CD28 signaling causes a sustained down-regulation of I kappa B alpha which can be prevented by the immunosuppressant rapamycin

Starvation Protects Hepatocytes from Inflammatory Damage through Paradoxical mTORC1 Signaling

Background and aims: Sepsis-related liver failure is associated with a particularly unfavorable clinical outcome. Calorie restriction is a well-established factor that can increase tissue resilience, protect against liver failure and improve outcome in preclinical models of bacterial sepsis. However, the underlying molecular basis is difficult to investigate in animal studies and remains largely unknown.

METHODS

We have used an immortalized hepatocyte line as a model of the liver parenchyma to uncover the role of caloric restriction in the resilience of hepatocytes to inflammatory cell damage. In addition, we applied genetic and pharmacological approaches to investigate the contribution of the three major intracellular nutrient/energy sensor systems, AMPK, mTORC1 and mTORC2, in this context.

RESULTS

We demonstrate that starvation reliably protects hepatocytes from cellular damage caused by pro-inflammatory cytokines. While the major nutrient- and energy-related signaling pathways AMPK, mTORC2/Akt and mTORC1 responded to caloric restriction as expected, mTORC1 was paradoxically activated by inflammatory stress in starved, energy-deprived hepatocytes. Pharmacological inhibition of mTORC1 or genetic silencing of the mTORC1 scaffold Raptor, but not its mTORC2 counterpart Rictor, abrogated the protective effect of starvation and exacerbated inflammation-induced cell death. Remarkably, mTORC1 activation in starved hepatocytes was uncoupled from the regulation of autophagy, but crucial for sustained protein synthesis in starved resistant cells.

CONCLUSIONS

AMPK engagement and paradoxical mTORC1 activation and signaling mediate protection against pro-inflammatory stress exerted by caloric restriction in hepatocytes.

CD28 Signaling Drives Notch Ligand Expression on CD4 T Cells

Notch signaling provides an important cue in the mammalian developmental process. It is a key player in T cell development and function. Notch ligands such as Delta-like ligands (DLL) 1, 3, 4, and JAG1, 2 can impact Notch signaling positively or negatively, by trans-activation or cis-inhibition. Trans and cis interactions are receptor-ligand interaction on two adjacent cells and interaction on the same cell, respectively. The former sends an activation signal and the later, a signal for inhibition of Notch. However, earlier reports suggested that Notch is activated in the absence of Notch ligand-expressing APCs in a purified population of CD4 T cells. Thus, the role of ligands in Notch activation, in a purified population of CD4 T cells, remains obscure. In this study, we demonstrate that mature CD4 T cells are capable of expressing Notch ligands on their surface very early upon activation with soluble antibodies against CD3 and CD28. Moreover, signaling solely through CD28 induces Notch ligand expression and CD3 signaling inhibits ligand expression, in contrast to Notch which is induced by CD3 signaling. Additionally, by using decoys, mimicking the Notch extracellular domain, we demonstrated that DLL1, DLL4, and JAG1, expressed on the T cells, can cis-interact with the Notch receptor and inhibit activation of Notch. Thus, our data indicate a novel mechanism of the regulation of Notch ligand expression on CD4 T cells and its impact on activated Notch.

Autophagy counters LPS-mediated suppression of lysozyme

Impaired Paneth cell expression of antimicrobial protein (AMP) lysozyme is found in patients with Crohn's disease with the autophagy gene ATG16L1 risk allele, in mice with mutations in autophagy genes Atg16L1, Atg5 and Atg7, and in Irgm1 knockout mice. Defective autophagy is also associated with expansion of resident Gram-negative bacteria in the intestinal lumen. These findings suggest that autophagy may control extracellular resident microbes by governing expression of lysozyme. To test the hypothesis that autophagy may have a defensive role in host response to resident extracellular microbes, we investigated the relationship between gut microbes, autophagy, and lysozyme. RAW 264.7 macrophages were treated with fecal slurry (FS), representing the resident microbial community; lipopolysaccharide (LPS); or butyrate, representing microbial products; or a representative resident Gram-negative bacterium Desulfovibrio vulgaris (DSV). FS, LPS, and DSV inhibited lysozyme expression, whereas butyrate had no effect. Induction of autophagy by rapamycin countered this inhibition, whereas silencing of the autophagy gene Irgm1 exacerbated the inhibitory effects of LPS on lysozyme expression. LPS also inhibited lysozyme activity against DSV and autophagy reversed this effect. Our results provide a novel insight into an interaction between gut bacteria, autophagy and AMP whereby autophagy may defend the host by countering the suppression of antimicrobial protein by Gram-negative bacteria.

CD28 costimulatory signals in T lymphocyte activation: Emerging functions beyond a qualitative and quantitative support to TCR signalling

CD28 is one of the most important co-stimulatory receptors necessary for full T lymphocyte activation. By binding its cognate ligands, B7.1/CD80 or B7.2/CD86, expressed on the surface of professional antigen presenting cells (APC), CD28 initiates several signalling cascades, which qualitatively and quantitatively support T cell receptor (TCR) signalling. More recent data evidenced that human CD28 can also act as a TCR-independent signalling unit, by delivering specific signals, which regulate the expression of pro-inflammatory cytokine/chemokines. Despite the enormous progresses made in identifying the mechanisms and molecules involved in CD28 signalling properties, much remains to be elucidated, especially in the light of the functional differences observed between human and mouse CD28. In this review we provide an overview of the current mechanisms and molecules through which CD28 support TCR signalling and highlight recent findings on the specific signalling motifs that regulate the unique pro-inflammatory activity of human CD28.

Cellular and molecular biology of aging endothelial cells

Cardiovascular disease (CVD) is the leading cause of death in the United States and aging is a major risk factor for CVD development. One of the major age-related arterial phenotypes thought to be responsible for the development of CVD in older adults is endothelial dysfunction. Endothelial function is modulated by traditional CVD risk factors in young adults, but advancing age is independently associated with the development of vascular endothelial dysfunction. This endothelial dysfunction results from a reduction in nitric oxide bioavailability downstream of endothelial oxidative stress and inflammation that can be further modulated by traditional CVD risk factors in older adults. Greater endothelial oxidative stress with aging is a result of augmented production from the intracellular enzymes NADPH oxidase and uncoupled eNOS, as well as from mitochondrial respiration in the absence of appropriate increases in antioxidant defenses as regulated by relevant transcription factors, such as FOXO. Interestingly, it appears that NFkB, a critical inflammatory transcription factor, is sensitive to this age-related endothelial redox change and its activation induces transcription of pro-inflammatory cytokines that can further suppress endothelial function, thus creating a vicious feed-forward cycle. This review will discuss the two macro-mechanistic processes, oxidative stress and inflammation, that contribute to endothelial dysfunction with advancing age as well as the cellular and molecular events that lead to the vicious cycle of inflammation and oxidative stress in the aged endothelium. Other potential mediators of this pro-inflammatory endothelial phenotype are increases in immune or senescent cells in the vasculature. Of note, genomic instability, telomere dysfunction or DNA damage has been shown to trigger cell senescence via the p53/p21 pathway and result in increased inflammatory signaling in arteries from older adults. This review will discuss the current state of knowledge regarding the emerging concepts of senescence and genomic instability as mechanisms underlying oxidative stress and inflammation in the aged endothelium. Lastly, energy sensitive/stress resistance pathways (SIRT-1, AMPK, mTOR) are altered in endothelial cells and/or arteries with aging and these pathways may modulate endothelial function via key oxidative stress and inflammation-related transcription factors. This review will also discuss what is known about the role of "energy sensing" longevity pathways in modulating endothelial function with advancing age. With the growing population of older adults, elucidating the cellular and molecular mechanisms of endothelial dysfunction with age is critical to establishing appropriate and measured strategies to utilize pharmacological and lifestyle interventions aimed at alleviating CVD risk. This article is part of a Special Issue entitled "SI: CV Aging".

