Co-delivery of STING and TLR7/8 agonists in antigen-based nanocapsules to dendritic cells enhances CD8+ T cell-mediated melanoma remission

Abstract

Insufficient efficacy of tumor vaccines still represents a major challenge due to poor adjuvant potency. Combining antigen and adjuvants of different classes bears the potential to induce a broad spectrum of anti-tumor immune responses. Here we demonstrate a novel nanocarrier (NC)-based vaccine combining the type I interferon-triggering STING agonist diamidobenzimidazole (diABZI) compound 3 and the well-established TLR7/8 agonist resiquimod (R848). Encapsulation of both adjuvants into polymeric nanocapsules enables the simultaneous transport of immunostimulatory molecules with tumor antigens. Thereby achieved co-delivery further improved DC stimulation and subsequent anti-tumor immune responses.Combined encapsulation of R848 and diABZI enhanced DC activation and induced stronger antigen-specific T cell responses compared to the single adjuvant NC treatment or using soluble forms of antigens and adjuvants in vitro and in vivo. This was determined by the vigorous expression of CD80, CD83, and CD86. Furthermore, the dual adjuvant therapy initiated the highest secretion levels of different pro-inflammatory cytokines and chemokines.Moreover, a substantial antigen-specific T cell proliferation led to robust tumor remission in a murine B16 melanoma model. Subcutaneous administration of R848/diABZI-loaded NCs induced enhanced infiltration of CD4+ and CD8+ T cells as well as neutrophils in tumor-draining lymph nodes (LN) and tumor tissue. Encapsulating the melanoma-specific antigenic peptide of TRP2 into the adjuvant-loaded NCs reduced the growth of B16 melanoma and prolonged the overall survival. The herein presented novel anti-tumor vaccination strategy avoids the use of structural compounds, increases the antigen load of dendritic cells, uses a fixed combination of antigen and two potent adjuvants and bears the potential to induce vigorous antigen-specific anti-cancer immunity.