Toll-like receptor 2 dependent immunogenicity of glycoconjugate vaccines containing chemically derived zwitterionic polysaccharides

Abstract

Group B Streptococcus (GBS) causes serious infection in neonates and is an important target of vaccine development. Zwitterionic polysaccharides (ZPS), obtained through chemical introduction of positive charges into anionic polysaccharides (PS) from GBS, have the ability to activate human and mouse antigen presenting cells (APCs) through toll-like receptor 2 (TLR2).To generate a polysaccharide vaccine with antigen (Ag) and adjuvant properties in one molecule, we have conjugated ZPS with a carrier protein. ZPS-glycoconjugates induce higher T-cell and Ab responses to carrier and PS, respectively, compared to control PS-glycoconjugates made with the native polysaccharide form. The increased immunogenicity of ZPS-conjugates correlates with their ability to activate dendritic cells (DCs). Moreover, protection of mothers or neonate offspring from lethal GBS challenge is better when mothers are immunized with ZPS-conjugates compared to immunization with PS-conjugates. In TLR2 knockout mice, ZPS-conjugates lose both their increased immunogenicity and protective effect after vaccination. When ZPS are coadministered as adjuvants with unconjugated tetanus toxoid (TT), they have the ability to increase the TT-specific antibody titer. In conclusion, glycoconjugates containing ZPS are potent vaccines. They target Ag to TLR2-expressing APCs and activate these APCs, leading to better T-cell priming and ultimately to higher protective Ab titers. Thus, rational chemical design can generate potent PS-adjuvants with wide application, including glycoconjugates and coadministration with unrelated protein Ags.adjuvant ͉ dendritic cell ͉ Group B Streptococcus C lassically, capsular polysaccharides (PS) from bacteria are considered to be T-independent Ags (1) able to activate B cells directly, without a contribution of help by CD4 ϩ T cells. Therefore, the immune response to PS fails to induce significant and prolonged titers of antibody with high avidity in infants and persistent Agspecific memory B cells in adults. For this reason, in vaccines, PS are mostly used conjugated with a carrier protein that provides T-cell help and consequently immunological memory (2). Glycoconjugate vaccines against the Gram-positive bacterium Group B Streptococcus (GBS) have been shown to confer serotype specific protection in mice and have been tested in clinical trials (3). In humans, addition of alum to the vaccine formulation did not further increase the immune response induced (4). In contrast, in animal models, adsorption to Al(OH) 3 (alum) enhances the immunogenicity of the glycoconjugate (5, 6) which may be explained by the possibility that animals are more naive to GBS than humans. Moreover, a number of commercially available glycoconjugate vaccines, such as those against Meningococcus C, Haemophilus influenza, and the 7-valent Pneumococcus vaccine, use alum or aluminium phosphate as an adjuvant. Thus, the combination of glycoconjugates with adjuvants likely generates potent vaccines, able to activate APCs and induce strong Ag-specific T and B c...

Use of defined TLR ligands as adjuvants within human vaccines

“…Administration of TLR2 ⁄ TLR1 agonists supports B-cell responses and T-cell stimulation. An example of this is shown by adjuvanting tetanus toxoid with of the derivatives of polysaccharide from Group B Streptococcus, which results in strong T-cell priming and high tetanus-specific antibody titers (39). Recent publications have also demonstrated that, when used as adjuvants, derivatives of the TLR2 ⁄ 6 ligand Mycoplasma fermentans macrophage activating lipopeptide (MALP-2) also stimulate strong T-cell and antibody responses.…”

Toward self-adjuvanting subunit vaccines: Model peptide and protein antigens incorporating covalently bound toll-like receptor-7 agonistic imidazoquinolines

“…38;39 This appears not to be the case for zwitterionic polysaccharides, however, which elicit potent CD4 + T cell responses. 40;41 We are keen to re-examine the structural determinants of T-dependent and -independent humoral responses, especially in light of recent findings of intrinsic TLR2 activation by zwitterionic polysaccharides, 42;43 and we are currently testing the hypothesis that polysaccharides with covalently linked TLR stimuli may be superior to carrier proteins. The free primary amine on the N 1 substituent of 1 lent itself eminently well to direct reductive amination with maltoheptaose, a model oligosaccharide with a reducing terminal maltose unit ( 7 , Scheme 2) which, gratifyingly, was found to be active in TLR7 assays (EC 50 : 528 nM; Fig.…”

Identification of Novel Synthetic Toll-like Receptor 2 Agonists by High Throughput Screening

“…However, inflammatory toxicity associated with strong TLR agonists limits their broad application (39,40). The TLR2-dependent adjuvants under development include lipopeptides, zwitterionic polysaccharides, and larger bacteria-derived proteins (22)(23)(24)(25)(26). Although we have not tested compounds A, B, and C for adjuvanticity, we have observed that these synthetic TLR2 agonists weakly induce TNF-␣ production from human monocytes (Fig.…”

“…Synthetic lipopeptide agonists for TLR2 exhibit strong adjuvant activity when either mixed with or directly conjugated to various antigens (22,23). In addition to lipopeptides, a variety of other natural TLR2 agonists exhibit adjuvant activity including zwitterionic polysaccharides from Group B Streptococcus (24), Type IIb heat labile enterotoxin from enteropathogenic Escherichia coli (25), and porin B from pathogenic Neisseriae sp. (26).…”