Vitamin A deficiency impairs vaccine-elicited gastrointestinal immunity

Maternal immunization and vitamin A sufficiency impact sow primary adaptive immunity and passive protection to nursing piglets against porcine epidemic diarrhea virus infection

Porcine epidemic diarrhea virus (PEDV) causes a highly contagious enteric disease with major economic losses to swine production worldwide. Due to the immaturity of the neonatal piglet immune system and given the high virulence of PEDV, improving passive lactogenic immunity is the best approach to protect suckling piglets against the lethal infection. We tested whether oral vitamin A (VA) supplementation and PEDV exposure of gestating and lactating VA-deficient (VAD) sows would enhance their primary immune responses and boost passive lactogenic protection against the PEDV challenge of their piglets. We demonstrated that PEDV inoculation of pregnant VAD sows in the third trimester provided higher levels of lactogenic protection of piglets as demonstrated by >87% survival rates of their litters compared with <10% in mock litters and that VA supplementation to VAD sows further improved the piglets' survival rates to >98%. We observed significantly elevated PEDV IgA and IgG antibody (Ab) titers and Ab-secreting cells (ASCs) in VA-sufficient (VAS)+PEDV and VAD+VA+PEDV sows, with the latter maintaining higher Ab titers in blood prior to parturition and in blood and milk throughout lactation. The litters of VAD+VA+PEDV sows also had the highest serum PEDV-neutralizing Ab titers at piglet post-challenge days (PCD) 0 and 7, coinciding with higher PEDV IgA ASCs and Ab titers in the blood and milk of their sows, suggesting an immunomodulatory role of VA in sows. Thus, sows that delivered sufficient lactogenic immunity to their piglets provided the highest passive protection against the PEDV challenge. Maternal immunization during pregnancy (± VA) and VA sufficiency enhanced the sow primary immune responses, expression of gut-mammary gland trafficking molecules, and passive protection of their offspring. Our findings are relevant to understanding the role of VA in the Ab responses to oral attenuated vaccines that are critical for successful maternal vaccination programs against enteric infections in infants and young animals.

Polyphenols: immunonutrients tipping the balance of immunometabolism in chronic diseases

Mounting evidence progressively appreciates the vital interplay between immunity and metabolism in a wide array of immunometabolic chronic disorders, both autoimmune and non-autoimmune mediated. The immune system regulates the functioning of cellular metabolism within organs like the brain, pancreas and/or adipose tissue by sensing and adapting to fluctuations in the microenvironment's nutrients, thereby reshaping metabolic pathways that greatly impact a pro- or anti-inflammatory immunophenotype. While it is agreed that the immune system relies on an adequate nutritional status to function properly, we are only just starting to understand how the supply of single or combined nutrients, all of them termed immunonutrients, can steer immune cells towards a less inflamed, tolerogenic immunophenotype. Polyphenols, a class of secondary metabolites abundant in Mediterranean foods, are pharmacologically active natural products with outstanding immunomodulatory actions. Upon binding to a range of receptors highly expressed in immune cells (e.g. AhR, RAR, RLR), they act in immunometabolic pathways through a mitochondria-centered multi-modal approach. First, polyphenols activate nutrient sensing via stress-response pathways, essential for immune responses. Second, they regulate mammalian target of rapamycin (mTOR)/AMP-activated protein kinase (AMPK) balance in immune cells and are well-tolerated caloric restriction mimetics. Third, polyphenols interfere with the assembly of NLR family pyrin domain containing 3 (NLRP3) in endoplasmic reticulum-mitochondria contact sites, inhibiting its activation while improving mitochondrial biogenesis and autophagosome-lysosome fusion. Finally, polyphenols impact chromatin remodeling and coordinates both epigenetic and metabolic reprogramming. This work moves beyond the well-documented antioxidant properties of polyphenols, offering new insights into the multifaceted nature of these compounds. It proposes a mechanistical appraisal on the regulatory pathways through which polyphenols modulate the immune response, thereby alleviating chronic low-grade inflammation. Furthermore, it draws parallels between pharmacological interventions and polyphenol-based immunonutrition in their modes of immunomodulation across a wide spectrum of socioeconomically impactful immunometabolic diseases such as Multiple Sclerosis, Diabetes (type 1 and 2) or even Alzheimer's disease. Lastly, it discusses the existing challenges that thwart the translation of polyphenols-based immunonutritional interventions into long-term clinical studies. Overcoming these limitations will undoubtedly pave the way for improving precision nutrition protocols and provide personalized guidance on tailored polyphenol-based immunonutrition plans.

Prediction Model with Validation for Polioseronegativity in Malnourished Children from Poliomyelitis Transmission High-Risk Area of the Democratic Republic of the Congo (DRC)

Background

Malnutrition is identified as a risk factor for insufficient polio seroconversion in the context of a vaccine-derived poliovirus (VDPV) outbreak-prone region. In the Democratic Republic of Congo (DRC), underweight decreased from 31% (in 2001) to 26% (in 2018). Since 2004, VDPV serotype 2 outbreaks (cVDPV2) have been documented and were geographically limited around the Haut-Lomami and Tanganyika Provinces.

Methods

To develop and validate a predictive model for poliomyelitis vaccine response in malnourished infants, a cross-sectional household study was carried out in the Haut-Lomami and Tanganyika provinces. Healthy children aged 6 to 59 months (n=968) were enrolled from eight health zones (HZ) out of 27, in March 2018. We performed a bivariate and multivariate logistics analysis. Final models were selected using a stepwise Wald method, and variables were selected based on the criterion p < 0.05. The association between nutritional variables, explaining polio seronegativity for the three serotypes, was assessed using the receiver operating characteristic curve (ROC curve).

Results

Factors significantly associated with seronegativity to the three polio serotypes were underweight, non-administration of vitamin A, and the age group of 12 to 59 months. The sensitivity was 10.5%, and its specificity was 96.4% while the positive predictive values (PPV) and negative (PNV) were 62.7% and 65.3%, respectively. We found a convergence of the curves of the initial sample and two split samples. Based on the comparison of the overlapping confidence intervals of the ROC curve, we concluded that our prediction model is valid.

Conclusion

This study proposed the first tool which variables are easy to collect by any health worker in charge of vaccination or in charge of nutrition. It will bring on top, the collaboration between the Immunization and the Nutritional programs in DRC integration policy, and its replicability in other low- and middle-income countries with endemic poliovirus.

