More than 95% of patients in three clinical trials had their immune systems restored, says the study published in The New England Journal of Medicine.

A novel form of gene therapy developed by UCLA and Great Ormond Street Hospital in London has effectively treated 48 of 50 infants born with a rare and fatal hereditary condition that makes them immune deficient.

Mutations in the ADA gene, which produces the enzyme adenosine deaminase, which is required for a healthy immune system, cause severe combined immunodeficiency due to adenosine deaminase deficiency, or ADA-SCID. Even routine activities such as going to school or playing with friends can lead to serious, life-threatening infections in children with the illness. ADA-SCID can be deadly in the first two years of life if left untreated.

First, a sample of the child’s blood-forming stem cells, which have the capacity to generate all types of blood and immune cells, is taken for use in the gene therapy research. An “viral vector” (a modified lentivirus) is then used to transfer a new copy of the ADA gene into the stem cells, according to the researchers’ unique method. To ensure a continuous supply of healthy immune cells that can fight illness, these repaired cells are returned to the child’s body.

Dr. Donald Kohn of UCLA and Dr. Claire Booth of Great Ormond Street Hospital, or GOSH, co-lead authors in a study published in the New England Journal of Medicine, report two and three-year outcomes for children treated with the investigational lentiviral gene therapy in clinical trials between 2012 and 2017.

“Between all three clinical trials, 50 patients were treated, and the overall results were very encouraging,” said the study authors.

“All the patients are alive and well, and in more than 95% of them, the therapy appears to have corrected their underlying immune system problems.”

There were no documented side effects or treatment-limiting occurrences among the participants. In most cases, the mild or moderate side effects of the gene therapy treatment or the re-building of the immune system were attributed to normal procedures or the actions of the immune system.

“Treatment was successful in all but two of the 50 cases, and both of those children were able to return to current standard-of care-therapies and treatments, with one eventually receiving a bone marrow transplant,” added the study authors.

For children with ADA-SCID, a one-time operation that may yield lasting results is a welcome new therapeutic option. Until a matched bone marrow donor, generally a close relative, can be found, they must continue to receive injections of the ADA enzyme. Lifelong injections, combined with antibiotics, antifungal medicines, and monthly immunoglobulin infusions, are required if a donor is not available. Patients in many nations cannot afford these treatments because they are so pricey.

“If approved in the future, this treatment could be standard for ADA-SCID, and potentially many other genetic conditions, removing the need to find a matched donor for a bone marrow transplant and the toxic side effects often associated with that treatment”.

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