PDT as a cytotoxic agent and biological response modifier: Implications for cancer prevention and treatment in immunosuppressed and immunocompetent patients.

PDT acts as a biological response modifier in addition to directly damaging target cells and their blood supply. The reduced efficacy of PDT in immunosuppressed patients demonstrates the importance of immune mechanisms in this therapy, and transplant recipients require aggressive optimization of direct cytotoxic pathways. However, immunocompetent individuals can benefit from PDT's effects on innate and adaptive immune responses, including the possibility of generating in situ anti-tumor vaccines.