Kinetics and immunophenotypic characterization of circulating hematopoietic progenitor cells after peripheral blood...

Hematopoietic progenitor cells (HPC) circulate in the peripheral blood (PB) before and after engraftment following autologous or allogeneic peripheral blood stem cell transplantation (PBSCT), although the characteristics of these cells are not known. CD34 protein is a reliable marker for identifying the fraction of hematopoietic cells in which HPC are contained. The CD34(+) cells represent a heterogeneous cell population consisting of both primitive uncommitted as well as pluripotent committed progenitors. The aim of this study was to investigate the kinetics and immunophenotypic characteristics of these post-transplant circulating progenitor cells.

Forty-seven auto-PBSCT and nine allo-PBSCT recipients were selected for this study. Samples of PB were taken from each patient 4, 9, 11, 14, 16 and 18 days after the transplant. Cells were incubated with the following combinations of monoclonal antibodies: CD34-FITC/CD90-PE/CD38-CyCrome; CD34-FITC/CD117-PE/HLA-DR-PerCP; CD34-FITC/CD13-PE/CD33-CyCrome and the cells were then analyzed by flow cytometry.

CD34(+) cells were undetectable on day +4; they reappeared from day +9 to day +18 along with neutrophil and platelet recovery. Subsets of CD34(+) HPC enriched in pluripotent stem cells (CD90(+)/CD38(low) or HLADR-) were hardly detected during the very early post-transplant period. HPC that expressed myeloid associated antigens (CD33, CD13, and CD117) increased after engraftment and constituted the largest proportion of the hematopoietic progenitor cells.

Circulating HPC could be detected in the early period after PBSCT. The qualitative and quantitative composition of these cells is similar to that found among HPC from mobilized PB.