Injectable silicone implants as vaccine delivery vehicles.

Area of Science:

• Veterinary immunology
• Biomaterials science
• Vaccinology

Background:

• Injectable silicone implants offer potential as sustained-release vaccine delivery vehicles.
• Previous in vitro studies demonstrated antigen release profiles for matrix and covered rod implants.

Purpose of the Study:

• To evaluate injectable silicone implants as vaccine delivery systems in sheep.
• To compare the immunogenicity and duration of antibody responses induced by two implant types against model antigens and clostridial toxoids.

Main Methods:

• Sheep were vaccinated using matrix or covered rod silicone implants containing model antigen (avidin) or clostridial toxoids, with or without adjuvant (recombinant ovine interleukin-1beta; rovIL-1beta).
• Antibody responses, including IgG isotypes, were measured and compared to conventional aluminum hydroxide adjuvant (alum) vaccination.
• Implant preparation avoided harsh conditions (temperature, pH, organic solvents).

Main Results:

• Matrix implants induced responses comparable to alum, while covered rod implants significantly enhanced antibody titres and prolonged response duration.
• Covered rod implants promoted a balanced IgG1 and IgG2 response, unlike alum or matrix implants where IgG1 predominated.
• Clostridial vaccination with covered rod implants achieved up to 4-fold higher protective antibody titres than alum controls.
• All implant responses were dependent on adjuvant inclusion.

Conclusions:

• Injectable silicone implants, particularly the covered rod type, are effective vaccine delivery vehicles in sheep, inducing superior and prolonged antibody responses.
• The covered rod implant's zero-order release profile is advantageous for long-term immunity and balanced isotype production.
• Silicone implants represent a promising alternative to conventional vaccination methods in veterinary medicine.