Condensed Consolidated Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Jul. 31, 2022	Jul. 31, 2021
Operating expenses:
Research and development	$ 18,186	$ 13,669
General and administrative	8,130	5,847
Total operating expenses	26,316	19,516
Operating loss	(26,316)	(19,516)
Other income:
Interest income	242	274
Foreign currency exchange (loss) gain	(517)	(51)
Other income	3,549	3,184
Total other income	3,274	3,407
Net loss	(23,042)	(16,109)
Other comprehensive (loss) income:
Foreign currency translation (loss) gain	(403)	49
Unrealized holding (loss) gain from marketable securities	98	(129)
Reclassification adjustment for realized loss (gain) on marketable securities included in net loss	16	23
Other comprehensive loss	(289)	(57)
Comprehensive loss	$ (23,331)	$ (16,166)
Net loss per share to common stockholders, basic	$ (0.94)	$ (0.66)
Net loss per share to common stockholders, diluted	$ (0.94)	$ (0.66)
Weighted average common shares outstanding, basic	24,557,615	24,429,919
Weighted average common shares outstanding, diluted	24,557,615	24,429,919