NKG2D receptor activation of NF-κB enhances inflammatory cytokine production in murine effector CD8(+) T cells

To induce strong immune responses, naïve CD8(+) T cells require stimulation through the TCR and costimulatory receptors. However, the biological effect of activating costimulatory receptors on effector T cells is still unclear. One costimulatory receptor that is likely to be engaged at the target site is NKG2D. This activating receptor is expressed on human and murine CD8(+) T cells with its ligands expressed on the majority of tumor cells and during some infections. In order to determine how activation of costimulatory receptors alters effector CD8(+) T cell functions, this study compared the activation of the NF-κB signaling pathway by two costimulatory receptors, CD28 and NKG2D. Compared to CD28 costimulation, activation of murine effector CD8(+) T cells through CD3 and NKG2D receptors enhanced activation of NF-κB as shown by increased phosphorylation of IKKα, IκBα, and NF-κB and IκBα degradation. NKG2D costimulation also increased activation, nuclear translocation, and DNA binding of NF-κB p65/p50 dimers. Activation of the NF-κB pathway also lead to increased gene expression and secretion of pro-inflammatory cytokines, including IFNα and IFNγ, and decreased gene expression and secretion of anti-inflammatory cytokines, including IL-10 and CCL2. Altered NF-κB activation also increased expression of the effector molecules TNFα, lymphotoxins α and β, and Fas ligand, and increased tumor cell killing through FasL. These data show that compared to CD28 costimulation, activation through the NKG2D receptor leads to the differential activation of the NF-κB signaling pathway and potentially enhances the anti-tumor and anti-viral functions of effector CD8(+) T cells.

Risk of infections in renal cell carcinoma (RCC) and non-RCC patients treated with mammalian target of rapamycin inhibitors

Background:

Mammalian target of rapamycin (mTOR) inhibitors are used in a variety of malignancies. Infections have been reported with these drugs. We performed an up-to-date meta-analysis to further characterise the risk of infections in cancer patients treated with these agents.

Methods:

Pubmed and oncology conferences' proceedings were searched for studies from January 1966 to June 2012. Studies were limited to phase II and III randomised controlled trials (RCTs) of everolimus or temsirolimus reporting on cancer patients with adequate safety profiles. Summary incidences, relative risks (RRs), and 95% confidence intervals (CIs) were calculated.

Results:

A total of 3180 patients were included. The incidence of all-grade and high-grade infections due to mTOR inhibitors was 33.1% (95% CI, 24.5–43.0%) and 5.6% (95% CI, 3.8–8.3%), respectively. Compared with controls, the RR of all-grade and high-grade infections due to mTOR inhibitors was 2.00 (95% CI, 1.76–2.28, P<0.001) and 2.60 (95% CI, 1.54–4.41, P<0.001), respectively. Subgroup analysis found no difference in incidences or risks between everolimus and temsirolimus or between different tumour types (renal cell carcinoma (RCC) vs non-RCC). Infections included respiratory tract (61.7%), genitourinary (29.4%), skin/soft tissue (4.2%), and others (4.9%).

Conclusion:

Treatment with mTOR inhibitors is associated with a significant increase in risk of infections. Close monitoring for any signs of infections is warranted.

A novel association between filamin A and NF-κB inducing kinase couples CD28 to inhibitor of NF-κB kinase α and NF-κB activation

CD28 costimulatory molecule plays a critical role in the activation of NF-κB. Indeed, while stimulation of T cells with either professional APCs or anti-TCR plus anti-CD28 antibodies efficiently activates NF-κB, TCR alone fails to do that. Moreover, CD28 stimulation by B7 in the absence of TCR may activate IκB kinase α (IKKα) and a non-canonical NF-κB2-like pathway, in human primary CD4(+) T cells. Despite its functional relevance in NF-κB activation, the molecules connecting autonomous CD28-mediated signals to IKKα and NF-κB activation remain still unknown. In searching for specific upstream activators linking CD28 to the IKKα/NF-κB cascade, we identify a novel constitutive association between filamin A (FLNa) and the NF-κB inducing kinase (NIK), in both Jurkat and human primary T cells. Following CD28 engagement by B7, in the absence of TCR, FLNa-associated NIK is activated and induces IKKα kinase activity. Both proline (P(208)YAP(211)P(212)) and tyrosine residues (Y(206)QPY(209)APP) within the C-terminal proline-rich motif of CD28 are involved in the recruitment of FLNa/NIK complexes to the membrane as well as in the activation of NIK and IKKα.

Monitoring molecular-specific pharmacodynamics of rapamycin in vivo with inducible Gal4->Fluc transgenic reporter mice

Rapamycin (Rap), a small-molecule inhibitor of mTOR, is an immunosuppressant, and several Rap analogues are cancer chemotherapeutics. Further pharmacologic development will be significantly facilitated if in vivo reporter models are available to enable monitoring of molecular-specific pharmacodynamic actions of Rap and its analogues. Herein we present the use of a Gal4→Fluc reporter mouse for the study of Rap-induced mTOR/FKBP12 protein-protein interactions in vivo with the use of a mouse two-hybrid transactivation strategy, a derivative of the yeast two-hybrid system applied to live mice. Upon treatment with Rap, a bipartite transactivator was reconstituted, and transcription of a genomic firefly luciferase reporter was activated in a concentration-dependent (K(d) = 2.3 nmol/L) and FK506-competitive (K(i) = 17.1 nmol/L) manner in cellulo, as well as in a temporal and specific manner in vivo. In particular, after a single dose of Rap (4.5 mg/kg, i.p.), peak Rap-induced protein-protein interactions were observed in the liver at 24 hours post treatment, with photon flux signals 600-fold over baseline, which correlated temporally with suppression of p70S6 kinase activity, a downstream effector of mTOR. The Gal4→Fluc reporter mouse provides an intact physiologic system to interrogate protein-protein interactions and molecular-specific pharmacodynamics during drug discovery and lead characterization. Imaging protein interactions and functional proteomics in whole animals in vivo may serve as a basic tool for screening and mechanism-based analysis of small molecules targeting specific protein-protein interactions in human diseases.

Mammalian target of rapamycin: discovery of rapamycin reveals a signaling pathway important for normal and cancer cell growth

Since the discovery of rapamycin, considerable progress has been made in unraveling the details of the mammalian target of rapamycin (mTOR) signaling network, including the upstream mechanisms that modulate mTOR signaling functions, and the roles of mTOR in the regulation of mRNA translation and other cell growth-related responses. mTOR is found in two different complexes within the cell, mTORC1 and mTORC2, but only mTORC1 is sensitive to inhibition by rapamycin. mTORC1 is a master controller of protein synthesis, integrating signals from growth factors within the context of the energy and nutritional conditions of the cell. Activated mTORC1 regulates protein synthesis by directly phosphorylating 4E-binding protein 1 (4E-BP1) and p70S6K (S6K), translation initiation factors that are important to cap-dependent mRNA translation, which increases the level of many proteins that are needed for cell cycle progression, proliferation, angiogenesis, and survival pathways. In normal physiology, the roles of mTOR in both glucose and lipid catabolism underscore the importance of the mTOR pathway in the production of metabolic energy in quantities sufficient to fuel cell growth and mitotic cell division. Several oncogenes and tumor-suppressor genes that activate mTORC1, often through the phosphatidylinositol 3-kinase (PI3K)/AKT pathway, are frequently dysregulated in cancer. Novel analogs of rapamycin (temsirolimus, everolimus, and deforolimus), which have improved pharmaceutical properties, were designed for oncology indications. Clinical trials of these analogs have already validated the importance of mTOR inhibition as a novel treatment strategy for several malignancies. Inhibition of mTOR now represents an attractive anti-tumor target, either alone or in combination with strategies to target other pathways that may overcome resistance. The far-reaching downstream consequences of mTOR inhibition make defining the critical molecular effector mechanisms that mediate the anti-tumor response and associated biomarkers that predict responsiveness to mTOR inhibitors a challenge and priority for the field.

