Editing single DNA letters erased a teenager's leukemia

Doctors at Great Ormond Street Hospital in London turned to an experimental therapy never used in a person before: donor immune cells with their DNA edited letter by letter so they would attack the cancer without attacking each other.

Researchers used base editing to change four genes in donor T cells, stripping markers that would let the cells be rejected or kill each other, then infused the engineered CAR7 cells into the girl in December 2022. Within a month her bone marrow showed no detectable leukemia.

A bone marrow transplant followed soon after to consolidate the remission, since the edited cells were not expected to last in her body indefinitely. She remained free of leukemia in follow-up reporting, but she is the only patient treated this way so far, and doctors are watching to see whether the approach works as well in others before calling it a cure.

One patient, four edited genes, one remission.