Starting with Neisseria meningitidis strain H44/76, a set of strains was constructed for use in production of a multivalent outer membrane vesicle vaccine. The aim was to remove unwanted outer membrane components and at the same time to improve the range of protection. This was accomplished through transformation with plasmid constructs made in Escherichia coli and their homologous recombination into the meningococcal chromosome. Deletion of the cps locus resulted in loss of expression of the group B capsular polysaccharide as well as the lacto-N-neotetraose structure in lipopolysaccharide. Deletion of the porB gene abolished expression of the class 3 outer membrane protein. Additional copies of the porA gene, encoding the immunodominant class 1 outer membrane protein, were inserted into one of the opa genes and into the rmpM gene encoding the class 4 outer membrane protein. This construction was done with three sets of porA alleles, resulting in three trivalent strains, each of which expressed a different combination of class 1 epitopes.