EARLY RECOVERY OF HOST-DERIVED HEMATOPOIESIS IN MARROW TRANSPLANT RECIPIENTS CONDITIONED WITH HIGH-DOSE BUSULFAN AND CYCLOPHOSPHAMIDE

Three marrow transplant recipients with hematologic malignancies (two AML, one myelodysplastic syndrome) experienced prolonged pancytopenia after allogeneic BMT following conditioning with non-TBI regimens cont aining high-dose busulfan and cyclophosphamide (Bu/CY), despite the us e of G-CSF. Early recovery of host-derived hematopoiesis ensued. Altho ugh neutrophil counts in these patients exceeded 500 x 10(6)/l by day 30 after transplant, these cells were of host origin. This early recov ery of host-derived hematopoiesis has been observed rarely among patie nts conditioned with TBI-based regimens. When patients conditioned wit h Bu/CY show delayed hematologic recovery, mixed chimerism should be c onsidered even in the presence of normal neutrophil recovery.