Dianthus Therapeutics (DNTH) 10-Q 5 Aug 21 2021 Q2 Quarterly report Financial data

Cover Page

Cover Page - shares	6 Months Ended
	Jun. 30, 2021	Jul. 31, 2021
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Quarterly Report	true
Document Transition Report	false
Document Period End Date	Jun. 30, 2021
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q2
Trading Symbol	MGTA
Entity Registrant Name	Magenta Therapeutics, Inc.
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 Common Stock, Shares Outstanding		58,567,273
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
City Area Code	857
Entity File Number	001-38541
Entity Tax Identification Number	81-0724163
Local Phone Number	242-0170

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 155,034	$ 58,152
Marketable securities	52,771	90,683
Prepaid expenses and other current assets	2,381	2,692
Total current assets	210,186	151,527
Restricted cash	1,780	1,780
Property and equipment, net	8,412	8,312
Total assets	220,378	161,619
Current liabilities:
Accounts payable	2,933	3,760
Accrued expenses and other current liabilities	8,150	7,670
Total current liabilities	11,083	11,430
Deferred rent	6,403	6,283
Total liabilities	17,486	17,713
Commitments and contingencies (Note 6)
Stockholders' Equity:
Preferred stock, $0.001 par value; 10,000,000 shares authorized; no shares issued or outstanding
Common stock, $0.001 par value; 150,000,000 shares authorized; 58,508,735 shares issued and outstanding as of June 30, 2021 and 48,541,601 shares issued and 48,533,135 shares outstanding as of December 31, 2020	59	49
Additional paid-in capital	491,679	398,311
Accumulated other comprehensive income (loss)	2	(23)
Accumulated deficit	(288,848)	(254,431)
Total stockholders' equity	202,892	143,906
Total liabilities and stockholders' equity	$ 220,378	$ 161,619

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Jun. 30, 2021	Dec. 31, 2020
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	58,508,735	48,541,601
Common stock, Shares outstanding	58,508,735	48,533,135

Consolidated Statements of Oper

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Operating expenses:
Research and development	$ 11,129	$ 12,610	$ 22,857	$ 26,573
General and administrative	6,481	7,402	13,450	14,683
Total operating expenses	17,610	20,012	36,307	41,256
Loss from operations	(17,610)	(20,012)	(36,307)	(41,256)
Interest and other income, net	682	933	1,890	2,166
Net loss	$ (16,928)	$ (19,079)	$ (34,417)	$ (39,090)
Net loss per share, basic and diluted	$ (0.32)	$ (0.48)	$ (0.67)	$ (0.99)
Weighted average common shares outstanding, basic and diluted	53,705,289	39,611,837	51,150,391	39,488,137
Comprehensive loss:
Net loss	$ (16,928)	$ (19,079)	$ (34,417)	$ (39,090)
Other comprehensive income (loss):
Unrealized gains (losses) on marketable securities	(7)	(210)	25	145
Total other comprehensive income (loss)	(7)	(210)	25	145
Total comprehensive loss	$ (16,935)	$ (19,289)	$ (34,392)	$ (38,945)

