Vaccines for Protecting Infants from Bacterial Causes of Diarrheal Disease

Designing a multi-epitope vaccine against Shigella dysenteriae using immuno-informatics approach

Shigella dysenteriae has been recognized as the second most prevalent pathogen associated with diarrhea that contains blood, contributing to 12.9% of reported cases, and it is additionally responsible for approximately 200,000 deaths each year. Currently, there is no S. dysenteriae licensed vaccine. Multidrug resistance in all Shigella spp. is a growing concern. Current vaccines, such as O-polysaccharide (OPS) conjugates, are in clinical trials but are ineffective in children but protective in adults. Thus, innovative treatments and vaccines are needed to combat antibiotic resistance. In this study, we used immuno-informatics to design a new multiepitope vaccine and identified S. dysenteriae strain SD197's membrane protein targets using in-silico methods. The target protein was prioritized using membrane protein topology analysis to find membrane proteins. B and T-cell epitopes were predicted for vaccine formulation. The epitopes were shortlisted based on an IC50 value <50, antigenicity, allergenicity, and a toxicity analysis. In the final vaccine construct, a total of 8 B-cell epitopes, 12 MHC Class I epitopes, and 7 MHC Class II epitopes were identified for the Lipopolysaccharide export system permease protein LptF. Additionally, 17 MHC Class I epitopes and 14 MHC Class II epitopes were predicted for the Lipoprotein-releasing ABC transporter permease subunit LolE. These epitopes were selected and linked via KK, AAY, and GGGS linkers, respectively. To enhance the immunogenic response, RGD (arginine-glycine-aspartate) adjuvant was incorporated into the final vaccine construct. The refined vaccine structure exhibits a Ramachandran score of 91.5% and demonstrates stable interaction with TLR4. Normal Mode Analysis (NMA) reveals low eigenvalues (3.925996e-07), indicating steady and flexible molecular mobility of docked complexes. Codon optimization was carried out in an effective microbial expression system of the Escherichia coli K12 strain using the recombinant plasmid pET-28a (+). Finally, the entire in-silico analysis suggests that the suggested vaccine may induce a significant immune response against S. dysenteriae, making it a promising option for additional experimental trials.

Repeat modules and N-linked glycans define structure and antigenicity of a critical enterotoxigenic E. coli adhesin

Enterotoxigenic Escherichia coli (ETEC) cause hundreds of millions of cases of infectious diarrhea annually, predominantly in children from low-middle income regions. Notably, in children, as well as human volunteers challenged with ETEC, diarrheal severity is significantly increased severity in blood group A (bgA) individuals. EtpA, is a secreted glycoprotein adhesin that functions as a blood group A lectin to promote critical interactions between ETEC and blood group A glycans on intestinal epithelia for effective bacterial adhesion and toxin delivery. EtpA is highly immunogenic resulting in robust antibody responses following natural infection and experimental challenge of human volunteers with ETEC. To understand how EtpA directs ETEC-blood group A interactions and stimulates adaptive immunity, we mutated EtpA, mapped its glycosylation by mass-spectrometry (MS), isolated polyclonal (pAbs) and monoclonal antibodies (mAbs) from vaccinated mice and ETEC-infected human volunteers, and determined structures of antibody-EtpA complexes by cryo-electron microscopy. Both bgA and mAbs that inhibited EtpA-bgA interactions and ETEC adhesion, bound to the C-terminal repeat domain highlighting this region as crucial for ETEC pathogen-host interaction. MS analysis uncovered extensive and heterogeneous N-linked glycosylation of EtpA and cryo-EM structures revealed that mAbs directly engage these unique glycan containing epitopes. Finally, electron microscopy-based polyclonal epitope mapping revealed antibodies targeting numerous distinct epitopes on N and C-terminal domains, suggesting that EtpA vaccination generates responses against neutralizing and decoy regions of the molecule. Collectively, we anticipate that these data will inform our general understanding of pathogen-host glycan interactions and adaptive immunity relevant to rational vaccine subunit design.

Testing S. sonnei GMMA with and without Aluminium Salt-Based Adjuvants in Animal Models

Shigellosis is one of the leading causes of diarrheal disease in low- and middle-income countries, particularly in young children, and is more often associated with antimicrobial resistance. Therefore, a preventive vaccine against shigellosis is an urgent medical need. We have proposed Generalised Modules for Membrane Antigens (GMMA) as an innovative delivery system for Shigella sonnei O-antigen, and an Alhydrogel formulation (1790GAHB) has been extensively tested in preclinical and clinical studies. Alhydrogel has been used as an adsorbent agent with the main purpose of reducing potential GMMA systemic reactogenicity. However, the immunogenicity and systemic reactogenicity of this GMMA-based vaccine formulated with or without Alhydrogel have never been compared. In this work, we investigated the potential adjuvant effect of aluminium salt-based adjuvants (Alhydrogel and AS37) on S. sonnei GMMA immunogenicity in mice and rabbits, and we found that S. sonnei GMMA alone resulted to be strongly immunogenic. The addition of neither Alhydrogel nor AS37 improved the magnitude or the functionality of vaccine-elicited antibodies. Interestingly, rabbits injected with either S. sonnei GMMA adsorbed on Alhydrogel or S. sonnei GMMA alone showed a limited and transient body temperature increase, returning to baseline values within 24 h after each vaccination. Overall, immunisation with unadsorbed GMMA did not raise any concern for animal health. We believe that these data support the clinical testing of GMMA formulated without Alhydrogel, which would allow for further simplification of GMMA-based vaccine manufacturing.