CD28 and CTLA-4 coreceptor expression and signal transduction

SUMMARY

T-cell activation is mediated by antigen-specific signals from the TCRzeta/CD3 and CD4-CD8-p56lck complexes in combination with additional co-signals provided by coreceptors such as CD28, inducible costimulator (ICOS), cytotoxic T-lymphocyte antigen-4 (CTLA-4), programmed death (PD-1), and others. CD28 and ICOS provide positive signals that promote and sustain T-cell responses, while CTLA-4 and PD-1 limit responses. The balance between stimulatory and inhibitory co-signals determines the ultimate nature of T-cell responses where response to foreign pathogen is achieved without excess inflammation and autoimmunity. In this review, we outline the current knowledge of the CD28 and CTLA-4 signaling mechanisms [involving phosphatidylinositol 3 kinase (PI3K), growth factor receptor-bound protein 2 (Grb2), Filamin A, protein kinase C theta (PKCtheta), and phosphatases] that control T-cell immunity. We also present recent findings on T-cell receptor-interacting molecule (TRIM) regulation of CTLA-4 surface expression, and a signaling pathway involving CTLA-4 activation of PI3K and protein kinase B (PKB)/AKT by which cell survival is ensured under conditions of anergy induction.

Use of rapamycin in the induction of tolerogenic dendritic cells

Rapamycin (RAPA), a macrocyclic triene antibiotic pro-drug, is a clinically-utilized 'tolerance-sparing' immunosuppressant that inhibits the activity of T, B, and NK cells. Furthermore, maturation-resistance and tolerogenic properties of dendritic cells (DC) can be supported and preserved by conditioning with RAPA. Propagation of murine bone marrow (BM)-derived myeloid DC (mDC) in clinically relevant concentrations of RAPA (RAPA-DC) generates phenotypically immature DC with low levels of MHC and significantly reduced co-stimulatory molecules (especially CD86), even when exposed to inflammatory stimuli. RAPA-DC are weak stimulators of T cells and induce hyporesponsiveness and apoptosis in allo-reactive T cells. An interesting observation has been that RAPA-DC retain the ability to stimulate and enrich the regulatory T cells (Treg). Presumably as a result of these properties, alloantigen (alloAg)-pulsed recipient-derived DC are effective in subverting anti-allograft immune responses in rodent transplant models, making them an attractive subject for further investigation of their tolerance-promoting potential.

BCL11B enhances TCR/CD28-triggered NF-kappaB activation through up-regulation of Cot kinase gene expression in T-lymphocytes

BCL11B is a transcriptional regulator with an important role in T-cell development and leukaemogenesis. We demonstrated recently that BCL11B controls expression from the IL (interleukin)-2 promoter through direct binding to the US1 (upstream site 1). In the present study, we provide evidence that BCL11B also participates in the activation of IL-2 gene expression by enhancing NF-kappaB (nuclear factor kappaB) activity in the context of TCR (T-cell receptor)/CD28-triggered T-cell activation. Enhanced NF-kappaB activation is not a consequence of BCL11B binding to the NF-kappaB response elements or association with the NF-kappaB-DNA complexes, but rather the result of higher translocation of NF-kappaB to the nucleus caused by enhanced degradation of IkappaB (inhibitor of NF-kappaB). The enhanced IkappaB degradation in cells with increased levels of BCL11B was specific for T-cells activated through the TCR, but not for cells activated through TNFalpha (tumour necrosis factor alpha) or UV light, and was caused by increased activity of IkappaB kinase, as indicated by its increase in phosphorylation. As BCL11B is a transcription factor, we investigated whether the expression of genes upstream of IkappaB kinase in the TCR/CD28 signalling pathway was affected by increased BCL11B expression, and found that Cot (cancer Osaka thyroid oncogene) kinase mRNA levels were elevated. Cot kinase is known to promote enhanced IkappaB kinase activity, which results in the phosphorylation and degradation of IkappaB and activation of NF-kappaB. The implied involvement of Cot kinase in BCL11B-mediated NF-kappaB activation in response to TCR activation is supported by the fact that a Cot kinase dominant-negative mutant or Cot kinase siRNA (small interfering RNA) knockdown blocked BCL11B-mediated NF-kappaB activation. In support of our observations, in the present study we report that BCL11B enhances the expression of several other NF-kappaB target genes, in addition to IL-2. In addition, we provide evidence that BCL11B associates with intron 2 of the Cot kinase gene to regulate its expression.

CD28 stimulation triggers NF-kappaB activation through the CARMA1-PKCtheta-Grb2/Gads axis

CD28 stimulation contributes to activation of the IL-2 promoter by up-regulating the activity of several transcription factors, including nuclear factor kappaB (NF-kappaB)/Rel family members. However, the signal-transducing cascades linking the CD28 molecule and activation of NF-kappaB remain unclear. Protein kinase C (PKC) , CARMA1 and Bcl10 have recently been reported to integrate TCR-mediated NF-kappaB activation. However, since the data in these studies were drawn from experiments in which T cells were usually stimulated with both TCR and CD28, the relative contributions of TCR- and CD28-mediated signals to initiation of the NF-kappaB pathway remain elusive. To examine the role of these molecules in NF-kappaB activation through CD28-mediated stimulation, Bcl10 was over-expressed in Jurkat cells and their NF-kappaB activation by CD28- or TCR-cross-linking was evaluated. We found that CD28 stimulation alone can induce NF-kappaB activation in Bcl10-over-expressing Jurkat cells, whereas TCR stimulation alone has only little effect. In addition, we found that Bcl10-induced NF-kappaB activation through CD28-mediated stimulation could be blocked by the dominant-negative form of PKC or CARMA1. Furthermore, genetic studies revealed that Grb2/Gads binding, but not phosphatidylinositol 3-kinase binding, is important in CD28-mediated NF-kappaB activation. These findings indicate that the PKC-CARMA1-Bcl10 signaling pathway participates in the CD28 co-stimulatory signal independently of the TCR-signaling pathway, which leads us to propose that the activation of the NF-kappaB-signaling pathway via PKC-CARMA1-Bcl10 may be markedly dependent on CD28 stimulation rather than TCR stimulation.

IL-1beta-driven ST2L expression promotes maturation resistance in rapamycin-conditioned dendritic cells

Maturation resistance and tolerogenic properties can be conferred on human and murine dendritic cells (DC), crucial regulators of T cell responses, by exposure to rapamycin (RAPA), a "tolerance-sparing" immunosuppressive agent. Mechanisms underlying this acquired unresponsiveness, typified by diminished functional responses to TLR or CD40 ligation, have not been identified. We report that in vitro and in vivo conditioning of murine myeloid DC with RAPA elicits the de novo production of IL-1beta by otherwise phenotypically immature DC. Interestingly, IL-1beta production promotes overexpression of the transmembrane form of the IL-1R family member, IL-1R-like 1, also know as ST2 on RAPA-conditioned DC (RAPA-DC). ST2 is the recently identified receptor for IL-33, a cytokine favoring Th2 responses. In addition, transmembrane ST2, or ST2L, has been implicated as a potent negative regulator of TLR signaling. RAPA-DC generated from ST2-/- mice exhibited higher levels of costimulatory molecules (CD86) than wild-type RAPA-DC. Consistent with its regulatory function, IL-1beta-induced ST2L expression suppressed the responsiveness of RAPA-DC to TLR or CD40 ligation. Thus, as a result of their de novo production of IL-1beta, RAPA-DC up-regulate ST2L and become refractory to proinflammatory, maturation-inducing stimuli. This work identifies a novel mechanism through which a clinically important immunosuppressant impedes the capacity of DC to mature and consequently stimulate effector/adaptive T cell responses.

