Fertility control through active immunization using placenta proteins

Numerous studies have demonstrated that antibodies to placental proteins in a variety of species are capable of preventing or disrupting gestation. Early work in this area was primarily directed towards the passive immunization of rodents with heterologous antisera to whole placental extracts. Toxicity and renal damage often accompanied fertility inhibition. More recent studies reported less toxicity and a higher specificity of antibodies to reproductive function when anti-placental antibodies were absorbed with serum and extracts of non-reproductive organs. Few studies have been reported in which active immunization with placental proteins was employed. The most detailed studies of active immunization have employed highly purified placental hormones. Immunizations of rats and rabbits with human placental lactogen have resulted in marked reduction in reproductive function. Immunization of human females with chemically altered (hapten-coupled/ HCG resulted in the production of antibodies reacting with unaltered HCG and pituitary LH. These antibodies were capable of reducing the level of endogenous serum LH in pre- and post-menopausal women. The also altered the events of the menstrual cycle in premenopausal women. More specific inhibition of chorionic gonadotrophin has been obtained by immunization of baboons with the beta subunit of HCG. Antifertility effects without alterations in the menstrual cycle of female baboons immunized with the beta subunit of HCG have been reported. The antibodies produced in these animals reacted significantly with human LH in vitro. The possibility of using hormonal and non-hormonal placental proteins as antigens for the specific immunological inhibition of fertility remains.