Leukemia drug study halted over deaths

The FDA has temporarily halted a midstage Juno Therapeutics study on a potential leukemia treatment following two patient deaths.

The development-stage biotechnology company is testing genetically engineered immune cells known as CAR-T cells to treat acute lymphoblastic leukemia in adults. It is the company’s most advanced drug candidate and therefore the most visible indicator of progress for investors.

The Seattle-based company said Thursday that the study has been put on hold after it added the chemotherapy drug fludarabine to the regimen. It has proposed continuing the study without fludarabine.

Midstage studies focus on a potential drug’s effectiveness and are a key step in the development and eventual approval process.

Dr. Stephan Grupp, Novotny Professor of Pediatrics at the University of Pennsylvania Perelman School of Medicine, is running a similar trial funded by Novartis CAR T cells to treat pediatric leukemia patients.

He notes that none of the patients in his trial — most of whom received the same chemotherapy drug added to the patients in Juno’s trial — have experienced significant brain swelling. Side effects related to the central nervous system seen in a small number of his patients include confusion, aphasia and seizures, “but these effects have all resolved,” he said.

“Obviously, it is always hard to attribute toxicity to the chemo as opposed to the CAR-T cells when both are given around the same time, but we believe the self-limited CNS side effects we have reported from our study are more likely to be due to the T cells,” Grupp said. “Right now, I don’t see this affecting other CAR-T trials or the field as a whole, since this issue appears not be seen more broadly. There may be some discussion about the appropriate role of the drug fludarabine, but this wouldn’t be a central issue.”

Shares of Juno Therapeutics Inc. dropped $11.15, or 27.3 percent, to $29.66 in morning trading. Its shares have fallen almost 40 percent over the past year.