Immunological response and ovarian histology of squirrel monkeys (Saimiri sciureus) immunized with porcine zona pellucida ZP3 (Mr = 55,000) macromolecules

Pathophysiology of white-tailed deer vaccinated with porcine zona pellucida immunocontraceptive

White-tailed deer (n=14 treated, n=7 control) were examined postmortem to identify any possible pathophysiology resulting from PZP immunocontraception vaccination. Deer were treated twice in 1997; given a booster in 1998, with six being revaccinated in September 2000. Granulomas were found at injection sites of most deer, even 2 years post-treatment. Eosinophilic oophoritis occurred in 6 of 8 (75%) deer vaccinated in 1998, and 3 of 6 (50%) revaccinated in 2000. The 2000 revaccinates without oophoritis, had significantly fewer normal secondary follicles than control females (P=0.03), and deer in the 1998 treatment group (P=0.04). PZP immunocontraceptive vaccine elicited ovarian pathologies in deer similar to those observed in other species.

Effect of porcine zonae pellucidae immunisation on ovarian follicular development and endocrine function in domestic ewes (Ovis aries)

Domestic ewes (Ovis aries) were immunised with porcine zonae pellucidae (pZP) or pZP conjugated to keyhole limpet haemocyanin (KLH) in adjuvant(s) to examine the feasibility of the species to serve as a model for further development of pZP-based vaccines in ungulates. Two immunisation groups were employed, with a third group receiving only adjuvant (n = 5 per group). Early in the study, oestrous activity was monitored by the use of a vasectomised ram fitted with a marking harness. Eventually, ewes were exposed to an intact ram for breeding. In addition, weekly serum and every-other-day faecal samples were collected to measure pZP antibodies and progesterone metabolite concentrations respectively. At the conclusion of the study, fecundity was established, and ovarian tissue was examined. Ewes immunised against pZP : KLH with adjuvant produced minimal antibody absorbance levels, displayed normal oestrous cycles, became pregnant upon introduction of the intact ram and exhibited normal ovarian histopathology. Ewes immunised against pZP with adjuvant produced high antibody absorbance levels, were acyclic following primary immunisation and were infertile. Examination of the ovarian tissue revealed atrophic changes that included: (1) the absence of growing follicles; (2) significant reduction in the number of primordial follicles; and (3) the presence of abnormal granulosa cell clusters lacking oocytes. Antisera displayed immunoreactivity to the major components of pZP, and immunohistochemical labelling of ovarian tissue showed specificity to the ZP. These data are the first generated in an ungulate species showing deleterious effects of pZP immunisation on folliculogenesis and oestrous cyclicity.

Immunologic responses and adverse reactions to Freund's-adjuvanted porcine zona pellucida immunocontraceptives in domestic cats

A vaccine of native PZP with Freund's adjuvant has been widely used in zoo and wild ungulates, but safety in felids has not been evaluated. General health, immune response, and ovarian histology were assessed in five domestic cats vaccinated with PZP-Freund's and five cats given Freund's adjuvant alone. Peak antibody titers occurred 3 weeks after the third vaccination, and no ovarian lesions were present 6 months after vaccination. Seven cats developed extensive granulomatous reactions at injection sites, lymph nodes, and multiple visceral organs including lungs and brain. Persistent hypercalcemia and compromised renal function occurred in three cats with elevated serum calcitriol of probable macrophage origin. One cat died from an injection site sarcoma. Because of these severe adverse reactions, Freund's adjuvant is contraindicated in cats, and other adjuvants for PZP vaccines should be tested in cats for adverse reactions before use.

