CD4+ T-cell memory: generation and multi-faceted roles for CD4+ T cells in protective immunity to influenza

A Recombinant Mosaic HAs Influenza Vaccine Elicits Broad-Spectrum Immune Response and Protection of Influenza a Viruses

The annual co-circulation of two influenza A subtypes, H1N1 and H3N2, viruses in humans poses significant public health threats worldwide. However, the continuous antigenic drift and shift of influenza viruses limited the effectiveness of current seasonal influenza vaccines, necessitating the development of new vaccines against both seasonal and pandemic viruses. One potential solution to this challenge is to improve inactivated vaccines by including multiple T-cell epitopes. In this study, we designed stabilized trimeric recombinant mosaic HA proteins named HAm, which contain the most potential HA T-cell epitopes of seasonal influenza A virus. We further evaluated the antigenicity, hemagglutinin activity, and structural integrity of HAm and compared its immunogenicity and efficacy to a commercial quadrivalent inactivated influenza vaccine (QIV) in mice. Our results demonstrated that the HAm vaccine was able to induce broadly cross-reactive antibodies and T-cell responses against homologous, heterologous, and heterosubtypic influenza-naive mice. Additionally, the HAm antigens outperformed QIV vaccine antigens by eliciting protective antibodies against panels of antigenically drifted influenza vaccine strains from 2009 to 2024 and protecting against ancestral viruses' lethal challenge. These results suggest that the HAm vaccine is a promising potential candidate for future universal seasonal and pandemic influenza vaccine development.

The dynamics and longevity of circulating CD4+ memory T cells depend on cell age and not the chronological age of the host

Quantifying the kinetics with which memory T cell populations are generated and maintained is essential for identifying the determinants of the duration of immunity. The quality and persistence of circulating CD4 effector memory (TEM) and central memory (TCM) T cells in mice appear to shift with age, but it is unclear whether these changes are driven by the aging host environment, by cell age effects, or both. Here, we address these issues by combining DNA labelling methods, established fate-mapping systems, a novel reporter mouse strain, and mathematical models. Together, these allow us to quantify the dynamics of both young and established circulating memory CD4 T cell subsets, within both young and old mice. We show that that these cells and their descendents become more persistent the longer they reside within the TCM and TEM pools. This behaviour may limit memory CD4 T cell diversity by skewing TCR repertoires towards clones generated early in life, but may also compensate for functional defects in new memory cells generated in old age.

The dynamics and longevity of circulating CD4+ memory T cells depend on cell age and not the chronological age of the host

Quantifying the kinetics with which memory T cell populations are generated and maintained is essential for identifying the determinants of the duration of immunity. The quality and persistence of circulating CD4+ effector memory (TEM) and central memory (TCM) T cells in mice appear to shift with age, but it is unclear whether these changes are driven by the aging host environment, by cell age effects, or both. Here we address these issues by combining DNA labelling methods, established fate-mapping systems, a novel reporter mouse strain, and mathematical models. Together, these allow us to quantify the dynamics of both young and established circulating memory CD4+ T cell subsets, within both young and old mice. We show that that these cells and their descendents become more persistent the longer they reside within the TCM and TEM pools. This behaviour may limit memory CD4 T cell diversity by skewing TCR repertoires towards clones generated early in life, but may also compensate for functional defects in new memory cells generated in old age.

Diet-induced obesity affects influenza disease severity and transmission dynamics in ferrets

Obesity, and the associated metabolic syndrome, is a risk factor for increased disease severity with a variety of infectious agents, including influenza virus. Yet, the mechanisms are only partially understood. As the number of people, particularly children, living with obesity continues to rise, it is critical to understand the role of host status on disease pathogenesis. In these studies, we use a diet-induced obese ferret model and tools to demonstrate that, like humans, obesity resulted in notable changes to the lung microenvironment, leading to increased clinical disease and viral spread to the lower respiratory tract. The decreased antiviral responses also resulted in obese animals shedding higher infectious virus for a longer period, making them more likely to transmit to contacts. These data suggest that the obese ferret model may be crucial to understanding obesity's impact on influenza disease severity and community transmission and a key tool for therapeutic and intervention development for this high-risk population.

Diet-induced obesity impacts influenza disease severity and transmission dynamics in ferrets

Obesity, and the associated metabolic syndrome, is a risk factor for increased disease severity with a variety of infectious agents, including influenza virus. Yet the mechanisms are only partially understood. As the number of people, particularly children, living with obesity continues to rise, it is critical to understand the role of host status on disease pathogenesis. In these studies, we use a novel diet-induced obese ferret model and new tools to demonstrate that like humans, obesity resulted in significant changes to the lung microenvironment leading to increased clinical disease and viral spread to the lower respiratory tract. The decreased antiviral responses also resulted in obese animals shedding higher infectious virus for longer making them more likely to transmit to contacts. These data suggest the obese ferret model may be crucial to understanding obesity's impact on influenza disease severity and community transmission, and a key tool for therapeutic and intervention development for this high-risk population.

Teaser

A new ferret model and tools to explore obesity's impact on respiratory virus infection, susceptibility, and community transmission.

SARS-CoV-2 infection risk is higher in vaccinated patients with inflammatory autoimmune diseases or liver transplantation treated with mycophenolate due to an impaired antiviral immune response: results of the extended follow up of the RIVALSA prospective cohort

Background

A relevant proportion of immunocompromised patients did not reach a detectable seroconversion after a full primary vaccination cycle against SARS-CoV-2. The effect of different immunosuppressants and the potential risks for SARS-CoV-2 infection in these subjects is largely unknown.

Methods

Patients from the Rivalsa prospective, observational cohort study with planned anti SARS-CoV-2 third dose mRNA vaccination between October and December 2021 were asked to participate to this follow-up study. Patients were asked about eventual confirmed positivity to SARS-CoV-2 infection within 6 months from the third dose and to undergo a blood draw to evaluate seroconversion status after the additional vaccine shot.

Results

19 out of 114 patients taking part in the survey developed a confirmed SARS-CoV-2 infection; we identified mycophenolate treatment as an independent predictor of an increased risk of infection even after the third vaccine dose (OR: 5.20, 95% CI: 1.70-20.00, p=0.0053). This result is in agreement with the in vitro evidence that MMF impairs both B and T lymphocytes driven immune responses (reduction both in memory B cells producing anti-spike antibodies and in proliferating CD4+ and CD8+ T cells).

Conclusions

Immunocompromised patients need an additional vaccine administration to reach a detectable seroconversion, thus fostering a more personalized approach to their clinical management. Moreover, patients undergoing mycophenolate treatment show a specific increased infection risk, with respect to other immunosuppressants thus supporting a closer monitoring of their health status.

Early peripheral blood lymphocyte subsets and cytokines in predicting the severity of influenza B virus pneumonia in children

Background

Children with influenza B virus infection have a higher susceptibility and higher severity of illness. The activation and disorder of immune function play an important role in the severity of influenza virus infection. This study aims to investigate whether early lymphocyte count and cytokines can provide predictive value for the progression in children with influenza B virus pneumonia.

Methods

A retrospective cohort study was conducted to analyze the clinical data of children with influenza B virus pneumonia from December 1, 2021, to March 31, 2022, in the National Children's Regional Medical Center (Shengjing Hospital of China Medical University). According to the severity of the disease, the children were divided into a mild group and a severe group, and the clinical characteristics, routine laboratory examination, lymphocyte subsets, and cytokines were compared.

