Birth control vaccines.

Birth control vaccines

Most vaccinations prime a person's immune system to fight an infectious disease. But clinical trials are under way around the world on a novel immunization procedure aimed at preventing unwanted pregnancies. The vaccine in clinical trials creates temporary infertility by targeting antibodies against a hormone crucial to pregnancy. However, biotechnology may produce a wide variety of potential antifertility vaccines.

"Vaccines are under development for at least eight of the many possible points where the reporductive cycle can be intercepted,' says G. P. Talwar, director of India's National Institute of Immunology at Jawaharal Nehru University in New Delhi. The most extensive work so far involves vaccines made of a subunit of the hormone human chorionic gonadotropin (beta-hCG). Four hCG vaccines are now in clinical trials. The hCG hormone is thought to signal the ovaries to sustain a gland called the corpus luteum during a pregnancy. In some of Talwar's work, beta-hCG is linked to tetanus toxoid in order to increase its overall immunity-stimulating potency while also producing immunity to tetanus.

Safety (phase I) trials of the hCG vaccine have been completed in six cities, Talwar says. No side effects, including menstrual abnormalities, were observed. Antibody levels gradually dropped during seven to 16 months and normal fertility returned. However, subjects showed a wide disparity in the levels of hCG antibodies produced, so the scientists are using a variety of techniques to increase the response. These include adding extra substances, called adjuvants, to the vaccine and adding another protein subunit to lock the beta-hCG into the optimal conformation. Biotechnology procedures are being used to isolate the beta-hCG gene and to insert the gene into viruses already used as vaccines.

Scientists are attempting to create birth control vaccines using each of four other reproductive hormones. In addition, they are searching for components of the sperm and egg surface that may be good targets for antibody attack. "We are using monoclonal antibodies to identify the targets and then fishing out the genes,' Talwar says. In animals, monoclonal antibodies to reproductive hormones have been used to terminate pregnancies without interfering with fertility.