The safety and immunogenicity of a group B meningococcal vaccine, consisting of N-propionylated (NPr) B capsular polysaccharide conjugated to tetanus toxoid, was tested for the first time, in 17 healthy male volunteers aged between 18 and 40 years. Four escalating dosages of vaccine were tested and each was given as three intramuscular injections at 4-week intervals. The vaccine was well tolerated and induced only mild and transient, dose-dependent, injection-site reactions. One month after the last injection, there was no evidence of the production of autoantibodies or antibodies binding to PSA-NCAM. The vaccine induced an increase in the pre-existing titres of IgM specific to B polysaccharide and NPr B polysaccharide. Moreover, it induced IgG antibodies specific to NPr B polysaccharide, which were undetectable before vaccination. However, no functional activity of vaccine-induced antibodies was demonstrated in bactericidal assays, opsonophagocytic tests or passive protection tests.