Results

A total of 93 children with influenza B virus pneumonia were enrolled, including 70 cases in the mild group and 23 cases in the severe group. Univariate analysis showed that drowsiness, dyspnea, white blood cell (WBC), lymphocytes, monocytes, procalcitonin, alanine aminotransferase (ALT), aspartate aminotransferase (AST), creatine kinase-MB (CK-MB), lactate dehydrogenase (LDH), fibrinogen (FIB), Immunoglobulin M (IgM), lung consolidation, total T cell count, CD4⁺ T cell count, CD8⁺ T cell count, NK cell count, NK cell % and B cell % had statistical differences between the mild and severe groups (P<0.05). In multivariate logistic regression analysis, reduced ALT (OR = 1.016), FIB (OR = 0.233), CD8⁺ T cell count (OR = 0.993) and NK cell count (OR = 0.987) were independently associated with the development of severe influenza B virus pneumonia.

Conclusions

The levels of T lymphocytes and NK cells were related to the progression of influenza B virus pneumonia in children, and the reduction of CD8⁺ T cell count and NK cell count can be used as independent risk factors for predicting the severity of influenza B virus pneumonia.

STAT1 Controls the Functionality of Influenza-Primed CD4 T Cells but Therapeutic STAT4 Engagement Maximizes Their Antiviral Impact

It is generally accepted that influenza A virus (IAV) infection promotes a Th1-like CD4 T cell response and that this effector program underlies its protective impact. Canonical Th1 polarization requires cytokine-mediated activation of the transcription factors STAT1 and STAT4 that synergize to maximize the induction of the "master regulator" Th1 transcription factor, T-bet. Here, we determine the individual requirements for these transcription factors in directing the Th1 imprint primed by influenza infection in mice by tracking virus-specific wild-type or T-bet-deficient CD4 T cells in which STAT1 or STAT4 is knocked out. We find that STAT1 is required to protect influenza-primed CD4 T cells from NK cell-mediated deletion and for their expression of hallmark Th1 attributes. STAT1 is also required to prevent type I IFN signals from inhibiting the induction of the Th17 master regulator, Rorγt, in Th17-prone T-bet-/- cells responding to IAV. In contrast, STAT4 expression does not appreciably impact the phenotypic or functional attributes of wild-type or T-bet-/- CD4 T cell responses. However, cytokine-mediated STAT4 activation in virus-specific CD4 T cells enhances their Th1 identity in a T-bet-dependent manner, indicating that influenza infection does not promote maximal Th1 induction. Finally, we show that the T-bet-dependent protective capacity of CD4 T cell effectors against IAV is optimized by engaging both STAT1 and STAT4 during Th1 priming, with important implications for vaccine strategies aiming to generate T cell immunity.

Immunomodulatory Mechanism and Potential Application of Dental Pulp-Derived Stem Cells in Immune-Mediated Diseases

Dental pulp stem cells (DPSCs) are mesenchymal stem cells (MSCs) derived from dental pulp tissue, which have high self-renewal ability and multi-lineage differentiation potential. With the discovery of the immunoregulatory ability of stem cells, DPSCs have attracted much attention because they have similar or even better immunomodulatory effects than MSCs from other sources. DPSCs and their exosomes can exert an immunomodulatory ability by acting on target immune cells to regulate cytokines. DPSCs can also migrate to the lesion site to differentiate into target cells to repair the injured tissue, and play an important role in tissue regeneration. The aim of this review is to summarize the molecular mechanism and target cells of the immunomodulatory effects of DPSCs, and the latest advances in preclinical research in the treatment of various immune-mediated diseases, providing new reflections for their clinical application. DPSCs may be a promising source of stem cells for the treatment of immune-mediated diseases.

Mettl14 sustains FOXP3 expression to promote the differentiation and functions of induced-regulatory T cells via the mTOR signaling pathway

Induced regulatory T cell (iTregs) can be generated in vitro. Thus, iTregs-based therapeutics are receiving increased attention for their potential to treat autoimmune diseases and prevent transplant rejection. However, iTregs fail to maintain FoxP3 expression and suppressive activity, which limits their clinical application. Increasing lines of evidence suggest that methyltransferase-like 14 (METTL14), a critical component of the m6A writer complex, regulates the stability and function of the Treg cells. However, beyond meeting the epigenetic modification of Treg cells, whether Mettl14 plays a role in the fate determination of iTregs is unclear. Here, we systemically investigated the potential function of METTL14 in iTregs differentiation and regulatory activity. In our study, iTregs were generated from CD4⁺ naïve T cells under iTreg-polarizing conditions, we found that the expression of METTL14 was increased in iTregs compared with CD4⁺ naïve T cells. Subsequently, the expression of METTL14 was knocked down by siRNA-METTL14 interference in CD4⁺ naïve T cells and cultured under iTreg-polarizing conditions. According to the results, Mettl14 deficiency resulted in the disruption of iTregs differentiation evidenced by the limited FoxP3 expression. Meanwhile, inflammatory cytokines such as IFN-γ and IL-17a were upregulated in cultured iTregs. We next determined the functional change in METTL14-deficient iTregs. The results of the colitis development in Rag1^-/- mice and CFSE assays revealed that loss of METTL14 significantly compromised the suppressive function of iTregs in vivo and in vitro. We further checked the altered signaling pathway in METTL14-deficient iTregs. We found that reduced METTL14 leads to activation of the mTOR pathway with increased p-mTOR and p-p70S6K, which are known to modulate the suppressive function of iTregs. In conclusion, our study revealed that Mettl14 plays a critical role in the development and suppressive function of iTregs in vitro and could thus serve as a regulatory element for stabilizing iTregs in cell-based therapy.

Optimizing the Boosting Schedule of Subunit Vaccines Consisting of BCG and "Non-BCG" Antigens to Induce Long-Term Immune Memory

Boosting Bacillus Calmette-Guérin (BCG) with subunit vaccine is expected to induce long-term protection against tuberculosis (TB). However, it is urgently needed to optimize the boosting schedule of subunit vaccines, which consists of antigens from or not from BCG, to induce long-term immune memory. To address it two subunit vaccines, Mtb10.4-HspX (MH) consisting of BCG antigens and ESAT6-CFP10 (EC) consisting of antigens from the region of difference (RD) of Mycobacterium tuberculosis (M. tuberculosis), were applied to immunize BCG-primed C57BL/6 mice twice or thrice with different intervals, respectively. The long-term antigen-specific immune responses and protective efficacy against M. tuberculosis H37Ra were determined. The results showed that following BCG priming, MH boosting twice at 12-24 weeks or EC immunizations thrice at 12-16-24 weeks enhanced the number and function of long-lived memory T cells with improved protection against H37Ra, while MH boosting thrice at 12-16-24 weeks or twice at 8-14 weeks and EC immunizations twice at 12-24 weeks or thrice at 8-10-14 weeks didn't induce long-term immunity. It suggests that following BCG priming, both BCG antigens MH boosting twice and "non-BCG" antigens EC immunizations thrice at suitable intervals induce long-lived memory T cell-mediated immunity.

A new nomogram model for prognosis of hepatocellular carcinoma based on novel gene signature that regulates cross-talk between immune and tumor cells

Background

The combined application of immune cells and specific biomarkers related to the tumor immune microenvironment has a better predictive value for the prognosis of HCC. The purpose of this study is to construct a new prognostic model based on immune-related genes that regulate cross-talk between immune and tumor cells to assess the prognosis and explore possible mechanisms.

Method

The immune cell abundance ratio of 424 cases in the TCGA-LIHC database is obtained through the CIBERSORT algorithm. The differential gene analysis and cox regression analysis is used to screen IRGs. In addition, the function of IRGs was preliminarily explored through the co-culture of M2 macrophages and HCC cell lines. The clinical validation, nomogram establishment and performing tumor microenvironment score were validated.

Results

We identified 4 immune cells and 9 hub genes related to the prognosis. Further, we identified S100A9, CD79B, TNFRSF11B as an IRGs signature, which is verified in the ICGC and GSE76427 database. Importantly, IRGs signature is closely related to the prognosis, tumor microenvironment score, clinical characteristics and immunotherapy, and nomogram combined with clinical characteristics is more conducive to clinical promotion. In addition, after co-culture with M2 macrophages, the migration capacity and cell pseudopod of MHCC97H increased significantly. And CD79B and TNFRSF11B were significantly down-regulated in MHCC97H, Huh7 and LM3, while S100A9 was up-regulated.

