Cytokine production patterns and lymphoproliferative responses in volunteers orally immunized with attenuated vaccine strains of Salmonella typhi

In situ immunomodulation of tumors with biosynthetic bacteria promote anti-tumor immunity

Immune checkpoint blockade (ICB) therapy potently revives T cell's response to cancer. However, patients suffered with tumors that had inadequate infiltrated immune cells only receive limited therapeutic benefits from ICB therapy. Synthetic biology promotes the alternative strategy of harnessing tumor-targeting bacteria to synthesize therapeutics to modulate immunity in situ. Herein, we engineered attenuated Salmonella typhimurium VNP20009 with gene circuits to synthetize granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin 7 (IL-7) within tumors, which recruited dendritic cells (DCs) and enhanced T cell priming to elicit anti-tumor response. The bacteria-produced GM-CSF stimulated the maturation of bone marrow-derived dendritic cells (BMDCs), while IL-7 promoted the proliferation of spleen isolated T cells and inhibited cytotoxicity T cell apoptosis in vitro. Virtually, engineered VNP20009 prefer to colonize in tumors, and inhibited tumor growth by enhancing DCs and T cell infiltration. Moreover, the tumor-toxic GZMB+ CD8+ T cell and IFN-γ+ CD8+ T cell populations conspicuously increased with the treatment of engineered bacteria. The combination of GM-CSF-IL-7-VNP20009 with PD-1 antibody synergistically stunted the tumor progress and stasis.

Controlled human infectious models, a path forward in uncovering immunological correlates of protection: Lessons from enteric fevers studies

Enteric infectious diseases account for more than a billion disease episodes yearly worldwide resulting in approximately 2 million deaths, with children under 5 years old and the elderly being disproportionally affected. Enteric pathogens comprise viruses, parasites, and bacteria; the latter including pathogens such as Salmonella [typhoidal (TS) and non-typhoidal (nTS)], cholera, Shigella and multiple pathotypes of Escherichia coli (E. coli). In addition, multi-drug resistant and extensively drug-resistant (XDR) strains (e.g., S. Typhi H58 strain) of enteric bacteria are emerging; thus, renewed efforts to tackle enteric diseases are required. Many of these entero-pathogens could be controlled by oral or parenteral vaccines; however, development of new, effective vaccines has been hampered by lack of known immunological correlates of protection (CoP) and limited knowledge of the factors contributing to protective responses. To fully comprehend the human response to enteric infections, an invaluable tool that has recently re-emerged is the use of controlled human infection models (CHIMs) in which participants are challenged with virulent wild-type (wt) organisms. CHIMs have the potential to uncover immune mechanisms and identify CoP to enteric pathogens, as well as to evaluate the efficacy of therapeutics and vaccines in humans. CHIMs have been used to provide invaluable insights in the pathogenesis, host-pathogen interaction and evaluation of vaccines. Recently, several Oxford typhoid CHIM studies have been performed to assess the role of multiple cell types (B cells, CD8+ T, Tregs, MAIT, Monocytes and DC) during S. Typhi infection. One of the key messages that emerged from these studies is that baseline antigen-specific responses are important in that they can correlate with clinical outcomes. Additionally, volunteers who develop typhoid disease (TD) exhibit higher levels and more activated cell types (e.g., DC and monocytes) which are nevertheless defective in discrete signaling pathways. Future critical aspects of this research will involve the study of immune responses to enteric infections at the site of entry, i.e., the intestinal mucosa. This review will describe our current knowledge of immunity to enteric fevers caused byS. Typhi and S. Paratyphi A, with emphasis on the contributions of CHIMs to uncover the complex immunological responses to these organisms and provide insights into the determinants of protective immunity.

Protection Conferred by Drinking Water Administration of a Nanoparticle-Based Vaccine against Salmonella Enteritidis in Hens

Salmonellosis remains a major medical and an unmet socioeconomic challenge. Worldwide, more than three million deaths per year are associated with Salmonella enterica serovar Enteritidis infections. Although commercially available vaccines for use in poultry exist, their efficacy is limited. We previously described a method for isolating a heat extract (HE) fraction of the cell surface of S. Enteritidis that contained major antigenic complexes immunogenic in hens naturally infected with the bacterium. One single dose of S. Enteritidis’ HE induced protection against lethal salmonellosis in mice. Furthermore, HE encapsulation in nanoparticles of the copolymer of methyl vinyl ether and maleic anhydride (PVM/MA), Gantrez AN, improved and prolonged the protection against the disease in mice. We formulated new preparations of Gantrez AN nanoparticles with HE S. Enteritidis and assessed their stability in drinking water and their efficacy in hens after experimental infection. The oral treatment of six-week-old hens with two doses of HE nanoparticles significantly reduced the Salmonella excretion in hens. Due to the effectiveness of the treatment in reducing bacterial excretion, we conclude that HE nanoencapsulation obtained from S. Enteritidis is a viable novel vaccination approach against salmonellosis in farms.

Diversity of Salmonella Typhi-responsive CD4 and CD8 T cells before and after Ty21a typhoid vaccination in children and adults

Typhoid fever is a life-threatening disease caused by the human-restricted pathogen Salmonella enterica serovar Typhi (S. Typhi). The oral live attenuated Ty21a typhoid vaccine protects against this severe disease by eliciting robust, multifunctional cell-mediated immunity (CMI), shown to be associated with protection in wild-type S. Typhi challenge studies. Ty21a induces S. Typhi-responsive CD8+ and CD4+ T cells but little is known about the response to this vaccine in children. To address this important gap in knowledge, we have used mass cytometry to analyze pediatric and adult pre- and post-Ty21a vaccination CMI in an autologous S. Typhi antigen presentation model. Here, using conventional supervised analytical tools, we show adult T cells are more multifunctional at baseline than those obtained from children. Moreover, pediatric and adult T cells respond similarly to Ty21a vaccination, but adult responders remain more multifunctional. The use of the unsupervised dimensionality reduction tool tSNE (t-distributed Stochastic Neighbor Embedding) allowed us to confirm these findings, as well as to identify increases and decreases in well-defined specific CD4+ and CD8+ T-cell populations that were not possible to uncover using the conventional gating strategies. These findings evidenced age-associated maturation of multifunctional S. Typhi-responsive T-cell populations, including those which we have previously shown to be associated with protection from, and/or delayed onset of, typhoid disease. These findings are likely to play an important role in improving pediatric vaccination strategies against S. Typhi and other enteric pathogens.

Characteristics of regulatory T-cell populations before and after Ty21a typhoid vaccination in children and adults

Typhoid fever, caused by the pathogen Salmonella enterica serovar Typhi (S. Typhi), is a serious global health concern. Challenge studies with wild type S. Typhi identified associations between gut-homing regulatory T cells (Treg) and development of typhoid disease. Whether oral live-attenuated Ty21a vaccination induces gut-homing Treg remains unclear. Here, we analyze pediatric and adult Treg pre- and post-Ty21a vaccination in an autologous S. Typhi-antigen presentation model to address this knowledge gap. We show that peripheral memory Treg populations change from childhood to adulthood, but not following Ty21a vaccination. Unsupervised dimensionality reduction with t-distributed stochastic neighbor embedding (tSNE) identifies homing, memory, and functional features which evidence age-associated maturation of multifunctional S. Typhi-responsive Treg, which were not impacted by Ty21a vaccination. These findings improve understanding of pediatric regulatory T cells, while identifying age-related differences in S. Typhi-responsive Treg, which may aid in the development of improved pediatric vaccination strategies against S. Typhi.

