Promising targets based on pattern recognition receptors for cancer immunotherapy

Pattern recognition receptors (PRRs) recognize pathogen-associated as well as endogenous damage-associated molecular patterns. Once ligand binding occurs, signaling cascades develop within the cells to activate effector molecules. Thus, PRRs play key roles in immune surveillance and immune tolerance. Due to their differences in cell localization, stage of action, and ligand recognition, PRRs form a defense network from the cell membrane to the cytoplasm, constituting the regulatory networks of the innate and adaptive immune systems in cancer. However, the activation of PRRs cannot only recruit and activate anti-tumor immune cells, but also promote the release of inflammatory cytokines, which may lead to the formation of the local inflammatory microenvironment in tumors, thus promoting the development of cancer. Therefore, the dual regulation of PRRs in the immune system has attracted much attention, with current research being focused on maximizing their anti-tumor immune activity. In addition to their expression in host cells, PRRs are also expressed in tumor cells; this is closely related to the occurrence and development of cancer. This review attempts to clarify the feasibility and directions for the development of PRR-based applications in cancer immunotherapy by elaborating on the mechanisms underlying the action of PRRs and the current status of immunotherapies.