Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Jul. 31, 2021	Jul. 31, 2020
Cash flows from operating activities
Net loss	$ (16,109)	$ (10,814)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	132	128
Stock-based compensation expense	2,795	1,188
Realized loss (gain) from sale of marketable securities	23	(70)
Non-cash operating lease expense	22	8
Amortization of premium on marketable securities	753	68
Foreign currency exchange loss (gain)	14	(432)
Changes in operating assets and liabilities:
Research and development tax credit receivable	(3,211)	4,462
Prepaid expenses and other current assets	(625)	1,301
Accounts payable	(528)	35
Accrued expenses	(1,001)	538
Net cash used in operating activities	(17,735)	(3,588)
Cash flows from investing activities
Purchases of marketable securities	(19,036)	(9,807)
Sales and maturities of marketable securities	34,204	15,342
Acquisition of property and equipment	(287)	(22)
Net cash provided by investing activities	14,881	5,513
Cash flows from financing activities
Issuance of common stock from equity incentive plans	608	46
Net cash provided by financing activities	608	46
Effect of exchange rate changes on cash and cash equivalents	(3)	254
Net (decrease) increase in cash and cash equivalents	(2,249)	2,225
Cash and cash equivalents at beginning of period	50,592	15,789
Cash and cash equivalents at end of period	$ 48,343	$ 18,014