The drug experienced a high profile late-stage failure, which Biogen later deemed successful enough to send on to the FDA. The Xirius trial failure may end up being just a slight blip on the radar of Biogen investors, who remain laser-focused on the aducanumab drama. Cotoretigene toliparvovec was not brought up on the company's first-quarter earnings call in April and was mentioned just in passing in recent analyst commentary. Biogen shares were trading fairly steadily as the market opened today.