Molecular regulation of interleukin-2 expression by CD28 co-stimulation and anergy

Streptococcal Arginine Deiminase Inhibits T Lymphocyte Differentiation In Vitro

Pathogenic microbes use arginine-metabolizing enzymes as an immune evasion strategy. In this study, the impact of streptococcal arginine deiminase (ADI) on the human peripheral blood T lymphocytes function in vitro was studied. The comparison of the effects of parental strain (Streptococcus pyogenes M49-16) with wild type of ArcA gene and its isogenic mutant with inactivated ArcA gene (Streptococcus pyogenes M49-16delArcA) was carried out. It was found that ADI in parental strain SDSC composition resulted in a fivefold decrease in the arginine concentration in human peripheral blood mononuclear cell (PBMC) supernatants. Only parental strain SDSCs suppressed anti-CD2/CD3/CD28-bead-stimulated mitochondrial dehydrogenase activity and caused a twofold decrease in IL-2 production in PBMC. Flow cytometry analysis revealed that ADI decreased the percentage of CM (central memory) and increased the proportion of TEMRA (terminally differentiated effector memory) of CD4+ and CD8+ T cells subsets. Enzyme activity inhibited the proliferation of all CD8+ T cell subsets as well as CM, EM (effector memory), and TEMRA CD4+ T cells. One of the prominent ADI effects was the inhibition of autophagy processes in CD8+ CM and EM as well as CD4+ CM, EM, and TEMRA T cell subsets. The data obtained confirm arginine's crucial role in controlling immune reactions and suggest that streptococcal ADI may downregulate adaptive immunity and immunological memory.

"IL-2 immunotherapy for targeting regulatory T cells in autoimmunity"

FOXP3+ regulatory T cells (Treg) are indispensable for immune homoeostasis and for the prevention of autoimmune diseases. Interleukin-2 (IL-2) signalling is critical in all aspects of Treg biology. Consequences of defective IL-2 signalling are insufficient numbers or dysfunction of Treg and hence autoimmune disorders in human and mouse. The restoration and maintenance of immune homoeostasis remain central therapeutic aims in the field of autoimmunity. Historically, broadly immunosuppressive drugs with serious side-effects have been used for the treatment of autoimmune diseases or prevention of organ-transplant rejection. More recently, ex vivo expanded or in vivo stimulated Treg have been shown to induce effective tolerance in clinical trials supporting the clinical benefit of targeting natural immunosuppressive mechanisms. Given the central role of exogenous IL-2 in Treg homoeostasis, a new and promising focus in drug development are IL-2-based approaches for in vivo targeted expansion of Treg or for enhancement of their suppressive activity. In this review, we summarise the role of IL-2 in Treg biology and consequences of dysfunctional IL-2 signalling pathways. We then examine evidence of efficacy of IL-2-based biological drugs targeting Treg with specific focus on therapeutic candidates in clinical trials and discuss their limitations.

New immunosuppressive agents in transplantation

Immunosuppressive agents have enabled the development of allogenic transplantation during the last 40 years, allowing considerable improvement in graft survival. However, several issues remain such as the nephrotoxicity of calcineurin inhibitors, the cornerstone of immunosuppressive regimens and/or the higher risk of opportunistic infections and cancers. Most immunosuppressive agents target T cell activation and may not be efficient enough to prevent allo-immunization in the long term. Finally, antibody mediated rejection due to donor specific antibodies strongly affects allograft survival. Many drugs have been tested in the last decades, but very few have come to clinical use. The most recent one is CTLA4-Ig (belatacept), a costimulation blockade molecule that targets the second signal of T cell activation and is associated with a better long term kidney function than calcineurin inhibitors, despite an increased risk of acute cellular rejection. The research of new maintenance long-term immunosuppressive agents focuses on costimulation blockade. Agents inhibiting CD40-CD40 ligand interaction may enable a good control of both T cells and B cells responses. Anti-CD28 antibodies may promote regulatory T cells. Agents targeting this costimulation pathways are currently evaluated in clinical trials. Immunosuppressive agents for ABMR treatment are scarce since anti-CD20 agent rituximab and proteasome inhibitor bortezomib have failed to demonstrate an interest in ABMR. New drugs focusing on antibodies removal (imlifidase), B cell and plasmablasts (anti-IL-6/IL-6R, anti-CD38…) and complement inhibition are in the pipeline, with the challenge of their evaluation in such a heterogeneous pathology.

NDRG1 is induced by antigen-receptor signaling but dispensable for B and T cell self-tolerance

Peripheral tolerance prevents the initiation of damaging immune responses by autoreactive lymphocytes. While tolerogenic mechanisms are tightly regulated by antigen-dependent and independent signals, downstream pathways are incompletely understood. N-myc downstream-regulated gene 1 (NDRG1), an anti-cancer therapeutic target, has previously been implicated as a CD4⁺ T cell clonal anergy factor. By RNA-sequencing, we identified Ndrg1 as the third most upregulated gene in anergic, compared to naïve follicular, B cells. Ndrg1 is upregulated by B cell receptor activation (signal one) and suppressed by co-stimulation (signal two), suggesting that NDRG1 may be important in B cell tolerance. However, though Ndrg1^-/- mice have a neurological defect mimicking NDRG1-associated Charcot-Marie-Tooth (CMT4d) disease, primary and secondary immune responses were normal. We find that B cell tolerance is maintained, and NDRG1 does not play a role in downstream responses during re-stimulation of in vivo antigen-experienced CD4⁺ T cells, demonstrating that NDGR1 is functionally redundant for lymphocyte anergy.

Lenalidomide bypasses CD28 co-stimulation to reinstate PD-1 immunotherapy by activating Notch signaling

Programmed cell death protein 1 (PD-1) checkpoint blockade therapy requires the CD28 co-stimulatory receptor for CD8⁺ T cell expansion and cytotoxicity. However, CD28 expression is frequently lost in exhausted T cells and during immune senescence, limiting the clinical benefits of PD-1 immunotherapy in individuals with cancer. Here, using a cereblon knockin mouse model that regains in vivo T cell response to lenalidomide, an immunomodulatory imide drug, we show that lenalidomide reinstates the anti-tumor activity of CD28-deficient CD8⁺ T cells after PD-1 blockade. Lenalidomide redirects the CRL4^Crbn ubiquitin ligase to degrade Ikzf1 and Ikzf3 in T cells and unleashes paracrine interleukin-2 (IL-2) and intracellular Notch signaling, which collectively bypass the CD28 requirement for activation of intratumoral CD8⁺ T cells and inhibition of tumor growth by PD-1 blockade. Our results suggest that PD-1 immunotherapy can benefit from a lenalidomide combination when treating solid tumors infiltrated with abundant CD28^- T cells.

Therapeutic potential of interleukin-2 in autoimmune diseases

Autoimmune diseases are characterized by dysregulation and aberrant activation of cells in the immune system. Therefore, restoration of the immune balance represents a promising therapeutic target in autoimmune diseases. Interleukin-2 (IL-2) can promote the expansion and differentiation of different immune cell subsets dose-dependently. At high doses, IL-2 can promote the differentiation and expansion of effector and memory T cells, whereas at low doses, IL-2 can promote the differentiation, survival, and function of regulatory T (T_reg) cells, a CD4⁺ T cell subset that is essential for the maintenance of immune homeostasis and immune tolerance. Therefore, IL-2 exerts immunostimulatory and immunosuppressive effects in autoimmune diseases. The immunoregulatory role of low-dose IL-2 has sparked excitement for the therapeutic exploration of modulating the IL-2-T_reg axis in the context of autoimmune diseases. In this review, we discuss recent advances in the therapeutic potential of IL-2 or IL-2-derived molecules in the treatment of autoimmune diseases.

