Juno Therapeutics said that it will end development of the experimental CAR-T therapy JCAR015 in adults with relapsed or refractory acute lymphoblastic leukaemia (ALL) following safety issues observed in a mid-stage trial, including a greater than expected incidence of severe neurotoxicity and five patient deaths due to cerebral oedema.

In July last year, the FDA placed a clinical hold on the ROCKET study of JCAR015 following the deaths of two patients from cerebral oedema, although the agency lifted the hold soon after. In November, Juno subsequently voluntarily placed the trial on clinical hold after the death of two further patients who suffered cerebral oedema.

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Juno noted that following an investigation into the toxicity of JCAR015, the company identified multiple factors that may have contributed to this increased risk, including patient-specific factors, the conditioning chemotherapy patients received and factors related to the drug. Juno indicated that although protocol modifications and process improvements could enable development of JCAR015 to proceed, the associated delay prompted the drugmaker and partner Celgene to decide to halt the programme.

Juno CEO Hans Bishop explained that the company will instead "begin a trial with a defined cell product candidate in adult ALL next year."