Immune Impairment Associated with Vitamin A Deficiency: Insights from Clinical Studies and Animal Model Research

Vitamin A (VA) is critical for many biological processes, including embryonic development, hormone production and function, the maintenance and modulation of immunity, and the homeostasis of epithelium and mucosa. Specifically, VA affects cell integrity, cytokine production, innate immune cell activation, antigen presentation, and lymphocyte trafficking to mucosal surfaces. VA also has been reported to influence the gut microbiota composition and diversity. Consequently, VA deficiency (VAD) results in the imbalanced production of inflammatory and immunomodulatory cytokines, intestinal inflammation, weakened mucosal barrier functions, reduced reactive oxygen species (ROS) and disruption of the gut microbiome. Although VAD is primarily known to cause xerophthalmia, its role in the impairment of anti-infectious defense mechanisms is less defined. Infectious diseases lead to temporary anorexia and lower dietary intake; furthermore, they adversely affect VA status by interfering with VA absorption, utilization and excretion. Thus, there is a tri-directional relationship between VAD, immune response and infections, as VAD affects immune response and predisposes the host to infection, and infection decreases the intestinal absorption of the VA, thereby contributing to secondary VAD development. This has been demonstrated using nutritional and clinical studies, radiotracer studies and knockout animal models. An in-depth understanding of the relationship between VAD, immune response, gut microbiota and infections is critical for optimizing vaccine efficacy and the development of effective immunization programs for countries with high prevalence of VAD. Therefore, in this review, we have comprehensively summarized the existing knowledge regarding VAD impacts on immune responses to infections and post vaccination. We have detailed pathological conditions associated with clinical and subclinical VAD, gut microbiome adaptation to VAD and VAD effects on the immune responses to infection and vaccines.

Changes in Systemic Regulatory T Cells, Effector T Cells, and Monocyte Populations Associated With Early-Life Stunting

Stunting and environmental enteric dysfunction (EED) may be responsible for altered gut and systemic immune responses. However, their impact on circulating immune cell populations remains poorly characterized during early life. A detailed flow cytometry analysis of major systemic immune cell populations in 53 stunted and 52 non-stunted (2 to 5 years old) children living in Antananarivo (Madagascar) was performed. Compared to age-matched non-stunted controls, stunted children aged 2-3 years old had a significantly lower relative proportion of classical monocytes. No significant associations were found between stunting and the percentages of effector T helper cell populations (Th1, Th2, Th17, Th1Th17, and cTfh). However, we found that HLA-DR expression (MFI) on all memory CD4⁺ or CD8⁺ T cell subsets was significantly lower in stunted children compared to non-stunted controls. Interestingly, in stunted children compared to the same age-matched non-stunted controls, we observed statistically significant age-specific differences in regulatory T cells (Treg) subsets. Indeed, in 2- to 3-year-old stunted children, a significantly higher percentage of memory Treg, whilst a significantly lower percentage of naive Treg, was found. Our results revealed that both innate and adaptive systemic cell percentages, as well as activation status, were impacted in an age-related manner during stunting. Our study provides valuable insights into the understanding of systemic immune system changes in stunted children.

All trans retinoic acid as a host-directed immunotherapy for tuberculosis

Tuberculosis (TB) is the top bacterial infectious disease killer and one of the top ten causes of death worldwide. The emergence of strains of multiple drug-resistant tuberculosis (MDR-TB) has pushed our available stock of anti-TB agents to the limit of effectiveness. This has increased the urgent need to develop novel treatment strategies using currently available resources. An adjunctive, host-directed therapy (HDT) designed to act on the host, instead of the bacteria, by boosting the host immune response through activation of intracellular pathways could be the answer. The integration of multidisciplinary approaches of repurposing currently FDA-approved drugs, with a targeted drug-delivery platform is a very promising option to reduce the long timeline associated with the approval of new drugs - time that cannot be afforded given the current levels of morbidity and mortality associated with TB infection. The deficiency of vitamin A has been reported to be highly associated with the increased susceptibility of TB. All trans retinoic acid (ATRA), the active metabolite of vitamin A, has proven to be very efficacious against TB both in vitro and in vivo. In this review, we discuss and summarise the importance of vitamin A metabolites in the fight against TB and what is known regarding the molecular mechanisms of ATRA as a host-directed therapy for TB including its effect on macrophages cytokine profile and cellular pathways. Furthermore, we focus on the issues behind why previous clinical trials with vitamin A supplementation have failed, and how these issues might be overcome.

Increased T-cell responses that control bovine leukemia virus proviral load in beef cattle under dietary vitamin A restriction for marbling

Bovine leukemia virus (BLV) proviral load is controlled by T-cell responses, which require vitamin A (VA) derived from food. However, whether dietary VA restriction for marbling impairs the T-cell responses that control BLV proviral load in beef cattle is unknown. We assessed T-cell subsets, interferon (IFN)-γ gene expression, and BLV proviral load in naturally BLV-infected Japanese Black cattle that were fed a diet with decreased VA levels. We found that the percentage of CD4⁺ T cells increased over time during dietary VA restriction. In addition, BLV proviral load was negatively correlated with the percentage of CD4⁺ T cells and with the level of IFN-γ gene expression. These observations suggest that dietary VA restriction for marbling enhances T-cell responses that control BLV proviral load and thus does not promote leukemogenesis in fattening beef cattle.

Dietary Intervention Impacts Immune Cell Functions and Dynamics by Inducing Metabolic Rewiring

Accumulating evidence has shown that nutrient metabolism is closely associated with the differentiation and functions of various immune cells. Cellular metabolism, including aerobic glycolysis, fatty acid oxidation, and oxidative phosphorylation, plays a key role in germinal center (GC) reaction, B-cell trafficking, and T-cell-fate decision. Furthermore, a quiescent metabolic status consolidates T-cell-dependent immunological memory. Therefore, dietary interventions such as calorie restriction, time-restricted feeding, and fasting potentially manipulate immune cell functions. For instance, intermittent fasting prevents the development of experimental autoimmune encephalomyelitis. Meanwhile, the fasting response diminishes the lymphocyte pool in gut-associated lymphoid tissue to minimize energy expenditure, leading to the attenuation of Immunoglobulin A (IgA) response. The nutritional status also influences the dynamics of several immune cell subsets. Here, we describe the current understanding of the significance of immunometabolism in the differentiation and functionality of lymphocytes and macrophages. The underlying molecular mechanisms also are discussed. These experimental observations could offer new therapeutic strategies for immunological disorders like autoimmunity.

Oral immunization induces a novel CXCR6+ β7+ intraepithelial lymphocyte subset predominating in the small intestine

Intestinal T cells form a central part of the front-line defence against foreign organisms and need to be situated in the mucosa where infection occurs. It is well accepted that immunization by a mucosal route favours localization of antigen-specific effector T cells in the mucosal epithelium, while systemic immunization does not. The aim of the study is to determine how homing receptors are specifically involved in retaining effector T cells in the small intestine after oral immunization. We here demonstrate that the chemokine receptor CXCR6, integrins β7 and CD29 contribute differentially to the epithelial retention phenotype of CD8⁺ T cells in the small intestine of mice. CD8⁺ intraepithelial lymphocytes (IELs) of unvaccinated mice are predominantly β7 single positives, and subcutaneous immunization-induced antigen-specific CD8⁺ effector IELs are mainly composed of CXCR6⁺ , CD29⁺ and CXCR6⁺ CD29⁺ cells. Strikingly, the majority of oral immunization-induced antigen-specific CD8⁺ effector IELs exhibit a distinct, tissue-specific CXCR6⁺ β7⁺ double-positive phenotype, cytotoxic potential and enhanced intraepithelial localization. Transfer of antigen-specific CD8⁺ T cells preactivated with certain immuno-stimuli (such as monophosphoryl lipid A) results in increased accumulation of donor IELs with the CXCR6⁺ β7⁺ phenotype. As β7 exclusively paired with αE on IELs, our results strongly suggest that CXCR6 may cooperate with the heterodimer αEβ7 to preferentially retain intestinally induced effector IELs in the epithelium. The identification of this novel IEL phenotype has significant implications for the development of vaccines and therapeutic strategies to enhance gut immunity.