The pharmacodynamic effect of sirolimus: individual variation of cytokine mRNA expression profiles in human whole blood samples

Sirolimus (SRL) has become an important alternative to calcineurin inhibitors due to its unique mechanism of action. Since rejection and poor graft outcome are still frequent problems despite therapeutic-range blood concentrations, pharmacodynamic measurements of its immunosuppressive effects would be of great clinical value to optimize treatment in individual patients. We performed a human whole blood assay using real time cytokine RT-PCR for the pharmacodynamic assessment of SRL. IL-2, IL-4 and IL-6 mRNA levels were quantitatively determined upon T-cell-specific stimulation in healthy individuals (n=11; in vitro) and in kidney-transplant patients (n=3; ex vivo). Furthermore, IL-2 protein secretion and T-cell proliferation was measured. After 24h incubation we observed a stronger suppression of IL-2 and IL-4 mRNA expression upon SRL addition (p<0.005; p<0.005) versus 4h (p<0.05; p<0.05). SRL effects displayed a remarkable interindividual variation, which proved to be independent of the concentration applied. Notably, 3/11 and 2/11 individuals had unaffected IL-2 and IL-4 mRNA expression after 4h incubation with SRL, respectively. In contrast, a general suppression of IL-2 protein secretion and T-cell proliferation was induced. Analysis of kidney-transplant patients verified interindividual variation and proved comparability of in vitro and ex vivo effects. We describe an individual degree of SRL-sensitivity that may correlate with clinical efficacy. Rather than analysis of one single peak, we suggest determination of two absolute cytokine mRNA peak levels for the pharmacodynamic assessment of SRL. However, prospective clinical studies are necessary to determine whether individual degrees of SRL-sensitivity correlate with clinical outcome.

Effects of ciclosporin A, tacrolimus and sirolimus on cytokine production in neonatal immune cells

BACKGROUND

It was the aim of this study to evaluate the effects of the well-known immunosuppressive drugs ciclosporin A (CsA), tacrolimus and sirolimus on the intracytoplasmic cytokine expression of neonatal immune cells.

METHODS

Immunosuppressive drugs were added to whole blood cultures of neonatal cord blood samples (n = 17) and peripheral blood samples of adults (n = 17) in vitro prior to stimulation of lymphocytes with phorbol 12-myristate 13-acetate (PMA)/ionomycin or monocytes.

RESULTS

Upon exposure to ciclosporin A (500 ng/mL) or tacrolimus (25 ng/mL) the number of cytokine expressing T cells was almost completely blocked in neonatal T cells while sirolimus (10 ng/mL) only inhibited intracytoplasmatic tumour necrosis factor alpha (TNF-alpha) expression (mean% positive cells; 4.0 +/- 2.1% vs. 1.09 +/- 0.6%, p = 0.003), but mildly stimulated the intracellular expression of interleukin (IL)-2 (24.4 +/- 6.5% vs. 28.1 +/- 7.1%, p = 0.041). In cord blood lymphocytes, the inhibitory effect of ciclosporin A and tacrolimus was dose-dependent (e.g. IL-2: control, 12.3 +/- 5.33%, ciclosporin A 5 ng/mL, 10.1 +/- 5.5%; 50 ng/mL, 7.1 +/- 4.7%; 500 ng/mL, 1.2 +/- 0.3%; tacrolimus 0.25 ng/mL, 9.3 +/- 4.9%; 2.5 ng/mL, 6.1 +/- 3.3%; 25 ng/mL, 1.0 +/- 0.6%), while the function of adult lymphocytes was only impaired at high doses of both compounds. In contrast, the number of cytokine expressing monocytes was not influenced by ciclosporin A and tacrolimus except for a minor decrease of TNF-alpha producing neonatal monocytes after addition of tacrolimus (17.9% vs. 13.9%, p = 0.031). Interestingly, sirolimus was shown to inhibit intracellular IL-6 production in adults (63.1 +/- 12.7% vs. 52.0 +/- 16.0%, p = 0.005), but in neonatal monocytes intracellular IL-6 expression was stimulated (53.5 +/- 22.0% vs. 64.7 +/- 19.1%, p = 0.041).

CONCLUSIONS

The potent dose-dependent inhibitory effect of ciclosporin A and tacrolimus in cord blood lymphocytes provides the basis for further studies on functional immaturity of the neonatal immune system and for future strategies to optimize umbilical cord blood transplantion. Sirolimus was demonstrated to have a distinct effect on neonatal immune cells as shown by increased expression of IL-2 in lymphocytes and IL-6 in monocytes, while only lymphocytic TNF-alpha expression was inhibited.

BCL11B participates in the activation of IL2 gene expression in CD4+ T lymphocytes

BCL11A and BCL11B are transcriptional regulators important for lymphopoiesis and previously associated with hematopoietic malignancies. Ablation of the mouse Bcl11b locus results in failure to generate double-positive thymocytes, implicating a critical role of Bcl11b in T-cell development. However, BCL11B is also expressed in CD4+ T lymphocytes, both in resting and activated states. Here we show both in transformed and primary CD4+ T cells that BCL11B participates in the control of the interleukin-2 (IL2) gene expression following activation through T-cell receptor (TCR). BCL11B augments expression from the IL2 promoter through direct binding to the US1 site. In addition, BCL11B associates with the p300 coactivator in CD4+ T cells activated through TCR, which may account for its transcriptional activation function. These results provide the first evidence that BCL11B, originally described as a transcriptional repressor, activates transcription of a target gene in the context of T-cell activation.

Countervailing effects of rapamycin (sirolimus) on nuclear factor-κB activities in neointimal and medial smooth muscle cells

OBJECTIVE

Local application of rapamycin (sirolimus) by drug-eluting stents prevents lumen obliteration after angioplasty by inhibition of neointimal hyperplasia. The effects of rapamycin on neointimal smooth muscle cells (niSMC) which are responsible for the occurrence of restenosis have not been investigated so far.

METHODS AND RESULTS

Rat niSMC and medial SMC (mSMC) were obtained from balloon catheter-injured arteries. The niSMC exhibited higher basal NF-kappaB activity and TNF-alpha mRNA levels. Nuclear protein binding to NF-kappaB-DNA was attenuated in niSMC by incubation with rapamycin (0.1 and 1 microg/ml) for 24 and 48 h. In contrast in mSMC, 0.1 microg/ml rapamycin had no effect and at 1 microg/ml even increased nuclear protein binding to NF-kappaB-DNA. After 12 h incubation, rapamycin (0.001-10 microg/ml) induced IkappaB-alpha protein in niSMC, whereas in mSMC it stimulated IkappaB-alpha at much lower levels. Prolonged rapamycin treatment (1 microg/ml for 72 h) had no effect on TNF-alpha mRNA level and NF-kappaB activity in niSMC, whereas it led to their increase in mSMC. Vascular endothelial growth factor (VEGF) secretion was higher in mSMC than in niSMC; rapamycin decreased VEGF levels in both cell types. Ultrastructural analysis suggested that rapamycin caused early signs of degeneration in niSMC, but enhanced protein synthesis in mSMC.

CONCLUSIONS

This study shows that rapamycin influences the inflammatory phenotypes of SMC in opposite directions: it reduces the high basal NF-kappaB activity in niSMC and enhances NF-kappaB activity and TNF-alpha expression in mSMC. In addition, rapamycin inhibits VEGF production regardless of the phenotype of SMC. These findings shed light on molecular mechanisms and structural changes underlying therapeutic applications of rapamycin in prevention of restenosis, inhibition of chronic transplant arteriosclerosis and reduction of secondary malignoma formation due to immunosuppression.

Prophylaxis and treatment of acute graft-versus-host disease

Acute graft-versus-host disease (GVHD) remains a major obstacle to successful allogeneic hematopoietic stem cell transplantation (HSCT). The ability to prevent GVHD--the application of successful prophylaxis--is crucial as treatment when prophylaxis fails or remains suboptimal. A calcineurin inhibitor in combination with methotrexate is still the mainstream regimen for prophylaxis of GVHD. Despite a steady increase in the repertoire of available drugs, corticosteroids remain the first-line therapy for patients who fail prevention and develop GVHD. Pan T-cell depletion studies suggest that success in prophylaxis and treatment of GVHD will depend on whether GVHD can be prevented without losing anti-malignancy and anti-infectious effects. Better understanding of the allogeneic response that is responsible for GVHD will facilitate the development of such an approach.

