member] \| Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation arrangement , requisite service period	4 years
Stock Option [Member] \| Employees, Directors and Consultants [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average fair value of stock options granted	$ 1.51
2018 Stock Option and Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock available for issuance	3,000,865
2019 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for issuance	663,548
Percentage of purchase price of common stock under the ESPP	85.00%
Common stock purchased	49,704	13,989
Stock issued, price per shares	$ 0.99	$ 6.15

Stock-Based Awards - Schedule of Stock Based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock based compensation expense	$ 1,507	$ 3,799	$ 5,257	$ 8,125
Research and Development Expenses [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock based compensation expense	315	1,335	1,304	3,276
General and Administrative Expenses [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock based compensation expense	$ 1,192	$ 2,464	$ 3,953	$ 4,849

Leases - Schedule of Components of the Company's Lease Expense (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2022	Sep. 30, 2022
Lease, Cost [Abstract]
Operating lease cost	$ 1,602	$ 4,805
Short-term lease cost	0	0
Variable lease cost	441	951
Lease cost	$ 2,043	$ 5,756

Leases - Schedule of Supplemental Disclosure Of Cash Flow Information Related To The Lease (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2022	Sep. 30, 2022
Leases [Abstract]
Cash paid for amounts included in the measurement of operating lease liabilities	$ 1,674	$ 4,891
Operating lease liabilities arising from obtaining right-of-use asset	$ 0	$ 0

Leases - Schedule of Weighted Average Remaining Lease Term And Discount Rate (Detail)	Sep. 30, 2022
Leases [Abstract]
Weighted-average remaining lease term - operating lease (in years)	5 years 5 months 1 day
Weighted-average discount rate - operating lease	11.00%

Leases - Schedule of Future Minimum Lease Payments Due Under Noncancelable Operating Lease (Detail) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Leases [Abstract]
2022		$ 6,375
2023		6,734
2024		7,100
2025		7,455
2026		7,828
Thereafter		9,617
Total future minimum lease payments		$ 45,109
2022 (three months)	$ 1,675
2023	6,936
2024	7,313
2025	7,679
2026	8,062
Thereafter	9,905
Total future minimum lease payments	41,570
Less: imputed interest	(10,772)
Total operating lease liabilities	$ 30,798

Leases - Schedule of Lease Liabilities (Detail) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Operating Lease Liabilities, Gross Difference, Amount [Abstract]
Current operating lease liability	$ 3,621	$ 0
Operating lease liability, net of current portion	27,177	$ 0
Total operating lease liabilities	$ 30,798

Leases - Additional Information (Detail) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
Leases - Additional Information (Detail) $ in Thousands	Sep. 30, 2022 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2022 USD ($)	Sep. 30, 2021 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 ft² Sublease	Jan. 01, 2022 ft²	Dec. 31, 2021 USD ($) ft²
Leases [Line Items]
Restricted cash	$ 1,780		$ 1,780					$ 1,780
Long-term deferred rent	0		$ 0					6,399
Deferred rent, current portion								$ 555
Property sublease, description			The Company has a sublease, as amended, for up to approximately 69,000 square feet of office and laboratory space in Cambridge, Massachusetts. The sublease is subject and subordinate to a prime lease between the sublandlord and the prime landlord. The term of the sublease commenced in June 2018 and expires in February 2028. The sublandlord has the right to terminate the sublease after five years.
Sublease termination period			5 years
Sublease expiration period			2028-02
Sublease commencement period			2018-06
Rent expense		$ 1,500		$ 4,600
Sub Sublease [Member]
Leases [Line Items]
Square feet of property subject to sublease \| ft²						27,000	26,114	13,643
Number of Sub-sublease \| Sublease						2
Rental payments receivable	1,500		$ 1,500
Other income from sub-sublease	800	$ 800	2,200	$ 2,700
Office and Lab Sublease [Member] \| Letter of Credit [Member]
Leases [Line Items]
Restricted cash	$ 1,800		$ 1,800
Office and Lab Sublease [Member] \| Paid By Sublandlord [Member]
Leases [Line Items]
Payments for tenant improvements					$ 5,200

