Investing.com -- Shares in Juno Therapeutic (NASDAQ:JUNO) tumbled as much as 30% on Thursday after the U.S. Food and Drug Administration placed a clinical hold on the Seattle-based drug company's experimental CAR-T trial to treat cancer, following the deaths of two Leukemia patients enrolled in their comprehensive study last week.
The hold has been placed on the Phase II clinical trial of JCAR015 adult patients with relapsed or refractory B cell acute lymphoblastic leukemia, known more commonly as the ROCKET trial. Typically, CAR-T therapies such as the one being undertaken by Juno, involve a complex process of engineering in which a patient's own immune cells are removed and identified to fight their own tumors. Once removed, the cells are genetically engineered to produce receptors that help T cells in the body recognize a specific protein in certain tumors. The cells are then grown in a laboratory setting until they increase exponentially before they are infused back into a patient's body in an effort to destroy the cancerous cells.
On Thursday, Juno Therapuetic said the two deceased patients were administered a chemotherapy agent known as Fludarabine in combination with a pre-conditioning regimen associated with the trial, which may have contributed to an increase in neurotoxicity that led to cerebral edema. Juno has made a proposal to the FDA to continue the ROCKET trial using JCAR015 with the pre-conditioning alone, the company said in a statement.
"We believe we have a clear path forward with this proposal," Juno Therapeutic CEO Hans Bishop said.
Addressing Wall Street analysts on a conference call on Thursday, Bishop said the company has systematically reviewed multiple potential factors that could have contributed to the increased levels of neurotoxicity. They include: patient characteristics, pre-conditioning, system management, product characteristics and cell dose, Bishop added. In addition, Bishop said the death of a third patient in May could have been related to cerebral edema brought about from the therapy.
"The hold will likely impact our ability to achieve our goal of getting (FDA) approval of JCAR015 as early as 2017," Bishop said.
Shares in Juno Therapeutics fell 11.32 or 27.73% to 29.50 in after-hours trading.