A single dose of Bluebird Bio’s gene therapy for cerebral adrenoleukodystrophy (cALD) stabilized the disease in 15 of 17 patients over more than two years of follow-up.

The interim results from the phase 2/3 trial—which have been published in the New England Journal of Medicine—suggest that Bluebird’s Lenti-D (elivaldogene tavalentivec) therapy could be the first alternative to stem cell transplantation using cells donated by another person for children with CALD, who typically die before the age of 10.

The company says it is already engaged in discussions with the FDA and European regulators to find a pathway toward approval of the therapy, which involves harvesting stem cells from patients, modifying them with the Lenti-D vector and then reinfusing them after a conditioning chemotherapy regimen.

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CALD, commonly known as Lorenzo’s Oil disease, is a devastating neurodegenerative disease that primarily affects males and is caused by progressive destruction of the myelin sheath that surrounds nerves. The result is a relentless deterioration to a vegetative state or death within a few years of diagnosis.

Bluebird’s gene therapy “has effectively arrested the progress” of cALD in 88% of boys treated, said lead study author David Williams, M.D., of Boston Children's Hospital and the Dana-Farber/Boston Children's Cancer and Blood Disorders Center in a release. He cautioned, however, that more follow-up is needed to get a picture of the duration of response and the long-term safety of the therapy.

All patients who participated in the clinical trial were expressing functional ALD protein, which their bodies had been unable to produce prior to gene therapy. The 15 responding patients were all in the early stages of cALD at enrollment and met the primary objective of being alive and with no major functional disability 24 months after infusion of Lenti-D. One boy died as a consequence of the disease during the study, and another has progressed despite the treatment.

It is one of the largest gene therapy trials targeting a single-gene disease to be published to date and has been granted regulatory approval to expand the number of patients. The boys enrolled to date have been offered the chance to participate in a 13-year study to gauge their long-term response.

Williams said that because the therapy uses the patient’s own cells, it overcomes the challenges of finding a matched sibling donor which can delay or even prevent treatment.

“The founding of bluebird bio was based in large part on the potential for Lenti-D to benefit boys with cALD,” said David Davidson, M.D., the company’s chief medical officer, in the release. “It is encouraging to see patients doing clinically well more than three years following treatment for this rare and devastating disease.”

The new data is a boost for Bluebird, which has been trying to rebuild confidence in its gene therapy portfolio after its LentiGlobin candidate for sickle cell disease failed to hit the mark in a clinical trial.

Other companies working on new therapies for ALD include NeuroVia, which recently raised $14 million in a series A round to fund its small-molecule NV1205 candidate; Minoryx Therapeutics, which has a PPAR gamma agonist MIN-102 in phase 1/2 testing, and MedDay Pharma, which has said it expects to report phase 2b/3 results with its biotin-based MD1003 candidate by the end of this year.