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Private Placement [Member]	Common Stock [Member]	Common Stock [Member]Private Placement [Member]	Additional Paid-in Capital [Member]	Additional Paid-in Capital [Member]Private Placement [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Accumulated Deficit [Member]
Beginning balance at Dec. 31, 2019	$ 141,193		$ 39		$ 320,641		$ 8	$ (179,495)
Beginning balance, shares at Dec. 31, 2019			39,260,532
Issuance of common stock upon public offering net of underwriting discounts, commissions and offering costs	64,563		$ 9		64,554
Issuance of common stock upon public offering net of underwriting discounts, commissions and offering costs , shares			8,625,000
Vesting of restricted stock, shares			125,673
Issuance of common stock upon exercise of stock options	1,817				1,817
Issuance of common stock upon exercise of stock options, shares			224,354
Issuance of common stock under Employee Stock Purchase Plan, shares			5,653
Issuance of common stock under Employee Stock Purchase Plan	42				42
Stock-based compensation expense	5,244				5,244
Unrealized gains on marketable securities	145						145
Net loss	(39,090)							(39,090)
Ending balance at Jun. 30, 2020	173,914		$ 48		392,298		153	(218,585)
Ending balance, shares at Jun. 30, 2020			48,241,212
Beginning balance at Dec. 31, 2019	141,193		$ 39		320,641		8	(179,495)
Beginning balance, shares at Dec. 31, 2019			39,260,532
Net loss	(74,900)
Ending balance at Dec. 31, 2020	143,906		$ 49		398,311		(23)	(254,431)
Ending balance, shares at Dec. 31, 2020			48,533,135
Beginning balance at Mar. 31, 2020	125,401		$ 39		324,505		363	(199,506)
Beginning balance, shares at Mar. 31, 2020			39,454,635
Issuance of common stock upon public offering net of underwriting discounts, commissions and offering costs	64,563		$ 9		64,554
Issuance of common stock upon public offering net of underwriting discounts, commissions and offering costs , shares			8,625,000
Vesting of restricted stock, shares			61,047
Issuance of common stock upon exercise of stock options	693				693
Issuance of common stock upon exercise of stock options, shares			94,877
Issuance of common stock under Employee Stock Purchase Plan, shares			5,653
Issuance of common stock under Employee Stock Purchase Plan	42				42
Stock-based compensation expense	2,504				2,504
Unrealized gains on marketable securities	(210)						(210)
Net loss	(19,079)							(19,079)
Ending balance at Jun. 30, 2020	173,914		$ 48		392,298		153	(218,585)
Ending balance, shares at Jun. 30, 2020			48,241,212
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 public offering net of underwriting discounts, commissions and offering costs		$ 86,097		$ 10		$ 86,087
Issuance of common stock upon public offering net of underwriting discounts, commissions and offering costs , shares				9,599,998
Vesting of restricted stock, shares			8,466
Issuance of common stock upon exercise of stock options	2,869				2,869
Issuance of common stock upon exercise of stock options, shares			353,147
Issuance of common stock under Employee Stock Purchase Plan, shares			13,989
Issuance of common stock under Employee Stock Purchase Plan	86				86
Stock-based compensation expense	4,326				4,326
Unrealized gains on marketable securities	25						25
Net loss	(34,417)							(34,417)
Ending balance at Jun. 30, 2021	202,892		$ 59		491,679		2	(288,848)
Ending balance, shares at Jun. 30, 2021			58,508,735
Beginning balance at Mar. 31, 2021	129,059		$ 49		400,921		9	(271,920)
Beginning balance, shares at Mar. 31, 2021			48,603,205
Issuance of common stock upon public offering net of underwriting discounts, commissions and offering costs		$ 86,097		$ 10		$ 86,087
Issuance of common stock upon public offering net of underwriting discounts, commissions and offering costs , shares				9,599,998
Issuance of common stock upon exercise of stock options	2,451				2,451
Issuance of common stock upon exercise of stock options, shares			291,543
Issuance of common stock under Employee Stock Purchase Plan, shares			13,989
Issuance of common stock under Employee Stock Purchase Plan	86				86
Stock-based compensation expense	2,134				2,134
Unrealized gains on marketable securities	(7)						(7)
Net loss	(16,928)							(16,928)
Ending balance at Jun. 30, 2021	$ 202,892		$ 59		$ 491,679		$ 2	$ (288,848)
Ending balance, shares at Jun. 30, 2021			58,508,735

