An orally-delivered immunocontraceptive vaccine is being developed for the
control of fox populations. A number of genes (PH-20,
LDH-C4, ZP3) encoding gamete proteins have been cloned,
produced in recombinant expression systems and used in fertility trials to
test the efficacy of these antigens. As the immunocontraceptive vaccine will
be delivered in a bait, there is a requirement for a greater understanding of
the immune responses of the reproductive mucosa in canids, and the assessment
of the best vaccine delivery system that will evoke a mucosal antibody
response. Several vaccine delivery systems including microencapsulated
antigens, and both vaccinia virus and bacterial vectors are being
investigated. Oral administration of
Salmonella typhimurium recombinants expressing different
fox sperm antigens stimulates both systemic IgG responses to the antigen and a
mucosal immune response within the female reproductive tract in the fox,
indicating that salmonella may have potential with respect to the oral
delivery of antigen. The enhancement of mucosal immune responses to
orally-delivered vaccines is also being examined, research focussing on the
possible use of fox-specific cytokines or the β-subunit of cholera toxin
in forming part of the vaccine construct.