C3-Liposome Delivery of MUC1 Peptide and TLR Agonists Enhances Adaptive Immunity and Results in Sex-Based Tumor Growth Differences

<b>Background</b>: Mucin-1 (MUC1) is a glycoprotein that is hypoglycosylated and overexpressed in most adenocarcinomas, making it a promising target for cancer vaccines. Our group previously demonstrated that C3 (OPSS)-liposomes enhance antigen uptake by antigen-presenting cells (APCs) via the complement C3 pathway and, when combined with toll-like receptor (TLR) agonists, reduce tumor growth in murine cancer models. <b>Methods</b>: In the present study, we evaluate the immunogenicity of MUC1 peptide vaccines encapsulated in C3-liposomes, with and without TLR agonists, using MUC1-tolerant transgenic mice challenged with Lewis lung carcinoma (LLC.MUC1) cells. To assess vaccine effectiveness, tumor volumes were measured, and flow cytometry and ELISA and ELISPOT assays were used to assess the immune response. <b>Results</b>: Both male and female C57BL/6 transgenic mice vaccinated with MUC1 C3-liposomes developed significantly smaller tumors than those vaccinated with free MUC1 peptide or PBS. Notably, a sex-dependent response emerged in mice vaccinated with MUC1 C3-liposomes with TLR agonists (TLR4, TLR7/8, and TLR9); male mice exhibited greater tumor suppression than females. Flow cytometry analysis revealed that female mice had significantly higher levels of CD11b⁺, LY6C⁺, and LY6G⁺ MDSC cells, suggesting a potential mechanism for the sex difference. Additionally, MUC1 C3-liposome vaccination elicited robust adaptive immune responses, including significantly higher levels of IFN-γ-producing T cells and MUC1-specific IgG antibodies compared to non-encapsulated MUC1 or TLR adjuvant-only formulations. <b>Conclusions</b>: These findings underscore the potential of C3-liposome-based antigen vaccines to enhance anti-tumor immunity and highlight the impact of sex differences in vaccine efficacy.