Recent Approaches for Solid Dose Vaccine Delivery

Recent studies on vaccine delivery systems are exploring the possibility of replacing liquid vaccines with solid dose vaccines due to the many advantages that solid dose vaccines can offer. These include the prospect of a needle-free vaccine delivery system leading to better patient compliance, cold chain storage, less-trained vaccinators and fewer chances for needle stick injury hazards. Some studies also indicate that vaccines in a solid dosage form can result in a higher level of immunogenicity compared to the liquid form, thus providing a dose-sparing effect. This review outlines the different approaches in solid vaccine delivery using various routes of administration including, oral, pulmonary, intranasal, buccal, sublingual, and transdermal routes. The various techniques and their current advancements will provide a knowledge base for future work to be carried out in this arena.

Parenteral Vaccination With a Tuberculosis Subunit Vaccine in Presence of Retinoic Acid Provides Early but Transient Protection to M. Tuberculosis Infection

Most microbes invading through mucosal surfaces cause disease and therefore strategies to induce mucosal immune responses are strongly needed. Vitamin A metabolites, such as retinoic acid (RA), play crucial roles in programming T and B cells to home to mucosal compartments, therefore we evaluated the capacity of RA to elicit mucosal immune responses against tuberculosis (TB) after parenteral vaccination. We found that mice immunized through subcutaneous injections with the TB subunit vaccine (CAF01+H56) in presence of RA show enhanced mucosal H56-specific IgA responses and enhanced Ag-specific CD4⁺ T lymphocytes homing to the lung as compared with control mice. Immunization with CAF01+H56 in presence of RA resulted in lower bacterial loads in the lungs of mice 14 days after challenge with virulent Mycobacterium tuberculosis (Mtb) as compared to mice immunized in the absence of RA or vaccinated with BCG. Higher amounts of IFNγ and IL-17 pro-inflammatory cytokines were found in lung homogenates of mice immunized with CAF01+H56 and RA 24 h after Mtb infection. However, 6 weeks after infection the protection was comparable in vaccinated mice with or without RA even though treatment with RA during immunization is able to better contain the inflammatory response by the host. Furthermore, at later stage of the infection a higher percentage of Mtb specific CD4⁺PD1⁺ T lymphocytes were found in the lungs of mice immunized with CAF01+H56 and RA. These data show that an enhanced mucosal immune response is generated during parenteral vaccination in presence of RA. Furthermore, RA treatment contained the bacterial growth at an early stage of the infection and limited the inflammatory response in the lung at later time points.

Neonatal vitamin A supplementation and immune responses to oral polio vaccine in Zimbabwean infants

Background

Micronutrient deficiencies may contribute to reduced oral vaccine immunogenicity in developing countries. We hypothesised that neonatal vitamin A supplementation (NVAS) would improve oral vaccine responses.

Methods

We performed a cross-sectional study of infants recruited at birth to the Zimbabwe Vitamin A for Mothers and Babies (ZVITAMBO) trial, a randomised controlled trial of single, high-dose NVAS vs placebo conducted in Zimbabwe between 1997–2001. We measured poliovirus-specific IgA to type 1–3 polio strains by semiquantitative capture ELISA in cryopreserved plasma samples collected at 6 months of age.

Results

A total of 181 infants fulfilled inclusion criteria, of whom 80 were randomised to NVAS and 101 to placebo. There were no significant differences in baseline characteristics between groups. At 6 months of age, median (IQR) vaccine titres for infants randomised to NVAS vs placebo were 932 (421–3001) vs 1774 (711–5431) for Sabin-1 (p=0.04); 1361 (705–3402) vs 2309 (1081–4283) for Sabin-2 (p=0.15); and 1584 (796–4216) vs 2260 (996–5723) for Sabin-3 (p=0.14), respectively. After adjusting for breast feeding status, birth weight, season and infant sex in a linear regression model, there was only weak evidence of difference in log mean titres between vitamin A and placebo groups for Sabin-1 (p=0.08) and no evidence of difference in log mean titres for Sabin-2 and Sabin-3.

Conclusions

NVAS did not augment oral polio vaccine responses in Zimbabwean infants. Further research is required to understand the impact of NVAS on responses to other oral vaccines.

The trial is registered with clinicaltrials.gov identifier: NCT00198718.

Interventions to improve oral vaccine performance: a systematic review and meta-analysis

BACKGROUND

Oral vaccines underperform in low-income and middle-income countries compared with in high-income countries. Whether interventions can improve oral vaccine performance is uncertain.

METHODS

We did a systematic review and meta-analysis of interventions designed to increase oral vaccine efficacy or immunogenicity. We searched Ovid-MEDLINE and Embase for trials published until Oct 23, 2017. Inclusion criteria for meta-analysis were two or more studies per intervention category and available seroconversion data. We did random-effects meta-analyses to produce summary relative risk (RR) estimates. This study is registered with PROSPERO (CRD42017060608).

FINDINGS

Of 2843 studies identified, 87 were eligible for qualitative synthesis and 66 for meta-analysis. 22 different interventions were assessed for oral poliovirus vaccine (OPV), oral rotavirus vaccine (RVV), oral cholera vaccine (OCV), and oral typhoid vaccines. There was generally high heterogeneity. Seroconversion to RVV was significantly increased by delaying the first RVV dose by 4 weeks (RR 1·37, 95% CI 1·16-1·62) and OPV seroconversion was increased with monovalent or bivalent OPV compared with trivalent OPV (RR 1·51, 95% CI 1·20-1·91). There was some evidence that separating RVV and OPV increased RVV seroconversion (RR 1·21, 95% CI 1·00-1·47) and that higher vaccine inoculum improved OCV seroconversion (RR 1·12, 95% CI 1·00-1·26). There was no evidence of effect for anthelmintics, antibiotics, probiotics, zinc, vitamin A, withholding breastfeeding, extra doses, or vaccine buffering.

INTERPRETATION

Most strategies did not improve oral vaccine performance. Delaying RVV and reducing OPV valence should be considered within immunisation programmes to reduce global enteric disease. New strategies to address the gap in oral vaccine efficacy are urgently required.

FUNDING

Wellcome Trust, Bill & Melinda Gates Foundation, UK Medical Research Council, and WHO Polio Research Committee.

Clinical Observations, Plasma Retinol Concentrations, and In Vitro Lymphocyte Functions in Children With Sickle Cell Disease

Background

Children with sickle cell disease (SCD) often have infections, growth deficits, and impaired immunity, problems that also are observed in individuals with a vitamin A deficiency (plasma retinol concentration <20 μg/dL). The goal of this study was to investigate the association between vitamin A, health status, and the in vitro immune function of children with SCD.

