Advances and Challenges of Nanoparticle-Based Macrophage Reprogramming for Cancer Immunotherapy

Despite the progress of modern medicine, oncological diseases are still among the most common causes of death of adult populations in developed countries. The current therapeutic approaches are imperfect, and the high mortality of oncological patients under treatment, the lack of personalized strategies, and severe side effects arising as a result of treatment force seeking new approaches to therapy of malignant tumors. During the last decade, cancer immunotherapy, an approach that relies on activation of the host antitumor immune response, has been actively developing. Cancer immunotherapy is the most promising trend in contemporary fundamental and practical oncology, and restoration of the pathologically altered tumor microenvironment is one of its key tasks, in particular, the reprogramming of tumor macrophages from the immunosuppressive M2-phenotype into the proinflammatory M1-phenotype is pivotal for eliciting antitumor response. This review describes the current knowledge about macrophage classification, mechanisms of their polarization, their role in formation of the tumor microenvironment, and strategies for changing the functional activity of M2-macrophages, as well as problems of targeted delivery of immunostimulatory signals to tumor macrophages using nanoparticles.