Photodynamic therapy (PDT) treatment enhances tumor cell antigenicity

Several groups, including our own, have reported that PDT enhances the host anti-tumor immune response and it is known that the enhanced immune response plays a role in the overall tumor response to PDT. The mechanism behind this enhancement is unknown, however it has been shown that the initiation of an inflammatory response and the infiltration of neutrophils into the tumor bed is critical to the tumor response. We have shown that PDT induces the expression of chemokines that play a critical role in neutrophil infiltration. Recent studies in our laboratory have shown that in addition to affecting the inflammatory and chemokine/cytokine response, PDT also alters the immunogenicity of the tumor, either through changes in antigen structure or enhancement of presentation of tumor associated antigens by host antigen presenting cells to tumor specific T cells. These recent studies and the underlying mechanisms will be discussed.