(239e) mRNA-Lnp Cancer Vaccines Adjuvanted with Co-Stimulatory Molecules Turn Cold Tumors Hot

Cancer immunotherapies have revolutionized the field of clinical oncology. However, current cancer immunotherapies are effective in less than 30% of patients suffering from solid tumors. Particularly low efficacy rates are observed in individuals suffering from cold tumors, or tumors that lack significant immune cell infiltration. In order to increase the effectiveness of FDA approved cancer immunotherapies, cold tumors must be turned into hot tumors by increasing T-cell infiltration and the overall inflammation of the tumor microenvironment. Cancer vaccines can be a means to increase and diversify the anti-tumor T-cell responses in tumors, which would make them highly effective in combination with checkpoint inhibitor therapy. Yet clinically there remains the problem of overall low immunogenicity of mRNA-LNP cancer vaccines, particularly the inability to mount strong enough CD8+ T-cell responses to overcome significant tumor burden. The goal of this study was to determine of co-stimulatory molecules could act as adjuvants in mRNA-LNP cancer vaccines to increase anti-tumor T-cell responses.

We set up a small library of seven co-stimulatory molecules predicted to increase the CD8+ T-cell responses when expressed on antigen presenting cells. It was found that a combination of three co-stimulatory molecules greatly enhanced the IFNy+ T-cell responses against a tumor-specific antigen. The triple co-stimulatory molecule was found to increase the Th1 T-cell responses for all tumor-specific antigens tested including those from melanoma, pancreatic, and lung tumor models. The therapeutic benefit of co-stimulatory molecule adjuvanted cancer vaccines were tested in two tumor mouse models. mRNA-LNP vaccines containing the co-stimulatory molecules significantly reduced tumor growth rate and increased survival compared to controls. Immunofluorescence staining and flow cytometry analysis of immune cells in the tumors revealed co-stimulatory molecule adjuvanted mRNA-LNP vaccines significantly increased the number of CD4+ and CD8+ T-cells infiltrating into the tumor microenvironment. Due to the increase in T-cell infiltration, the co-stimulatory molecule adjuvanted vaccine worked synergistically with anti-PD1 therapy in tumor models which are normally resistant to checkpoint inhibitor therapy.

In conclusion, co-stimulatory molecules act as adjuvants in mRNA-LNP cancer vaccines by increasing the T-cell responses against tumor-specific antigens. The optimal triple combination significantly increased the CD4+ and CD8+ T-cell responses against multiple tumor-specific antigens and showed therapeutic benefit in multiple tumor models. Additionally, the co-stimulatory molecules enhanced T-cell infiltration into the tumor microenvironment in cold tumor models and significantly increased the response rate to checkpoint inhibitors in tumor models that are normally resistant.