Glycoprotein conjugate vaccines

The polysaccharide capsule which surrounds bacterial species like Haemophil us influenzae, Streptococcus pneumoniae, Neisseria meningitidis, Salmonella typhi, is a potent virulence factor. It protects the bacterium from phagoc ytosis, but capsule specific antibodies plus complement binding to the caps ule opsonise the organism for phagocytosis and elimination. Purified capsul es elicit T-independent antibody responses without a memory function, and a re often poorly immunogenic in infants where much of invasive H. influenzae type b (Hib) and pneumococcal infection is seen. Covalent linkage of the p olysaccharide, or fractions thereof, to immunogenic carrier proteins create s glycoconjugates which are T-dependent antigens and which prime for boosti ng either with the glycoconjugate or the capsular polysaccharide; During th e 1990s, four Hib glycoconjugate vaccines have been introduced and in count ries that have vaccinated the majority of children, the success has been st unning. In countries with very high immunization coverage the disease has b een virtually eliminated and, to a decline of over 95% in countries with sl ightly lower vaccine rates. Worldwide use of Hib glycoconjugate vaccines of fers the possibility of elimination of invasive Hib disease. Pneumococcal ( 11 serotypes with coverage of approximately 85% of invasive disease) and me ningococcal (A, C, W 135, Y but not B) glycoconjugates are in pre-registrat ion phases and offer the prospect of being as successful as the Hib glycoco njugates. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.