Comparison of the distribution and binding of monoclonal antibodies labeled with 131-iodine or 111-indium.

The distribution of two monoclonal antibodies with reactivity against human leukemia/lymphoma associated antigens (BA-1 antibody) and carcinoembryonic antigen (202 antibody) when labeled with 131I or 111In was studied in normal Balb/c mice. The BA-1 antibody of the IgM subclass was labeled with 131I by the micro iodine monochloride method at a 12:1 molar ratio and with 111In by the cyclic DTPA anhydride method at a 10:1 molar ratio. In vitro, the 131I-labeled BA-1 antibody bound 35.5% to 10(7) KM-3 leukemic cells while the 111In-labeled BA-1 antibody bound 29.9% to the same number of KM-3 cells. In vivo, the 111In-labeled BA-1 antibody showed a higher accumulation in liver, spleen, and kidney than the 131I-labeled BA-1 antibody. The 202 antibody of the IgG1 subclass was labeled with 131I at a 5:1 molar ratio and with 111In at a 7:1 molar ratio. In vitro, the 131I-labeled 202 antibody bound 30.9%, 27.4%, and 30.0% to 10(7) CO-112, WIDR, and LS-174T colon cancer cells, respectively. The 111In-labeled 202 antibody bound 20.5%, 30.2%, and 33.6%, respectively to the same number of colon cancer cells. In vivo, the 131I-labeled 202 antibody showed a higher tissue to blood ratio in liver, spleen, and kidney than the 111In-labeled 202 antibody. The data indicate that the relative distribution of 131I-labeled versus 111In-labeled monoclonal antibody may depend on the immunoglobulin subclass of the antibody and the molar ratio used in labeling.