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Chapter 6
Multivalent Meningococcal Conjugate Vaccines: Chemical Conjugation Strategies Used for the Preparation of Vaccines Licensed or in Clinical Trials Francesco Berti* Technical R&D, GSK Vaccines, Siena 53100, Italy *E-mail:
[email protected].
Several multi-valent carbohydrate-based vaccines have been licensed or are currently in clinical development, so far, to prevent bacterial infection caused by several serogroup of Neisseria meningitidis. In this chapter, the conjugation strategies, including the chemical structures and functional groups involved in the covalent coupling of polysaccharides to carrier proteins for the preparation of tetravalent meningococcal serogroup A, C, W, Y glycoconjugates vaccines, have been described in depth.
© 2018 American Chemical Society Prasad; Carbohydrate-Based Vaccines: From Concept to Clinic ACS Symposium Series; American Chemical Society: Washington, DC, 2018.
Introduction Meningococcal disease is caused by the gram-negative diplococcus Neisseria meningitidis (Nm). It was identified as one of the causative agents of bacterial meningitis by Weichselbaum in 1887. Reports of this disease date back to 1807 and nowadays meningococci are known as one of the major causes of bacterial meningitis. The incidence of invasive meningococcal disease (IMD) varies according to geographical location and time, and usually results in septicemia and/or meningitis, and can be complicated by purpuric rash, purpura fulminans, arthritis, myocarditis, pericarditis, endophthalmitis, or pneumonia. The symptoms of bacterial meningitis include headache, stiff neck, fever, chills, malaise, and prostration (1). Meningococcal disease is predominantly a disease of infants and young children, although the disease does have a bimodal distribution with a second age peak in adolescents. Neonates are relatively protected against meningococcal disease as a result of passive acquisition of transplacental maternal antibodies (2). With increasing age, there is a decreasing level of maternal antibodies and increasing susceptibility to meningococcal disease. The lowest antibody levels are found in infants between 6 months and 2 years of age after which natural immunity begins to appear. The antigenic diversity is defined by chemically and immunologically distinctive capsular polysaccharides which led to serogroup definition, from which 12 different serogroups have been reported. The additional 13th serogroup D initially reported does not exist. The structure has not been described yet and genetic analyses revealed that the attributed serogroup D isolate was found to contain serogroup C capsule biosynthesis genes with internal stop codons in some genes resulting in an unencapsulated phenotype (3). Multiple serogroups are associated with IMD (i.e. serogroup A, B, C, W and Y). However, recently, serogroup X has become important in some regions (4). The meningococcal capsular polysaccharides have the following chemical structure (5, 6): NmA: →6)-α-D-ManpNAc(3/4OAc)-(1→OPO3→ NmB: →8)-α-D-Neu5Ac-(2→ NmC: →9)-α-D-Neu5Ac(7/8OAc)-(2→ NmW: →6)-α-D-Galp-(1→4)-α-D-Neu5Ac(7/9OAc)-(2→ NmY: →6)-α-D-Glcp-(1→4)-α-D-Neu5Ac(7/9OAc)-(2→ NmX: →4)-α-D-GlcpNAc-(1→OPO3→ Vaccine formulations containing purified meningococcal polysaccharides (bivalent, serogroups A and C; trivalent, serogroups A, C and W; tetravalent, serogroups A, C, W and Y), lyophilized together with lactose excipient and to be reconstituted with diluent before use, have been available. Tetravalent serogroup A, C, W and Y polysaccharide vaccines (Mencevax®, GSK Vaccines; Menomune®, Sanofi Pasteur) were licensed in the 1980s (7). Immunization with the meningococcal serogroup B polysaccharide antigen, which is composed of the →8)-α-D-Neu5Ac-(2→ repeating unit that mimics a protein-attached glycan expressed in the foetus meaning that immune tolerance exists against this structure (8), resulted in a very low antibody responses. 124 Prasad; Carbohydrate-Based Vaccines: From Concept to Clinic ACS Symposium Series; American Chemical Society: Washington, DC, 2018.
Molecular mimetics of meningococcal serogroup B polysaccharide epitopes have also been explored as potential vaccine candidates (9, 10). Using a N-propionyl-tetanus toxoid conjugate vaccine, Granoff et al. produced a panel of anti-N-propionyl meningococcal serogroup B polysaccharide monoclonal antibodies (mAbs) that were reactive with N. meningitidis serogroup B infection but were either not cross-reactive or minimally cross-reactive with purified polysaccharide or human polysialic acid antigens (11). Nevertheless, the manufacturers have been reluctant to test a system that may result in a breach of immune tolerance against a foetal glycan associated with neural development. The development focus of vaccines against N. meningitidis serogroup B infection was later shifted towards protein-based antigens. Outer membrane vesicles (OMVs) containing outer membrane proteins (OMPs), chemically treated by detergent to reduce reactogenicity, and, more recently, a limited selection of recombinant OMPs selected by searching the genome have been used as antigens to prepare vaccine formulations with a wide strains coverage (12–14). Vaccines containing both meningococcal polysaccharide of serogroups C and OMPs of serogroup B (VA-Mengoc-BC, Finley Institute), or containing recombinant OMPs only (Trumenba®, Pfizer), or a combination of recombinant OMPs and OMVs (Bexsero®, GSK Vaccines) have been developed and licensed (15). Polysaccharide vaccines, which have been used for over 40 years, have proven immunogenicity and an acceptable tolerability and safety profiles, but they suffer fromsome limitations. As T-cell independent antigens, they are poorly immunogenic in individuals younger than 2 years of age, they cannot induce immune memory and may induce hyporesponsiveness. To overcome these limitations, conjugate vaccines in which a capsular polysaccharide is chemically linked to a protein that is thus termed a ‘carrier protein’ have been successfully developed and used, as discussed in earlier chapters (see Lockhart et al. (16), Chapter 2; Duke and Avci (17), Chapter 3; and Prasad et al. (18), Chapter 4). In contrast to polysaccharide vaccines, the conjugate vaccines induce T cell-dependent responses and therefore, they induce immunological memory. They are also highly immunogenic, even when used in infants, and have a longer duration of protection than polysaccharide vaccines. The conjugate vaccines may induce a robust immune response that reduces nasopharyngeal carriage, and have the potential to provide herd immunity.7
Conjugate Vaccines As the culmination of an intensive 5 year clinical trial research programme sponsored by the Department of Health (DH) for England, whith the objective to accelerate the availability a vaccine aganst meningococcal serogroup C disease, in November 1999 the UK became the first country implementing a large immunisation programme using protein conjugate vaccines. Three vaccines (Meningitec®, Nuron Biotech, formerly Pfizer; Menjugate®, GSK Vaccines, formerly Novartis Vaccines; NeisVac-C®, Pfizer, formerly Baxter) were developed, licensed and introduced as part of routine immunization of all 125 Prasad; Carbohydrate-Based Vaccines: From Concept to Clinic ACS Symposium Series; American Chemical Society: Washington, DC, 2018.
children aged >4 months to
