Bacterial ghosts as a delivery system for zona pellucida-2 fertility control vaccines for brushtail possums (Trichosurus vulpecula).

The introduced brushtail possum is a serious pest in New Zealand and there is much interest in the development of an immunocontraceptive vaccine for population control. Immunisation of female possums against recombinant possum zona pellucida protein-2 (ZP2) is known to reduce embryo production by 72-75% but successful development of fertility control will depend on a delivery system that is effective for field use. Bacterial ghost vaccine technology is a promising system to formulate a non-living vaccine for bait or aerosol delivery. The N-terminal (amino acid residues 41-316, ZP2N) and C-terminal (amino acid residues 308-636, ZP2C) regions of possum ZP2 were fused to maltose-binding protein and expressed in the periplasmic space of Escherichia coli NM522 bacterial ghosts. Female possums (n=20 per treatment group) were immunised with 20mg of either plain ghosts, ZP2N ghosts, or ZP2C ghosts in phosphate-buffered saline applied to the nostrils and eyes (nasal/conjunctival mucosa) at weeks 0, 2 and 4. Effects of immunisation on fertility were assessed following superovulation and artificial insemination. Both constructs evoked humoral (antibody) and cell-mediated immune responses in possums and significantly fewer eggs were fertilised in females immunised against ZP2C ghosts. Results in this study indicate that bacterial ghosts containing possum ZP antigens can reduce possum fertility when delivered by mucosal immunisation and offer a promising delivery system for fertility control of wild possum populations.