Methods

Fifty-nine children (40 SS, 11 SC, and 8 Sβ^thalassemia [Sβ^thal] hemoglobin genotypes) 9 months to 18 years old were investigated for plasma levels of retinol, retinol binding protein, C-reactive protein, alpha-1-acid glycoprotein, lymphocyte proliferation, and interleukin (IL)-2 activity in supernatant of phytohemagglutinin-treated lymphocytes.

Results

The plasma retinol concentrations of children with SCD (mean 57.6 μg/dL, range 4.6-116 μg/dL) were not different from those of 21 normal individuals (mean 62 μg/dL, range 28.7-162 μg/dL). Plasma retinol concentrations did not vary by hemoglobin genotype but were lower in boys than in girls (P < 0.05) and were also lower in children with inflammation (P = 0.1). Seven children (11.9%) (6 HbSS, 1 HbSβ^0thal) were vitamin A-deficient, and 9 children (15.3%) had suboptimal vitamin A status (plasma retinol concentration of 20-29 μg/dL). Children with vitamin A deficiency had slightly lower height (P = 0.09) and weight mean percentiles, lymphocyte proliferative responses, and IL-2 activity (P > 0.1), but higher means of C-reactive protein (P = 0.05), pain crisis episodes and inflammation (P = 0.1), and health scores (P > 0.1) than children who were not vitamin A-deficient. Lymphocyte proliferative responses negatively correlated with health score, pain crisis episodes, and blood units received, but positively correlated with retinol binding protein (P < 0.05 to P = 0.1).

Conclusion

Identification and correction of suboptimal vitamin A status in children with SCD may improve immunity and attenuate certain health complications associated with this disease.

Risk factors for diphtheria outbreak in children aged 1-10 years in East Kalimantan Province, Indonesia

Background: Diphtheria remains a health problem, especially in developing countries. In November 2017, the Indonesian Ministry of Health stated that there was a diphtheria outbreak in Indonesia. East Kalimantan is one of the provinces that experienced this disease outbreak. This study analyzes the risk factors for diphtheria outbreak in children aged 1-10 years. Methods: A case-control study was conducted on 37 respondents. Research variables consist of immunization status against diphtheria, pertussis and tetanus (DPT), nutritional status, children mobility, source of transmission, physical home environment (natural lighting, ventilation area, occupancy density, wall and floor type), knowledge of diphtheria and attitudes towards the diphtheria prevention program. Results: We found that the most of the children who had diphtheria had been immunized against DPT. Additionally the nutritional status of children (p=0.049), mobility (p=0.000) and the source of transmission (p=0.020) were significantly associated with diphtheria. Conclusions: Child/parent mobility (OR=8.456) is the main risk factor for diphtheria outbreak. It is recommended to limit the mobility of children to travel to areas that are experiencing increased cases of diphtheria, improve the nutritional status, and further research on the effectiveness of diphtheria vaccine.

Combined HDAC and BET Inhibition Enhances Melanoma Vaccine Immunogenicity and Efficacy

The combined inhibition of histone deacetylases (HDAC) and the proteins of the bromodomain and extraterminal (BET) family have recently shown therapeutic efficacy against melanoma, pancreatic ductal adenocarcinoma, testicular, and lymphoma cancers in murine studies. However, in such studies, the role of the immune system in therapeutically controlling these cancers has not been explored. We sought to investigate the effect of the HDAC inhibitor romidepsin (RMD) and the BET inhibitor IBET151, both singly and in combination, on vaccine-elicited immune responses. C57BL/6 mice were immunized with differing vaccine systems (adenoviral, protein) in prime-boost regimens under treatment with RMD, IBET151, or RMD+IBET151. The combined administration of RMD+IBET151 during vaccination resulted in a significant increase in the frequency and number of Ag-specific CD8⁺ T cells. RMD+IBET151 treatment significantly increased the frequency of vaccine-elicited IFN-γ⁺ splenic CD8⁺ T cells and conferred superior therapeutic and prophylactic protection against B16-OVA melanoma. RNA sequencing analyses revealed strong transcriptional similarity between RMD+IBET151 and untreated Ag-specific CD8⁺ T cells except in apoptosis and IL-6 signaling-related genes that were differentially expressed. Serum IL-6 was significantly increased in vivo following RMD+IBET151 treatment, with recombinant IL-6 administration replicating the effect of RMD+IBET151 treatment on vaccine-elicited CD8⁺ T cell responses. IL-6 sufficiency for protection was not assessed. Combined HDAC and BET inhibition resulted in greater vaccine-elicited CD8⁺ T cell responses and enhanced therapeutic and prophylactic protection against B16-OVA melanoma. Increased IL-6 production and the differential expression of pro- and anti-apoptotic genes following RMD+IBET151 treatment are likely contributors to the enhanced cancer vaccine responses.

Pathophysiology of environmental enteric dysfunction and its impact on oral vaccine efficacy

Environmental enteric dysfunction (EED) refers to a subclinical disorder of intestinal function common in tropical countries and in settings of poverty and economic disadvantage. The enteropathy that underlies this syndrome is characterized by mucosal inflammation and villus blunting mediated by T cell activation. Epithelial cell disruption and microbial translocation drive systemic inflammation. EED in young children is associated geographically with growth failure, malnutrition, and greatly impaired responses to oral vaccines, notably rotavirus and poliovirus vaccines. In this review, we describe the pathophysiology of EED and examine the evidence linking EED and oral vaccine failure. This evidence is far from conclusive. Although our understanding of EED is still sketchy, there is limited evidence of disturbed innate immunity, B cell disturbances including aggregation into lymphoid follicles, and autoantibody generation. Pathways of T cell activation and the possibility of dendritic cell anergy, which could help explain oral vaccine failure, require further work.

Retinoic acid elicits a coordinated expression of gut homing markers on T lymphocytes of Zambian men receiving oral Vivotif, but not Rotarix, Dukoral or OPVERO vaccines

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ATRA increased vaccine specific IgA in gut secretions to Vivotif but not Dukoral or Rotarix.

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ATRA increased α4β7 and CCR9 gut marker expression in a coordinated manner only when given simultaneously with Vivotif vaccine.

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In individuals with coordinated gut marker expression Vivotif specific IgA increase was much stronger.

All-trans retinoic acid (ATRA) up-regulates, in laboratory animals, the expression of the gut homing markers α4β7 integrin and CCR9 on lymphocytes, increasing their gut tropism. Here, we show that, in healthy adult volunteers, ATRA induced an increase of these gut homing markers on T cells in vivo in a time dependent manner. The coordinated increase of α4β7 and CCR9 by ATRA was seen in 57% (12/21) of volunteers and only when given together with an oral Vivotif vaccine. When this coordinated response to ATRA and Vivotif vaccine was present, it was strongly correlated with the gut immunoglobulin A (IgA) specific response to vaccine LPS (ρ = 0.82; P = 0.02). Using RNA-Seq analysis of whole blood transcription, patients receiving ATRA and Vivotif in conjunction showed transcriptomic changes in immune-related pathways, particularly including interferon α/β signaling pathway, membrane-ECM interactions and immune hubs. These results suggest that exogenous ATRA can be used to manipulate responses to a subclass of oral vaccines, so far limited to a live attenuated Vivotif vaccine.