Prenatal Cadmium Exposure Alters Proliferation in Mouse CD4+ T Cells via LncRNA Snhg7

Objective

Prenatal cadmium (Cd) exposure leads to immunotoxic phenotypes in the offspring affecting coding and non-coding genes. Recent studies have shown that long non-coding RNAs (lncRNAs) are integral to T cell regulation. Here, we investigated the role of long non-coding RNA small nucleolar RNA host gene 7 (lncSnhg7) in T cell proliferation.

Methods

RNA sequencing was used to analyze the expression of lncRNAs in splenic CD4+ T cells with and without CD3/CD28 stimulation. Next, T cells isolated from offspring exposed to control or Cd water throughout mating and gestation were analyzed with and without stimulation with anti-CD3/CD28 beads. Quantitative qPCR and western blotting were used to detect RNA and protein levels of specific genes. Overexpression of a miR-34a mimic was achieved using nucleofection. Apoptosis was measured using flow cytometry and luminescence assays. Flow cytometry was also used to measure T cell proliferation in culture. Finally, lncSnhg7 was knocked down in splenic CD4+ T cells with lentivirus to assess its effect on proliferation.

Results

We identified 23 lncRNAs that were differentially expressed in stimulated versus unstimulated T cells, including lncSnhg7. LncSnhg7 and a downstream protein, GALNT7, are upregulated in T cells from offspring exposed to Cd during gestation. Overexpression of miR-34a, a regulator of lncSnhg7 and GALNT7, suppresses GALNT7 protein levels in primary T cells, but not in a mouse T lymphocyte cell line. The T cells isolated from Cd-exposed offspring exhibit increased proliferation after activation in vitro, but Treg suppression and CD4+ T cell apoptosis are not affected by prenatal Cd exposure. Knockdown on lncSnhg7 inhibits proliferation of CD4+ T cells.

Conclusion

Prenatal Cd exposure alters the expression of lncRNAs during T cell activation. The induction of lncSnhg7 is enhanced in splenic T cells from Cd offspring resulting in the upregulation of GALNT7 protein and increased proliferation following activation. miR-34a overexpression decreased GALNT7 expression and knockdown of lncSnhg7 inhibited proliferation suggesting that the lncSnhg7/miR-34a/GALNT7 is an important pathway in primary CD4+ T cells. These data highlight the need to understand the consequences of environmental exposures on lncRNA functions in non-cancerous cells as well as the effects in utero.

Interleukin-2 and regulatory T cells in rheumatic diseases

Failure of regulatory T (T_reg) cells to properly control immune responses leads invariably to autoimmunity and organ damage. Decreased numbers or impaired function of T_reg cells, especially in the context of inflammation, has been documented in many human autoimmune diseases. Restoration of T_reg cell fitness and/or expansion of their numbers using low-dose natural IL-2, the main cytokine driving T_reg cell survival and function, has demonstrated clinical efficacy in early clinical trials. Genetically modified IL-2 with an extended half-life and increased selectivity for T_reg cells is now in clinical development. Administration of IL-2 combined with therapies targeting other pathways involved in the expression of autoimmune diseases should further enhance its therapeutic potential. Ongoing clinical efforts that capitalize on the early clinical success of IL-2 treatment should bring the use of this cytokine to the forefront of biological treatments for autoimmune diseases.

First-in-human study of the safety, tolerability, pharmacokinetics, and pharmacodynamics of ALPN-101, a dual CD28/ICOS antagonist, in healthy adult subjects

ALPN-101 (ICOSL vIgD-Fc) is an Fc fusion protein of a human inducible T cell costimulatory ligand (ICOSL) variant immunoglobulin domain (vIgD) designed to inhibit the cluster of differentiation 28 (CD28) and inducible T cell costimulator (ICOS) pathways simultaneously. A first-in-human study evaluated the safety, tolerability, pharmacokinetics (PK), and pharmacodynamics (PD) of ALPN-101 in healthy adult subjects. ALPN-101 was generally well-tolerated with no evidence of cytokine release, clinically significant immunogenicity, or severe adverse events following single subcutaneous (SC) doses up to 3 mg/kg or single intravenous (IV) doses up to 10 mg/kg or up to 4 weekly IV doses of up to 1 mg/kg. ALPN-101 exhibited a dose-dependent increase in exposure with an estimated terminal half-life of 4.3-8.6 days and SC bioavailability of 60.6% at 3 mg/kg. Minimal to modest accumulation in exposure was observed with repeated IV dosing. ALPN-101 resulted in a dose-dependent increase in maximum target saturation and duration of high-level target saturation. Consistent with its mechanism of action, ALPN-101 inhibited cytokine production in whole blood stimulated by Staphylococcus aureus enterotoxin B ex vivo, as well as antibody responses to keyhole limpet hemocyanin immunization, reflecting immunomodulatory effects upon T cell and T-dependent B cell responses, respectively. In conclusion, ALPN-101 was well-tolerated in healthy subjects with dose-dependent PK and PD consistent with the known biology of the CD28 and ICOS costimulatory pathways. Further clinical development of ALPN-101 in inflammatory and/or autoimmune diseases is therefore warranted.

T cell markers recount the course of immunosenescence in healthy individuals and chronic kidney disease

Aging results in substantial changes in almost all cellular subpopulations within the immune system, including functional and phenotypic alterations. T lymphocytes, as the main representative population of cellular immunity, have been extensively studied in terms of modifications and adjustments during aging. Phenotypic alterations are attributed to three main mechanisms; a reduction of naïve T cell population with a shift to more differentiated forms, a subsequent oligoclonal expansion of naïve T cells characterized by repertoire restriction, and replicative insufficiency after repetitive activation. These changes and the subsequent phenotypic disorders are comprised in the term "immunosenescence". Similar changes seem to occur in chronic kidney disease, with T cells of young patients resembling those of healthy older individuals. A broad range of surface markers can be utilized to identify immunosenescent T cells. In this review, we will discuss the most important senescence markers and their potential connection with impaired renal function.

Engagement of CD45 alters early signaling events in human T cells co-stimulated through TCR + CD28

Previously our lab has shown that co-stimulation of human T cells through different co-stimulatory molecules tune differentiation to different phenotypes. An open question is where in the signaling pathways induced by the co-stimulation do differences occur that contribute to outcome of differentiation. In this project, we investigate the early signaling process by comparing events that follow engagement of CD45 alone or in association with a co-stimulatory molecule: CD28. CD45 plays a crucial role to initiate T cell signaling by dephosphorylating a negatively regulatory tyrosine residue in Src family kinases such as Lck. First, we observed that engagement of CD45 alone induced signaling in T cells. We observed that TCR/CD3 stimulation with CD45 promoted prolonged Lck association with TCR/CD3 complex and Lck remained associated during TCR/CD3 + CD28 + CD45 stimulation as well. We concluded that Lck association is dependent on TCR/CD3 and CD45 engagement. Hence, CD45 altered early signaling events in T cells.

