Recipient Cells Are the Source of Hematologic Malignancies After Graft Failure and Mixed Chimerism in Adults with SCD

Non-myeloablative hematopoietic cell transplantation (HCT) is a curative option for individuals with sickle cell disease (SCD). Our traditional goal with this approach has been to achieve a state of mixed donor/recipient chimerism. Recently, we reported an increased risk of hematologic malignancies (HMs) in adults with SCD following graft failure or mixed chimerism. To evaluate the origin of HMs, we performed chimerism analyses of 5 patients with SCD who developed HMs after non-myeloablative HCT. DNA was extracted from sorted peripheral blood or bone marrow cells representing mature cell lineages or leukemic blasts and subjected to chimerism analysis by PCR amplification of polymorphic short tandem repeats. Unlike mature cell lineages in patients with mixed chimerism, which still showed a donor-derived fraction of cells, leukemic blast cells were found to be 99-100% recipient-derived in all patients. Non-myeloablative conditioning allows for the survival of patients’ cells that might harbor pre-leukemic clones that possess the capacity to evolve under genotoxic or environmental stress into malignancies; therefore, we have modified our HCT protocols with the goal of full donor chimerism to mitigate the risk of HM development.