POTENTIATION OF PHOTODYNAMIC THERAPY-ELICITED ANTITUMOR RESPONSE BY LOCALIZED TREATMENT WITH GRANULOCYTE-MACROPHAGE COLONY-STIMULATING FACTOR

Murine squamous cell carcinoma (SCCVII) cells were genetically enginee red to produce murine granulocyte-macrophage colony-stimulating factor (GM-CSF), GM-CSF immunotherapy, based on the peritumoral injection of lethally irradiated GM-CSF-producing SCCVII cells, was examined as ad juvant to photodynamic therapy (PDT) treatment of this tumor, The GM-C SF immunotherapy administered three times in 48-h intervals, starting 2 days before the light treatment, substantially improved the curative effect of Photofrin-mediated PDT, A comparable effect of GM-CSF immun otherapy was observed in the combination with benzoporphyrin derivativ e-mediated PDT, The tumor-localized GM-CSF immunotherapy alone had no obvious effect on the growth of parental SCCVII tumors, This treatment did not significantly alter the differential peripheral WBC count and appeared not to affect tumor leukocyte infiltration. However, GM-CSF treatment did increase the cytotoxic activity of tumor-associated macr ophages against SCCVII tumor cells. It appears, therefore, that tumor- localized immune stimulation by GM-CSF amplifies a PDT-induced antitum or immune reaction, which has a potentiating effect on tumor control.