Polysaccharide nanoadjuvants with precise drug composition for enhanced STING-mediated APC activation

Abstract

Antigen presenting cells (APCs) dominate the activation of cytotoxic T cells via major histocompatibility molecules, and further ameliorate tumor immunosuppressive environment. The combination and codelivery of immune adjuvants for APC activation presents a highly promising methodology to enhance the therapeutic efficiency of tumor immunotherapy. Here we report a general methodology to engineer polysaccharide nanoadjuvants with defined drug loading and composition for APC activation via the stimulator of interferon genes (STING) and toll-like receptor (TLR) pathways. Both STING and TLR agonists were conjugated to the polysaccharide nanocarrier via the strain-promoted azide-alkyne copper-free click reactions, where the total drug loading and composition were determined by the number of clickable groups of the polysaccharide and the molar ratio of the agonists respectively. These polysaccharide nanoadjuvants were water soluble and could release the STING and TLR agonists after the breakage of ester or carbamate linkages. The polysaccharide nanoadjuvants induced macrophage M1 polarization by upregulating various cell surface markers and cytokines, such as CD86, inducible nitric oxide synthase (iNOS), tumor necrosis factor alpha (TNF-α), which further caused severe cancer cell death. Meanwhile, those polysaccharide nanoadjuvants also promoted dendritic cell (DC) maturation with enhanced expression of CD80 and CD86, TNF-α and interleukin-6 (IL-6). Macrophages and DCs were activated mainly mediated by the STING pathway revealed via upregulation of p-STING, p-TBK1 and p-IRF3, which correlated with the drug efficiency for APC activation. This work provides a robust methodology for facile engineering of polysaccharide nanoadjuvants with defined drug composition for STING-mediated APC activation.