Attenuated Oral Typhoid Vaccine Ty21a Elicits Lamina Propria and Intra-Epithelial Lymphocyte Tissue-Resident Effector Memory CD8 T Responses in the Human Terminal Ileum

Tissue-resident memory T cells (T_RM) are newly defined memory T cells (T_M) distinct from circulating T_M subsets which have the potential to mount rapid protective immune responses at the site of infection. However, very limited information is available regarding the role and contribution of T_RM in vaccine-mediated immune responses in humans at the site of infection. Here, we studied the role and contribution of tissue resident memory T cells (T_RM) located in the terminal ileum (TI) (favored site of infection for S. Typhi) following oral Ty21a immunization in humans. We examined TI-lamina propria mononuclear cells (LPMC) and intra-epithelial lymphocytes (IEL) CD8+ T_RM subsets obtained from healthy volunteers undergoing medically-indicated colonoscopies who were either immunized with Ty21a or unvaccinated. No significant differences in the frequencies of LPMC CD8+ T_RM and CD8+CD69+CD103– T cells subsets were observed following Ty21a-immunization. However, LPMC CD8+ T_RM exhibited significantly higher levels of cytokines (IFN-γ, IL-17A, and TNF-α) ex-vivo in Ty21a-vaccinated than in unvaccinated volunteers. LPMC CD8+ T_RMS. Typhi-specific responses were evaluated using S. Typhi-infected targets and found to produce significantly higher levels of S. Typhi-specific IL-17A. In contrast, LPMC CD8+CD69+CD103- T cells produced significantly increased S. Typhi-specific levels of IFN-γ, IL-2, and IL-17A. Finally, we assessed CD8+ T_RM in IEL and observed that the frequency of IEL CD8+ T_RM is significantly lower following Ty21a immunization. However, ex-vivo IEL CD8+ T_RM elicited by Ty21a immunization spontaneously produced significantly higher levels of cytokines (IFN-γ, IL-17A, IL-2, and TNF-α). This study provides the first demonstration of the effect of oral Ty21a vaccination on CD8+ T_RM subsets (spontaneous and S. Typhi-specific) responses in the LPMC and IEL compartment of the human terminal ileum mucosa, contributing novel information to our understanding of the generation of mucosal immune responses following oral Ty21a-immunization.

Cell mediated immune responses elicited in volunteers following immunization with candidate live oral Salmonella enterica serovar Paratyphi A attenuated vaccine strain CVD 1902

The incidence of Salmonella enterica serovar Paratyphi A (PA) infection is on the rise and no licensed vaccines are available. We evaluated cell mediated immune (CMI) responses elicited in volunteers following immunization with a single dose (10⁹ or 10¹⁰ cfu) of a novel attenuated live oral PA-vaccine strain (CVD 1902). Results showed increases in PA-lipopolysaccharide-specific IgG- and/or IgA B-memory cells and production of IFN-γ, TNF-α, IL-10, IL-23 and RANTES following stimulation with PA-antigens by peripheral blood mononuclear cells obtained 28 days post immunization. Flow cytometry assays revealed that vaccine elicited PA-specific CD8+ and/or CD4+ T effector/memory cells were predominantly multifunctional concomitantly expressing CD107a and/or producing IFN-γ, TNF-α and/or IL-2. Similar proportions of these MF cells expressed, or not, the gut homing marker integrin α4β7. The results suggest that immunization with CVD 1902 elicits CMI responses against PA supporting its further evaluation as a potential vaccine candidate against paratyphoid A fever.

Age-Associated Heterogeneity of Ty21a-Induced T Cell Responses to HLA-E Restricted Salmonella Typhi Antigen Presentation

Human-restricted Salmonella enterica serovar Typhi (S. Typhi) is the causative agent of typhoid fever—a life-threatening disease of great global health significance, particularly in the developing world. Ty21a is an oral live-attenuated vaccine that protects against the development of typhoid disease in part by inducing robust T cell responses, among which multifunctional CD8⁺ cytotoxic T lymphocytes (CTL) play an important role. Following Ty21a vaccination, a significant component of adult CTL have shown to be targeted to S. Typhi antigen presented by the conserved major histocompatibility complex (MHC) class Ib molecule, human leukocyte antigen-E (HLA-E). S. Typhi challenge studies have shown that baseline, multifunctional HLA-E responsive T cells are associated with protection from, and delayed onset of, typhoid disease. However, despite the overwhelming burden of typhoid fever in school-aged children, and due to limited availability of pediatric samples, incomplete information is available regarding these important HLA-E-restricted responses in children, even though studies have shown that younger children may be less likely to develop protective cell mediated immune (CMI) responses than adults following vaccination. To address this gap, we have studied this phenomenon in depth by using mass cytometry to analyze pediatric and adult T cell responses to HLA-E-restricted S. Typhi antigen presentation, before and after Ty21a vaccination. Herein, we show variable responses in all age strata following vaccination among T effector memory (T_EM) and T effector memory CD45RA⁺ (T_EMRA) cells based on conventional gating analysis. However, by utilizing the dimensionality reduction tool tSNE (t-distributed Stochastic Neighbor Embedding), we are able to identify diverse, highly multifunctional gut-homing- T_EM and T_EMRA clusters of cells which are more abundant in adult and older pediatric participants than in younger children. These findings highlight a potential age-associated maturation of otherwise conserved HLA-E restricted T cell responses. Such insights, coupled with the marked importance of multifunctional T cell responses to combat infection, may better inform future pediatric vaccination strategies against S. Typhi and other infectious diseases.

Is a Human CD8 T-Cell Vaccine Possible, and if So, What Would It Take? CD8 T-Cell-Mediated Protective Immunity and Vaccination against Enteric Bacteria

Although induction of CD8⁺ responses is widely accepted as critical in clearing viral infections and necessary for effective vaccines against viruses, much less is known regarding the role of these cells in bacterial and other infections, particularly those that enter the host via the gastrointestinal tract. In this commentary, I discuss the likelihood that CD8⁺ responses are also important in protection from intestinal Gram-negative bacteria, as well as the many factors that should be taken into consideration during the development of vaccines, based on eliciting long-term protection predominantly mediated by CD8⁺ responses against these organisms.

Differences Between Pediatric and Adult T Cell Responses to In Vitro Staphylococcal Enterotoxin B Stimulation

Toxic shock syndrome (TSS) is capable of inducing life-threatening fever, rash, and systemic organ failure, though the specific mechanisms behind these symptoms remain poorly understood. Staphylococcal enterotoxin B (SEB) and other superantigens have shown to be important factors in TSS, capable of promoting cross-linking between T cell receptors and major histocompatibility complexes which results in overwhelming T cell activation, proliferation, and cytokine production. The resulting proinflammatory cytokine cascade, often referred to as the “cytokine storm,” seems to be critical to the development of disease. Interestingly, clinical studies have shown that children exhibit less severe TSS-associated morbidity than adults, though the mechanism behind this phenomenon has not been addressed. Indeed, despite the fact that most novel antigen exposure occurs early in life, be it from environmentally acquired pathogens or routine vaccination, normal pediatric T cell immune functions remain critically underexplored. This is largely due to difficulty in obtaining enough samples to explore more than a narrow sliver of the cell-mediated immune compartment. To address this limitation, we optimized a T effector (T_eff)/circulating T follicular helper (cT_FH) cell mass cytometry panel which allowed us to analyze a wide array of T cell populations and effector functions following in vitro SEB stimulation. We show that T cell activation—as measured by CD69 expression—following SEB stimulation is lower in pediatric participants, increasing throughout childhood, and reaching adult levels by around 15 years old. Further, while individual CD4⁺ effector memory T cell (T_EM) effector molecules show limited age-associated differences following SEB stimulation, multifunctional CD4⁺ T_EM are shown to positively correlate with increasing age through adolescence. Individual CD8⁺ T_EM effectors and multifunctional phenotypes also show very strong age-associated increases following SEB stimulation. SEB stimulation has little impact on cT_FH activation or functional cellular markers, regardless of age. These results, coupled with the fact that a robust proinflammatory cytokine response seems critical to developing severe TSS, suggest a possible connection between the significantly reduced T cell activation and multifunctional populations following in vitro SEB stimulation in our pediatric participants and clinical observations relating to reduced TSS mortality in children.