Revisiting IL-2: Biology and therapeutic prospects

Interleukin-2 (IL-2), the first cytokine that was molecularly cloned, was shown to be a T cell growth factor essential for the proliferation of T cells and the generation of effector and memory cells. On the basis of this activity, the earliest therapeutic application of IL-2 was to boost immune responses in cancer patients. Therefore, it was a surprise that genetic deletion of the cytokine or its receptor led not only to the expected immune deficiency but also to systemic autoimmunity and lymphoproliferation. Subsequent studies established that IL-2 is essential for the maintenance of Foxp3⁺ regulatory T cells (T_reg cells), and in its absence, there is a profound deficiency of T_reg cells and resulting autoimmunity. We now know that IL-2 promotes the generation, survival, and functional activity of T_reg cells and thus has dual and opposing functions: maintaining T_reg cells to control immune responses and stimulating conventional T cells to promote immune responses. It is well documented that certain IL-2 conformations result in selective targeting of T_reg cells by increasing reliance on CD25 binding while compromising CD122 binding. Recent therapeutic strategies have emerged to use IL-2, monoclonal antibodies to IL-2, or IL-2 variants to boost T_reg cell numbers and function to treat autoimmune diseases while dealing with the continuing challenges to minimize the generation of effector and memory cells, natural killer cells, and other innate lymphoid populations.

Epithelial membrane protein 3 (Emp3) downregulates induction and function of cytotoxic T lymphocytes by macrophages via TNF-α production

Tetraspanin membrane protein, epithelial membrane protein 3 (Emp3), is expressed in lymphoid tissues. Herein, we have examined the Emp3 in antigen presenting cell (APC) function in the CD8⁺ cytotoxic T lymphocytes (CTLs) induction. Emp3-overexpressing RAW264.7 macrophage cell line derived from BALB/c mice reduced anti-C57BL/6 alloreactive CTL induction, while Emp3-knockdown RAW264.7 enhanced it compared with parent RAW267.4. Emp3-overexpressing RAW264.7 inhibited, but Emp3-knockdown RAW264.7 augmented, CD8⁺ T cell proliferation, interferon-γ secretion, IL-2 consumption, and IL-2Rα expression on CD8⁺ T cells. The supernatant from co-culture with Emp3-overexpressing RAW264.7 contained higher amount of TNF-α, and TNF- α neutralization significantly restored all these inhibitions and the alloreactive CTL induction. These results suggest that Emp3 in allogeneic APCs possesses the inhibitory function of alloreactive CTL induction by downregulation of IL-2Rα expression CD8⁺ T cells via an increase in TNF-α production. This demonstrates a novel mechanism for regulating CTL induction by Emp3 in APCs through TNF-α production.

α-galactosylceramide generates lung regulatory T cells through the activated natural killer T cells in mice

Our previous study showed that intraperitoneal injection of α-galactosylceramide (α-GalCer) has the ability to activate lung iNKT cells, but α-GalCer-activated iNKT cells do not result in airway inflammation in wild-type (WT) mice. Many studies showed that iNKT cells had the capacity to induce Treg cells, which gave rise to peripheral tolerance. Therefore, we examined the influence of intraperitoneal administration of α-GalCer on the expansion and suppressive activity of lung Treg cells using iNKT cell-knockout mice and co-culture experiments in vitro. We also compared airway inflammation and airway hyperresponsiveness (AHR) after α-GalCer administration in specific anti-CD25 mAb-treated mice. Our data showed that intraperitoneal injection of α-GalCer could promote the expansion of lung Treg cells in WT mice, but not in iNKT cell-knockout mice. However, α-GalCer administration could not boost suppressive activity of Treg cells in WT mice and iNKT cell-knockout mice. Interestingly, functional inactivation of Treg cells could induce airway inflammation and AHR in WT mice treated with α-GalCer. Furthermore, α-GalCer administration could enhance iNKT cells to secrete IL-2, and neutralization of IL-2 reduced the expansion of Treg cells in vivo and in vitro. Thus, intraperitoneal administration of α-GalCer can induce the generation of lung Treg cells in mice through the release of IL-2 by the activated iNKT cells.

Immunomodulators targeting the PD-1/PD-L1 protein-protein interaction: From antibodies to small molecules

Cancer immunotherapy has made great strides in the recent decade, especially in the area of immune checkpoint blockade. The outstanding efficacy, prolonged durability of effect, and rapid assimilation of anti-PD-1 and anti-PD-L1 monoclonal antibodies in clinical practice have been nothing short of a medical breakthrough in the treatment of numerous malignancies. The major advantages of these therapeutic antibodies over their small molecule counterparts have been their high binding affinity and target specificity. However, antibodies do have their flaws including immune-related toxicities, inadequate pharmacokinetics and tumor penetration, and high cost burden to manufacturers and consumers. These limitations hinder broader clinical applications of the antibodies and have heightened interests in developing the alternative small molecule platform that includes peptidomimetics and peptides to target the PD-1/PD-L1 immune checkpoint system. The progress on these small molecule alternatives has been relatively slow compared to that of the antibodies. Fortunately, recent structural studies of the interactions among PD-1, PD-L1, and their respective antibodies have revealed key hotspots on PD-1 and PD-L1 that may facilitate drug discovery efforts for small molecule immunotherapeutics. This review is intended to discuss key concepts in immuno-oncology, describe the successes and shortcomings of PD-1/PD-L1 antibody-based therapies, and to highlight the recent development of small molecule inhibitors of the PD-1/PD-L1 protein-protein interaction.

RNA stability regulates human T cell leukemia virus type 1 gene expression in chronically-infected CD4 T cells

Regulation of expression of HTLV-1 gene products from integrated proviruses plays an important role in HTLV-1-associated disease pathogenesis. Previous studies have shown that T cell receptor (TCR)- and phorbol ester (PMA) stimulation of chronically infected CD4 T cells increases the expression of integrated HTLV-1 proviruses in latently infected cells, however the mechanism remains unknown. Analysis of HTLV-1 RNA and protein species following PMA treatment of the latently HTLV-1-infected, FS and SP T cell lines demonstrated rapid induction of tax/rex mRNA. This rapid increase in tax/rex mRNA was associated with markedly enhanced tax/rex mRNA stability while the stability of unspliced or singly spliced HTLV-1 RNAs did not increase. Tax/rex mRNA in the HTLV-1 constitutively expressing cell lines exhibited high basal stability even without PMA treatment. Our data support a model whereby T cell activation leads to increased HTLV-1 gene expression at least in part through increased tax/rex mRNA stability.

TNF and CD28 Signaling Play Unique but Complementary Roles in the Systemic Recruitment of Innate Immune Cells after Staphylococcus aureus Enterotoxin A Inhalation

Staphylococcus aureus enterotoxins cause debilitating systemic inflammatory responses, but how they spread systemically and trigger inflammatory cascade is unclear. In this study, we showed in mice that after inhalation, Staphylococcus aureus enterotoxin A rapidly entered the bloodstream and induced T cells to orchestrate systemic recruitment of inflammatory monocytes and neutrophils. To study the mechanism used by specific T cells that mediate this process, a systems approach revealed inducible and noninducible pathways as potential targets. It was found that TNF caused neutrophil entry into the peripheral blood, whereas CD28 signaling, but not TNF, was needed for chemotaxis of inflammatory monocytes into blood and lymphoid tissue. However, both pathways triggered local recruitment of neutrophils into lymph nodes. Thus, our findings revealed a dual mechanism of monocyte and neutrophil recruitment by T cells relying on overlapping and nonoverlapping roles for the noninducible costimulatory receptor CD28 and the inflammatory cytokine TNF. During sepsis, there might be clinical value in inhibiting CD28 signaling to decrease T cell-mediated inflammation and recruitment of innate cells while retaining bioactive TNF to foster neutrophil circulation.

