Immune Response Induced by Hematoporphyrin Derivatives Mediated Photodynamic Therapy: Immunogenic Cell Death and Elevated Costimulatory Molecules*

Photodynamic therapy (PDT) not only destroys tumor cells directly but also induced anti-tumor immune response through damage-associated molecular patterns (DAMPs). It is reported that anti-tumor response was associated with light dose and photosensitizer used in PDT. In this study, 4T1 tumor cells were implanted on both the right and left flanks of mice. Only the right tumor was treated by HpD-PDT, while the left tumor was not irradiated. The anti-tumor immune response induced by HpD-PDT was investigated. The expression of DAMPs and co-stimulatory molecules induced by HpD-PDT were tested by immunofluorescence and flow cytometry in vivo. Different light doses of PDT were designed to treat 4T1 cells. The killing effect was assessed by CCK-8 kit and apoptosis kit. The expression of DAMPs on 4T1 cells after HpD-PDT were evaluated by flow cytometry, western blot and ATP kit. This study showed that CD4+T, CD8+T and the production of IFN-γ were increased significantly on day 10 in right-tumor after PDT treatment compared with control group. HpD-PDT enhanced the expression of calreticulin (CRT) on tumor tissue. Importantly, co-stimulatory molecular OX-40 and 4-1BB were elevated on CD8+T cells. In vitro, immunogenic death of 4T1 cells was induced after PDT. Besides, the expression of DAMPs increased with the increasing of energy density. This study indicates that anti-tumor immune effect was induced by HpD-PDT. The knowledge of the involvement of CRT, ATP and costimulatory molecules uncovers important mechanistic insight into the anti-tumor immunogenicity. It was the first time that co-stimulatory molecules were investigated and found to elevate after PDT.