Rapamycin antagonizes NF-kappaB nuclear translocation activated by TNF-alpha in primary vascular smooth muscle cells and enhances apoptosis

Several lines of evidence support the view that rapamycin inhibits NF-kappaB. TNF-alpha, a potent inducer of NF-kappaB, is released after artery injury (e.g., balloon angioplasty) and plays an important role in inflammation and restenosis. We investigated the effect of rapamycin on NF-kappaB activation and apoptosis in vascular smooth muscle cells (VSMCs) stimulated with TNF-alpha. Using EMSA, we found that TNF-alpha caused NF-kappaB nuclear translocation in VSMCs after 1 h of incubation. Rapamycin inhibited IkappaBalpha degradation, thereby preventing nuclear translocation. Activation of NF-kappaB was accompanied by an increase of Bcl-xL and Bfl-1/A1 proteins, detected by Western blot assay, whereas rapamycin prevented the TNF-alpha-induced enhancement of these antiapoptotic proteins. The extent of apoptosis of VSMCs exposed to TNF-alpha was significantly enhanced by rapamycin. The effect of rapamycin appeared to be independent of the phosphatidylinositol 3-kinase/Akt-protein kinase B survival pathway, because the phosphatidylinositol 3-kinase inhibitor wortmannin neither prevented IkappaBalpha degradation nor increased apoptosis of cells incubated with TNF-alpha. Finally, we demonstrate that the large immunophilin FK-506 binding protein FKBP51 is essential for TNF-alpha-induced NF-kappaB activation in VSMCs. Our findings show that rapamycin inhibits NF-kappaB activation and acts in concert with TNF-alpha in induction of VSMC apoptosis.

A rapamycin derivative (everolimus) controls proliferation through down-regulation of truncated CCAAT enhancer binding protein {beta} and NF-{kappa}B activity in Hodgkin and anaplastic large cell lymphomas

The immunosuppressive macrolide rapamycin and its derivative everolimus (SDZ RAD, RAD) inhibit the mammalian target of rapamycin (mTOR) signaling pathway. In this study, we provide evidence that RAD has profound antiproliferative activity in vitro and in NOD/SCID mice in vivo against Hodgkin lymphoma (HL) and anaplastic large cell lymphoma (ALCL) cells. Moreover, we identified 2 molecular mechanisms that showed how RAD exerts antiproliferative effects in HL and ALCL cells. RAD down-regulated the truncated isoform of the transcription factor CCAAT enhancer binding protein beta (C/EBPbeta), which is known to disrupt terminal differentiation and induce a transformed phenotype. Furthermore, RAD inhibited constitutive nuclear factor kappaB (NF-kappaB) activity, which is a critical survival factor of HL cells. Pharmacologic inhibition of the mTOR pathway by RAD therefore interferes with essential proliferation and survival pathways in HL and ALCL cells and might serve as a novel treatment option.

Rapamycin inhibits doxorubicin-induced NF-kappaB/Rel nuclear activity and enhances the apoptosis of melanoma cells

Inhibition of nuclear factor (NF)-kappaB/Rel can sensitise many tumour cells to death-inducing stimuli, including chemotherapeutic agents, and there are data suggesting that disruption of NF-kappaB may be of therapeutic interest in melanoma. We found that rapamycin sensitised a human melanoma cell line, established from a patient, to the cytolytic effects of doxorubicin. Doxorubicin is a striking NF-kappaB/Rel-inducer, we therefore investigated if rapamycin interfered with the pathway of NF-kappaB/Rel activation, i.e. IkappaBalpha-phosphorylation, -degradation and NF-kappaB/Rel nuclear translocation, and found that the macrolide agent caused a block of IKK kinase activity that was responsible for a reduced nuclear translocation of transcription factors. Western blots for Bcl-2 and c-IAP1 showed increased levels of these anti-apoptotic proteins in cells incubated with doxorubicin, in accordance with NF-kappaB/Rel activation, while rapamycin clearly downmodulated these proteins, in line with its pro-apoptotic ability. The effect of the macrolide on NF-kappa B/Rel induction appeared to be independent of the block in the PI3k/Akt pathway, because it could not be reproduced by the phosphatidyl inositol 3 kinase (PI3k) inhibitor, wortmannin. Recently, the immunophilin, FKBP51, has been shown to be essential for the function of IKK kinase. We found high expression levels of FKBP51 in melanoma cells. Moreover, we confirmed the involvement of this immunophilin in the control of IKK activity. Indeed, IkappaBalpha could not be degraded when FKBP51 was downmodulated by short-interfering RNAs (siRNAs). These findings provide a possible mechanism for the downmodulation of NF-kappaB by rapamycin, since the macrolide agent specifically inhibits FKBP51 isomerase activity. In conclusion, our study demonstrates that rapamycin blocked NF-kappaB/Rel activation independently of PI3k/Akt inhibition suggesting that the macrolide agent could synergise with NF-kappaB-inducing anti-cancer drugs in PTEN-positive tumours.

Platelet-Independent defect in hemostasis associated with sirolimus use

Sirolimus is currently used to prevent rejection of solid organ transplant, and sirolimus-eluting stents have shown promise for the prevention of coronary artery restenosis. Thrombocytopenia is a well-known adverse effect of sirolimus limiting its use. Herein we report on a patient in whom sirolimus caused a platelet-independent hemostasis defect. The patient was a 52-year-old woman who underwent renal transplant with consequent normal kidney function. The immunosuppressive regimen included basiliximab, steroids, and cyclosporine induction later shifted to sirolimus and mycophenolate due to biopsy findings of tubular necrosis on day 6 posttransplantation. At discharge the serum creatinine was 0.7 mg/dL. Four months after transplantation the patient was admitted to our hospital because of fever (37.5 degrees C to 38 degrees C), anorexia, and asthenia. Blood analysis showed: creatinine 1.7 mg/dL, Hb 9.6 g/dL, WBC 6 x 10(3)/microL, PLT 123 x 10(3)/microL, liver function tests normal, LDH 720 mU/mL, fibrinogen 628 mg/dL, d-dimer 0.42 ng/mL, FDP > 40 ng/mL, INR 1.10, PT 87%, aPTT 40 seconds. Cultures and tests for infection were negative. Serum sirolimus level was 25.9 ng/mL. The following day the serum creatinine rose to 2.3 mg/dL and diuresis fell to 20 mL/h. Multiple bleeding times (Ivy test) performed before the renal biopsy were repeatedly over 30 minutes (normal 3 to 5 minutes), despite normal platelet count and platelet function studies. There was no spontaneous aggregation and in vitro aggregation was normal (collagen, ADP, adrenalin, and ristocetin induced). Coagulation studies showed a defect in fibrin formation and a reduction of fibrinolysis. Suspension of sirolimus treatment was followed by remission of fever, improvement of renal function (serum creatinine 1.2 mg/dL), and normalization of bleeding time.

Sirolimus, tacrolimus, and low-dose methotrexate for graft-versus-host disease prophylaxis in mismatched related donor or unrelated donor transplantation

We studied the feasibility and activity of adding sirolimus to tacrolimus and low-dose methotrexate as graft-versus-host disease (GVHD) prophylaxis in recipients of alternative donor transplants. Forty-one patients with hematologic malignancies were conditioned with cyclophosphamide and total body irradiation. Marrow stem cells were from an HLA-A, -B, and -DR compatible, unrelated donor (n = 26, 68%), from a 5 of 6 antigen-matched unrelated donor (n = 8, 20%), or from a 5 of 6 antigen-matched family member (n = 5, 12%). Therapeutic serum levels of sirolimus were attained in most patients. All evaluable patients engrafted. An absolute neutrophil count of 500/microL was achieved on day +18 (range, 11-32 days). Sustained platelet counts of more than 20 000/ microL were attained on day +29 (range, 14-98 days). Grades 0-I acute GVHD occurred in 75% of patients. Grades II, III, and IV acute GVHD occurred in 13%, 8%, and 5%, respectively (total grades II-IV GVHD, 26%). Median survival is 366 days (95% CI 185, not estimable) and actuarial survival at 1 year is 52%. Oral sirolimus is tolerable, adequate blood levels are achievable, and there is a low rate of acute GVHD compared with historical data in this high-risk population. This novel agent is worthy of further study in allogeneic transplantation.