Pleiotropic Effects of IL-2 on Cancer: Its Role in Cervical Cancer

IL-2 receptor (IL-2R) signalling is critical for normal lymphocyte proliferation, but its role in cervical cancer is not fully understood. The receptor is composed of three chains: IL-2α, IL-2β, and IL-2γ. Intracellular signalling is initiated by ligand-induced heterodimerization of the IL-2β and IL-2γ chains, resulting in the activation of multiple intracellular kinases. Recently, IL-2R was shown to be expressed on nonhaematopoietic cells, especially on several types of tumour cells. However, the function of this receptor on malignant cells has not been clearly defined. The expression of IL-2R and the production of IL-2 in cervical cancer cells have been documented as well as expression of molecules of the JAK-STAT pathway. In the current review we have highlighted the differences in the responses of molecules downstream from the IL-2R in normal lymphocytes and tumour cells that could explain the presence of tumour cells in an environment in which cytotoxic lymphocytes also exist and compete and also the effect of different concentrations of IL-2 that could activate effector cells of the immune system cells, which favour the elimination of tumour cells, or concentrations that may promote a regulatory microenvironment in which tumour cells can easily grow.

Positive Regulation of Interleukin-2 Expression by a Pseudokinase, Tribbles 1, in Activated T Cells

Tribbles 1 (TRB1), a member of the Tribbles family, is a pseudokinase that is conserved among species and implicated in various human diseases including leukemia, cardiovascular diseases, and metabolic disorders. However, the role of TRB1 in the immune response is not understood. To evaluate this role, we examined regulation of TRB1 expression and the function of TRB1 in interleukin-2 (IL-2) induction in Jurkat cells, a human acute T cell leukemia cell line. We found that TRB1 was strongly induced by phorbol 12-myristate 13-acetate (PMA) and ionomycin in these cells. IL-2 expression was induced in Jurkat cells activated by PMA and ionomycin; however, knockdown of TRB1 resulted in decreased induction of IL-2. TRB1 null Jurkat cells established using the CRISPR/Cas9 system also showed reduction of IL-2 expression on PMA/ionomycin stimulation. TRB1 knockdown also markedly inhibited IL-2 promoter activation. To determine the mechanism of the stimulatory effect on IL-2 induction, we focused on histone deacetylases (HDACs), and found that HDAC1 preferentially interacts with TRB1. TRB1 suppressed the interaction of HDAC1 with nuclear factor of activated T cells 2 (NFAT2), which is a crucial transcription factor for IL-2 induction. These results indicate that TRB1 is a positive regulator of IL-2 induction in activated T cells.

Feeding an army: The metabolism of T cells in activation, anergy, and exhaustion

Through the direct control of infection or by providing cytokine signals to other cellular players, T cells play a central role in the orchestration of the immune response. However, in many disease states, T cells are rendered dysfunctional, unable to carry out their effector functions. As T cell activation is bioenergetically demanding, some T cell dysfunction can have metabolic underpinnings. In this review, we will discuss how T cells are programmed to fuel their effector response, and how programmed or pathologic changes can disrupt their ability to generate the energy needed to proliferate and carry out their critical functions.

Antigen-Specific Regulatory T Cells and Low Dose of IL-2 in Treatment of Type 1 Diabetes

Regulatory T cells (Tregs) play an important role in preventing effector T-cell (Teff) targeting of self-antigens that can lead to tissue destruction in autoimmune settings, including type 1 diabetes (T1D). Autoimmunity is caused in part by an imbalance between Teff and Tregs. Early attempts to treat with immunosuppressive agents have led to serious side effects, thus requiring a more targeted approach. Low-dose IL-2 (LD IL-2) can provide immunoregulation with few side effects by preferentially acting on Tregs to drive tolerance. The concept of LD IL-2 as a therapeutic approach is supported by data in mouse models where autoimmunity is cured and further strengthened by success in human clinical studies in hepatitis C virus-induced vasculitis, chronic graft-versus-host disease, and Alopecia areata. Treatment will require identification of a safe therapeutic window, which is a difficult task given that patients are reported to have deficient or defective IL-2 production or signaling and have experienced mild activation of NK cells and eosinophils with LD IL-2 therapy. In T1D, an LD IL-2 clinical trial concluded that Tregs can be safely expanded in humans; however, the study was not designed to address efficacy. Antigen-specific therapies have also aimed at regulation of the autoimmune response but have been filled with disappointment despite an extensive list of diverse islet antigens tested in humans. This approach could be enhanced through the addition of LD IL-2 to the antigenic treatment regimen to improve the frequency and function of antigen-specific Tregs, without global immunosuppression. Here, we will discuss the use of LD IL-2 and islet antigen to enhance antigen-specific Tregs in T1D and focus on what is known about their immunological impact, their safety, and potential efficacy, and need for better methods to identify therapeutic effectiveness.

Immune homeostasis enforced by co-localized effector and regulatory T cells

FOXP3(+) regulatory T cells (Treg cells) prevent autoimmunity by limiting the effector activity of T cells that have escaped thymic negative selection or peripheral inactivation. Despite the information available about molecular factors mediating the suppressive function of Treg cells, the relevant cellular events in intact tissues remain largely unexplored, and whether Treg cells prevent activation of self-specific T cells or primarily limit damage from such cells has not been determined. Here we use multiplex, quantitative imaging in mice to show that, within secondary lymphoid tissues, highly suppressive Treg cells expressing phosphorylated STAT5 exist in discrete clusters with rare IL-2-positive T cells that are activated by self-antigens. This local IL-2 induction of STAT5 phosphorylation in Treg cells is part of a feedback circuit that limits further autoimmune responses. Inducible ablation of T cell receptor expression by Treg cells reduces their regulatory capacity and disrupts their localization in clusters, resulting in uncontrolled effector T cell responses. Our data thus reveal that autoreactive T cells are activated to cytokine production on a regular basis, with physically co-clustering T cell receptor-stimulated Treg cells responding in a negative feedback manner to suppress incipient autoimmunity and maintain immune homeostasis.

Tuftsin-derived T-peptide prevents cellular immunosuppression and improves survival rate in septic mice

The primary mechanisms of sepsis induced cellular immunesuppression involve immune dysfunction of T lymphocytes and negative immunoregulation of regulatory T cells (Tregs). It has been found that tuftsin is an immune modulating peptide derived from IgG in spleen. T-peptide is one of tuftsin analogs. Herein, we examined the effect of T-peptide on cell-mediated immunity in the presence of lipopolysaccharide (LPS) and the survival rate in septic mice. T-peptide regulated the proliferative ability of CD4⁺CD25⁻ T cells in dual responses. Meanwhile, 10 and 100 μg/ml T-peptides were able to enhance the apoptotic rate of CD4⁺CD25⁻ T cells compared with 1 μg/ml T-peptide, but markedly lowered interleukin (IL)-2 levels. When CD4⁺CD25⁺ Tregs were treated with T-peptide for 24 hours, and co-cultured with normal CD4⁺CD25⁻ T cells, the suppressive ability of CD4⁺CD25⁺ Tregs on CD4⁺CD25⁻ T cells was significantly lowered, along with decreased expression in forkhead/winged helix transcription factor p-3 (Foxp-3) as well as cytotoxic T lymphocyte-associated antigen (CTLA)-4, and secretion of transforming growth factor (TGF)-β. Moreover, T-peptide has the ability to improve outcome of septic mice in a dose- and time- dependent manner, and associated with improvement in the microenvironment of cellular immunosuppression in septic mice.

