T cell mediated immunity induced by the live-attenuated Shigella flexneri 2a vaccine candidate CVD 1208S in humans

An intranasal adjuvanted, recombinant influenza A/H5 vaccine candidate induces broad priming against diverse influenza A/H5N1 virus clades in a phase I randomized trial in healthy adults

We conducted a randomized, controlled phase I trial (NCT05397119) of a novel adjuvanted recombinant influenza A/H5 (A/Indonesia/05/2005, clade 2.1) hemagglutinin vaccine, administered intranasally in two doses 28 days apart at three antigen levels. Control groups received unadjuvanted recombinant H5 or formulation buffer placebo. Six months later, participants received a heterologous unadjuvanted inactivated influenza A/H5N1 (A/Vietnam/1203/2004, clade 1) vaccine intramuscularly. All vaccines were safe and well tolerated. After the primary intranasal series, serum hemagglutination inhibition and microneutralization responses were minimal. Increases in mucosal and serum IgG/IgA, serum surface plasmon resonance antibody binding, memory B cell and CD4 T cell activity, and antibody-dependent cell-mediated cytotoxicity were observed only in recipients primed intranasally with adjuvanted H5 vaccine. Following the inactivated H5N1 boost, robust responses across all immune assays, as well as microneutralization responses against diverse H5N1 clades (including currently circulating clade 2.3.4.4b), occurred in adjuvanted vaccine recipients, demonstrating successful priming and broad responses.

A multi-epitope protein vaccine encapsulated in alginate nanoparticles as a candidate vaccine against Shigella sonnei

Shigellosis, caused by the Gram-negative bacterium Shigella, is a major global health challenge. Despite extensive research over the past two decades, no commercial vaccine is available to prevent Shigella infection. Developing multi-epitope vaccines offers a promising and innovative approach to tackling infectious diseases. In this study, we produced a multi-epitope vaccine candidate using E. coli BL21 (DE3) plysS bacteria and purified the vaccine protein with Ni-NTA affinity chromatography. We then prepared alginate nanoparticles containing the vaccine protein, with a particle size of 122 ± 6 nm, PDI 0.17, SPAN 0.83, and zeta potential of -27 ± 2 mV. Successful protein loading was confirmed through nanodrop and ATR-FTIR analyses. To evaluate the immunogenicity of the encapsulated vaccine, mice were orally vaccinated, and their serum was analyzed for IgG, IL-4, and IFN-γ levels cytokines. The results showed a significant increase in IgG level in the vaccinated group compared to controls. Additionally, the vaccinated group exhibited a notable increase in IL-4 and IFN-γ cytokines, indicating a robust Th-cell-mediated immune response essential for combating Shigella. Our nano-vaccine demonstrated high efficacy in activating both humoral and cellular immunity, effectively protecting against the bacteria. The alginate-based oral vaccine candidate thus emerges as a promising strategy for developing a multi-epitope vaccine candidate against Shigella.

Further characterization of Shigella-specific (memory) B cells induced in healthy volunteer recipients of SF2a-TT15, a Shigella flexneri 2a synthetic glycan-based vaccine candidate

Shigellosis is common worldwide, and it causes significant morbidity and mortality mainly in young children in low- and middle- income countries. To date, there are not broadly available licensed Shigella vaccines. A novel type of conjugate vaccine candidate, SF2a-TT15, was developed against S. flexneri serotype 2a (SF2a). SF2a-TT15 is composed of a synthetic 15mer oligosaccharide, designed to act as a functional mimic of the SF2a O-antigen and covalently linked to tetanus toxoid (TT). SF2a-TT15 was recently shown to be safe and immunogenic in a Phase 1 clinical trial, inducing specific memory B cells and sustained antibody response up to three years after the last injection. In this manuscript, we advance the study of B cell responses to parenteral administration of SF2a-TT15 to identify SF2a LPS-specific B cells (SF2a+ B cells) using fluorescently labeled bacteria. SF2a+ B cells were identified mainly within class-switched B cells (SwB cells) in volunteers vaccinated with SF2a-TT15 adjuvanted or not with aluminium hydroxide (alum), but not in placebo recipients. These cells expressed high levels of CXCR3 and low levels of CD21 suggesting an activated phenotype likely to represent the recently described effector memory B cells. IgG SF2a+ SwB cells were more abundant than IgA SF2a + SwB cells. SF2a+ B cells were also identified in polyclonally stimulated B cells (antibody secreting cells (ASC)-transformed). SF2a+ ASC-SwB cells largely maintained the activated phenotype (CXCR3 high, CD21 low). They expressed high levels of CD71 and integrin α4β7, suggesting a high proliferation rate and ability to migrate to gut associated lymphoid tissues. Finally, ELISpot analysis showed that ASC produced anti-SF2a LPS IgG and IgA antibodies. In summary, this methodology confirms the ability of SF2a-TT15 to induce long-lived memory B cells, initially identified by ELISpots, which remain identifiable in blood up to 140 days following vaccination. Our findings expand and complement the memory B cell data previously reported in the Phase 1 trial and provide detailed information on the immunophenotypic characteristics of these cells. Moreover, this methodology opens the door to future studies at the single-cell level to better characterize the development of B cell immunity to Shigella.

