Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Jul. 31, 2020	Jul. 31, 2019
Cash flows from operating activities
Net loss	$ (10,814)	$ (7,338)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	128	121
Stock-based compensation expense	1,188	1,074
Realized gain from sale of marketable securities	(70)	(29)
Non-cash operating lease expense	8	1
Amortization of premium on marketable securities	68	35
Foreign currency exchange (gain) loss	(432)	454
Changes in operating assets and liabilities:
Research and development tax credit receivable	4,462	(2,060)
Prepaid expenses and other current assets	1,301	561
Accounts payable	35	392
Accrued expenses	538	(1,117)
Deferred revenue		(3,369)
Net cash used in operating activities	(3,588)	(11,275)
Cash flows from investing activities
Purchases of marketable securities	(9,807)	(19,646)
Sales and maturities of marketable securities	15,342	18,214
Acquisition of property and equipment	(22)	(98)
Net cash provided by (used in) investing activities	5,513	(1,530)
Cash flows from financing activities
Issuance of common stock, net of offering expenses		11,422
Issuance of common stock from equity incentive plans	46	32
Finance lease principal payments		(54)
Net cash provided by financing activities	46	11,400
Effect of exchange rate changes on cash and cash equivalents	254	(494)
Net increase (decrease) in cash and cash equivalents	2,225	(1,899)
Cash and cash equivalents at beginning of period	15,789	32,006
Cash and cash equivalents at end of period	$ 18,014	30,107
Supplemental disclosures of cash flow information:
Acquisition of property and equipment in accounts payable		$ 47