Juno Therapeutics said Thursday that the Food and Drug Administration has put a clinical hold on a phase 2 clinical trial of one of its products after two patients died last week.
After a trading halt, the stock reopened down about 30 percent in after-hours trading.
The trial included adult patients with either relapsed or refractory B cell acute lymphoblastic leukemia.
The company said that the deaths occurred after it added fludarabine, a chemotherapy drug, to its pre-conditioning regimen. Juno suggested to the FDA that clinical trials continue using cyclophosphamide pre-conditioning on its own.
The FDA has asked Juno to submit a complete response to the hold, which would require the company to revise documents like an informed consent form and trial protocol. Juno said it would submit the materials this week.
Juno said that trials and plans for other CAR-T cell product candidates are not affected.
CAR-T therapies involve a complicated process of extracting immune system T cells from an individual patient, altering their DNA so that the cells can better spot and kill cancer cells and infusing them back into the same patient.
The company had previously anticipated approval by 2017.