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Cash flows from operating activities:
Net loss	$ (34,417)	$ (39,090)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	4,326	5,244
Depreciation and amortization expense	953	988
Loss on disposal of property and equipment	90
Net amortization of premiums on marketable securities	437	63
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	311	738
Accounts payable	(1,996)	(238)
Accrued expenses and other current liabilities	402	(3,805)
Deferred rent	120	238
Net cash used in operating activities	(29,774)	(35,862)
Cash flows from investing activities:
Purchases of property and equipment	(118)	(167)
Purchases of marketable securities		(4,974)
Maturities of marketable securities	37,500	45,500
Net cash provided by investing activities	37,382	40,359
Cash flows from financing activities:
Proceeds from private investment	86,400
Proceeds from public offerings, net of underwriting discounts and commissions		64,860
Payments of offering costs	(81)
Proceeds from exercise of common stock options	2,869	1,817
Proceeds from issuance of common stock under Employee Stock Purchase Plan	86	42
Net cash provided by financing activities	89,274	66,719
Net increase in cash, cash equivalents and restricted cash	96,882	71,216
Cash, cash equivalents and restricted cash at beginning of period	59,932	66,851
Cash, cash equivalents and restricted cash at end of period	156,814	138,067
Supplemental disclosure of non-cash investing and financing activities:
Purchase of property and equipment included in accounts payable and accrued expenses	1,025
Offering costs included in accounts payable and accrued expenses	$ 222	$ 297

Nature of the Business and Basi

Nature of the Business and Basis of Presentation	6 Months Ended
	Jun. 30, 2021
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 to bring the curative power of stem cell transplants 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 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 novel coronavirus (“COVID-19”) In May 2021, the Company issued and sold 9,599,998 shares of its common stock in a private placement at a purchase price of $9.00 per share, resulting in net proceeds of $86.1 million, after deducting offering expenses. In connection with the private placement, the Company filed a resale registration statement with the Securities and Exchange Commission (the “SEC”) in June 2021 to register the resale of these shares by the purchasers in the private placement. In June 2020, the Company issued and sold 8,625,000 shares of its common stock, including the underwriters’ exercise in full of their option to purchase additional shares of common stock, in a follow-on The Company has a shelf registration statement on Form S-3 “at-the-market” The Company has incurred recurring losses since inception, including net losses of $34.4 million and $74.9 million for the six months ended June 30, 2021 and the year ended December 31, 2020, respectively. As of June 30, 2021, the Company had an accumulated deficit of $288.8 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 expects its expenses to increase substantially in connection with ongoing activities, particularly as the Company advances its preclinical activities and clinical trials for its product candidates in development. Accordingly, the Company will need to obtain substantial additional funding in connection with continuing operations. 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”).

Summary of Significant Accounti

Summary of Significant Accounting Policies	6 Months Ended
	Jun. 30, 2021
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, 2020 was derived from audited financial statements but does not include all disclosures required by GAAP. The accompanying unaudited consolidated financial statements as of June 30, 2021 and for the three and six months ended June 30, 2021 and 2020 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, 2020 included in the Company’s Annual Report on Form 10-K, 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 more-likely-than-not penalties 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 six months ended June 30, 2021 and 2020, 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 affect is anti-dilutive. The Company reported a net loss for the three and six months ended June 30, 2021 and 2020. 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 June 30, 2021 2020 Stock options to purchase common stock 6,115,903 5,809,118 Unvested restricted common stock and units 510,000 68,245 Shares of common stock issuable under Employee Stock Purchase Plan 11,238 8,213 6,637,141 5,885,576 Recently Issued Accounting Pronouncements In February 2016, the FASB issued ASU No. 2016-02, Leases 2016-02”). 2016-02 right-of-use No. 2020-05, 2016-02 2018-11, Leases (Topic 842) Targeted Improvements 2016-02 right-of-use In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments – Credit Losses (Topic 326) the No. 2019-10, those

