Photodynamic therapy and antitumor immune response

Photodynamic therapy (PDT) is the combination of photosensitizers and visible light used as a treatment for cancer and infections. As a direct consequence of PDT, reactive oxygen species and other "danger signals" activate the innate immune system and by doing so generate acute inflammation. This cascade of effects is followed by priming of tumor-specific T lymphocytes that have the potential to destroy distant untreated tumor cells, in addition to developing an innate memory "shield" that can be effective in combating recurrence of the cancer. Moreover, PDT can be successfully applied for overcoming the escaping mechanisms employed by progressing tumors attempting to evade immune attack. Furthermore, PDT can assert a beneficial effect on cases of bacterial infection through attracting and accumulating neutrophils into the infected regions rather than by directly killing the bacterial cells.