Peripheral blood stem cells mobilized from patients with acute myeloid leukaemia have different platelet repopulating abilities compared with those mobilized from patients with other diseases.

Peripheral blood stem cell (PBSC) transplantation gives rapid recovery of neutrophils and platelets and sustained haemopoiesis. However in patients with acute myeloid leukaemia (AML) platelet recovery has a distinctive rapid rise and then secondary fall between 3 to 8 weeks post-transplant. This study compares platelet and neutrophil recovery after PBSC transplantation in 15 patients with AML and 29 patients with other diseases consecutively transplanted in a single unit. PBSC were collected during recovery from consolidation chemotherapy in AML patients and after cyclophosphamide or cytokine administration in the other patient groups. Mononuclear cell numbers collected were similar but CFU-GM numbers were greater from the AML patients. A significant secondary fall occurred only in the platelet count and only in AML patients. Long-term recovery of the platelet count was the same in AML as in the other patients. In AML patients, the fall was the same in the long term remitters as in those who eventually relapsed. Previous studies have not, demonstrated a difference in type of precursors mobilized by differing methods, but have not included AML patients. Megakaryocyte precursors were assayed in this study and showed no consistent differences in number between patient groups however pre-progenitor assays are not yet established especially in the megakaryocytic lineage. The possible explanation for this secondary fall in AML patients is discussed.