Intranasal co-administration of recombinant active fragment of Zonula occludens toxin and truncated recombinant EspB triggers potent systemic, mucosal immune responses and reduces span of E. coli O157:H7 fecal shedding in BALB/c mice

Evaluation of the protective effect of the intranasal vaccines adjuvanted with bacterium-like particles against intestinal infection

Mucosal vaccination presents a promising complement to parenteral vaccination. Bacterium-like particles (BLPs), peptidoglycan structures prepared from lactic acid bacteria, are explored as potential nasal vaccine adjuvants for respiratory infections. To date, studies on BLP-adjuvanted nasal vaccines against intestinal infections have remained limited. In this study, we demonstrated the efficacy of intranasal BLP-adjuvanted vaccination in controlling intestinal infections using the Citrobacter rodentium (C. rodentium) model in C57BL/6 mice. Intranasal vaccination of Intimin, an adhesin critical for intimate bacterial adhesion to colonic epithelial cells, combined with BLP (BLP+I) elicited robust Intimin-specific intestinal secretory IgA production, reduced bacterial load in feces and almost completely inhibited colonic hyperplasia, a characteristic symptom of C. rodentium infection in mice. Conversely, parenteral vaccination with Alhydrogel-adjuvanted Intimin failed to induce intestinal Intimin-specific IgA production, resulting in poor protection against C. rodentium infection. This underscores the pivotal role of mucosal IgA responses elicited by intranasal immunization in its protective efficacy. As this study did not delineate the precise protective mechanism conferred by BLP+I intranasal immunization against C. rodentium infection, further elucidation of the mechanisms underlying intranasal BLP+I immunization is required.

GlnH, a Novel Antigen That Offers Partial Protection against Verocytotoxigenic Escherichia coli Infection

Verotoxin-producing Escherichia coli (VTEC) causes zoonotic infections, with potentially devastating complications, and children under 5 years old are particularly susceptible. Antibiotic treatment is contraindicated, and due to the high proportion of infected children that suffer from severe and life-changing complications, there is an unmet need for a vaccine to prevent VTEC infections. Bacterial adhesins represent promising candidates for the successful development of a vaccine against VTEC. Using a proteomic approach to identify bacterial proteins interacting with human gastrointestinal epithelial Caco-2 and HT-29 cells, we identified eleven proteins by mass spectrometry. These included a glutamine-binding periplasmic protein, GlnH, a member of the ABC transporter family. The glnH gene was identified in 13 of the 15 bovine and all 5 human patient samples tested, suggesting that it is prevalent. We confirmed that GlnH is involved in the host cell attachment of an O157:H7 prototype E. coli strain to gastrointestinal cells in vitro. Recombinant GlnH was expressed and purified prior to the immunisation of mice. When alum was used as an adjuvant, GlnH was highly immunogenic, stimulating strong serological responses in immunised mice, and it resulted in a modest reduction in faecal shedding but did not reduce colonisation. GlnH immunisation with a T-cell-inducing adjuvant (SAS) also showed comparable antibody responses and an IgG1/IgG2a ratio suggestive of a mixed Th1/Th2 response but was partially protective, with a 1.5-log reduction in colonisation of the colon and caecum at 7 days relative to the adjuvant only (p = 0.0280). It is clear that future VTEC vaccine developments should consider the contribution of adjuvants in addition to antigens. Moreover, it is likely that a combined cellular and humoral response may prove more beneficial in providing protective interventions against VTEC.

Development of a Gold Nanoparticle Vaccine against Enterohemorrhagic Escherichia coli O157:H7

Enterohemorrhagic E. coli O157:H7 is a human pathogen and the causative agent of diarrhea and hemorrhagic colitis, which can progress to hemolytic uremic syndrome. These complications represent a serious global public health problem that requires laborious public health interventions and safety control measures to combat recurrent outbreaks worldwide. Today, there are no effective interventions for the control of EHEC infections, and, in fact, the use of antibiotics is counterindicated for EHEC disease. Therefore, a viable alternative for the prevention of human infections is the development of vaccines; however, no such vaccines are approved for human use. In this study, we developed a novel gold nanoparticle platform which acts as a scaffold for the delivery of various antigens, representing a nanovaccine technology which can be applied to several disease models.

Here we exploit the natural properties of a synthetic nanoparticle (NP) scaffold as a subunit vaccine against enterohemorrhagic Escherichiacoli (EHEC). Two EHEC-specific immunogenic antigens, namely, LomW and EscC, either alone or in combination, were covalently linked on the surface of gold nanoparticles (AuNPs) and used to immunize mice prior to challenge with EHEC O157:H7 strain 86-24. LomW is a putative outer membrane protein encoded in bacteriophage BP-933W, while EscC is a structural type III secretion system protein which forms a ring in the outer membrane. The resulting AuNP preparations, AuNP-LomW and AuNP-EscC, showed that the nanoparticles were able to incorporate the antigens, forming stable formulations that retained robust immunogenicity in vivo after subcutaneous immunization. When administered subcutaneously, AuNP-LomW or AuNP-EscC or a combination containing equivalent amounts of both candidates resulted in higher IgG titers in serum and secretory IgA titers in feces. The serum IgG titers correlated with a significant reduction in EHEC intestinal colonization after 3 days postinoculation. In addition, we showed that serum from antigen-coated AuNP-immunized mice resulted in a reduction of adherence to human intestinal epithelial cells for EHEC, as well as for two other E. coli pathotypes (enteropathogenic E. coli [EPEC], encoding EscC, and enteroaggregative E. coli [EAEC], encoding LomW). Further, the serum had antigen-specific bactericidal properties, engaging the classical complement pathway. Overall, our results demonstrate the immunogenicity and stability of a novel nanovaccine against EHEC. These results also strengthen the prospect of development of a synthetic nanoparticle vaccine conjugated to E. coli antigens as a promising platform against other enteric pathogens.