Tumor Immunotherapy in the Mouse with the Use of 131I-labeled Monoclonal Antibodies

This report describes the use of 131I-labeled monoclonal antibodies in two experimental models for tumor immunotherapy. In vitro treatment of the radiation-induced murine thymoma ITT-1-75NS with radiolabeled anti-Ly-2.1 significantly impaired subsequent tumor growth in vivo. However, in vivo treatment of this tumor, which previously had been injected into C57BL/6 mice, was unsuccessful. By contrast, in vitro treatment of a human colorectal tumor cell line (COLO 205) with 131I-labeled 250-30.6--a monoclonal antibody directed against a secretory component of normal and malignant gastrointestinal epithelium--completely inhibited subsequent tumor growth in BALB/c nude (nu/nu) mice. Furthermore, in vivo treatment of preexisting human colorectal tumor xenografts significantly impaired progressive tumor growth. Although some tumor inhibition was also produced by unlabeled 250-30.6 antibody, this response was considerably amplified by treatment with [131I]-labeled 250-30.6 (P less than .05), suggesting that in vivo treatment of human tumors with the use of 131I-labeled monoclonal antibodies may be clinically beneficial. The antithyroid drug propylthiouracil was used to reduce dehalogenation of the radiolabeled immunoglobulins in an attempt to improve their therapeutic efficacy.