Unifying concepts in CD28, ICOS and CTLA4 co-receptor signalling

Many studies have shown the central importance of the co-receptors CD28, inducible costimulatory molecule (ICOS) and cytotoxic T lymphocyte antigen 4 (CTLA4) in the regulation of many aspects of T-cell function. CD28 and ICOS have both overlapping and distinct functions in the positive regulation of T-cell responses, whereas CTLA4 negatively regulates the response. The signalling pathways that underlie the function of each of the co-receptors indicate their shared and unique properties and provide compelling hints of functions that are as yet uncovered. Here, we outline the shared and distinct signalling events that are associated with each of the co-receptors and provide unifying concepts that are related to signalling functions of these co-receptors.

Sirolimus: its discovery, biological properties, and mechanism of action

Sirolimus is the USAN-assigned generic name for the natural product rapamycin. Sirolimus is produced by a strain of Streptomyces hygroscopicus, isolated from a soil sample collected from Rapa Nui commonly known as Easter Island. Although sirolimus was isolated as an antifungal agent with potent anticandida activity, subsequent studies revealed impressive antitumor and immunosuppressive activities. Sirolimus demonstrates activity against several murine tumors, such as B16 43 melanocarcinoma, Colon 26 tumor, EM ependymoblastoma, and mammary and colon 38 solid tumors. Sirolimus is a potent inhibitor of antigen-induced proliferation of T cells, B cells, and antibody production. Demonstration of the potent immunosuppressive activity of sirolimus in animal models of organ transplantation led to clinical trials and subsequent approval by regulatory authorities for prophylaxis of renal graft rejection. Interest in sirolimus as an immunosuppressive therapy in organ transplantation derives from its unique mechanism of action, its unique side-effect profile, and its ability to synergize with other immunosuppressive agents. The molecular mechanism underlying the antifungal, antiproliferative, and immunosuppressive activities of sirolimus is the same. Sirolimus forms an immunosuppressive complex with intracellular protein, FKBP12. This complex blocks the activation of the cell-cycle-specific kinase, TOR. The downstream events that follow the inactivation of TOR result in the blockage of cell-cycle progression at the juncture of G1 and S phase.

It's all Rel-ative: NF-kappaB and CD28 costimulation of T-cell activation

Costimulatory signals complement or modify the signals provided to a lymphocyte through antigen receptors. For productive T-cell activation, the CD28 molecule is apparently the most important, although not the only, costimulatory receptor. CD28 can provide a signal that is at least partially distinct from that delivered by the T cell receptor (TCR)-CD3 complex. Several lines of evidence indicate that the nuclear factor (NF)-kappaB pathway is perhaps the most relevant biochemical or transcriptional target for the costimulatory activity of CD28. Although many questions remain, recent years have witnessed significant progress in understanding the signal transduction pathways leading from the TCR and CD28 to Rel/NF-kappaB-dependent transcription.

DQ 65-79, a peptide derived from HLA class II, induces I kappa B expression

A synthetic peptide corresponding to residues 65-79 of the alpha helix of the alpha-chain of the class II HLA molecule DQA03011 (DQ 65-79) inhibits the proliferation of human T lymphocytes in an allele nonrestricted manner. By using microarray technology, we found that expression of 29 genes was increased or decreased in a human CTL cell line after treatment with DQ 65-79. This study focuses on one of these genes, IkappaB-alpha, whose expression is increased by DQ 65-79. IkappaB proteins, including IkappaB-alpha and IkappaB-beta, are increased in T cells treated with DQ 65-79. Nuclear translocation of the NF-kappaB subunits p65 and p50 is decreased in T cells after treatment with DQ 65-79, while elevated levels of p65 and p50 are present in cytosol. DQ 65-79 inhibits the degradation of IkappaB-alpha mRNA and inhibits the activity of IkappaB kinase. These findings indicate that the DQ 65-79 peptide increases the level of IkappaB proteins, thereby preventing nuclear translocation of the transcription factor, NF-kappaB, and inhibiting T cell proliferation.

Sirolimus: a comprehensive review

Sirolimus (Rapamune), Wyeth-Ayerst, Madison, NJ) is a new, potent, immunosuppressant that is emerging as a foundation for long-term immunosuppressive therapy in renal transplantation. The drug acts during both co-stimulatory activation and cytokine-driven pathways via a unique mechanism: inhibition of a multifunctional serine-threonine kinase, mammalian target of rapamycin (mTOR). Although there is no a priori reason to assume it, sirolimus displays a synergistic interaction to enhance the efficacy of cyclosporin A (CsA). In trials wherein the concentrations of CsA and sirolimus were tightly controlled, rates of acute rejection episodes were < 10%, despite markedly reduced exposures to each agent. In pivotal multi-centre blinded dose-controlled trials, the rates of acute rejection episodes within 12 months following administration of 2 or 5 mg/day sirolimus in combination with CsA and steroids were reduced to 19 and 14%, respectively. Since the inhibitory effect of sirolimus disables virtually all responses to cytokine mediators due to the widespread involvement of mTOR in multiple signalling pathways, the agent is likely also to retard proliferation of endothelial and vascular smooth muscle cells, an important component of the immuno-obliterative processes associated with chronic rejection. The advantages of this unique therapeutic action combined with an intrinsic lack of nephrotoxicity are counterbalanced by myelosuppressive and hyperlipidaemic side effects. Ongoing studies are assessing whether the long-term benefits of sirolimus to permit reduction in exposure to or elimination of calcineurin inhibitors ameliorate the progression of chronic nephropathy, the condition that erodes long-term renal transplant survival.

Contemporary immunosuppression in renal transplantation

Over the past 3 decades, renal allograft survival has improved significantly as a result of the development of powerful immunosuppressive agents. Nevertheless, the overall half-life of renal allografts has increased marginally during that time period, owing to drug-related nephrotoxicity and chronic rejection. New immunosuppressive agents are being evaluated because of the need for a reduction in the dose of nephrotoxic calcineurin inhibitors and corticosteroids. Additional agents have demonstrated the ability to retard the onset of chronic rejection in preclinical transplant models. In concert with these efforts, approaches are in development to alleviate the ever increasing shortage of donor organs, including the as yet unrealized goals of successful and practical xenotransplantation and the bioartificial kidney. Further identification and development of novel agents that target the specific components of the allograft response will provide the key to the achievement of donor-specific tolerance, the "Holy Grail" of solid organ transplantation.

Western and Chinese antirheumatic drug-induced T cell apoptotic DNA damage uses different caspase cascades and is independent of Fas/Fas ligand interaction

Spontaneous or therapeutic induction of T cell apoptosis plays a critical role in establishing transplantation tolerance and maintaining remission of autoimmune diseases. We investigated the mechanisms of apoptosis induced by Chinese and Western antirheumatic drugs (ARDs) in human T cells. We found that hydroxychloroquine, Tripterygium wilfordii hook F, and tetrandrine (Tet), but not methotrexate, at therapeutic concentrations can cause T cell death. In addition, Tet selectively killed T cells, especially activated T cells. Although ARD-induced cytotoxicity was mediated through apoptotic mechanisms, Fas/Fas ligand interaction was not required. We further demonstrated that the processes of phosphatidylserine externalization and DNA damage along the ARD-induced T cell apoptotic pathway could operate independently, and that selective inhibition of DNA damage by caspase inhibitors did not prevent T cells from undergoing cell death. Moreover, we found that Tet- and Tripterygium wilfordii hook F-induced T cell DNA damage required caspase-3 activity, and hydroxychloroquine-induced T cell DNA damage was mediated through a caspase-3- and caspase-8-independent, but Z-Asp-Glu-Val-Asp-fluomethyl ketone-sensitive, signaling pathway. Finally, the observation that ARD-induced activation of caspase-3 in both Fas-sensitive and Fas-resistant Jurkat T cells indicates that Fas/Fas ligand interaction plays no role in ARD-induced T cell apoptosis. Our observations provide new information about the complex apoptotic mechanisms of ARDs, and have implications for combining Western and Chinese ARDs that have different immunomodulatory mechanisms in the therapy of autoimmune diseases and transplantation rejection.