Diarrheal disease and associated factors among children aged 6 to 59 months in Oda Bultum District, Eastern Ethiopia: a community-based cross-sectional study

BACKGROUND

Diarrhea is a serious health problem in children under the age of five that is both preventable and treatable. In low-income countries like Ethiopia, children under the age five years frequently experience diarrhea. However, the burden and associated factors of these diarrheal diseases are understudied in Eastern Ethiopia, Thus, this study aimed to determine the factors associated with the prevalence of diarrheal diseases in Eastern Ethiopia from September 1-30, 2022.

METHODS

A cross-sectional study was conducted on the total of 602 children aged 6 to 59 months in Oda Bultum district in eastern Ethiopia. A multistage sampling method was used. Three kebeles were selected from nine kebeles by the lottery method. Data was entered into Epi data 4.0.2 and exported to SPSS version 21 for analysis. Descriptive analysis was used for frequency, mean, and standard deviations. In addition, bivariable, and multivariable Poisson regression model was used to identify predictors of diarrhea along with a 95% confidence interval. Finally, statistical significance was declared at a p-value of 0.05.

RESULT

A total of 602 children were included in this study. The prevalence of diarrhea 7.4% (47/602), 95% CI; 5.5-9.7%) among the children. Factors such as being unvaccinated for any vaccine (AOR = 10.82, 95%CI; 4.58-25.48) and born from a mother who had medium level of empowerment (AOR = 0.34, 95%CI; 0.11-0.88) in the household had statistically significant association with diarrhea among the children compared to their counterparts.

CONCLUSION

The study found that nearly one out of thirteen children aged 6 to 59 months had any form of diarrheal diseases in Oda Bultum District, Eastern Ethiopia. In addition, the study revealed that children who were vaccinated for their age developed diarrhea less likely compared to those who did not receive any form of vaccine for their age. Moreover, children with mothers who had a medium level of empowerment were less likely to get diarrhea than children with mothers who had a low level of empowerment.

Vaccine value profile for enterotoxigenic Escherichia coli (ETEC)

Enterotoxigenic Escherichia coli (ETEC) is one of the leading bacterial causes of diarrhoea, especially among children in low-resource settings, and travellers and military personnel from high-income countries. WHO's primary strategic goal for ETEC vaccine development is to develop a safe, effective, and affordable ETEC vaccine that reduces mortality and morbidity due to moderate-to-severe diarrhoeal disease in infants and children under 5 years of age in LMICs, as well as the long-term negative health impact on infant physical and cognitive development resulting from infection with this enteric pathogen. An effective ETEC vaccine will also likely reduce the need for antibiotic treatment and help limit the further emergence of antimicrobial resistance bacterial pathogens. The lead ETEC vaccine candidate, ETVAX, has shown field efficacy in travellers and has moved into field efficacy testing in LMIC infants and children. A Phase 3 efficacy study in LMIC infants is projected to start in 2024 and plans for a Phase 3 trial in travellers are under discussion with the U.S. FDA. Licensing for both travel and LMIC indications is projected to be feasible in the next 5-8 years. Given increasing recognition of its negative impact on child health and development in LMICs and predominance as the leading etiology of travellers' diarrhoea (TD), a standalone vaccine for ETEC is more cost-effective than vaccines targeting other TD pathogens, and a viable commercial market also exists. In contrast, combination of an ETEC vaccine with other vaccines for childhood pathogens in LMICs would maximize protection in a more cost-effective manner than a series of stand-alone vaccines. This 'Vaccine Value Profile' (VVP) for ETEC is intended to provide a high-level, holistic assessment of available data to inform the potential public health, economic and societal value of pipeline vaccines and vaccine-like products. This VVP was developed by a working group of subject matter experts from academia, non-profit organizations, public private partnerships, and multi-lateral organizations. All contributors have extensive expertise on various elements of the ETEC VVP and collectively aimed to identify current research and knowledge gaps. The VVP was developed using only existing and publicly available information.

