Induction of anti-tumor immunity by photodynamic therapy (PDT)

Abstract

Tumor directed PDT has been shown by a number of pre-clinical studies to enhance a specific anti-tumor immune response, which appears to be critical to long-term tumor growth control by PDT. The PDT enhanced immune response is T cell dependent, however the mechanism behind the potentiation of the immune response by PDT is unknown. Induction of T cell dependent immunity depends upon the presence of activated antigen presenting cells. Therefore we have examined the ability of PDT to stimulate maturation and activation of antigen presenting cells in the PDT-treated tumor bed and tumor draining lymph node. Our studies demonstrate and increase in the number of activated antigen presenting cells in the tumor bed 24h following treatment of EMT6 murine tumors with Photofrin-PDT. Tumor draining lymph nodes also showed increased levels of activated antigen presenting cells within 4h of treatment. The levels peaked at 24h and declined by 48h after PDT. These results demonstrate that PDT-enhanced anti-tumor immunity is accompanied by an increase in antigen presenting cell activity. Therefore it is possible that T cell dependent immunity is enhanced following PDT through enhanced antigen presenting cell activity.