SP: Writing review & editing, Investigation, Validation. expressing fHbp, NHBA and NadA produced antibodies to all the antigens. Furthermore, serum bactericidal activity (SBA) was induced by the immunisation, with mOMVs expressing NadA displaying high SBA titres against anadA+MenB strain. The work highlights the potential of mOMVs fromN. cinereato induce functional immune responses against multiple antigens involved in the protective immune response to meningococcal disease. Keywords:modified outer membrane vesicles, mOMVs,Neisseria cinerea, Flupirtine maleate meningitidis, fHbp, NHBA, NadA,Neisseria meningitidis == Introduction == Neisseria meningitidisis a Gram-negative diplococcus that asymptomatically colonises the nasopharyngeal mucosa of healthy carriers. On some occasions, the bacterium traverses the mucosal epithelium and invades the bloodstream, leading to invasive meningococcal disease (IMD), a potentially life-threatening disease and a major cause of bacterial meningitis and septicaemia worldwide (1). There are 13 serogroups ofN. meningitidisbased on the composition of polysaccharide capsule, with most IMD cases primarily caused by serogroups A, B, C, W, Y and X Rabbit Polyclonal to CFLAR (2). Although conjugated polysaccharide vaccines are used for immunization againstN. meningitidisserogroups A, C, Y, and W (2), this has not been the case forN. meningitidisserogroup B (MenB). A polysaccharide-based vaccine for MenB was disregarded for two major reasons: its theoretical risk for autoimmunity due to the similarity of the chemical composition to sialic acid found on many human cell types and its low immunogenicity (3,4). Therefore, several non-capsular outer membrane vesicle (OMV) vaccines were used during epidemics of MenB (5), and vaccines based on recombinant proteins identified by proteomic and reverse vaccinology approaches are currently available (6,7). Two protein-based vaccines against MenB currently in use are the four-component 4CMenB vaccine (Bexsero, GlaxoSmithKline) and the bivalent fHbp2086 vaccine (Trumenba, Pfizer). These vaccines use subcapsular proteins that are widely present not only in serogroup B strains, but also across different meningococcus serogroups (8,9). The factor H binding protein (fHbp) vaccine (formally known as LP2086) consists of two lipidated fHbp (8). The 4CMenB vaccine contains three components that were identified by reverse vaccinology based on the complete genome sequence of a pathogenic reference MenB strain (strain MC58): the fHbp variant 1.1 fused to the genome-derivedNeisseriaantigen (GNA) 2091, theNeisseriaadhesin A variant 2/3 peptide 8 (NadA-8), and theNeisseriaHeparin binding antigen peptide 2 (NHBA-2) fused to GNA1030 (9). Besides these three recombinant surface-exposed protein antigens, the vaccine contains detergent-extracted OMVs from the New Zealand strain NZ98/254 containing porin A (PorA) P1.4 (10). While these vaccines have successfully decreased the incidence of group B meningitis in both infants and adults, the challenge of high production costs persists (11). FHbp is a surface-exposed protein expressed in almost allN. meningitidisstrains and divided in two subfamilies, A and B (12). Due to the variations in amino acid sequences, each fHbp protein can be identified by an ID number (12). FHbp binds to human factor H, a negative regulator of the alternative pathway of complement activation and is an immune-evasion factor inNeisseria(13,14). NHBA is a surface protein that binds to heparin, which can confer a level of serum resistance as well as binding to heparin sulphate proteoglycans to aid in bacterial adherence to epithelium (15,16). An additional role of NHBA is to promote biofilm development through the binding with extracellular DNA involved in the initial stages of cell-to-cell attachment (17). NHBA is present in Flupirtine maleate allN. meningitidis, N. gonorrhoeaeand some commensalNeisseriaspecies (18). NadA is an outer membrane protein (OMP) that promotes adhesion to and invasion of host cells during bacterial infection and colonisation of the human respiratory tract (18). There are four variants of NadA, with variants 1 and 2/3 found in invasive meningococci (19). Unlike fHbp and NHBA, thenadAgene is only found in approximately 30% ofN. meningitidisisolates, but importantly it is present in approximately 75% of hypervirulent MenB strains (18,20,21). In vitromeasurement of functional antibodies Flupirtine maleate has been considered for decades as a correlate of protection against many bacterial species (22). Serum bactericidal activity (SBA) assays are commonly used as correlates of protection for vaccines againstN. meningitidis(2326), with SBA titres having been used to prioritise antigens for incorporation.