Biotechnology firm bluebird bio has reported positive long-term follow-up data from the Phase II/III Starbeam clinical trial of Lenti-D gene therapy in treating cerebral adrenoleukodystrophy (CALD).

CALD is a rare genetic disorder that could cause severe loss of neurologic function and death.

The Starbeam trial is designed to evaluate the safety and efficacy of Lenti-D in boys aged 17 and under. Its primary efficacy endpoint is the proportion of patients alive and free of major functional disabilities (MFDs) at 24 months.

MFDs are loss of communication ability, total incontinence, complete loss of voluntary movement, the need for tube feeding, cortical blindness and wheelchair dependence.

New data revealed that 88% of patients who received the gene therapy and reached follow-up of 24 months were free of major functional disabilities (MFDs) at two years and retained the response up to five years.

bluebird bio added that 14 participants who are currently on assessment have less than 24 months of follow-up and did not exhibit any evidence of MFDs.

Of the total 32 patients treated with Lenti-D, three did not or are expected not to meet the primary efficacy endpoint, while two discontinued the trial and one had rapid disease progression that led to death.

The trial’s secondary and exploratory efficacy outcomes include changes in neurologic function score (NFS), which is used to assess the gross neurologic dysfunction severity. Of the 32 treated subjects, 30 were observed to experience stable NFS.

Patients did not show any acute or chronic graft-versus-host disease (GvHD) events by month 24, the primary safety endpoint of the study.

The adverse events during the trial were generally consistent with myeloablative conditioning.

bluebird bio chief medical officer David Davidson said: “These results support the potential of Lenti-D as a treatment for CALD, which we hope may become an option for the boys and their families affected by this devastating disease.”

The company also announced favourable results from the ongoing observational study of allogeneic hematopoietic stem cell transplant (allo-HSCT) in CALD patients.