IDENTIFICATION OF MEGAKARYOCYTE PRECURSORS IN PERIPHERAL-BLOOD STEM-CELL COLLECTIONS FROM NORMAL DONORS

Platelet engraftment, the time course and magnitude of platelet recove ry (PR) post-transplant, is imprecisely defined but is most often repo rted as the time to transfusion (tx) independence and/or a platelet co unt greater than or equal to 20,000/mu l. While correlations between e ngraftment time for granulocytes (PMN) and the dose of CD34-positive c ells per kilogram are established, such associations have not been est ablished for platelet engraftment. The objective of this study was to quantify subpopulations of CD34-positive cells in peripheral blood ste m cell (PBSC) collections of normal, colony-stimulating factor-granulo cyte) (G-CSF) primed donors that might represent megakaryocyte (MK) pr ecursors, and to determine whether there is a statistical association between the dose transfused and the time course of the recovery. Based on previously published data of the sequential expression of CD34, HL A-DR, and CD61, among others, during MK maturation, a combination of c orresponding antibodies for the detection of various antigen coexpress ions by now cytometry fluorescence-activated cell sorting [FACS] was c hosen. CD34-positive cells were further subdivided into CD34++ (bright ) and + (dim). Ploidy of density-gradient separated cells was examined in subsequent donor samples by FAGS. For the entire group of patients , there was no strong correlation between any of the studied subpopula tions and time to PR. Only in a selected groups of patients whose plat elet counts showed a sustained increase during the first 6 days after engraftment, there was a weak correlation between the time to PR and t he quantity of CD34+/+CD61+ (r = -0.57) and CD34++HLA-DR-CD61+ (r = -0 .62) cells infused. The magnitude of platelet production in these pt., a product of the peripheral blood platelet count and the patient's bl ood volume, was correlated with the time to PR (r = -0.73). We conclud e from this study that subpopulations within CD34+ cells are making so me contribution to PR in allogeneic peripheral blood stem cell transpl antation, but the correlations are not sufficiently strong because the re are probably too many unpredictable and unknown variables in the al logeneic setting that influence the pattern of engraftment. (C) 1998 W iley-Liss, Inc.