Quantitation of human tumor-reactive monoclonal antibody 16.88 in the circulation and localization of 16.88 in colorectal metastatic tumor tissue using murine antiidiotypic antibodies.

Detection of administered human monoclonal antibodies in the tissues and circulation of patients requires special reagents to overcome interference by normal endogenous immunoglobulin. A practical approach is the development of antiidiotypic antibodies to the human monoclonal antibody and their application in immunoassays specific for the human monoclonal antibody. Accordingly, antiidiotypic antibodies were made to the monoclonal antibody 16.88, a human IgM class anti-colon carcinoma antibody being developed for applications in antibody-targeted immunotherapy of cancer. Three stable clones were obtained that produced antiidiotypic antibodies reactive with 16.88 but nonreactive with human polyclonal IgM or 16.52, a patient-matched IgM monoclonal antibody with different specificity than 16.88. One antiidiotypic antibody, MID 65, was used in a capture format radioimmunoassay to detect 16.88 in the sera of patients who had received 108-mg doses of unlabeled 16.88 coadministered with trace doses of 131I-16.88. Using this assay it was demonstrated that unlabeled 16.88 antibody and 131I-labeled 16.88 antibody did not differ significantly in blood retention for up to 24 h after administration, the period during which the immunoreactivity of the administered antibody remained over 90%. Indirect microautoradiography using exogenously applied 125I-MID 65 to localize 16.88 in frozen metastatic tumor tissue from patients given 16.88 8 days prior to surgery demonstrated the accumulation of 16.88 in areas of apparently healthy tumor cells. Much less 16.88 was detected in stroma or areas of tumor cell necrosis. The accumulation of antibody in nonnecrotic tumor sites encourages the further development of 16.88 for radioimmunotherapy of colon cancer and provides support for further development of human anticytokeratin monoclonal antibodies for cancer therapy.