Toward a Shigella Vaccine: Opportunities and Challenges to Fight an Antimicrobial-Resistant Pathogen

Shigellosis causes more than 200,000 deaths worldwide and most of this burden falls on Low- and Middle-Income Countries (LMICs), with a particular incidence in children under 5 years of age. In the last decades, Shigella has become even more worrisome because of the onset of antimicrobial-resistant strains (AMR). Indeed, the WHO has listed Shigella as one of the priority pathogens for the development of new interventions. To date, there are no broadly available vaccines against shigellosis, but several candidates are being evaluated in preclinical and clinical studies, bringing to light very important data and information. With the aim to facilitate the understanding of the state-of-the-art of Shigella vaccine development, here we report what is known about Shigella epidemiology and pathogenesis with a focus on virulence factors and potential antigens for vaccine development. We discuss immunity after natural infection and immunization. In addition, we highlight the main characteristics of the different technologies that have been applied for the development of a vaccine with broad protection against Shigella.

A tetravalent Shigella Outer Membrane Vesicles based candidate vaccine offered cross-protection against all the serogroups of Shigella in adult mice

In today's world and mostly in low and middle income countries, S. flexneri and S. sonnei remains the major causative agent of clinical bacillary dysentery. Based on contemporary epidemiology, a tetravalent Outer Membrane Vesicle (OMVs) based immunogen was formulated using the most commonly circulating Shigella strains, namely, S. flexneri 2a, S. flexneri 3a, S. flexneri 6 and S. sonnei I, in a 1:1:1:1 ratio. Adult BALB/c mice were orally immunized in a prime-boost-boost manner. Tetravalent Shigella OMVs immunogen induced significant and persistent serum and mucosal antibodies against OMVs, Outer Membrane Proteins (OMPs) and lipopolysaccharides (LPS). Tetravalent OMVs also primed cell mediated immune response effectively. Protective efficacy against six heterologous Shigella strains was checked in an intra-peritoneal mouse model. Immunized mice survived lethal infection better than the non-immunized mice cohort with fewer replicating bacteria isolated from their gut. This study establishes the possibilities of tetravalent OMVs immunogen to become a potent vaccine candidate against human shigellosis, overcoming the limitations of sero-specific cross-protection of Shigella species.

T cell responses to SARS-CoV-2 in people with and without neurologic symptoms of long COVID

Many people experiencing long COVID syndrome, or post-acute sequelae of SARS-CoV-2 infection (PASC), suffer from debilitating neurologic symptoms (Neuro-PASC). However, whether virus-specific adaptive immunity is affected in Neuro-PASC patients remains poorly understood. We report that Neuro-PASC patients exhibit distinct immunological signatures composed of elevated humoral and cellular responses toward SARS-CoV-2 Nucleocapsid protein at an average of 6 months post-infection compared to healthy COVID convalescents. Neuro-PASC patients also had enhanced virus-specific production of IL-6 from and diminished activation of CD8+ T cells. Furthermore, the severity of cognitive deficits or quality of life disturbances in Neuro-PASC patients were associated with a reduced diversity of effector molecule expression in T cells but elevated IFN-γ production to the C-terminal domain of Nucleocapsid protein. Proteomics analysis showed enhanced plasma immunoregulatory proteins and reduced pro-inflammatory and antiviral response proteins in Neuro-PASC patients compared with healthy COVID convalescents, which were also correlated with worse neurocognitive dysfunction. These data provide new insight into the pathogenesis of long COVID syndrome and a framework for the rational design of predictive biomarkers and therapeutic interventions.