A recombinant protein of Salmonella Typhi induces humoral and cell-mediated immune responses including memory responses

Gram negative enteric bacteria, Salmonella enterica serovar Typhi (S. Typhi), the etiological agent of typhoid fever is a major public health problem in developing countries. While a permanent solution to the problem would require improved sanitation, food and water hygiene, controlling the infection by vaccination is urgently required due to the emergence of multidrug resistant strains in multiple countries. The currently licensed vaccines are moderately efficacious with limited applicability, and no recommended vaccines exist for younger children. We had previously reported that a candidate vaccine based on recombinant outer membrane protein (rT2544) of S. Typhi is highly immunogenic and protective in mice. Here we show that rT2544-specific antiserum is capable of mediating bacterial lysis by the splenocytes through Antibody-Dependent Cellular Cytotoxicity (ADCC). Increased populations of rT2544-specific IgA and IgG secreting plasma cells are found in the spleen, mesenteric lymph nodes and peyer's patches. Cell-Mediated Immune Responses (CMIR) induced by rT2544 consist of Th1 cell differentiation and generation of cytotoxic T lymphocytes (CTL), which produce IFN-γ and are capable of destroying cells displaying T2544-derived antigens. rT2544 elicits pro-inflammatory cytokines (TNF-α, IL-6) from Bone Marrow-Derived Dendritic cells (BMDCs), while in vitro re-stimulation of rT2544-primed CD4+ T cells induces cell proliferation and generates higher amounts of Th1 cytokines, such as IFN-gamma, TNF-α and IL-2. Finally, the candidate vaccine induces immunological memory in the form of memory B and T lymphocytes. Taken together, the study further supports the potential of rT2544 as a novel and improved vaccine candidate against S. Typhi.

Expression of intra- and extracellular granzymes in patients with typhoid fever

BACKGROUND

Typhoid fever, caused by the intracellular pathogen Salmonella (S.) enterica serovar Typhi, remains a major cause of morbidity and mortality worldwide. Granzymes are serine proteases promoting cytotoxic lymphocytes mediated eradication of intracellular pathogens via the induction of cell death and which can also play a role in inflammation. We aimed to characterize the expression of extracellular and intracellular granzymes in patients with typhoid fever and whether the extracellular levels of granzyme correlated with IFN-γ release.

METHODS AND PRINCIPAL FINDINGS

We analyzed soluble protein levels of extracellular granzyme A and B in healthy volunteers and patients with confirmed S. Typhi infection on admission and day of discharge, and investigated whether this correlated with interferon (IFN)-γ release, a cytokine significantly expressed in typhoid fever. The intracellular expression of granzyme A, B and K in subsets of lymphocytic cells was determined using flow cytometry. Patients demonstrated a marked increase of extracellular granzyme A and B in acute phase plasma and a correlation of both granzymes with IFN-γ release. In patients, lower plasma levels of granzyme B, but not granzyme A, were found at day of discharge compared to admission, indicating an association of granzyme B with stage of disease. Peripheral blood mononuclear cells of typhoid fever patients had a higher percentage of lymphocytic cells expressing intracellular granzyme A and granzyme B, but not granzyme K, compared to controls.

CONCLUSION

The marked increase observed in extra- and intracellular levels of granzyme expression in patients with typhoid fever, and the correlation with stage of disease, suggests a role for granzymes in the host response to this disease.

Importance of Salmonella Typhi-Responsive CD8+ T Cell Immunity in a Human Typhoid Fever Challenge Model

Typhoid fever, caused by the human-restricted organism Salmonella enterica serovar Typhi (S. Typhi), constitutes a major global health problem. The development of improved attenuated vaccines is pressing, but delayed by the lack of appropriate preclinical models. Herein, we report that high levels of S. Typhi-responsive CD8+ T cells at baseline significantly correlate with an increased risk of disease in humans challenged with a high dose (~10⁴ CFU) wild-type S. Typhi. Typhoid fever development was associated with higher multifunctional S. Typhi-responsive CD8+ T effector memory cells at baseline. Early decreases of these cells in circulation following challenge were observed in both S. Typhi-responsive integrin α₄β₇− and integrin α₄β₇+ CD8+ T effector memory (T_EM) cells, suggesting their potential to home to both mucosal and extra-intestinal sites. Participants with higher baseline levels of S. Typhi-responsive CD8+ T memory cells had a higher risk of acquiring disease, but among those who acquired disease, those with a higher baseline responses took longer to develop disease. In contrast, protection against disease was associated with low or absent S. Typhi-responsive T cells at baseline and no changes in circulation following challenge. These data highlight the importance of pre-existing S. Typhi-responsive immunity in predicting clinical outcome following infection with wild-type S. Typhi and provide novel insights into the complex mechanisms involved in protective immunity to natural infection in a stringent human model with a high challenge dose. They also contribute important information on the immunological responses to be assessed in the appraisal and selection of new generation typhoid vaccines.

Impact of CD4+ T Cell Responses on Clinical Outcome following Oral Administration of Wild-Type Enterotoxigenic Escherichia coli in Humans

Enterotoxigenic Escherichia coli (ETEC) is a non-invasive enteric pathogen of considerable public health importance, being one of the most common attributable causes of diarrheal illness in infants and young children in developing countries and the most common cause of traveler’s diarrhea. To enhance study-to-study consistency of our experimental challenge model of ETEC in volunteers, and to allow concomitant multi-site trials to evaluate anti-ETEC immunoprophylactic products, hundreds of vials, each containing a standardized inoculum of virulent wild-type (wt) ETEC strain H10407 (serotype O78:H11 expressing colonization factor antigen I and heat-labile and heat-stable enterotoxins), were prepared under current Good Manufacturing Practices (cGMP) and frozen. Following thawing, the contents of each vial can be used (diluted as necessary) to prepare consistent challenge inoculum, even at different study sites. A preliminary human experimental challenge study using this cGMP inoculum was conducted on a research isolation ward and the clinical and cell-mediated immune responses evaluated. Of the 6 healthy adult volunteers challenged 83% (5/6) developed diarrhea and 50% developed moderate-to-severe diarrhea (MSD). Moderate and severe diarrhea were defined as passage of ≥ 1 liter or ≥ 3 liters of diarrheal stool respectively. We compared the CD4+ T cell responses of volunteers who developed MSD against those who did not and identified significant differences in ETEC-specific cytokine production and gut homing potential. We furthermore demonstrated that increased expression of the gut-homing molecule integrin α4β7 by peripheral T follicular helper cells (pT_fh) correlated with decreased stool volume and increased ETEC-specific IgA B memory cell (B_M) development. Collectively, despite small numbers of volunteers, our results indicate a potential role for CD4+ T cells, in particular pT_fh, in modulating disease outcome following exposure to wt ETEC in a volunteer experimental challenge model.

Enterotoxigenic Escherichia coli (ETEC) is an important cause of diarrheal illness in infants and young children in the developing world, as well as in individuals traveling to endemic areas. Due to the lack of suitable animal models for human ETEC infection, we performed a human challenge study in which volunteers ingested wild-type ETEC in a controlled clinical setting. In addition to closely monitoring their clinical status, we studied their ETEC-specific T cell responses prior to and after challenge and studied the presence of associations between CD4+ T cell responses and clinical outcome. We observed differences in the immunological responses of individuals who developed moderate to severe diarrhea following challenge compared to those who did not. These results indicate that T cells may be an important component of the immune response against ETEC.

Live Attenuated Human Salmonella Vaccine Candidates: Tracking the Pathogen in Natural Infection and Stimulation of Host Immunity

Salmonellosis, caused by members of the genus Salmonella, is responsible for considerable global morbidity and mortality in both animals and humans. In this review, we will discuss the pathogenesis of Salmonella enterica serovar Typhi and Salmonella enterica serovar Typhimurium, focusing on human Salmonella infections. We will trace the path of Salmonella through the body, including host entry sites, tissues and organs affected, and mechanisms involved in both pathogenesis and stimulation of host immunity. Careful consideration of the natural progression of disease provides an important context in which attenuated live oral vaccines can be rationally designed and developed. With this in mind, we will describe a series of attenuated live oral vaccines that have been successfully tested in clinical trials and demonstrated to be both safe and highly immunogenic. The attenuation strategies summarized in this review offer important insights into further development of attenuated vaccines against other Salmonella for which live oral candidates are currently unavailable.

