N-dihydrogalactochitosan (GC) is developed for inducing immune responses. Synthesized from chitosan and galactose, GC is a new chemical entity that significantly enhances the immune-stimulating properties of its parental material, chitosan, making it a promising therapeutic agent. When used in combination with antigenic material, GC stimulates innate and adaptive antitumor and antiviral immunities. However, the mechanism of GC has not been fully investigated. Herein we demonstrate that GC drives type I IFN production and IFN responses in antigen presenting cells (APCs) and has superior potency compared to its corresponding chitosan. More importantly, GC drives alternative activation of STING leading to inflammatory cell death that enhances dendritic cell (DC) activation, which triggers a variety of nucleic acid sensing pattern recognition receptors (PRRs) and IL-1b production. In vivo, GC induced a potent response of type I IFN and upregulated genes associated with STING signaling within the tumor microenvironment (TME). Moreover, intratumoral delivery of GC reduced the numbers of M2-like macrophages residing within the TME, while subsequently increasing the number of DCs. Our findings demonstrate GC's unique ability to activate STING and stimulate a broad type I IFN response which holds therapeutic promise in generating antitumor and antiviral immunities.
The tumor microenvironment (TME) promotes pro-tumor and anti-inflammatory metabolisms and suppresses the host immune system. It prevents immune cells from fighting against cancer effectively, resulting in limited efficacy of many current cancer treatment modalities. Different therapies aim to overcome the immunosuppressive TME by combining various approaches to synergize their effects for enhanced anti-tumor activity and augmented stimulation of the immune system. Immunotherapy has become a major therapeutic strategy because it unleashes the power of the immune system by activating, enhancing, and directing immune responses to prevent, control, and eliminate cancer. Phototherapy uses light irradiation to induce tumor cell death through photothermal, photochemical, and photo-immunological interactions. Phototherapy induces tumor immunogenic cell death, which is a precursor and enhancer for anti-tumor immunity. However, phototherapy alone has limited effects on long-term and systemic anti-tumor immune responses. Phototherapy can be combined with immunotherapy to improve the tumoricidal effect by killing target tumor cells, enhancing immune cell infiltration in tumors, and rewiring pathways in the TME from anti-inflammatory to pro-inflammatory. Phototherapy-enhanced immunotherapy triggers effective cooperation between innate and adaptive immunities, specifically targeting the tumor cells, whether they are localized or distant. Herein, the successes and limitations of phototherapy combined with other cancer treatment modalities will be discussed. Specifically, we will review the synergistic effects of phototherapy combined with different cancer therapies on tumor elimination and remodeling of the immunosuppressive TME. Overall, phototherapy, in combination with other therapeutic modalities, can establish anti-tumor pro-inflammatory phenotypes in activated tumor-infiltrating T cells and B cells and activate systemic anti-tumor immune responses.
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