Fair Value of Financial Assets

Fair Value of Financial Assets	6 Months Ended
	Jun. 30, 2021
Fair Value of Financial Assets	3. Fair Value of Financial Assets As of June 30, 2021, marketable securities by security type consisted of (in thousands): Amortized Gross Gross Estimated U.S. treasury notes (due within one year) $ 52,769 $ 2 $ — $ 52,771 Total $ 52,769 $ 2 $ — $ 52,771 As of December 31, 2020, marketable securities by security type consisted of (in thousands): Amortized Gross Gross Estimated U.S. treasury notes (due within one year) $ 90,706 $ — $ (23 ) $ 90,683 Total $ 90,706 $ — $ (23 ) $ 90,683 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 June 30, 2021 Using: Level 1 Level 2 Level 3 Total Cash equivalents: Money market funds $ 154,973 $ — $ — $ 154,973 Marketable securities: U.S. treasury notes — 52,771 — 52,771 Total $ 154,973 $ 52,771 $ — $ 207,744 Fair Value Measurements at December 31, 2020 Using: Level 1 Level 2 Level 3 Total Cash equivalents: Money market funds $ 43,182 $ — $ — $ 43,182 U.S. treasury notes — 14,999 — 14,999 Marketable securities: U.S. treasury notes — 90,683 — 90,683 Total $ 43,182 $ 105,682 $ — $ 148,864

Accrued Expenses and Other Curr

Accrued Expenses and Other Current Liabilities	6 Months Ended
	Jun. 30, 2021
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): June 30, 2021 December 31, 2020 Accrued external research and development expenses $ 3,412 $ 2,662 Accrued payroll and related expenses 2,121 3,107 Accrued professional fees 999 693 Deferred rent, current portion 555 555 Accrued lease-related expenses 803 347 Accrued other 260 306 $ 8,150 $ 7,670

Stock-Based Awards

Stock-Based Awards	6 Months Ended
	Jun. 30, 2021
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 June 30, 2021, 3,382,809 shares of common stock were available for issuance under the 2018 Plan. 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 Grant of Stock Options During the six months ended June 30, 2021, the Company granted options to certain employees and directors with service-based vesting conditions for the purchase of 1,550,116 shares of common stock with a weighted average grant date fair value of $7.56 per share. Grant of Performance Restricted Stock Units During the six months ended June 30, 2021, the Company granted 260,000 performance-based restricted stock units to certain employees with a weighted average grant date fair value of $10.84 per share. These performance-based restricted stock units vest upon the occurrence of certain operational and financial events. At the achievement of the performance-based vesting criteria, each performance-based restricted stock unit entitles the holder to a specified number of shares of common stock. Stock-Based Compensation Stock-based compensation expense was classified in the statements of operations and comprehensive loss as follows (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2021 2020 2021 2020 Research and development expenses $ 996 $ 780 $ 1,941 $ 1,802 General and administrative expenses 1,138 1,724 2,385 3,442 $ 2,134 $ 2,504 $ 4,326 $ 5,244 As of June 30, 2021, unrecognized compensation expense related to unvested share-based awards with service-based vesting conditions was $21.4 million, which is expected to be recognized over a weighted average period of 2.7 years. Additionally, the Company had unrecognized compensation cost of $3.4 million related to the unvested performance restricted stock units for which the performance conditions are not considered probable of achievement as of June 30, 2021.

