Molecular mechanisms underlying differential contribution of CD28 versus non-CD28 costimulatory molecules to IL-2 promoter activation

A promising target for breast cancer: B7-H3

Breast cancer (BC) is the second-leading factor of mortality for women globally and is brought on by a variety of genetic and environmental causes. The conventional treatments for this disease have limitations, making it difficult to improve the lifespan of breast cancer patients. As a result, extensive research has been conducted over the past decade to find innovative solutions to these challenges. Targeting of the antitumor immune response through the immunomodulatory checkpoint protein B7 family has revolutionized cancer treatment and led to intermittent patient responses. B7-H3 has recently received attention because of its significant demodulation and its immunomodulatory effects in many cancers. Uncontrolled B7-H3 expression and a bad outlook are strongly associated, according to a substantial body of cancer research. Numerous studies have shown that BC has significant B7-H3 expression, and B7-H3 induces an immune evasion phenotype, consequently enhancing the survival, proliferation, metastasis, and drug resistance of BC cells. Thus, an innovative target for immunotherapy against BC may be the B7-H3 checkpoint.In this review, we discuss the structure and regulation of B7-H3 and its double costimulatory/coinhibitory function within the framework of cancer and normal physiology. Then we expound the malignant behavior of B7-H3 in BC and its role in the tumor microenvironment (TME) and finally focus on targeted drugs against B7-H3 that have opened new therapeutic opportunities in BC.

Cooperation of RNA-Binding Proteins – a Focus on Roquin Function in T Cells

Post-transcriptional gene regulation by RNA-binding proteins (RBPs) is important in the prevention of inflammatory and autoimmune diseases. With respect to T cell activation and differentiation, the RBPs Roquin-1/2 and Regnase-1 play pivotal roles by inducing degradation and/or translational silencing of target mRNAs. These targets encode important proinflammatory mediators and thus Roquin and Regnase-1 functions dampen cellular programs that can lead to inflammation and autoimmune disease. Recent findings demonstrate direct physical interaction of both RBPs. Here, we propose that cooperativity of trans-acting factors may be more generally used to reinforce the regulatory impact on selected targets and promote specific cell fate decisions. We develop this concept for Roquin and Regnase-1 function in resting and activated T cells and discuss the involvement in autoimmunity as well as how the therapeutic potential can be used in anti-tumor therapies.

Inherited human c-Rel deficiency disrupts myeloid and lymphoid immunity to multiple infectious agents

We studied a child with severe viral, bacterial, fungal, and parasitic diseases, who was homozygous for a loss-of-function mutation of REL, encoding c-Rel, which is selectively expressed in lymphoid and myeloid cells. The patient had low frequencies of NK, effector memory cells reexpressing CD45RA (Temra) CD8+ T cells, memory CD4+ T cells, including Th1 and Th1*, Tregs, and memory B cells, whereas the counts and proportions of other leukocyte subsets were normal. Functional deficits of myeloid cells included the abolition of IL-12 and IL-23 production by conventional DC1s (cDC1s) and monocytes, but not cDC2s. c-Rel was also required for induction of CD86 expression on, and thus antigen-presenting cell function of, cDCs. Functional deficits of lymphoid cells included reduced IL-2 production by naive T cells, correlating with low proliferation and survival rates and poor production of Th1, Th2, and Th17 cytokines by memory CD4+ T cells. In naive CD4+ T cells, c-Rel is dispensable for early IL2 induction but contributes to later phases of IL2 expression. The patient's naive B cells displayed impaired MYC and BCL2L1 induction, compromising B cell survival and proliferation and preventing their differentiation into Ig-secreting plasmablasts. Inherited c-Rel deficiency disrupts the development and function of multiple myeloid and lymphoid cells, compromising innate and adaptive immunity to multiple infectious agents.

Bacillus toyonensis BCT-7112T transient supplementation improves vaccine efficacy in ewes vaccinated against Clostridium perfringens epsilon toxin

AIM

The aim of the present study was to examine the vaccine immune response in ewes supplemented with Bacillus toyonensis BCT-7112^T during a period of 5-day supplementation before vaccination against a recombinant Clostridium perfringens epsilon toxin (rETX).

METHODS AND RESULTS

Ewes were vaccinated with 200 µg of rETX adjuvanted with 10% aluminium hydroxide. The treat group was orally supplemented with B. toyonensis BCT-7112^T (3 × 10⁸ viable spores) for 5 days prior to the first and second vaccination. Ewes supplemented with B. toyonensis BCT-7112^T showed higher neutralizing antibody titres than the non-supplemented ewes (P < 0·05), with an increase in serum levels for total IgG anti-rETX by 3·2-fold (P < 0·0001), and for both IgG isotypes IgG1 and IgG2 by 2·1-fold and 2·3-fold (P < 0·01), respectively, compared with the control group. The peripheral blood mononuclear cells of ewes in the supplemented group had a higher (P < 0·05) cytokine mRNA transcription levels for IL-2 (6·4-fold increase), IFN-γ (2·9-fold increase) and transcription factor Bcl6 (2·3-fold increase) compared with the control group.

CONCLUSION

We conclude that a 5 days of supplementation with B. toyonensis BCT-7112^T prior vaccination is sufficient to significantly improve the humoral immune response of ewes against C. perfringens recombinant ETX vaccine.

SIGNIFICANCE AND IMPACT OF THE STUDY

These findings open a new perspective in the utilization of B. toyonensis BCT-7112^T as an immunomodulator since a 5 days period of probiotic supplementation is sufficient to improve the vaccine immune response.

B7-H3: A promising therapeutic target for autoimmune diseases

B7-H3 as a newly identified costimulatory molecule that belongs to B7 ligand family, is broadly expressed in both lymphoid and non-lymphoid tissues. The overexpression of B7-H3 has been verified to be correlated with the poor prognosis and poor clinical outcome of several human cancers. In recent years, researchers reveal that B7-H3 is involved in the pathogenesis of various autoimmune diseases, such as systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), multiple sclerosis (MS), Sjögren's syndrome (SS), ankylosing spondylitis (AS), etc. In this review, we will discuss the biological function of B7-H3 and summarize the progress made over past years regarding its role in the occurrence and development of autoimmune diseases. The insights gained from these findings could serve as the foundation for future therapies of these diseases.

