Self-Adjuvanting α-Helical Polypeptide Enhances mRNA Delivery and Dendritic Cell Activation

Abstract mRNA-based vaccines have demonstrated tremendous success during the era of COVID-19, but their therapeutic potential for treating cancer, especially poorly immunogenic solid tumors, remains under-achieved. Herein we report a class of self-adjuvanting α-helical polypeptides that can markedly improve the antitumor efficacy of tumor neoantigen-encoding mRNAs. Ideal carriers for antigen-encoding mRNAs should not only facilitate antigen expression in DCs but also activate DCs and induce effective processing and presentation of expressed antigens. Herein we report the development of cationic α-helical polypeptides as a self-adjuvanting delivery vehicle for antigen-encoding mRNAs.The α-helical polypeptides facilitate intracellular delivery of mRNAs into dendritic cells (DCs) via temporary membrane disruption, simultaneously activate DCs by regulating NF-κB and IRF pathways, and improve the ability of DCs to process and present mRNA-encoded neoantigens. The cationic polypeptide condenses and stabilizes mRNAs, promotes internalization via its cell-penetrating property, and increases the expression of activation markers (CD86, MHCII, CD40, and CCR7) on DCs by upregulating NF-κB, IRF, and STING pathways. Molecular docking and simulation confirm the stable complexation between mRNA and α-helical polypeptides.Upon subcutaneous administration, the polyplex migrates to draining lymph nodes, where it transfects and activates DCs, eliciting a strong neoantigen-specific cytotoxic T lymphocyte (CTL) response in vivo. Compared to mRNA-SM102 lipid nanoparticles or Lipofectamine 3000 lipoplexes, the polyplex enhances antigen expression and presentation by DCs, leading to significantly improved priming of antigen-specific CD8+ T cells in vitro and in vivo. The polyplex achieves 83.3% and 33.3% tumor-free survival in E.G7-OVA lymphoma and 4T1 triple-negative breast cancer (TNBC), respectively. This is far exceeding the 0% tumor-free survival of conventional formulations. Polyplexes composed of α-helical L-PPOB50-G and mRNAs encoding 4T1 TNBC neoantigens elicit potent neoantigen-specific CD8+ T cell responses while showing no detectable toxicity in major organs. The polyplex also reprograms the immunosuppressive tumor microenvironment by enriching DCs, M1-phenotype CD86+ macrophages, and CD8+ T cells in tumors. We also observed increased PD-1 expression on intratumoral CD8+ T cells and PD-L1 on 4T1 tumor cells after polyplex treatment and demonstrated synergistic effects between the polyplex vaccine and anti-PD-1 therapy. Our polyplex system provides a facile and generalizable approach to developing robust mRNA-based cancer vaccines. Citation Format: Jiadiao Zhou. Self-adjuvanting α-helical polypeptide simultaneously delivers neoantigen mRNAs and activates dendritic cells to eradicate tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 6692.