Cross-reactive multifunctional CD4+ T cell responses against Salmonella enterica serovars Typhi, Paratyphi A and Paratyphi B in humans following immunization with live oral typhoid vaccine Ty21a

The live oral typhoid vaccine Ty21a elicits predominantly CD8+, as well as CD4+ T cells mediated immune responses. Clinical field studies showed that Ty21a is moderately effective against S. Typhi and S. Paratyphi B, but not S. Paratyphi A infections. In this study we describe the in depth characterization of S. Typhi, S. Paratyphi A and S. Paratyphi B cross-reactive CD4+ T cell responses elicited following immunization with Ty21a. PBMC samples were collected from 16 healthy volunteers before and 42/84days after Ty21a immunization and stimulated ex-vivo with Salmonella-infected targets. Multiparametric flow cytometry was used to detect the vaccine elicited Salmonella-specific responses in T effector/memory (T_EM) and CD45RA+ T effector/memory (T_EMRA) CD4+ cell subsets, by measuring CD4+ multifunctional (MF) cells that concomitantly produced IFN-γ, TNF-α, IL-2, MIP-1β, IL-17A and/or expressed CD107a. Post-vaccination increases in S. Typhi-specific MF cells were observed in CD4+ T_EM and T_EMRA subsets which predominantly produced IFN-γ and/or TNF-α, while IL-2 was produced by a smaller cell subset. A small proportion of those MF cells also produced MIP-1β, IL-17A and expressed CD107a (a marker associated with cytotoxicity). Approximately one third of these specific MF cells have the potential to migrate to the gut mucosa, as evidenced by co-expression of the gut-homing molecule integrin α₄β₇. In contrast to our previous observations with CD8+ T cells, MF CD4+ T cell responses to the different Salmonella serovars evaluated were similar in magnitude and characteristics. We conclude that although induction of cross-reactive CD4+ MF effector T cells suggest a possible role in Salmonella-immunity, these responses are unlikely to provide an immunological basis for the observed efficacy of Ty21a against S. Typhi and S. Paratyphi B, but not to S. Paratyphi A.

Salmonella Typhi-specific multifunctional CD8+ T cells play a dominant role in protection from typhoid fever in humans

BACKGROUND

Typhoid fever, caused by the human-restricted organism Salmonella Typhi (S. Typhi), is a major public health problem worldwide. Development of novel vaccines remains imperative, but is hampered by an incomplete understanding of the immune responses that correlate with protection.

METHODS

Recently, a controlled human infection model was re-established in which volunteers received ~10(3) cfu wild-type S. Typhi (Quailes strain) orally. Twenty-one volunteers were evaluated for their cell-mediated immune (CMI) responses. Ex vivo PBMC isolated before and up to 1 year after challenge were exposed to three S. Typhi-infected targets, i.e., autologous B lymphoblastoid cell-lines (B-LCL), autologous blasts and HLA-E restricted AEH B-LCL cells. CMI responses were evaluated using 14-color multiparametric flow cytometry to detect simultaneously five intracellular cytokines/chemokines (i.e., IL-17A, IL-2, IFN-g, TNF-a and MIP-1b) and a marker of degranulation/cytotoxic activity (CD107a).

RESULTS

Herein we provide the first evidence that S. Typhi-specific CD8+ responses correlate with clinical outcome in humans challenged with wild-type S. Typhi. Higher multifunctional S. Typhi-specific CD8+ baseline responses were associated with protection against typhoid and delayed disease onset. Moreover, following challenge, development of typhoid fever was accompanied by decreases in circulating S. Typhi-specific CD8+ T effector/memory (TEM) with gut homing potential, suggesting migration to the site(s) of infection. In contrast, protection against disease was associated with low or no changes in circulating S. Typhi-specific TEM.

CONCLUSIONS

These studies provide novel insights into the protective immune responses against typhoid disease that will aid in selection and development of new vaccine candidates.

Igg Subclasses Targeting the Flagella of Salmonella enterica Serovar Typhimurium Can Mediate Phagocytosis and Bacterial Killing

Invasive non-typhoidal Salmonella are a common cause of invasive disease in immuno-compromised individuals and in children. Multi-drug resistance poses challenges to disease control, with a critical need for effective vaccines. Flagellin is an attractive vaccine candidate due to surface exposure and high epitope copy number, but its potential as a target for opsonophacytic antibodies is unclear. We examined the effect of targeting flagella with different classes of IgG on the interaction between Salmonella Typhimurium and a human phagocyte-like cell line, THP-1. We tagged the FliC flagellar protein with a foreign CD52 mimotope (TSSPSAD) and bacteria were opsonized with a panel of humanised CD52 antibodies with the same antigen-binding V-region, but different constant regions. We found that IgG binding to flagella increases bacterial phagocytosis and reduces viable intracellular bacterial numbers. Opsonisation with IgG3, followed by IgG1, IgG4, and IgG2, resulted in the highest level of bacterial uptake and in the highest reduction in the intracellular load of viable bacteria. Taken together, our data provide proof-of-principle evidence that targeting flagella with antibodies can increase the antibacterial function of host cells, with IgG3 being the most potent subclass. These data will assist the rational design of urgently needed, optimised vaccines against iNTS disease.

Immunization with Ty21a live oral typhoid vaccine elicits crossreactive multifunctional CD8+ T-cell responses against Salmonella enterica serovar Typhi, S. Paratyphi A, and S. Paratyphi B in humans

Previously we have extensively characterized Salmonella enterica serovar Typhi (S. Typhi)-specific cell-mediated immune (CMI) responses in volunteers orally immunized with the licensed Ty21a typhoid vaccine. In this study we measured Salmonella-specific multifunctional (MF) CD8+ T-cell responses to further investigate whether Ty21a elicits crossreactive CMI against S. Paratyphi A and S. Paratyphi B that also cause enteric fever. Ty21a-elicited crossreactive CMI responses against all three Salmonella serotypes were predominantly observed in CD8+ T effector/memory (T(EM)) and, to a lesser extent, in CD8+CD45RA+ T(EM) (T(EMRA)) subsets. These CD8+ T-cell responses were largely mediated by MF cells coproducing interferon-γ and macrophage inflammatory protein-1β and expressing CD107a with or without tumor necrosis factor-α. Significant proportions of Salmonella-specific MF cells expressed the gut-homing molecule integrin α4β7. In most subjects, similar MF responses were observed to S. Typhi and S. Paratyphi B, but not to S. Paratyphi A. These results suggest that Ty21a elicits MF CMI responses against Salmonella that could be critical in clearing the infection. Moreover, because S. Paratyphi A is a major public concern and Ty21a was shown in field studies not to afford cross-protection to S. Paratyphi A, these results will be important in developing a S. Typhi/S. Paratyphi A bivalent vaccine against enteric fevers.

Mucosal Immune Responses to Escherichia coli and Salmonella Infections

The best-characterized mucosa-associated lymphoid tissue (MALT), and also the most relevant for this review, is the gastrointestinal-associated lymphoid tissue (GALT). The review reviews our understanding of the importance of mucosal immune responses in resisting infections caused by E. coli and Salmonella spp. It focuses on the major human E. coli infections and discusses whether antigen-specific mucosal immune responses are important for resistance against primary infection or reinfection by pathogenic E. coli. It analyzes human data on mucosal immunity against E. coli, a growing body of data of mucosal responses in food production animals and other natural hosts of E. coli, and more recent experimental studies in mice carrying defined deletions in genes encoding specific immunological effectors, to show that there may be considerable conservation of the effective host mucosal immune response against this pathogen. The species Salmonella enterica contains a number of serovars that include pathogens of both humans and animals; these bacteria are frequently host specific and may cause different diseases in different hosts. Ingestion of various Salmonella serovars, such as Typhimurium, results in localized infections of the small intestine leading to gastroenteritis in humans, whereas ingestion of serovar Typhi results in systemic infection and enteric fever. Serovar Typhi infects only humans, and the review discusses the mucosal immune responses against serovar Typhi, focusing on the responses in humans and in the mouse typhoid fever model.