Conclusion

We constructed an IRGs signature and discussed possible mechanisms. The nomogram established based on IRGs can accurately predict the prognosis of HCC patients. These findings may provide a suitable therapeutic target for HCC.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-022-09465-9.

An In Vitro System to Model the Establishment and Reactivation of HIV-1 Latency in Primary Human CD4+ T Cells

HIV-1 establishes latency primarily by infecting activated CD4+ T cells that later return to quiescence as memory cells. Latency allows HIV-1 to evade immune responses and to persist during antiretroviral therapy, which represents an important problem in clinical practice. Here we describe both the original and a simplified version of HIV-1 latency models that mimics this process using replication competent viruses. Our model allows generation of large numbers of latently infected CD4+ T cell to dissect molecular mechanisms of HIV latency and reactivation.

Multiple developmental pathways lead to the generation of CD4 T-cell memory

Long-term immunological memory mediated by CD4 T cells provides a rapid protection against previously encountered pathogens or antigens. However, it is still controversial how memory CD4 T cells are generated and maintained. Unclear definitions of T-cell memory may be partially responsible for this controversy. It is becoming clear that diverse pathways are responsible for the differentiation and long-term persistence of memory T cells. We herein discuss the diversity of memory cell generation, describing a novel population of resting memory CD4 T cells and their precursors.

Heterologous expression of Intimin and IpaB fusion protein in Lactococcus lactis and its mucosal delivery elicit protection against pathogenicity of Escherichia coli O157 and Shigella flexneri in a murine model

Escherichia coli O157:H7 and Shigella flexneri are the predominant diarrhoeal pathogens and those strains producing Shiga toxins cause life-threatening sequelae including hemolytic uremic syndrome (HUS) upon their entry into the host. Intimate adherence of E. coli O157 and invasion of S. flexneri in the host intestinal epithelial cells is mainly mediated by Intimin and IpaB proteins, respectively. In this study, we have synthesized chimera of immunodominant regions of Intimin (eae) and IpaB (ipaB) designated as EI and expressed it in Lactococcus lactis (LL-EI) to develop a combinatorial oral vaccine candidate. Immune parameters and protective efficacy of orally administered LL-EI were assessed in the murine model. Significant EI-specific serum IgG, IgA, and fecal IgA antibody titer were observed in the LL-EI group. Considerable increase in EI-specific splenocyte proliferation and a concurrent upregulation of both Th1 and Th2 cytokines was observed in LL-EI immunized mice. Flow cytometry analysis also revealed a significant increase in CD4 and CD8 cell counts in LL-EI immunized group compared to PBS, LL control group.In vitro studies using LL-EI immunized mice sera showed substantial protection against bacterial adhesion and invasion caused by E. coli O157 and Shigella flexneri¸ respectively. LL-EI immunized group challenged with E. coli O157 ceased fecal shedding within 6 days, and mice challenged with S. flexneri showed 93% survival with minimal bacterial load in the lungs. Our results indicate that LL-EI immunization elicits systemic, mucosal and cell-mediated immune responses, and can be a promising candidate for oral vaccine development against these pathogens.

Identification of Differentially Expressed miRNAs in the Response of Spleen CD4+ T Cells to Electroacupuncture in Senescence-Accelerated Mice

Immunological aging impairs immune system protection in the body and is associated with high morbidity and mortality in aged people. Electroacupuncture (EA) has been proven to boost immunity. The purpose of this study was to identify the effect of EA on miRNA expression in the immune system of senescence-accelerated mouse P8 (SAMP8) mice. We utilized SAMP8 mice as an aging model and detected the altered expression of miRNAs in CD4⁺ T cells after EA stimulation by deep sequencing. Differentially expressed miRNAs in different groups were identified using Venn diagrams and functional analysis was performed. The effect of EA on the expression of the identified miRNAs was investigated in natural-aged C57BL/6J mice and the biological functions of miR-301a-3p and miR-181a-1-3p in CD4⁺ T cells were identified. Four upregulated and two downregulated miRNAs were identified in group I (EA-SAMP8 vs. shEA-SAMP8); 41 upregulated and nine downregulated miRNAs were identified in group II (EA-SAMP8 vs. SAMP8); 42 upregulated and eight downregulated miRNAs were identified in group III (shEA-SAMP8 vs. SAMP8). The three groups shared four overlapping differentially expressed miRNAs, and 10 miRNAs were only found in group II. Gene Ontology enrichment analysis of these 14 miRNAs revealed that their target genes were enriched in 229 "biological process" categories. Kyoto Encyclopedia of Genes and Genomes pathway analysis showed that the targets were significantly mapped in 76 pathways. Furthermore, five significant pathways were involved in T cell differentiation. MiRNA-gene-net showed that miR-582-5p, miR-17-5p, miR-144-3p, miR-451a, and miR-301a-3p regulated the most important target genes in these pathways. The expression of these miRNAs was also regulated by EA in aged C57BL/6J mice. In addition, miR-301a-3p was involved in regulating the expression of inflammatory factors by mediating the differentiation of CD4⁺ T cells in C57BL/6J mice. Analysis of miRNAs indicated that EA contributes to maintaining the balance of CD4⁺ T cell differentiation in the aging immune system. These results provide novel insights into the effect of EA in immunological aging.

Enhanced Cell Division Is Required for the Generation of Memory CD4 T Cells to Migrate Into Their Proper Location

CD4 T cell memory is fundamental for long-lasting immunity and effective secondary responses following infection or vaccination. We have previously found that memory CD4 T cells specific for systemic antigens preferentially reside in the bone marrow (BM) and arise from splenic CD49b⁺T-bet⁺ CD4 T cells. However, how BM-homing memory precursors are generated during an immune reaction is unknown. We show here that BM memory precursors are generated via augmented rates of cell division throughout a primary immune response. Treatment with the cytostatic drug cyclophosphamide or blockade of the CD28/B7 co-stimulatory pathway at the beginning of the contraction phase abrogates the generation of BM memory precursors. We determine that, following a critical number of cell divisions, memory precursors downregulate CCR7 and upregulate IL-2Rβ, indicating that loss of CCR7 and gain of IL-2 signal are required for the migration of memory precursors toward the BM.

Long-Lasting Mucosal and Systemic Immunity against Influenza A Virus Is Significantly Prolonged and Protective by Nasal Whole Influenza Immunization with Mucosal Adjuvant N3 and DNA-Plasmid Expressing Flagellin in Aging In- and Outbred Mice

Background: Vaccination is commonly used to prevent and control influenza infection in humans. However, improvements in the ease of delivery and strength of immunogenicity could markedly improve herd immunity. The aim of this pre-clinical study is to test the potential improvements to existing intranasal delivery of formalin-inactivated whole Influenza A vaccines (WIV) by formulation with a cationic lipid-based adjuvant (N3). Additionally, we combined WIV and N3 with a DNA-encoded TLR5 agonist secreted flagellin (pFliC(-gly)) as an adjuvant, as this adjuvant has previously been shown to improve the effectiveness of plasmid-encoded DNA antigens. Methods: Outbred and inbred mouse strains were intranasally immunized with unadjuvanted WIV A/H1N1/SI 2006 or WIV that was formulated with N3 alone. Additional groups were immunized with WIV and N3 adjuvant combined with pFliC(-gly). Homo and heterotypic humoral anti-WIV immune responses were assayed from serum and lung by ELISA and hemagglutination inhibition assay. Homo and heterotypic cellular immune responses to WIV and Influenza A NP were also determined. Results: WIV combined with N3 lipid adjuvant the pFliC(-gly) significantly increased homotypic influenza specific serum antibody responses (>200-fold), increased the IgG2 responses, indicating a mixed Th1/Th2-type immunity, and increased the HAI-titer (>100-fold). Enhanced cell-mediated IFNγ secreting influenza directed CD4⁺ and CD8⁺ T cell responses (>40-fold) to homotypic and heterosubtypic influenza A virus and peptides. Long-term and protective immunity was obtained. Conclusions: These results indicate that inactivated influenza virus that was formulated with N3 cationic adjuvant significantly enhanced broad systemic and mucosal influenza specific immune responses. These responses were broadened and further increased by incorporating DNA plasmids encoding FliC from S. typhimurum as an adjuvant providing long lasting protection against heterologous Influenza A/H1N1/CA09pdm virus challenge.