Vaccine value profile for Shigella

Shigella is the leading bacterial cause of diarrhoea and the second leading cause of diarrhoeal mortality among all ages. It also exhibits increasing levels of antibiotic resistance. The greatest burden is among children under five in low- and middle-income countries (LMICs). As such, a priority strategic goal of the World Health Organization (WHO) is the development of a safe, effective and affordable vaccine to reduce morbidity and mortality from Shigella-attributable dysentery and diarrhea, including long term outcomes associated with chronic inflammation and growth faltering, in children under 5 years of age in LMICs. In addition, a safe and effective Shigella vaccine is of potential interest to travellers and military both to prevent acute disease and rarer, long-term sequelae. An effective Shigella vaccine is also anticipated to reduce antibiotic use and thereby help diminish further emergence of enteric pathogens resistant to antimicrobials. The most advanced vaccine candidates are multivalent, parenteral formulations in Phase 2 and Phase 3 clinical studies. They rely on O-antigen-polysaccharide protein conjugate technologies or, alternatively, outer membrane vesicles expressing penta-acylated lipopolysaccharide that has been detoxified. Other parenteral and oral formulations, many delivering a broader array of Shigella antigens, are at earlier stages of clinical development. These formulations are being assessed in alignment with the WHO Preferred Product Characteristics, which call for a 1 to 2 dose primary immunization series given during the first 12 months of life, ideally starting at 6 months of age. This 'Vaccine Value Profile' (VVP) for Shigella is intended to provide a high-level, holistic assessment of the information and data that are currently available to inform the potential public health, economic and societal value of pipeline vaccines and vaccine-like products. This VVP was developed by a working group of subject matter experts from academia, non-profit organizations, government agencies and multi-lateral organizations. All contributors have extensive expertise on various elements of the Shigella VVP and collectively aimed to identify current research and knowledge gaps. The VVP was developed using only existing and publicly available information.

Anti-Toxin Responses to Natural Enterotoxigenic Escherichia coli (ETEC) Infection in Adults and Children in Bangladesh

A sero-epidemiology study was conducted in Dhaka, Bangladesh between January 2020 and February 2021 to assess the immune responses to ETEC infection in adults and children. (1) Background: Enterotoxigenic Escherichia coli infection is a main cause of diarrheal disease in endemic countries. The characterization of the immune responses evoked by natural infection can guide vaccine development efforts. (2) Methods: A total of 617 adult and 480 pediatric diarrheal patients were screened, and 43 adults and 46 children (below 5 years of age) with an acute ETEC infection completed the study. The plasma samples were analyzed for antibody responses against the ETEC toxins. (3) Results: Heat-stable toxin (ST)-positive ETEC is the main cause of ETEC infection in adults, unlike in children in an endemic setting. We detected very low levels of anti-ST antibodies, and no ST-neutralizing activity. However, infection with ETEC strains expressing the heat-labile toxin (LT) induced systemic antibody responses in less than 25% of subjects. The antibody levels against LTA and LTB, as well as cholera toxin (CT), correlated well. The anti-LT antibodies were shown to have LT- and CT- neutralizing activity. The antibody reactivity against linear LT epitopes did not correlate with toxin-neutralizing activity. (4) Conclusions: Unlike LT, ST is a poor antigen and even adults have low anti-ST antibody levels that do not allow for the detection of toxin-neutralizing activity.

T helper cell responses in adult diarrheal patients following natural infection with enterotoxigenic Escherichia coli are primarily of the Th17 type

Background

Infection with enterotoxigenic Escherichia coli (ETEC) gives rise to IgA antibodies against both the heat labile toxin (LT) and colonization factors (CFs), which are considered to synergistically protect against ETEC diarrhea. Since the development of ETEC-specific long lived plasma cells and memory B cells is likely to be dependent on T helper (Th) cells, we investigated if natural ETEC diarrhea elicits ETEC-specific Th cells and their relation to IgA responses.

Methods

Th cell subsets were analyzed in adult Bangladeshi patients hospitalized due to ETEC diarrhea by flow cytometric analysis of peripheral blood mononuclear cells (PBMCs) isolated from blood collected day 2, 7, 30 and 90 after hospitalization as well as in healthy controls. The LT- and CF-specific Th responses were determined by analysis of IL-17A and IFN-γ in antigen stimulated PBMC cultures using ELISA. ETEC-specific IgA secreted by circulating antibody secreting cells (plasmablasts) were analyzed by using the antibodies in lymphocyte supernatants (ALS) ELISA-based method and plasma IgA was also measured by ELISA.

Results

ETEC patients mounted significant ALS and plasma IgA responses against LTB and CFs on day 7 after hospitalization. ETEC patients had significantly elevated proportions of memory Th cells with a Th17 phenotype (CCR6+CXCR3-) in blood compared to controls, while frequencies of Th1 (CCR6-CXCR3+) or Th2 (CCR6-CXCR3-) cells were not increased. Antigen stimulation of PBMCs revealed IL-17A responses to LT, most clearly observed after stimulation with double mutant heat labile toxin (dmLT), but also with LT B subunit (LTB), and to CS6 in samples from patients with LT+ or CS6+ ETEC bacteria. Some individuals also mounted IFN-γ responses to dmLT and LTB. Levels of LTB specific IgA antibodies in ALS, but not plasma samples correlated with both IL-17A (r=0.5, p=0.02) and IFN-γ (r=0.6, p=0.01) responses to dmLT.

