Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Jul. 31, 2022	Jul. 31, 2021
Cash flows from operating activities
Net loss	$ (23,042)	$ (16,109)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	158	132
Stock-based compensation expense	2,642	2,795
Realized loss (gain) from sale of marketable securities	16	23
Non-cash operating lease expense	23	22
Amortization of premium on marketable securities	391	753
Foreign currency exchange loss (gain)	426	14
Changes in operating assets and liabilities:
Research and development tax credit receivable	(3,570)	(3,211)
Prepaid expenses and other assets	1,935	(625)
Accounts payable	(678)	(528)
Accrued expenses	(1,043)	(1,001)
Net cash used in operating activities	(22,742)	(17,735)
Cash flows from investing activities
Purchases of marketable securities	(10,102)	(19,036)
Sales and maturities of marketable securities	41,066	34,204
Acquisition of property and equipment	(920)	(287)
Net cash provided by investing activities	30,044	14,881
Cash flows from financing activities
Issuance of common stock from equity incentive plans	168	608
Net cash provided by financing activities	168	608
Effect of exchange rate changes on cash and cash equivalents	(339)	(3)
Net increase (decrease) in cash and cash equivalents	7,131	(2,249)
Cash and cash equivalents at beginning of period	30,732	50,592
Cash and cash equivalents at end of period	37,863	$ 48,343
Supplemental disclosures of non-cash activities:
Right of use assets obtained in exchange for operating lease liabilities	1,192
Property and equipment included in accounts payable and accrued expenses:	$ 144