Recent progress of nanoparticle-enabled modulation of macrophages for cancer immunotherapy

Macrophages play an important role in maintaining homeostasis of the body, and they are also one of the most abundant immune cells in the tumor microenvironment (TME). These macrophages are often called tumor-associated macrophages (TAMs), which play an important role in the development of tumor and are an important target for tumor therapy. Studies have shown that tumor growth and metastasis can be inhibited by regulating the function of macrophages, but the therapeutic efficacy was often hampered by the poor performance of the drugs such as lack of targeting, poor solubility, low bioavailability, and severe side effects. After introduction of the background of macrophage and tumor therapy, this review focuses on the research progress of nano-drug delivery systems in the modulation of the function of macrophages to enhance tumor immunotherapy. Nano-drug delivery systems are diverse in structures and functions, and can regulate macrophage functions through a variety of mechanisms. Four important aspects of macrophage modulation, which included TAMs depletion, repolarization of TAMs, promoted phagocytosis of TAMs, and combinational modulation of TAMs were summarized. Each strategy together with typical examples was reviewed and future directions in this field were also prospected.