Decreased performance of live attenuated, oral rotavirus vaccines in low-income settings: causes and contributing factors

INTRODUCTION

Numerous studies have shown that the oral rotavirus vaccines are less effective in infants born in low income countries compared to those born in developed countries. Identifying the specific factors in developing countries that decrease and/or compromise the protection that rotavirus vaccines offer, could lead to a path for designing new strategies for the vaccines' improvement.

AREAS COVERED

We accessed PubMed to identify rotavirus vaccine performance studies (i.e., efficacy, effectiveness and immunogenicity) and correlated performance with several risk factors. Here, we review the factors that might contribute to the low vaccine efficacy, including passive transfer of maternal rotavirus antibodies, rotavirus seasonality, oral polio vaccine (OPV) administered concurrently, microbiome composition and concomitant enteric pathogens, malnutrition, environmental enteropathy, HIV, and histo blood group antigens.

EXPERT COMMENTARY

We highlight two major factors that compromise rotavirus vaccines' efficacy: the passive transfer of rotavirus IgG antibodies to infants and the  co-administration of rotavirus vaccines with OPV. We also identify other potential risk factors that require further research because the data about their interference with the efficacy of rotavirus vaccines are inconclusive and at times conflicting.

The regulation of gut mucosal IgA B-cell responses: recent developments

The majority of activated B cells differentiate into IgA plasma cells, with the gut being the largest producer of immunoglobulin in the body. Secretory IgA antibodies have numerous critical functions of which protection against infections and the role for establishing a healthy microbiota appear most important. Expanding our knowledge of the regulation of IgA B-cell responses and how effective mucosal vaccines can be designed are of critical importance. Here we discuss recent developments in the field that shed light on the uniqueness and complexity of mucosal IgA responses and the control of protective IgA responses in the gut, specifically.

Effects of Donor Vitamin A Deficiency and Pharmacologic Modulation of Donor T Cell Retinoic Acid Pathway on the Severity of Experimental Graft-versus-Host Disease

Graft-versus-host disease (GVHD) is the major cause of morbidity and mortality after allogeneic hematopoietic stem cell transplantation (HSCT). A combination of genetic and nongenetic factors dictates the incidence and severity of GVHD. Recent studies have identified the potential role of the retinoic acid (RA)/retinoic acid receptor (RAR) pathway in the pathogenesis of GVHD. RA is the active metabolite of vitamin A. Thus, a clinically relevant question is whether HSCT donor and/or recipient vitamin A status affects the development of GVHD. It has been previously reported that recipient vitamin A deficiency is associated with reduced intestinal GVHD and prolonged overall survival after experimental allogeneic HSCT. However, it is still unknown whether donor vitamin A status influences GVHD development. In the current study, we report that chronic vitamin A deficiency changes the composition of T cell compartment of donor mice with a reduction in the percentage of CD4⁺ T cells. We showed that although vitamin A deficiency does not affect donor T cell alloreactivity on a per cell basis, a decreased proportion of donor CD4⁺ T cells in marrow graft inoculums leads to reduced incidence and severity of GVHD. Furthermore, our proof of principle studies using a pan-RAR antagonist demonstrated that transient inhibition of donor T cell RAR signaling can reduce T cell alloreactivity and their ability to cause lethal GVHD. Our studies provide preclinical evidence that donor vitamin A deficiency may be a nongenetic factor that can modulate the severity of GVHD and pharmacologic interfering RA/RAR pathway in donor T cells might be a valuable approach for mitigating GVHD after allogeneic HSCT.

Low and disparate seroprotection after pentavalent childhood vaccination in the Lao People's Democratic Republic: a cross-sectional study

OBJECTIVE

In Lao People's Democratic Republic, the high burden of vaccine-preventable diseases is thought to be mainly due to low vaccine coverage. We investigated the seroprotective response against diphtheria-tetanus-whole cell pertussis-hepatitis B-Haemophilus influenzae type b (DTPw-HepB-Hib) vaccine in children.

METHODS

Serum was collected from 1131 children aged 9 to 50 months and their mothers in a cross-sectional study between December 2013 and July 2014. All children had records of three injections of the DTPw-HepB-Hib vaccine. Serum was analysed for hepatitis B surface antigen (HBsAg), anti-HBsAg (anti-HBs), anti-hepatitis B virus core antigen (anti-HBc), anti-diphtheria and anti-tetanus antibodies. Stool samples were collected for detection of parasites. Demographic and nutritional information were also obtained.

RESULTS

Protective levels of anti-HBs antibodies were found in 394 (37.9%) of 1039 children; 529 (55.7%) of 950 and 809 (85.2%) of 950 children were seroprotected against diphtheria and tetanus. Time since vaccination, age, home birth and malnutrition only partially explained the poor vaccine responses. Overall, 81 (7.8%) of 1039 children and 445 (40.3%) of 1105 of mothers were anti-HBc positive. Ten (1.0%) of 1039 of the children and 77 (7.0%) of 1105 of the mothers were HBsAg carriers.

CONCLUSIONS

After a full documented course of vaccination, seroprotective rates were unusually low and disparate against components of the pentavalent vaccine. These can only partially be explained by the negative predictors identified. Although many children had been infected, only few were chronic carriers of HBsAg. Our study demonstrates an urgent need to monitor the serologic response to vaccination, particularly in resource-poor countries.

Immediate Dysfunction of Vaccine-Elicited CD8+ T Cells Primed in the Absence of CD4+ T Cells

CD4(+) T cell help is critical for optimal CD8(+) T cell memory differentiation and maintenance in many experimental systems. In addition, many reports have identified reduced primary CD8(+) T cell responses in the absence of CD4(+) T cell help, which often coincides with reduced Ag or pathogen clearance. In this study, we demonstrate that absence of CD4(+) T cells at the time of adenovirus vector immunization of mice led to immediate impairments in early CD8(+) T cell functionality and differentiation. Unhelped CD8(+) T cells exhibited a reduced effector phenotype, decreased ex vivo cytotoxicity, and decreased capacity to produce cytokines. This dysfunctional state was imprinted within 3 d of immunization. Unhelped CD8(+) T cells expressed elevated levels of inhibitory receptors and exhibited transcriptomic exhaustion and anergy profiles by gene set enrichment analysis. Dysfunctional, impaired effector differentiation also occurred following immunization of CD4(+) T cell-deficient mice with a poxvirus vector. This study demonstrates that following priming with viral vectors, CD4(+) T cell help is required to promote both the expansion and acquisition of effector functions by CD8(+) T cells, which is accomplished by preventing immediate dysfunction.

