Abstract 937: mRNA-encoded HPV16/18 therapeutic vaccine with co-stimulator to activate antigen presenting cells and promote T cell-mediated anti-tumor activity

Abstract Background: Persistent infection with human papillomavirus (HPV) 16 and 18, two most prevalent high-risk subtypes, is a predominant cause to human cancers such as head and neck, and cervical cancers. Although prophylactic vaccines can provide protection from infection, therapeutic and efficacious drugs for already developed HPV-related cancers are badly needed. The conventional therapeutic vaccines based on protein or peptides have not reached satisfactory efficacy for patients due to a lack of strong immunogenicity to fully unleash the power of T cell immunity. Here, we developed a lipid nanoparticle (LNP)-encapsulated mRNA-encoding for multiple antigenic signals: E6/E7 antigens from both HPV16 and 18, and an optimized co-stimulatory adjuvant to help both antigen presentation and T cell stimulation. Methods: The mRNA backbone of the vaccine was designed with mutated HPV16/18 E6/E7 at the N-terminus to bypass p53 and pRb degradation, thus avoiding carcinogenic risk. A T2A element is used to space genes from co-stimulatory signals. A suitable LNP was identified both in vitro and in vivo for its expression efficiency and safety profiles. The efficacy and mechanistic studies of the lead mRNA-LNP were further evaluated in both TC-1(HPV16+) and HPV18 transgenic MC38 syngeneic models. Results: Our lead LNP MLX0487-23 could effectively target the splenic dendritic cells and macrophage, leading to dose- and time-dependent tumor eradication in tumor-bearing mice. The optimized mRNA antigen construct named as P016-2 translated the proteins at high level in vitro and as desired, with p53 and pRb remaining intact. Our lead mRNA-LNP showed superior anti-tumor activity both in the HPV16+ TC-1 and the HPV18+ MC38 models, as compared to the benchmark construct lacking co-stimulatory signals OX40L and/or GM-CSF. We observed an expansion of HPV-specific CD8+ T cells and intra-tumoral infiltration of T cells into tumors. After rechallenging with the same TC-1 tumor cells in the contralateral dorsal skin in the complete regression mice induced by P016-2, no tumor was formed, indicating long-term immune memory. Conclusion: We conclude that MLX0487-23 (LNP) encapsulated P016-2, a 4 antigen and GM-CSF expressing mRNA, effectively expanded HPV-specific CD8+ T cells and mediated potent anti-tumor efficacy in the preclinical models, making it an excellent candidate therapeutic mRNA vaccine for clinical testing its safety and efficacy in HPV-driven malignancies. Citation Format: Qiang Zhang, Beibei Cao, Lei Li, Shaoli Liu, Xiaoju Zhang, Andong Liu, Xiaoyun Ma, Hongya Han, Wei Xu. mRNA-encoded HPV16/18 therapeutic vaccine with co-stimulator to activate antigen presenting cells and promote T cell-mediated anti-tumor activity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 937.