Tumor radioimmunolocalization in a murine system using monoclonal antibodies

Tumor localization was obtained in a murine system by use of 131I-labeled monoclonal antibodies, both of IgG and IgM class. The A6 IgG2 monoclonal antibody (which recognizes the gp70 of MuLV) and the B3 IgM monoclonal antibody (which recognizes a proteic structure widely exposed on chemically induced tumors), which both manifest an in vitro cytotoxic activity for various types of murine lymphomas, were injected in tumor-bearing (B6 X BALB/c)F1 mice and B6 mice, respectively, at the dose of 1 microgram per mouse. The radioactivity count demonstrated an optimal tumor accumulation of the radiolabeled monoclonal antibodies 96 h after iodine injection, although an initial accumulation was already present 48 h after injection. The scanning detection was less sensitive, since at 48 h no tumor localization was possible. In the experiments with the A6 antibody, the presence of the gp70 in the circulating form, demonstrated by the detection of immunocomplexes in kidney and spleen of tumor-bearing mice injected with the A6, did not prevent radioactivity accumulation in the tumor. This accumulation was found to increase with tumor size only up to 1 g of tumor weight, then a decreased binding index was observed, whereas in the kidney the accumulation was progressive and paralleled the increase in tumor weight.