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.

Ubiquitin enzymes in the regulation of immune responses

Ubiquitination plays a central role in the regulation of various biological functions including immune responses. Ubiquitination is induced by a cascade of enzymatic reactions by E1 ubiquitin activating enzyme, E2 ubiquitin conjugating enzyme, and E3 ubiquitin ligase, and reversed by deubiquitinases. Depending on the enzymes, specific linkage types of ubiquitin chains are generated or hydrolyzed. Because different linkage types of ubiquitin chains control the fate of the substrate, understanding the regulatory mechanisms of ubiquitin enzymes is central. In this review, we highlight the most recent knowledge of ubiquitination in the immune signaling cascades including the T cell and B cell signaling cascades as well as the TNF signaling cascade regulated by various ubiquitin enzymes. Furthermore, we highlight the TRIM ubiquitin ligase family as one of the examples of critical E3 ubiquitin ligases in the regulation of immune responses.

Ubiquitin signaling in immune responses

Ubiquitination has emerged as a crucial mechanism that regulates signal transduction in diverse biological processes, including different aspects of immune functions. Ubiquitination regulates pattern-recognition receptor signaling that mediates both innate immune responses and dendritic cell maturation required for initiation of adaptive immune responses. Ubiquitination also regulates the development, activation, and differentiation of T cells, thereby maintaining efficient adaptive immune responses to pathogens and immunological tolerance to self-tissues. Like phosphorylation, ubiquitination is a reversible reaction tightly controlled by the opposing actions of ubiquitin ligases and deubiquitinases. Deregulated ubiquitination events are associated with immunological disorders, including autoimmune and inflammatory diseases.

Transmembrane TNF-TNFR2 Impairs Th17 Differentiation by Promoting Il2 Expression

The double-edged sword nature by which IL-2 regulates autoimmunity and the unpredictable outcomes of anti-TNF therapy in autoimmunity highlight the importance for understanding how TNF regulates IL-2. Transmembrane TNF (tmTNF) preferentially binds TNFR2, whereas soluble TNF (sTNF) binds TNFR1. We previously showed reduced IL-2 production in TNFR1(-/-) TNFR2(-/-) CD4(+) T cells. In this study, we generated TNFR1(-/-), TNFR2(-/-), or TNFR1(-/-) TNFR2(-/-) 5C.C7 TCR Il2-GFP mice and report that CD4(+) T cell-intrinsic tmTNF/TNFR2 stimulates Il2 promoter activity and Il2 mRNA stability. We further used tmTNF Foxp3 gfp reporter mice and pharmacological TNF blockade in wild-type mice to report a tmTNF/TNFR2 interaction for Il2 expression. IL-17 is critical for host defense, but its overabundance promotes autoimmunity. IL-2 represses Th17 differentiation, but the role for TNFR2 in this process is not well understood. We report elevated expression of TNFR2 under Th17-polarization conditions. Genetic loss-of-function experimental models, as well as selective TNF blockade by etanercept and XPro1595 in wild-type mice, demonstrate that impaired tmTNF/TNFR2, but not sTNF/TNFR1, promotes Th17 differentiation in vivo and in vitro. Under Th17-polarizing conditions, elevated IL-17 production by TNFR2-knockout CD4(+) T cells was associated with increased STAT3 activity and decreased STAT5 activity. Increased IL-17 production in TNFR2-knockout T cells was prevented by adding exogenous IL-2. We conclude that CD4(+) T cell-intrinsic tmTNF/TNFR2 promotes IL-2 production that inhibits the generation of Th17 cells in a Foxp3-independent manner. Moreover, under Th17-polarizing conditions, selective blockade of CD4(+) T cell-intrinsic TNFR2 appears to be sufficient to promote Th17 differentiation.

Amaranthus leucocarpus lectin recognizes a moesin-like O-glycoprotein and costimulates murine CD3-activated CD4(+) T cells

The Galβ1,3GalNAcα1,O-Ser/Thr specific lectin from Amaranthus leucocarpus (ALL) binds a ∼70 kDa glycoprotein on murine T cell surface. We show that in the absence of antigen presenting cells, murine CD4⁺ T cells activated by an anti-CD3 antibody plus ALL enhanced cell proliferation similar to those cells activated via CD3/CD28 at 48 h of culture. Moreover, ALL induced the production of IL-4, IL-10, TNF-alpha, and TGF-beta in CD3-activated cells. Proteomic assay using two-dimensional electrophoresis and far-Western blotting, ALL recognized two prominent proteins associated to the lipid raft microdomains in CD3/CD28-activated CD4⁺ T cells. By mass spectrometry, the peptide fragments from ALL-recognized proteins showed sequences with 33% homology to matricin (gi|347839 NCBInr) and 41% identity to an unnamed protein related to moesin (gi|74186081 NCBInr). Confocal microscopy analysis of CD3/CD28-activated CD4⁺ T cells confirmed that staining by ALL colocalized with anti-moesin FERM domain antibody along the plasma membrane and in the intercellular contact sites. Our findings suggest that a moesin-like O-glycoprotein is the ALL-recognized molecule in lipid rats, which induces costimulatory signals on CD4⁺ T cells.

