CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 123,472	$ 138,509
Short-term investments		1,474
Federal contract revenue receivable	2,650	1,646
Prepaid expenses and other current assets	3,676	4,638
Total current assets	129,798	146,267
Property and equipment, net	1,894	1,945
Other assets	2,167	2,250
Total assets	133,859	150,462
Current liabilities:
Accounts payable	5,167	2,211
Accrued expenses	10,954	8,518
Total current liabilities	16,121	10,729
Other long-term liabilities	2,404	2,534
Total liabilities	18,525	13,263
Stockholders' equity:
Series A convertible preferred stock, $0.001 par value; 25,000,000 shares authorized, 4,753 shares issued and outstanding at March 31, 2021	4,469	4,469
Common stock, $0.001 par value; 150,000,000 shares authorized, 36,640,797 issued and 36,633,490 outstanding at March 31, 2021 and 36,585,767 issued and 36,578,400 outstanding at December 31, 2020	37	37
Additional paid-in capital	449,898	444,622
Treasury stock at cost, 7,307 shares at March 31, 2020 and December 31, 2020
Accumulated deficit	(339,070)	(311,929)
Total stockholders' equity	115,334	137,199
Total liabilities and stockholders' equity	$ 133,859	$ 150,462