Multifunctional cytokine production reveals functional superiority of memory CD4 T cells

T cell protective immunity is associated with multifunctional memory cells that produce several different cytokines. Currently, our understanding of when and how these cells are generated is limited. We have used an influenza virus mouse infection model to investigate whether the cytokine profile of memory T cells is reflective of primary responding cells or skewed toward a distinct profile. We found that, in comparison to primary cells, memory T cells tended to make multiple cytokines simultaneously. Analysis of the timings of release of cytokine by influenza virus‐specific T cells, demonstrated that primary responding CD4 T cells from lymphoid organs were unable to produce a sustained cytokine response. In contrast CD8 T cells, memory CD4 T cells, and primary responding CD4 T cells from the lung produced a sustained cytokine response throughout the restimulation period. Moreover, memory CD4 T cells were more resistant than primary responding CD4 T cells to inhibitors that suppress T cell receptor signaling. Together, these data suggest that memory CD4 T cells display superior cytokine responses compared to primary responding cells. These data are key to our ability to identify the cues that drive the generation of protective memory CD4 T cells following infection.

Mesenchymal Stem Cells Improve Rheumatoid Arthritis Progression by Controlling Memory T Cell Response

In the last years, mesenchymal stem cell (MSC)-based therapies have become an interesting therapeutic opportunity for the treatment of rheumatoid arthritis (RA) due to their capacity to potently modulate the immune response. RA is a chronic autoimmune inflammatory disorder with an incompletely understood etiology. However, it has been well described that peripheral tolerance defects and the subsequent abnormal infiltration and activation of diverse immune cells into the synovial membrane, are critical for RA development and progression. Moreover, the imbalance between the immune response of pro-inflammatory and anti-inflammatory cells, in particular between memory Th17 and memory regulatory T cells (Treg), respectively, is well admitted to be associated to RA immunopathogenesis. In this context, MSCs, which are able to alter the frequency and function of memory lymphocytes including Th17, follicular helper T (Tfh) cells and gamma delta (γδ) T cells while promoting Treg cell generation, have been proposed as a candidate of choice for RA cell therapy. Indeed, given the plasticity of memory CD4⁺ T cells, it is reasonable to think that MSCs will restore the balance between pro-inflammatory and anti-inflammatory memory T cells populations deregulated in RA leading to prompt their therapeutic function. In the present review, we will discuss the role of memory T cells implicated in RA pathogenesis and the beneficial effects exerted by MSCs on the phenotype and functions of these immune cells abnormally regulated in RA and how this regulation could impact RA progression.

Advax augments B and T cell responses upon influenza vaccination via the respiratory tract and enables complete protection of mice against lethal influenza virus challenge

Administration of influenza vaccines via the respiratory tract has potential benefits over conventional parenteral administration, inducing immunity directly at the site of influenza exposure as well as being needle free. In this study, we investigated the suitability of Advax™, a stable particulate polymorph of inulin, also referred to as delta inulin, as a mucosal adjuvant for whole inactivated influenza vaccine (WIV) administered either as a liquid or dry powder formulation. Spray freeze-drying produced Advax-adjuvanted WIV powder particles in a size range (1-5 μm) suitable for inhalation. The physical and biological characteristics of both WIV and Advax remained unaltered both by admixing WIV with Advax and by spray freeze drying. Upon intranasal or pulmonary immunization, both liquid and dry powder formulations containing Advax induced significantly higher systemic, mucosal and cellular immune responses than non-adjuvanted WIV formulations. Furthermore, pulmonary immunization with Advax-adjuvanted WIV led to robust memory B cell responses along with an increase of lung localization factors i.e. CXCR3, CD69, and CD103. A less pronounced but still positive effect of Advax was seen on memory T cell responses. In contrast to animals immunized with WIV alone, all animals pulmonary immunized with a single dose of Advax-adjuvanted WIV were fully protected with no visible clinical symptoms against a lethal dose of influenza virus. These data confirm that Advax is a potent mucosal adjuvant that boosts vaccine-induced humoral and cellular immune responses both in the lung and systemically with major positive effects on B-cell memory and complete protection against live virus. Hence, respiratory tract immunization, particularly via the lungs, with Advax-adjuvanted WIV formulation as a liquid or dry powder is a promising alternative to parenteral influenza vaccination.

Nucleoside-modified mRNA immunization elicits influenza virus hemagglutinin stalk-specific antibodies

Currently available influenza virus vaccines have inadequate effectiveness and are reformulated annually due to viral antigenic drift. Thus, development of a vaccine that confers long-term protective immunity against antigenically distant influenza virus strains is urgently needed. The highly conserved influenza virus hemagglutinin (HA) stalk represents one of the potential targets of broadly protective/universal influenza virus vaccines. Here, we evaluate a potent broadly protective influenza virus vaccine candidate that uses nucleoside-modified and purified mRNA encoding full-length influenza virus HA formulated in lipid nanoparticles (LNPs). We demonstrate that immunization with HA mRNA-LNPs induces antibody responses against the HA stalk domain of influenza virus in mice, rabbits, and ferrets. The HA stalk-specific antibody response is associated with protection from homologous, heterologous, and heterosubtypic influenza virus infection in mice.

Seasonal Influenza Split Vaccines Confer Partial Cross-Protection against Heterologous Influenza Virus in Ferrets When Combined with the CAF01 Adjuvant

Influenza epidemics occur annually, and estimated 5–10% of the adult population and 20–30% of children will become ill from influenza infection. Seasonal vaccines primarily work through the induction of neutralizing antibodies against the principal surface antigen hemagglutinin (HA). This important role of HA-specific antibodies explains why previous pandemics have emerged when new HAs have appeared in circulating human viruses. It has long been recognized that influenza virus-specific CD4(+) T cells are important in protection from infection through direct effector mechanisms or by providing help to B cells and CD8(+) T cells. However, the seasonal influenza vaccine is poor at inducing CD4(+) T-cell responses and needs to be combined with an adjuvant facilitating this response. In this study, we applied the ferret model to investigate the cross-protective efficacy of a heterologous trivalent influenza split-virion (TIV) vaccine adjuvanted with the CAF01 adjuvant, with proven ability to induce CD4(+) T-cell and antibody responses in mice, ferrets, pigs, primates, and humans. Our results indicate that CAF01-adjuvanted vaccine induces HA inhibition (HAI)-independent protection after heterologous challenge, manifested as reduced viral load and fever. On the other hand, we observe increased inflammation in the airways and more neutrophil and mononuclear cell infiltration in these ferrets when compared with optimally protected animals, i.e., ferrets receiving the same vaccine but a homologous challenge. This suggest that HAI-independent immunity induced by TIV + CAF01 can reduce viral shedding and systemic disease symptoms, but does not reduce local inflammation in the nasal cavity.

