Shares of Juno Therapeutics were down more than 32 percent Friday after a clinical trial was put on hold.

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Shares of Seattle-based Juno Therapeutics opened down more than 20 percent Friday and continued to fall throughout the day.

The Seattle biotech announced Thursday that one of its most promising cancer treatment trials had been placed on clinical hold by the Food and Drug Administration following the deaths of two patients last week.

The two patients died from cerebral edema caused by neurotoxicity. Juno CEO Hans Bishop said in a conference call Thursday that the company believes the deaths were tied to the addition of a chemotherapy drug, fludarabine, into the treatment plan.

Bishop reiterated Juno’s commitment to the trial on the call with analysts Thursday. Juno will submit documents this week to the FDA to propose continuing the trial without fludarabine.

”We are optimistic that we will achieve results comparable to those obtained in the phase 1 trial….and address a significant unmet need in these patients, most of whom have exhausted all other therapies,” he said.

Juno’s “Rocket” trial treats adult patients with relapsed acute lymphoblastic leukemia by injecting patients with engineered T-cells that attack cancer cells.

Juno went public in 2014 in the largest biotech IPO of the year. The company’s share price closed at $27.81 Friday, down more than 31 percent from Thursday’s closing price.