Alyssa Tapley, now 16, was the first person dosed with base edited CAR T cells, a gene editing tool that changes a single DNA letter without breaking the DNA strand. Beam Therapeutics is preparing to file the first such therapy for FDA approval by the end of 2026.
In May 2022, doctors at Great Ormond Street Hospital told the family of Alyssa Tapley, a 13-year-old from Leicester, that she had weeks to live. Her T-cell leukaemia had relapsed after a bone marrow transplant, and conventional options were exhausted. The team offered one last experiment: a cell therapy engineered with a tool most of the public had not heard of, base editing, a form of gene editing that rewrites a single letter of DNA at a time without cutting the strand in two. Four years later, the cells that put Alyssa into molecular remission are about to face the kind of scrutiny that only a regulatory filing brings.
Alyssa Tapley is now 16 and remains in remission, according to a [December 2025 long-term follow-up in Blood](https://www.sciencedirect.com/science/article/pii/S0006497125037887) and UCL News coverage of the same cohort. Her case, [first told in a New Scientist feature](https://www.newscientist.com/article/2532296-im-the-first-person-whose-life-was-saved-by-crispr-base-editing/), is the original proof that base-edited cells can be manufactured, infused, and made to persist in a human being. It is also the clinical evidence now anchoring a much bigger commercial story: the first regulatory submission for a base editor in the United States.
That submission is being prepared not by the London team, but by Beam Therapeutics, a Cambridge, Massachusetts biotech founded on the same David Liu lab technology used in Alyssa's cells. Beam's lead candidate, BEAM-101, is a base editor for sickle cell disease, and the company has told investors and trade press that it intends to file a Biologics License Application (BLA), the formal request for FDA marketing approval, "as early as the end of 2026." If that filing lands on schedule, the platform that began as a single compassionate-use experiment at a London children's hospital will have traversed from bedside to FDA submission in roughly four years, an unusually short arc for a gene therapy modality.
The speed matters because base editing is not the same product as the CRISPR therapy most readers have heard of. Vertex and CRISPR Therapeutics's Casgevy, approved by the FDA in December 2023 for sickle cell disease and beta thalassemia, uses a conventional CRISPR-Cas9 system. Cas9 works by cutting both strands of the DNA double helix and letting the cell's repair machinery rejoin them, which is powerful but introduces the risk of off-target cuts at unintended sites in the genome. Base editing skips the cut entirely. It uses a modified Cas protein fused to a deaminase enzyme to chemically convert one DNA base (a C, say) into another (a T) at a precise location. The result, in theory, is a more controllable edit with fewer of the genomic scars that have dogged earlier gene-editing clinical work.
Alyssa's case was designed to exploit that control. She had relapsed T-cell acute lymphoblastic leukaemia (T-ALL), a fast-moving blood cancer that arises from the very T cells a CAR-T therapy would normally be built from. The team at Great Ormond Street, led by consultant immunologist Prof Waseem Qasim at UCL's Great Ormond Street Institute of Child Health, manufactured universal "off-the-shelf" CAR-T cells from a healthy donor. To stop those donor cells from killing each other, attacking the patient, or being rejected by the patient's immune system, they used base editing to simultaneously disable three genes: CD7 (the leukaemia's marker), CD52 (a target of the preconditioning antibody), and TRAC (the T-cell receptor that would otherwise trigger graft-versus-host disease). The result was a stealth T cell, [described in the original New England Journal of Medicine report](https://pubmed.ncbi.nlm.nih.gov/37314354/) as a "T-cell Trojan horse" (TvT), invisible to the patient's defences and to its own kind, but lethal to the leukaemia.
Alyssa went into molecular remission within 28 days of infusion. The [December 2025 Blood paper](https://www.sciencedirect.com/science/article/pii/S0006497125037887) reports that the durability seen in the early cases has held up over years of follow-up, with no evidence of the chromosomal abnormalities or off-target editing events that have been the field's biggest theoretical worry. That is the safety record Beam Therapeutics is now leaning on as it pivots from oncology-adjacent, single-patient "n-of-1" use to a registrational dataset in a far more common disease.
The pipeline beyond BEAM-101 is broader than the sickle cell story suggests. Verve Therapeutics, a cardiovascular gene-editing biotech that has licensed base-editing targets from Beam, is running in vivo base-editing trials that edit genes directly inside the patient's body, in the liver, to lower cholesterol or other cardiovascular risk markers. If those work, they will mark the technology's first move out of the hospital cell-processing suite and into an outpatient injection.
The limits are still real. Alyssa's story is one patient, treated on a last-resort basis, in a single-arm Phase 1 trial. The "life was saved" framing is hers and her family's, and the reader should hold it alongside the trial data, not in place of it. Base editing's commercial path is also still on company guidance: Beam's BLA timing is management's projection, not a regulatory commitment, and an FDA filing that arrives "as early as" the end of 2026 could still slip into 2027. The FDA's prior approval of Casgevy, a different modality, does not pre-approve base editors; the agency will examine Beam's off-target editing data, manufacturing controls, and long-term safety follow-up on its own terms.
What to watch next: Beam's formal BLA filing announcement (expected late 2026 or early 2027), the FDA's decision on whether to convene an advisory committee for the application, and the first read-outs from Verve's in vivo cardiovascular base-editing trials. Alyssa, for her part, is now finishing school, four years past the date her doctors had given her.