Construction of a multivalent meningococcal vaccine strain based on the class 1 outer membrane protein

Outer membrane complexes (OMCs) are promising vaccine candidates for protection against meningococcal disease. However, a major obstacle to this approach is the fact that the protective antibodies induced are generally type specific. In an attempt to overcome this problem, we have investigated the possibility of constructing a multivalent vaccine strain by insertion of an additional class 1 outer membrane protein-encoding gene. Starting with a derivative of strain H44/76 deficient in class 3 outer membrane protein, a second class 1 gene was inserted into the chromosome, through homologous recombination with a suicide plasmid carrying the class 1 gene from strain 2996 placed within a class 5 gene. In this way, a strain was obtained in which a class 3 protein was in effect replaced by a class 1 protein from another subtype, i.e. P1.5,2 in addition to the P1.7,16 protein of H44/76. Immunization of mice with such OMCs resulted in high bactericidal titers against both H44/76 and 2996, where normally only strain-specific antibodies are induced. Mutational removal of class 3 protein from the immunizing OMCs had no detectable effect on the bactericidal titer against H44/76, whereas removal of class 1 protein led to a strong reduction. These results demonstrate the dominant role of the subtype-specific sequences of class 1 protein in the induction of bactericidal antibodies and show that construction of a multivalent OMC-based vaccine should be feasible.