Commitments and Contingencies

Commitments and Contingencies	6 Months Ended
	Jun. 30, 2021
Commitments and Contingencies	6. Commitments and Contingencies Leases In May 2018, the Company entered into 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 is obligated to pay real estate taxes and other costs related to the premises, including costs of operations and management of the leased premises. 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 June 30, 2021 and December 31, 2020. As of June 30, 2021 and December 31, 2020, the Company had long-term deferred rent of $6.4 million and $6.3 million, respectively, related to lease incentives and payment escalations. As of June 30, 2021 and December 31, 2020, the short-term portion of deferred rent of $0.6 million for each period was included in accrued expenses and other current liabilities. The Company recorded rent expense of $1.6 million during each of the three months ended June 30, 2021 and 2020. The Company recorded rent expense of $3.1 million during each of the six months ended June 30, 2021 and 2020. As of June 30, 2021, the future minimum lease payments due under the noncancelable operating lease is as follows (in thousands): Remainder of 2021 (six months) $ 3,097 2022 6,375 2023 6,734 2024 7,100 2025 7,455 Thereafter 17,444 $ 48,205 In 2018, the Company entered into two two-year sub-subleases sub-subleases sub-sublease sub-subleases sub-subleases. sub-subleases. 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 each of the three months ended June 30, 2021 and 2020, 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 the six months ended June 30, 2021 and 2020, the Company recorded $0.4 million and less than $0.1 million, respectively, of research and development expense related to this agreement for upfront technology access fees, research exclusivity fees and research support. 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 country-by-country The Company has a license agreement with Novartis International Pharmaceutical Ltd. (“Novartis”), entered into in April 2017, to use and develop certain patent rights (the “Novartis License”). Under the Novartis License, the Company was granted an exclusive, worldwide, sublicensable license to research, develop and commercialize certain licensed products that contain Novartis compounds for the expansion of cord blood derived non-gene-edited/-modified product-by-product country-by-country 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 three and six months ended June 30, 2021 and 2020, 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 June 30, 2021. 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

401(k) Savings Plan	6 Months Ended
	Jun. 30, 2021
401(k) Savings Plan	7. 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. To date, the Company has not made any contributions to the plan.

Related Parties

Related Parties	6 Months Ended
	Jun. 30, 2021
Related Parties	8. Related Parties National Marrow Donor Program (as successor in interest to Be The Match BioTherapies Collection Services, LLC (formerly known as Be The Match BioTherapies, LLC)) 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 the three months ended June 30, 2021 and 2020, the Company recorded expense of $0.2 million and less than $0.1 million, respectively, related to these agreements. For the six months ended June 30, 2021 and 2020, the Company recorded expense of $0.3 million and $0.2 million, respectively, related to these agreements. As of June 30, 2021 and December 31, 2020, amounts on the balance sheet related to these agreements were ,

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	6 Months Ended
	Jun. 30, 2021
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, 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	Unaudited Interim Financial Information The consolidated balance sheet at December 31, 2020 was derived from audited financial statements but does not include all disclosures required by GAAP. The accompanying unaudited consolidated financial statements as of June 30, 2021 and for the three and six months ended June 30, 2021 and 2020 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, 2020 included in the Company’s Annual Report on Form 10-K,
Fair Value Measurements	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	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 more-likely-than-not penalties
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 six months ended June 30, 2021 and 2020, the Company’s only element of other comprehensive income (loss) was unrealized gains (losses) on marketable securities.
Net Loss per Share	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 affect is anti-dilutive. The Company reported a net loss for the three and six months ended June 30, 2021 and 2020. 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 June 30, 2021 2020 Stock options to purchase common stock 6,115,903 5,809,118 Unvested restricted common stock and units 510,000 68,245 Shares of common stock issuable under Employee Stock Purchase Plan 11,238 8,213 6,637,141 5,885,576
Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements In February 2016, the FASB issued ASU No. 2016-02, Leases 2016-02”). 2016-02 right-of-use No. 2020-05, 2016-02 2018-11, Leases (Topic 842) Targeted Improvements 2016-02 right-of-use In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments – Credit Losses (Topic 326) the No. 2019-10, those

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	6 Months Ended
	Jun. 30, 2021
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 June 30, 2021 2020 Stock options to purchase common stock 6,115,903 5,809,118 Unvested restricted common stock and units 510,000 68,245 Shares of common stock issuable under Employee Stock Purchase Plan 11,238 8,213 6,637,141 5,885,576

