Induction of immune cell infiltration into murine SCCVII tumour by photofrin-based photodynamic therapy.

Cellular populations in the squamous cell carcinoma SCCVII, growing in C3H/HeN mice given Photofrin, were examined at various time intervals during the photodynamic light treatment and up to 8 h later. Cell populations present within excised tumours were identified by monoclonal antibodies directed against cell type-specific membrane markers using a combination of the indirect immunoperoxidase and Wright staining or by flow cytometry. Photofrin-based photodynamic therapy (PDT) induced dramatic changes in the level of different cellular populations contained in the treated tumour. The most pronounced was a rapid increase in the content of neutrophils, which increased 200-fold within 5 min after the initiation of light treatment. This was followed immediately by an increase in the levels of mast cells, while another type of myeloid cells, most likely monocytes, invaded the tumour between 0 and 2 h after PDT. The examination of cytolysis of in vitro cultured SCCVII tumour cells mediated by macrophages harvested from the SCCVII tumour revealed a pronounced increase in the tumoricidal activity of tumour-associated macrophages isolated at 2 h post PDT. It seems, therefore, that the PDT-induced acute inflammatory infiltration of myeloid cells into the treated tumour is associated with functional activation of immune cells.