Multigenic DNA vaccine induces protective cross-reactive T cell responses against heterologous influenza virus in nonhuman primates

Recent avian and swine-origin influenza virus outbreaks illustrate the ongoing threat of influenza pandemics. We investigated immunogenicity and protective efficacy of a multi-antigen (MA) universal influenza DNA vaccine consisting of HA, M2, and NP antigens in cynomolgus macaques. Following challenge with a heterologous pandemic H1N1 strain, vaccinated animals exhibited significantly lower viral loads and more rapid viral clearance when compared to unvaccinated controls. The MA DNA vaccine induced robust serum and mucosal antibody responses but these high antibody titers were not broadly neutralizing. In contrast, the vaccine induced broadly-reactive NP specific T cell responses that cross-reacted with the challenge virus and inversely correlated with lower viral loads and inflammation. These results demonstrate that a MA DNA vaccine that induces strong cross-reactive T cell responses can, independent of neutralizing antibody, mediate significant cross-protection in a nonhuman primate model and further supports development as an effective approach to induce broad protection against circulating and emerging influenza strains.

Selective pre-priming of HA-specific CD4 T cells restores immunological reactivity to HA on heterosubtypic influenza infection

A hallmark of the immune response to influenza is repeated encounters with proteins containing both genetically conserved and variable components. Therefore, the B and T cell repertoire is continually being remodeled, with competition between memory and naïve lymphocytes. Our previous work using a mouse model of secondary heterosubtypic influenza infection has shown that this competition results in a focusing of CD4 T cell response specificity towards internal virion proteins with a selective decrease in CD4 T cell reactivity to the novel HA epitopes. Strikingly, this shift in CD4 T cell specificity was associated with a diminished anti-HA antibody response. Here, we sought to determine whether the loss in HA-specific reactivity that occurs as a consequence of immunological memory could be reversed by selectively priming HA-specific CD4 T cells prior to secondary infection. Using a peptide-based priming strategy, we found that selective expansion of the anti-HA CD4 T cell memory repertoire enhanced HA-specific antibody production upon heterosubtypic infection. These results suggest that the potentially deleterious consequences of repeated exposure to conserved influenza internal virion proteins could be reversed by vaccination strategies that selectively arm the HA-specific CD4 T cell compartment. This could be a potentially useful pre-pandemic vaccination strategy to promote accelerated neutralizing antibody production on challenge with a pandemic influenza strain that contains few conserved HA epitopes.

Staphylococcus aureus-dependent septic arthritis in murine knee joints: local immune response and beneficial effects of vaccination

Staphylococcus aureus is the major cause of human septic arthritis and osteomyelitis, which deserve special attention due to their rapid evolution and resistance to treatment. The progression of the disease depends on both bacterial presence in situ and uncontrolled disruptive immune response, which is responsible for chronic disease. Articular and bone infections are often the result of blood bacteremia, with the knees and hips being the most frequently infected joints showing the worst clinical outcome. We report the development of a hematogenous model of septic arthritis in murine knees, which progresses from an acute to a chronic phase, similarly to what occurs in humans. Characterization of the local and systemic inflammatory and immune responses following bacterial infection brought to light specific signatures of disease. Immunization of mice with the vaccine formulation we have recently described (4C-Staph), induced a strong antibody response and specific CD4+ effector memory T cells, and resulted in reduced bacterial load in the knee joints, a milder general inflammatory state and protection against bacterial-mediated cellular toxicity. Possible correlates of protection are finally proposed, which might contribute to the development of an effective vaccine for human use.

Heterosubtypic T-Cell Immunity to Influenza in Humans: Challenges for Universal T-Cell Influenza Vaccines

Influenza A virus (IAV) remains a significant global health issue causing annual epidemics, pandemics, and sporadic human infections with highly pathogenic avian or swine influenza viruses. Current inactivated and live vaccines are the mainstay of the public health response to influenza, although vaccine efficacy is lower against antigenically distinct viral strains. The first pandemic of the twenty-first century underlined the urgent need to develop new vaccines capable of protecting against a broad range of influenza strains. Such “universal” influenza vaccines are based on the idea of heterosubtypic immunity, wherein immune responses to epitopes conserved across IAV strains can confer protection against subsequent infection and disease. T-cells recognizing conserved antigens are a key contributor in reducing viral load and limiting disease severity during heterosubtypic infection in animal models. Recent studies undertaken during the 2009 H1N1 pandemic provided key insights into the role of cross-reactive T-cells in mediating heterosubtypic protection in humans. This review focuses on human influenza to discuss the epidemiological observations that underpin cross-protective immunity, the role of T-cells as key players in mediating heterosubtypic immunity including recent data from natural history cohort studies and the ongoing clinical development of T-cell-inducing universal influenza vaccines. The challenges and knowledge gaps for developing vaccines to generate long-lived protective T-cell responses is discussed.

Identification of a CD4 T-cell epitope in the hemagglutinin stalk domain of pandemic H1N1 influenza virus and its antigen-driven TCR usage signature in BALB/c mice

The stalk region of the influenza virus hemagglutinin is relatively well conserved compared with the globular head domain, which makes it a potential target for use as a universal vaccine against influenza. However, the role of CD4 T cells in the hemagglutinin stalk-specific immune response is not clear. Here we identified a mouse CD4 T-cell epitope that encompasses residues HA2_113-131 from the hemagglutinin stalk domain after a sub-lethal infection of influenza. In response to stimulation with the identified epitope, splenocytes derived from the infected mice showed significant polyfunctionality as shown by IL-2, TNF-α and IFN-γ production as well as degranulation. Moreover, mice immunized with the peptide corresponding to this CD4 T-cell epitope exhibited interindividual sharing of the CD4 T-cell receptor β sequences, and they had a higher survival rate following a challenge with a lethal dose of pandemic H1N1 influenza virus. Thus, our data demonstrated a crucial role of hemagglutinin stalk-specific CD4 T cells in the host immune response against influenza virus infection.

Presentation of high antigen-dose by splenic B220(lo) B cells fosters a feedback loop between T helper type 2 memory and antibody isotype switching

Effective humoral immunity ensues when antigen presentation by B cells culminates in productive cooperation with T lymphocytes. This collaboration, however, remains ill-defined because naive antigen-specific B cells are rare and difficult to track in vivo. Herein, we used a defined transfer model to examine how B lymphocytes, as antigen-presenting cells, shape the development of T-cell memory suitable for generation of relevant antibody responses. Specifically, we examined how B cells presenting different doses of antigen during the initial priming phase shape the development of CD4 T-cell memory and its influence on humoral immunity. The findings indicate that B cells presenting low dose of antigen favour the development of T helper type 1 (Th1) type memory, while those presenting a high antigen dose yielded better Th2 memory cells. The memory Th2 cells supported the production of antibodies by effector B cells and promoted isotype switching to IgG1. Moreover, among the B-cell subsets tested for induction of Th2 memory, the splenic but not peritoneal B220(lo) cells were most effective in sustaining Th2 memory development as well as immunoglobulin isotype switching, and this function involved a tight control by programmed death 1-programmed death ligand 2 interactions.

Identification of the Zinc Finger Protein ZRANB2 as a Novel Maternal Lipopolysaccharide-binding Protein That Protects Embryos of Zebrafish against Gram-negative Bacterial Infections

Zinc finger ZRANB2 proteins are widespread in animals, but their functions and mechanisms remain poorly defined. Here we clearly demonstrate that ZRANB2 is a newly identified LPS-binding protein present abundantly in the eggs/embryos of zebrafish. We also show that recombinant ZRANB2 (rZRANB2) acts as a pattern recognition receptor capable of identifying the bacterial signature molecule LPS as well as binding the Gram-negative bacteria Escherichia coli, Vibrio anguilarum, and Aeromonas hydrophila and functions as an antibacterial effector molecule capable of directly killing the bacteria. Furthermore, we reveal that N-terminal residues 11-37 consisting of the first ZnF_RBZ domain are indispensable for ZRANB2 antimicrobial activity. Importantly, microinjection of rZRANB2 into early embryos significantly enhanced the resistance of the embryos against pathogenic A. hydrophila challenge, and this enhanced bacterial resistance was markedly reduced by co-injection of anti-ZRANB2 antibody. Moreover, precipitation of ZRANB2 in the embryo extracts by preincubation with anti-ZRANB2 antibody caused a marked decrease in the antibacterial activity of the extracts against the bacteria tested. In addition, the N-terminal peptide Z1/37 or Z11/37 with in vitro antibacterial activity also promoted the resistance of embryos against A. hydrophila, but the peptide Z38/198 without in vitro antibacterial activity did not. Collectively, these results indicate that ZRANB2 is a maternal LPS-binding protein that can protect the early embryos of zebrafish against pathogenic attacks, a novel role ever assigned to ZRANB2 proteins. This work also provides new insights into the immunological function of the zinc finger proteins that are widely distributed in various animals.