EFFECTS OF PORCINE ZONA PELLUCIDA IMMUNOCONTRACEPTIVES IN ZOO FELIDS

Methods of contraception are necessary for management of zoo felids; however, the most commonly used contraceptive (melengestrol acetate implant) is associated with serious adverse reactions with long-term use. Porcine zona pellucida (pZP) vaccines are promising as contraceptives, but their safety in zoo felids has not been tested. pZP vaccine was administered to 27 female felids representing 10 species, including African lion (Panthera leo), Asian leopard (P. pardus), jaguar (P. onca), tiger (P. tigris), snow leopard (P. uncia), cougar (Felis concolor), Siberian lynx (F. lynx), Canada lynx (F. canadensis), serval (F. serval), and bobcat (F. rufus), in 15 facilities. Over 6 wk, each animal received three i.m. injections of 65 microg pZP with Freund's complete adjuvant (FCA), Freund's incomplete adjuvant, or carbopol as the adjuvant. Behavioral signs of estrus were seen in 14 of the vaccinated felids. An unacceptably high incidence of adverse reactions was seen including injection site swelling, lameness, limb swelling, or abscessation (or all) in five felids after injection with FCA as the initial adjuvant. Adverse behavioral signs, including increased irritability and aggression, were seen in four felids. Six of the felids were assayed for antibodies against pZP during the 12 mo after vaccination; all showed antibody production. Antibody levels appeared to peak 1-4 mo after vaccination began, although elevated antibody levels persisted in two animals for > 12 mo after the first injection. All vaccinated felids were ovariohysterectomized 3-13 mo after vaccination. Folliculogenesis was present in all treated animals, and there was no histopathologic evidence of inflammatory damage to ovaries. Contraceptive efficacy was not specifically evaluated in this study; however, two of the three felids housed with an intact male became pregnant during the study, one of which gave birth to healthy cubs.

Impact of feline zona pellucida glycoprotein B-derived synthetic peptides on in vitro fertilization of cat oocytes

Although immunocontraception based on porcine zona pellucida (ZP) proteins is widely applied in many species, it is not suitable for cat contraception due to the lack of cross-reactivity. Since the first ZP gene expressed during oocyte growth in domestic cats is ZPB, we assumed that immunization with feline ZPB (fZPB)-derived synthetic peptides may cause irreversible infertility, which would be preferable in stray cats. Thus, the present study evaluated the immunogenicity and the contraceptive potential of synthetic fZPB peptides. Antigenic epitope sequences were detected via epitope mapping using specific rabbit anti-fZP antibodies. Six peptides representing the recognized epitopes were synthesized subsequently. Two out of six peptides (ZPB amino acid residue 130–149 = P3 and 175–193 = P6) cross-reacted with anti-fZP antiserum in dot blot analysis and ELISA. Coupled to BSA, both peptides were utilized to produce specific antibodies in rats. Despite several booster injections the antibody titers monitored by ELISA did not exceed 1:5000. Both rat antisera were tested for contraceptive potential in cat in vitro maturation/in vitro fertilization (IVF). Antiserum against peptide P3 significantly inhibited sperm binding and fertilization of cat oocytes in vitro (57.3% of sperm binding; 41.5% of fertilization), whereas the inhibition by anti-P6 was not significant. Pre-incubation of sperm cells with both peptides before IVF failed to affect either sperm binding or fertilization (22.3 ± 3.7 sperm/egg vs 25.5 ± 5.8 for P3 and 20.7 ± 4.0 for P6, respectively). In conclusion, antibodies directed against one of the two identified antigenic determinants of fZPB inhibited sperm binding and IVF and therefore showed promising results as a contraceptive. However, the specific immune response and anti-fertile properties of this synthetic vaccine have to be examined in vivo to verify the suitability of its components.

The contraceptive potential of ZP3 and ZP3 peptides in a primate model

It has been known for some time that antibodies raised against ZP3, the major component of the glycoprotein shell that surrounds all mammalian oocytes, can successfully inhibit sperm-egg interaction in vitro. In our own studies using the non-human primate Callithrix jacchus, active immunisation was successfully achieved when homologous or heterologous ZP3 was used as an immunogen. However this long-term suppression of fertility was at the expense of ovarian function. An ovarian pathology was observed which was characterised by a disruption of folliculogenesis and depletion of the primordial follicle pool. Adverse auto-immune reactions have also been observed in mice following induction of immunity to mouse ZP3. Following careful selection of B-cell epitopes on mouse ZP3, peptide vaccines were formulated which could circumvent these adverse side effects and induce reversible infertility in actively immunised mice. To identify similar epitopes on primate ZP3, epitope mapping studies were performed and several candidate regions of the molecule were identified. These were incorporated into chimeric peptide vaccines and administered as single or triple peptide vaccines. Active immunisation successfully induced antibodies that bound exclusively to the zona pellucida of marmoset and human ovarian sections. These antibodies were able to suppress human sperm-egg binding by up to 60% in vitro. Encouragingly, no adverse side effects on ovarian function were observed following long-term immunisation however, no loss of fertility was consistently observed in vivo. Thus considerable research is still required to identify a combination of ZP epitopes that will induce reversible infertility in the absence of any ovarian dysfunction.