Recombinant Salmonella Expressing Burkholderia mallei LPS O Antigen Provides Protection in a Murine Model of Melioidosis and Glanders

Burkholderia pseudomallei and Burkholderia mallei are the etiologic agents of melioidosis and glanders, respectively. These bacteria are highly infectious via the respiratory route and can cause severe and often fatal diseases in humans and animals. Both species are considered potential agents of biological warfare; they are classified as category B priority pathogens. Currently there are no human or veterinary vaccines available against these pathogens. Consequently efforts are directed towards the development of an efficacious and safe vaccine. Lipopolysaccharide (LPS) is an immunodominant antigen and potent stimulator of host immune responses. B. mallei express LPS that is structurally similar to that expressed by B. pseudomallei, suggesting the possibility of constructing a single protective vaccine against melioidosis and glanders. Previous studies of others have shown that antibodies against B. mallei or B. pseudomallei LPS partially protect mice against subsequent lethal virulent Burkholderia challenge. In this study, we evaluated the protective efficacy of recombinant Salmonella enterica serovar Typhimurium SL3261 expressing B. mallei O antigen against lethal intranasal infection with Burkholderia thailandensis, a surrogate for biothreat Burkholderia spp. in a murine model that mimics melioidosis and glanders. All vaccine-immunized mice developed a specific antibody response to B. mallei and B. pseudomallei O antigen and to B. thailandensis and were significantly protected against challenge with a lethal dose of B. thailandensis. These results suggest that live-attenuated SL3261 expressing B. mallei O antigen is a promising platform for developing a safe and effective vaccine.

CD4+ T cell epitopes of FliC conserved between strains of Burkholderia: implications for vaccines against melioidosis and cepacia complex in cystic fibrosis

Burkholderia pseudomallei is the causative agent of melioidosis characterized by pneumonia and fatal septicemia and prevalent in Southeast Asia. Related Burkholderia species are strong risk factors of mortality in cystic fibrosis (CF). The B. pseudomallei flagellar protein FliC is strongly seroreactive and vaccination protects challenged mice. We assessed B. pseudomallei FliC peptide binding affinity to multiple HLA class II alleles and then assessed CD4 T cell immunity in HLA class II transgenic mice and in seropositive individuals in Thailand. T cell hybridomas were generated to investigate cross-reactivity between B. pseudomallei and the related Burkholderia species associated with Cepacia Complex CF. B. pseudomallei FliC contained several peptide sequences with ability to bind multiple HLA class II alleles. Several peptides were shown to encompass strong CD4 T cell epitopes in B. pseudomallei-exposed individuals and in HLA transgenic mice. In particular, the p38 epitope is robustly recognized by CD4 T cells of seropositive donors across diverse HLA haplotypes. T cell hybridomas against an immunogenic B. pseudomallei FliC epitope also cross-reacted with orthologous FliC sequences from Burkholderia multivorans and Burkholderia cenocepacia, important pathogens in CF. Epitopes within FliC were accessible for processing and presentation from live or heat-killed bacteria, demonstrating that flagellin enters the HLA class II Ag presentation pathway during infection of macrophages with B. cenocepacia. Collectively, the data support the possibility of incorporating FliC T cell epitopes into vaccination programs targeting both at-risk individuals in B. pseudomallei endemic regions as well as CF patients.

Complex adaptive immunity to enteric fevers in humans: lessons learned and the path forward

Salmonella enterica serovar Typhi (S. Typhi), the causative agent of typhoid fever, and S. Paratyphi A and B, causative agents of paratyphoid fever, are major public health threats throughout the world. Although two licensed typhoid vaccines are currently available, they are only moderately protective and immunogenic necessitating the development of novel vaccines. A major obstacle in the development of improved typhoid, as well as paratyphoid vaccines is the lack of known immunological correlates of protection in humans. Considerable progress has been made in recent years in understanding the complex adaptive host responses against S. Typhi. Although the induction of S. Typhi-specific antibodies (including their functional properties) and memory B cells, as well as their cross-reactivity with S. Paratyphi A and S. Paratyphi B has been shown, the role of humoral immunity in protection remains undefined. Cell mediated immunity (CMI) is likely to play a dominant role in protection against enteric fever pathogens. Detailed measurements of CMI performed in volunteers immunized with attenuated strains of S. Typhi have shown, among others, the induction of lymphoproliferation, multifunctional type 1 cytokine production, and CD8(+) cytotoxic T-cell responses. In addition to systemic responses, the local microenvironment of the gut is likely to be of paramount importance in protection from these infections. In this review, we will critically assess current knowledge regarding the role of CMI and humoral immunity following natural S. Typhi and S. Paratyphi infections, experimental challenge, and immunization in humans. We will also address recent advances regarding cross-talk between the host's gut microbiota and immunization with attenuated S. Typhi, mechanisms of systemic immune responses, and the homing potential of S. Typhi-specific B- and T-cells to the gut and other tissues.

Immunological Evaluation of Formulated Drugs against Typhoid

OBJECTIVES: Typhoid fever an important causes of illness and death, particularly among children and adolescents in south-central and Southeast Asia, where enteric fever is associated with poor sanitation and unsafe food and water. Cell-mediated immunity (CMI) plays an important role for the survival of the host in experimental salmonellosis. Nitric oxide (NO) is the one of the product of macrophages activated by cytokines, microbial compounds or both, is derived from the amino acid L-arginine by the enzymatic activity of inducible nitric oxide synthase (iNOS or NOS2) which acts as antimicrobial molecule.AIM: The aim was to examine the induction of DTH reaction in the animals treated with L-Arginine, ciprofloxacin and their combination followed by immunization with S. typhimurium cell lysate  as assessed by the footpad swelling test.RESULTS: The results of the present study showed that the induction of DTH reaction in the animals treated with L-Arginine, ciprofloxacin and their combination followed by immunization with S. typhimurium cell lysate using an antigen revealed that the treatment with combination increased foot pad swelling significantly as compared to saline treated control animals at 48 hour which was followed by a decrease of the swelling at 72 hour.CONCLUSIONS: Animal treated with L-arginine, ciprofloxacin and their combination showed increased cell mediated immune responses as evident by DTH response whereas groups (B+S) shows decreases CMI responses.

Live oral Salmonella enterica serovar Typhi vaccines Ty21a and CVD 909 induce opsonophagocytic functional antibodies in humans that cross-react with S. Paratyphi A and S. Paratyphi B

Live oral Salmonella enterica serovar Typhi vaccine Ty21a induces specific antibodies that cross-react against Salmonella enterica serovar Paratyphi A and Salmonella enterica serovar Paratyphi B, although their functional role in clearance remains unknown. We utilized an in vitro assay with THP-1 macrophages to compare the phagocytosis and survival of Salmonella opsonized with heat-inactivated human sera obtained before and after vaccination with Ty21a or a live oral S. Typhi vaccine, CVD 909. Opsonization with postvaccination sera predominantly increased the phagocytosis of S. Typhi relative to the corresponding prevaccination sera, and increases were also observed with S. Paratyphi A and S. Paratyphi B, albeit of lower magnitudes. Relative to prevaccination sera, opsonization with the postvaccination sera reduced the survival inside macrophages of S. Typhi but not of S. Paratyphi A or S. Paratyphi B. Higher anti-S. Typhi O antigen (lipopolysaccharide [LPS]) IgG, but not IgA, antibody titers correlated significantly with postvaccination increases in opsonophagocytosis. No differences were observed between immunization with four doses of Ty21a or one dose of CVD 909. Ty21a and CVD 909 induced cross-reactive functional antibodies, predominantly against S. Typhi. IgG anti-LPS antibodies may be important in phagocytic clearance of these organisms. Therefore, measurement of functional antibodies might be important in assessing the immunogenicity of a new generation of typhoid and paratyphoid A vaccines. (The CVD 909 study has been registered at ClinicalTrials.gov under registration no. NCT00326443.).

