A 13-year-old girl named Alyssa has been totally cleared of a deadly, incurable cancer after doctors used a technology called “base editing” to build her a new, living medication. Alyssa was diagnosed with T-cell acute lymphoblastic leukemia in May of last year. With this particular type of cancer, the body’s T-cells—which are designed to fight off infections—instead mutate and multiply out of control. Despite trying chemotherapy and a bone marrow transplant, Alyssa’s cancer still persisted, and earlier this year she was given just months to live. In an amazing feat of science, however, a team of doctors and scientists were able to use an experimental new tool called “base editing” to engineer brand new T-cells—ones specially equipped to hunt and kill off Alyssa’s cancerous T-cells. After just one round of this new treatment, Alyssa has been declared cancer-free, and can now spend Christmas with her family