Background
While patient-specific cancer vaccines derived from tumor antigens show promise as a therapeutic strategy, coordinating the delivery of vaccine components to elicit antitumor responses poses significant challenges. To address these, we employ a novel nanoplatform known as the Protein-Like Polymer (PLP), enabling the sustained and targeted delivery of tumor antigens along with small molecule adjuvants.
Methods
Peptide antigen-containing PLPs were synthesized through ring-opening metathesis polymerization (ROMP) and underwent characterization. We developed a library of compounds with various sidechain linkage chemistries, degrees of polymerization (DP), and the presence or absence of oligo-ethylene glycol (OEG) to identify the design principles for immune activation. To evaluate their efficacy, we conducted cell uptake and functional assays with payload-specific T cells. Immunization trials in three distinct tumor models were carried out to confirm general applicability. Additionally, we tested the PLPs’ capacity to co-deliver adjuvants by electrostatically coupling them with the small molecule STING agonist, 2’3’ cGAMP.
Results
By attaching peptide antigens to the polymer using a cleavable disulfide linkage that breaks down within APCs, we achieved greater endosomal localization and elevated levels of T cell proliferation, cytokine production, and activation markers in both CTLs and APCs. Including a small amount of OEG side chains decreased enzymatic degradation while boosting immunogenicity and uptake. Furthermore, increasing the degree of polymerization (DP), and thus the density of antigen side chains, enhanced vaccine efficacy and resistance to proteolysis. Antigen-PLP conjugates improved dendritic cell activation and T-cell response exclusively when paired with their cognate system, with no activity in immune cells lacking receptors for the payload, demonstrating antigen specificity. Mice with established B16F10, MC38, or TC-1 tumors treated with PLPs containing gp100, adpgk, or E7 respectively exhibited increased survival times, reduced tumor burden, and immunological memory upon rechallenge, with corresponding changes in immune cell profiles. Notably, mice treated with STING-PLP complexes had significantly smaller tumors compared to controls on day 14 (0.038g vs. 0.76g; p < 0.0001), allowing for subcutaneous administration of 2’3’ cGAMP, which typically requires intratumoral injection. Research on the effects of vaccinating with pools of neoantigens multiplexed onto a single PLP is ongoing.
Conclusions
This study demonstrates the groundbreaking potential of PLPs to overcome critical barriers in cancer vaccine development. The platform’s modular design facilitates the construction of intricate nano-architectures, enabling the subcutaneous delivery of challenging compounds, such as small molecule STING agonists, through electrostatic coupling underscoring its capacity to revolutionize the field of cancer vaccinology.