Immunotherapy of human glioma xenografts with unlabeled, 131I-, or 125I-labeled monoclonal antibody 425 to epidermal growth factor receptor.

Monoclonal antibody (mAb) 425 (IgG2a) binds to the external domain of the epidermal growth factor receptor. This determinant is highly expressed by human glioma tissues but rarely by normal brain tissues, and is absent on peripheral blood lymphocytes and bone marrow cells. The mAb exerts variable cytotoxic effects against cultured human glioma cells in conjunction with human and murine effector cells. Inhibition of growth of s.c. glioma xenografts in nude mice by the mAb may be mediated by murine macrophages or may be related to the capacity of the mAb to antagonize growth stimulation of glioma cells by epidermal growth factor. In approaches to radioimmunotherapy of human glioma with mAb 425, the 125I-labeled mAb 425 exhibited more significant antitumor effects than the 131I-labeled mAb both in vitro and in vivo in xenotransplanted nude mice. These differences may be due to enhanced nuclear damage caused by 125I-labeled versus 131I-labeled fragments following their internalization into the glioma cells. Our studies provide the rationale for immunotherapy of glioma patients with either unlabeled or 125I-labeled anti-epidermal growth factor receptor mAb 425.