Gene variability and degree of expression of vaccine candidate factor H binding protein in clinical isolates of Neisseria meningitidis

The factor H binding protein (fHbp) is currently being evaluated in clinical trials as a vaccine candidate for a meningococcal group B vaccine. We have previously described the prevalence and sequence variation of fHbp (Jacobsson et al., 2009) and here we investigate the expression of the antigen. The present study includes isolates from carriers (n = 62) and patients with invasive Neisseria meningitidis infections (n = 146), of which 62 had a fatal outcome. Among the invasive isolates from patients with fatal and non‐fatal infections fHbp allele 1 was most common (42% and 29% respectively), but it was only identified in 3% of the carrier isolates, where allele 16 was most frequent (13%). The Fluorescence‐activated cell sorting analysis identified fHbp expression in all except seven isolates and further analysis by Western blot showed that five of these seven samples were indeed negative using a polyclonal anti‐fHbp serum. The negative isolates belonged to serogroup B fHbp allele 24, Y allele 104, and W‐135 allele 16 (all invasive). Two were non‐serogroupable carrier isolates (allele 21 and 101). An interesting finding is that isolates from invasive infections with fatal outcome had lower expression of fHbp or lower affinity for the fHbp antibody compared to isolates from non‐fatal invasive infections and carriers.