Expression of a novel human pan leucocyte differentiation antigen on leukaemic cells

A murine monoclonal antibody has been produced which identifies a novel surface membrane antigen present on virtually all normal human leucocytes and leukaemic cells. The antibody, designated WM-65, reacted with over 95% of peripheral blood, tonsil and thymic lymphocytes, and with a similar proportion of monocytes and granulocytes. A majority of nucleated normal bone marrow cells were also reactive with WM-65; however, these included only a small proportion of myeloid progenitor cells. WM-65 reacted with a wide range of acute and chronic leukaemias of both myeloid and lymphoid types, and with corresponding cell lines, but did not react with non-haemopoietic cells. By immunoprecipitation and SDS-PAGE, WM-65 identifies a heavily glycosylated surface protein of molecular weight between 40 and 50 kD. This property, and the broad non-lineage-specific distribution of the antigen on haemopoietically-derived cells, indicates that WM-65 is different from other monoclonal antibodies with “leucocyte common” reactivity patterns. The extensive reactivity of WM-65 with leukaemic cells raises the possibility of therapeutic applications of the antibody in haematological malignancies.