Commitments and Contingencies - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021	Mar. 31, 2018	Nov. 30, 2016
Other Commitments [Line Items]
Research and development expense	$ 11,201,000	$ 10,795,000	$ 39,351,000	$ 33,652,000
Research and Development Expenses [Member]
Other Commitments [Line Items]
Research and development expense	0	0	0	100,000
Achievement of Development Milestone [Member]
Other Commitments [Line Items]
Research and development expense			2,000,000.0
Collaboration Agreement [Member]
Other Commitments [Line Items]
Research and development expense	$ 0	$ 100,000	400,000	$ 400,000
Collaboration Agreement [Member] \| Development, Regulatory and Commercial Milestone [Member] \| Per Target [Member] \| Maximum [Member]
Other Commitments [Line Items]
Potential milestone payments due					$ 83,500,000
License Agreement With Harvard [Member] \| Maintenance [Member] \| Annual [Member] \| Maximum [Member]
Other Commitments [Line Items]
Payment obligation						$ 100,000
License Agreement With Harvard [Member] \| Achievement of Development and Regulatory Milestones [Member] \| Maximum [Member]
Other Commitments [Line Items]
Potential milestone payments due						$ 7,400,000
License Agreement With Third Parties [Member] \| License [Member]
Other Commitments [Line Items]
Research and development expense			$ 100,000

401(k) Savings Plan - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Retirement Benefits [Abstract]
Defined contribution plan,Employers matching contributions subject to time based vesting requirements			2.00%
Defined Contribution Plan, Employer Discretionary Contribution Amount	$ 0.1	$ 0.1	$ 0.2	$ 0.1

Related Parties - Additional Information (Detail) - Match Bio Therapies [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021	Dec. 31, 2021
Related Party Transaction [Line Items]
Expenses paid to related party	$ 0.1	$ 0.2	$ 0.2	$ 0.5
Accounts Payable, Accrued Expenses and Other Current Liabilities [Member] \| Maximum [Member]
Related Party Transaction [Line Items]
Amounts owed to related party	0.1		0.1		$ 0.2
Prepaid Expenses and Other Current Assets [Member] \| Maximum [Member]
Related Party Transaction [Line Items]
Prepaid expense and other current assets related parties	$ 0.1		$ 0.1

- Definition

Carrying amount as of the balance sheet date of obligations due all related parties. For classified balance sheets, represents the current portion of such liabilities (due within one year or within the normal operating cycle if longer).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 10
-Section S99
-Paragraph 1B
-Subparagraph (SX 210.13-02(a)(4)(iii)(C))
-URI https://asc.fasb.org/extlink&oid=126975872&loc=SL124442552-122756

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 10
-Section S99
-Paragraph 1B
-Subparagraph (SX 210.13-02(a)(5))
-URI https://asc.fasb.org/extlink&oid=126975872&loc=SL124442552-122756

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (d)
-URI https://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 10
-Section S99
-Paragraph 1A
-Subparagraph (SX 210.13-01(a)(4)(iv))
-URI https://asc.fasb.org/extlink&oid=126975872&loc=SL124442526-122756

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 10
-Section S99
-Paragraph 1A
-Subparagraph (SX 210.13-01(a)(4)(iii)(B))
-URI https://asc.fasb.org/extlink&oid=126975872&loc=SL124442526-122756

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 10
-Section S99
-Paragraph 1A
-Subparagraph (SX 210.13-01(a)(5))
-URI https://asc.fasb.org/extlink&oid=126975872&loc=SL124442526-122756

Reference 7: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19(a))
-URI https://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 8: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(k)(1))
-URI https://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 10
-Section S99
-Paragraph 1B
-Subparagraph (SX 210.13-02(a)(4)(iv))
-URI https://asc.fasb.org/extlink&oid=126975872&loc=SL124442552-122756

+ Details