Juno Therapeutics has put a stop to the development of its experimental leukaemia therapy following the deaths of five trial patients. 

The candidate, known as JCAR015, is a type of chimeric antigen receptor (CAR) T-cell immunotherapy which activates the immune system to kill cancer cells.

The therapy was being tested in patients with relapsed/refractory B-cell acute lymphoblastic leukaemia (ALL) as part of its phase 2 ROCKET trial.

Development of the treatment had been put on hold four months previous following the deaths of two additional patients to the three that died in July.

All five deaths so far have been the result of cerebral oedema – an excess accumulation of fluid in the intracellular or extracellular spaces of the brain.

“We have decided not to move forward with the ROCKET trial or JCAR015 at this time, even though it generated important learnings for us and the immunotherapy field,” said Juno president and CEO Hans Bishop. “We remain committed to developing better treatments for patients battling ALL and believe an approach using our defined cell technology is the best platform to pursue.

In keeping with his statement, Juno intends to launch a new trial in adult ALL next year, however, which therapy will be investigated has not been detailed.

The company’s other CAR-T therapy, JCAR017, has shown promising phase 1 results in non-Hodgkins lymphoma (NHL). In preliminary data released in December, the therapy led to an 80% overall response rate and 60% complete response rate in relapsed/refractory aggressive NHL.

Unlike JCAR015, JCAR017 relies on a “secondary signal” that amplifies its activaation of CAR-T cells, leading to a better signal for T-cells to multiply and kill cancer cells, according to Juno.

In contrast to Juno’s difficulties, Kite Pharma recently unveiled positive data for its CAR-T candidate. The drug resulted in an objective response rate of 82% in patients with chemorefractory aggressive B-cell NHL.