Ndrg1 is a T-cell clonal anergy factor negatively regulated by CD28 costimulation and interleukin-2

Induction of T-cell clonal anergy involves serial activation of transcription factors, including NFAT and Egr2/3. However, downstream effector mechanisms of these transcription factors are not fully understood yet. Here we identify Ndrg1 as an anergy factor induced by Egr2. Ndrg1 is upregulated by anergic signalling and maintained at high levels in resting anergic T cells. Overexpression of Ndrg1 mimics the anergic state and knockout of the gene prevents anergy induction. Interestingly, Ndrg1 is phosphorylated and degraded by CD28 signalling in a proteasome-dependent manner, explaining the costimulation dependence of anergy prevention. Similarly, IL-2 treatment of anergic T cells, under conditions that lead to the reversal of anergy, also induces Ndrg1 phosphorylation and degradation. Finally, older Ndrg1-deficient mice show T-cell hyperresponsiveness and Ndrg1-deficient T cells aggravate inducible autoimmune inflammation. Thus, Ndrg1 contributes to the maintenance of clonal anergy and inhibition of T-cell-mediated inflammation.

The Role of PKC-θ in CD4+ T Cells and HIV Infection: To the Nucleus and Back Again

Protein kinase C (PKC)-θ is the only member of the PKC family that has the ability to translocate to the immunological synapse between T cells and antigen-presenting cells upon T cell receptor and MHC-II recognition. PKC-θ interacts functionally and physically with other downstream effector molecules to mediate T cell activation, differentiation, and migration. It plays a critical role in the generation of Th2 and Th17 responses and is less important in Th1 and CTL responses. PKC-θ has been recently shown to play a role in the nucleus, where it mediates inducible gene expression in the development of memory CD4+ T cells. This novel PKC (nPKC) can up-regulate HIV-1 transcription and PKC-θ activators such as Prostratin have been used in early HIV-1 reservoir eradication studies. The exact manner of the activation of virus by these compounds and the role of PKC-θ, particularly its nuclear form and its association with NF-κB in both the cytoplasmic and nuclear compartments, needs further precise elucidation especially given the very important role of NF-κB in regulating transcription from the integrated retrovirus. Continued studies of this nPKC isoform will give further insight into the complexity of T cell signaling kinases.

Role of glycine N-methyltransferase in the regulation of T-cell responses in experimental autoimmune encephalomyelitis

Glycine N-methyltransferase (GNMT) is known for its function as a tumor suppressor gene. Since 100% of female Gnmt(-/-) mice developed hepatocellular carcinoma, we hypothesized that Gnmt(-/-) mice may have defective immune surveillance. In this study, we examined the immune modulation of GNMT in T-cell responses using experimental autoimmune encephalomyelitis (EAE). The results showed that EAE severity was reduced significantly in Gnmt(-/-) mice. Pathological examination of the spinal cords revealed that Gnmt(-/-) mice had significantly lower levels of mononuclear cell infiltration and demyelination than the wild-type mice. In addition, quantitative real-time PCR showed that expression levels of proinflammatory cytokines, including interferon (IFN)-γ and interleukin (IL)-17A, were much lower in the spinal cord of Gnmt(-/-) than in that of wild-type mice. Accordingly, myelin oligodendrocyte glycoprotein (MOG)-specific T-cell proliferation and induction of T-helper (Th)1 and Th17 cells were markedly suppressed in MOG(35-55)-induced Gnmt(-/-) mice. Moreover, the number of regulatory T (Treg) cells was increased significantly in these mice. When the T-cell receptor was stimulated, the proliferative capacity and the activation status of mTOR-associated downstream signaling were decreased significantly in Gnmt(-/-) CD4(+) T cells via an IL-2- and CD25-independent manner. Moreover, GNMT deficiency enhanced the differentiation of Treg cells without affecting the differentiation of Th1 and Th17 cells. Furthermore, the severity of EAE in mice adoptive transferred with GNMT-deficient CD4(+) T cells was much milder than in those with wild-type CD4(+) T cells. In summary, our findings suggest that GNMT is involved in the pathogenesis of EAE and plays a crucial role in the regulation of CD4(+) T-cell functions.

Immunomodulation of human intestinal T cells by the synthetic CD80 antagonist RhuDex®

Deregulated activation of mucosal lamina propria T cells plays a central role in the pathogenesis of intestinal inflammation. One of the means to attenuate T cell activation is by blocking the CD28/CD80 co-stimulatory pathway. Here we investigate RhuDex®, a small molecule that binds to human CD80, for its effects on the activation of lamina propria T cells employing a gut-culture model of inflammation. To this end, lamina propria leukocytes (LPL) and peripheral blood lymphocytes (PBL) were stimulated either through the CD3/T-cell-receptor complex or the CD2-receptor (CD2) employing agonistic monoclonal antibodies. Co-stimulatory signals were provided by CD80/CD86 present on lamina propria myeloid cells or LPS-activated peripheral blood monocytes. Results show that RhuDex® caused a profound reduction of LPL and PBL proliferation, while Abatacept (CTLA-4-Ig) inhibited LPL proliferation to a small degree, and had no effect on PBL proliferation. Furthermore, Abatacept significantly inhibited IL-2, TNF-α, and IFN-γ release from LPL, primarily produced by CD4⁺ T cells, where IL-2 blockage was surprisingly strong, suggesting a down-regulating effect on regulatory T cells. In contrast, in the presence of RhuDex®, secretion of IL-17, again mostly by CD4⁺ T cells, and IFN-γ was inhibited in LPL and PBL, yet IL-2 remained unaffected. Thus, RhuDex® efficiently inhibited lamina propria and peripheral blood T-cell activation in this pre-clinical study making it a promising drug candidate for the treatment of intestinal inflammation.

Co-expression of tumor antigen and interleukin-2 from an adenoviral vector augments the efficiency of therapeutic tumor vaccination

We have previously shown that for the majority of antigens, adenoviral vaccines expressing the target antigen fused to the MHC associated invariant chain (Ii) induce an accelerated, augmented, and prolonged transgene-specific CD8(+) T-cell response. Here we describe a new adenoviral vaccine vector approach where the target antigen fused to Ii is expressed from the adenoviral E1 region and IL-2 is expressed from the E3 region. Immunization of mice with this new vector construct resulted in an augmented primary effector CD8(+) T-cell response. Furthermore, in a melanoma model we observed significantly prolonged tumor control in vaccinated wild type (WT) mice. The improved tumor control required antigen-specific cells, since no tumor control was observed, unless the melanoma cells expressed the vaccine targeted antigen. We also tested our new vaccine in immunodeficient (CD80/86 deficient) mice. Following vaccination with the IL-2 expressing construct, these mice were able to raise a delayed but substantial CD8(+) T-cell response, and to control melanoma growth nearly as efficaciously as similarly vaccinated WT mice. Taken together, these results demonstrate that current vaccine vectors can be improved and even tailored to meet specific demands: in the context of therapeutic vaccination, the capacity to promote an augmented effector T-cell response.

STAT heterodimers in immunity: A mixed message or a unique signal?

Cytokine signals are essential for generating a robust and specialized immune response. These signals are typically transmitted via canonical STAT homodimers. However, the number of STAT molecules utilized by cytokine signaling cascades within immune cells are limited, and so the mechanism used to deliver complex signals remains elusive. Heterodimerization of STAT proteins is one potential mechanism for signals to be modified downstream of the receptor and may play an important role in dictating the targets of specific cytokine signaling. In this review, we discuss our current understanding of the prevalence of STAT heterodimers, how they are formed and what their physiologic role may be in vivo.

