GM 58/8: a monoclonal antibody that identifies a new lineage-specific determinant expressed by myeloid progenitors (CFU-GM) and their progeny.

A cytotoxic (IgM) monoclonal antibody (McAb) raised against human erythroleukaemia cell line HEL appears specific for the myelomonocytic lineage. Indirect immunofluorescence and fluorescence-activated cell sorter analyses of peripheral blood and bone marrow cells showed that this McAb (designated GM 58/8) reacts exclusively with more than 90% of the granulocytes, monocytes and myeloid precursors. The positive (fluorescent) fraction sorted from McAb-treated bone marrow buffy coat cells showed a marked enrichment of myeloid precursors, while nonmyeloid cells were recovered in the negative fraction. GM 58/8 specifically inhibited the growth of 90-100% of the committed myelomonocytic progenitors (CFU-GM) in five complement-mediated cytotoxicity experiments. GM 58/8 had virtually no effect on the erythroid progenitor (BFU-E and CFU-E) growth. Cell sorting experiments using this McAb resulted in recovery of 84% of CFU-GM among the fluorescent fractions. Comparisons with other anti-myelomonocytic McAbs reported so far suggest that GM 58/8 has more restricted reactivity and shows more efficient CFU-GM cytotoxicity. Patterns of reactivity with normal cells and established lines indicate that the antigenic determinant identified by GM 58/8 is different from that recognized by previously described anti-myelomonocytic McAbs. McAb GM 58/8 could be used to isolate or remove pure populations of progenitors and/or more differentiated cells of the myelomonocytic lineage for in vitro studies. This study also provides evidence that the HEL cell line, derived originally from an erythroleukaemia patient, expresses an antigenic determinant shared by the normal cells of myelomonocytic lineage.