The Shigella Vaccines Pipeline

Shigella is the leading cause of global diarrheal deaths that currently lacks a licensed vaccine. Shigellosis drives antimicrobial resistance and leads to economic impact through linear growth faltering. Today, there is a robust pipeline of vaccines in clinical development which are broadly divided into parenteral glycoconjugate vaccines, consisting of O-antigen conjugated to carrier proteins, and oral live attenuated vaccines, which incorporate targeted genetic mutations seeking to optimize the balance between reactogenicity, immunogenicity and ultimately protection. Proof of efficacy has previously been shown with both approaches but for various reasons no vaccine has been licensed to date. In this report, we outline the requirements for a Shigella vaccine and describe the current pipeline in the context of the many candidates that have previously failed or been abandoned. The report refers to papers from individual vaccine developers in this special supplement of Vaccines which is focused on Shigella vaccines. Once readouts of safety and immunogenicity from current trials of lead candidate vaccines among the target population of young children in low- and middle-income countries are available, the likely time to licensure of a first Shigella vaccine will become clearer.

Recent Progress in Shigella and Burkholderia pseudomallei Vaccines

Significant advancement has been made in the development of vaccines against bacterial pathogens. However, several roadblocks have been found during the evaluation of vaccines against intracellular bacterial pathogens. Therefore, new lessons could be learned from different vaccines developed against unrelated intracellular pathogens. Bacillary dysentery and melioidosis are important causes of morbidity and mortality in developing nations, which are caused by the intracellular bacteria Shigella and Burkholderia pseudomallei, respectively. Although the mechanisms of bacterial infection, dissemination, and route of infection do not provide clues about the commonalities of the pathogenic infectious processes of these bacteria, a wide variety of vaccine platforms recently evaluated suggest that in addition to the stimulation of antibodies, identifying protective antigens and inducing T cell responses are some additional required elements to induce effective protection. In this review, we perform a comparative evaluation of recent candidate vaccines used to combat these two infectious agents, emphasizing the common strategies that can help investigators advance effective and protective vaccines to clinical trials.

Functional antibodies and innate immune responses to WRSS1, a live oral Shigella sonnei vaccine candidate in Bangladeshi adults and children

Background

We demonstrated in a randomized placebo-controlled trial that WRSS1, a live oral Shigella sonnei vaccine candidate, is safe in Bangladeshi adults and children, and elicits antigen-specific antibodies. Here, we describe functional antibody and innate immune responses to WRSS1.

Methods

Adults (18–39 years) and children (5–9 years) received 3 doses of 3 × 10⁵ or 3 × 10⁶ colony forming units (CFU) of WRSS1 or placebo, 4 weeks apart; children additionally received 3 × 10⁴ CFU. Blood and stool were collected at baseline and 7 days after each dose. Functional antibodies were measured using serum bactericidal antibody (SBA) assay. Cytokine/chemokine concentrations were measured in lymphocyte cultures. Host defense peptides LL-37, HBD-1, and HD-5 were analyzed in plasma and stool.

Results

Children showed increased SBA titers over baseline after the third dose of 3 × 10⁶ CFU (P = .048). Significant increases of Th-17 and proinflammatory cytokines (TNF-α, G-CSF, MIP-1β), and reduction of anti-inflammatory and Th2 cytokines (IL-10, IL-13, GM-CSF) were observed in children. Plasma HBD-1 and LL-37 decreased in children after vaccination but were increased/unchanged in adults.

Conclusions

Functional antibodies and Th1/Th17 cytokine responses in children may serve as important indicators of immunogenicity and protective potential of WRSS1.

Clinical Trials Registration: NCT01813071.

Glycoconjugate vaccines against Salmonella enterica serovars and Shigella species: existing and emerging methods for their analysis

The global spread of enteric disease, the increasingly limited options for antimicrobial treatment and the need for effective eradication programs have resulted in an increased demand for glycoconjugate enteric vaccines, made with carbohydrate-based membrane components of the pathogen, and their precise characterisation. A set of physico-chemical and immunological tests are employed for complete vaccine characterisation and to ensure their consistency, potency, safety and stability, following the relevant World Health Organization and Pharmacopoeia guidelines. Variable requirements for analytical methods are linked to conjugate structure, carrier protein nature and size and O-acetyl content of polysaccharide. We investigated a key stability-indicating method which measures the percent free saccharide of Salmonella enterica subspecies enterica serovar Typhi capsular polysaccharide, by detergent precipitation, depolymerisation and HPAEC-PAD quantitation. Together with modern computational approaches, a more precise design of glycoconjugates is possible, allowing for improvements in solubility, structural conformation and stability, and immunogenicity of antigens, which may be applicable to a broad spectrum of vaccines. More validation experiments are required to establish the most effective and suitable methods for glycoconjugate analysis to bring uniformity to the existing protocols, although the need for product-specific approaches will apply, especially for the more complex vaccines. An overview of current and emerging analytical approaches for the characterisation of vaccines against Salmonella Typhi and Shigella species is described in this paper. This study should aid the development and licensing of new glycoconjugate vaccines aimed at the prevention of enteric diseases.

