Molecular requirements for CD8-mediated rejection of a MUC1-expressing pancreatic carcinoma: Implications for tumor vaccines

Previous studies have indicated that different effector cells are required to eliminate MUC1-expressing tumors derived from different organ sites and that different vaccine strategies may be necessary to generate these two different MUC1-specific immune responses. In this study, we characterized molecular components that are required to produce immune responses that eliminate Panc02.MUC1 tumors in vivo by utilizing mice genetically deficient in molecules related to immunity. A parallel study has been reported for a B16.MUC1 tumor model. We confirmed that a CD8⁺ effector cell was required to eliminate MUC1-expressing Panc02 tumors, and demonstrated that T cells expressing TCR-α/β and co-stimulation through CD28 and CD40:CD40L interactions played critical roles during the initiation of the anti-Panc02.MUC1 immune response. TCR-α/β⁺ cells were required to eliminate Panc02.MUC1 tumors, while TCR-γ/δ⁺ cells played a suppressive non-MUC1-specific role in anti-Panc02 tumor immunity. Type 1 cytokine interferon-gamma (IFN-γ), but not interleukin-12 (IL-12), was essential for eliminating MUC1-expressing tumors, while neither IL-4 nor IL-10 (type 2 cytokines) were required for tumor rejection. In vitro studies demonstrated that IFN-γ upregulated MHC class I, but not MHC class II, on Panc02.MUC1 tumor cells. Surprisingly, both perforin and FasL played unique roles during the effector phase of immunity to Panc02.MUC1, while lymphotoxin-α, but not TNFR-1, was required for immunity against Panc02.MUC1 tumors. The findings presented here and in parallel studies of B16.MUC1 immunity clearly demonstrate that different effector cells and cytolytic mechanisms are required to eliminate MUC1-expressing tumors derived from different organ sites, and provide insight into the immune components required to eliminate tumors expressing the same antigen but derived from different tissues.