CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 122,927	$ 138,509
Short-term investments		1,474
Accounts receivable	2,629	1,646
Contract asset	557
Prepaid expenses and other current assets	5,565	4,638
Total current assets	131,678	146,267
Property and equipment, net	2,499	1,945
Other assets	2,663	2,250
Total assets	136,840	150,462
Current liabilities:
Accounts payable	3,126	2,211
Refund liability	21,233
Accrued expenses	16,207	8,518
Total current liabilities	40,566	10,729
Notes payable, net of deferred financing costs	40,809
Other long-term liabilities	1,979	2,534
Total liabilities	83,354	13,263
Stockholders' equity:
Series A convertible preferred stock, $0.001 par value; 25,000,000 shares authorized, 4,575 shares issued and outstanding at December 31, 2021 and 4,753 issued and outstanding at December 31, 2020	4,302	4,469
Common stock, $0.001 par value; 150,000,000 shares authorized, 36,797,561 issued and 36,790,254 outstanding at December 31, 2021 and 36,585,767 issued and 36,578,460 outstanding at December 31, 2020	37	37
Additional paid-in capital	459,852	444,622
Treasury stock at cost, 7,307 shares at December 31, 2021 and December 31, 2020
Accumulated deficit	(410,705)	(311,929)
Total stockholders' equity	53,486	137,199
Total liabilities and stockholders' equity	$ 136,840	$ 150,462