Functional Differences between Subpopulations of Mobilized Peripheral Blood‐Derived CD34+Cells Expressing Different Levels of HLA‐DR, CD33, CD38 and c‐kit Antigens

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Abstract
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‐kitlow 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‐kithigh 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‐kithigh 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.

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