Conclusions

Our results show that ETEC diarrhea induces T cell responses, which are predominantly of the Th17 type. The correlations between IL-17A and IFN-g and intestine-derived plasmablast responses support that Th responses may contribute to the development of protective IgA responses against ETEC infection. These observations provide important insights into T cell responses that need to be considered in the evaluation of advanced ETEC vaccine candidates.

The Immunogenicity and Properties of a Whole-Cell ETEC Vaccine Inactivated with Psoralen and UVA Light in Comparison to Formalin

Inactivated whole-cell vaccines present a full repertoire of antigens to the immune system. Formalin treatment, a standard method for microbial inactivation, can modify or destroy protein antigenic epitopes. We tested the hypothesis that photochemical inactivation with psoralen and UVA light (PUVA), which targets nucleic acid, would improve the immunogenicity of an Enterotoxigenic E. coli (ETEC) vaccine relative to a formalin-inactivated counterpart. Exposure of ETEC H10407 to PUVA using the psoralen drug 4'-Aminomethyltrioxsalen hydrochloride (AMT) yielded replication-incompetent bacteria that retained their metabolic activity. CFA/I-mediated mannose-resistant hemagglutination (MRHA) was equivalent for PUVA-inactivated and live ETEC, but was severely reduced for formalin-ETEC, indicating that PUVA preserved fimbrial protein functional integrity. The immunogenicity of PUVA-ETEC and formalin-ETEC was compared in mice ± double mutant heat-labile enterotoxin (dmLT) adjuvant. Two weeks after an intramuscular prime/boost, serum anti-ETEC IgG titers were similar for the two vaccines and were increased by dmLT. However, the IgG responses raised against several conserved ETEC proteins were greater after vaccination with PUVA-ETEC. In addition, PUVA-ETEC generated IgG specific for heat-labile toxin (LT) in the absence of dmLT, which was not a property of formalin-ETEC. These data are consistent with PUVA preserving ETEC protein antigens in their native-like form and justify the further testing of PUVA as a vaccine platform for ETEC using murine challenge models.

Production of monoclonal antibody of heat-labile toxin A subunit to identify enterotoxigenic Escherichia coli by epitope mapping using synthetic peptides

Background

Enterotoxigenic Escherichia coli (ETEC) is a major cause of diarrhea through two enterotoxins, a heat-labile toxin and a heat-stable toxin. These toxins alter the cellular signaling pathways, ultimately triggering an increase in chloride secretion and watery diarrhea.

Objective

For the development of an ETEC vaccine, we attempted to construct a peptide-specific monoclonal antibody library against heat-labile enterotoxin A subunit (LT-A) by epitope mapping using synthetic peptides.

Methods

Sera produced by five mice immunized with recombinant LT-A protein were examined for specific recognition with synthetic 15-mer and 34-mer peptides of LT-A proteins using enzyme-linked immunosorbent assay. The analysis revealed that the synthetic peptides number 8, 16, 24, 33, 36, 38, and 39 reacted with an anti-LT-A polyclonal antibody. For the possible prediction of LT-A epitopes, each full-length protein sequence was subjected to BCPreds analysis and three-dimensional protein structure analysis. The data showed that three peptides (synthetic peptide numbers: 33, 36, and 38-39) have identical antigenic specificities with LT-A protein, suggesting the usefulness of these linear peptide epitopes.

Results

Based on these peptides, we produced monoclonal antibodies to improve the specificity of LT-A detection. Monoclonal antibodies produced from two peptides (numbers 33 and 36) showed affinity for an LT-A recombinant antigen. Moreover, peptide epitope prediction analysis showed that the sites of the three peptides were identical to those exhibiting actual antigenicity. Also, it was confirmed that the amino acid sequence that actually showed antigenicity was included in the peptide predicted only by ETEC-LT-A-33. Also, the specificity of the antibody for ETEC-LT-A-33 was validated using bacterial cells, and the neutralizing effect of the antibody was determined by assessing cytokine release in infected HCT-8 cells.

Conclusion

The monoclonal antibodies produced in this study are useful toolsfor vaccine production against ETEC and can be used to identify peptide antigencandidates.