Tachykinin activation of human monocytes from patients with rheumatoid arthritis: in vitro and ex-vivo effects of cyclosporin A

Three types of tachykinin receptors, namely NK1, NK2 and NK3, are known to preferentially interact with substance P (SP), neurokinin A (NKA) and neurokinin B (NKB), respectively. We previously demonstrated that NK1 and NK2 receptors are present on human monocytes, SP and NKA inducing superoxide anion production and tumor necrosis factor-alpha (TNF-alpha) mRNA expression. NK2 receptor stimulation also triggered an enhanced respiratory burst in monocytes isolated from rheumatoid arthritis (RA) patients. This study was aimed to evaluate the in vitro and ex-vivo effects of cyclosporin A (CsA) on tachykinins-evoked TNF-alpha release from monocytes of healthy donors and RA patients. CsA (100 ng/ml) potently inhibited phorbol ester- and tachykinin-evoked TNF-alpha secretion. In RA patients treated with CsA (Sandimmun Neoral 2.5 mg/kg/day, a significant time-dependent reduction in TNF-alpha secretion from monocytes was measured. This may contribute to the CsA therapeutic activity in RA.

Immunosuppressive agents in transplantation: mechanisms of action and current anti-rejection strategies

Over the past century, the concept of interfering with the immune response at various sites by blocking the formation, stimulation, proliferation, and differentiation of lymphocytes has led to relentless development of new immunosuppressive drugs. These agents are associated with reduced risk of short- and long-term toxicity and have dramatically improved allograft and patient survival, especially in recipients of solid organ transplants. Current protocols in such patients are nearly all calcineurin-inhibitor based, using cyclosporine or tacrolimus, as part of dual, triple, or sequential therapy. This review focuses on agents currently in clinical use at transplant centers in United States. The drugs are described in terms of their basic mechanisms of action, therapeutic uses, clinical studies, and adverse effects. In addition, the efficacy and toxicity of a few promising new therapeutic approaches are examined. Finally, important challenges regarding pharmacological immunosuppression as it relates to solid organ and composite tissue allotransplantation are discussed.

Akt provides the CD28 costimulatory signal for up-regulation of IL-2 and IFN-gamma but not TH2 cytokines

A region of the interleukin-2 (IL-2) promoter known as the RE/AP element is activated in concert by signals that originate from the T cell antigen receptor and the CD28 coreceptor. We show here that the serine-threonine kinase Akt can provide a costimulatory signal for RE/AP activation that is indistinguishable from the signal provided by CD28. This includes the ability of Akt, like antibodies to CD28, to synergize with protein kinase C theta (PKC-theta) in the induction of RE/AP. Retrovirus-mediated expression of activated Akt in primary T cells from CD28-deficient mice is capable of selectively restoring production of IL-2 and interferon gamma, but not IL-4 or IL-5. Our results provide evidence that CD28 costimulation of different cytokines is mediated by discrete signaling pathways, one of which includes Akt.

The NF-kappa B signaling pathway is not required for Fas ligand gene induction but mediates protection from activation-induced cell death

Stimulation of T cells by antigens or mitogens triggers multiple signaling pathways leading to activation of genes encoding interleukin-2 and other growth-regulatory cytokines. The same stimuli also activate the gene encoding an apoptosis-inducing molecule, Fas ligand (FasL), which contributes to activation-induced cell death. It has been proposed that the signaling pathways involved in cytokine gene induction also contribute to activation-induced FasL expression; however, genetic evidence for this proposal is lacking. In the present study, the role of the NF-kappaB signaling pathway in FasL gene expression was examined using a mutant T cell line deficient in an essential NF-kappaB signaling component, IkappaB kinase gamma. These mutant cells have a blockade in signal-induced activation of NF-kappaB but remained normal in the activation of NF-AT and AP-1 transcription factors. Interestingly, the NF-kappaB signaling defect has no effect on mitogen-stimulated FasL gene expression, although it completely blocks the interleukin-2 gene induction. We further demonstrate that NF-kappaB activation is required for protecting T cells from apoptosis induction by mitogens and an agonistic anti-Fas antibody. These genetic results suggest that the NF-kappaB signaling pathway is not required for activation-induced FasL expression but rather mediates cell growth and protection from activation-induced cell death.

Repression of IL-2 promoter activity by the novel basic leucine zipper p21SNFT protein

IL-2 is the major autocrine and paracrine growth factor produced by T cells upon T cell stimulation. The inducible expression of IL-2 is highly regulated by multiple transcription factors, particularly AP-1, which coordinately activate the promoter. Described here is the ability of the novel basic leucine zipper protein p21SNFT to repress AP-1 activity and IL-2 transcription. A detailed analysis of the repression by p21SNFT repression on the IL-2 promoter distal NF-AT/AP-1 site demonstrates that it can bind DNA with NF-AT and Jun, strongly suggesting that it represses NF-AT/AP-1 activity by competing with Fos proteins for Jun dimerization. The importance of this repression is that p21SNFT inhibits the trans-activation potential of protein complexes that contain Jun, thereby demonstrating an additional level of control for the highly regulated, ubiquitous AP-1 transcription factor and the IL-2 gene.

Control of CD4 T cell fate by antigen re-stimulation with or without CTLA-4 engagement 24 h after priming

After two consecutive inoculations with Staphylococcus enterotoxin B (SEB) at 24 h intervals in vivo, CD4 T cells became anergic to the antigen challenge in vitro. Administration of anti-CTLA-4 mAb in conjunction with the second SEB inoculation 24 h after antigen priming interfered with anergy and CD4 T cells became T(h)2 cells. However, the anergy induction was not ablated when SEB and anti-CTLA-4 mAb were administered 48 or 72 h after antigen priming. Moreover, anti-CTLA-4 mAb without SEB did not interfere with anergy nor promoted the T(h)2 differentiation. T-antigen-presenting cell (APC) interaction in vitro in the presence of high doses of antigen and anti-CTLA-4 mAb induced a T(h)2-polarizing cytokine IL-6 and IL-10. IL-10 then down-modulated a T(h)1-polarizing cytokine IL-12. The results demonstrate that 24 h after the initial antigen stimulation, CD4 T cells enter the critical activation phase where antigen re-stimulation with or without CTLA-4 engagement alters the fate of the cell, anergy or differentiation respectively. Once anergy is interfered with, T(h)2-polarizing cytokines produced upon prolonged T-APC interaction favor the T(h)2 differentiation.

Somatic mutagenesis studies of NF-kappa B signaling in human T cells: evidence for an essential role of IKK gamma in NF-kappa B activation by T-cell costimulatory signals and HTLV-I Tax protein

NF-kappa B plays a pivotal role in normal T-cell activation and may also mediate human T-cell leukemia virus (HTLV)-induced T-cell transformation. Activation of NF-kappa B by both T-cell costimulatory signals and the HTLV Tax protein involves stimulation of I kappa B kinase (IKK). As a genetic approach to dissect the intermediate steps involved in NF-kappa B activation in human T cells, we performed somatic cell mutagenesis to isolate signaling-defective mutant Jurkat T-cell lines. One of the mutant cell lines was shown to have a specific blockade in the IKK signaling pathway but remained competent in the c-Jun N-terminal kinase and MAP kinase pathways. Interestingly, this mutant cell line lacks expression of IKK gamma, a non-catalytic component of the IKK complex. Expression of exogenous IKK gamma in the mutant cells restored NF-kappa B activation by both the T-cell costimulation agents and Tax. These findings provide genetic evidence for the requirement of IKK gamma in NF-kappa B signaling triggered by both T-cell costimulatory signals and HTLV-I Tax protein.

