Photodynamic therapy and antitumor immune response

Photodynamic therapy has great potential to treat diverse types of cancer and infections. PDT involves the use of a photoactive drug called photosensitizer and visible light of the appropriate wavelength. The excited photosensitizer generates reactive oxygen species, which kill the cancer cells and microorganisms and destroy the tumor. PDT also generates immune responses by generating acute inflammation that activates the innate immune response. This is followed by priming of tumor-specific T lymphocytes that have the potential to destroy distant untreated tumor cells, besides developing a long-term memory "shield" that is effective in fighting possible recurrence of the cancer. Additionally, PDT can play a role in overcoming the escape mechanism used by progressing tumors trying to escape immune attack. Moreover, in cases of infections, PDT can have a beneficial effect by attracting and accumulating neutrophils into the infected area that can directly kill the bacterial cells.