Anti-idiotypic antibodies to monoclonal antibody CO17-1A

Anti-idiotypic antibodies (Ab2) raised during the course of monoclonal antibody (MAb) therapy against anti-colorectal carcinoma (CRC) MAb CO17-1A were characterized in 142 patients with carcinomas of the colon, rectum or pancreas. Ab2 comprised between 21 and 80% of the total human anti-mouse IgG antibodies in various patients, and up to 42 micrograms of Ab2 were isolated per ml serum. In one patient significant levels of Ab2 could be detected for greater than 770 days. Between 20 and 70% of Ab2 in various patients bound to the combining site of MAb CO17-1A and may therefore bear the internal image of the 17-1A tumor antigen. Furthermore, Ab2 isolated from different patients showed considerable cross-reactivities. A beneficial role of the Ab2 responses in the cancer patients who improved clinically following MAb immunotherapy is discussed in light of induction by Ab2 of anti-anti-idiotypic antibodies (Ab3) with tumor-binding activities.