Expression of HPCA-1 and HLA-DR antigens on growth factor- and stroma-dependent colony forming cells.

The expression of HLA-DR and HPCA-1 antigens (recognized by the L243 and BI.3C5 antibodies respectively) on adult human bone marrow cells was examined by fluorescence activated cell sorting and colony assays. Nearly all the (day 14) lineage restricted and multipotential colony forming cells analysed in methylcellulose cultures in the presence of added growth factors express HLA-DR and HPCA-1 determinants. Two colour cell sorting reveals that the lineage restricted HLA-DR positive progenitors express variable levels of BI.3C5 positivity whereas most of the multipotential progenitors, the multi-CFC or CFU-GEMM, are highly BI.3C5 positive. The isolated HLA-DR and BI.3C5 positive populations also contain haemopoietic precursors which adhere to and form colonies on pre-formed stromal layers. Thus, haemopoietic progenitors assayed in both types of culture system can be analysed and enriched by simultaneous two-colour sorting using anti-HLA-DR and BI.3C5 monoclonal antibodies. Similarities in the antigenic phenotype of such cells, however, precludes the use of these reagents for segregating growth factor-dependent from stroma-dependent progenitors.