Protein kinase C signaling and cell cycle regulation

A link between T cell proliferation and the protein kinase C (PKC) family of serine/threonine kinases has been recognized for about 30 years. However, despite the wealth of information on PKC-mediated control of, T cell activation, understanding of the effects of PKCs on the cell cycle machinery in this cell type remains limited. Studies in other systems have revealed important cell cycle-specific effects of PKC signaling that can either positively or negatively impact proliferation. The outcome of PKC activation is highly context-dependent, with the precise cell cycle target(s) and overall effects determined by the specific isozyme involved, the timing of PKC activation, the cell type, and the signaling environment. Although PKCs can regulate all stages of the cell cycle, they appear to predominantly affect G0/G1 and G2. PKCs can modulate multiple cell cycle regulatory molecules, including cyclins, cyclin-dependent kinases (cdks), cdk inhibitors and cdc25 phosphatases; however, evidence points to Cip/Kip cdk inhibitors and D-type cyclins as key mediators of PKC-regulated cell cycle-specific effects. Several PKC isozymes can target Cip/Kip proteins to control G0/G1 → S and/or G2 → M transit, while effects on D-type cyclins regulate entry into and progression through G1. Analysis of PKC signaling in T cells has largely focused on its roles in T cell activation; thus, observed cell cycle effects are mainly positive. A prominent role is emerging for PKCθ, with non-redundant functions of other isozymes also described. Additional evidence points to PKCδ as a negative regulator of the cell cycle in these cells. As in other cell types, context-dependent effects of individual isozymes have been noted in T cells, and Cip/Kip cdk inhibitors and D-type cyclins appear to be major PKC targets. Future studies are anticipated to take advantage of the similarities between these various systems to enhance understanding of PKC-mediated cell cycle regulation in T cells.

NF-κB and Rheumatoid Arthritis: Will Understanding Genetic Risk Lead to a Therapeutic Reward?

NF-κB has long been known to play an important role in autoimmune diseases such as rheumatoid arthritis (RA). Indeed, as our understanding of how NF-κB is utilized has increased, we have been hard put to find a process not associated with this transcription factor family in some way. However, new data originating, in part, from genome-wide association studies have demonstrated that very specific alterations in components of the NF-κB pathway are sufficient to confer increased risk of developing disease. Here we review the data which have identified specific components of the NF-κB pathway, and consider what is known of their mechanisms of action and how these mechanisms might play into the disease process. In addition, the use of genetic information to predict RA is considered.

The ubiquitin ligase Peli1 negatively regulates T cell activation and prevents autoimmunity

T cell activation is subject to tight regulation to avoid inappropriate responses to self antigens. Here we show that genetic deficiency in the ubiquitin ligase Peli1 caused hyperactivation of T cells and rendered T cells refractory to suppression by regulatory T cells and transforming growth factor-β (TGF-β). As a result, Peli1-deficient mice spontaneously developed autoimmunity characterized by multiorgan inflammation and autoantibody production. Peli1 deficiency resulted in the nuclear accumulation of c-Rel, a member of the NF-κB family of transcription factors with pivotal roles in T cell activation. Peli1 negatively regulated c-Rel by mediating its Lys48 (K48) ubiquitination. Our results identify Peli1 as a critical factor in the maintenance of peripheral T cell tolerance and demonstrate a previously unknown mechanism of c-Rel regulation.

An enigmatic tail of CD28 signaling

CD28 costimulation regulates a wide range of cellular processes, from proliferation and survival to promoting the differentiation of specialized T-cell subsets. Since first being identified over 20 years ago, CD28 has remained a subject of intense study because of its profound consequences on T cell function and its potential for therapeutic manipulation. In this review we highlight the signaling cascades initiated by the major signaling motifs in CD28, focusing on PI-3 kinase-dependent and -independent pathways and how these are linked to specific cellular outcomes. Recent studies using gene targeted knockin mice have clarified the relative importance of these motifs on in vivo immune responses; however, much remains to be elucidated. Understanding the mechanism behind costimulation holds great potential for development of new clinically relevant reagents, a fact beginning to be realized with the advent of drugs that prevent CD28 ligation and signaling.

c-Rel phenocopies PKCtheta but not Bcl-10 in regulating CD8+ T-cell activation versus tolerance

Elucidating the signaling events that promote T-cell tolerance versus activation provides important insights for manipulating immunity in vivo. Previous studies have suggested that the absence of PKCtheta results in the induction of anergy and that the balance between the induction of the transcription factors NFAT, AP1 and NF-kappaB plays a key role in determining whether T-cell anergy or activation is induced. Here, we examine whether Bcl-10 and specific family members of NF-kappaB act downstream of PKCtheta to alter CD8(+) T-cell activation and/or anergy. We showed that T cells from mice deficient in c-Rel but not NF-kappaB1 (p50) have increased susceptibility to the induction of anergy, similar to T cells from PKCtheta-deficient mice. Surprisingly T cells from Bcl-10-deficient mice showed a strikingly different phenotype to the PKCtheta-deficient T cells, with a severe block in TCR-mediated activation. Furthermore, we have also shown that survival signals downstream of NF-kappaB, are uncoupled from signals that mediate T-cell anergy. These results suggest that c-Rel plays a critical role downstream of PKCtheta in controlling CD8(+) T-cell anergy induction.

T cell-intrinsic role of Nod2 in promoting type 1 immunity to Toxoplasma gondii

Nod2 belongs to the (NOD)-like receptor (NLR) family of proteins, which function as intracellular pathogen sensors in innate immune cells. Nod2-deficiency results in an impaired immune response against bacterial pathogens. However, our understanding of how this protein promotes host defense against intracellular parasites is unknown. Here we found that Nod2^−/− mice showed reduced clearance of Toxoplasma gondii and decreased interferon-γ production. Reconstitution of T-cell deficient mice with Nod2^−/− T cells followed by T. gondii infection revealed a T cell-intrinsic defect. Nod2^−/− CD4⁺ T cells displayed poor helper T cell differentiation, which was associated with impaired IL-2 production and nuclear accumulation of c-Rel. These data revealed a T cell-intrinsic role of Nod2 signaling that is critical for host defense against T. gondii.