Challenges and opportunities in developing a Shigella-containing combination vaccine for children in low- and middle-income countries: Report of an expert convening

The gram-negative bacterium Shigella is an enteric pathogen responsible for significant morbidity and mortality due primarily to severe diarrhea and dysentery, mainly among children younger than five years of age living in low- and middle-income countries (LMICs). Long considered a priority target for vaccine development, recent scientific advances have led to a number of promising Shigella vaccine candidates now entering advanced stages of clinical testing. Yet, there is no guarantee that even a highly efficacious Shigella vaccine will be recommended, prioritized, purchased, and widely adopted-especially if it requires additional doses in the immunization schedule and/or visits within the immunization program. This uncertainty is due to a variety of factors, including continuing declines in Shigella-specific and overall diarrheal disease mortality rates, the increasing complexity and cost of infant immunization programs in LMICs, and the recent availability of other high-priority vaccines. Since combining a Shigella vaccine with an existing infant vaccine would conceivably increase its attractiveness, there is a need to systematically consider the challenges determining the public health value, clinical development, manufacturing, licensure, policy recommendations, and financing for a Shigella-containing combination vaccine. The international non-governmental health organization PATH convened an independent panel of 34 subject matter experts across academic, industry, philanthropic, and global health sectors to discuss hypothetical combinations of a notional parenteral Shigella vaccine with three existing vaccines in order to begin exploring the challenges associated with their development. The resulting insights and recommendations from this meeting contribute to PATH's broader effort to evaluate the public health value of potential Shigella vaccines. They may also help guide future combination vaccine development efforts more broadly.

Heat-Stable Enterotoxin Secretions Assessed via ICP-MS Reveal Iron-Mediated Regulation of Virulence in CFA/I- and CS6-Expressing ETEC Isolates

Enterotoxigenic Escherichia coli (ETEC) are a significant cause of childhood diarrhea in low-resource settings. ETEC are defined by the production of heat-stable enterotoxin (ST) and/or heat-labile enterotoxin (LT), which alter intracellular cyclic nucleotide signaling and cause the secretion of water and electrolytes into the intestinal lumen. ETEC take cues from chemicals (e.g., glycans, bile salts, and solutes) that may be liberated following enterotoxin activity to recognize entrance into the host. ETEC then alter the expression of surface adhesins called colonization factors (CFs) to attach to the intestinal epithelium, proliferate, and cause disease. Here, we used an in vivo model of oral ST intoxication to determine its impact on luminal ion concentrations via ICP-MS. We also used functional assays, including Western blots, qPCR, and toxin activity assays, to assess the impact of luminal ion flux on CF and toxin expression. Finally, we assessed ETEC strains with CFs CFA/I or CS6 in a streptomycin mouse model of ETEC colonization. ST causes rapid and significant increases in luminal chloride but significant decreases in luminal magnesium and iron. We confirmed that increased sodium chloride suppresses CFA/I production in ETEC H10407 but does not affect CS6 production in ETEC 214-4. CFA/I production in ETEC H10407 is increased when magnesium becomes limiting, although it does not affect CS6 production in ETEC 214-4. Iron restriction via deferoxamine induces CFA/I expression in ETEC H10407 but not CS6 expression in ETEC 214-4. We demonstrate that ST production is suppressed via iron restriction in H10407, 214-4, and over 50 other ETEC clinical isolates. Lastly, we demonstrate that the iron restriction of mice using oral deferoxamine pre-treatment extends the duration of ETEC H10407 (CFA/I⁺) fecal shedding while accelerating ETEC 214-4 (CS6⁺) fecal shedding. Combined, these data suggest that enterotoxins modulate luminal ion flux to influence ETEC virulence including toxin and CF production.

Strong Association between Diarrhea and Concentration of Enterotoxigenic Escherichia coli Strain TW10722 in Stools of Experimentally Infected Volunteers

Enterotoxigenic Escherichia coli (ETEC) strains are a major cause of diarrheal illness in children and travelers in low- and middle-income countries. When volunteers are infected with ETEC strains, as part of experimental infection studies, some do not develop diarrhea. To improve our understanding of how these volunteers are protected, we investigated the association between stool ETEC DNA concentration, as determined by quantitative PCR, and the development and severity of disease in 21 volunteers who had been experimentally infected with ETEC strain TW10722. We found a strong association between maximum stool ETEC DNA concentration and the development of diarrhea: all of the 11 volunteers who did not develop diarrhea had <0.99% TW10722-specific DNA in their stools throughout the follow-up period of up to 9 days, while all of the 10 volunteers who did develop diarrhea had maximum DNA concentrations of ≥0.99%. Most likely, these maximum stool TW10722 DNA concentrations reflect the level of intestinal colonization and the risk of experiencing diarrhea, thereby, seems to be directly dependent on the level of colonization. Thus, the development and availability of vaccines and other prophylactic measures, even if they only partially reduce colonization, could be important in the effort to reduce the burden of ETEC diarrhea.

