John B. Robbins

Shigellosis, an enteric disease, is on the World Health Organization's priority prevention list. In one study, the Shigella sonnei O-specific polysaccharide (O-SP)-protein conjugate showed 72% protection against disease in Israeli army recruits exposed to high rates (8–14%) of infection. The protection was related to vaccine-induced IgG anti-O-SP levels. Synthetic oligosaccharides of Shigella dysenteriae type 1, bound by their reducing ends to a carrier protein (“sun”-type configuration), induced significantly higher antibody levels than the native O-SP bound to protein by multiple-point attachments (“lattice”-type configuration). Attempts to synthesize the S. sonnei O-SP based oligosaccharides were not successful. Here, we describe the isolation, characterization, and conjugation of low-molecular-mass O-SP-core (O-SPC) fragments. The O-SPC fragments were bound by their reducing ends similar to the preparation of the synthetic S. dysenteriae type 1 conjugates. The O-SPC conjugates used oxime linkages between the terminal Kdo residues at the reducing ends of the S. sonnei saccharides and aminooxy linkers bound to BSA or a recombinant diphtheria toxin. The coupling reaction was carried out at a neutral pH and room temperature. IgG antibody levels induced in young outbred mice by the S. sonnei O-SPC conjugates were significantly higher then those elicited by the O-SP conjugates. Accordingly, we propose to evaluate clinically these conjugates.

A critical level of serum IgG pertussis toxin antibody is both essential and sufficient to confer individual and herd immunity to pertussis. Monocomponent pertussis toxoid conferred such immunity in Sweden and in Denmark. We refute the notion that filamentous hemagglutinin, pertactin, and fimbriae add to the immunity conferred by pertussis toxoid and describe the artifact created when efficacy is estimated for multicomponent pertussis vaccines. Lastly, the genetically-inactivated mutant pertussis toxoid is safer, more immunogenic, and should be more effective than the current chemically-inactivated pertussis toxin.

Endemic and epidemic shigellosis, an acute invasive disease of the lower intestines, afflicts millions of people worldwide with an estimated one million fatalities per annum at a low infectious dose. Our approach to vaccine development against Shigella is based on the hypothesis that serum IgG antibodies to the O-specific polysaccharide (O-SP) domains of the LPS of these organisms confer protection to infection. The synthetic oligosaccharides corresponding to the tetrasaccharide repeating unit of the O-SP of Shigella dysenteriae type 1 covalently linked to human serum albumin elicited O-SP-specific IgG in mice. The antibody levels were a function of both the saccharide chain length and their loading on the protein. These synthetic saccharide conjugates elicited significantly higher levels of IgG anti O-SP than conjugates prepared with the O-SP from the bacteria. Here, we evaluated the influence of the nonreducing terminal monosaccharide on the serum antibody response. To this end, we prepared synthetic oligosaccharides comprising hexa- to tridecasaccharide fragments of the native O-SP, having one of the four monosaccharide residues that constitute the repeating unit at their termini and bound them to BSA by a single-point attachment. The conjugates contained an average of 19 saccharide chains per BSA. The synthetic oligosaccharides inhibited the binding of serum raised against whole bacteria to its LPS to a similar extent but lower than the native O-SP. The highest anti-LPS levels were elicited by conjugates having N-acetylglucosamine (10-mer) or galactose residues (7- and 11-mers) at their nonreducing termini.

Haemophilus influenzae was first described by Pfeiffer in 1892 ([30][1]). Forty years later Pittman identified six capsular polysaccharides (types) of H. influenzae (a, b, c, d, e, and f) whose structures were later elucidated (Table [1][2]) ([12][3], [31][4], [40][5]). Systemic infections in

The O -specific polysaccharide (O-SP) domain of Shigella LPS is both an essential virulence factor and a protective antigen for this genus. A critical level of serum IgG anti-O-SP was shown to confer immunity to shigellosis, likely by complement-mediated bacteriolysis of the inoculum. Conjugate Shigella O-SP vaccines were shown to be safe and immunogenic in children, and, in a preliminary study, Shigella sonnei vaccine was protective in young adults. Characteristic of shigellosis is bacterial invasion of intestinal cells. Incubation of shigellae with postimmunization but not preimmunization sera of children vaccinated with S. sonnei or Shigella flexneri 2a O-SP conjugate vaccines inhibited in a type-specific and dose-dependent manner in vitro invasion of intestinal epithelial cells (Caco-2) and the infection-associated increases in IL-1β and IL-8 mRNA and extracellular cytokine levels. Pretreatment of these sera or of Caco-2 cells with O-SP abrogated these effects also in a type-specific and dose-dependent manner. Confocal microscopy demonstrated antibody-specific inhibition of bacterial adhesion to HeLa cells. These protective effects were duplicated by IgG purified from these sera. These results suggest a dual role for IgG anti-O-SP. In addition to lysis of the inoculum in immune individuals, the newly synthesized IgG anti-O-SP in patients may terminate an established infection by inhibiting shigellae released from epithelial cells from invading new ones. A critical level of IgG anti-O-SP could, therefore, have a protective as well as a curative role in shigellosis.

Replacement of cellular with acellular pertussis (aP) vaccines has considerably reduced the systemic reactions observed with diphtheria-tetanus toxoids-pertussis vaccine but has not eliminated the extensive swelling (sometimes involving an entire limb) observed after the fifth injection of diphtheria-tetanus toxoids-aP (DTaP) vaccine. This local reaction, which is likely an Arthus hypersensitivity reaction caused by high levels of antibodies reacting with DTaP vaccine, could discourage its use in adults, who serve as the major reservoir of pertussis for infants. That a critical level of antibodies to pertussis toxin is both essential and sufficient to prevent infection with Bordetella pertussis is derived from data from animal and clinical studies, including data showing the similarities between the immunity induced by diphtheria and pertussis toxoids. The genetically inactivated diphtheria and pertussis mutant toxins are more immunogenic and, therefore, induce comparable levels of antitoxin at lower protein levels than do the formalin-treated native toxins. Replacement of the diphtheria and aP components with these improved antigens will reduce the amount of protein in DTaP vaccine and, most likely, the incidence and severity of local reactions in teenagers and adults.

The implementation of PCR technology to study the incidence, age distribution, and etiology of bacterial meningitis in Burkina Faso, a country that is representative of the “meningitis belt” of sub-Saharan Africa, unearthed several important aspects of this disease [1]. The study was conducted during an unusual epidemic of meningococcal meningitis in which serogroup W135, rather than serogroup A, was the predominant pathogen. Population-based surveillance with PCR technology, as well as with culture and capsular polysaccharide antigen detection, permitted greater test sensitivity for the identification of pathogens.

Endemic and epidemic group A meningococcal meningitis remains a major cause of morbidity and mortality in sub-Saharan Africa, despite the availability of the safe and inexpensive group A meningococcal polysaccharide vaccine, which is protective at all ages when administered as directed. Despite optimal therapy, meningococcal meningitis has a 10% fatality rate and at least 15% central nervous system damage. WHO's policy of epidemic containment prevents, at best, about 50% of cases and ignores endemic meningitis, which is estimated at 50,000 cases per year. The effectiveness of group A, C, W135, and Y capsular polysaccharides is the basis for recommending universal vaccination with group A meningococcal polysaccharide twice in infancy, followed by the four-valent vaccine in children aged two and six years. This could eliminate epidemic and endemic disease, prepare for the use of conjugates when they become available, and probably could have prevented the recent epidemics of groups A and W135 meningitis in Burkina Faso.