ARE HUMAN ANTIIDIOTYPIC ANTI-OC125 ANTIBODIES FORMED AFTER IMMUNIZATION WITH THE ANTI-CA125 ANTIBODY B43.13

The two monoclonal antibodies (MAb) OC125 and B43.13 both recognize an tigenic determinants on the cancer antigen 125 (CA125) molecule, The a im of the present study was to clarify how far antibodies formed by pa tients treated with B43.13 may cross-react with idiotopes of OC125. Se rum samples from 15 ovarian cancer patients treated with B43.13 were t ested for the presence of anti-idiotypic anti-OC125 antibodies; 4 of t hese patients previously had received OC125 F(ab')(2) fragments. Six p atients treated only with B43.13 and all patients pretreated with OC12 5 fragments developed a considerable increase of human anti-mouse anti bodies after B43.13 infusion, indicating an immune response to antibod y infusion, However, none of the patients treated only with B43-13 dev eloped detectable levels of anti-idiotypic anti-OC125 antibodies, wher eas in 2 patients pretreated with OC125 fragments, the pre-existing co ncentration of anti-idiotypic anti-OC125 antibodies further increased after B43.13 infusion. The binding of these newly formed antibodies to OC125 was not inhibited by the B43.13, but about 70% of the binding w as inhibited by the CA125 antigen, The present data suggest that the i diotopes expressed on the antibodies B43.13 and OC125, respectively, a re completely different, Thus, anti-idiotypic anti-B43.13 antibodies m ay not cross-react with OC125, A greater number of cases is needed to clarify how far the increase of anti-idiotypic anti-OC125 antibodies o bserved in 2 patients pretreated with OC125 fragments really is due to B43.13 infusion.