Id1 expression promotes T regulatory cell differentiation by facilitating TCR costimulation

T regulatory (Treg) cells play crucial roles in the regulation of cellular immunity. The development of Treg cells depends on signals from TCRs and IL-2Rs and is influenced by a variety of transcription factors. The basic helix-loop-helix proteins are known to influence TCR signaling thresholds. Whether this property impacts Treg differentiation is not understood. In this study, we interrogated the role of basic helix-loop-helix proteins in the production of Treg cells using the CD4 promoter-driven Id1 transgene. We found that Treg cells continued to accumulate as Id1 transgenic mice aged, resulting in a significant increase in Treg cell counts in the thymus as well as in the periphery compared with wild-type controls. Data from mixed bone marrow assays suggest that Id1 acts intrinsically on developing Treg cells. We made a connection between Id1 expression and CD28 costimulatory signaling because Id1 transgene expression facilitated the formation of Treg precursors in CD28(-/-) mice and the in vitro differentiation of Treg cells on thymic dendritic cells despite the blockade of costimulation by anti-CD80/CD86. Id1 expression also allowed in vitro Treg differentiation without anti-CD28 costimulation, which was at least in part due to enhanced production of IL-2. Notably, with full strength of costimulatory signals, however, Id1 expression caused modest but significant suppression of Treg induction. Finally, we demonstrate that Id1 transgenic mice were less susceptible to the induction of experimental autoimmune encephalomyelitis, thus illustrating the impact of Id1-mediated augmentation of Treg cell levels on cellular immunity.

Activation of silenced cytokine gene promoters by the synergistic effect of TBP-TALE and VP64-TALE activators

Recent work has shown that the combinatorial use of multiple TALE activators can selectively activate certain cellular genes in inaccessible chromatin regions. In this study, we aimed to interrogate the activation potential of TALEs upon transcriptionally silenced immune genes in the context of non-immune cells. We designed a unique strategy, in which a single TALE fused to the TATA-box binding protein (TBP-TALE) is coupled with multiple VP64-TALE activators. We found that our strategy is significantly more potent than multiple TALE activators alone in activating expression of IL-2 and GM-CSF in diverse cell origins in which both genes are otherwise completely silenced. Chromatin analysis revealed that the gene activation was due in part to displacement of a distinctly positioned nucleosome. These studies provide a novel epigenetic mechanism for artificial gene induction and have important implications for targeted cancer immunotherapy, DNA vaccine development, as well as rational design of TALE activators.

mTOR, metabolism, and the regulation of T-cell differentiation and function

Upon antigen recognition, naive T cells undergo rapid expansion and activation. The energy requirements for this expansion are formidable, and T-cell activation is accompanied by dramatic changes in cellular metabolism. Furthermore, the outcome of antigen engagement is guided by multiple cues derived from the immune microenvironment. Mammalian target of rapamycin (mTOR) is emerging as a central integrator of these signals playing a critical role in driving T-cell differentiation and function. Indeed, multiple metabolic programs are controlled by mTOR signaling. In this review, we discuss the role of mTOR in regulating metabolism and how these pathways intersect with the ability of mTOR to integrate cues that guide the outcome of T-cell receptor engagement.

The early phase of human sepsis is characterized by a combination of apoptosis and proliferation of T cells

PURPOSE

T cell activation as well as unresponsiveness has been described in separate studies in sepsis. Our aim was to establish the coexistence of both T cell fate in human sepsis.

PATIENTS AND METHODS

This is a cross-sectional study of 48 patients presenting with severe sepsis or septic shock and 15 healthy controls. Cytofluorometric techniques were used to quantify T cell activation, apoptosis, proliferation, expression of costimulatory molecules, and cytokine secretion.

RESULTS

Patients with sepsis were characterized by a significant increase in the percentage of activated T cell subsets, as measured using CD69 marker, compared with healthy controls (P<.05). T cell proliferation as measured through Ki67 expression was obvious in infected patients for both CD4 and CD8 T cell subsets compared with controls (P ≤.006). T cell subset apoptosis as measured using Hoechst dye was also increased in infected patients compared with controls (P ≤.002). CD4 T cell proliferation was correlated with interleukin 2 secretion (R(2)=0.84, P<.001), whereas up-regulation of CD4 T cell apoptosis was correlated with CTLA-4 expression (R(2)=0.24, P=.001). No such similar relationship was observed for CD8(+) T cells.

CONCLUSIONS

Concomitant T cell proliferation and T cell apoptosis are observed in human sepsis, being related to a different pathway.

Dimeric MHC-peptides inserted into an immunoglobulin scaffold as new immunotherapeutic agents

The interactions of the T cell receptor (TCR) with cognate MHC-peptide and co-stimulatory molecules expressed at surface of antigen presenting cells (APC) leads to activation or tolerance of T cells. The development of molecular biological tools allowed for the preparation of soluble MHC-peptide molecules as surrogate for the APC. A decade ago a monomeric class II MHC molecule in which the peptide was covalently linked to β-chain of class II molecule was generated. This type of molecule had a low-binding affinity and did not cause the multimerization of TCR. The requirement of multimerization of TCR led to development of a new class of reagents, chimeric peptides covalently linked to MHC that was dimerized via Fc fragment of an immunoglobulin and linked to 3' end of the β-chain of MHC class II molecule. These soluble dimerized MHC-peptide chimeric molecules display high affinity for the TCR and caused multimerization of TCR without processing by an APC. Because dimeric molecules are devoid of co-stimulatory molecules interacting with CD28, a second signal, they induce anergy rather the activation of T cells. In this review, we compare the human and murine dimerized MHC class II-peptides and their effect on CD4(+) T cells, particularly the generation of T regulatory cells, which make these chimeric molecules an appealing approach for the treatment of autoimmune diseases.

Protein kinase Ctheta is a specific target for inhibition of the HIV type 1 replication in CD4+ T lymphocytes

Integration of HIV-1 genome in CD4(+) T cells produces latent reservoirs with long half-life that impedes the eradication of the infection. Control of viral replication is essential to reduce the size of latent reservoirs, mainly during primary infection when HIV-1 infects CD4(+) T cells massively. The addition of immunosuppressive agents to highly active antiretroviral therapy during primary infection would suppress HIV-1 replication by limiting T cell activation, but these agents show potential risk for causing lymphoproliferative disorders. Selective inhibition of PKC, crucial for T cell function, would limit T cell activation and HIV-1 replication without causing general immunosuppression due to PKC being mostly expressed in T cells. Accordingly, the effect of rottlerin, a dose-dependent PKC inhibitor, on HIV-1 replication was analyzed in T cells. Rottlerin was able to reduce HIV-1 replication more than 20-fold in MT-2 (IC(50) = 5.2 μM) and Jurkat (IC(50) = 2.2 μM) cells and more than 4-fold in peripheral blood lymphocytes (IC(50) = 4.4 μM). Selective inhibition of PKC, but not PKCδ or -ζ, was observed at <6.0 μM, decreasing the phosphorylation at residue Thr(538) on the kinase catalytic domain activation loop and avoiding PKC translocation to the lipid rafts. Consequently, the main effector at the end of PKC pathway, NF-κB, was repressed. Rottlerin also caused a significant inhibition of HIV-1 integration. Recently, several specific PKC inhibitors have been designed for the treatment of autoimmune diseases. Using these inhibitors in combination with highly active antiretroviral therapy during primary infection could be helpful to avoid massive viral infection and replication from infected CD4(+) T cells, reducing the reservoir size at early stages of the infection.

