Differences between A7 antibody and anti-CEA antibody

The specificity of A7 monoclonal antibody (A7 MoAb), raised against a human colon cancer, was investigated in detail and compared with that of anti-CEA MoAb. Firstly, the biodistributions of radiolabeled A7 MoAb and anti-CEA MoAb were examined in human colon cancer (LS-174T)-, glioblastoma- and lung cancer (Lu-65)-bearing nude mice. 125I-A7 MoAb was highly concentrated into LS-174T and also, to a lesser extent, in glioblastoma, whereas 125I-anti-CEA MoAb was significantly taken up only by LS-174T. Both of these antibodies were taken up at only very low concentrations into Lu-65. Secondly, in vitro binding studies of 125I-A7 MoAb and 125I-anti-CEA MoAb with LS-174T cells and glioblastoma cells revealed high binding activity of these MoAbs to LS-174T cells, though A7 MoAb had a much higher affinity than that of anti-CEA MoAb. Neither of them showed high affinity for glioblastoma cells. Thirdly, competitive binding assay using A7 MoAb and anti-CEA MoAb to LS-174T cells showed that the binding of each 125I-MoAb was not inhibited by the other MoAb. Finally, in radioimmuno-imaging studies of LS-174T- and glioblastoma-bearing mice with 131I-A7 MoAb and -anti-CEA MoAb, both tumors were clearly visualized with the former, while the latter visualized only LS-174T. The A7 MoAb is clearly different from anti-CEA MoAb and may be useful for the in vivo radioimmunodetection and treatment of colon cancer.