Reprogramming Tumor Associated Macrophages toward M1 Phenotypes with Nanomedicine for Anticancer Immunotherapy

Tumor-associated macrophages (TAMs), one of the most important constituents in tumor immunosuppressive microenvironments, are a potential therapeutic target due to their essential role in promoting tumor progression and metastasis. Macrophages are usually divided into two categories of protumoral M2-like TAMs and antitumoral M1 phenotypes at the two extremes. Reprogramming M2-like TAMs toward tumoricidal M1 phenotype is especially intriguing in terms of the restoration of antitumor immunity for anticancer immunotherapy. In this review, the recent advances of nanomedicine-mediated reprogramming of TAMs from M2 to M1 to elicit the antitumor immunity are discussed. This reprogramming can be achieved via direct re-education by targeted delivery of various active agents to TAMs and indirect re-education by modulating the abnormal tumor microenvironment. Perspectives on nanomedicine mediated TAMs-M1 reprogramming for effective anticancer immunotherapy are also presented.