The Cytocidal Activity of OK‐432‐activated Mononuclear Cells against Human Glioma Cells is Partly Mediated through the Fas Ligand/Fas System

We have been applying an adoptive immunotherapy protocol to patients with malignant brain tumors using OK‐432‐activated peripheral blood mononuclear cells (OK‐MCs). In order to elucidate the mechanism of OK‐MCs' cytotoxicity, we examined the expression of Fas ligand mRNA in OK‐MCs and the cytocidal activity of these cells against a human glioma cell line, T98G which expresses a high level of Fas. The expression of Fas ligand mRNA was low in non‐treated peripheral blood mononuclear cells and was elevated by treatment with OK‐432, irrespective of the dose employed. Apoptosis of T98G cells induced by OK‐MCs was unequivocally inhibited by the pretreatment of T98G cells with ZB4 monoclonal antibody, which binds to Fas and blocks the binding of Fas ligand to Fas. These data indicate that the cytotoxic activity of OK‐MCs via apoptosis seems to be at least partly mediated by the Fas ligand/Fas system. Adoptive immunotherapy using the Fas ligand/Fas system could be a new treatment modality for human malignant brain tumors.