Monoclonal antibodies detect subpopulations of bone marrow stem cells

Hybridomas secreting monoclonal antibodies cross-reacting with the mouse bone marrow stem cell (CFUs) have been derived from rats immunized with mouse thymocytes and platelets, cells which have been shown to exhibit antigenic lineage relationships with the stem cell. Anti-stem cell activity in hybridoma supernatants occurs at low frequency. Of 418 hybridomas screened, 6 showed initial positivity while two yielded stable cloned cell lines. Both of these monoclonal antibodies, 1C10 and 13C6, bind to subpopulations of stem cells in the bone marrow resulting in 50-65% inhibition of spleen colony formation in lethally irradiated mice. Protein-A binding studies showed the antibodies to be rat IgG. Quantitative absorption and indirect binding studies suggest that the antigens recognized by 1C10 and 13C6 monoclonal antibodies are minor components of the inoculating cell membrane. 1C10 and 13C6 bind to minor subpopulations of cells in the bone marrow, 13 and 5% of cells being rosetted, respectively, at plateau values. These results indicate that, used in conjunction with other monoclonal antibodies or selection tecniques, these antibodies may be useful in stem cell purification.