Alyssa, 13, was diagnosed with T-cell acute lymphoblastic leukemia last May. T cells are an important part of the body’s immune system, but Alyssa’s T cells became dangerous and out of control. Her cancer was malignant and neither chemotherapy nor a bone marrow transplant could cure it. With no experimental treatments available, Alyssa’s only option was a less painful death. Doctors at Great Ormond Street Hospital in London used an experimental ‘base editing’ technique and her cancer became undetectable six months later. Invented six years ago, base editing came as scientists refined the gene-editing tool CRISPR to more easily change individual “letters” of DNA in the genetic code, rather than inserting or deleting entire genes. In the study, the team of doctors and scientists started with healthy T cells donated by healthy donors: the first base editing shut down the T cell’s targeting mechanism to prevent it from attacking Alyssa; the second knocked out one of the T cells. Chemically marks CD7; the third edit is an invisibility cloak that prevents it from being killed by chemotherapy drugs. The final stage of base editing is to instruct the modified cells to seek out all T cells with CD7, killing any cancerous T cells. Alyssa is the first patient treated with base editing technology.
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