Improved radioimmunolocalization of carcinomas using Fab fragments with anti-CEA specificity

A model system with human colonic grafts containing carcinoembryonic antigen (CEA) in nude mice was used to improve specificity and sensitivity of the radioimmunolocalization method. Monoclonal antibody MAb I-38S1 and monkey anti-CEA appeared to have high in vitro and in vivo specificity. Fab fragments of MAb I-38S1 improved localization ratios. A reduced time for optimal immunolocalization was obtained with Fab compared with MAb of the same specificity. Combinations of Fab:s, vasoactive compounds or anti-IgG treatment to reduce background levels did not further improve speed of localization or sensitivity.