Adjuvant potential of low dose all-trans retinoic acid during oral typhoid vaccination in Zambian men

Multicomponent Pathogen-Mimicking Nanoparticles Induce Intestinal Immune Responses against Paratuberculosis

Given the worldwide problem posed by enteric pathogens, the discovery of safe and efficient intestinal adjuvants combined with novel antigen delivery techniques is essential to the design of mucosal vaccines. In this work, we designed poly (lactic-co-glycolic acid) (PLGA)-based nanoparticles (NPs) to codeliver all-trans retinoic acid (atRA), novel antigens, and CpG. To address the insolubility of the intestinal adjuvant atRA, we utilized PLGA to encapsulate atRA and form a "nanocapsid" with polydopamine. By leveraging polydopamine, we adsorbed the water-soluble antigens and the TLR9 agonist CpG onto the NPs' surface, resulting in the pathogen-mimicking PLPCa NPs. In this study, the novel fusion protein (HBf), consisting of the Mycobacterium avium subspecies paratuberculosis antigens HBHA, Ag85B, and Bfra, was coloaded onto the NPs. In vitro, PLPCa NPs were shown to promote the activation and maturation of bone marrow-derived dendritic cells. Additionally, we found that PLPCa NPs created an immune-rich microenvironment at the injection site following intramuscular administration. From the results, the PLPCa NPs induced strong IgA levels in the gut in addition to enhancing powerful systemic immune responses. Consequently, significant declines in the bacterial burden and inflammatory score were noted in PLPCa NPs-treated mice. In summary, PLPCa can serve as a novel and safe vaccine delivery platform against gut pathogens, such as paratuberculosis, capable of activating both systemic and intestinal immunity.

Immunity to enteric viruses

Pathogenic enteric viruses are a major cause of morbidity and mortality, particularly among children in developing countries. The host response to enteric viruses occurs primarily within the mucosa, where the intestinal immune system must balance protection against pathogens with tissue protection and tolerance to harmless commensal bacteria and food. Here, we summarize current knowledge in natural immunity to enteric viruses, highlighting specialized features of the intestinal immune system. We further discuss how knowledge of intestinal anti-viral mechanisms can be translated into vaccine development with particular focus on immunization in the oral route. Research reveals that the intestine is a complex interface between enteric viruses and the host where environmental factors influence susceptibility and immunity to infection, while viral infections can have lasting implications for host health. A deeper mechanistic understanding of enteric anti-viral immunity with this broader context can ultimately lead to better vaccines for existing and emerging viruses.

Immunomodulation as a Novel Strategy for Prevention and Treatment of Bordetella spp. Infections

Well-adapted pathogens have evolved to survive the many challenges of a robust immune response. Defending against all host antimicrobials simultaneously would be exceedingly difficult, if not impossible, so many co-evolved organisms utilize immunomodulatory tools to subvert, distract, and/or evade the host immune response. Bordetella spp. present many examples of the diversity of immunomodulators and an exceptional experimental system in which to study them. Recent advances in this experimental system suggest strategies for interventions that tweak immunity to disrupt bacterial immunomodulation, engaging more effective host immunity to better prevent and treat infections. Here we review advances in the understanding of respiratory pathogens, with special focus on Bordetella spp., and prospects for the use of immune-stimulatory interventions in the prevention and treatment of infection.

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.

Longevity of duodenal and peripheral T-cell and humoral responses to live-attenuated Salmonella Typhi strain Ty21a

BACKGROUND

We have previously demonstrated that polyfunctional Ty21a-responsive CD4+ and CD8+ T cells are generated at the duodenal mucosa 18 days following vaccination with live-attenuated S. Typhi (Ty21a). The longevity of cellular responses has been assessed in peripheral blood, but persistence of duodenal responses is unknown.

METHODS

We vaccinated eight healthy adults with Ty21a. Peripheral blood and duodenal samples were acquired after a median of 1.5 years (ranging from 1.1 to 3.7 years) following vaccination. Cellular responses were assessed in peripheral blood and at the duodenal mucosa by flow cytometry. Levels of IgG and IgA were also assessed in peripheral blood by enzyme-linked immunosorbent assay.

RESULTS

No T-cell responses were observed at the duodenal mucosa, but CD4+ T-cell responses to Ty21a and FliC were observed in peripheral blood. Peripheral anti-lipopolysaccharide IgG and IgA responses were also observed. Early immunoglobulin responses were not associated with the persistence of long-term cellular immune responses.

