Human CD34 is coexpressed with early hematopoietic surface markers in bone marrow and down-regulated with differentiation.

(A) Flow cytometric analysis of human and murine CD34 staining of bone marrow cells from a transgenic mouse (right panel) and a wild-type littermate (left panel). (B) Flow cytometric analysis of bone marrow cells from human CD34 transgenic animals demonstrates a decrease in transgene expression with differentiation. Coexpression of lineage-specific cell surface markers was performed to define the expression pattern with cell maturation. Double-positive populations were detected when costaining for markers found on cells corresponding to a more immature phenotype (Sca-1, c-Kit, and Thy1) whereas a decrease in double-staining cells was detected when costaining for markers defining more mature phenotypes (myeloid markers Gr-1 and Mac-1, and T-cell markers CD4 and CD8). A significant percentage of human CD34⁺ cells are Thy1 positive; murine stem cells have a Thy1^lo phenotype.48 A small percentage of the human CD34⁺ cells express Mac-1, which has also been detected on murine stem and progenitor cells,59-61 and the pan-B cell marker B220, which is expressed on pro-B cells62 and has also been detected on murine CD34⁺ cells.47