Group B Streptococcal Type II and III Conjugate Vaccines: Physicochemical Properties That Influence Immunogenicity

Abstract

Recent efforts toward developing vaccines against group B streptococci (GBS) have focused on increasing the immunogenicity of GBS polysaccharides by conjugation to carrier proteins. However, partial depolymerization of GBS polysaccharides for the production of vaccines is a difficult task because of their acid-labile, antigenically critical sialic acids. Here we report a method for the partial depolymerization of type II and III polysaccharides by mild deaminative cleavage to antigenic fragments with reducing-terminal 2,5-anhydro-Dmannose residues. Through the free aldehydes of their newly formed end groups, the fragments were conjugated to tetanus toxoid by reductive amination. The resulting conjugates stimulated the production in animals of high-titer type II-and III-specific antibodies which induced opsonophagocytic killing of type II and III strains of group B streptococci. For the type II conjugates, immunogenicity increased as oligosaccharide size decreased, whereas for type III conjugates, the size of the oligosaccharides did not significantly influence immunogenicity. When oligosaccharides of defined size were conjugated through sialic acid residues, the resulting cross-linkages were shown to affect immunogenicity. When oligosaccharides were conjugated through terminal aldehyde groups generated by deamination, modification of the exocyclic chain of sialic acid did not influence immunogenicity.Group B streptococci (GBS) are an important cause of neonatal sepsis and meningitis and of invasive infections in nonpregnant adults with underlying illnesses (7). Although antibodies directed to the capsular polysaccharide (CPS) antigens are protective, these antigens are variably immunogenic (6). The immunogenicity of GBS CPS antigens has been increased by covalent coupling to proteins to form CPS-protein conjugate vaccines (1-5, 18, 21, 23, 25, 29). Experimental GBS type III polysaccharide (GBSP-III)-and oligosaccharide-tetanus toxoid conjugate vaccines of different designs have been developed and their immunogenicity tested in animals (21, 29). (The term "oligosaccharide" is generally used to designate carbohydrates containing between 2 and 10 monosaccharide units per molecule [12]. For convenience and consistency with related published material [12,15,23,25,29], the term oligosaccharide is used in this paper to indicate a fragment obtained by chemical or enzymatic cleavage of a native polysaccharide.) Generating GBS oligosaccharides is a difficult task because of the acid-labile, antigenically critical sialic acid residues present at the termini of the side chains of all GBS CPS serotypes. Enzymatic digestion of the type III CPS with endo-␤-galactosidase allowed the production of oligosaccharide-tetanus toxoid (TT) conjugates which proved to be immunogenic in animals (21). Unfortunately, the specificity of the endo-␤-galactosidase is restricted to type III CPS. We sought a facile chemical degradation for the type III polysaccharide (PS) and possibly those of other CPS serotypes, keeping in mind the acid labilit...

Protection against Streptococcus suis Serotype 2 Infection Using a Capsular Polysaccharide Glycoconjugate Vaccine

“…genicity may arise from the higher percentage of total CPS in the 2:1 than in the 1:1 mixed conjugate, which might influence the capacity of the conjugate to modulate the immune cells, including antigen-presenting cells (APCs), presumably through its higher molecular mass/size, which might ease uptake and internalization. In this regard, it has been shown that the polysaccharide size used for conjugation, the obtained conjugate size, and the degree of polysaccharide-protein cross-linking influence the immunogenicity and protective efficacy of a GBS type III-TT conjugate vaccine (74,77,78). Further studies evaluating how the aforementioned parameters affect the immunogenicity of an S. suis type 2 CPS conjugate, which can contribute to improvements of the design of the conjugate vaccine, are under way.…”

Research progress of Streptococcus pneumoniae capsular polysaccharide-protein conjugate vaccines

“…PLDpolysaccharide conjugate vaccines were prepared from CPS serotypes 6B, 14, 19F and 23F by reductive amination and TT-polysaccharide conjugate vaccines were similarly prepared and used for comparison. The PLD conjugates were generally equivalent to or better than the TT conjugates in CPS-specific responses (Michon et al, 1998). The pneumococcal toxin pneumolysin is an important pneumococcal virulence factor, which appears to satisfy the necessary criteria for use in vaccines.…”

“…A genetically detoxified pneumolysin, pneumolysoid (PLD) was investigated as a carrier protein for pneumococcal capsular polysaccharide (CPS). Such a CPS-PLD conjugate might provide additional protection against pneumococcal infections and result in tissue damage (Michon et al, 1998) Ply is a potent hemolytic cytotoxin, which can be produced by all essential strains of S. pneumoniae isolated clinically. Its status as an important virulence protein has been confirmed by previous demonstration that genetically defined Ply-negative mutant pneumococcus strains have significantly reduced virulence (Paton et al, 1991).…”

“…Even with reasonable antibiotic therapy, pneumococcal infections still cause high morbidity and mortality. To date, vaccine is still an effective method to prevent pneumococcal invasive disease (Beery and Paton, 2000;Michon et al, 1998).…”

Specificity of the Immune Response to a Modified Group B Meningococcal Polysaccharide Conjugate Vaccine

“…Following the collection of the unbound effluent from each of the columns, bound antibodies were eluted with 3.0 M KSCN. Fractions collected from the columns were analyzed by ELISA (18). Representative ELISAs of column profiles eluted with 3.0 M KSCN following loading are shown in Fig.…”