Alyssa Tapley became the first person whose life was saved by CRISPR base editing, a cutting-edge genetic technique that directly rewrites DNA letters without cutting the double helix. At 13 years old, Tapley faced terminal acute lymphoblastic leukaemia after standard chemotherapy and other treatments failed.
Doctors at Great Ormond Street Hospital in London offered her an experimental procedure using base editing, developed by David Liu and colleagues at the Broad Institute of MIT and Harvard. This approach differs from conventional CRISPR gene editing, which requires cutting both strands of DNA and risks off-target mutations. Base editing converts one DNA letter into another with minimal damage.
In Tapley's case, clinicians used the technique to modify her own immune T cells, converting cytosine to thymine in genes that would normally restrict the cells' ability to attack cancer. This created customized cells capable of targeting her leukaemia more effectively. The edited cells were reintroduced into her body.
Within weeks of the treatment, her leukaemia entered remission. Two years later, she remains cancer-free with no sign of relapse.
The success marks a watershed moment for base editing, published in the New England Journal of Medicine. While CRISPR genome editing has already entered clinical practice, base editing represents a refinement that theoretically reduces unwanted genetic changes. The technique opens pathways for treating genetic diseases and blood cancers where conventional approaches prove inadequate.
However, the case represents a single patient outcome. Long-term safety data remains limited, and researchers must verify whether base-edited cells remain stable over decades. The procedure also required careful in vitro modification before reintroduction. Scaling this for broader use and optimizing delivery for in vivo applications present ongoing challenges.
Tapley's recovery demonstrates base editing's therapeutic potential but not yet its