LONDON — Patients once told their T-cell acute lymphoblastic leukemia (T-ALL) was “incurable” are now disease-free after receiving a world-first base-edited CAR T cell therapy in an early-stage trial at Great Ormond Street Hospital and King’s College Hospital, with results just published in the New England Journal of Medicine. The experimental BE-CAR7 treatment re-writes donor immune cells so they can seek and destroy CD7-positive leukemia while avoiding the “friendly fire” that hampers conventional CAR T approaches, Dec. 10, 2025.
In the phase 1 study, 11 children and adults with relapsed or refractory T-ALL who had exhausted chemotherapy and transplant options received a single dose of BE-CAR7, then proceeded to stem cell transplant once their leukemia was cleared. In a recent UCL announcement, the team reported that 82% of patients entered very deep remission and about 64% remain disease-free up to three years later — striking outcomes for a group previously facing palliative care.
How base-edited CAR T works
Unlike standard CAR T therapies, which engineer each patient’s own T cells, base-edited CAR T starts with T cells from healthy donors. Using base editing — a version of CRISPR that swaps single DNA “letters” without cutting the double helix — scientists delete the native T-cell receptor and two surface markers, CD7 and CD52, then add a chimeric antigen receptor that targets CD7 on malignant T cells.
The result is a base-edited CAR T product that can attack leukemia cells, avoid attacking itself and be manufactured and banked in advance as an off-the-shelf “living drug.” Waseem Qasim, a professor of cell and gene therapy at University College London who led the work, said the prospect of routinely rewriting donor immune cells to cure resistant leukemia “would have been science fiction” only a few years ago.
From first-in-human case to early trial
The therapy’s story began with a single teenager. In 2022, Alyssa, then 13, became the first person in the world to receive this form of base-edited CAR T for resistant T-ALL, entering remission within a month and going on to a bone marrow transplant that rebuilt her immune system, as described in the world-first use of base-edited CAR T-cells in 2022.
Interim results from the first three patients were later reported in 2023 as a phase 1 study in the New England Journal of Medicine, showing that base-edited CAR7 cells could induce molecular remissions with manageable toxicities. The newly published data, which add more children and adults to the original cohort, suggest those early signals can be reproduced in a larger group.
Cautious optimism and remaining risks
The expanded results have been greeted with cautious optimism beyond the trial centres. In an analysis from Blood Cancer UK, experts called the trial a major step forward for the roughly one in five T-ALL patients whose disease does not respond to standard treatment, noting that base-edited CAR T followed by transplant may offer some families their first realistic chance of cure.
Doctors involved in the study stress that BE-CAR7 remains experimental. The trial is small, has no control arm and depends on intensive follow-up stem cell transplantation, and some patients did not respond or later relapsed despite therapy. Side effects such as low blood counts, cytokine release syndrome and viral infections were common but generally manageable within experienced specialist centres.
Researchers are now extending the trial and exploring how base-edited CAR T might be tested in larger, multi-centre studies, and whether some patients might eventually avoid transplantation altogether. Before the approach can move beyond a handful of expert units, questions around large-scale manufacturing, long-term immune recovery and cost will have to be answered — but for patients once labelled “incurable,” base-edited CAR T has already shifted expectations of what gene editing can do in the clinic.
