Flow cytometric characterization of CD34+ hematopoietic progenitor cells in mobilized peripheral blood and bone marrow of cancer patients

Background. Hematopoietic progenitor cells (HPC), identified by expression of the CD34 surface antigen, show morphological and phenotypic heterogeneity in bone marrow (BM) and peripheral blood (PB). Methods. CD34⁺ HPC subpopulations present in 18 PB leukaphereses after high-dose chemotherapy in cancer patients and in 11 BM samples from patients with stage IA lymphoma were characterized. In order to identify CD34⁺ HPC subsets within these two compartments, the expression of lineage- or activation- associated antigens and the c-kit gene product (CD117) was studied by flow cytometry, using a large panel of monoclonal antibodies (MoAb) in double labelling. Results. We observed a higher proportion of CD34⁺/CD13⁺ and CD34⁺/CD33⁺ cells (myeloid commitment) in harvested leukapheresis products than in BM. On the contrary, a higher percentage of CD34⁺/CD10⁺ and CD34⁺/CD19⁺ cells (B-lymphoid commitment) was found in BM. The percentage of the most immature subset of CD34⁺ HPC (CD38^- and HLA-DR^-) was also higher in BM than in mobilized PB. No differences in proportions were found with respect to the expression of CD14, CD15, CD45RA (myeloid commitment), CD2, CD5, CD7 (T-lymphoid commitment), CD117, CD71 and CD45RO antigens. In terms of absolute values, however, significantly higher amounts of CD34⁺ HPC co-expressing CD13, CD33, CD5, CD7, CD71, CD117, CD45RA, CD45RO were detected in leukaphereses than in BM. The absolute number of immature HPC (CD34⁺/CD38^- and CD34⁺/HLA-Dr^-) was also significantly increased in mobilized PB. Conclusions. Our data confirm the heterogeneous phenotypic profile of HPC, thus supporting the hypothesis that different CD34⁺ subpopulations may have clinical relevance on the rapidity and long-term durability of engraftment in patients who undergo high-dose chemotherapy followed by rescue with HPC. We also demonstrated that mobilized PB is a particularly rich source of both primitive and committed HPC, more than BM.