Photodynamic Therapy and Immune Checkpoint Blockade†

Abstract Immune checkpoints including PD‐1 and CTLA‐4 help to regulate the intensity and timeframe of the immune response. Since they become upregulated in cancer and prevent sufficient antitumor immunity, monoclonal antibodies against these checkpoints have shown clinical promise for a range of cancers. Multimodal treatment plans combining immune checkpoint inhibitors with other therapies, including photodynamic therapy (PDT), may help to expand treatment efficacy and minimize side effects. PDT's cytotoxic effects are spatially limited by the light activation process, constraining PDT direct effects to the treatment field. The production of damage‐associated molecular patterns and tumor‐associated antigens from PDT can encourage accumulation and maturation of antigen‐presenting cells and reprogram the tumor microenvironment to be more susceptible to therapies targeting immune checkpoints.