Unexpected heterogeneity of multifunctional T cells in response to superantigen stimulation in humans

Toxic shock syndrome (TSS) is a potentially life threatening condition characterized by fever, rash, shock, and multi-organ failure. Staphylococcal enterotoxin B (SEB) is a well characterized superantigen that has been shown to play an important role in TSS. Although the precise mechanisms by which SEB and other superantigens cause TSS are unknown, induction of a pro-inflammatory cytokine cascade appears central to this phenomenon. We show that CD4+ and CD8+ Teffector/memory (T(EM)) and other subsets produce IL-17A following SEB stimulation. We also show that IL-17A is co-produced with other pro-inflammatory cytokines (i.e., IL-2, IFN-γ and TNF-α). These responses are significantly different than those elicited by mitogenic stimulation. Multifunctional IL-17A producing cells possess markers typical of the T(H)17/T(C)17 and T(H)1 subsets, including CCR6, IL-22, and transcription factors retinoic acid receptor-related orphan nuclear receptor (ROR)-γt and T-bet. These results suggest a possible role for IL-17A-producing multifunctional T cells in the pathogenesis of TSS.

Heterogeneity of multifunctional IL-17A producing S. Typhi-specific CD8+ T cells in volunteers following Ty21a typhoid immunization

Salmonella enterica serovar Typhi (S. Typhi), the causative agent of typhoid fever, continues to cause significant morbidity and mortality world-wide. CD8+ T cells are an important component of the cell mediated immune (CMI) response against S. Typhi. Recently, interleukin (IL)-17A has been shown to contribute to mucosal immunity and protection against intracellular pathogens. To investigate multifunctional IL-17A responses against S. Typhi antigens in T memory subsets, we developed multiparametric flow cytometry methods to detect up to 6 cytokines/chemokines (IL-10, IL-17A, IL-2, interferon-γ (IFN-γ), tumor necrosis factor-α (TNF-α) and macrophage inflammatory protein-1β (MIP-1β)) simultaneously. Five volunteers were immunized with a 4 dose regimen of live-attenuated S. Typhi vaccine (Ty21a), peripheral blood mononuclear cells (PBMC) were isolated before and at 11 time points after immunization, and CMI responses were evaluated. Of the 5 immunized volunteers studied, 3 produced detectable CD8+ T cell responses following stimulation with S. Typhi-infected autologous B lymphoblastoid cell lines (B-LCL). Additionally, 2 volunteers had detectable levels of intracellular cytokines in response to stimulation with S. Typhi-infected HLA-E restricted cells. Although the kinetics of the responses differed among volunteers, all of the responses were bi- or tri-phasic and included multifunctional CD8+ T cells. Virtually all of the IL-17A detected was derived from multifunctional CD8+ T cells. The presence of these multifunctional IL-17A+ CD8+ T cells was confirmed using an unsupervised analysis program, flow cytometry clustering without K (FLOCK). This is the first report of IL-17A production in response to S. Typhi in humans, indicating the presence of a Tc17 response which may be important in protection. The presence of IL-17A in multifunctional cells co-producing Tc1 cytokines (IL-2, IFN-γ and TNF-α) may also indicate that the distinction between Tc17 and Tc1 responses in humans is not as clearly delineated as suggested by in vitro experiments and animal models.

Live oral typhoid vaccine Ty21a induces cross-reactive humoral immune responses against Salmonella enterica serovar Paratyphi A and S. Paratyphi B in humans

Enteric fever caused by Salmonella enterica serovar Paratyphi A infection has emerged as an important public health problem. Recognizing that in randomized controlled field trials oral immunization with attenuated S. enterica serovar Typhi live vaccine Ty21a conferred significant cross-protection against S. Paratyphi B but not S. Paratyphi A disease, we undertook a clinical study to ascertain whether humoral immune responses could explain the field trial results. Ty21a immunization of adult residents of Maryland elicited predominantly IgA antibody-secreting cells (ASC) that recognize S. Typhi lipopolysaccharide (LPS). Cross-reactivity to S. Paratyphi A LPS was significantly lower than that to S. Paratyphi B LPS. ASC producing IgG and IgA that bind LPS from each of these Salmonella serovars expressed CD27 and integrin α4β7 (gut homing), with a significant proportion coexpressing CD62L (secondary lymphoid tissue homing). No significant differences were observed in serum antibody against LPS of the different serovars. Levels of IgA B memory (B(M)) cells to S. Typhi LPS were significantly higher than those against S. Paratyphi A or B LPS, with no differences observed between S. Paratyphi A and B. The response of IgA B(M) to outer membrane proteins (OMP) from S. Typhi was significantly stronger than that to OMP of S. Paratyphi A but similar to that to OMP of S. Paratyphi B. The percentages of IgG or IgA B(M) responders to LPS or OMP from these Salmonella strains were similar. Whereas cross-reactive humoral immune responses to S. Paratyphi A or B antigens are demonstrable following Ty21a immunization, they cannot explain the efficacy data gleaned from controlled field trials.

Immunology of gut mucosal vaccines

Understanding the mechanisms underlying the induction of immunity in the gastrointestinal mucosa following oral immunization and the cross-talk between mucosal and systemic immunity should expedite the development of vaccines to diminish the global burden caused by enteric pathogens. Identifying an immunological correlate of protection in the course of field trials of efficacy, animal models (when available), or human challenge studies is also invaluable. In industrialized country populations, live attenuated vaccines (e.g. polio, typhoid, and rotavirus) mimic natural infection and generate robust protective immune responses. In contrast, a major challenge is to understand and overcome the barriers responsible for the diminished immunogenicity and efficacy of the same enteric vaccines in underprivileged populations in developing countries. Success in developing vaccines against some enteric pathogens has heretofore been elusive (e.g. Shigella). Different types of oral vaccines can selectively or inclusively elicit mucosal secretory immunoglobulin A and serum immunoglobulin G antibodies and a variety of cell-mediated immune responses. Areas of research that require acceleration include interaction between the gut innate immune system and the stimulation of adaptive immunity, development of safe yet effective mucosal adjuvants, better understanding of homing to the mucosa of immunologically relevant cells, and elicitation of mucosal immunologic memory. This review dissects the immune responses elicited in humans by enteric vaccines.

Immunity to salmonellosis

Salmonella enterica is a genetically broad species harboring isolates that display considerable antigenic heterogeneity and significant differences in virulence potential. Salmonella generally exhibit an invasive potential and they can survive for extended periods within cells of the immune system. They cause acute or chronic infections that can be local (e.g. gastroenteritis) or systemic (e.g. typhoid). In vivo Salmonella infections are complex with multiple arms of the immune system being engaged. Both humoral and cellular responses can be detected and characterized, but full protective immunity is not always induced, even following natural infection. The murine model has proven to be a fertile ground for exploring immune mechanisms and observations in the mouse have often, although not always, correlated with those in other infectable species, including humans. Host genetic studies have identified a number of mammalian genes that are central to controlling infection, operating both in innate and acquired immune pathways. Vaccines, both oral and parenteral, are available or under development, and these have been used with some success to explore immunity in both model systems and clinically in humans.

Salmonella synthesizing 1-dephosphorylated [corrected] lipopolysaccharide exhibits low endotoxic activity while retaining its immunogenicity

The development of safe live, attenuated Salmonella vaccines may be facilitated by detoxification of its LPS. Recent characterization of the lipid A 1-phosphatase, LpxE, from Francisella tularensis allowed us to construct recombinant, plasmid-free strains of Salmonella that produce predominantly 1-dephosphorylated lipid A, similar to the adjuvant approved for human use. Complete lipid A 1-dephosphorylation was also confirmed under low pH, low Mg(2+) culture conditions, which induce lipid A modifications. LpxE expression in Salmonella reduced its virulence in mice by five orders of magnitude. Moreover, mice inoculated with these detoxified strains were protected against wild-type challenge. Candidate Salmonella vaccine strains synthesizing pneumococcal surface protein A (PspA) were also confirmed to possess nearly complete lipid A 1-dephosphorylation. After inoculation by the LpxE/PspA strains, mice produced robust levels of anti-PspA Abs and showed significantly improved survival against challenge with wild-type Streptococcus pneumoniae WU2 compared with vector-only-immunized mice, validating Salmonella synthesizing 1-dephosphorylated lipid A as an Ag-delivery system.

