SPECIFICITY OF HUMAN BACTERICIDAL ANTIBODIES AGAINST PORA P1.7,16 INDUCED WITH A HEXAVALENT MENINGOCOCCAL OUTER-MEMBRANE VESICLE VACCINE

A set of isogenic strains was constructed from the meningococcal refer ence strain H44/76 (B:15:P1.7,16) which differed only in their outer m embrane protein (OMP) compositions. First, three isogenic strains lack ing the expression of either class 3 (PorB) or class 4 (RmpM) OMP or b oth were obtained. Second, three isogenic class 1 OMP loop-deficient s trains of H44/76 lacking the predicted loop 1 or 4 or both of class 1 OMP (PorA) were obtained. Third, three isogenic class 1 OMP strains wh ich differed by point mutations in the predicted loop 4 of subtype P1. 16 were constructed. Strains were constructed through transformation w ith gene constructs made in Escherichia coli and their homologous reco mbination into the meningococcal chromosome. This study describes the contribution of one of the six class 1 OMPs, PorA P1.7,16, in the deve lopment of bactericidal antibodies after a single immunization of adul t volunteers with 50 or 100 mu g g of protein within a hexavalent PorA outer membrane vesicle vaccine. PorA-, PorB-, and RpmM-deficient isog enic strains were used to define the human immune response against Por A. The loop-deficient isogenic strains were used to define the contrib ution of loops 1 and 4 of PorA in the development of bactericidal anti -PorA antibodies. The isogenic strains carrying a point mutation in lo op 4 were used to study the cross-reactivity of the induced bactericid al antibodies against target strains showing microheterogeneity. The r esults indicate that a single immunization with the hexavalent PorA va ccine induced a dose-dependent bactericidal immune response, which is directed mainly against PorA. The epitope specificity of antibodies is directed mostly against loop 1, although loop 4 and as-yet-unidentifi ed epitopes of PorA P1.7,16 are also involved.