Abstract B059: Signaling Requirements for Enhanced CD8+ T Cell Responses in mRNA Cancer Vaccine Immunotherapy

Abstract The development of nucleoside-modified mRNA vaccines in ionizable lipid-containing nanoparticles (iLNPs) has established a robust cancer immunization platform targeting tumor-associated antigens (TAAs). The substitution of uridine (U) with N1-methylpseudouridine (m1ψ) in these vaccines abrogates innate immune activation, maximizes antigen expression, and enhances the in vivo priming and expansion of adoptively transferred naïve CD8+ T cells. However, antigen-specific T cells primed under immunosilent conditions with m1ψ mRNA-iLNPs exhibit suboptimal effector functions, including impaired cytotoxic cytokine secretion and memory development. Our laboratory has demonstrated that U-mRNA-iLNP vaccines, which elicit a strong type I IFN response, achieve more prolonged tumor growth suppression compared to m1Ψ-mRNA-iLNP vaccines in a preclinical murine model of melanoma. Despite this, the clinical translation of U-mRNA-iLNP vaccines is constrained by dose-limiting toxicities in humans, mediated by cytokines such as IL-1β and IL-6. To overcome this limitation, we explored the co-delivery of a tumor antigen-encoding m1Ψ mRNA-iLNP vaccine and type I IFN in m1ψ mRNA within the context of adoptive cell transfer. Our results demonstrate that prime-boost vaccination with an mRNA-iLNP vaccine, which allows for high antigen expression and a tunable type I IFN response, significantly increases the frequency of antigen-specific CD8+ T cells in circulation and secondary lymphoid organs. Transcriptional profiling of CD8+ T cell subsets expanded by our mRNA vaccine platform revealed a polyfunctional effector signature, including Ifng, Prf1, Gzmb, Tnfα, Klrg1, and Lamp1, as well as enhanced expression of interferon-stimulated genes and costimulatory receptors. We are currently assessing the in vivo efficacy of our mRNA-vaccine platform in melanoma and PDAC orthotopic and liver metastatic models. These studies aim to provide comprehensive mechanistic insights into the requirements of a cancer mRNA-vaccine to generate potent anti-tumor CD8+ T cell responses. Citation Format: Khalid Rashid, Hailey R Lee, Amanda L Creech, Tony Luu, Katelyn Nguyen, Pu Lin Teng, Weihang Zhao, Alykhan M Premji, Evan R. Abt, Thuc M Le, Ting-Ting Wu, Norbert Pardi, Caius G Radu. Signaling Requirements for Enhanced CD8+ T Cell Responses in mRNA Cancer Vaccine Immunotherapy [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Tumor Immunology and Immunotherapy; 2024 Oct 18-21; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2024;12(10 Suppl):Abstract nr B059.