Immunogenicity of HLA Class I and II Double Restricted Influenza A-Derived Peptides

The aim of the present study was to identify influenza A-derived peptides which bind to both HLA class I and -II molecules and by immunization lead to both HLA class I and class II restricted immune responses. Eight influenza A-derived 9-11mer peptides with simultaneous binding to both HLA-A*02:01 and HLA-DRB1*01:01 molecules were identified by bioinformatics and biochemical technology. Immunization of transgenic HLA-A*02:01/HLA-DRB1*01:01 mice with four of these double binding peptides gave rise to both HLA class I and class II restricted responses by CD8 and CD4 T cells, respectively, whereas four of the double binding peptides did result in HLA-A*02:01 restricted responses only. According to their cytokine profile, the CD4 T cell responses were of the Th2 type. In influenza infected mice, we were unable to detect natural processing in vivo of the double restricted peptides and in line with this, peptide vaccination did not decrease virus titres in the lungs of intranasally influenza challenged mice. Our data show that HLA class I and class II double binding peptides can be identified by bioinformatics and biochemical technology. By immunization, double binding peptides can give rise to both HLA class I and class I restricted responses, a quality which might be of potential interest for peptide-based vaccine development.

Recombinant Bivalent Fusion Protein rVE Induces CD4+ and CD8+ T-Cell Mediated Memory Immune Response for Protection Against Yersinia enterocolitica Infection

Studies investigating the correlates of immune protection against Yersinia infection have established that both humoral and cell mediated immune responses are required for the comprehensive protection. In our previous study, we established that the bivalent fusion protein (rVE) comprising immunologically active regions of Y. pestis LcrV (100–270 aa) and YopE (50–213 aa) proteins conferred complete passive and active protection against lethal Y. enterocolitica 8081 challenge. In the present study, cohort of BALB/c mice immunized with rVE or its component proteins rV, rE were assessed for cell mediated immune responses and memory immune protection against Y. enterocolitica 8081. rVE immunization resulted in extensive proliferation of both CD4 and CD8 T cell subsets; significantly high antibody titer with balanced IgG1: IgG2a/IgG2b isotypes (1:1 ratio) and up-regulation of both Th1 (TNF-α, IFN-γ, IL-2, and IL-12) and Th2 (IL-4) cytokines. On the other hand, rV immunization resulted in Th2 biased IgG response (11:1 ratio) and proliferation of CD4+ T-cell; rE group of mice exhibited considerably lower serum antibody titer with predominant Th1 response (1:3 ratio) and CD8+ T-cell proliferation. Comprehensive protection with superior survival (100%) was observed among rVE immunized mice when compared to the significantly lower survival rates among rE (37.5%) and rV (25%) groups when IP challenged with Y. enterocolitica 8081 after 120 days of immunization. Findings in this and our earlier studies define the bivalent fusion protein rVE as a potent candidate vaccine molecule with the capability to concurrently stimulate humoral and cell mediated immune responses and a proof of concept for developing efficient subunit vaccines against Gram negative facultative intracellular bacterial pathogens.

Regulatory T Cells Modulate DNA Vaccine Immunogenicity at Early Time via Functional CD4(+) T Cells and Antigen Duration

The development of an effective vaccine against HIV has proved to be difficult. Many factors including natural regulatory T cells (Treg cells) can dampen the CD8 T-cell immunogenicity. In this study, we aimed to understand how Treg cells control CD8(+) T-cell immune responses during DNA prime-boost immunization. Animals were immunized with plasmid HIV IIIB gp120 DNA following elimination of Treg cells by administration of anti-CD25 neutralizing antibody. Results demonstrated that the pool size of CD4(+) T cells producing both IL-2 and/or IFN-γ (CD4(+)/IL-2(+)/IFN-γ(+)) was increased solely during the priming phase. An increment of tetramer binding and intracellular cytokine IFN-γ expression, however, were elevated in both primary and secondary stages in CD8(+) T cells. The speed of antigen clearance was also investigated by using DNA luciferase. Surprisingly, DNA luciferase expression was declined to basal level over the ensuing observation period when Treg cells were depleted. Importantly, we found for the first time that DNA expression pattern in Treg-depleted animals was similar to that of the regular memory phase. Moreover, in mice that were exposed to antigen over 5 days prior to Treg cell depletion, CD8(+) T-cell memory response was not affected. Thus, in the present study, we propose a new concept and prove that the enhanced immune response following the depletion of Treg cells during the priming phase likely adds one more set of memory response to the immune system. Taken together, our findings support the notion that Treg cells control DNA vaccine immunogenicity at an early time via antigen duration and functional CD4(+) T-cell responses.

MHC Class II-Restricted Epitopes Containing an Oxidoreductase Activity Prompt CD4(+) T Cells with Apoptosis-Inducing Properties

Abrogating an unwanted immune response toward a specific antigen without compromising the entire immune system is a hoped-for goal in immunotherapy. Instead of manipulating dendritic cells and suppressive regulatory T cells, depleting effector T cells or blocking their co-stimulatory pathways, we describe a method to specifically inhibit the presentation of an antigen eliciting an unwanted immune reaction. Inclusion of an oxidoreductase motif within the flanking residues of MHC class II epitopes polarizes CD4(+) T cells to cytolytic cells capable of inducing apoptosis in antigen presenting cells (APCs) displaying cognate peptides through MHC class II molecules. This novel function results from an increased synapse formation between both cells. Moreover, these cells eliminate by apoptosis bystander CD4(+) T cells activated at the surface of the APC. We hypothesize that they would thereby block the recruitment of cells of alternative specificity for the same autoantigen or cells specific for another antigen associated with the pathology, providing a system by which response against multiple antigens linked with the same disease can be suppressed. These findings open the way toward a novel form of antigen-specific immunosuppression.

Low expression of activation marker CD69 and chemokine receptors CCR5 and CXCR3 on memory T cells after 2009 H1N1 influenza A antigen stimulation in vitro following H1N1 vaccination of HIV-infected individuals

Unlike well-studied antibody responses to pandemic 2009 H1N1 influenza A virus vaccines in human immunodeficiency virus-infected (HIV+) individuals, less well understood are cell-mediated immune (CMI) responses to this antigen in this susceptible population. We investigated such influenza-specific CMI responses in 61 HIV+ individuals and in 20 HIV-negative (HIV-) healthy controls. Each was vaccinated with a single licensed dose of inactivated, split-virion vaccine comprised of the influenza A/California/7/2009 (H1N1) virus-like strain. Cells collected just prior to vaccination and at 1 and 3 months afterwards were stimulated in vitro with dialyzed vaccine antigen and assayed by flow cytometry for cytokines TNF-α, IFN-γ, IL-2, and IL-10, for degranulation marker CD107a, as well as phenotypes of memory T-cell subpopulations. Comparable increases of cytokine-producing and CD107a-expressing T cells were observed in both HIV+ subjects and healthy HIV-controls. However, by 3 months post-vaccination, in vitro antigen stimulation of peripheral blood mononuclear cells induced greater expansion in controls of both CD4 and CD8 central memory and effector memory T cells, as well as higher expression of the activation marker CD69 and chemokine receptors CCR5 and CXCR3 than in HIV+ subjects. We concluded CD4+ and CD8+ memory T cells produce cytokines at comparable levels in both groups, whereas the expression after in vitro stimulation of molecules critical for cell migration to infection sites are lower in the HIV+ than in comparable controls. Further immunization strategies against influenza are needed to improve the CMI responses in people living with HIV.

