Figure 2.

Intratumoral immunotherapy involves direct injection of immunotherapeutic agents into tumors. The immunosuppressive tumor microenvironment of an injected tumor is stimulated to turn the immunosuppressive state into an immunostimulatory state by using the injected agents, involving innate and adaptive immunity depending on the class of agents. The immune-active tumor microenvironment promotes recruitment of NK and DC cells as well as recognition of tumor antigens by DCs. The tumor antigen-loaded DCs present tumor antigens to T cells, triggering the generation of polyclonal effector and memory T cells. Then, the primed T cells circulate systemically to infiltrate into injected tumors and noninjected tumors to achieve durable and global antitumor immune responses to eliminate and contain tumor cells.