The Dual Role of Lipids of the Lipoproteins in Trumenba, a Self-Adjuvanting Vaccine Against Meningococcal Meningitis B Disease

Toll-like receptor 2 (TLR2) initiates potent immune responses by recognizing diacylated and triacylated lipopeptides. Its ligand specificity is controlled by whether it heterodimerizes with TLR1 or TLR6. We have determined the crystal structures of TLR2-TLR6-diacylated lipopeptide, TLR2-lipoteichoic acid, and TLR2-PE-DTPA complexes. PE-DTPA, 1,2-dimyristoyl-sn-glycero-3-phosphoethanolamine-N-diethylenetriaminepentaacetic acid, is a synthetic phospholipid derivative. Two major factors contribute to the ligand specificity of TLR2-TLR1 or TLR2-TLR6 heterodimers. First, the lipid channel of TLR6 is blocked by two phenylalanines. Simultaneous mutation of these phenylalanines made TLR2-TLR6 fully responsive not only to diacylated but also to triacylated lipopeptides. Second, the hydrophobic dimerization interface of TLR2-TLR6 is increased by 80%, which compensates for the lack of amide lipid interaction between the lipopeptide and TLR2-TLR6. The structures of the TLR2-lipoteichoic acid and the TLR2-PE-DTPA complexes demonstrate that a precise interaction pattern of the head group is essential for a robust immune response by TLR2 heterodimers. Copyright 2009 Elsevier Inc. All rights reserved.

Meningococcal outer membrane proteins have been used for over 20 years in more than 80 million doses; either as carrier protein in a Haemophilus influenzae type b (Hib) polysaccharide conjugate vaccine or as vesicle vaccine formulations against meningococcal disease. Conventional wild-type outer membrane vesicle (wtOMV) vaccines are the only formulations that have shown efficacy against serogroup B meningococcal disease. This has been demonstrated in Cuba, Norway and New Zealand; where epidemics, dominated by one particular strain or clone, were causing high rates of disease and wtOMV vaccines have been used for epidemic control. The most significant limitation for widespread use of wtOMV is that the immune response is strain-specific in infants, mostly directed against the immuno-dominant porin protein, PorA. The natural orientation of surface-exposed membrane antigens and the preservation of good physico-chemical stability are key features of OMV vaccines. The efficacy, tolerability and safety of wtOMV vaccines have been well proven. The most recent experience from New Zealand demonstrated a vaccine effectiveness of 80% for children less than 5 years of age, over a period of 24 months. Such results are encouraging for the further use of "tailor-made" OMV vaccines for epidemic control. Moreover, it provides opportunities for development of OMV vaccines with various additional cross-protective potential. There is good reason to believe that in the coming few years the "OMV-concept" will be exploited further and that a number of cross-protective "universal" antigens will be included in vaccines against serogroup B meningococcal disease. The desire to have a global vaccine strategy that enables susceptible individuals to be protected against all the relevant serogroups of meningococcal disease may become a reality.

Neisseria meningitidis binds factor H (fH), a key regulator of the alternative complement pathway. A approximately 29 kD fH-binding protein expressed in the meningococcal outer membrane was identified by mass spectrometry as GNA1870, a lipoprotein currently under evaluation as a broad-spectrum meningococcal vaccine candidate. GNA1870 was confirmed as the fH ligand on intact bacteria by 1) abrogation of fH binding upon deleting GNA1870, and 2) blocking fH binding by anti-GNA1870 mAbs. fH bound to whole bacteria and purified rGNA1870 representing each of the three variant GNA1870 families. We showed that the amount of fH binding correlated with the level of bacterial GNA1870 expression. High levels of variant 1 GNA1870 expression (either by allelic replacement of gna1870 or by plasmid-driven high-level expression) in strains that otherwise were low-level GNA1870 expressers (and bound low amounts of fH by flow cytometry) restored high levels of fH binding. Diminished fH binding to the GNA1870 deletion mutants was accompanied by enhanced C3 binding and increased killing of the mutants. Conversely, high levels of GNA1870 expression and fH binding enhanced serum resistance. Our findings support the hypothesis that inhibiting the binding of a complement down-regulator protein to the neisserial surface by specific Ab may enhance intrinsic bactericidal activity of the Ab, resulting in two distinct mechanisms of Ab-mediated vaccine efficacy. These data provide further support for inclusion of this molecule in a meningococcal vaccine. To reflect the critical function of this molecule, we suggest calling it fH-binding protein.