Mechanisms of action of adjuvants in pigs

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Adjuvants are substances which enhance immune responses to vaccines. To date, adjuvants have been used in billions of doses of vaccines for animals. Despite their extensive use, little is known about how adjuvants work. A famous immunologist once stated that "adjuvants are the immunologist's dirty little secret". The lack of detailed understanding of how adjuvants work is a barrier to their rational use in vaccines. Furthermore, knowing how adjuvants work would alleviate some perceptions regarding their safety.  There is a consensus that most adjuvants act by stimulating innate immunity which in turn directs the development of antigen-specific immunity. There is plenty of evidence to support that adjuvants influence various aspects of innate immunity including; the production of chemical mediators (cytokines and chemokines), recruitment of immune cells and the promotion of antigen transport to draining lymph nodes. We have published extensively on the strong activity of a novel adjuvant PCEP, which is a synthetic biodegradable polyphosphazene polymer. We have shown that PCEP dramatically increases immune responses to a variety of experimental bacterial and viral vaccines. Most of these earlier studies were done in mice, but we have recently demonstrated that PCEP is a promising adjuvant in pigs. We have explored the potential of PCEP in improving swine influenza virus (SIV) vaccines for pigs in other projects. Prior to our work of the past few years, no information was available on how PCEP works in pigs. Since most adjuvants act by stimulating innate immunity, we reasoned that investigating how PCEP activates innate immunity will provide valuable information on how this adjuvant works in pigs. In the past several years we have obtained evidence from in vivo studies in pigs indicating that PCEP induces alterations in expression of immune genes, production of chemical mediators (cytokines and chemokines) and cell recruitment to the site of injection. We will now build on these studies to further elucidate how PCEP works by continuing in vivo studies and start on in vitro studies to provide insight into how the adjuvant interacts with the target cells. We propose the following studies; 1) Identify immune cells recruit to injection site by PCEP, 2) Determine whether antigen contributes adjuvant activity in a vaccine, 3) Compare immune cells recruited by PCEP injected ID versus IM injection, 4) Determine whether formation of a depot is required for adjuvant activity of PCEP, 5) Investigate activation of immune cells by PCEP in vitro, and 6) Study PCEP-induced phosphorylation signalling in porcine cells in vitro. Understanding how adjuvants work will provide valuable information on their rational use and also on their safety. Results from the proposed work will be a significant contribution to this end. In addition, the proposed studies will lay groundwork for similar studies with other adjuvants used in animal vaccines.