Five days after a cancer drug trial was paused due to three patient deaths, the trial is back on - and the stock is jumping

Shares of Seattle-based biotech company Juno Therapeutics jumped in after-hours trading Thursday after the company announced that its leading clinical trial was back on.

Juno, which has been developing a treatment called JCAR015 that uses genetically engineered cells to go after a form of adult leukemia, said Thursday that its phase 2 trial had been put on clinical hold by the Food and Drug Administration because of two patient deaths that occurred the week before. A third death had also occurred in May. The delay, Juno said, would push back the drug's approval timeline, which was expected to happen in 2017. In a call Thursday, Juno said it was now shooting for approval in 2018.

Five days later, the hold came off, so the trial could resume, and the stock jumped back up almost 30%.

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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 in our immune system response.

The two deaths happened after Juno added fludarabine, a chemotherapy drug, to the treatment that patients received before going through the gene engineering process. The death in May was also in a patient receiving fludarabine.

Now that it's resumed, the trial will not include fudarabine in its preconditioning program.