Use of a novel proteomimetic nanoplatform for simultaneous delivery of antigens with adjuvants to impact tumor growth in multiple tumor models.

40 Background: Patient-specific cancer vaccines derived from tumor antigen have been explored as a promising therapeutic strategy, however, challenges delivering vaccine components in a coordinated fashion to elicit antitumor responses remain. To overcome these, we utilize a novel nanoplatform called the Protein-Like Polymer (PLP), which allows for sustained and targeted delivery of tumor antigens in conjunction with adjuvants. Methods: PLPs containing peptide antigens were synthesized via ROMP and characterized. A library of compounds with different sidechain linkage chemistries, degrees of polymerization (DP), and inclusion/exclusion of Oligo-ethylene glycol (OEG) were made to determine design rules for immune activation. Cell uptake and functional assays using payload-specific T Cells were conducted. Immunization in three independent tumor models was done to show generalizability. Ability of PLPs to co-deliver adjuvants was tested by electrostatically coupling small molecule STING agonist, 2’3’ cGAMP. Results: Conjugating antigens to the polymer via a cleavable disulfide linkage, which reduces intracellularly in APCs, resulted in increased endosomal localization, higher levels of induced T cell proliferation, cytokine production, and expression of activation markers in CTLs and APCs. Incorporating a diluent amount of OEG side chains reduced enzymatic degradation while increasing immunogenicity and uptake. Additionally, increasing the DP, and therefore the density of antigen side chains, further improved vaccine efficacy and resistance to proteolysis. Antigen-PLP conjugates enhanced dendritic cell activation and T-cell response only when paired with cells from their cognate system, with no activity in immune cells not expressing receptors for the payload demonstrating antigen-specificity. Mice bearing established B16F10, MC38, or TC-1 tumors treated with PLPs containing gp100, adpgk, or E7 respectively all showed increased survival times, reduced tumor burden with corresponding changes in immune cell profiles, and immunological memory upon rechallenge. Impressively, mice treated with STING-PLP complexes had significantly smaller tumors vs control at day 14 (0.038g vs 0.76g; p < 0.0001) and allowed for subcutaneous administration of 2’3’ cGAMP, which traditionally requires intratumoral injection. Studies on the effects of vaccinating with pools of neoantigens multiplexed onto one PLP are ongoing. Conclusions: This work validates the ability of PLPs to overcome major limitations in cancer vaccine development. The modularity of the platform allows for complex nano-architectures including systems capable of delivering challenging compounds, ie small molecule STING agonists, subcutaneously through electrostatic coupling, highlighting its potential to revolutionize cancer vaccinology.