A maternal vaccine to protect neonates against Group B Streptococcus invasive infection is an unmet medical need. Such a vaccine should ideally be offered during the third trimester of pregnancy and induce strong immune responses after a single dose to maximize the time for placental transfer of protective antibodies. A key target antigen is the capsular polysaccharide, an anti-phagocytic virulence factor that elicits protective antibodies when conjugated to carrier proteins. The most prevalent polysaccharide serotypes conjugated to tetanus or diphtheria toxoids have been tested in humans as monovalent and multivalent formulations, showing excellent safety profiles and immunogenicity. However, responses were suboptimal in unprimed individuals after a single shot, the ideal schedule for vaccination during the third trimester of pregnancy. In the present study, we obtained and optimized self-assembling virus-like particles conjugated to Group B Streptococcus capsular polysaccharides. The resulting glyco-nanoparticles elicited strong immune responses in mice already after one immunization, providing pre-clinical proof of concept for a single-dose vaccine.

Gonococcus, a bacterium resistant to most antibiotics, causes more than 80 million cases of gonorrhea annually and is considered a high-priority pathogen by the World Health Organization. Recently, vaccine development prospects were boosted by reports that licensed meningococcus serogroup B (MenB) vaccines provided partial protection against gonococcal infection. To determine antigens responsible for cross-protection, memory B cells isolated from 4CMenB-vaccinated volunteers were single cell–sorted to identify antibodies that kill gonococcus in a bactericidal assay. Nine different antibodies, all deriving from the IGHV4-34 germline and carrying an unusually long heavy-chain complementarity-determining region 3, recognized the PorB protein; four others recognized the lipooligosaccharide; and another four had unknown specificity. One of the PorB-specific antibodies provided protection in a mouse model of gonococcus infection. The identification of PorB and lipooligosaccharide as key antigens of gonococcal and meningococcal immunity provides a mechanistic explanation of the cross-protection observed in the clinic and shows that isolating human monoclonal antibodies from vaccinees can be instrumental for bacterial antigen discovery.

Protein self-assembling nanoparticles (NPs) can be used as carriers for antigen delivery to increase vaccine immunogenicity. NPs mimic the majority of invading pathogens, inducing a robust adaptive immune response and long-lasting protective immunity. In this context, we investigated the potential of NPs of different sizes and shapes—ring-, rod-like, and spherical particles—as carriers for bacterial oligosaccharides by evaluating in murine models the role of these parameters on the immune response. Oligosaccharides from Neisseria meningitidis type W capsular polysaccharide were conjugated to ring-shape or nanotubes of engineered Pseudomonas aeruginosa Hemolysin-corregulated protein 1 (Hcp1cc) and to spherical Helicobacter pylori ferritin. Glycoconjugated NPs were characterized using advanced technologies such as High-Performance Liquid Chromatography (HPLC), Asymmetric Flow-Field Flow fractionation (AF4), and Transmission electron microscopy (TEM) to verify their correct assembly, dimensions, and glycosylation degrees. Our results showed that spherical ferritin was able to induce the highest immune response in mice against the saccharide antigen compared to the other glycoconjugate NPs, with increased bactericidal activity compared to benchmark MenW-CRM₁₉₇. We conclude that shape is a key attribute over size to be considered for glycoconjugate vaccine development.

The tetrasaccharide (2-O-methyl-4-(3-hydroxy-3-methylbutamido)-4,6-dideoxy-α-d-glucopyranosyl-(1→3)-α-l-rhamnopyranosyl-(1→3)-α-l-rhamnopyranosyl-(1→2)-l-rhamnopyranose) from the major exosporium protein (BclA) of Bacillus anthracis has been proposed as a target for development of diagnostics and immune therapy or prophylaxis. While the immunodominant character of the anthrose residue has been previously elucidated, the role of the stereochemical configuration of the downstream rhamnose is unknown. Because the linkage of this residue to the GlcNAc bridging the glycan and the protein is lost during isolation of the tetrasaccharide, its α- and β-glycoforms have been synthesized. Herein, we prepared neoglycoconjugates from a series of fragments of the tetrasaccharide, including the complete α- and β-tetrasaccharide glycoforms, a 2-demethoxylated version of the α-tetrasaccharide, and the α- and β-trirhamnosides and CRM₁₉₇. By immunization of mice, we showed that the anti α- and β-tetrasaccharide serum equally recognized both glycoforms. In contrast the sera produced following immunization with the α- and β-trirhamnoside fragments exhibited higher recognition for their own antigens than for their anomeric counterparts. The anti α- and β-tetrasaccharide sera recognized Sterne spores in a comparable fashion. ΔBclA spores not expressing the major exosporium protein were also recognized by the same sera, while mutants that produced the carbohydrate antigen with deletion of either rhamnose or anthrose were not. The tetrasaccharide could, therefore, be expressed in proteins other than BlcA. This work proves that α- and β-tetrasaccharide are equally potent immunogens.

A 3-in-1 glycoconjugate vaccine, incorporating multiple copies of three antigens from Staphylococcus aureus and Pseudomonas aeruginosa into one construct, was generated, leveraging a histidine-directed conjugation, and elicited a strong immune response against each antigen in mice.

Despite decades of research, an effective vaccine against Neisseria gonorrhoeae remains elusive due to the pathogen's antigenic variability and immune evasion capabilities. Retrospective studies of OMV-based meningococcal vaccines have shown a partial effectiveness against gonorrhea, reigniting hopes for a feasible vaccine. Our study focused on the role of gonococcal lipooligosaccharides (LOS), the most abundant antigens on the surface, in stimulating functional immune responses. By employing detoxified OMV from Neisseria gonorrhoeae isogenic strains expressing different LOS glycoforms, we observed that antibodies targeting LOS with long α-chain oligosaccharides correlated with bactericidal activity against a wide range of gonococcal isolates, whereas antibodies that also recognized the β-chain and consequently the 2C7 epitope could achieve a broader bacterial adhesion-inhibiting effect. The results obtained underscore the potential of targeting defined LOS structures to elicit cross-strain protective immunity. Insights from our findings may guide the design of vaccine strategies to combat the threat posed by antimicrobial-resistant gonorrhea.