Shigella: Antibiotic-Resistance Mechanisms And New Horizons For Treatment

Shigella spp. are a common cause of diarrheal disease and have remained an important pathogen responsible for increased rates of morbidity and mortality caused by dysentery each year around the globe. Antibiotic treatment of Shigella infections plays an essential role in reducing prevalence and death rates of the disease. However, treatment of these infections remains a challenge, due to the global rise in broad-spectrum resistance to many antibiotics. Drug resistance in Shigella spp. can result from many mechanisms, such as decrease in cellular permeability, extrusion of drugs by active efflux pumps, and overexpression of drug-modifying and -inactivating enzymes or target modification by mutation. Therefore, there is an increasing need for identification and evolution of alternative therapeutic strategies presenting innovative avenues against Shigella infections, as well as paying further attention to this infection. The current review focuses on various antibiotic-resistance mechanisms of Shigella spp. with a particular emphasis on epidemiology and new mechanisms of resistance and their acquisition, and also discusses the status of novel strategies for treatment of Shigella infection and vaccine candidates currently under evaluation in preclinical or clinical phases.

Role of antigen specific T and B cells in systemic and mucosal immune responses in ETEC and Shigella infections, and their potential to serve as correlates of protection in vaccine development

The generation of robust systemic and mucosal antibody and cell-mediated immune (CMI) responses that are protective, long-lasting, and can quickly be recalled upon subsequent re-exposure to the cognate antigen is the key to the development of effective vaccine candidates. These responses, whether they represent mechanistic or non-mechanistic immunological correlates of protection, usually entail the activation of T cell memory and effector subsets (T-CMI) and induction of long-lasting memory B cells. However, for ETEC and Shigella, the precise role of these key immune cells in primary and secondary (anamnestic) immune responses remains ill-defined. A workshop to address immune correlates for ETEC and Shigella, in general, and to elucidate the mechanistic role of T-cell subsets and B-cells, both systemically and in the mucosal microenvironment, in the development of durable protective immunity against ETEC and Shigella was held at the recent 2nd Vaccines against Shigella and ETEC (VASE) conference in June 2018. This report is a summary of the presentations and the discussion that ensued at the workshop.

Screening for coeliac disease in children and adults living in a slum of Dhaka, Bangladesh

Background and objective

Serological screening with a confirmation through biopsy has improved the understanding of coeliac disease (CD) epidemiology worldwide. Prevalence of CD in Bangladesh is not yet explored and therefore, we aimed to assess the seroprevalence of CD in slum-dwelling malnourished children and adults in Dhaka.

Methods

Serum samples were collected from three different cohorts: stunted (length-for-age Z-scores (LAZ) <−2) and at risk of stunting children (LAZ <−1 to −2) and malnourished adults (body mass index <18.5 kg/m²). Samples from all the participants were assessed for anti-tissue transglutaminase antibody (tTG-IgA) and total serum IgA by ELISA. Positive tTG-IgA and randomly selected low IgA values were reconfirmed using anti-tTG-IgG and gliadin IgG ELISA. CD was diagnosed when second screening tests were found positive and the participants were further investigated by small bowel biopsy.

Results

A total of 818 participants (240 stunted, 272 at risk of stunting children and 306 malnourished adults) were enrolled in the study. Overall, anti-tTG-IgA was positive in 5/818 (0.6%; 95% CI 0.25% to 1.46%). Of the five positive cases, anti-tTG-IgG and gliadin IgG were found positive in only one participant. Duodenal biopsy of positive participant revealed characteristic lesions of CD. Randomly selected low IgA values were found negative in tTG-IgG and gliadin IgG for all the participants. No participant was found total IgA deficient.

Conclusion

The incidence of coeliac autoimmunity is low in malnourished slum dwellers regardless of age in Bangladesh. It is important to investigate the nationwide prevalence to reveal the definite picture.

Characterization of a serologically atypical Shigella flexneri Z isolated from diarrheal patients in Bangladesh and a proposed serological scheme for Shigella flexneri

Background

Atypical Shigella flexneri Z variant, that agglutinate with E1037 group factor specific monoclonal antisera against Shigella flexneri IV-I but not with other group or type specific antisera, has continuously being isolated in Bangladesh since 1997. Later this serotype has been reported in Indonesia, China and Argentina. Despite being a provisional serotype, continuous isolation of these strains in diverse geographical regions implicated a great necessity to study the overall characteristics of these strains. Therefore, we extensively characterized S. flexneri Z strains using various phenotypic and molecular tools.

