PRIMITIVE HEMATOPOIETIC-CELLS IN MURINE BONE-MARROW EXPRESS THE CD34 ANTIGEN

The CD34 antigen is expressed on most, if not all, human hematopoietic stem cells (HSCs) and hematopoietic progenitor cells, and its use for the enrichment of HSCs with repopulating potential is well establishe d. However, despite homology between human and murine CD34, its expres sion on subsets of primitive murine hematopoietic cells has not been e xamined in full detail. To address this issue, we used a novel monoclo nal antibody against murine CD34 (RAM34) to fractionate bone marrow (B M) cells that were then assayed in vitro and in vivo with respect to d iffering functional properties. A total of 4% to 17% of murine BM cell s expressed CD34 at intermediate to high levels, representing a marked improvement over the resolution obtained with previously described po lyclonal anti-CD34 antibodies. Sixty percent of CD34(+) BM cells lacke d lineage (Lin) markers expressed on mature lymphoid or myeloid cells. Eighty-five percent of Sca-1(+)Thy-1(lo)Lin(-/lo) cells that are high ly enriched in HSCs expressed intermediate, but not high, levels of CD 34 antigen. The remainder of these phenotypically defined stem cells w ere CD34(-). In vitro colony-forming cells, day-8 and -12 spleen colon y-forming units (CFU-S), primitive progenitors able to differentiate i nto B lymphocytes in vitro or into T lymphocytes in SCID mice, and ste m cells with radioprotective and competitive long-term repopulating ac tivity were all markedly enriched in the CD34(+) fraction after single -parameter cell sorting. In contrast, CD34(-) BM cells were depleted o f such activities at the cell doses tested and were capable of only sh ort-term B-cell production in vitro, The results indicate that a signi ficant proportion of murine HSCs and multilineage progenitor cells exp ress detectable levels of CD34, and that the RAM34 monoclonal antibody is a useful tool to subset primitive murine hematopoietic cells. Thes e findings should facilitate more direct comparisons of the biology of CD34(+) murine and human stem and progenitor cells. (C) 1996 by The A merican Society of Hematology.