Functional differences between subpopulations of mobilized peripheral blood-derived CD34(+) cells expressing different levels of HLA-DR, CD33, CD38 and c-kit antigens

We have investigated the functional characteristics of peripheral blood-derived CD34(+) cells mobilized by a combination of chemotherapy and G-CSF (mobilized peripheral blood-derived [MPB] CD34(+) cells). In this study, subpopulations of MPB CD34(+) cells have been directly compared in clonal cultures, long-term cultures with bone marrow (BM) stromal cells, and single-cell cultures. MPB CD34(+) cells could be subdivided by expression levels of HLA-DR (DR), CD38, CD33 and c-kit antigens. The majority of MPB CD34(+) cells expressed DR and CD38 antigens. In contrast, approximately 60% and 20% of the MPB CD34(+) cells expressed CD33 and c-kit antigens, respectively. Interestingly, MPB CD34(+) cells can be subdivided into three fractions which express high, low or negative levels of c-kit receptor. All types of committed progenitors were observed in populations of CD34(+)DR(+), CD34(+)DR(-), CD34(+)CD33(-), CD34(+)CD38(+) and CD34(+) c-kit(low) cells. Colony forming unit-granulocyte/macrophage was highly enriched in the population of CD34(+)CD33(+) cells, whereas BFU-E was highly enriched in the population of CD34(+) C-kit(high) cells. In the population of CD34(+)CD38(-) cells, however, a few myeloid progenitors were detected. In addition, limiting dilution analyses clearly showed that the long-term culture-initiating cell (LTC-IC) is enriched in the populations of CD34(+)DR(-), CD34(+)CD33(-) and CD34(+)c-kit(- or low) cells, but very few in CD34(+) c-kit(high) cells, and that CD38 antigen is not a useful marker for the enrichment of LTC-IC derived from MPB CD34(+) cells. Moreover, single cell clone sorting experiments clearly demonstrated the functional differences between CD34(+)CD38(+) and CD34(+)CD38(-) cells as well as CD34(+) cells expressing different levels of c-kit receptor. Our results suggest that an immunophenotype of LTC-IC is different between BM-, cord blood- and MPB-derived CD34(+) cells and that primitive and committed progenitors existing in these sources may be functionally different.