Sustained CD28 expression delays multiple features of replicative senescence in human CD8 T lymphocytes

CD28 costimulatory signal transduction in T lymphocytes is essential for optimal telomerase activity, stabilization of cytokine mRNAs, and glucose metabolism. During aging and chronic infection with HIV-1, there are increased proportions of CD8 T lymphocytes that lack CD28 expression and show additional features of replicative senescence. Moreover, the abundance of these cells correlates with decreased vaccine responsiveness, early mortality in the very old, and accelerated HIV disease progression. Here, we show that sustained expression of CD28, via gene transduction, retards the process of replicative senescence, as evidenced by enhanced telomerase activity, increased overall proliferative potential, and reduced secretion of pro-inflammatory cytokines. Nevertheless, the transduced cultures eventually do reach senescence, which is associated with increased CTLA-4 gene expression and a loss of CD28 cell surface expression. These findings further elucidate the central role of CD28 in the replicative senescence program, and may ultimately lead to novel therapies for diseases associated with replicative senescence.

Opposite effects of high and low doses of interleukin-2 on T cell-mediated hepatitis in mice (interleukin-2 on hepatitis)

PURPOSE

Concanavalin A (Con A)-induced hepatitis is an extensively used animal model of T cell-mediated acute hepatitis. A variety of cytokines, including interleukin 4 (IL-4), interferon gamma (IFN-γ), and tumor necrosis factor alpha (TNF-α), have been shown to play important roles in Con A-induced liver injury. However, the role of IL-2, a critical cytokine in the development and function of T cells and a clinical therapeutics for virus infection and tumor, has not been carefully examined in this model.

METHODS

In this study, we investigated the function of IL-2 in Con A-induced hepatitis by using various strategies of rhIL-2 pretreatment. We treated mice with two rhIL-2 administration strategies: a single injection of high dose of rhIL-2 (IL-2(hi), 50 × 10(3) U/mouse) and four injections of low dose of rhIL-2 (IL-2(4lo), 5 × 10(3) U/mouse).

RESULTS

IL-2(hi) pretreatment ameliorated Con A-induced liver injury, while IL-2(4lo) aggravated Con A-induced liver injury. IL-2(hi) pretreatment reduced Con A-induced elevation of serum TNF-α while IL-2(4lo) pretreatment did not. Serum IL-4 and TNF-α were high 6 h after Con A injection in IL-2(4lo) mice, while it was undetectable in IL-2(hi) and non-pretreated mice. IL-2(hi) pretreatment reduced Con A-induced accumulation of T cells in liver while IL-2(4lo) pretreatment increased accumulation of NK cells.

CONCLUSION

Various strategies of rhIL-2 administration play different roles in Con A-induced hepatitis, suggesting the importance of IL-2 administrative regime in clinical liver diseases.

B7 family molecules as regulators of the maternal immune system in pregnancy

Placental and fetal growth and development are associated with chronic exposure of the maternal immune system to fetally derived, paternally inherited antigens. Because maternal lymphocytes are aware of fetal antigens, active tolerance mechanisms are required to ensure unperturbed progression of pregnancy and delivery of a healthy newborn. These mechanisms of tolerance may include deletion, receptor downregulation, and anergy of fetal antigen-specific cells in lymphoid tissues, as well as regulation at the maternal-fetal interface by a variety of locally expressed immunoregulatory molecules. The B7 family of costimulatory molecules comprises one group of immunoregulatory molecules present in the decidua and placenta. B7 family members mediate both inhibitory and stimulatory effects on T-cell activation and effector functions and may play a critical role in maintaining tolerance to the fetus. Here, we review the known functions of the B7 family proteins in pregnancy.

Mitochondrial reactive oxygen species control T cell activation by regulating IL-2 and IL-4 expression: mechanism of ciprofloxacin-mediated immunosuppression

This article shows that T cell activation-induced expression of the cytokines IL-2 and -4 is determined by an oxidative signal originating from mitochondrial respiratory complex I. We also report that ciprofloxacin, a fluoroquinolone antibiotic, exerts immunosuppressive effects on human T cells suppressing this novel mechanism. Sustained treatment of preactivated primary human T cells with ciprofloxacin results in a dose-dependent inhibition of TCR-induced generation of reactive oxygen species (ROS) and IL-2 and -4 expression. This is accompanied by the loss of mitochondrial DNA and a resulting decrease in activity of the complex I. Consequently, using a complex I inhibitor or small interfering RNA-mediated downregulation of the complex I chaperone NDUFAF1, we demonstrate that TCR-triggered ROS generation by complex I is indispensable for activation-induced IL-2 and -4 expression and secretion in resting and preactivated human T cells. This oxidative signal (H(2)O(2)) synergizes with Ca(2+) influx for IL-2/IL-4 expression and facilitates induction of the transcription factors NF-kappaB and AP-1. Moreover, using T cells isolated from patients with atopic dermatitis, we show that inhibition of complex I-mediated ROS generation blocks disease-associated spontaneous hyperexpression and TCR-induced expression of IL-4. Prolonged ciprofloxacin treatment of T cells from patients with atopic dermatitis also blocks activation-induced expression and secretion of IL-4. Thus, our work shows that the activation phenotype of T cells is controlled by a mitochondrial complex I-originated oxidative signal.

Adenosine deaminase modulation of telomerase activity and replicative senescence in human CD8 T lymphocytes

Increased proportions of CD8 T lymphocytes lacking expression of the CD28 costimulatory receptor have been documented during both aging and chronic infection with HIV-1, and their abundance correlates with numerous deleterious clinical outcomes. CD28-negative cells also arise in cell cultures of CD8(+)CD28(+) following multiple rounds of Ag-driven proliferation, reaching the end stage of replicative senescence. The present study investigates the role of a second T cell costimulatory receptor component, adenosine deaminase (ADA), on the process of replicative senescence. We had previously reported that CD28 signaling is required for optimal telomerase upregulation. In this study, we show that the CD8(+)CD28(+) T lymphocytes that are ADA(+) have significantly greater telomerase activity than those that do not express ADA and that ADA is progressively lost as cultures progress to senescence. Because ADA converts adenosine to inosine, cells lacking this enzyme might be subject to prolonged exposure to adenosine, which has immunosuppressive effects. Indeed, we show that chronic exposure of CD8 T lymphocytes to exogenous adenosine accelerates the process of replicative senescence, causing a reduction in overall proliferative potential, reduced telomerase activity, and blunted IL-2 gene transcription. The loss of CD28 expression was accelerated, in part due to adenosine-induced increases in constitutive caspase-3, known to act on the CD28 promoter. These findings provide the first evidence for a role of ADA in modulating the process of replicative senescence and suggest that strategies to enhance this enzyme may lead to novel therapeutic approaches for pathologies associated with increases in senescent CD8 T lymphocytes.

Post-transcriptional regulation in lymphocytes: the case of CD154

The control of mRNA decay is emerging as an important control point and a major contributor to gene expression in both immune and non-immune cells. The identification of protein factors and cis-acting elements responsible for transcript degradation has illuminated a comprehensive picture of precisely orchestrated events required to both regulate and establish the decay process. One gene that is highly regulated at the post-transcriptional level is CD40 ligand (CD154 or CD40L). CD154 on CD4(+) T cells is tightly controlled by an interacting network of transcriptional and post-transcriptional processes that result in precise surface levels of protein throughout an extended time course of antigen stimulation. The activation-induced stabilization of the CD154 transcript by a polypyrimidine tract-binding protein (PTB)-complex is a key event that corresponds to the temporal expression of CD154. In this review, we discuss known and potential roles of major mRNA decay pathways in lymphocytes and focus on the unique post-transcriptional mechanisms leading to CD154 expression by activated CD4(+) T cells.

