CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Operating activities
Net loss	$ (22,521)	$ (19,342)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	1,410	404
Depreciation	764	903
Amortization (accretion) of available-for-sale securities	357	(46)
Changes in operating assets and liabilities:
Accounts receivable from related party	(482)
Prepaid expenses and other current assets	(1,534)	251
Accounts payable	10	75
Accrued expenses and other current liabilities	1,356	(159)
Deferred rent and lease incentive	(288)	(241)
Deferred collaboration liability	(948)	(1,860)
Other long-term liabilities	(79)	185
Net cash used in operating activities	(21,955)	(19,830)
Investing activities
Purchases of available-for-sale securities	(147,223)
Proceeds from maturities of available-for-sale securities	26,530	13,750
Proceeds from sale of property and equipment	42
Purchases of property and equipment	(102)	(151)
Net cash (used in) provided by investing activities	(120,753)	13,599
Financing activities
Proceeds from the issuance of Series D convertible preferred stock	27,400
Proceeds from issuance of common stock upon completion of initial public offering net of commissions and underwriting discounts	128,240
Payment of initial public offering costs	(3,255)
Proceeds from the exercise of stock options	18
Principal payments on equipment financing	(94)
Repurchases of early exercised restricted stock	(1)
Net cash provided by financing activities	152,308
Net increase (decrease) in cash, cash equivalents and restricted cash	9,600	(6,231)
Cash, cash equivalents and restricted cash at beginning of period	29,218	20,039
Cash, cash equivalents and restricted cash at end of period	38,818	13,808
Supplemental disclosure of non-cash activities:
Vesting of early exercised restricted stock	$ (9)	$ (27)