Fair Value of Financial Assets

Fair Value of Financial Assets (Tables)	6 Months Ended
	Jun. 30, 2021
Schedule of Marketable Securities by Security Type	As of June 30, 2021, marketable securities by security type consisted of (in thousands): Amortized Gross Gross Estimated U.S. treasury notes (due within one year) $ 52,769 $ 2 $ — $ 52,771 Total $ 52,769 $ 2 $ — $ 52,771 As of December 31, 2020, marketable securities by security type consisted of (in thousands): Amortized Gross Gross Estimated U.S. treasury notes (due within one year) $ 90,706 $ — $ (23 ) $ 90,683 Total $ 90,706 $ — $ (23 ) $ 90,683
Schedule of Financial Assets Measured at Fair Value on Recurring Basis	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 June 30, 2021 Using: Level 1 Level 2 Level 3 Total Cash equivalents: Money market funds $ 154,973 $ — $ — $ 154,973 Marketable securities: U.S. treasury notes — 52,771 — 52,771 Total $ 154,973 $ 52,771 $ — $ 207,744 Fair Value Measurements at December 31, 2020 Using: Level 1 Level 2 Level 3 Total Cash equivalents: Money market funds $ 43,182 $ — $ — $ 43,182 U.S. treasury notes — 14,999 — 14,999 Marketable securities: U.S. treasury notes — 90,683 — 90,683 Total $ 43,182 $ 105,682 $ — $ 148,864

Accrued Expenses and Other Cu_2

Accrued Expenses and Other Current Liabilities (Tables)	6 Months Ended
	Jun. 30, 2021
Schedule of Accrued Expenses and Other Current Liabilities	Accrued expenses and other current liabilities consisted of the following (in thousands): June 30, 2021 December 31, 2020 Accrued external research and development expenses $ 3,412 $ 2,662 Accrued payroll and related expenses 2,121 3,107 Accrued professional fees 999 693 Deferred rent, current portion 555 555 Accrued lease-related expenses 803 347 Accrued other 260 306 $ 8,150 $ 7,670

Stock-Based Awards (Tables)

Stock-Based Awards (Tables)	6 Months Ended
	Jun. 30, 2021
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 June 30, Six Months Ended June 30, 2021 2020 2021 2020 Research and development expenses $ 996 $ 780 $ 1,941 $ 1,802 General and administrative expenses 1,138 1,724 2,385 3,442 $ 2,134 $ 2,504 $ 4,326 $ 5,244

Commitments and Contingencies (

Commitments and Contingencies (Tables)	6 Months Ended
	Jun. 30, 2021
Schedule of Future Minimum Lease Payments Due Under Noncancelable Operating Lease	As of June 30, 2021, the future minimum lease payments due under the noncancelable operating lease is as follows (in thousands): Remainder of 2021 (six months) $ 3,097 2022 6,375 2023 6,734 2024 7,100 2025 7,455 Thereafter 17,444 $ 48,205

Nature of the Business and Ba_2

Nature of the Business and Basis of Presentation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	Jun. 30, 2020	Aug. 08, 2019	May 31, 2021	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Entity incorporation date						Jun. 1, 2015
Entity incorporation state code						DE
Net loss				$ (16,928)	$ (19,079)	$ (34,417)	$ (39,090)	$ (74,900)
Accumulated deficit				$ (288,848)		$ (288,848)		$ (254,431)
Net proceeds from common stock							$ 64,860
Maximum [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Shelf offering value		$ 350,000
Private Placement [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Stock issued, shares			9,599,998
Stock issued, price per shares			$ 9
Sale of stock net consideration received on the transaction			$ 86,100
Common Stock [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Stock issued, shares	8,625,000				8,625,000		8,625,000
Stock issued, price per shares	$ 8				$ 8		$ 8
Net proceeds from common stock	$ 64,600
Common Stock [Member] | Private Placement [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Stock issued, shares				9,599,998		9,599,998
Cowen and Company LLC [Member] | Maximum [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
ATM offering value		$ 100,000

