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.