Characterization of CRTAM gene promoter: AP-1 transcription factor control its expression in human T CD8 lymphocytes

Class-I MHC-restricted T-cell associated molecule (CRTAM) is a member of the Nectin-like adhesion molecule family. It is rapidly induced in NK, NKT and CD8(+) T cells. Interaction with its ligand Nectin-like 2 results in increased secretion of IFN-gamma by activated CD8(+) T lymphocytes. Through sequential bioinformatic analyses of the upstream region of the human CRTAM gene, we detected cis-elements potentially important for CRTAM gene transcription. Analyzing 2kb upstream from the ATG translation codon by mutation analysis in conjunction with luciferase reporter assays, electrophoretic mobility shify assay (EMSA) and supershift assays, we identified an AP-1 binding site, located at 1.4kb from the ATG translation codon of CRTAM gene as an essential element for CRTAM expression in activated but not resting human CD8(+) T cells. CRTAM expression was reduced in activated CD8(+) T cells treated with the JNK inhibitor SP600125, indicating that CRTAM expression is driven by the JNK-AP-1 signaling pathway. This study represents the first CRTAM gene promoter analysis in human T cells and indicates that AP-1 is a positive transcriptional regulator of this gene, a likely important finding because CRTAM has recently been shown to play a role in IFN-gamma and IL-17 production and T cell proliferation.

Biphasic regulation of Il2 transcription in CD4+ T cells: roles for TNF-alpha receptor signaling and chromatin structure

We describe a novel biphasic regulation of Il2 transcription in naive CD4(+) T cells. Few ( approximately 5%) CD4(+) T cells transcribe Il2 within 6 h of anti-TCR-beta plus anti-CD28 stimulation (early phase). Most naive CD4(+) T cells do not initiate Il2 transcription until after an additional approximately 12 h of T cell stimulation (late phase). In comparison, essentially all previously activated (Pre-Ac) CD4(+) T cells that transcribe Il2 do so with an early-phase response. Late-phase Il2 expression mostly requires c-Rel, CD28, and TNFR signaling. In contrast, early-phase transcription is only partly c-Rel and CD28 dependent and TNFR independent. There was also increased stable DNA accessibility at the Il2 locus and elevated c-Rel expression in resting Pre-Ac CD4(+) cells. Upon T cell activation, a faster and greater increase in DNA accessibility as well as c-Rel nuclear expression were observed in Pre-Ac CD4(+) cells relative to naive CD4(+) T cells. In addition, both acetylated histone H3 and total H3 decreased at the Il2 locus upon rechallenge of Pre-Ac CD4(+) T cells, whereas increased acetylated histone H3 with no change in total H3 was observed following activation of naive CD4(+) T cells. We propose a model in which nucleosome disassembly facilitates rapid initiation of Il2 transcription in CD4(+) T cells, and suggest that a threshold level of c-Rel must be reached for Il2 promoter activity in both naive and Pre-Ac CD4(+) T cells. This is provided, at least partially, by TNFR signaling during priming, but not during recall.

TCR/CD28-stimulated actin dynamics are required for NFAT1-mediated transcription of c-rel leading to CD28 response element activation

TCR/CD28 engagement triggers the initiation of a variety of signal transduction pathways that lead to changes in gene transcription. Although reorganization of the actin cytoskeleton is required for T cell activation, the molecular pathways controlled by the actin cytoskeleton are ill defined. To this end, we analyzed TCR/CD28-stimulated signaling pathways in cytochalasin D-treated T cells to determine the cytoskeletal requirements for T cell activation. Cytochalasin D treatment impaired T cell activation by causing a reduction in TCR/CD28-mediated calcium flux, and blocked activation of two regulatory elements within the IL-2 promoter, NFAT/AP-1 and CD28RE/AP. Treatment had no effect on signaling leading to the activation of either AP-1 or NF-kappaB. Significantly, we found that NFAT1 is required for optimal c-rel up-regulation in response to TCR/CD28 stimulation. In fact, NFAT1 could be detected bound at the c-rel promoter in response to TCR/CD28 stimulation, and targeting of NFAT1 using RNA interference in human CD4(+) T cells abrogated c-rel transcription. Overall, these findings establish that disrupting actin cytoskeletal dynamics impairs TCR/CD28-mediated calcium flux required for NFAT1-mediated c-rel transcription and, thus, activation of the CD28RE/AP.

Suppressive activity of epinastine hydrochloride on TARC production from human peripheral blood CD4+ T cells in-vitro

Thymus- and activation-regulated chemokine (TARC) is an important molecule in the development and maintenance of allergic diseases. However, there is little information about the influence of anti-allergic agents on TARC production. The aim of this study is to examine the influence of epinastine hydrochloride, an H1-receptor antagonist, on TARC production from human peripheral blood CD4+ T cells using an in-vitro cell culture technique. CD4+ T cells prepared from healthy subjects were cultured in wells coated with a combination of OKT3 and anti-CD28 monoclonal antibody in the presence or absence of epinastine HCl for 24 h. The cells were also stimulated with interleukin (IL)-4 in a similar manner. Levels of TARC and IL-4 in culture supernatants were examined by ELISA. The addition of epinastine HCl exerted a dose-dependent suppressive effect on the production of both TARC and IL-4 from CD4+ T cells under co-stimulatory molecule stimulation. The minimum concentration of the agent showing a significant suppressive effect on TARC and IL-4 production was 5.0 microM and 2.5 microM, respectively. Epinastine HCl also suppressed the ability of cells to produce TARC in response to IL-4 stimulation, when the agent was added to cell cultures at more than 2.5 microM. It was concluded that this inhibitory action of epinastine HCl may be partially responsible for epinastine's attenuating effect on allergic diseases.