Prime-boost vaccination strategy with bacillus Calmette-Guérin (BCG) and liposomized alpha-crystalline protein 1 reinvigorates BCG potency

Bacillus Calmette-Guérin (BCG) remains the only available and most widely administered vaccine against Mycobacterium tuberculosis (Mtb), yet it fails to protect vaccinated individuals either from primary infection or reactivation of latent tuberculosis (TB). Despite BCG's variable efficacy against TB, the fact remains that BCG imparts protection in children against the disease, indicating that BCG possesses a wide protective antigenic repertoire. However, its failure to impart protection in adulthood can be linked to its failure to generate long-lived memory response and elicitation of an inadequate immune response against latency-associated antigens. Therefore, to improve the protective efficacy of BCG, a novel vaccination strategy is required. Consequently, in the present study, we have exploited the vaccination potential of liposomized α-crystalline 1 (Acr1L), a latency-associated antigen to induce enduring protective immunity against Mtb in BCG-primed animals. It is noteworthy that an increase in the multi-functional [interferon (IFN)-γ(hi) /tumour necrosis factor (TNF)-α(hi) ] CD4 and CD8 T cells were observed in BCG-primed and Acr1L-boosted (BCG-Acr1L) animals, compared to BCG alone. Further, substantial expansion of both central memory (CD44(hi) /CD62L(hi) ) and effector memory (CD44(hi) /CD62L(lo) ) populations of CD4 and CD8 T cells was noted. Importantly, BCG-Acr1L exhibited significantly better protection than BCG, as evidenced by a reduction in the bacterial burden and histopathological data of the lungs. In essence, BCG-Acr1L could be a potent future vaccination strategy to reinvigorate BCG potency.

IRF3 deficiency impacts granzyme B expression and maintenance of memory T cell function in response to viral infection

The role of interferon regulatory factor 3 (IRF3) in the innate immune response to infection has been well studied. However, less is known about IRF3 signaling in shaping the adaptive T cell response. To determine the role of IRF3 in the generation and maintenance of effective anti-viral T cell responses, mice deficient in IRF3 were infected with a potentially persistent virus, Theiler's murine encephalomyelitis virus (TMEV) or with a model acute infection, influenza A virus (IAV). IRF3 was required to prevent TMEV persistence and induce robust TMEV specific effector T cell responses at the site of infection. This defect was more pronounced in the memory phase with an apparent lack of TMEV-specific memory T cells expressing granzyme B (GrB) in IRF3 deficient mice. In contrast, IRF3 had no effect on antigen specific T cell responses at the effector stage during IAV infection. However, memory T cell responses to IAV were also impaired in IRF3 deficient mice. Furthermore, addition of cytokines during peptide restimulation could not restore GrB expression in IRF3 deficient memory T cells. Taken together, IRF3 plays an important role in the maintenance of effective anti-viral T cell memory responses.

Early effector cells survive the contraction phase in malaria infection and generate both central and effector memory T cells

CD4 T cells orchestrate immunity against blood-stage malaria. However, a major challenge in designing vaccines to the disease is poor understanding of the requirements for the generation of protective memory T cells (Tmem) from responding effector T cells (Teff) in chronic parasite infection. In this study, we use a transgenic mouse model with T cells specific for the merozoite surface protein (MSP)-1 of Plasmodium chabaudi to show that activated T cells generate three distinct Teff subsets with progressive activation phenotypes. The earliest observed Teff subsets (CD127(-)CD62L(hi)CD27(+)) are less divided than CD62L(lo) Teff and express memory genes. Intermediate (CD62L(lo)CD27(+)) effector subsets include the most multicytokine-producing T cells, whereas fully activated (CD62L(lo)CD27(-)) late effector cells have a terminal Teff phenotype (PD-1(+), Fas(hi), AnnexinV(+)). We show that although IL-2 promotes expansion, it actually slows terminal effector differentiation. Using adoptive transfer, we show that only early Teff survive the contraction phase and generate the terminal late Teff subsets, whereas in uninfected recipients, they become both central and effector Tmem. Furthermore, we show that progression toward full Teff activation is promoted by increased duration of infection, which in the long-term promotes Tem differentiation. Therefore, we have defined markers of progressive activation of CD4 Teff at the peak of malaria infection, including a subset that survives the contraction phase to make Tmem, and show that Ag and cytokine levels during CD4 T cell expansion influence the proportion of activated cells that can survive contraction and generate memory in malaria infection.

Phase II, randomized, open, controlled study of AS03-adjuvanted H5N1 pre-pandemic influenza vaccine in children aged 3 to 9 years: follow-up of safety and immunogenicity persistence at 24 months post-vaccination

Background

An AS03-adjuvanted H5N1 influenza vaccine elicited broad and persistent immune responses with an acceptable safety profile up to 6 months following the first vaccination in children aged 3–9 years.

Methods

In this follow-up of the Phase II study, we report immunogenicity persistence and safety at 24 months post-vaccination in children aged 3–9 years. The randomized, open-label study assessed two doses of H5N1 A/Vietnam/1194/2004 influenza vaccine (1·9 μg or 3·75 μg hemagglutinin antigen) formulated with AS03_A or AS03_B (11·89 mg or 5·93 mg tocopherol, respectively). Control groups received seasonal trivalent influenza vaccine. Safety was assessed prospectively and included potential immune-mediated diseases (pIMDs). Immunogenicity was assessed by hemagglutination-inhibition assay 12 and 24 months after vaccination; cross-reactivity and cell-mediated responses were also assessed. (NCT00502593).

Results

The safety population included 405 children. Over 24 months, five events fulfilled the criteria for pIMDs, of which four occurred in H5N1 vaccine recipients, including uveitis (n = 1) and autoimmune hepatitis (n = 1), which were considered to be vaccine-related. Overall, safety profiles of the vaccines were clinically acceptable. Humoral immune responses at 12 and 24 months were reduced versus those observed after the second dose of vaccine, although still within the range of those observed after the first dose. Persistence of cell-mediated immunity was strong, and CD4⁺ T cells with a T_H1 profile were observed.

Conclusions

Two doses of an AS03-adjuvanted H5N1 influenza vaccine in children showed low but persistent humoral immune responses and a strong persistence of cell-mediated immunity, with clinically acceptable safety profiles up to 24 months following first vaccination.

Rabbit nasal immunization against influenza by dry-powder form of chitosan nanospheres encapsulated with influenza whole virus and adjuvants

Influenza virus is one of the main causes of respiratory diseases in human. Although different vaccines have been produced during past decades, there is still a huge demand for a safe influenza vaccine with the ability to induce mucosal immune responses and sufficient protection, especially in elderly patients. In this study, chitosan nanospheres were employed as the drug delivery system. Influenza virus, CpG oligodeoxynucleotide (CpG ODN) and Quillaja saponins (QS) were incorporated in this nanospheric system. Three doses of dry powder nanosphere vaccine were nasally administered to rabbits on days 0, 45 and 60, followed by a final booster injection on day 75. Both humoral and cellular immune responses were investigated. Hemagglutination inhibition (HI) antibody titer was elevated in all groups compared to the control group at the end of vaccination in rabbits receiving nanospheres loaded with virus and CpG, CH(WV+CpG) (P<0.001). Rabbit serum IgG raised significantly in all the vaccinated groups, with the highest responses in CH(WV+CpG) group. CH(WV+CpG) and CH(WV) induced significant sIgA titers (P<0.001). CpG adjuvant also showed a prominent role in the stimulation and secretion of of IL-2 and IFN-γ cytokines (3 and 3.5 fold increase, respectively). Finally, as CH(WV+CpG) depicted to be effective in induction of humoral and cellular immune responses after nasal administration, this nanoparticulate adjuvant could be identified as an efficient adjuvant/delivery system for mucosal immunization against influenza virus.