Method

Of 3569 S. flexneri isolated between 1997 and 2015, 95 strains were identified as S. flexneri Z using a panel of polyvalent absorbed antisera and monoclonal antisera of S. flexneri (MASF). Of them, randomly selected 65 strains were molecular O-serotyped using multiplex PCR and characterized using different phenotypic and molecular techniques (i.e.biotyping, plasmid profile, virulence marker and PFGE) to determine relationship with other subserotypes of S. flexneri.

Results

All these atypical S. flexneri Z strains were agglutinated with MASF B and IV-I antisera. Concordantly, these strains were positive to opt-gene, responsible for MASF IV-I sero-positive phenotype. However, molecular O-serotyping of all 65 strains could not differentiate between Z and Yb giving similar amplification products (wzx1-5 and opt). Contrarily, MASF based serotypic scheme distinguished among Z and Yb as well as Ya. All these S. flexneri Z showed typical biochemical reaction of S. flexneri, harboured a 140 MDa virulence plasmid and virulence markers namely ipaH, ial, sen, sigA and sepA genes. Along with the virulence plasmid, small plasmids (2.6, 1.8 and 1.6 MDa) were present as core plasmid. Moreover, a middle ranged plasmid and a 4.0 MDa sized plasmid were observed in 65% and 20% strains, respectively. Analysis of PFGE on XbaI-digested chromosomal DNA of Bangladeshi strains showed that S. flexneri Z had a close relatedness with Ya and Yb but completely different than the strains of Xa, Xb, 2a and 2b. This observation was found to be unequivocal while the overall result of biotyping, plasmid profile, and virulence factors was compared. Therefore, we conclude that these atypical serotype Z isolated in Bangladesh had a clonal relationship with Ya and Yb of Bangladesh and the opt gene played an important role in serotypic switching among them. Current serotyping scheme of S. flexneri strains fails to place many such atypical strains (1c, 1c+6, 1d, type 4, and 4c) including S. flexneri Z isolated from different parts of the world. Therefore, an updated serotyping scheme for identification of subserotypes of S. flexneri has been proposed to avoid multiple naming of the same subserotype having similar agglutination pattern.

A Novel Shigella Proteome Microarray Discriminates Targets of Human Antibody Reactivity following Oral Vaccination and Experimental Challenge

Shigella spp. are a major cause of diarrhea and dysentery in children under 5 years old in the developing world. The development of an effective vaccine remains a public health priority, necessitating improved understanding of immune responses to Shigella and identification of protective antigens. We report the development of a core Shigella proteome microarray consisting of 2,133 antigen targets common to all Shigella species. We evaluated the microarray with serum samples from volunteers immunized with either an inactivated whole-cell S. flexneri serotype 2a (Sf2aWC) vaccine or a live attenuated S. flexneri 2a vaccine strain (CVD 1204) or challenged with wild-type S. flexneri 2a (Sf2a challenge). Baseline reactivities to most antigens were detected postintervention in all three groups. Similar immune profiles were observed after CVD 1204 vaccination and Sf2a challenge. Antigens with the largest increases in mean reactivity postintervention were members of the type three secretion system (T3SS), some of which are regarded as promising vaccine targets: these are the invasion plasmid antigens (Ipas) IpaB, IpaC, and IpaD. In addition, new immunogenic targets (IpaA, IpaH, and SepA) were identified. Importantly, immunoreactivities to antigens in the microarray correlated well with antibody titers determined by enzyme-linked immunosorbent assay (ELISA), validating the use of the microarray platform. Finally, our analysis uncovered an immune signature consisting of three conserved proteins (IpaA, IpaB, and IpaC) that was predictive of protection against shigellosis. In conclusion, the Shigella proteome microarray is a robust platform for interrogating serological reactivity to multiple antigens at once and identifying novel targets for the development of broadly protective vaccines.IMPORTANCE Each year, more than 180 million cases of severe diarrhea caused by Shigella occur globally. Those affected (mostly children in poor regions) experience long-term sequelae that severely impair quality of life. Without a licensed vaccine, the burden of disease represents a daunting challenge. An improved understanding of immune responses to Shigella is necessary to support ongoing efforts to identify a safe and effective vaccine. We developed a microarray containing >2,000 proteins common to all Shigella species. Using sera from human adults who received a killed whole-cell or live attenuated vaccine or were experimentally challenged with virulent organisms, we identified new immune-reactive antigens and defined a T3SS protein signature associated with clinical protection.