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share (Detail) - shares	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share, amount	6,637,141	5,885,576
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	6,115,903	5,809,118
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	510,000	68,245
Shares of common stock issuable under the ESPP [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share, amount	11,238	8,213

Fair Value of Financial Asset_2

Fair Value of Financial Assets - Schedule of Marketable Securities by Security Type (Detail) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Marketable Securities [Line Items]
Amortized Cost	$ 52,769	$ 90,706
Gross Unrealized Gains	2
Gross Unrealized Losses		(23)
Estimated Fair Value	52,771	90,683
United States Treasury Notes [Member]
Marketable Securities [Line Items]
Amortized Cost	52,769	90,706
Gross Unrealized Gains	2
Gross Unrealized Losses		(23)
Estimated Fair Value	$ 52,771	$ 90,683

Fair Value of Financial Asset_3

Fair Value of Financial Assets - Schedule of Financial Assets Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	$ 52,771	$ 90,683
Fair Value on Recurring Basis [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total	207,744	148,864
Level 1 [Member] | Fair Value on Recurring Basis [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total	154,973	43,182
Level 2 [Member] | Fair Value on Recurring Basis [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total	52,771	105,682
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	154,973	43,182
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	154,973	43,182
United States Treasury Notes [Member] | Fair Value on Recurring Basis [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents		14,999
Marketable securities	52,771
United States 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]
Cash equivalents		14,999
Marketable securities	52,771
United States Treasury Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	$ 52,771	90,683
United States Treasury Notes [Member] | Fair Value on Recurring Basis [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities		90,683
United States 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		$ 90,683

Accrued Expenses and Other Cu_3

Accrued Expenses and Other Current Liabilities - Schedule of Accrued Expenses and Other Current Liabilities (Detail) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Payables and Accruals [Abstract]
Accrued external research and development expenses	$ 3,412	$ 2,662
Accrued payroll and related expenses	2,121	3,107
Accrued professional fees	999	693
Deferred rent, current portion	555	555
Accrued lease-related expenses	803	347
Accrued other	260	306
Total	$ 8,150	$ 7,670

Stock-Based Awards - Additional

Stock-Based Awards - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized stock-based compensation expense	$ 21.4
Period for recognition of unrecognized expense	2 years 8 months 12 days
Employees And Directors [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	1,550,116
Weighted average fair value of stock options granted	$ 7.56
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized stock-based compensation expense	$ 3.4
Performance Shares [member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant of restricted stock	260,000
Grant weighted average grant date fair value per share	$ 10.84
2018 Stock Option and Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock available for issuance	3,382,809
2019 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock available for issuance	136,835
Percentage of purchase price of common stock under the ESPP	85.00%
Common stock purchased	13,989	5,653
Stock issued, price per shares	$ 6.15	$ 7.51

Stock-Based Awards - Schedule o

Stock-Based Awards - Schedule of Stock Based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock based compensation expense	$ 2,134	$ 2,504	$ 4,326	$ 5,244
Research and Development Expenses [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock based compensation expense	996	780	1,941	1,802
General and Administrative Expenses [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock based compensation expense	$ 1,138	$ 1,724	$ 2,385	$ 3,442

