Adsorption of antigen to polymeric nanoparticles enhances cytotoxic T-cell responses and anti-tumor immunity by targeting conventional type 1 dendritic cells.

Tumor rejection is primarily mediated by cytotoxic T cells, making them critical targets for therapeutic cancer vaccines. Vaccine adjuvants can modulate innate immunity, influencing adaptive immune responses. For particulate adjuvants, such as polymeric nanoparticles, physicochemical properties-including size, charge, composition and antigen location within the formulation-can shape these responses. Free-soluble antigens typically fail to induce sufficient dendritic cell maturation and cross-presentation needed for robust CD8⁺ T-cell activation. However, this can be enhanced by delivering antigen with nanoparticles of appropriate size. While adjuvants like oil-in-water emulsions do not require antigen association for vaccine efficacy, the importance of antigen location in the adjuvanticity of polymeric nanoparticles is less clear. We demonstrate that colocalization of antigen and polymeric nanoparticles through antigen adsorption enhances proliferation and activation of antigen-specific CD8⁺ T cells following intramuscular vaccination. While type 1 conventional dendritic cells (cDC1) can prime CD8⁺ T cells in other settings, their requirement with polymeric nanoparticles has not been fully addressed. We show that nanoparticle-induced CD8⁺ T-cell responses rely on cDC1s. The therapeutic efficacy of a polymeric nanoparticle vaccine was significantly enhanced when antigen was adsorbed on nanoparticles, leading to reduced tumor growth and prolonged survival in mice challenged with immunologically hot (MC38) and cold (B16F10) tumors expressing ovalbumin. Furthermore, vaccination with nanoparticle-adsorbed antigen synergized with anti-PD-1 checkpoint blockade, enhancing protection, especially against B16F10-ovalbumin tumors. This work highlights the role of antigen association with polymeric nanoparticles in eliciting CD8⁺ T-cell responses for the development of effective therapeutic cancer vaccines.