Bortezomib induces selective depletion of alloreactive T lymphocytes and decreases the production of Th1 cytokines

We explored the ability of the proteasome inhibitor bortezomib, which prevents nuclear factor kappaB (NF-kappaB) activation, to block T-cell activation, proliferation, and survival within alloreactive compared with resting T cells. For this purpose, T cells were stimulated with PHA, alphaCD3/alphaCD28, or allogeneic dendritic cells or through mixed lymphocyte cultures. NF-kappaB expression increased in activated T lymphocytes compared with resting T cells. Of interest, the higher the NF-kappaB expression, the more intense the proliferative blockade induced by bortezomib. Moreover, after mixed lymphocyte reaction (MLR) cultures, alloreactive T cells were 2 logs more sensitive to bortezomib-induced apoptosis than the resting T-cell counterpart. This effect was due to a selective induction of apoptosis among activated T cells that was related to caspase activation and cleavage of the antiapoptotic bcl-2 protein and was partially abolished by the addition of the pancaspase inhibitor Z-VAD-FMK. In addition, after secondary MLR, the number of activated T cells was significantly reduced among T lymphocytes previously cultured with bortezomib when cells from the same donor were used as stimulating cells. By contrast, when third-party donor cells were used as stimulating cells, no significant differences were observed between T lymphocytes previously exposed or not to the drug, indicating a highly specific depletion of T lymphocytes alloreactive against primary donor antigens. The addition of bortezomib decreased not only the proliferation and viability of activated T lymphocytes but also the levels of IFNgamma and IL-2, which were significantly decreased among activated T cells cultured with bortezomib at doses ranging from 10 to 100 nM. In conclusion, at concentrations reached in the clinical setting, bortezomib induces selective apoptosis and decreases Th1 response among alloreactive T lymphocytes while it barely affects unstimulated T cells. These results establish the basis for the clinical use of bortezomib in the management of graft-versus-host disease (GVHD).

NF-kappaB-inducing kinase is involved in the activation of the CD28 responsive element through phosphorylation of c-Rel and regulation of its transactivating activity

Previous evidence suggested that NF-kappaB-inducing kinase (NIK) might regulate IL-2 synthesis. However, the molecular mechanism is not understood. In this study, we show that NIK is involved in CD3 plus CD28 activation of IL-2 transcription. Splenic T cells from aly/aly mice (that have a defective NIK protein) have a severe impairment in IL-2 and GM-CSF but not TNF secretion in response to CD3/CD28. This effect takes place at the transcriptional level as overexpression of alyNIK inhibits IL-2 promoter transcription. NIK activates the CD28 responsive element (CD28RE) of the IL-2 promoter and strongly synergizes with c-Rel in this activity. We found that NIK interacts with the N-terminal domain of c-Rel, mapping this interaction to aa 771-947 of NIK. Moreover, NIK phosphorylates the c-Rel C-terminal transactivation domain (TAD) and induces Gal4-c-Rel-transactivating activity. Anti-CD28 activated Gal4-c-Rel transactivation activity, and this effect was inhibited by a NIK-defective mutant. Deletion studies mapped the region of c-Rel responsive to NIK in aa 456-540. Mutation of several serines, including Ser471, in the TAD of c-Rel abrogated the NIK-enhancing activity of its transactivating activity. Interestingly, a Jurkat mutant cell line that expresses one of the mutations of c-Rel (Ser471Asn) has a severe defect in IL-2 and CD28RE-dependent transcription in response to CD3/CD28 or to NIK. Our results support that NIK may be controlling CD28RE-dependent transcription and T cell activation by modulating c-Rel phosphorylation of the TAD. This leads to more efficient transactivation of genes which are dependent on CD28RE sites where c-Rel binds such as the IL-2 promoter.

IL-2 induction by simian immunodeficiency virus involves MAP kinase signaling but is independent of calcineurin/NF-AT activity

The major T cell growth factor interleukin-2 (IL-2) is secreted by activated T cells in response to antigenic stimulation. This requires signal transduction via the CD3/TCR complex and the CD28 coreceptor, leading to activation of mitogen-activated protein kinase (MAPK) and calcineurin/NF-AT signaling pathways. We observed that simian immunodeficiency virus derived from African green monkeys (SIVagm3) is a potent activator of IL-2 gene expression. IL-2 promoter studies in A3.01 T cells demonstrated that SIVagm3 induced an up to 38-fold increased transcriptional activation of the IL-2 promoter. Inhibition of MAPK signaling pathways using inhibitors of MEK, JNK or p38 abolished SIVagm3-induced IL-2 activation in a dose-dependent manner. In contrast, the immunosuppressive drug cyclosporin A (CyA), a classical IL-2 inhibitor that blocks calcineurin activity, had no effect. Consistent with this finding, the nuclear factor of activated T cells (NF-AT), which is activated by calcineurin, was not induced by SIVagm3. Analyzing further transcription factor binding sites located on the IL-2 promoter we found that SIVagm3 did mainly promote transcriptional activation of the CD28/AP-1 and NF-kappaB responsive elements. These DNA elements were also induced by the viral transactivator protein (Tat) and expression of Tat was sufficient to activate IL-2 induction in stimulated cells. Our results show that SIVagm3 is capable of stimulating IL-2 gene expression via molecular mechanisms different from those induced during classical T cell activation.

Involvement of phosphatidylinositol-3 kinase–Akt and nuclear factor kappa-B pathways in the effect of frutalin on human lymphocyte

The mechanisms involved in the mitogenic effect of lectins are not fully understood and are thought to involve a cascade of intracellular signals related to T cell receptor activation. This study shows that frutalin, the alpha-D-galactose-binding lectin from Artocarpus incisa seeds, is a potent mitogenic activator of human lymphocytes. This effect is inhibited by D-galactose and PI3K inhibitors, and is accompanied by an increase in IL-2 receptor expression and by a PI3K-dependent IL-2 gene expression and IL-2 protein synthesis. Frutalin also induces Akt-phosphorylation and activates NF-kappaB, inducing its translocation from the cytosol to the nucleus. Both effects are blocked in the presence of D-galactose or by PI3K inhibitors. In summary, frutalin, interacting with alpha-D-galactose, activates signaling pathways related to TCR, and thereby triggers PI3K/Akt and NF-kappaB pathway, which modulates T cell proliferation, IL-2 synthesis and IL-2R expression. Frutalin might be a useful tool to study intracellular mechanisms following T cell activation that link upstream signaling pathways to downstream events.