In vivo and in vitro adjuvant activities of the B subunit of Type IIb heat-labile enterotoxin (LT-IIb-B5) from Escherichia coli

The pentameric B subunit of the Escherichia coli LT-IIb enterotoxin (LT-IIb-B(5)) activates TLR2 signaling in macrophages. Herein we demonstrate that LT-IIb-B(5), in contrast to a TLR2-nonbinding point mutant, induces functional activation of bone marrow-derived dendritic cells and stimulates CD4(+) T cell proliferation, activities which suggested that LT-IIb-B(5) might function as an adjuvant in vivo. Indeed, in an intranasal mouse immunization model, LT-IIb-B(5) augmented specific mucosal and serum antibody responses to a co-administered immunogen, at levels which were almost comparable to those induced by intact LT-IIb holotoxin, a potent but toxic adjuvant. Therefore, LT-IIb-B(5) displays useful adjuvant properties which, combined with lack of enterotoxicity and relative stability against degradation, may find application in mucosal vaccines.

Naive CD4 t cell proliferation is controlled by mammalian target of rapamycin regulation of GRAIL expression

In this study, we demonstrate that the E3 ubiquitin ligase gene related to anergy in lymphocytes (GRAIL) is expressed in quiescent naive mouse and human CD4 T cells and has a functional role in inhibiting naive T cell proliferation. Following TCR engagement, CD28 costimulation results in the expression of IL-2 whose signaling through its receptor activates the Akt-mammalian target of rapamycin (mTOR) pathway. Activation of mTOR allows selective mRNA translation, including the epistatic regulator of GRAIL, Otubain-1 (Otub1), whose expression results in the degradation of GRAIL and allows T cell proliferation. The activation of mTOR appears to be the critical component of IL-2R signaling regulating GRAIL expression. CTLA4-Ig treatment blocks CD28 costimulation and resultant IL-2 expression, whereas rapamycin and anti-IL-2 treatment block mTOR activation downstream of IL-2R signaling. Thus, all three of these biotherapeutics inhibit mTOR-dependent translation of mRNA transcripts, resulting in blockade of Otub1 expression, maintenance of GRAIL, and inhibition of CD4 T cell proliferation. These observations provide a mechanistic pathway sequentially linking CD28 costimulation, IL-2R signaling, and mTOR activation as important requirements for naive CD4 T cell proliferation through the regulation of Otub1 and GRAIL expression. Our findings also extend the role of GRAIL beyond anergy induction and maintenance, suggesting that endogenous GRAIL regulates general cell cycle and proliferation of primary naive CD4 T cells.

Modulation of T lymphocyte replicative senescence via TNF-{alpha} inhibition: role of caspase-3

Expanded populations of CD8(+) T lymphocytes lacking CD28 expression are associated with a variety of deleterious clinical outcomes, including early mortality in the elderly, more rapid progression to AIDS, cardiovascular disease, and enhanced tumor cell growth. In cell culture, irreversible loss of CD28 expression correlates with increased production of TNF-alpha as CD8(+) T cells are driven to the nonproliferative end stage of replicative senescence by multiple rounds of Ag-driven cell division. Interestingly, in patients with rheumatoid arthritis, inhibition or neutralization of TNF-alpha reduces the proportion of T cells lacking CD28 in the disease joints, consistent with studies showing a direct involvement of this cytokine in CD28 gene transcription. Here, we show that modulation of TNF-alpha levels in long-term cultures of human CD8(+) T lymphocytes, by chronic exposure either to a neutralizing Ab or to an inhibitor of the TNF-alpha receptor-1, increases proliferative potential, delays loss of CD28 expression, retards cytokine profile changes, and enhances telomerase activity. We also show that constitutive caspase-3, one of the downstream effectors of TNF-alphaR1 binding, increases in parallel with the loss of CD28 in long-term cultures, but this effect is blunted in the presence of the TNF-alpha inhibitors. Consistent with the in vitro culture data, CD8(+)CD28(-) T lymphocytes tested immediately ex vivo also show significantly higher levels of caspase-3 compared with their CD28(+) counterparts. These findings help elucidate the complex nature of CD28 gene regulation, and may ultimately lead to novel therapeutic approaches for diseases associated with increased proportions of CD28(-) T lymphocytes.

Enhanced T-cell apoptosis in human septic shock is associated with alteration of the costimulatory pathway

T-cell apoptosis during septic shock (SS) has been associated with deleterious outcome, but the mechanisms of apoptosis are not well understood. As T-cells are not infected in bacterial infection, our hypothesis was that deleterious interactions between lymphocytes and monocytes could be involved. This is a cross-sectional study of 27 patients presenting with community-acquired SS, 23 infected patients without SS and 18 controls. Cytofluorometric techniques were used to study apoptosis, the costimulatory pathway and cytokine synthesis. Apoptosis was increased in SS compared to infected patients without SS and controls: the median values were 18, 2 and 3%, respectively, for CD4(+) T-cells (P < 0.001), and 12, 5 and 2%, respectively, for CD8(+) T-cells (P < 0.001). Patients with SS exhibited significant CD152 over-expression on T-cells, while CD86 expression was decreased on monocytes (P = 0.004). The synthesis of interleukin-2 was decreased in patients with SS compared to the other groups, while secretions of interferon-gamma and TNF-alpha were not altered. Ten surviving patients with SS showed a trend towards the normalisation of these parameters on day 7. In SS, T-cell apoptosis is related, at least in part, to the alteration of the costimulatory pathway, which, in turn, leads to significant modification of the cytokine network.

Effect of naturally occurring hydroxychavicol acetate on the cytokine production in T helper cells

Naturally occurring phenolic compounds, such as chavicol analogues, have been shown to have potent antioxidant and anti-inflammatory activities. We have previously isolated two chavicol acetate analogues, acetoxychavicol acetate (ACA) and hydroxychavicol acetate (HCA) from the rhizomes of Alpinia galanga. Although the function of ACA has been studied in many systems, the function of HCA has yet to be systemically examined. In this study, we have comparably examined the functions of ACA and HCA on the cytokine production in Th cells. ACA exhibited potent antioxidant activity and increased cell apoptosis; therefore, cytokine production by Th cells was diminished. Although HCA had neither antioxidant activity nor pro-apoptotic function, it was shown to increase IL-2 production and attenuate IFNgamma expression in Th cells. In addition, we demonstrated that HCA suppressed T-bet expression, which is responsible for IL-2 suppression and IFNgamma induction in Th cells and inhibited T-bet-mediated Th1 cell differentiation. Therefore, we suggest that HCA may be beneficial as therapeutics for treating inflammatory immune disorders caused by extravagant activation of Th1-mediated immune responses.

Impaired phenotype and function of monocyte derived dendritic cells in pulmonary tuberculosis

Pulmonary tuberculosis (PTB) is often associated with impaired immunological functions. Blood monocytes, which can differentiate into dendritic cells upon cytokine stimulation, play a central role in adequate immune reactivity. Here, we investigated the morphologic, phenotypic and functional characteristics of in vitro-generated monocyte derived dendritic cells (MoDC) from PTB patients in comparison with healthy subjects. Phenotypic analysis revealed a defective differentiation of MoDC in PTB patients as assessed by a strong down regulation of CD1a, MHC II, CD80 and CD83 expression and impaired allostimulatory function under the influence of IL-4 and GM-CSF. In contrast, the expression of CD86 was not affected and remained same as in healthy subjects. Furthermore, the maturation status of lipopolysaccharide (LPS) stimulated MoDC was not optimal in PTB. However, the MoDC of PTB patients produced significantly higher levels of TNF-alpha and IL-6 but lower levels of IL-12 compared to healthy subjects. These findings suggest that there is a fundamental defect in the differentiation and maturation of dendritic cells during PTB that may compromise the antigen presentation and subsequent immune functions.