In vivo H-2K and H-2D antigen expression in two allogeneic mouse tumours of low immunogenicity

The B16 melanoma of C57BL/6 mice immunizes very poorly, even against its own major histocompatibility complex (MHC) antigens. B16 cells expressed both H-2K and H-2D antigens in vitro as judged by binding of monoclonal antibodies to these antigens in indirect immunofluorescence staining. The in vivo MHC antigen expression of B16 was examined and compared with that of a second C57BL/6 tumour, the Lewis lung carcinoma (3LL), whose defective immunogenicity has been attributed to a selective deficiency in H-2K antigen expression. We found that 125I-labelled cells of both tumours expressed sufficient allo-antigen in vivo to be lysed in BALB/c mice which had been pre-immunized with C57BL/6 lymphoid cells. 125I-B16 cells were also lysed in MHC-recombinant mice which had been immunized against either H-2Kb or H-2Db, indicating that B16 cells express both of these MHC antigens in vivo. This contrasted with our findings with 125I-3LL cells which were destroyed in mice immunized against H-2Db but not in those immunized against H-2Kb. Thus, B16 illustrates a different deficiency in tumour cell immunogenicity which appears not to be attributable to an absence of either of the class I MHC antigens.