Potential for use of retinoic acid as an oral vaccine adjuvant

Despite the heavy burden of diarrhoeal disease across much of the tropical world, only two diarrhoea-causing pathogens, cholera and rotavirus, are the target of commercially available vaccines. Oral vaccines are generally less immunogenic than the best parenteral vaccines, but the reasons for this are still debated. Over the past decade, several lines of evidence from work in experimental animals have suggested that all-trans retinoic acid (ATRA), a form of vitamin A which is highly transcriptionally active, can alter the homing receptor expression of T lymphocytes. Increased expression of α4β7 integrin and the chemokine receptor CCR9 following exposure to ATRA can be used to redirect T cells to the gut. Early work in human volunteers suggests that oral ATRA administration 1 h prior to dosing with oral typhoid vaccine can augment secretion of specific IgA against vaccine-derived lipopolysaccharide into gut secretions. In this review, we set out the rationale for using ATRA in this way and assess its likely applicability to vaccination programmes for protection of children in low-income countries from the considerable mortality caused by diarrhoeal disease. Comparison of recent work in experimental animals, non-human primates and men suggests that a more detailed understanding of ATRA dosage and kinetics will be important to taking forward translational work into human vaccinology.

Vitamin A: a missing link in diabetes?

Vitamin A has a critical role in embryonic development, immunity and the visual cycle. In recent years, evidence has demonstrated that vitamin A can also regulate metabolic pathways implicated in the pathogenesis of obesity and diabetes. This has increased interest in the possible antiobesity and antidiabetic properties of natural and synthetic vitamin A derivatives. However, whether vitamin A deficiency or aberrations in vitamin A metabolism contribute to the pathogenesis of diabetes is not known. This perspective article will review what is currently known and new data regarding the link between vitamin A and the clinical manifestations of common and atypical forms of diabetes.

Delivery strategies to enhance oral vaccination against enteric infections

While the majority of human pathogens infect the body through mucosal sites, most licensed vaccines are injectable. In fact the only mucosal vaccine that has been widely used globally for infant and childhood vaccination programs is the oral polio vaccine (OPV) developed by Albert Sabin in the 1950s. While oral vaccines against Cholera, rotavirus and Salmonella typhi have also been licensed, the development of additional non-living oral vaccines against these and other enteric pathogens has been slow and challenging. Mucosal vaccines can elicit protective immunity at the gut mucosa, in part via antigen-specific secretory immunoglobulin A (SIgA). However, despite their advantages over the injectable route, oral vaccines face many hurdles. A key challenge lies in design of delivery strategies that can protect antigens from degradation in the stomach and intestine, incorporate appropriate immune-stimulatory adjuvants and control release at the appropriate gastrointestinal site. A number of systems including micro and nanoparticles, lipid-based strategies and enteric capsules have significant potential either alone or in advanced combined formulations to enhance intestinal immune responses. In this review we will outline the opportunities, challenges and potential delivery solutions to facilitate the development of improved oral vaccines for infectious enteric diseases.

Diphtheria in Lao PDR: Insufficient Coverage or Ineffective Vaccine?

Background

During late 2012 and early 2013 several outbreaks of diphthe-ria were notified in the North of the Lao People’s Democratic Republic. The aim of this study was to determine whether the re-emergence of this vaccine-preventable disease was due to insufficient vaccination coverage or reduction of vaccine effectiveness within the affected regions.

Methods

A serosurvey was conducted in the Huaphan Province on a cluster sampling of 132 children aged 12–59 months. Serum samples, socio-demographic data, nutri-tional status and vaccination history were collected when available. Anti-diphtheria and anti-tetanus IgG antibody levels were measured by ELISA.

Results

Overall, 63.6% of participants had detectable diphtheria antibodies and 71.2% tetanus antibodies. Factors independently associated with non-vaccination against diphtheria were the distance from the health centre (OR: 6.35 [95% CI: 1.4–28.8], p = 0.01), the Lao Theung ethnicity (OR: 12.2 [95% CI:1,74–85, 4], p = 0.01) and the lack of advice on vac-cination given at birth (OR: 9.8 [95% CI: 1.5–63.8], (p = 0.01) while the level of maternal edu-cation was a protective factor (OR: 0.08 [95% CI: 0.008–0.81], p = 0.03). Most respondents claimed financial difficulties as the main reason for non-vaccination. Out of 55 children whose vaccination certificates stated that they were given all 3 doses of diphtheria-containing vaccine, 83.6% had diphtheria antibodies and 92.7% had tetanus antibodies. Furthermore, despite a high prevalence of stunted and underweight children (53% and 25.8%, respectively), the low levels of anti-diphtheria antibodies were not correlated to the nutritional status.

Conclusions

Our data highlight a significant deficit in both the vaccination coverage and diphtheria vaccine effectiveness within the Huaphan Province. Technical defi-ciencies in the methods of storage and distribution of vaccines as well as unreliability of vac-cination cards are discussed. Several hypotheses are advanced to explain such a decline in immunity against diphtheria and recommendations are provided to prevent future outbreaks.

Feeding immunity: skepticism, delicacies and delights

Immunologists studying the relationship between nutrition and immunological function face many challenges. We discuss here some of the historical skepticism with which nutritional research has often been faced and the complexities that need to be overcome in order to provide meaningful mechanistic insights.

Leukocyte homing, fate, and function are controlled by retinoic acid

Although vitamin A was recognized as an "anti-infective vitamin" over 90 years ago, the mechanism of how vitamin A regulates immunity is only beginning to be understood. Early studies which focused on the immune responses in vitamin A-deficient (VAD) animals clearly demonstrated compromised immunity and consequently increased susceptibility to infectious disease. The active form of vitamin A, retinoic acid (RA), has been shown to have a profound impact on the homing and differentiation of leukocytes. Both pharmacological and genetic approaches have been applied to the understanding of how RA regulates the development and differentiation of various immune cell subsets, and how RA influences the development of immunity versus tolerance. These studies clearly show that RA profoundly impacts on cell- and humoral-mediated immunity. In this review, the early findings on the complex relationship between VAD and immunity are discussed as well as vitamin A metabolism and signaling within hematopoietic cells. Particular attention is focused on how RA impacts on T-cell lineage commitment and plasticity in various diseases.

Strategies for design and application of enteric viral vaccines

Enteric viral infections in domestic animals cause significant economic losses. The recent emergence of virulent enteric coronaviruses [porcine epidemic diarrhea virus (PEDV)] in North America and Asia, for which no vaccines are available, remains a challenge for the global swine industry. Vaccination strategies against rotavirus and coronavirus (transmissible gastroenteritis virus) infections are reviewed. These vaccination principles are applicable against emerging enteric infections such as PEDV. Maternal vaccines to induce lactogenic immunity, and their transmission to suckling neonates via colostrum and milk, are critical for early passive protection. Subsequently, in weaned animals, oral vaccines incorporating novel mucosal adjuvants (e.g., vitamin A, probiotics) may provide active protection when maternal immunity wanes. Understanding intestinal and systemic immune responses to experimental rotavirus and transmissible gastroenteritis virus vaccines and infection in pigs provides a basis and model for the development of safe and effective vaccines for young animals and children against established and emerging enteric infections.

Pre-birth world and the development of the immune system: mum's diet affects our adult health: new insight on how the diet during pregnancy permanently influences offspring health and immune fitness

Secondary lymphoid organs form in utero through an inherited and well-established developmental program. However, maternal non-heritable features can have a major impact on the gene expression of the embryo, hence influencing the future health of the offspring. Recently, maternal retinoids were shown to regulate the formation of immune structures, shedding light on the role of maternal nutrition in the genetic signature of emergent immune cells. Here we highlight evidence showing how the maternal diet influences the establishment of the immune system, and we also discuss how unbalanced maternal diets may set the response to infection and vaccination in the progeny.

