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PROGRESS IN HUMAN REPRODUCTION RESEARCH. 1992; (22):4-5.During 1986-1988, the WHO Special Programme of Research, Development and Research Training in Human Reproduction used the diphtheria toxoid as a carrier for a fragment of the human chorionic gonadotropin (hCG) molecule (a conjugate immunogen) and an immunostimulant in a phase I clinical trial of this prototype antifertility vaccine in sterilized women. Between 1990 and 1991, it conducted teratology studies in rats and rabbits to determine whether the vaccine causes fetal abnormalities. The vaccine did not adversely affect either the animals or their fetuses. Clinical trials of the vaccine's effectiveness (phase II trials) are scheduled for 1992. At least 2 injections several weeks apart, are needed to produce an anti-hCG immune response which is only effective for 3-6 months, however. So the same components of the original vaccine were placed in a polymer to deliver the vaccine slowly over a prolonged and predetermined time frame. WHO hoped that this advanced vaccine would raise effective immunity levels long enough to last for at least 1 year after 1 injection. WHO is conducting dose-response and toxicity studies of this prototype vaccine in rabbits and baboons to identify the optimal dose which would elicit an effective immunity level over a desired period of time and would be safe for testing in humans. WHO hopes to begin a phase I clinical trial with this advanced anti-hCG vaccine in late 1992. WHO anticipates that the preclinical and clinical trials will reveal a need for further modifications and improvements. WHO is supported multicenter research on antitrophoblast vaccines which target membrane cells of the preimplantation embryo since 1985. It uses monoclonal antibodies (MABs) and recombinant DNA technology to identify and isolate surface molecules. So far this research has tested 15,000 MABs but is centering on 9 MAbs. A study in baboons showed that 1 MAB reduced fertility, even though researchers could only use minute amounts of the protein in the injection.