Plant alkaloid tetrandrine and its analog block CD28-costimulated activities of human peripheral blood T cells: potential immunosuppressants in transplantation immunology

BACKGROUND

T lymphocyte activation mediated by CD28 costimulation plays a critical role in graft rejection. Plant alkaloid tetrandrine, purified from a Chinese antirheumatic herb, is a potent immunosuppressant. Here, we examined its effects on several CD28-costimulated T-cell activities. In addition, such effects were readily compared with the effects of three tetrandrine analogs.

METHODS

T lymphocytes were purified from whole blood by negative selection. The stimuli that mimic CD28 costimulation included both anti-CD3 + anti-CD28 monoclonal antibody and PMA+anti-CD28 monoclonal antibody. The determination of CD28-costimulated cell proliferation was performed by tritium uptake, cytokine production by ELISA, cell surface interleukin 2Ra and CD69 expression by flow cytometry, and mixed leukocyte reaction by tritium uptake. Drug cytotoxicity was determined by trypan blue exclusion, propidium iodide staining, and MTT colorimetric assays.

RESULTS

Tetrandrine inhibited CD28-costimulated T-cell proliferation and cytokine production through a mechanism different from that of cyclosporine. In addition, tetrandrine down-regulated both T helper 1 and T helper 2 cytokine production in CD4+ and CD8+ T-cell subpopulations. By examining cytokine production and T-cell activation marker expression, we further demonstrated that, among tetrandrine and its analogs tested, dauricine was the most potent suppressor of CD28-costimulated T-cell activities. Furthermore, the different immunosuppressive activities of these compounds were not associated with their cytotoxic capacities. Finally, the unparalleled inhibitory potency of dauricine on both mixed leukocyte reaction and CD28-costimulated T-cell proliferation suggests that dauricine preferentially targeted CD28-costimulated T-cell activities.

CONCLUSIONS

This is the first report to show that tetrandrine and its analogs potently inhibited both PMA+CD28-costimulated and CD3 + CD28-costimulated activation of human peripheral blood T cells. Based upon their structural similarity and different immunosuppressive potency, these in vitro data also provide very useful information for further identification and development of more potent and less toxic immunosuppressants to achieve transplantation success.

The Inhibitory Action of Mycobacterium ulcerans Soluble Factor on Monocyte/T Cell Cytokine Production and NF-κB Function

Buruli ulcer is a chronic and progressive necrotizing ulcer for which there is no medical treatment. Historically, a soluble toxin (factor) derived from the causative Mycobacterium ulcerans was found to induce the massive necrosis of skin and s.c. tissue seen in this condition. However, the persistence of the disease is thought to be caused by a lack of any immune response. We therefore investigated whether the factor was related to immunosuppression. A protocol to partially purify the factor was developed, and its effects on immune competent cells were tested. The factor produced &gt;95% inhibition of LPS-induced release of TNF and IL-10 from human monocytes and caused a loss of adherence of these cells without cell death. The factor also blocked the production of IL-2 from activated T lymphocytes. The factor had no effect on TNF-induced cytotoxicity, but abrogated TNF-induced NF-κB activation. Surprisingly, a synergy was observed between the factor and phorbol ester-directed NF-κB activation. The factor had no effect on IL-1- or LPS-induced NF-κB activity, indicating selective activity of the factor. The factor did not inhibit the degradation of IκBα induced by TNF, indicating that the target for its activity lies within an undefined part of the TNF signaling mechanism. The data indicate that the localized immunosuppression associated with Buruli ulcer relates to the activity of the released factor, and this may provide a target for future therapeutic strategies for this intractable disease.

IL-2-Independent Activation and Proliferation in Human T Cells Induced by CD28

Although the role of CD28 in T cell costimulation is firmly established, the mechanisms by which it exerts its costimulatory actions are less clear. In many circumstances it is difficult to distinguish the effects of CD28 from subsequent actions of cytokines, such as IL-2, on T cell proliferation. Here, we report a model of CD28 costimulation using PMA plus the natural ligand CD80 that resulted in very limited stimulation of IL-2, as evidenced by both cytokine production and IL-2 promoter stimulation. Promoter assays revealed CD28-dependent effects on both NF-κB and AP-1, but not on NF-AT or the intact IL-2 promoter. In addition, T cell proliferation was completely resistant to the actions of the immunosuppressant cyclosporin A (CsA). Moreover T cell proliferation was unaffected by the addition of blocking Abs to both IL-2 and the IL-2 receptor, demonstrating that this form of costimulation by CD28 was independent of IL-2. We also investigated the effects of stimulating T cell blasts with CD80 alone and found that there was a limited requirement for IL-2 in this system. We conclude that CD28 costimulation can cause substantial T cell proliferation in the absence of IL-2, which is driven by a soluble factor independent of NF-AT transactivation.

CD28-Mediated Regulation of mRNA Stability Requires Sequences Within the Coding Region of the IL-2 mRNA

Using sequence-tagged genomic reporter constructs, we investigated the contribution of IL-2 sequences to CD28-mediated regulation of mRNA stability. We find that CD28 signaling acts transiently to stabilize the IL-2 mRNA following T cell activation. Such stabilization requires sequences within both exon 2 and the coding region of exon 4. Unexpectedly, CD28 signaling at later times enhances the decay of the IL-2 mRNA. This CD28-dependent decay of IL-2 mRNA requires sequences localized between exon 3 and the stop codon. Our findings demonstrate that the coding region of the IL-2 mRNA contains previously undefined CD28-responsive sequence elements that are critical for the regulation of mRNA stability.

Cytokine-induced apoptosis in epithelial HT-29 cells is independent of nitric oxide formation. Evidence for an interleukin-13-driven phosphatidylinositol 3-kinase-dependent survival mechanism

A combination of the pro-inflammatory cytokines interleukin (IL)-1alpha, interferon (IFN)-gamma, and tumor necrosis factor (TNF)-alpha induces nitric oxide synthase mRNA expression and nitric oxide (NO) generation in the human colon carcinoma cell line HT-29. This can be inhibited by pretreatment with IL-13 via a phosphatidylinositol (PI) 3-kinase-dependent mechanism (Wright, K., Ward, S. G., Kolios, G., and Westwick, J. (1997) J. Biol. Chem. 272, 12626-12633). Since NO has been implicated in regulating mechanisms leading to cell death, while activation of PI 3-kinase-dependent signaling cascades are thought to be involved with promoting cell survival events, we have investigated the outcome of these cytokine treatments on apoptosis and cell survival of HT-29 cells. Initiation of apoptosis can be achieved by the combinations of IFN-gamma/TNF-alpha, IFN-gamma/CD95, IL-1alpha/IFN-gamma, and IL-1alpha/IFN-gamma/TNF-alpha to varying extents. Induction of apoptotic markers by HT-29 cells in response to cytokine treatment is not dependent on NO production. Pretreatment with IL-13 protects against IL-1alpha/IFN-gamma/TNF-alpha- and IFN-gamma/TNF-alpha- as well as IFN-gamma/CD95-induced (but not IL-1alpha/IFN-gamma-induced) cell death. In addition, IFN-gamma/TNF-alpha and IL-1alpha/IFN-gamma/TNF-alpha stimulate activation of caspase-8 and caspase-3, which IL-13 pretreatment was able to partially inhibit and delay. IL-13 also stimulates activation of the major PI 3-kinase effector, protein kinase B. The PI 3-kinase inhibitors wortmannin and LY294002 inhibit IL-13 stimulation of protein kinase B as well as the cell survival effects of IL-13. These data demonstrate that cytokine-induced apoptosis of HT-29 cells is NO-independent and that the activation of a PI 3-kinase-dependent signaling cascade by IL-13 is a key signal responsible for the inhibition of apoptosis.