Antibody response and characteristics of antibodies in women immunized with three contraceptive vaccines inducing antibodies against human chorionic gonadotropin.

Data are presented on antibody titers generated in 88 women immunized with three formulations of antihuman chorionic gonadotropin (hCG) vaccine, namely, beta-hCG (formulation B); beta-hCG associated with alpha-subunit of ovine luteinizing hormone (LH) (formulation A) and beta-hCG + beta-ovine LH (formulation M), each linked to tetanus toxoid and cholera toxin chain B as carriers. Each formulation was tested at two dose levels (100 and 500 micrograms). All women without exception developed anti-hCG antibodies having hCG-binding capacity above 20 ng mL-1 (0.5 nM), a level considered to be the threshold for prevention of pregnancy. Formulations A and B gave relatively better immunogenic response in human subjects than M. In each case, the antibody response was reversible. The mean duration of response above 20 ng was 35 to 37 weeks for formulation A, 34 weeks for B, and 17 to 20 weeks for M. Antibodies induced by three formulations of the vaccine had high-affinity (Ka 10(9)-10(10)M-1) for binding with hCG. They were devoid of cross-reaction with human follicle-stimulating hormone and thyroid-stimulating hormone but, as expected, cross-reacted with human LH. Antibodies were competent to block the hCG induced ovarian hyperemia.