Outer Membrane Proteins of Francisella tularensis as Acellular Vaccines

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Outer membrane proteins (OMPs) and lipoproteins (IPs) of Gram-negative bacteria are of enormous importance as virulence factors, stabilizers of outer membrane integrity, and protective immune targets (vaccines). To date, little has been known regarding the OMPs of Francisella tularensis (Type A) strains that are pathogenic for humans (e.g., F. tularensis SCHU S4). However, selected OMPs could prove invaluable as subunit vaccines for tularemia. In this regard, we have achieved two important milestones that warrant further investigation of the OMPs as acellular vaccines for tularemia. First, we developed a sucrose density gradient method for the physical separation of the outer and cytoplasmic membranes of F. tularensis (J.F. Huntley et al., 2007, J. Bacteriol. 189:561). This method has allowed, for the first time, direct examination of the OMP components of this important Category A select agent. Second, we have demonstrated that OMP-immunized mice are protected against intranasal challenge with SCHU S4. We now wish to extend these studies by completing the identification of the entire spectrum of OMPs in F. tularensis SCHU S4 (Aim 1). We also will test native and recombinant OMPs of SCHU S4 for their vaccinogenic potentials using mouse models of tularemia (Aim 2). Various routes for mouse immunizations (intraperitoneal, intranasal) and pulmonary challenges (intranasal, aerosol) will be employed. As part of this initiative, we also will examine newer adjuvants (e.g., cationic lipid-DNA liposomes, ISCOMs, CpG, and AdDP) to potentially enhance immunoprotection. In Aim 3, we shall investigate the humoral aspect of protective immunity induced by OMP vaccines by performing passive transfer experiments in mice, and by assessing antibody classes and isotypes elicited. Included in these studies will be assessments of key correlates of protective immunity (Th1 and Th2 cytokines, regulators, etc.); humanized mice may be particularly useful for these studies. As an off-shoot of this project, we also shall evaluate the roles of selected OMPs and LPs as virulence factors for F. tularensis by examining OMP-deficient mutants in both in vitro (infection/growth in human monocytes) and in vivo (mouse infection) systems. The combined studies will provide important new knowledge for understanding F. tularensis pathogenesis and for devising new acellular vaccines for tularemia.