CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 112,493	$ 138,509
Short-term investments		1,474
Federal contract revenue receivable	4,201	1,646
Prepaid expenses and other current assets	4,230	4,638
Total current assets	120,924	146,267
Property and equipment, net	1,984	1,945
Other assets	2,081	2,250
Total assets	124,989	150,462
Current liabilities:
Accounts payable	3,311	2,211
Accrued expenses	13,383	8,518
Total current liabilities	16,694	10,729
Notes payable, net of deferred financing costs	10,970
Other long-term liabilities	2,266	2,534
Total liabilities	29,930	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 June 30, 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, 36,739,709 issued and 36,747,016 outstanding at June 30, 2021 and 36,585,767 issued and 36,578,460 outstanding at December 31, 2020	37	37
Additional paid-in capital	453,613	444,622
Treasury stock at cost, 7,307 shares at June 30, 2021 and December 31, 2020
Accumulated deficit	(362,893)	(311,929)
Total stockholders' equity	95,059	137,199
Total liabilities and stockholders' equity	$ 124,989	$ 150,462