ANTIBODY-RESPONSE AGAINST EPITOPES ON HCG MAPPED BY MONOCLONAL-ANTIBODIES IN WOMEN IMMUNIZED WITH AN ANTI-HCG VACCINE AND ITS IMPLICATIONS FOR BIONEUTRALIZATION

The immunological determinants on hCG, to which an antibody response i s generated in women by the contraceptive HSD vaccine, were mapped by using a panel of anti-hCG monoclonal antibodies. Two types of inhibiti on enzyme immunoassays (EIAs) were used to analyze 126 serum samples f rom 18 subjects immunized with the vaccine and protected from pregnanc y. Monoclonal antibody (MAb) 357-2, which recognizes beta-hCG loop pep tide 38-57, did not inhibit significantly the binding of immune sera t o hCG. Moreover, none of the sera reacted with this loop peptide in a direct binding EIA, suggesting weak immunogenicity of this epitope. Al l sera competed with MAb 206 and a preponderance of antibodies was see n against this epitopic region on beta-hCG. The antibody titers agains t the MAb 206 epitope showed a good correlation with the bioneutraliza tion capacity of the sera throughout the course of immunization. These studies indicate the presence of an immunodominant antigenic determin ant on hCG as recognized by the human immune system.