CONCLUSIONS

Early T-cell responses which we have previously observed at the duodenal mucosa 18 days following oral vaccination with Ty21a could not be detected at a median of 1.5 years. Peripheral responses were observed at this time. Immunoglobulin responses observed shortly after vaccination were not associated with cellular immune responses at 1.5 years, suggesting that the persistence of cellular immunity is not associated with the strength of the initial humoral response to vaccination.

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.

Properties and applications of nanoparticle/microparticle conveyors with adjuvant characteristics suitable for oral vaccination

Vaccination is one of the most effective approaches in the prevention and control of disease worldwide. Oral vaccination could have wide applications if effective protection cannot be achieved through traditional (eg, parenteral) routes of vaccination. However, oral administration is hampered by the difficulties in transferring vaccines in vivo. This has led to the development of materials such as carriers with potential adjuvant effects. Considering the requirements for selecting adjuvants for oral vaccines as well as the advantages of nanoparticle/microparticle materials as immune effectors and antigen conveyors, synthetic materials could improve the efficiency of oral vaccination. In this review, nanoparticles and microparticles with adjuvant characteristics are described with regard to their potential importance for oral immunization, and some promising and successful modification strategies are summarized.

Retinoic acid pre-treatment down regulates V. cholerae outer membrane vesicles induced acute inflammation and enhances mucosal immunity

Bacterial outer membrane vesicles have been extensively investigated and considered as a next generation vaccine. Recently, we have demonstrated that the cholera pentavalent outer membrane vesicles (CPMVs) immunogen induced adaptive immunity and had a strong protective efficacy against the circulating V. cholerae strains in a mouse model. In this present study, we are mainly focusing on reducing outer membrane vesicle (OMV) -mediated toxicity without altering its antigenic property. Therefore, we have selected All-trans Retinoic Acid (ATRA), active metabolites of vitamin A, which have both anti-inflammatory and mucosal adjuvant properties. Pre-treatment of ATRA significantly reduced CPMVs induced TLR2 mediated pro-inflammatory responses in vitro and in vivo. Furthermore, we also found ATRA pre-treatment significantly induced mucosal immune response and protective efficacy after two doses of oral immunization with CPMVs (75µg). This study can help to reduce OMV based vaccine toxicity and induce better protective immunity where children and men suffered from malnutrition mainly in developing countries.

Chemical Synthesis, Versatile Structures and Functions of Tailorable Adjuvants for Optimizing Oral Vaccination

Oral vaccines have become a recent focus because of their potential significance in disease prevention and therapy. In the development of oral vaccine-based therapeutics, synthetic materials with tailorable structures and versatile functions can act as antigen conveyers with adjuvant effects, reduce the time cost for vaccine optimization, and provide high security and enhanced immunity. This review presents an overview of the current status of tailoring synthetic adjuvants for oral vaccination, modification strategies for producing effectors with specific structures and functions, enhancement of immune-associated efficiencies, including the barrier-crossing capability to protect antigens in the gastrointestinal tract, coordination of the antigens penetrating mucosa and cell barriers, targeting of concentrated antigens to immune-associated cells, and direct stimulation of immune cells. Finally, we focus on prospective synthetic adjuvants that facilitate the use of oral vaccines via two approaches, namely, in vivo antigen expression and cancer immunotherapy.

Retinoic Acid Signaling in B Cells Is Required for the Generation of an Effective T-Independent Immune Response

Retinoic acid (RA) plays an important role in the balance of inflammation and tolerance in T cells. Furthermore, it has been demonstrated that RA facilitates IgA isotype switching in B cells in vivo. However, it is unclear whether RA has a direct effect on T-independent B cell responses in vivo. To address this question, we generated a mouse model where RA signaling is specifically silenced in the B cell lineage. This was achieved through the overexpression of a dominant negative receptor α for RA (dnRARα) in the B cell lineage. In this model, we found a dramatic reduction in marginal zone (MZ) B cells and accumulation of transitional 2 B cells in the spleen. We also observed a reduction in B1 B cells in the peritoneum with a defect in the T-independent B cell response against 2,4,6-trinitrophenyl. This was not a result of inhibited development of B cells in the bone marrow, but likely the result of both defective expression of S1P₁ in MZ B cells and a defect in the development of MZ and B1 B cells. This suggests that RARα expression in B cells is important for B cell frequency in the MZ and peritoneum, which is crucial for the generation of T-independent humoral responses.

