Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 56,779	$ 57,052
Marketable securities	68,771	55,862
Accounts receivable		2,000
Unbilled accounts receivable	657	531
Prepaid expenses and other current assets	2,304	4,065
Total current assets	128,511	119,510
Property and equipment, net	7,745	8,397
Restricted cash	1,092	1,092
Other assets	531	578
Total assets	137,879	129,577
Current liabilities:
Accounts payable	4,498	4,079
Accrued expenses and other current liabilities	7,643	7,267
Deferred lease incentive, current portion	469	469
Deferred revenue, current portion	9,900	14,910
Total current liabilities	22,510	26,725
Deferred rent, excluding current portion	1,662	1,649
Deferred lease incentive, excluding current portion	2,817	3,051
Deferred revenue, excluding current portion		2,971
Total liabilities	26,989	34,396
Commitments and contingencies (Note 12)
Stockholders’ equity:
Preferred stock, $0.001 par value; 5,000,000 shares authorized; no shares issued or outstanding
Common stock, $0.001 par value; 200,000,000 shares authorized; 32,706,863 and 28,067,402 shares issued as of June 30, 2021 and December 31, 2020, respectively; 32,659,740 and 27,941,566 shares outstanding as of June 30, 2021 and December 31, 2020, respectively	33	28
Additional paid-in capital	369,133	316,775
Accumulated other comprehensive loss	(9)	(2)
Accumulated deficit	(258,267)	(221,620)
Total stockholders’ equity	110,890	95,181
Total liabilities and stockholders’ equity	$ 137,879	$ 129,577