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) $ in Thousands	1 Months Ended	3 Months Ended				6 Months Ended
	Apr. 30, 2017USD ($)	Jun. 30, 2021USD ($)	Jun. 30, 2020USD ($)	Mar. 31, 2020USD ($)	Dec. 31, 2018ft²Sublease	Jun. 30, 2021USD ($)Milestone	Jun. 30, 2020USD ($)	Dec. 31, 2020USD ($)	May 31, 2018USD ($)ft²	Nov. 30, 2016USD ($)
Other Commitments [Line Items]
Sublease commencement period						2018-06
Sublease expiration period						2028-02
Property sublease, description						In May 2018, the Company entered into 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
Long-term deferred rent		$ 6,403				$ 6,403		$ 6,283
Deferred rent, current portion		555				555		555
Rent expense		1,600		$ 1,600		3,100	$ 3,100
Rental payments receivable		1,600				1,600
Research and development expense		11,129	$ 12,610			22,857	26,573
Research and Development Expenses [Member]
Other Commitments [Line Items]
Research and development expense						100
Long Term Deferred Rent [Member]
Other Commitments [Line Items]
Long-term deferred rent		6,400				6,400		6,300
Short Term Deferred Rent [Member]
Other Commitments [Line Items]
Deferred rent, current portion		600				600		$ 600
Maximum [Member] | Office and Lab Sublease [Member]
Other Commitments [Line Items]
Square feet of property subject to sublease | ft²									69,000
Tenant improvement allowance									$ 5,200
Sub-Sublease [Member]
Other Commitments [Line Items]
Square feet of property subject to sublease | ft²					27,000
Lease agreement maturity period					2 years
Number of Sub-sublease | Sublease					2
Other income from sub-sublease		700	700			$ 1,900	1,400
License Agreement with Novartis International Pharmaceutical Ltd. [Member]
Other Commitments [Line Items]
Number of milestones met | Milestone						0
License Agreement with Novartis International Pharmaceutical Ltd. [Member] | Maximum [Member]
Other Commitments [Line Items]
License agreement royalty percentage	20.00%
License Agreement with Novartis International Pharmaceutical Ltd. [Member] | Achievement of Clinical and Regulatory Milestones [Member] | Maximum [Member]
Other Commitments [Line Items]
Payment obligation	$ 177,000
License Agreement with Novartis International Pharmaceutical Ltd. [Member] | Development and Regulatory Milestones [Member] | Maximum [Member]
Other Commitments [Line Items]
Payment obligation	$ 125,000
Collaboration Agreement [Member] | Maximum [Member]
Other Commitments [Line Items]
Research and development expense		100	100			$ 400	$ 100
Collaboration Agreement [Member] | Development, Regulatory and Commercial Milestone [Member] | Per Target [Member] | Maximum [Member]
Other Commitments [Line Items]
Payment obligation		83,500				$ 83,500
License Agreement With Harvard [Member] | Maintenance [Member] | Annually Through 2019 [Member] | Maximum [Member]
Other Commitments [Line Items]
Payment obligation										$ 100
License Agreement With Harvard [Member] | Achievement of Development and Regulatory Milestones [Member] | Maximum [Member]
Other Commitments [Line Items]
Payment obligation										$ 7,400
License Agreement With Third Parties [Member] | License [Member]
Other Commitments [Line Items]
Research and development expense		$ 0	$ 0
Letter of Credit [Member] | Office and Lab Sublease [Member]
Other Commitments [Line Items]
Cash balance to secure letter of credit associated with sublease									$ 1,800

Commitments and Contingencies_2

Commitments and Contingencies - Schedule of Future Minimum Lease Payments Due Under Noncancelable Operating Lease (Detail) $ in Thousands	Jun. 30, 2021USD ($)
Operating Leased Assets [Line Items]
Remainder of 2021 (six months)	$ 3,097
2022	6,375
2023	6,734
2024	7,100
2025	7,455
Thereafter	17,444
Operating leases future minimum payments due	$ 48,205

Related Parties - Additional In

Related Parties - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Related Party Transaction [Line Items]
Amounts owed to related party	$ 0.1		$ 0.1		$ 0.1
Match Bio Therapies [Member]
Related Party Transaction [Line Items]
Expenses paid to related party	0.2	$ 0.1	0.3	$ 0.2
Match Bio Therapies [Member] | Prepaid Expenses and Other Current Assets [Member]
Related Party Transaction [Line Items]
Amounts owed to related party	$ 0.1		$ 0.1		$ 0.1