As part of its program to develop contraceptive tools to aid in the management of overabundant wildlife populations, the NWRC has developed a single-injection GnRH immunocontraceptive vaccine called GonaCon™. GonaCon™ has been tested and shown to provide contraceptive effects lasting up to five years in many overabundant species, including white-tailed deer, domestic and feral pigs, bison, wild horses, cats, dogs and California ground squirrels.
A single-shot vaccine that provides a multi-year contraceptive effect requires:
(1) optimization of the vaccine structural design,
(2) optimization of the dose for each target species,
(3) use of the best adjuvant available, and
(4) development of a delivery system that will protect the injected antigen from rapid destruction by the animal's immune system.
Multiple-shot vaccines are much less demanding with regard to optimal vaccine design.
The design of the GnRH vaccine mimics the repetitive epitopes found in many pathogens. An epitope is the part of a macromolecule that is recognized by the immune system, specifically by antibodies, B cells, or T cells. Pathogenic viruses and bacteria typically exhibit rigid, highly-organized, highly-repetitive protein epitopes. High epitope density in a highly-organized, repetitive arrangement is important in ß-cell responsiveness. Although ß cells are unresponsive to repetitive epitopes that are poorly organized, repetitive epitopes of proper spacing can stimulate multiple surface receptors of similar spacing. The repetitive epitope pattern permits a cross-linking activation of ß-cell receptors, providing an extremely strong, long-lasting immune response. Mimicry of the repetitive nature of pathogen epitopes is an important aspect of the KLH-GnRH conjugate design. The GnRH peptide, which is analogous to the repetitive epitope, was designed to ensure consistent alignment of the peptide when coupled to the KLH carrier.
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