CD2 activation of human lamina propria lymphocytes reduces CD3 responsiveness

Lamina propria lymphocytes (LPLs) are thought to be antigen-activated memory T cells. Yet, they respond better to ligation of the CD2 receptor than the CD3 receptor by mitogenic antibodies. This study defines their constitutive state of activation and relates it to their CD3 hyporesponsiveness. The activated state of LPLs was demonstrated by their heightened display of the activated CD2 epitope, T11(3). Constitutive CD2 activation was shown by the reduction in spontaneous proliferation when the CD2-CD58 interaction was blocked. LPLs preferentially recognized CD58 rather than the major histocompatibility complex molecules on monocytes, triggering proliferation and interferon-gamma (IFN-gamma) secretion that was inhibited by blocking the CD2-CD58 interaction. To determine whether CD2 activation of LPLs contributes to their CD3 hyporesponsiveness, they were first stimulated with mitogenic CD2 antibodies and then tested for CD3-induced proliferation. The responses were greatly reduced by prior CD2 stimulation compared with LPLs cultured in medium alone. This effect was not caused by apoptosis or by changes in CD3 expression induced by CD2 triggering. This study shows that LPLs are constitutively activated through CD2, that they preferentially recognize CD58 on monocytes and that CD2 stimulation leads to CD3 hyporesponsiveness.

Control of interleukin-2 gene transcription: a paradigm for inducible, tissue-specific gene expression

Interleukin-2 (IL-2) is a key cytokine that controls immune cell function, in particular the adaptive arm of the immune system, through its ability to control the clonal expansion and homeostasis of peripheral T cells. IL-2 is produced almost exclusively by T cells in response to antigenic stimulation and thus provides an excellent example of a cell-specific inducible gene. The mechanisms that control IL-2 gene transcription have been studied in detail for the past 20 years and our current understanding of the nature of the inducible and tissue-specific controls will be discussed.

Notch1 augments NF-kappaB activity by facilitating its nuclear retention

Notch1 specifically upregulates expression of the cytokine interferon-gamma in peripheral T cells through activation of NF-kappaB. However, how Notch mediates NF-kappaB activation remains unclear. Here, we examined the temporal relationship between Notch signaling and NF-kappaB induction during T-cell activation. NF-kappaB activation occurs within minutes of T-cell receptor (TCR) engagement and this activation is sustained for at least 48 h following TCR signaling. We used gamma-secretase inhibitor (GSI) to prevent the cleavage and subsequent activation of Notch family members. We demonstrate that GSI blocked the later, sustained NF-kappaB activation, but did not affect the initial activation of NF-kappaB. Using biochemical approaches, as well as confocal microscopy, we show that the intracellular domain of Notch1 (N1IC) directly interacts with NF-kappaB and competes with IkappaBalpha, leading to retention of NF-kappaB in the nucleus. Additionally, we show that N1IC can directly regulate IFN-gamma expression through complexes formed on the IFN-gamma promoter. Taken together, these data suggest that there are two 'waves' of NF-kappaB activation: an initial, Notch-independent phase, and a later, sustained activation of NF-kappaB, which is Notch dependent.

c-Rel-dependent priming of naive T cells by inflammatory cytokines

The intrinsic refractoriness of naive T cells for cytokine production is counteracted by cells of the innate immune system. Upon sensing danger via Toll-like receptors, these cells upregulate T cell costimulatory molecules and secrete cytokines that enhance T cell activation. We show that cytokine-mediated priming of naive T cells requires the NF-kappaB family member c-Rel. In resting naive cells c-Rel is associated primarily with IkappaBbeta, an inhibitory molecule that is not effectively degraded by TCR signals. Exposure of T cells to proinflammatory cytokines, TNF-alpha and IL-1beta, shifts c-Rel to IkappaBalpha-associated complexes that are readily targeted by the TCR. As a consequence, IL-2 and IFN-gamma mRNA are produced more quickly, and at higher levels, in cytokine-primed T cells. This mechanism does not operate in effector T cells where cytokine gene expression is c-Rel-independent. We propose that c-Rel plays a crucial role as a target of innate signals in T cells.

The tetraspanin web modulates immune-signalling complexes

The tetraspanin web represents a new concept of molecular interactions in the immune system. Whereas most surface immune-modulating molecules involve receptor-ligand interactions, tetraspanins associate with partner proteins and facilitate their lateral positioning in the membrane. Moreover, the same tetraspanin molecule can associate with different proteins depending on the cell type. Most importantly, members of this family tend to associate with each other, together with their partners, in membrane microdomains that provide a scaffold for the transmission of external stimuli to intracellular-signalling components.

Fate and function of anti-CD3/CD28-activated T cells following adoptive transfer: IL-2 promotes development of anti-tumor memory T cells in vivo

BACKGROUND

Adoptive immunotherapy with T cells activated through CD3 alone requires exogenous IL-2 for T-cell function and survival after transfer, but the in vivo cytokine requirement of T cells activated through CD3 and CD28 is unknown. We hypothesized that CD3/CD28-activated T cells, unlike those activated through CD3 alone, might develop into long-lived memory T cells, either with or without systemic IL-2.

METHODS

We used MHC class I-restricted TCR transgenic T cells from the OT-1 mouse, specific for the surrogate tumor Ag ovalbumin (OVA), to assess the trafficking kinetics, antigenic responsiveness and anti-tumor efficacy of dual-activated T cells in vivo as a function of IL-2 administration. At days 7, 14, and 28 after transfer, lymph node cells and splenocytes were examined for donor cell persistence and antigenic responsiveness by FACS and ELISA, respectively.

RESULTS

In IL-2-treated mice, donor CD8+ T cells persisted and developed a memory phenotype, based on CD44 and Ly6c expression at day 28, while mice given no IL-2 had fewer donor cells at all time points. OVA-specific release of IFN-gamma was higher from lymphocytes of IL-2-treated mice compared with no-IL-2 mice (P<0.02 at all time points). In mice challenged with an OVA-bearing subline of the AML leukemia model C1498, IL-2 did not confer added protection from tumor challenge at 1 or 2 weeks after adoptive transfer, but gave improved survival at 4 weeks post-transfer.

