The increasing human population, particularly in several developing countries of Asia and Africa, has severe consequences on depletion of natural resources, scarcity of drinking water, threatening food security, in addition to its impact on the environment.
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Contraceptive vaccines can be broadly categorized into three groups. One group of the vaccines aims to inhibit production of gametes (spermatozoa and egg). These vaccines work by immune-mediated neutralization of gonadotropin releasing hormone (GnRH) secreted by hypothalamus. (...) Second group of vaccines involves generating immune response against spermatozoa- or oocyte-specific proteins with an aim to interfere with their functions and hence blocking fertilization process. Third group of vaccines target immune-mediated neutralization of human chorionic gonadotropin (hCG).
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Active immunization of female rhesus monkeys with the β-subunit of ovine LH (β-oLH) led to inhibition of fertility, which was accompanied by reduced progesterone levels during luteal phase.40 The anti-fertility effect mediated by active immunization with β-oLH could be reversed by administration of medroxyprogesterone acetate.41
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However, after two years, in spite of high anti-FSH antibody titers, immunized animals showed return of spermatogenesis with sperm count in the normal range. The sperm morphology, motility and their ability to penetrate zona-free hamster eggs was normal.45 In another study, active immunization of male bonnet monkeys with oFSH led to a significant decrease in the sperm count in the semen ejaculate, within 150 d post-immunization.46 Immunization with oFSH had no significant effect on testosterone levels and animals had normal libido. The immunized male monkeys when used for mating with normal females, failed to impregnate suggesting that this immunization procedure led to infertility. The block in fertility was reversible as concomitant with the decline in the anti-oFSH antibody levels, animals regained fertility.47 Active immunization with oFSH did not lead to any side effects.47
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The results from initial Phase-I studies on oFSH-based contraceptive vaccine in men are encouraging. However, the potential of FSH and/or its receptor based contraceptive vaccines warrant further investigations to establish a workable proposition for achieving contraception without any untoward side-effects.
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Observed infertility was invariably associated with ovarian dystrophy accompanied by follicular attresia. However, use of highly purified native porcine zona proteins supplemented with adjuvants other than complete Freund’s adjuvant led to a significant decrease in ovarian pathology.98-100
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However, β-hCG based contraceptive vaccine, only one that has been evaluated in humans, has not shown contraceptive efficacy that is comparable to any of the other alternative available contraceptive options described above.
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Attempts have been made to address this issue in women immunized with β-hCG based contraceptive vaccine. The anti-fertility effect of the vaccine was reversible as women with low anti-hCG antibody titers conceived and pregnancy progressed to term.150 Children born showed normal early developmental parameters.150
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