Systemic immunosuppression induced by peritoneal photodynamic therapy

Abstract

Although photodynamic therapy is being used increasingly for the diagnosis and treatment of human cancer, its effect on immune responses has received little attention. This aspect was examined in a murine model. Mice given peritoneal photodynamic therapy had markedly decreased contact hypersensitivity responsiveness, not observed with cutaneous photodynamic therapy. The immunosuppression was systemic, because contact hypersensitivity was depressed at distal, unirradiated sites. Photodynamic therapy induced adoptively transferable cells that inhibited contact hypersensitivity responses in naive mice. The immunosuppression was reversible, but persisted for 3 weeks after photodynamic therapy. An acute-phase response characterized by leukocytosis and elevated serum amyloid P levels was observed in mice given photodynamic therapy but not in mice treated with either laser or dye alone. These data suggest a link between the acute-phase response and immunosuppression. Thus, although photodynamic therapy shows promise in cancer treatment, the induction of decreased systemic immunoresponsiveness is an important observation with potentially detrimental consequences.