Multipronged CD4(+) T-cell effector and memory responses cooperate to provide potent immunity against respiratory virus

Over the last decade, the known spectrum of CD4(+) T-cell effector subsets has become much broader, and it has become clear that there are multiple dimensions by which subsets with a particular cytokine commitment can be further defined, including their stage of differentiation, their location, and, most importantly, their ability to carry out discrete functions. Here, we focus on our studies that highlight the synergy among discrete subsets, especially those defined by helper and cytotoxic function, in mediating viral protection, and on distinctions between CD4(+) T-cell effectors located in spleen, draining lymph node, and in tissue sites of infection. What emerges is a surprising multiplicity of CD4(+) T-cell functions that indicate a large arsenal of mechanisms by which CD4(+) T cells act to combat viruses.

Long-term booster schedules with AS03A-adjuvanted heterologous H5N1 vaccines induces rapid and broad immune responses in Asian adults

BACKGROUND

The pandemic potential of avian influenza A/H5N1 should not be overlooked, and the continued development of vaccines against these highly pathogenic viruses is a public health priority.

METHODS

This open-label extension booster study followed a Phase III study of 1206 adults who had received two 3.75 μg doses of primary AS03A-adjuvanted or non-adjuvanted H5N1 split-virus vaccine (A/Vietnam/1194/2004; clade 1) (NCT00449670). The aim of the extension study was to evaluate different timings for heterologous AS03A-adjuvanted booster vaccination (A/Indonesia/5/2005; clade 2.1) given at Month 6, 12, or 36 post-primary vaccination. Immunogenicity was assessed 21 days after each booster vaccination and the persistence of immune responses against the primary vaccine strain (A/Vietnam) and the booster strain (A/Indonesia) was evaluated up to Month 48 post-primary vaccination. Reactogenicity and safety were also assessed.

RESULTS

After booster vaccination given at Month 6, HI antibody responses to primary vaccine, and booster vaccine strains were markedly higher with one dose of AS03A-H5N1 booster vaccine in the AS03A-adjuvanted primary vaccine group compared with two doses of booster vaccine in the non-adjuvanted primary vaccine group. HI antibody responses were robust against the primary and booster vaccine strains 21 days after boosting at Month 12 or 36. At Month 48, in subjects boosted at Month 6, 12, or 36, HI antibody titers of ≥1:40 against the booster strain persisted in 39.2%, 61.2%, and 95.6% of subjects, respectively. Neutralizing antibody responses and cell-mediated immune responses also showed that AS03A-H5N1 heterologous booster vaccination elicited robust immune responses within 21 days of boosting at Month 6, 12, or 36 post-primary vaccination. The booster vaccine was well tolerated, and no safety concerns were raised.

CONCLUSIONS

In Asian adults primed with two doses of AS03A-adjuvanted H5N1 pandemic influenza vaccine, strong cross-clade anamnestic antibody responses were observed after one dose of AS03A-H5N1 heterologous booster vaccine given at Month 6, 12, or 36 after priming, suggesting that AS03A-adjuvanted H5N1 vaccines may provide highly flexible prime-boost schedules. Although immunogenicity decreased with time, vaccinated populations could potentially be protected for up to three years after vaccination, which is likely to far exceed the peak of the a pandemic.

Protective immunity to H7N9 influenza viruses elicited by synthetic DNA vaccine

Despite an intensive vaccine program influenza infections remain a major health problem, due to the viruses' ability to change its envelope glycoprotein hemagglutinin (HA), through shift and drift, permitting influenza to escape protection induced by current vaccines or natural immunity. Recently a new variant, H7N9, has emerged in China causing global concern. First, there have been more than 130 laboratory-confirmed human infections resulting in an alarmingly high death rate (32.3%). Second, genetic changes found in H7N9 appear to be associated with enabling avian influenza viruses to spread more effectively in mammals, thus transmitting infections on a larger scale. Currently, no vaccines or drugs are effectively able to target H7N9. Here, we report the rapid development of a synthetic consensus DNA vaccine (pH7HA) to elicit potent protective immunity against the H7N9 viruses. We show that pH7HA induces broad antibody responses that bind to divergent HAs from multiple new members of the H7N9 family. These antibody responses result in high-titer HAI against H7N9. Simultaneously, this vaccine induces potent polyfunctional effector CD4 and CD8T cell memory responses. Animals vaccinated with pH7HA are completely protected from H7N9 virus infection and any morbidity associated with lethal challenge. This study establishes that this synthetic consensus DNA vaccine represents a new tool for targeting emerging infection, and more importantly, its design, testing and development into seed stock for vaccine production in a few days in the pandemic setting has significant implications for the rapid deployment of vaccines protecting against emerging infectious diseases.

Early Decision: Effector and Effector Memory T Cell Differentiation in Chronic Infection

As effector memory T cells (Tem) are the predominant population elicited by chronic parasitic infections, increasing our knowledge of their function, survival and derivation, as phenotypically and functionally distinct from central memory and effector T cells will be critical to vaccine development for these diseases. In some infections, memory T cells maintain increased effector functions, however; this may require the presence of continued antigen, which can also lead to T cell exhaustion. Alternatively, in the absence of antigen, only the increase in the number of memory cells remains, without enhanced functionality as central memory. In order to understand the requirement for antigen and the potential for longevity or protection, the derivation of each type of memory must be understood. A thorough review of the data establishes the existence of both memory (Tmem) precursors and effector T cells (Teff) from the first hours of an immune response. This suggests a new paradigm of Tmem differentiation distinct from the proposition that Tmem only appear after the contraction of Teff. Several signals have been shown to be important in the generation of memory T cells, such as the integrated strength of “signals 1-3” of antigen presentation (antigen receptor, co-stimulation, cytokines) as perceived by each T cell clone. Given that these signals integrated at antigen presentation cells have been shown to determine the outcome of Teff and Tmem phenotypes and numbers, this decision must be made at a very early stage. It would appear that the overwhelming expansion of effector T cells and the inability to phenotypically distinguish memory T cells at early time points has masked this important decision point. This does not rule out an effect of repeated stimulation or chronic inflammatory milieu on populations generated in these early stages. Recent studies suggest that Tmem are derived from early Teff, and we suggest that this includes Tem as well as Tcm. Therefore, we propose a testable model for the pathway of differentiation from naïve to memory that suggests that Tem are not fully differentiated effector cells, but derived from central memory T cells as originally suggested by Sallusto et al. in 1999, but much debated since.

Immunodominance in CD4 T-cell responses: implications for immune responses to influenza virus and for vaccine design

CD4 T cells play a primary role in regulating immune responses to pathogenic organisms and to vaccines. Antigen-specific CD4 T cells provide cognate help to B cells, a requisite event for immunoglobulin switch and affinity maturation of B cells that produce neutralizing antibodies and also provide help to cytotoxic CD8 T cells, critical for their expansion and persistence as memory cells. Finally, CD4 T cells may participate directly in pathogen clearance via cell-mediated cytotoxicity or through production of cytokines. Understanding the role of CD4 T-cell immunity to viruses and other pathogens, as well as evaluation of the efficacy of vaccines, requires insight into the specificity of CD4 T cells. This review focuses on the events within antigen-presenting cells that focus CD4 T cells toward a limited number of peptide antigens within the pathogen or vaccine. The molecular events are discussed in light of the special challenges that the influenza virus poses, owing to the high degree of genetic variability, unpredictable pathogenicity and the repeated encounters that human populations face with this highly infectious pathogenic organism.