Lineage Commitment of HLA-DR/CD38-Defined Progenitor Cell Subpopulations in Bone Marrow and Mobilized Peripheral Blood Assessed by Four-Color Immunofluorescence

We used four-color fluorescence analysis to compare lineage antigen expression in relationship to CD38 and HLA-DR on CD34+ progenitor cells in adult human bone marrow and mobilized peripheral blood. Each of four progenitor cell subpopulations defined by HLA-DR and CD38 intensity (CD38–/HLA-DR–, CD38–/HLA-DR+, CD38+/HLA-DR+, and CD38+/HLA-DR–) were present in both progenitor cell sources in similar ratios. The most prevalent subpopulation consisted of cells that expressed both CD38 and HLA-DR. Virtually all progenitor cells that lacked CD38 also lacked lineage antigens regardless of their HLA-DR expression. In contrast, the majority of the cells within both CD38+ progenitor cell subpopulations possessed either lineage antigens or the proliferation-associated antigen, CD71. Furthermore, CD71 was expressed on three times the number of CD38⁺/HLA-DR– cells when compared with the CD38–/HLA-DR– subpopulation. Within CD34+ progenitor cell subpopulations defined by the expression of CD38 and HLA-DR, the CD38+/HLADR– component appears to be the most mature, based on the expression of CD71 and various lineage-associated antigens, including representative markers characterizing early lymphoid, myeloid, and erythroid precursors. Thus, selection of the most immature CD34+ progenitor cells based solely on the lack of HLA-DR expression results in isolation of two distinct cell populations with markedly different maturation status and resultant growth characteristics.