Influence of the microbiota on vaccine effectiveness

Studies of the relationship between the microbiome and the development and function of the immune system are demonstrating novel concepts that could significantly alter the way we treat disease and promote wellness. Several diseases, including inflammatory bowel disease, allergy/asthma, and diabetes, are associated with changes in composition of the microbiome. Recent findings suggest novel complex mechanisms by which the microbiome impacts immune cell development and differentiation. A major implication of these findings is that the composition of microbiome may ultimately affect vaccine efficacy. We explore here the potential role of the microbiome in vaccine responses in the context of our growing understanding of the relationship between the gastrointestinal microbiota, resident immune cell populations, and systemic immunity.

Vitamin A deficiency impairs adaptive B and T cell responses to a prototype monovalent attenuated human rotavirus vaccine and virulent human rotavirus challenge in a gnotobiotic piglet model

Rotaviruses (RV) are a major cause of gastroenteritis in children. Widespread vitamin A deficiency is associated with reduced efficacy of vaccines and higher incidence of diarrheal infections in children in developing countries. We established a vitamin A deficient (VAD) gnotobiotic piglet model that mimics subclinical vitamin A deficiency in children to study its effects on an oral human rotavirus (HRV) vaccine and virulent HRV challenge. Piglets derived from VAD and vitamin A sufficient (VAS) sows were orally vaccinated with attenuated HRV or mock, with/without supplemental vitamin A and challenged with virulent HRV. Unvaccinated VAD control piglets had significantly lower hepatic vitamin A, higher severity and duration of diarrhea and HRV fecal shedding post-challenge as compared to VAS control pigs. Reduced protection coincided with significantly higher innate (IFNα) cytokine and CD8 T cell frequencies in the blood and intestinal tissues, higher pro-inflammatory (IL12) and 2-3 fold lower anti-inflammatory (IL10) cytokines, in VAD compared to VAS control pigs. Vaccinated VAD pigs had higher diarrhea severity scores compared to vaccinated VAS pigs, which coincided with lower serum IgA HRV antibody titers and significantly lower intestinal IgA antibody secreting cells post-challenge in the former groups suggesting lower anamnestic responses. A trend for higher serum HRV IgG antibodies was observed in VAD vs VAS vaccinated groups post-challenge. The vaccinated VAD (non-vitamin A supplemented) pigs had significantly higher serum IL12 (PID2) and IFNγ (PID6) compared to vaccinated VAS groups suggesting higher Th1 responses in VAD conditions. Furthermore, regulatory T-cell responses were compromised in VAD pigs. Supplemental vitamin A in VAD pigs did not fully restore the dysregulated immune responses to AttHRV vaccine or moderate virulent HRV diarrhea. Our findings suggest that that VAD in children in developing countries may partially contribute to more severe rotavirus infection and lower HRV vaccine efficacy.

Seroprevalence of neutralizing antibodies to human adenoviruses type-5 and type-26 and chimpanzee adenovirus type-68 in healthy Chinese adults

Replication-defective adenoviruses have been utilized as candidate vaccine vectors. However, clinical application of the best-studied human adenovirus type-5 (AdHu5) is limited by the high prevalence of preexisting neutralizing antibodies resulting from natural infection. Therefore, rare adenovirus serotypes, such as human adenovirus type-26 (AdHu26) and chimpanzee adenovirus type-68 (AdC68), have been employed as substitutes for AdHu5. However, few studies have described the epidemiology of pre-existing immunity to these adenoviruses in China. Thus, 1,154 participants from six regions in China were examined to assess the presence of neutralizing antibodies against AdHu5, AdHu26, and AdC68. The seroprevalence rates of neutralizing antibodies were as follows: AdHu5, 73.1% (844/1,154) (95% confidence interval: 70.5-75.6%); AdHu26, 35.3% (407/1,154) (95% confidence interval: 32.6-38.1%); and AdC68, 12.7% (147/1,154) (95% confidence interval: 10.9-14.8%), respectively. The most frequently detected and highest titer antibodies were specific for AdHu5. The results indicate that AdHu26 and AdC68 serve as more suitable vaccine vectors than AdHu5.

Prenatally acquired vitamin A deficiency alters innate immune responses to human rotavirus in a gnotobiotic pig model

We examined how prenatally acquired vitamin A deficiency (VAD) modulates innate immune responses and human rotavirus (HRV) vaccine efficacy in a gnotobiotic (Gn) piglet model of HRV diarrhea. The VAD and vitamin A-sufficient (VAS) Gn pigs were vaccinated with attenuated HRV (AttHRV) with or without concurrent oral vitamin A supplementation (100,000 IU) and challenged with virulent HRV (VirHRV). Regardless of vaccination status, the numbers of conventional and plasmacytoid dendritic cells (cDCs and pDCs) were higher in VAD piglets prechallenge, but decreased substantially postchallenge as compared with VAS pigs. We observed significantly higher frequency of CD103 (integrin αEβ7) expressing DCs in VAS versus VAD piglets postchallenge, indicating that VAD may interfere with homing (including intestinal) phenotype acquisition. Post-VirHRV challenge, we observed longer and more pronounced diarrhea and higher VirHRV fecal titers in nonvaccinated VAD piglets. Consistent with higher VirHRV shedding titers, higher IFN-α levels were induced in control VAD versus VAS piglet sera at postchallenge day 2. Ex vivo HRV-stimulated mononuclear cells (MNCs) isolated from spleen and blood of VAD pigs prechallenge also produced more IFN-α. In contrast, at postchallenge day 10, we observed reduced IFN-α levels in VAD pigs that coincided with decreased TLR3(+) MNC frequencies. Numbers of necrotic MNCs were higher in VAD pigs in spleen (coincident with splenomegaly in other VAD animals) prechallenge and intestinal tissues (coincident with higher VirHRV induced intestinal damage) postchallenge. Thus, prenatal VAD caused an imbalance in innate immune responses and exacerbated VirHRV infection, whereas vitamin A supplementation failed to compensate for these VAD effects.

Characterization of humoral and cellular immune responses elicited by a recombinant adenovirus serotype 26 HIV-1 Env vaccine in healthy adults (IPCAVD 001)

BACKGROUND

Adenovirus serotype 26 (Ad26) has been developed as a novel candidate vaccine vector for human immunodeficiency virus type 1 (HIV-1) and other pathogens. The primary safety and immunogenicity data from the Integrated Preclinical/Clinical AIDS Vaccine Development Program (IPCAVD) 001 trial, the first-in-human evaluation of a prototype Ad26 vector-based vaccine expressing clade A HIV-1 Env (Ad26.ENVA.01), are reported concurrently with this article. Here, we characterize in greater detail the humoral and cellular immune responses elicited by Ad26.ENVA.01 in humans.

METHODS

Samples from the IPCAVD 001 trial were used for humoral and cellular immunogenicity assays.

