Reproduction in Domestic Animals

Controlling Animal Populations Using Anti-Fertility Vaccines 181strongly conserved among species (Benoff 1997) and it ispossible that species-specificity of fertilization may bemoderated by differences in carbohydrates on the zonasurface. Current data demonstrate that vaccination withthe three pZP glycoproteins induces immunocontraceptionin multiple species of mammals. To explainspecies-specificity of the carbohydrates and the speciesindependenteffect of pZP, the author suggests that thehypothesis still has some merit. Binding of anti-pZP IgGto surface carbohydrate epitopes probably preventssperm binding by direct and indirect interference. Thisis supported by the observation that 63% glycosidicrecognition capability of our anti-pZP antibodies(Barber 2001). The remainder of the polyclonal IgGantibodies recognizes the exposed protein matrix. Bindingof the ZP protein matrix by these IgGs probablycompletely blocks the induction of the acrosomereaction. Hence polyclonal IgGs block fertilization bypartial hindrance of binding and possible blockade ofacrosome reaction induction (Mahi-Brown et al. 1985;Henderson et al. 1988).Vaccine preparationThe ZP glycoproteins are secreted to combine with eachother in the perivitelline space in a coordinated process.However, in vitro, the protein harvesting of pZP forimmunocontraceptive vaccines varies from laboratoryto laboratory. We also know that the purification andstorage of the ZP glycoproteins varies from laboratoryto laboratory. The production and storage differencesmight also alter the site of presentation of the ZPglycoproteins. The purification and storage of theproteins might be extremely critical to antigen bioavailability.How have the glycoproteins recombined andwhat antigenic sites have been exposed? More importantly,does this represent the in vivo structure? Formouse proteins, we know that the individual glycoproteinsrecombine or repolymerize in an homomeric orheteromeric manner (Litscher et al. 2008). Repolymerizationoccurs under non-denaturing conditions evenafter the treatment of the glycoproteins with SDS, heat,urea or lyophilization. In the in vivo environment, thepolymerization of ZPs probably occurs in a coordinatedmolar integration. However, under in vitro conditions,especially with homomeric or heteromeric repolymerization,there could be novel aggregate presentations.The novel presentation could be in part an explanationof the effect on multiple species. The same rules ofantigen presentation also apply to synthetic vaccines.For the synthetic or recombinant vaccines, the antigenicityis also associated with the site of the source DNAsequence, the amount and quality of glycosylation, andthe tertiary assembly.The use of a complete vaccine containing all threepZP glycoproteins clearly works (Liu et al. 1989; Fayrer-Hoskenet al. 2000a,b, 2002; Delsink et al. 2002;Stoops et al. 2006) as an immunocontraceptive agent indifferent species. A more defined synthetic or recombinantvaccine might be safer and more effective. Thenecessity to standardize a vaccine product and have aready source has lead to the research into synthetic ZPvaccines (Choudhury et al. 2007; Duckworth et al.2007), but to date no synthetic vaccine has been usedextensively.Another consideration for vaccine usage is the role ofadjuvants. When ZP glycoproteins are adjuvented byconjugation, the ZP proteins are conjoined through thesulfhydryl linkages, and are presented to the immunesystem in a specific conformation. This might explainmore profound and unique effects of an adjuvant. Wehave used pZP with an adjuvant ImjectÒ (ThermoFisher, IL, USA), a maliamide-activated keyhole limpethaemocyanin. The conjugated product produced immunocontraceptionin gilts and showed significant degenerativepathology of the follicles and was probably due topresentation of B-cell epitopes. The other aspect of thevaccination is the role of the adjuvant. The role of addedadjuvants to the pZP appears to be vitally important. Todate, complete Freund’s (Delsink et al. 2007), incompleteFreund’s (Hannesdottir et al. 2004; Duckworth et al.2007), modified Freund’s (Lyda et al. 2005) and synthetictrehalose dicorynomycolate (STDCM) (Fayrer-Hoskenet al. 2002) have been used successfully. The adjuvantand pZP combination lead to stimulation of the immunemechanism. How much of it is due to the immunostimulantrole of the adjuvant and how much of it is dueto the pZP glycoprotein assembly after harvesting?Vaccination method and route of deliveryFor free-roaming populations, the antigen and adjuvantsgenerally will have to be delivered remotely. Thevaccine might be delivered with darts or in baits. Incase of dart delivery, the measure of success ispredicated by field conditions as this might includestalking on foot to helicopter delivery and the degree ofsuccess varies. From captive situations, e.g. elephants inzoos where there are controlled conditions, vaccinationsgenerally result in 100% efficacy (Fayrer-Hoskenet al. 1999). This is when compared with 80–100%vaccination titre efficacy in field when darting from ahelicopter (Fayrer-Hosken et al. 2000b). The practicalreality is that in the field, darting does not alwaysdeliver an intramuscular injection. Therefore, this is thepractical reality of field vaccination. The vaccineformulation also plays a role in the success of administration.The use of vaccine pellets (Turner et al. 2002;Lane et al. 2007) or lactide-glycolide (Kirkpatrick et al.1996; Liu et al. 2005) preparations for longer-actingvaccines makes the administration difficult. Oral baitingof a species-specific fertility vaccination would be veryexciting as a strategy, as seen with oral vaccinationagainst rabies (Tordo et al. 2006). The possibility oforal vaccines that employ plants (Tacket 2005) that areengineered to produce a glycosylated ZP product is anexciting possibility (Polkinghorne et al. 2005). Oralvaccines may provide a viable administration route,especially for populations that are difficult to reach.Species-specificity or bait-specificity to deliver theimmunocontraceptive to only the target species presentsthe most worrisome contraindication. While theremight be a possibility that baited or species-specificsites for intra-nasal (Corner et al. 2001; Costantinoet al. 2007) delivery of immunocontraceptives, this canonly be evaluated in situ. The most important facet ofÓ 2008 The Author. Journal compilation Ó 2008 Blackwell Verlag