Neutrophils as in inflammatory and immune effectors in photodynamic therapy-treated mouse SCCVII tumours

Neutrophils have become recognised as important contributors to the effectiveness of tumour eradication by photodynamic therapy (PDT). In this study, we have used the mouse SCCVII squamous cell carcinoma model to investigate the activity of neutrophils in tumours treated by PDT. Tumour levels of neutrophilic myeloperoxidase (MPO) demonstrated not only a massive and sustained sequestration of these cells in PDT-treated tumours but also revealed their activated state evidenced by the presence of released MPO. Among the adhesion molecules expressed on tumour vascular endothelium, ICAM-1 appears to be of primary importance in the invasion of neutrophils into PDT-treated tumours, because its functional blocking with monoclonal antibodies reduced the tumour cure rate. A marked upregulation of its ligands CD11b/CD18 and CD11c/CD18 found on neutrophils associated with PDT-treated tumours supports this assumption. To evaluate the role of inflammatory cytokines regulating neutrophil activity, neutralising antibodies were given to mice before PDT treatment. The results suggest that IL-1beta activity is critical for the therapeutic outcome, since its neutralisation diminished the cure rates of PDT-treated tumours. No significant effect was observed with anti-IL-6 and anti-TNF-alpha treatment. Further flow cytometry-based examination of neutrophils found in PDT-treated tumours revealed that these cells express MHC class II molecules, which suggests their engagement as antigen-presenting cells and involvement in the development of antitumour immune response.