Redirecting cytomegalovirus immunity against breast tumors for immunotherapy

Background: Breast tumors, particularly triple-negative cancers, are aggressive and frequently resistant to chemotherapy, with limited responses to immunotherapy. Despite high mutational burden and T-cell infiltration, clinical efficacy remains low. Based on evidence that neo/novel neoantigens elicit strong antitumor immunity, we hypothesize that systemic delivery of viral antigens combined with the tumor-targeting peptide iRGD can redirect pre-existing antiviral immunity to eliminate breast tumors. Methods: Cytomegalovirus (CMV), a beta-herpesvirus, was chosen due to its high prevalence in the human population and its ability to elicit a robust and broadly reactive memory T cell response. Mice latently infected with murine CMV (MCMV) were orthotopically implanted with murine E0771 breast tumor cells in the mammary fat pad and subsequently treated with systemic administration of MCMV-derived T cell epitopes. Tumor progression was assessed biweekly via tumor size measurements using caliper, and immune cell infiltration and response were evaluated using histological analysis and flow cytometry. Statistical significance was determined using two-way ANOVA with Sidak's post hoc correction, one-way ANOVA with Turkey's post hoc correction and t-test. Results: Our new results demonstrate that MCMV-based therapy promotes the preferential accumulation of MCMV-specific T cells within breast tumors, leading to delayed tumor progression in mice infected and treated with MCMV-specific peptides compared with uninfected treated mice or infected mice treated with vehicle. The therapeutic efficacy was independent of iRGD co-administration. Notably, we observed heterogeneity in tumor growth control in the E0771 breast tumor model, allowing the identification of responder and non-responder groups. Immunophenotyping analyses revealed that tumor-infiltrating T cells displayed a highly activated phenotype, as well as enhanced cytotoxic potential, evidenced by elevated expression of granzymes A and B. These immune features correlated with increased tumor necrosis and enhanced T-cell infiltration within the tumor tissue of infected mice treated with MCMV-specific peptides. Conclusions: These findings demonstrate that CMV-specific memory T cells can be redirected to control breast tumors via systemic administration of CMV epitopes, and they were effective in curtailing tumor growth. Given that CMV infection is endemic and induces a huge memory T cell pool, this approach may have broad clinical applicability.