DISCUSSION

We conclude that exogenous IL-2 is not required for anti-tumor activity of CD3/CD28-activated CD8+ cells early after adoptive transfer, but promotes T-cell persistence that confers disease protection at more remote times.

CD63 as an activation-linked T cell costimulatory element

Dendritic cells (DC) are unique in their capacity to either stimulate or regulate T cells, and receptor/ligand pairs on DC and T cells are critically involved in this process. In this study we present such a molecule, which was discovered by us when analyzing the functional effects of an anti-DC mAb. This mAb, 11C9, reacted strongly with DC, but only minimally with lymphocytes. In MLR it constantly reduced DC-induced T cell activation. Therefore, we assumed that mAb 11C9 primarily exerts its functions by binding to a DC-structure. This does not seem to be the case, however. Preincubation of DC with mAb 11C9 before adding T cells had no inhibitory effect on T cell responses. Retroviral expression cloning identified the 11C9 Ag as CD63. This lysosomal-associated membrane protein (LAMP-3), is only minimally expressed on resting T cells but can, as we show, quickly shift to the surface upon stimulation. Cross-linkage of that structure together with TCR-triggering induces strong T cell activation. CD63 on T cells thus represents an alternative target for mAb 11C9 with its binding to activated T cells rather than DC being responsible for the observed functional effects. This efficient CD63-mediated costimulation of T cells is characterized by pronounced induction of proliferation, strong IL-2 production and compared with CD28 enhanced T cell responsiveness to restimulation. Particularly in this latter quality CD63 clearly surpasses several other CD28-independent costimulatory pathways previously described. CD63 thus represents an activation-induced reinforcing element, whose triggering promotes sustained and efficient T cell activation and expansion.

Hyperresponse to T-cell receptor signaling and apoptosis of Id1 transgenic thymocytes

The basic helix-loop-helix transcription factors, E2A and HEB, play important roles in T-cell development at multiple checkpoints. Expression of their inhibitor, Id1, abolishes the function of both transcription factors in a dose-dependent manner. The Id1 transgenic thymus is characterized by an accumulation of CD4- CD8- CD44+ CD25- thymocytes, a dramatic reduction of CD4+ CD8+ thymocytes, and an abundance of apoptotic cells. Here we show that these apoptotic cells carry functional T-cell receptors (TCRs), suggesting that apoptosis occurs during T-cell maturation. In contrast, viable Id1 transgenic CD4 single positive T cells exhibit costimulation-independent proliferation upon treatment with anti-CD3 antibody, probably due to a hyperresponse to TCR signaling. Furthermore, Id1 expression causes apoptosis of CD4 and CD8 double- or single-positive thymocytes in HY- or AND-TCR transgenic mice under conditions that normally support positive selection. Collectively, these results suggest that E2A and HEB proteins are crucial for controlling the threshold for TCR signaling, and Id1 expression lowers the threshold, resulting in apoptosis of developing thymocytes.

Murine B7-H3 is a negative regulator of T cells

T cell activation is regulated by the innate immune system through positive and negative costimulatory molecules. B7-H3 is a novel B7-like molecule with a putative receptor on activated T cells. Human B7-H3 was first described as a positive costimulator, most potently inducing IFN-gamma production and cellular immunity. In this study we examined the expression and function of mouse B7-H3. B7-H3 is mostly expressed on professional APCs; its expression on dendritic cells appears to be up-regulated by LPS. In contrast to human B7-H3, we found that mouse B7-H3 protein inhibited T cell activation and effector cytokine production. An antagonistic mAb to B7-H3 enhanced T cell proliferation in vitro and led to exacerbated experimental autoimmune encephalomyelitis in vivo. Therefore, mouse B7-H3 serves as a negative regulator of T cell activation and function.

Costimulation via Glucocorticoid-Induced TNF Receptor in Both Conventional and CD25+Regulatory CD4+T Cells

The glucocorticoid-induced TNF receptor (GITR), which is a member of the TNF receptor family, is expressed preferentially at high levels on CD25+CD4+ regulatory T cells and plays a key role in the peripheral tolerance that is mediated by these cells. GITR is also expressed on conventional CD4+ and CD8+ T cells, and its expression is enhanced rapidly after activation. In this report we show that the GITR provides a potent costimulatory signal to both CD25+ and CD25- CD4+ T cells. GITR-mediated stimulation induced by anti-GITR mAb DTA-1 or GITR ligand transfectants efficiently augmented the proliferation of both CD25-CD4+ and CD25+CD4+ T cells under the limited dose of anti-CD3 stimulation. The augmentation of T cell activation was further confirmed by the enhanced cell cycle progression; early induction of the activation Ags, CD69 and CD25; cytokine production, such as IL-2, IFN-gamma, IL-4, and IL-10; anti-CD3-induced redirected cytotoxicity; and intracellular signaling, assessed by translocation of NF-kappaB components. GITR costimulation showed a potent ability to produce high amounts of IL-10, which resulted in counter-regulation of the enhanced proliferative responses. Our results highlight evidence that GITR acts as a potent and unique costimulator for an early CD4+ T cell activation.

Inhibition of NF-kappaB activity by IkappaBbeta in association with kappaB-Ras

IkappaBbeta, one of the major IkappaB proteins, is only partially degraded in response to most extracellular signals. However, the molecular mechanism of this event is unknown. We show here that IkappaBbeta exists in at least two different forms: one that is bound to the NF-kappaB dimer and the other bound to both NF-kappaB and kappaB-Ras, a Ras-like small G protein. Removal of cellular kappaB-Ras enhances whereas excess kappaB-Ras blocks induced IkappaBbeta degradation. Remarkably, kappaB-Ras functions in both GDP- and GTP-bound states, and mutations of the conserved guanine-binding residues of kappaB-Ras abrogate its ability to block degradation of IkappaBbeta. kappaB-Ras also directly blocks the in vitro phosphorylation of IkappaBbeta by IKKbeta. These observations suggest that IkappaBbeta in the ternary complex is resistant to degradation by most signals. We suggest that specific signals, in addition to those that activate only IKK, are essential for the complete degradation of IkappaBbeta.