Molecular basis of sperm-egg interaction and the prospects for immunocontraception

As the molecular basis of sperm-egg interaction is resolved, so new opportunities are created for the development of immunological approaches to disrupt the process of conception. Thus, realisation that the zona glycoprotein, ZP3, serves as a specific receptor for spermatozoa, has prompted a detailed examination of its contraceptive potential. In primate models, recombinant ZP3 has been shown to suppress fertility very efficiently, however this efficacy is tempered by the appearance of adverse side-effects involving accelerated primordial follicle depletion and a lymphocytic infiltration of the ovarian stroma. Synthetic peptides encoding B-cell epitopes have been found to circumvent the lymphocyte response although the effectiveness of such reagents in preventing the loss of primordial follicles has not yet been determined. The induction of active immunity against sperm-specific antigens has also been shown to generate long term infertility in both males and females. Molecular and immunological techniques are now being used to produce a rapidly expanding list of unique sperm antigens which are currently being evaluated to determine their potential contribution to the development of safe, effective, contraceptive vaccines.

Evaluation of the contraceptive potential of recombinant human ZP3 and human ZP3 peptides in a primate model: their safety and efficacy

PROBLEM

The unique recognition events that result in the avid binding of mammalian spermatozoa to the surface of the zona pellucida (ZP) are being exploited in the development of contraceptive vaccines. In this study, the safety and efficacy of a vaccination strategy based on the induction of active immunity against purified, glycosylated, recombinant human ZP3 (rhZP3) has been evaluated in a primate model, Callithrix jacchus.

METHOD OF STUDY

Long-term infertility was established after immunization with rhZP3 and the resulting immune sera reacted with rhZP3 on an enzyme-linked immunosorbent assay (ELISA) and immunolocalized exclusively to the outer surface of native ZP on marmoset ovarian sections. However, this contraceptive effect was inevitably associated with the eventual appearance of an ovarian pathology characterized by a depletion of primordial follicles. In an attempt to circumvent this side effect, human ZP3 (hZP3) was epitope mapped and four continuous, immunodominant B-cell epitopes (hZP3(45-64), hZP3(93-110), hZP3(172-190) and hZP3(341-360) were evaluated for contraceptive efficacy in vivo. Using peptide-tetanus toxoid (TT) conjugates to enhance immunogenicity, antipeptide antibodies were raised against these immunogens, which also cross-reacted with rhZP3 on ELISA. In addition, antibodies against hZP3(45-64) and hZP3(172-190) recognized native ZP on marmoset ovarian sections when a microwave technique was used to enhance epitope presentation.

RESULTS

No ovarian pathology was observed after the long-term administration of these peptide immunogens, and fertility was suppressed when compared with TT controls but could not be correlated to the antibody titer.

CONCLUSION

Clearly, further research is required to identify optimal B-cell epitopes that will reliably induce infertility, free from any ovarian pathology.

Contraceptive vaccines

The basic principle of a contraceptive (or anti-fertility) vaccine is to use the body's own immune defence mechanisms to provide protection against an unplanned pregnancy. Factors such as: economic production, convenience of use, relatively long-lasting but reversible action, low failure rate, and the avoidance of mechanical devices or exogenous hormones make this approach a potentially attractive option for family planning programmes in both developing and developed countries. The major efforts in research and development have involved the prospect of active immunization against specific antigens of sperm, ovum, zygote and early embryo, and the pregnancy hormone hCG. Several anti-hCG vaccines have entered clinical trials and show promising results. These vaccines operate by preventing or interrupting pregnancy at the peri-implantation stage probably by neutralizing the luteotrophic action of hCG. The most refined vaccine is one directed against the unique C-terminal peptide on the beta-subunit of hCG. This vaccine provokes antibodies that are specific for hCG and do not cross react with hLH. Future research efforts aim to optimize the anti hCG approach, utilize new vaccine delivery systems, and broaden the spectrum of target antigens of potential utility for contraceptive vaccines.

Vaccines against fertility

The first evidence for the efficacy of a birth control vaccine in humans is now available from the Phase II trials on the human chorionic gonadotrophin vaccine in India. Several sperm antigens have been identified as potential contraceptive immunogens and zona pellucida antigens have been reported that reversibly control fertility.