A single-cell solution to a transplant mystery.

In this Backstory, the authors recount how tailored single-cell sequencing solved a diagnostic puzzle in a young woman who developed myelodysplastic neoplasm after allogeneic hematopoietic stem cell transplantation. Conventional diagnostics could not determine whether the mutant clone was donor- or recipient-derived. Combining transcriptome profiling with targeted U2AF1 enrichment pinpointed the clone's origin and guided a second transplant, leading to remission.