Targeting microRNAs as key modulators of tumor immune response

The role of immune response is emerging as a key factor in the complex multistep process of cancer. Tumor microenvironment contains different types of immune cells, which contribute to regulate the fine balance between anti and protumor signals. In this context, mechanisms of crosstalk between cancer and immune cells remain to be extensively elucidated. Interestingly, microRNAs (miRNAs) have been demonstrated to function as crucial regulators of immune response in both physiological and pathological conditions. Specifically, different miRNAs have been reported to have a role in controlling the development and the functions of tumor-associated immune cells. This review aims to describe the most important miRNAs acting as critical modulators of immune response in the context of different solid tumors. In particular, we discuss recent studies that have demonstrated the existence of miRNA-mediated mechanisms regulating the recruitment and the activation status of specific tumor-associated immune cells in the tumor microenvironment. Moreover, various miRNAs have been found to target key cancer-related immune pathways, which concur to mediate the secretion of immunosuppressive or immunostimulating factors by cancer or immune cells. Modalities of miRNA exchange and miRNA-based delivery strategies are also discussed. Based on these findings, the modulation of individual or multiple miRNAs has the potential to enhance or inhibit specific immune subpopulations supporting antitumor immune responses, thus contributing to negatively affect tumorigenesis. New miRNA-based strategies can be developed for more effective immunotherapeutic interventions in cancer.