Protection against group B Neisseria meningitidis disease: preparation of soluble protein and protein-polysaccharide immunogens

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Abstract
Although effective polysaccharide vaccines have been developed for meningococcal groups A, C, Y and W135, the purified group B polysaccharide has proven to be nonimmunogenic. Earlier studies indicated that serotype 2 outer membrane protein vaccines induced bactericidal antibodies in animals and protected them from meningococcal challenge. However, a similar vaccine induced only low levels of antiprotein antibodies in both adults and children. Methods were therefore developed to produce more immunogenic serotype 2 protein vaccines. By growing the organism for 65-72 h at 32.degree. C, 3-4 times more outer membrane protein was released into the culture medium than could be extracted from overnight-grown cells. The outer membranes were therefore purified directly from the broth by ultrafiltration followed by ammonium sulfate precipitation. Most of the lipopolysaccharide was selectively removed from the membranes by treatment with the nonionic detergent Brij-96. The Brij-96 was then removed and the resulting vaccine was filter sterilized. Some vaccines were prepared by combining equal parts of detergent-treated membrane protein and high-MW group B polysaccharide producing highly soluble vaccines. These new vaccines were compared by using an enzyme-linked immunosorbent inhibition assay to an insoluble vaccine (E-06) found to be poorly immunogenic in humans. A human serum with serotype 2 specificity was used in the inhibition assay; 5 .mu.g of E-06 was required for 50% inhibition, whereas < 1 .mu.g of the soluble vaccines was required. Addition of group B polysaccharide slightly increased the inhibitory capacity of the protein component.