Meningococcal meningitis is a devastating disease that can kill children and young adults within hours despite the availability of antibiotics. Pizza et al., 2000, Science 287:1816-1820. Meningitis is characterized as an inflammation of the meninges resulting in an intense headache, fever, loss of appetite, intolerance to light and sound, rigidity of muscles, especially in the neck, and in severe cases convulsions, vomiting and delirium leading to death. The symptoms of meningococcal meningitis appear suddenly and culminate in meningococcal septicemia with its characteristic hemorrhagic rash. A rapid diagnosis and immediate treatment with large doses of antibiotics is critical if there is to be any chance of survival. 2000. Bantam Medical Dictionary, Third Edition 302.
Meningococcal meningitis is caused by Neisseria meningitidis (the meningococcus), a Gram-negative, capsulated bacterium that has been classified into several pathogenic serogroups including A, B, C, D, W-135, X, Y, Z and 29E. Serogroup B strains of N. meningitidis are a major cause of meningococcal disease throughout the world. For example, it is reported in the medical literature that serogroup B is responsible for about 50% of bacterial meningitis in infants and children residing in the United States and Europe. No vaccine currently exists to prevent meningococcal disease caused by N. meningitidis serogroup B.
Developing an immunogenic composition for the prevention of serogroup B meningococcal disease has been a challenge to researchers since the work of Goldschneider et al. over thirty years ago. Goldschneider et al., 1969, J. Exp. Med 129(6):1307-26; Goldschneider et al, 1969, J. Exp. Med 129(6):1327-48; Gotschlich et al., 1969, J. Exp. Med. 129(6):1385-95; and Gotschlich et al., 1969, J. Exp. Med. 129(6):1367-84. Unlike serogroup A disease, which virtually disappeared from North America after World War II, Achtman, M., 1995, Trends in Microbiology 3(5):186-92, disease caused by serogroup B and C organisms remains endemic throughout much of the economically developed world. The incidence of disease varies from <1/100,000 where endemic disease is rare to 200/100,000 in high risk populations during epidemics.
Vaccines based on polysaccharide conjugates have been developed against N. meningitidis serogroups A and C and appear to be effective in preventing disease. Currently, an immunogenic composition made of capsular polysaccharide from serogroups A, C, Y, & W-135 is available. Ambrosch et al., 1983, Immunogenicity and side-effects of a new tetravalent. Bulletin of the World Health Organization 61(2):317-23. However, this immunogenic composition elicits a T-cell independent immune response, is not effective in young children, and provides no coverage for serogroup B strains, which cause upwards of 50% of meningococcal disease.
Others have also attempted to develop immunogenic compositions using capsular polysaccharides. Recently, immunogenic compositions for serogroup C disease prepared by conjugating the serogroup C capsular material to proteins have been licensed for use in Europe. However, the serogroup B capsule may be unsuitable as a vaccine candidate because the capsule polysaccharide is composed of polysialic acid which bears a similarity to carbohydrate moieties on developing human neural tissues. This sugar moiety is recognized as a self-antigen and is thus poorly immunogenic in humans.
Outer membrane proteins (OMP's) have been developed as alternative vaccine antigens for serogroup B disease. Monoclonal antibody binding to the two variable regions of PorA define the serosubtyping scheme for meningococci. PorA proteins thus serve as the serosubtyping antigens (Abdillahi et al., 1988, Microbial Pathogenesis 4(1):27-32) for meningococcal strains and are being actively investigated as components of a serogroup B immunogenic composition (Poolman, 1996, Adv. Exp. Med. Biol. 397:73-7), since they can elicit bactericidal antibodies (Saukkonen, 1987, Microbial Pathogenesis 3(4):261-7). Bactericidal antibodies are thought to be an indicator of protection and any new immunogenic composition candidate should elicit these functional antibodies.
Studies in humans as well as animals indicate that the serosubtyping antigen, PorA, elicits bactericidal antibodies. However, the immune response to Por A is generally serosubtype specific. In particular, serosubtyping data indicate that an immunogenic composition made of PorAs may require a PorA for each serosubtype to be covered by such an immunogenic composition, perhaps as many as six to nine. Therefore, 6-9 PorAs will be needed to cover 70-80% of serogroup B strains. Thus, the variable nature of this protein requires a multivalent vaccine composition to protect against a sufficient number of meningococcal serosubtype clinical isolates.
Developing an immunogenic composition for serogroup B meningococci has been so difficult that recently several groups have sequenced the genomes from strains representing both serogroups A and B to assist in identifying new immunogenic composition candidates. Tettelin, 2000, Science, 287(5459):1809-15; Pizza et al., 2000, Science 287:1816-1820. Identifying new immunogenic composition candidates, even with the knowledge of the neisserial genome, is a challenging process for which adequate mathematical algorithms do not currently exist. In fact, a recent report indicates that despite identifying hundreds of open reading frames (“ORFs”) containing theoretical membrane spanning domains, problems with expression, purification, and inducing surface reactive, and functionally active antibodies have led investigators to only seven candidates for a serogroup B meningococcal immunogenic composition. See Id. One of these was previously known.
Accordingly, there remains a need for immunogenic compositions that (1) elicit bactericidal antibodies to multiple neisserial strains; (2) react with the surface of multiple strains; (3) confer passive protection against a live challenge; and/or (4) prevent colonization.
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