Comparative biodistributions and rates of catabolism of radiolabelled anti-CEA monoclonal antibody and control immunoglobulin in nude mice with human tumour xenografts showing specific antibody localization.

The rate of catabolism of a radiolabelled monoclonal anti-CEA antibody has been compared with that of control IgG1 in control nude mice and in mice with CEA producing xenografts and antigen negative xenografts. The rate of catabolism of antibody, but not of IgG, was increased 3-4 fold in mice with xenografts localizing the antibody, but not in mice with antigen negative tumours. There was no evidence of immune complex formation and/or clearance of antibody from the serum of xenografted mice and the current interpretation of these findings is that following tumour immune directed fixation, antibody is subsequently catabolized faster than in the general metabolic pool. The present data indicates that this is about six times as rapid as in the animal as a whole on a weight to weight tissue basis.