Exploring the Role of GMMA Components in the Immunogenicity of a 4-Valent Vaccine against Shigella

Shigellosis is the leading cause of diarrheal disease, especially in children of low- and middle-income countries, and is often associated with anti-microbial resistance. Currently, there are no licensed vaccines widely available against Shigella, but several candidates based on the O-antigen (OAg) portion of lipopolysaccharides are in development. We have proposed Generalized Modules for Membrane Antigens (GMMA) as an innovative delivery system for OAg, and a quadrivalent vaccine candidate containing GMMA from S. sonnei and three prevalent S. flexneri serotypes (1b, 2a and 3a) is moving to a phase II clinical trial, with the aim to elicit broad protection against Shigella. GMMA are able to induce anti-OAg-specific functional IgG responses in animal models and healthy adults. We have previously demonstrated that antibodies against protein antigens are also generated upon immunization with S. sonnei GMMA. In this work, we show that a quadrivalent Shigella GMMA-based vaccine is able to promote a humoral response against OAg and proteins of all GMMA types contained in the investigational vaccine. Proteins contained in GMMA provide T cell help as GMMA elicit a stronger anti-OAg IgG response in wild type than in T cell-deficient mice. Additionally, we observed that only the trigger of Toll-like Receptor (TLR) 4 and not of TLR2 contributed to GMMA immunogenicity. In conclusion, when tested in mice, GMMA of a quadrivalent Shigella vaccine candidate combine both adjuvant and carrier activities which allow an increase in the low immunogenic properties of carbohydrate antigens.

Setup and Characterization of a High-Throughput Luminescence-Based Serum Bactericidal Assay (L-SBA) to Determine Functionality of Human Sera against Shigella flexneri

Shigellosis represents a major public health problem worldwide. The morbidity of the disease, especially in children in developing countries, together with the increase of antimicrobial resistance make a vaccine against Shigella an urgent medical need. Several vaccines under development are targeting Shigella lipopolysaccharide (LPS), whose extreme diversity renders necessary the development of multivalent vaccines. Immunity against Shigella LPS can elicit antibodies capable of killing bacteria in a serotype-specific manner. Therefore, although a correlation of protection against shigellosis has not been established, demonstration of vaccine-elicited antibody bactericidal activity may provide one means of vaccine protection against Shigella. To facilitate Shigella vaccine development, we have set up a high-throughput serum bactericidal assay based on luminescence readout (L-SBA), which has been already used to determine the functionality of antibodies against S. sonnei in multiple clinical trials. Here we present the setup and intra-laboratory characterization of L-SBA against three epidemiologically relevant Shigella flexneri serotypes using human sera. We assessed the linearity, repeatability and reproducibility of the method, demonstrating high assay specificity to detect the activity of antibodies against each homologous strain without any heterologous aspecificity against species-related and non-species-related strains; this assay is ready to be used to determine bactericidal activity of clinical sera raised by multivalent vaccines and in sero-epidemiological studies.

The role of CFA/I in adherence and toxin delivery by ETEC expressing multiple colonization factors in the human enteroid model

Enterotoxigenic Escherichia coli (ETEC) is a primary causative agent of diarrhea in travelers and young children in low-to-middle-income countries (LMICs). ETEC adhere to intestinal epithelia via colonization factors (CFs) and secrete heat-stable toxin (ST) and/or heat-labile toxin (LT), causing dysregulated cellular ion transport and water secretion. ETEC isolates often harbor genes encoding more than one CF that are targets as vaccine antigens. CFA/I is a major CF that is associated with ETEC that causes moderate-to-severe diarrhea and plays an important role in pathogenesis. The Global Enteric Multicenter Study finding that 78% of CFA/I-expressing ETEC also encode the minor CF CS21 prompted investigation of the combined role of these two CFs. Western blots and electron microscopy demonstrated growth media-dependent and strain-dependent differences in CFA/I and CS21 expression. The critical role of CFA/I in adherence by ETEC strains expressing CFA/I and CS21 was demonstrated using the human enteroid model and a series of CFA/I- and CS21-specific mutants. Furthermore, only anti-CFA/I antibodies inhibited adherence by global ETEC isolates expressing CFA/I and CS21. Delivery of ST and resulting cGMP secretion was measured in supernatants from infected enteroid monolayers, and strain-specific ST delivery and time-dependent cGMP production was observed. Interestingly, cGMP levels were similar across wildtype and CF-deficient strains, reflecting a limitation of this static aerobic infection model. Despite adherence by ETEC and delivery of ST, the enteroid monolayer integrity was not disrupted, as shown by the lack of decrease in transepithelial electrical resistance and the lack of IL-8 cytokines produced during infection. Taken together, these data demonstrate that targeting CFA/I in global clinical CFA/I-CS21 strains is sufficient for adherence inhibition, supporting a vaccine strategy that focuses on blocking major CFs. In addition, the human enteroid model has significant utility for the study of ETEC pathogenesis and evaluation of vaccine-induced functional antibody responses.