RESULTS

We observed a dose-dependent expansion of the magnitude, breadth, and epitopic diversity of Env-specific binding antibody responses elicited by this vaccine. Antibody-dependent cell-mediated phagocytosis, virus inhibition, and degranulation functional activity were also observed. Env-specific cellular immune responses induced by the vaccine included multiple CD8(+) and CD4(+) T-lymphocyte memory subpopulations and cytokine secretion phenotypes, although cellular immune breadth was limited. Baseline vector-specific T-lymphocyte responses were common but did not impair Env-specific immune responses in this study.

CONCLUSION

Ad26.ENVA.01 elicited a broad diversity of humoral and cellular immune responses in humans. These data support the further clinical development of Ad26 as a candidate vaccine vector.

CLINICAL TRIALS REGISTRATION

NCT00618605.

Type-I IFN signaling is required for the induction of antigen-specific CD8(+) T cell responses by adenovirus vector vaccine in the gut-mucosa

Adenovirus vector (Adv) vaccination at a systemic site, such as intramuscular (i.m.) immunization, can induce antigen-specific CD8(+) T cell responses in both systemic and mucosal compartments. It remains unclear, however, how antigen-specific CD8(+) T cell response is induced in the mucosa. In this study, we found that type-I IFN signaling is required for the induction of mRNA expression of retinal dehydrogenase in the draining lymph nodes following the i.m. Adv vaccination. We show that type-I IFN signaling is required for the induction of antigen-specific CD8(+) T cell response in the gut-mucosal compartment following the i.m. Adv vaccination.

Vitamin A deficiency disrupts vaccine-induced antibody-forming cells and the balance of IgA/IgG isotypes in the upper and lower respiratory tract

Vaccination by intranasal (IN) inoculation with a replication-competent virus forms the basis of licensed and novel candidate respiratory viral vaccines (e.g., the cold-adapted influenza virus vaccine). A positive global impact of vaccination depends on vaccine efficacy in developing countries where dietary deficiencies are commonplace. The current study was designed using Sendai virus (SeV) as a model respiratory viral vaccine to test antibody-forming cell (AFC) residence and isotype expression in the context of a vitamin A deficiency (VAD). Samples were taken 1 mo after vaccination when AFCs generally reach their peak in healthy animals. In control animals on a healthy diet, SeV induced an antibody response with a relative bias toward IgA in the upper respiratory tract (URT, as sampled by nasal wash), and IgG in the lower respiratory tract (LRT, as sampled by bronchoalveolar lavage [BAL]). In the context of VAD, the SeV-specific IgA antibodies in the nasal wash were significantly reduced in favor of enhanced IgG antibodies in the BAL. When AFCs were examined in diffuse nasal-associated lymphoid tissues (d-NALT), lungs, cervical lymph nodes (CLN), and mediastinal lymph nodes (MLN), a similar pattern emerged. AFCs were most frequent in the d-NALT and most expressed IgA in control mice. In the context of VAD, these IgA-producing AFCs were significantly reduced in number, skewing the natural balance of IgA and IgG. Taken together, the results show that the VAD diet, which is well known for its association with immune defects in the gut, significantly alters AFC induction and isotype expression in the respiratory tract.

The current challenges for vaccine development

Vaccine development has played a hugely important role in combating infectious disease. Despite this success, there is still a great need for new vaccines and these are emerging far more slowly than we would wish. Despite the massive expansion in understanding of immune responses to infection, research is often hindered by a lack of understanding of the immune responses required specifically for protection, or by a lack of approved adjuvants and delivery systems to induce the required responses. In addition, the financial commitment required to license new vaccines is significant, and the more lucrative markets are often not those with the greatest need. In this review, we discuss many of the hurdles that new vaccines must overcome in order to reduce morbidity and mortality, and some of the initiatives that are being attempted to supply new vaccines to those that need them most.

Induction of gut IgA production through T cell-dependent and T cell-independent pathways

The gut immune system protects against mucosal pathogens, maintains a mutualistic relationship with the microbiota, and establishes tolerance against food antigens. This requires a balance between immune effector responses and induction of tolerance. Disturbances of this strictly regulated balance can lead to infections or the development inflammatory diseases and allergies. Production of secretory IgA is a unique effector function at mucosal surfaces, and basal mechanisms regulating IgA production have been the focus of much recent research. These investigations have aimed at understanding how long-term IgA-mediated mucosal immunity can best be achieved by oral or sublingual vaccination, or at analyzing the relationship between IgA production, the composition of the gut microbiota, and protection from allergies and autoimmunity. This research has lead to a better understanding of the IgA system; but at the same time seemingly conflicting data have been generated. Here, we discuss how gut IgA production is controlled, with special focus on how differences between T cell-dependent and T cell-independent IgA production may explain some of these discrepancies.

Induced CD4+Foxp3+ regulatory T cells in immune tolerance

Regulatory T lymphocytes are essential to maintain homeostasis of the immune system, limiting the magnitude of effector responses and allowing the establishment of immunological tolerance. Two main types of regulatory T cells have been identified--natural and induced (or adaptive)-and both play significant roles in tuning down effector immune responses. Adaptive CD4(+)Foxp3(+) regulatory T (iTreg) cells develop outside the thymus under a variety of conditions. These include not only antigen presentation under subimmunogenic or noninflammatory conditions, but also chronic inflammation and infections. We speculate that the different origin of iTreg cells (noninflammatory versus inflammatory) results in distinct properties, including their stability. iTreg cells are also generated during homeostasis of the gut and in cancer, although some cancers also favor expansion of natural regulatory T (nTreg) cells. Here we review how iTreg cells develop and how they participate in immunological tolerance, contrasting, when possible, iTreg cells with nTreg cells.

The impact of perinatal immune development on mucosal homeostasis and chronic inflammation

The mucosal surfaces of the gut and airways have important barrier functions and regulate the induction of immunological tolerance. The rapidly increasing incidence of chronic inflammatory disorders of these surfaces, such as inflammatory bowel disease and asthma, indicates that the immune functions of these mucosae are becoming disrupted in humans. Recent data indicate that events in prenatal and neonatal life orchestrate mucosal homeostasis. Several environmental factors promote the perinatal programming of the immune system, including colonization of the gut and airways by commensal microorganisms. These complex microbial-host interactions operate in a delicate temporal and spatial manner and have an important role in the induction of homeostatic mechanisms.

Vitamin A and immune regulation: role of retinoic acid in gut-associated dendritic cell education, immune protection and tolerance

The vitamin A (VA) metabolite all-trans retinoic acid (RA) plays a key role in mucosal immune responses. RA is produced by gut-associated dendritic cells (DC) and is required for generating gut-tropic lymphocytes and IgA-antibody-secreting cells (IgA-ASC). Moreover, RA modulates Foxp3(+) regulatory T cell (T(REG)) and Th17 effector T cell differentiation. Thus, although RA could be used as an effective "mucosal adjuvant" in vaccines, it also appears to be required for establishing intestinal immune tolerance. Here we discuss the roles proposed for RA in shaping intestinal immune responses and tolerance at the gut mucosal interface. We also focus on recent data exploring the mechanisms by which gut-associated DC acquire RA-producing capacity.