Characterization of HLA-DR antigens on leukaemic cells

A large series of leukaemias (1,512 cases) and leukaemic cell lines (40) have been tested for selective expression of a monomorphic HLR-DR determinant using a monoclonal antibody (DA2). Relatively mature myeloid leukaemias (APML, CGL) and erythroid leukemias are DR-, in contrast to most (72% leukaemias of myeloid precursors (e.g. AML) which are DR+. Non-T ALL are DR+ but T (thymic) ALL are invariably DR-. In contrast to the latter, some leukaemias with mature T cell phenotypes are DR+. Leukaemias or lymphomas of B cells and B cell precursors (e.g. pre-BALL) are invariably DR+, whereas myeloma or plasma cell leukaemias are DR-. This pattern of selective expression appears to closely parallel that seen in normal haemopoietic differentiation. Biochemical features of HLA-DR structures on leukaemic cells have been compared with the known features of B cell derived DR molecules and in one case ALL compared with an autologous (EBV transformed) B cell line. Most leukemic cells showed the same general alpha and beta two chain structure. However, B cell line and most chronic leukaemias showed the presence of an extra band of molecular weight 30,000 daltons (p30) with an intermediate electrophoretic mobility on SDS-PAGE between that of the alpha and beta DR chains. In acute leukaemias and leukaemic cell lines (i.e. immature cells) p30 was not seen unless short labelling times were used. Two dimensional NEPHGE/SDS-PAGE under appropriate labelling conditions showed that the pattern of spots obtained from an ALL line (Nalm-6) and its autologous EBV transformed partner (B85) were similar though not identical. Pulse chase labelling of Nalm-6 and B85 showed that the turnover rate of p30 relative to DR alpha and beta chains, differed in the two lines.