Antigen-specific IgA B memory cell responses to Shigella antigens elicited in volunteers immunized with live attenuated Shigella flexneri 2a oral vaccine candidates

We studied the induction of antigen-specific IgA memory B cells (B(M)) in volunteers who received live attenuated Shigella flexneri 2a vaccines. Subjects ingested a single oral dose of 10(7), 10(8) or 10(9) CFU of S. flexneri 2a with deletions in guaBA (CVD 1204) or in guaBA, set and sen (CVD 1208). Antigen-specific serum and stool antibody responses to LPS and Ipa B were measured on days 0, 7, 14, 28 and 42. IgA B(M) cells specific to LPS, Ipa B and total IgA were assessed on days 0 and 28. We show the induction of significant LPS-specific IgA B(M) cells in anti-LPS IgA seroresponders. Positive correlations were found between anti-LPS IgA B(M) cells and anti-LPS IgA in serum and stool; IgA B(M) cell responses to IpaB were also observed. These B(M) cell responses are likely play an important role in modulating the magnitude and longevity of the humoral response.

Antibody and Th1-type cell-mediated immune responses in elderly and young adults immunized with the standard or a high dose influenza vaccine

A comparative analysis of antibody and cell-mediated immune responses was performed in ambulatory medically stable elderly and young adults who received the standard-dose of trivalent inactivated influenza vaccine, containing 15 μg of hemagglutinin (HA) per virus strain, or a high-dose vaccine containing 60 μg HA per virus strain. Among the elderly, the high dose vaccine induced greater HAI (hemagglutination inhibition) and virus neutralization antibody titers than the standard dose vaccine. These responses, however, did not achieve the magnitude of those induced by the standard dose vaccine in young adults. Vaccine-specific circulating T cells producing IFN-γ were detected in the elderly and young adults following immunization. However, there were no significant differences in the IFN-γ responses among groups. On the other hand, the standard dose vaccine in the elderly resulted in the highest proportion of complete non-responders who failed to elicit either an HAI or an IFN-γ response. This study provides further evidence that a higher dose vaccine for the elderly may result in enhanced immune responses which are predicted to improve protection although still of lower magnitude than those induced in younger healthier individuals.

Oral priming with Salmonella Typhi vaccine strain CVD 909 followed by parenteral boost with the S. Typhi Vi capsular polysaccharide vaccine induces CD27+IgD-S. Typhi-specific IgA and IgG B memory cells in humans

Attenuated live oral typhoid vaccine candidate CVD 909 constitutively expresses Salmonella Typhi capsular polysaccharide antigen (Vi). A randomized, double-blind, heterologous prime-boost clinical study was conducted to determine whether immunity to licensed parenteral Vi vaccine could be enhanced by priming with CVD 909. Priming with CVD 909 elicited higher and persistent, albeit not significant, anti-Vi IgG and IgA following immunization with Vi, than placebo-primed recipients. Vi-specific IgA B memory (B(M)) cells were significantly increased in CVD 909-primed subjects. S. Typhi-specific LPS and flagella IgA B(M) cells were observed in subjects immunized with CVD 909 or with the licensed Vi-negative oral typhoid vaccine Ty21a. CVD 909-induced B(M) cells exhibited a classical B(M) phenotype (i.e., CD3(-)CD19(+)IgD(-)CD27(+)). This is the first demonstration of classical B(M) cells specific for bacterial polysaccharide or protein antigens following typhoid immunization. The persistent IgA B(M) responses demonstrate the capacity of oral typhoid vaccines to prime mucosally relevant immune memory.

Ex Vivo kinetics of early and long-term multifunctional human leukocyte antigen E-specific CD8+ cells in volunteers immunized with the Ty21a typhoid vaccine

T cells are likely to play an important role in the host defense against Salmonella enterica serovar Typhi, the causative agent of typhoid fever. We have shown that HLA-E can function as a restriction element for S. Typhi-specific CD8(+) T cells. Because of the potential importance of HLA-E-restricted CD8(+) responses in resistance to Salmonella infection, we characterized these responses and investigated their kinetics of appearance and persistence in volunteers immunized orally with the licensed attenuated Ty21a strain typhoid vaccine. Cells were obtained from volunteers before and at days 2, 4, 7, 10, 14, 28, 42, 56, 120, 180, 360, and 720 after immunization. An ex vivo multicolor staining panel including antibodies to CD107a and -b, interleukin-2, gamma interferon (IFN-gamma), and tumor necrosis factor alpha (TNF-alpha) was used to functionally assess memory T-cell subsets by flow cytometry. Increases in cytokine-secreting CD8(+) cells were observed in the T effector/memory (T(EM)) and CD45RA(+) T(EM) (T(EMRA)) subsets as early as 4 days after immunization and persisted, particularly in the T(EMRA) subset, up to 2 years after immunization. The majority of HLA-E-restricted CD8(+) cells 28 to 56 days after immunization coexpressed CD107, IFN-gamma, and TNF-alpha, showing characteristic features of multifunctional T cells. In summary, the multifunctionality and longevity of the HLA-E-restricted CD8 responses observed in this study highlight their significance in adaptive immunity to S. Typhi. Finally, this is the first demonstration, in either animals or humans, of the presence of long-term multifunctional HLA-E-restricted CD8(+) cells after immunization.

Priming of Salmonella enterica serovar typhi-specific CD8(+) T cells by suicide dendritic cell cross-presentation in humans

BACKGROUND

The emergence of antibiotic-resistant strains of Salmonella enterica serovar Typhi (S. Typhi), the etiologic agent of typhoid fever, has aggravated an already important public health problem and added new urgency to the development of more effective typhoid vaccines. To this end it is critical to better understand the induction of immunity to S. Typhi. CD8(+) T cells are likely to play an important role in host defense against S. Typhi by several effector mechanisms, including killing of infected cells and IFN-gamma secretion. However, how S. Typhi regulates the development of specific CD8(+) responses in humans remains unclear. Recent studies in mice have shown that dendritic cells (DC) can either directly (upon uptake and processing of Salmonella) or indirectly (by bystander mechanisms) elicit Salmonella-specific CD8(+) T cells.

METHODOLOGY/PRINCIPAL FINDINGS

We report here that upon infection with live S. Typhi, human DC produced high levels of pro-inflammatory cytokines IL-6, IL-8 and TNF-alpha, but low levels of IL-12 p70 and IFN-gamma. In contrast, DC co-cultured with S. Typhi-infected cells, through suicide cross-presentation, uptake S. Typhi-infected human cells and release high levels of IFN-gamma and IL-12p70, leading to the subsequent presentation of bacterial antigens and triggering the induction of memory T cells, mostly CD3(+)CD8(+)CD45RA(-)CD62L(-) effector/memory T cells.

CONCLUSIONS/SIGNIFICANCE

This study is the first to demonstrate the effect of S. Typhi on human DC maturation and on their ability to prime CD8(+) cells and highlights the significance of these phenomena in eliciting adaptive immunity to S. Typhi.

Salmonella enterica serovar Typhi live vector vaccines finally come of age

Attenuated Salmonella Typhi vaccine strains hold great promise as live vectors for presentation of foreign antigens from unrelated bacterial, viral and parasitic pathogens to the immune system. Although this approach has proved quite successful in experimental animal models for eliciting antigen-specific mucosal, humoral and cellular responses, results have been disappointing for clinical trials carried out thus far. We hypothesize that the paucity of human responses to foreign antigens delivered by live vectors suggests that the strains and genetic approaches used to date have resulted in overattenuated vaccine strains with severely reduced immunogenicity. However, remarkable advances have now been made in the genetics of foreign antigen expression, understanding mechanisms of live vector immunity and refining immunization strategies. The time has now come for development of multivalent live vectors in which stable antigen expression and export is balanced with metabolic fitness to create highly immunogenic vaccines.

