Last year, Bluebird Bio claimed anFDA breakthrough designation for its Lenti-D gene therapy for cerebral adrenoleukodystrophy (CALD) it has now revealed additional data to support a fast-track approval.

The updated results from the biotechs phase 2/3 Starbeam study were revealed at the European Paediatric Neurology Society (EPNS) congress in Athens, Greece.

CALD is caused by progressive destruction of the myelin sheath that surrounds nerves responsible for thinking and muscle control, resulting in a relentless deterioration that typically leads to a vegetative state or death within a few years of diagnosis. The condition mostly affects young males, with the majority of patients dying before the age of ten.

The only current treatment for the disease is stem cell transplant, but it carries a significant risk from the high-dose chemotherapy used to prepare patients for the procedure. Other potential complications include graft-versus-host (GvHD) disease, when the transplanted cells recognise the recipients cells as foreign and attack them.

Bluebird's treatment works by extracting patients' stem cells and modifying them with Lenti-D. They are then infused back into the patient, where they thenhave the potential to develop into multiple cell types that can produce a functional version of the ALD protein that is lacking in CALD.

Of the patient population involved in the study, as of 25 April 2019, 15 had completed the trial and are enrolled in a long-term follow-up study, 14 are currently still on-study, and three are no longer on-study.

The primary efficacy endpoint of the study is the number of patients who are alive and free of MFDs at month 24 MFDS are the six severe disabilities commonly attributed to CALD, which have the most severe effect on a patients ability to function independently.

The study demonstrated that of those patients who have or would reach 24 months of followup and complete the study, 88% continue to be MFD-free and alive. The 14 patients currently on study have less than 24 months of follow-up and have so far shown no evidence of MFDs.

Out of the 32 treated patients, three did not or will not meet the primary efficacy endpoint, two patients withdrew from the study and one experienced rapid disease progression early, which lead to MFDs and death.

The primary safety endpoint the number of patients experiencing GvHD by month 24 was also met. According to Bluebird, no events of acute or chronic GvHD were reported posttreatment and there were no reports of graft failure, cases of insertional oncogenesis or replication competent lentivirus. There were three adverse events potentially related to treatment of Lenti-D, but these resolved using standard measures.

Lenti-D is Bluebirds lead gene therapy programme,but the company has also made significant progress with its Celgene-partnered CAR-T cancer immunotherapy programme, reporting dramatic responses with its multiple myeloma candidatebb2121 last December.

It also received approval for its gene therapy Zynteglo earlier this year. The one-time gene therapy has been approved for patients 12 years and older with transfusion-dependent -thalassaemia (TDT), and has been shown in a series of small studies to free a majority of patients from the need to have regular blood transfusions.

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Bluebird bio reveals further encouraging data for CALD gene therapy - PMLiVE