Shares of Seattle-based biotech company Juno Therapeutics plunged in after-hours trading Thursday following news that its leading drug candidate led to two deaths last week.
The stock was down as much as 30% in late trading.
Juno, which has been developing a treatment called JCAR015 that uses genetically engineered cells to go after a form of adult leukemia, said that the phase 2 trial had been put on clinical hold by the Food and Drug Administration. The delay will push back the drug's approval timeline, which was expected to happen in 2017. In a call Thursday, Juno said it's now shooting for approval in 2018.
The type of treatment is known as CAR-T, or chimeric antigen receptor T cells. This kind of treatment, in Juno's case, uses a patient's own T cells, a type of blood cell that's involved our immune system response.
The two deaths happened after Juno added fludarabine, a chemotherapy drug, to the treatment patients received before going through the gene engineering process. A third death also occurred in May in a patient that was also receiving fludarabine.
"This is a humbling experience," Juno CEO Hans Bishop told Forbes. "No doubt it is difficult for the physicians who are looking after these patients and their families. Clearly these therapies are potent, that's why they offer the potential for cures. We're still learning to use them in the safest, most efficacious way."
*An earlier version of this post misstated when the deaths occurred. It was last week, not this week.
