B cell acute lymphoblastic leukemia (ALL) in donor cells following bone marrow transplantation for T cell ALL

Leukemia recurred in a child with acute lymphoblastic leukemia after a bone marrow transplant. The pre-transplant leukemia was of T cell origin whereas the post-transplant relapse leukemia was of B cell origin. The recurrence was shown to be in donor cells by analysis of chromosomes and restriction fragment length polymorphisms. Although the mechanism of leukemia induction is uncertain, the possibilities of donor relapse due to EBV infection or chromosomal exchange were disproven. An alternative mechanism must account for leukemia induction in this patient.