Tumor Matrix-Targeted Polymeric Glyco-Adjuvant For In Situ Cancer Vaccination

Cancer vaccination is challenging due to a lack of strong, clinically approved adjuvants and difficulty in identifying cancer-specific antigens. Here, in order to address these challenges, we report the creation of a targeted therapeutic cancer vaccine with two components: (1) a mannosylated, toll-like receptor 7 (TLR7)-agonizing polymer, p(Man-TLR7), and (2) a fusion protein consisting of serum albumin (SA) fused to a collagen binding domain (CBD), namely the A3 domain of von Willebrand factor. p(Man-TLR7) has been shown to elicit strong CD8+ T cell responses, which are vital for the success of cancer vaccines. As such, we hypothesized that chemically linking p(Man-TLR7) to a tumor-targeting protein would localize our polymeric glyco-adjuvant to the tumor, promoting the immunogenic processing of endogenous tumor antigens and bypassing the need to pre-identify tumor-specific antigens. In the approach presented here, CBD-SA acts as our tumor-targeting protein by actively binding to collagen in the tumor microenvironment via the CBD, in addition to utilizing the passive targeting of SA. Upon successful and reproducible generation of CBD-SA-p(Man-TLR7) conjugates, we observed that the conjugates retained the ability to bind both collagen I and collagen III. We then assessed the in vivo anti-tumor efficacy of our conjugates in B16F10 tumor-bearing mice, testing both murine CBD-SA-p(Man-TLR7) and human CBD-SA-p(Man-TLR7) conjugates to evaluate the translatability of our approach. We observed an 84% decrease in average B16F10 tumor size and improved overall survival compared to untreated controls when mice were treated with intravenously-delivered murine CBD-SA-p(Man-TLR7) in combination with anti-PD-1 and anti-CTLA-4 antibodies. In the case of intravenously-delivered human CBD-SA-p(Man-TLR7), a 60% decrease in average tumor size compared to untreated controls was observed when mice were treated with our vaccine as a monotherapy. Further improved anti-tumor efficacy (an 85% decrease in average tumor size compared to untreated controls) and improved overall survival were observed when we combined our human CBD-SA-p(Man-TLR7) vaccination with anti-PD-1 and anti-CTLA-4 antibodies. In conclusion, in situ vaccination with CBD-SA-p(Man-TLR7) is a translatable approach that synergizes with checkpoint antibody therapy to provide therapeutic benefit in treatment of a poorly immunogenic melanoma model. Citation Format: Laura T. Gray, D. Scott Wilson, Jun Ishihara, Koichi Sasaki, Michal Raczy, Melody Swartz, Jeffrey Hubbell. Tumor matrix-targeted polymeric glyco-adjuvant for in situ cancer vaccination [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4582.