IgG subclass distribution of anti-hCG and anti-diphtheria toxoid antibodies in women immunized with a beta-hCG based immunocontraceptive vaccine.

IgG subclass distribution of antibodies against human chorionic gonadotropin (hCG) and diphtheria toxoid (DT) was determined in the sera of women recruited into Phase II clinical trials of a beta-hCG based immunocontraceptive vaccine. Serum samples from 30 different individuals were analyzed. Anti-hCG antibody response was predominantly of IgG1 subclass, with a mean titer of 537.94 +/- 560 antibody units (AU). The other 3 subclasses showed considerably lower mean levels (IgG2, 16.46 +/- 8.33; IgG3, 3.22 +/- 8.48; IgG4, 56.65 +/- 82.60 AU). A good correlation was observed between the anti-hCG IgG1 antibody titers (r = 0.57, P < 0.01) and the bioneutralization capacity of sera. However, bioneutralization capacity of the sera from subjects capable of inducing IgG4 response was not significantly different from subjects not showing IgG4 antibodies. Similarly, a dominant IgG1 response was observed against diphtheria toxoid (DT) which has been used as one of the carrier proteins in the vaccine.