Abstract 4372: Proteolysis-targeting vaccines, or PROTAX, for robust tumor combination immunotherapy

Abstract Current peptide vaccines elicit limited antitumor T cell responses, leading to suboptimal tumor therapeutic efficacy. Here, we present proteolysis-targeting vaccines (PROTAX) that facilitate antigen proteolytic processing and cross-presentation to potentiate T cell responses for robust tumor immunotherapy in combination with immune checkpoint blockade (ICB). PROTAX are peptide antigens conjugated with a E3 ligase-binding ligand via linkers. In antigen-presenting cells (APCs), PROTAX bind to E3 ligases to rapidly ubiquitinate PROTAX antigens, facilitating antigen proteolytic processing by proteasome, and thereby promoting antigen cross-presentation to T cells. In mice, PROTAX promoted both the quantity and quality of CD8+ T cell responses against antigens, such as multivalent melanoma-associated antigen Trp2-gp100-Trp1 (TgT) and synthetic long peptide human papillomavirus (HPV)-16 E7. In melanoma-bearing mice, PROTAX-TgT + ICB remodeled the tumor immune microenvironment and enhanced tumor complete regression (CR) rates, in a manner dependent on classic type-1 dendritic cells (cDC1) and CD8+ T cells. PROTAX-TgT + ICB eradicated 100% large BrafV600E SM1 melanomas (∼300 mm3), and promoted the CR rates of M3 melanoma and highly immunosuppressive BrafCA+ M2 melanoma with low TgT antigen expression. In an autochthonous BrafV600E melanoma in BrafV600E/Pten-/- mice, PROTAX-TgT + ICB reduced the molecular and cellular immunosuppression in the tumor, inhibited tumor progression and metastasis, and extended mouse median survival from 21 days to 66 days post initial tumor treatment. Similarly, PROTAX-E7 + ICB resulted in 43% CR of large TC-1 tumors (∼300 mm3). In human leukocyte antigen (HLA)-A02:01 human PBMCs from healthy donors and HPV-16+ Head and Neck Squamous Cell Carcinoma (HNSCC) patients, HLA-A02:01-restricted trivalent PROTAXE6-(E7)2 promoted tri-specific CD8+ T cell responses, characterized with enhanced antigen-specific T cell expansion and production of human interferon-γ (IFN-γ) and tumor necrosis factor-α (TNF-α). Therefore, PROTAX hold the potential for robust tumor combination immunotherapy. Citation Format: Qiyan Wang, wenhua li, Shaomeng Wang, Guizhi Julian Zhu. Proteolysis-targeting vaccines, or PROTAX, for robust tumor combination immunotherapy [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 4372.