A joint UCL–UCLA team reported multi‑year follow‑up showing a gene therapy approach restored immune function in 95% of treated children with ADA‑SCID, with no serious long‑term safety signals reported. The study, published in The New England Journal of Medicine, presents durable correction of the underlying enzyme deficiency. Researchers used a lentiviral vector to deliver a functional ADA gene to patients’ hematopoietic stem cells, leading to sustained immune reconstitution and elimination of severe infections that define the disease. Investigators emphasize the therapy’s curative potential compared with lifelong enzyme replacement or the risks of transplant. Authors and clinical teams highlighted consistent engraftment and immune recovery across treated patients; they note broader access and manufacturing scale remain challenges for wider adoption. The milestone strengthens the case for gene therapies as curative options in rare pediatric immunodeficiencies.