Figure 4.

Schematic diagram of PDT. The photosensitizer (PS) will be activated by light with an appropriate wavelength, causing the accumulation of ROS in the cells. Exceeded ROS damages tumor cells directly and epithelial cells of tumor-associated vessels. As the impairment of the tumor cell membrane, some pro-inflammatory cytokines will be released, facilitating the recruitment of immune cells in the tumor microenvironment (TME). On the other hand, as the tumor-associated vessels are also damaged, nutrients and oxygen supplements for the tumor will decrease; moreover, the neutrophils and macrophages can transport into the TME, suppressing tumor proliferation.