Primary Graft Failure but Treatment Success: A Case of Reversion to Heterozygosity After Allogeneic Hematopoietic Cell Transplantation With Autologous Hematopoietic Recovery in a Child With CBL-related Juvenile Myelomonocytic Leukemia.

Juvenile myelomonocytic leukemia (JMML) typically requires allogeneic hematopoietic cell transplantation with full donor chimerism for cure. Certain genetic subtypes, including JMML due to germline mutations in CBL, can have a more indolent course. We describe a young male patient with CBL-related JMML who experienced primary graft failure after allogeneic hematopoietic cell transplantation. Despite autologous recovery, the resulting hematopoietic tissue did not harbor the original homozygous CBL mutations, due to reversion of prior loss of heterozygosity of the 11q chromosomal region. The patient remains disease free without further leukemia-directed therapy.