Anticancer immune response and photodynamic therapy

Photodynamic therapy (PDT) is a relatively new modality for anticancer treatment. It has been proposed as a promising minimally invasive therapeutic approach that employs three essential elements to induce cell death: a photosensitizer, light of a specific wavelength, and molecular oxygen.The combination of photosensitizer uptake in malignant tissues and selective delivery of light of laser provides effective therapy, with direct tumor cytotoxicity and minimal damage of normal tissue. The photodynamic therapy enhances systemic antitumor immunity and can effectively stimulate both the innate and the adaptive immune systems. It has long been known that the long-term efficacy of PDT depends on the presence of an intact adaptive immune system. It has been shown that PDT can triggering the release of various pro-inflammatory and acute-phase response mediators that lead to infiltration of the treated site by a large number of neutrophils, dendritic cells and lymphocytes. PDT enhances T-cells and natural killer (NK) cells activity. NK cells have been shown to have an indirect effect on the control of tumour growth by PDT. It was demonstrate that tumor cells have increased sensitivity to NK cell lyses following PDT. This review describes the basic mechanisms of action of PDT on the anti-tumor immune response by activation of cytotoxic lymphocytes.