Unexpected Deaths Put Promising Immunotherapy on Hold

The U.S. Food and Drug Administration halted an important study of immune therapy on Thursday after three patients died of toxic reactions.

The trial, being conducted by Juno Therapeutics of Seattle, is among the most advanced exploring the use of genetically modified T cells to treat cancer.

Juno said it believed the deaths, the result of brain swelling, were caused by a preconditioning treatment, fludarabine, not by the T cells themselves. According to Forbes, which first reported the FDA action, the study is expected to resume with modifications.

“Everyone here comes to work to develop cures, but this is humbling to all of us,” Juno CEO Hans Bishop said in a conference call with stock analysts yesterday afternoon.

Juno’s trial, called ROCKET, was seeking to erase cancers from the bodies of adults with acute lymphoblastic leukemia. That’s done by genetically modifying a patient’s immune T cells to attack the cancer.

Overall, about eight in 10 patients treated in Juno’s leukemia studies have seen their tumors disappear. But the treatments are extremely powerful. The same Juno program was put on hold in 2014 after two other patients died from immune reactions caused by the T cells.

In fact, by some measures, patient deaths in T-cell trials have been almost routine, including fatalities in studies by the National Cancer Institute and at the University of Pennsylvania.

The news of the trial’s suspension sent Juno’s stock down more than 30 percent. The company went public in 2014 in one of the largest biotech IPOs ever and had hoped to win approval by 2017, a deadline it is now unlikely to meet.

Instead, competitors such as Kite Pharma and Novartis could become the first to bring such a therapy to market. Kite’s treatment is being tested in non-Hodgkin’s lymphoma, another blood cancer, while Novartis is studying childhood leukemia.

Juno’s treatment, known as JCAR015, was being tested in adults facing their third or fourth bouts with leukemia. Such patients have very poor odds of beating the cancer, which makes testing risky treatments acceptable.

Michel Sadelain, the scientist at Memorial Sloan Kettering Cancer Center in New York who originally developed the T cell treatment being tested by Juno, says he only learned of the deaths this week. He says the fatalities did not occur in New York but at other centers participating in the trial. 

“We have not seen this particular complication in over 50 adult [leukemia] patients treated at MSK,” he says. “These new medicines are powerful and the field is still learning how to harness this power. I don't think these events change in any way the long-term potential for engineered T cells.”

(Read more: Forbes, Juno Therapeutics statement, “Biotech’s Coming Cancer Cure”)