Rapid generation of Shigella flexneri GMMA displaying natural or new and cross-reactive O-Antigens

Generalized modules for membrane antigens (GMMA) are exosomes released from engineered Gram-negative bacteria and represent an attractive vaccine platform for the delivery of the O-Antigen (OAg), recognized as the key target for protective immunity against several pathogens such as Shigella. Shigella is a major cause of disease in Low- and Middle-Income countries and the development of a vaccine needs to deal with its large serotypic diversity. All S. flexneri serotypes, except serotype 6, share a conserved OAg backbone, corresponding to serotype Y. Here, a GMMA-producing S. flexneri scaffold strain displaying the OAg backbone was engineered with different OAg-modifying enzymes, either individually or in combinations. This strategy rapidly yielded GMMA displaying 12 natural serotypes and 16 novel serotypes expressing multiple epitopes combinations that do not occur in nature. Importantly, a candidate GMMA displaying a hybrid OAg elicited broadly cross-bactericidal antibodies against a large panel of S. flexneri serotypes.

Towards a Four-Component GMMA-Based Vaccine against Shigella

Shigellosis remains a major public health problem around the world; it is one of the leading causes of diarrhoeal disease in low- and middle-income countries, particularly in young children. The increasing reports of Shigella cases associated with anti-microbial resistance are an additional element of concern. Currently, there are no licensed vaccines widely available against Shigella, but several vaccine candidates are in development. It has been demonstrated that the incidence of disease decreases following a prior Shigella infection and that serum and mucosal antibody responses are predominantly directed against the serotype-specific Shigella O-antigen portion of lipopolysaccharide membrane molecules. Many Shigella vaccine candidates are indeed O-antigen-based. Here we present the journey towards the development of a potential low-cost four-component Shigella vaccine, eliciting broad protection against the most prevalent Shigella serotypes, that makes use of the GMMA (Generalized Modules for Membrane Antigens) technology, a novel platform based on bacterial outer membranes for delivery of the O-antigen to the immune system.

Combination of High-Resolution Multistage Ion Mobility and Tandem MS with High Energy of Activation to Resolve the Structure of Complex Chemoenzymatically Synthesized Glycans

Carbohydrates, in particular microbial glycans, are highly structurally diverse biomolecules, the recognition of which governs numerous biological processes. Of special interest, glycans of known monosaccharide composition feature multiple possible isomers, differentiated by the anomerism and position of their glycosidic linkages. Robust analytical tools able to circumvent this extreme structural complexity are increasing in demand to ensure not only the correct determination of naturally occurring glycans but also to support the rapid development of enzymatic and chemoenzymatic glycan synthesis. In support to the later, we report the use of complementary strategies based on mass spectrometry (MS) to evaluate the ability of 14 engineered mutants of sucrose-utilizing α-transglucosylases to produce type/group-specific Shigella flexneri pentasaccharide bricks from a single lightly protected non-natural tetrasaccharide acceptor substrate. A first analysis of the reaction media by UHPLC coupled to high-accuracy MS led to detect six reaction products of enzymatic glucosylation out of the eight possible ones. A seventh structure was evidenced by an additional step of ion mobility at a resolving power (R_p) of approximately 100. Finally, a R_p of about 250 in ion mobility made it possible to detect the eighth and last of the expected structures. Complementary to these measurements, tandem MS with high activation energy charge transfer dissociation (CTD) allowed us to unambiguously characterize seven regioisomers out of the eight possible products of enzymatic glucosylation. This work illustrates the potential of the recently described powerful IMS and CTD-MS methods for the precise structural characterization of complex glycans.

A colloidal gold immunochromatographic strip assay for the rapid detection of Shigella in milk and meat products

Anti-Shigella mAb was produced using IpaC and an immunochromatographic strip was developed to detect different serotypes of Shigella in food.

Efficient production of immunologically active Shigella invasion plasmid antigens IpaB and IpaH using a cell-free expression system

Abstract

Shigella spp. invade the colonic epithelium and cause bacillary dysentery in humans. Individuals living in areas that lack access to clean water and sanitation are the most affected. Even though infection can be treated with antibiotics, Shigella antimicrobial drug resistance complicates clinical management. Despite decades of effort, there are no licensed vaccines to prevent shigellosis. The highly conserved invasion plasmid antigens (Ipa), which are components of the Shigella type III secretion system, participate in bacterial epithelial cell invasion and have been pursued as vaccine targets. However, expression and purification of these proteins in conventional cell-based systems have been challenging due to solubility issues and extremely low recovery yields. These difficulties have impeded manufacturing and clinical advancement. In this study, we describe a new method to express Ipa proteins using the Xpress^+TM cell-free protein synthesis (CFPS) platform. Both IpaB and the C-terminal domain of IpaH1.4 (IpaH-CTD) were efficiently produced with this technology at yields > 200 mg/L. Furthermore, the expression was linearly scaled in a bioreactor under controlled conditions, and proteins were successfully purified using multimode column chromatography to > 95% purity as determined by SDS-PAGE. Biophysical characterization of the cell-free synthetized IpaB and IpaH-CTD using SEC-MALS analysis showed well-defined oligomeric states of the proteins in solution. Functional analysis revealed similar immunoreactivity as compared to antigens purified from E. coli. These results demonstrate the efficiency of CFPS for Shigella protein production; the practicality and scalability of this method will facilitate production of antigens for Shigella vaccine development and immunological analysis.