SopB of Salmonella enterica serovar Typhimurium is a potential DNA vaccine candidate in conjugation with live attenuated bacteria

The immune response against Salmonella is multi-faceted involving both the innate and the adaptive immune system. The characterization of specific Salmonella antigens inducing immune response could critically contribute to the development of epitope based vaccines for Salmonella. We have tried to identify a protective T cell epitope(s) of Salmonella, as cell mediated immunity conferred by CD8+ T cells is the most crucial subset conferring protective immunity against Salmonella. It being a proven fact that secreted proteins are better in inducing cell mediated immunity than cell surface and cytosolic antigens, we have analyzed all the genbank annotated Salmonella pathogenicity island 1 and 2 secreted proteins of Salmonella enterica serovar Typhimurium (S. typhimurium) and S. enterica serovar Typhi (S. typhi). They were subjected to BIMAS and SYFPEITHI analysis to map MHC-I and MHC-II binding epitopes. The huge profile of possible T cell epitopes obtained from the two classes of secreted proteins were tabulated and using a scoring system that considers the binding affinity and promiscuity of binding to more than one allele, SopB and SifB were chosen for experimental confirmation in murine immunization model. The entire SopB and SifB genes were cloned into DNA vaccine vectors and were administered along with live attenuated Salmonella and it was found that SopB vaccination reduced the bacterial burden of organs by about 5-fold on day 4 and day 8 after challenge with virulent Salmonella and proved to be a more efficient vaccination strategy than live attenuated bacteria alone.

Antigen-specific B memory cell responses to lipopolysaccharide (LPS) and invasion plasmid antigen (Ipa) B elicited in volunteers vaccinated with live-attenuated Shigella flexneri 2a vaccine candidates

We evaluated B memory responses in healthy adult volunteers who received one oral dose of live-attenuated Shigella flexneri 2a vaccine. LPS-specific B(M) cells increased from a median of 0 at baseline to 20 spot forming cells (SFC)/10(6) expanded cells following vaccination (p=0.008). A strong correlation was found between post-vaccination anti-LPS B(M) cell counts and peak serum anti-LPS IgG titers (rs=0.95, p=0.0003). Increases in B(M) specific for IpaB approaching significance were also observed. In sum, oral vaccination with live-attenuated S. flexneri 2a elicits B(M) cells to LPS and IpaB, suggesting that B(M) responses to Shigella antigens should be further studied as a suitable surrogate of protection in shigellosis.

Generation of specific effector and memory T cells with gut- and secondary lymphoid tissue- homing potential by oral attenuated CVD 909 typhoid vaccine in humans

Induction of effective memory T cells is likely to be critical to the level and duration of protection elicited by novel live oral typhoid vaccines. Using cells from volunteers who ingested Salmonella Typhi vaccine strain CVD 909, we characterized the induction of interferon (IFN)-gamma-secreting central (T(CM), CD45RO(+)CD62L(+)) and effector (T(EM), CD45RO(+)CD62L(-)) memory T populations, and their gut-homing potential based on integrin alpha4/beta7 expression. Both CD4(+) T(EM) and T(CM) populations secreted IFN-gamma. However, although CD4(+) T(EM) expressed, or not, integrin alpha(4)/beta(7), CD4(+) T(CM) cells were predominantly integrin alpha(4)/beta(7)(+). In contrast, IFN-gamma-secreting CD8(+) cells were predominantly classical T(EM) and CD45RA(+) T(EM) (T(EMRA), CD45RO(-)CD62L(-)) subsets. However, although CD8(+) T(EM) expressed, or not, integrin alpha(4)/beta(7), CD8(+) T(EMRA) were predominantly integrin alpha(4)/beta(7)(+). This is the first demonstration that oral immunization of humans with S. Typhi elicits diverse IFN-gamma-secreting CD4(+) and CD8(+) T(CM) and T(EM) subsets able to migrate to the gut and other lymphoid tissues.

Differential activation of human TLR4 by Escherichia coli and Shigella flexneri 2a lipopolysaccharide: combined effects of lipid A acylation state and TLR4 polymorphisms on signaling

The lipid A of LPS activates TLR4 through an interaction with myeloid differentiation protein-2 (MD-2) and the degree of lipid A acylation affects TLR4 responsiveness. Two TLR4 single nucleotide polymorphisms (Asp299Gly and Thr399Ile) have been associated with LPS hyporesponsiveness. We hypothesized that the combination of hypoacylation and these single nucleotide polymorphisms would exhibit a compounded effect on TLR4 signaling. HEK293T transfectants expressing wild-type or polymorphic TLR4 were stimulated with Escherichia coli (predominantly hexaacylated lipid A) or Shigella flexneri 2a (a mixture of hexaacylated, pentaacylated, and predominantly tetraacylated lipid A) LPS, or hexaacylated vs pentaacylated synthetic lipid As. NF-kappaB-reporter activity was significantly lower in response to S. flexneri 2a than E. coli LPS and further decreased in polymorphic transfectants. Neither hexaacylated nor pentaacylated synthetic lipid A induced NF-kappaB activity in wild-type transfectants under the identical transfection conditions used for LPS; however, increasing human MD-2 expression rescued responsiveness to hexaacylated lipid A only, while murine MD-2 was required to elicit a response to pentaacylated lipid A. Adherent PBMC of healthy volunteers were also compared for LPS-induced TNF-alpha, IL-6, IL-1beta, and IL-10 production. Cytokine levels were significantly lower (approximately 20-90%) in response to S. flexneri than to E. coli LPS/lipid A and PBMC from polymorphic individuals secreted decreased cytokine levels in response to both LPS types and failed to respond to pentaacylated lipid A. Thus, the combination of acylation state and host genetics may significantly impact vaccine immunogenicity and/or efficacy, whether LPS is an integral component of a whole organism vaccine or included as an adjuvant.

Cell-mediated immunity and antibody responses elicited by attenuated Salmonella enterica Serovar Typhi strains used as live oral vaccines in humans

The development of improved typhoid vaccines is a high global public health priority. However, their development has been hampered by a lack of information regarding the specific determinants of protective immunity to Salmonella enterica serovar Typhi (S. Typhi) infection in humans. Although antibodies to S. Typhi O, H, and Vi appear to be involved in protection against S. Typhi infection, it is unknown whether such antibodies mediate protection, act in conjunction with other adaptive responses, or serve as a surrogate for the presence of other, more dominant protective immune responses (e.g., cell-mediated immunity [CMI]). CMI responses elicited by immunization of subjects with attenuated S. Typhi oral vaccines include lymphoproliferation; production of type 1 cytokines (e.g., interferon- gamma and tumor necrosis factor- alpha ); and classical major histocompatibility complex (MHC) class Ia-restricted and novel, nonclassical MHC class Ib (human leukocyte antigen [HLA]-E)-restricted CD8(+) cytotoxic T cell responses. In sum, human immunity to S. Typhi elicited by immunization is unexpectedly broad and complex. However, the immunologic correlates of protection remain largely undefined.

Is there evidence that the gut contributes to mucosal immunity in humans?

BACKGROUND

Our understanding of the common mucosal immune system derives from animal studies. Antigen-sensitized lymphocytes in the gut-associated lymphoid tissue (GALT) migrate via the blood to mucosal tissues to generate the mucosal-associated lymphoid tissue (MALT). In these sites, B cells differentiate into plasma cells and produce antigen-specific secretory IgA, the principal specific immune antiviral and antibacterial defense of moist mucosal surfaces. Responses to oral intake seem necessary to actively maintain this system in health. Experimentally, lack of enteral stimulation with parenteral feeding alters GALT and MALT size and function. These alterations disturb intestinal and extraintestinal mucosal immunity.

METHODS

This review is an overview of current and classical studies demonstrating the human mucosal immune system and interactions with nutrition.

RESULTS

Human evidence of the mucosal immune system exists, although most data are indirect. Gut stimulation after oral intake induces a generalized immune response in the human MALT through a mucosal-immune network. Examples include neonatal development of GALT influenced by enteral feeding, the presence of antigen-specific IgA and antigen-specific IgA-secreting plasma cells in distant mucosal effector sites such as the breast after gut luminal antigen exposure, and isolation of IgA-producing cells from circulating blood.

CONCLUSIONS

It is unlikely that clinical studies will ever completely define the effect of route of feeding in all patient populations. This may be possible, however, if investigators understand, define and characterize nutrition-dependent immunologic mechanisms, allowing clinicians to examine clinical responses to nutrition in specific patient populations. This might allow generation of new approaches to protect mucosal immunity.