Pseudomonas aeruginosa (PA) is a common encapsulated, gram-negative opportunistic pathogen that causes nosocomial infections. It has one of the highest mortality rates (as high as 60% in some cases) and unfortunately, current antibiotics are rendered inefficient due to the emergence of multi-drug resistant bacteria. Despite several efforts, no successful vaccine against PA has been commercialized. OprF (outer membrane porin F) plays an important role in regulating the cell structure of PA. Preliminary results show that specific OprF domains elicit a high immune response and therefore, could be potential vaccine targets. Further, it has been reported that the use of adjuvants such as N-palmitoyl-S-[2,3-bis(palmitoyloxy)-(R,S)-propyl]-(R)-cysteinyl-seryl(lysyl)3-lysine (Pam3CysSK4) induces a helper TH-1 response that is related to an improved survival rate in PA patients. We have successfully expressed a chimeric form of OprF (OprF4DOMCys) that consists of four antigenic linear B-cell domains linked together and a terminal cysteine for conjugation. We have also synthesized the lipid adjuvant with a terminal maleimide to covalently bind to the antigen. To formulate a successful delivery system for our vaccine, we used a combination of two neutral lipids that were prepared by the extrusion method. Groups of mice were injected using the characterized formulations, with and without the antigen, and the immune responses were monitored. We obtained promising results from our current set of vaccinations and obtained antibodies that recognize PA. Data from an MTT assay shows that our current vaccine formulation is non-toxic. Furthermore, we are in the process of preparing a glycoconjugate by coupling the protein (OprF4DOMCys) to an LPS-based trisaccharide antigen via an aldehyde linker to obtain an improved immune response. We were successful in forming the glycoconjugate with OprF4DOMCys using an aminoxy-model sugar. Final glycoconjugates will be formulated into vaccines and studied in mice.

Formulating a liposomal based vaccine construct for testing against Pseudomonas aeruginosa

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