Key points

• First report of Shigella IpaB and IpaH produced at high purity and yield using CFPS

• CFPS-IpaB and IpaH perform similarly to E. coli–produced proteins in immunoassays

• CFPS-IpaB and IpaH react with Shigella-specific human antibodies and are immunogenic in mice.

Graphical abstract

Impact of O-Acetylation on S. flexneri 1b and 2a O-Antigen Immunogenicity in Mice

Shigellosis is a diarrheal disease caused prevalently by Shigella flexneri and S. sonnei and representing a major global health risk, particularly in developing countries. Bacterial O-antigen (OAg) is the primary target of the host immune response and modifications of its oligosaccharide units, including O-acetylation, are responsible for the variability among the circulating S. flexneri serotypes. No vaccines are widely available against shigellosis and the understanding of the immunogenicity induced by the OAg is fundamental for the design of a vaccine that could cover the most prevalent Shigella serotypes. To understand whether a different O-acetylation pattern could influence the immune response elicited by S. flexneri OAg, we employed as a vaccine technology GMMA purified from S. flexneri 2a and 1b strains that were easily engineered to obtain differently O-acetylated OAg. Resulting GMMA were tested in mice, demonstrating not only no major impact of O-acetyl decorations on the immune response elicited by the two OAg against the homologous strains, but also that the O-acetylation of the Rhamnose III residue (O-factor 9), shared among serotypes 1b, 2a and 6, does not induce cross-reactive antibodies against these serotypes. This work contributes to the optimization of vaccine design against Shigella, providing indication about the ability of shared epitopes to elicit broad protection against S. flexneri serotypes and supporting the identification of critical quality attributes of OAg-based vaccines.

Comparison and Optimization of Quantification Methods for Shigella flexneri Serotype 6 O-antigen Containing Galacturonic Acid and Methyl-Pentose

Shigella is a leading diarrheal cause of morbidity and mortality worldwide, especially in low- and middle-income countries and in children under five years of age. Increasing levels of antimicrobial resistance make vaccine development an even higher global health priority. S. flexneri serotype 6 is one of the targets of many multicomponent vaccines in development to ensure broad protection against Shigella. The O-antigen (OAg) is a key active ingredient and its content is a critical quality attribute for vaccine release in order to monitor their stability and to ensure appropriate immune response. Here, the optimization of two methods to quantify S. flexneri 6 OAg is reported together with the characterization of their performances. The optimized Dische colorimetric method allows a tenfold increment of the sensitivity with respect to the original method and is useful for fast analysis detecting selectively methyl-pentoses, as rhamnose in S. flexneri 6 OAg. Also, a more specific HPAEC-PAD method was developed, detecting the dimer galacturonic acid-galactosamine (GalA-GalN) coming from S. flexneri 6 OAg acid hydrolysis. These methods will facilitate characterization of S. flexneri 6 OAg based vaccines. The colorimetric method can be used for quantification of other polysaccharide containing methyl-pentoses, and the HPAEC-PAD could be extended to other polysaccharides containing uronic acids.

The prospect of orally administered monoclonal secretory IgA (SIgA) antibodies to prevent enteric bacterial infections

Eliminating diarrheal diseases as a leading cause of childhood morbidity and mortality in low- and middle-income countries (LMICs) will require multiple intervention strategies. In this review, we spotlight a series of preclinical studies investigating the potential of orally administered monoclonal secretory IgA (SIgA) antibodies (MAbs) to reduce disease associated with three enteric bacterial pathogens: Campylobacter jejuni, enterotoxigenic Escherichia coli (ETEC), and invasive Salmonella enterica serovar Typhimurium. IgA MAbs targeting bacterial surface antigens (flagella, adhesins, and lipopolysaccharide) were generated from mice, humanized mice, and human tonsillar B cells. Recombinant SIgA1 and/or SIgA2 derivates of those MAbs were purified from supernatants following transient transfection of 293 cells with plasmids encoding antibody heavy and light chains, J-chain, and secretory component (SC). When administered to mice by gavage immediately prior to (or admixed with) the bacterial challenge, SIgA MAbs reduced infection C. jejuni, ETEC, and S. Typhimurium infections. Fv-matched IgG1 MAbs by comparison were largely ineffective against C. jejuni and S. Typhimurium under the same conditions, although they were partially effective against ETEC. While these findings highlight future applications of orally administered SIgA, the studies also underscored the fundamental challenges associated with using MAbs as prophylactic tools against enteric bacterial diseases.