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: Dan Granoff
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Research

OVERVIEW OF MAIN RESEARCH PROJECTS

Neisseria meningitidis is a Gram-negative encapsulated bacterium that causes meningitis and sepsis. There are no broadly effective vaccines available for prevention of disease caused by group B strains, which account for 50% or more of cases of disease in the US and Europe. Because the group Bcapsule is an autoantigen, alternative vaccine strategies are needed. We are investigating the vaccine-potential of an antigen called “factor H binding protein” (fHbp), which is a surface-exposed lipoprotein that was discovered by genome mining. We have shown that serumanti-fHbp antibodies bind to the bacteria, activate complement-mediated bacteriolysis, and inhibit bindingof the human complement down-regulatory protein, factor H (fH). In the absence of bound fH, the organismbecomes more susceptible to complement-mediated bacteriolysis. One limitation of fHbp as a vaccine isantigenic variability (3 groups with subvariants within groups). Antibodies elicited by fHbp in the  variant group 1 are not bactericidal against strains expressing variant 2 or 3 proteins (and vice versa). To circumvent thisproblem, we are constructing recombinant chimeric fHbp molecules that express epitopes from different variant groups. In mice, a prototype chimeric fHbp vaccine we prepared elicited serum bactericidal antibodies against strains expressing fHbp variant 1, 2 or 3.

Because recombinant fHbp expressed and purified from E. coli may not express all of the epitopes important for eliciting broad serum bactericidal activity, we are preparing native outer membrane vesicle (OMV) vaccines from N. meningitidis strains engineered to over-express fHbp. Since detergent treatments used to removeendotoxin from conventional OMV vaccines extract fHbp, we attenuate endotoxin activity by inactivating a lipidA biosynthesis gene, LpxL1. A native OMV from the mutant was 1000- to 10,000-fold less active in stimulatinghuman PBMCs to produce proinflammatory cytokines than OMV from the wildtype strain. In mice, a nativeOMV vaccine from a LpxL1 knockout mutant with over-expressed fHbp elicited broader serum bactericidal activity than control recombinant fHbp or detergent-extracted OMV vaccines.

Meningococci also cause explosive epidemics in sub-Saharan Africa. Although most cases are caused by capsular group A strains, group W-135 and X strains also cause epidemics in this region. A second project is to develop a meningococcal vaccine for Africa that targets strains from all capsular groups. Our approach builds on our experience with “group B protein-based vaccines”, which also elicit protective antibodies against strains with other capsules. Our hypothesis is that a native OMV vaccine prepared from mutant strains from Africa will elicit broad serum bactericidal antibodies directed at fHbp, porin molecules (PorA) and other antigens expressed by strains from Africa. To develop a vaccine for Africa, we are investigating genetic lineages and sequence diversity of genes encoding fHbp, PorA and other vaccine antigens among meningococcal isolates from a geographically diverse collection of African strains. The results will be used to select antigenic variants and strains to engineer mutants, which will be used to prepare native OMV vaccines that target disease in Africa. If successful, our findings support development of an OMV vaccine for humans for control of meningococcal epidemics in sub-Sahara caused by strains from all capsular groups. Details of published work on this and other projects are provided in separate links to this website.

Our research on these approaches is described in detail on the following links to downloadable pdf files:

Revised: Friday, November 14, 2014 2:07 PM

 


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