Upon light irradiation, compared with the tumor‐bearing mice treated with free 1MT and free PpIX, as well as PpIX‐1MT NPs without laser, the PpIX‐1MT NP‐treated mice not only showed significantly inhibited tumor growth, but also increased activation of CD8+ T lymphocytes due to IDO blockade (Figure 17b–d). The gene discussed is IDO1; the disease is neoplasm.