Presentation of endogenous tumor antigens to CD4 + T lymphocytes by murine melanoma cells transfected with major histocompatibility complex class II genes

In a previous study, we demonstrated that K1735 transfectants expressing either K k or A k antigens alone produced tumors in syngeneic mice, whereas transfectants that expressed both antigens were rejected. In this study, we investigated whether K1735 transfectants expressing A k molecules can present endogenous tumor antigens to CD4 + T lymphocytes in the absence of normal accessory cells. Our results indicate that K1735 transfectants expressing K k and A k molecules presented antigen to both CD4 + and CD8 + T lymphocytes, whereas K1735 transfectants expressing only the A k or the K k antigen preferentially stimulated either CD4 + or CD8 + T cells. Analogous to endogenous antigens, K1735 transfectants expressing A k molecules also presented exogenous hen egg lysozyme (HEL) to HEL‐specific 3A9 hybridomas in the absence of normal accessory cells. These results demonstrate that K1735 murine melanoma cells expressing A k molecules can function as antigen‐presenting cells and that the generation of an effective antitumor immune response by K1735 melanoma cells expressing K k and A k antigens is due to their ability to present endogenous tumor antigens to both helper and cytotoxic T cells. J. Leukoc. Biol. 56: 469–474; 1994.