N/A

N/A

A novel ELISPOT assay to enhance detection of antigen-specific T cells employing antigen-presenting cells expressing vector-driven human B7-1

The ELISPOT assay is used to detect T-cell responses in patients enrolled in vaccine clinical trials; it is a relatively sensitive assay that can be performed without in vitro stimulation (IVS) of PBMC. However, this assay may be limited in some cases because of a weak signal 1 (as is the case for tumor-associated antigens [TAA]), or by a limited number of PBMC available from patients. The objective of this study is to enhance the sensitivity of the ELISPOT by increasing the level of signal 2, in this case, B7-1 expression on antigen-presenting cells (APC), allowing for a more sensitive detection of antigen-specific T-cell precursors. C1RA2 cells were used as APC and were uninfected, or infected with either recombinant avipox (fowlpox)-B7-1 (rF-B7-1) or control fowlpox wild-type (FP-WT) vector. The expressions of B7-1, MHC Class II, as well as HLA-A2 on the infected cells were analyzed by flow cytometry. A nearly threefold increase in B7-1 mean fluorescence intensity (MFI) occurred in the rF-B7-1-infected C1RA2 cells with no changes in MHC Class II or HLA-A2 expression. Various PBMC/APC ratios were used to further analyze the use of rF-B7-1-infected C1RA2 cells as APC in the ELISPOT assay. Fewer APC were required to activate PBMC when C1RA2 infected with rF-B7-1 were used as APC. Furthermore, using a PBMC/APC ratio of 1:1, similar detection was achieved using fewer PBMC. In addition, we demonstrated that the reactivity can be blocked by adding anti-B7-1 antibody. We performed the assay using APC on five normal healthy donors. All five donors showed substantial increases in PF to the Flu matrix peptide (Flu peptide) using the rF-B7-1-infected C1RA2 cells. Finally, we evaluated five cancer patients who received a carcinoembryonic antigen (CEA) vaccine-based therapy. Increases in CEA peptide precursors were noted in all five patients using the B7-1-infected APC. In conclusion, we have demonstrated the ability to enhance the sensitivity of the ELISPOT assay through infection of C1RA2 with rF-B7-1.

B7S1, a novel B7 family member that negatively regulates T cell activation

T cell activation by antigen-presenting cells (APC) is regulated by positive and negative costimulatory molecules in the B7 family. Here we describe a novel addition in this family, designated as B7S1, which is uniquely anchored to the cell membrane via a GPI linkage. B7S1 is expressed on professional APC and widely distributed in nonlymphoid tissues. A soluble B7S1-Ig fusion protein binds to activated but not naive T cells. B7S1-Ig inhibits T cell activation and IL-2 production. A monoclonal antibody that blocks binding of B7S1 to its receptor enhances T cell proliferation in vitro and exacerbates experimental autoimmune encephalomyelitis in vivo. This study identifies a novel negative regulator of T cell activation and further reveals complex costimulatory regulation of immune responses.

Immunotolerance of liver allotransplantation induced by intrathymic inoculation of donor soluble liver specific antigen

AIM: To study the effects of liver specific antigen (LSA) on the immunoreaction of liver allotransplantation and its significance.

METHODS: Orthotopic liver transplantation was used in this study. Group I: syngeneic control (Wistar-to-Wistar); Group II: acute rejection (SD-to-Wistar). Group III: acute rejection treated by intramuscular injection of cyclosporine A (CsA) (SD-to-Wistar + CsA). Group IV: Intrathymic inoculation of SD rat LSA one week before transplantation (LSA + SD-to-Wistar). The common situation and survival time, rejection grades, NF-κB activity of splenocytes and intragraft cytokine gene expression were observed to analyze the acute rejection severity and immune state of animals.

RESULTS: The common situation of Wistar-to-Wistar group was very good after the transplantation and no signs of rejection were found. Recipients of SD-to-Wistar group lost body weight progressively. All died within 9 to 13 d after transplantation with the median survival time of 10.7 ± 0.51 d. It was an optimal control for acute rejection. The common situation of SD-to-Wistar + CsA group was bad during CsA medication but only with mild rejection. As for LSA + SD-to-Wistar group, 5 of 6 recipients survived for a long time and common situation was remarkably better than that of SD-to-Wistar group and SD-to-Wistar + CsA group. Its rejection grades were significantly lower than that of SD-to-Wistar group (P = 0.026). Furthermore, no significant discrepancies of rejection were found between SD-to-Wistar group and LSA + SD-to-Wistar group at day 7 and day 12 (P = 0.067). NF-κB activity, IFN-γ and IL-2mRNA expression were significantly inhibited in LSA + SD-to-Wistar group compared with that of SD-to-Wistar group (P < 0.05).

CONCLUSION: LSA is an important transplantation antigen which involves in the immunorejection of liver transplantation directly. We reported for the first time that intrathymic inoculation of LSA can induce immnotolerance of liver allotransplantation and grafts can survive for a long time thereby, thus leading to a novel way to liver transplantation immunotolerance.

SS-A/Ro52, an autoantigen involved in CD28-mediated IL-2 production

An autoantibody against SS-A/Ro52 (Ro52) is most frequently found in the sera of patients with Sjögren's syndrome, systemic lupus erythematosus, and congenital heart block from anti-Ro52 Ab-positive mother. However, the physiological function of the autoantigen SS-A/Ro52 has not yet been elucidated. In this study, we describe the role of Ro52 protein in T cell activation. Overexpression of SS-A/Ro52 in Jurkat T cell resulted in enhanced IL-2 production following CD28 stimulation. Furthermore, transfection of anti-Ro52-specific small RNA duplexes partially blocked the expression of native and overexpressed Ro52 in Jurkat T cell, resulting in decreased IL-2 production via CD28 pathway in these cells. Finally, intracellular localization of Ro52 dramatically changed following CD28 stimulation. Our data reveal a novel function of Ro52 in CD28-mediated pathway, which eventually contributes to cytokine production and expression of the T cell biological programs.

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.