Retinaldehyde dehydrogenase 2 as a molecular adjuvant for enhancement of mucosal immunity during DNA vaccination

In order for vaccines to induce efficacious immune responses against mucosally transmitted pathogens, such as HIV-1, activated lymphocytes must efficiently migrate to and enter targeted mucosal sites. We have previously shown that all-trans retinoic acid (ATRA) can be used as a vaccine adjuvant to enhance mucosal CD8⁺ T cell responses during vaccination and improve protection against mucosal viral challenge. However, the ATRA formulation is incompatible with most recombinant vaccines, and the teratogenic potential of ATRA at high doses limits its usage in many clinical settings. We hypothesized that increasing in vivo production of retinoic acid (RA) during vaccination with a DNA vector expressing retinaldehyde dehydrogenase 2 (RALDH2), the rate-limiting enzyme in RA biosynthesis, could similarly provide enhanced programming of mucosal homing to T cell responses while avoiding teratogenic effects. Administration of a RALDH2- expressing plasmid during immunization with a HIVgag DNA vaccine resulted in increased systemic and mucosal CD8⁺ T cell numbers with an increase in both effector and central memory T cells. Moreover, mice that received RALDH2 plasmid during DNA vaccination were more resistant to intravaginal challenge with a recombinant vaccinia virus expressing the same HIVgag antigen (VACVgag). Thus, RALDH2 can be used as an alternative adjuvant to ATRA during DNA vaccination leading to an increase in both systemic and mucosal T cell immunity and better protection from viral infection at mucosal sites.

Immune Dysfunction as a Cause and Consequence of Malnutrition

Malnutrition, which encompasses under- and overnutrition, is responsible for an enormous morbidity and mortality burden globally. Malnutrition results from disordered nutrient assimilation but is also characterized by recurrent infections and chronic inflammation, implying an underlying immune defect. Defects emerge before birth via modifications in the immunoepigenome of malnourished parents, and these may contribute to intergenerational cycles of malnutrition. This review summarizes key recent studies from experimental animals, in vitro models, and human cohorts, and proposes that immune dysfunction is both a cause and a consequence of malnutrition. Focusing on childhood undernutrition, we highlight gaps in current understanding of immune dysfunction in malnutrition, with a view to therapeutically targeting immune pathways as a novel means to reduce morbidity and mortality.

Undernourished children principally die of common infections, and immune defects are consistently demonstrated in under- and overnutrition.

Parental malnutrition leads to epigenetic modifications of infant immune and metabolic genes.

Healthy gut development relies on sensing of dietary nutrients, commensal, and pathogenic microbes via immune receptors.

Recurrent infections, chronic inflammation, and enteropathy compound clinical malnutrition by altering gut structure and function.

Immune cell activation and systemic proinflammatory mediator levels are increased in malnutrition.

Malnutrition impairs immune priming by DC and monocytes, and impairs effector memory T cell function.

Immune dysfunction can directly drive pathological processes in malnutrition, including malabsorption, increased metabolic demand, dysregulation of the growth hormone and HPA axes, and greater susceptibility to infection.

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.

Induction of cellular and molecular immunomodulatory pathways by vitamin A and flavonoids

INTRODUCTION

A detailed study of reports on the immunomodulatory properties of vitamin A and select flavonoids may pave the way for using these natural compounds or compounds with similar structures in novel drug and vaccine designs against infectious and autoimmune diseases and cancers.

AREAS COVERED

Intracellular transduction pathways, cellular differentiation and functional immunomodulatory responses have been reviewed. The reported studies encompass in vitro, in vivo preclinical and clinical studies that address the role of vitamin A and select flavonoids in induction of innate and adaptive B- and T-cell responses, including TH1, TH2 and regulatory T cells (Treg).

EXPERT OPINION

While the immunomodulatory role of vitamin A, and related compounds, is well-established in many preclinical studies, its role in humans has begun to gain wider acceptance. In contrast, the role of flavonoids is mostly controversial in clinical trials, due to the diversity of the various classes of these compounds, and possibly due to the purity and the selected doses of the compounds. However, current preclinical and clinical studies warrant further detailed studies of these promising immunomodulatory compounds.