Immunosuppressive cytotoxic T lymphocyte associated antigen-4 immunoglobulin fusion proteins (CTLA4-Ig) block the CD28:CD80/86 costimulatory pathway. On a cellular level, CTLA4-Ig is understood to dampen T cell responses. As a mechanism, CTLA4-Ig has been reported to affect dendritic cell (DC) function via inducing the immunosuppressive indoleamine 2,3 dioxygenase (IDO) pathway and promoting a DC regulatory phenotype. We here probed cellular mechanisms of CTLA4-Ig immunoregulation in an allogeneic setting using C57BL/6 splenic or bone marrow derived DCs (BMDCs) as stimulators of allogeneic Balb/c derived T cells. To address whether CTLA4-Ig immunosuppression affected DCs, we pre-exposed C57BL/6 splenic or BMDCs to CTLA4-Ig and removed unbound CTLA4-Ig before co-culture with allogeneic T cells. CTLA4-Ig disappeared rapidly (within 4 h) from the cell membrane by combined internalization and dissociation. These CTLA4-Ig pre-exposed DCs were fully capable of stimulating allogeneic T cell proliferation, suggesting that CTLA4-Ig does not impair the DC stimulatory capacity. Only the presence of CTLA4-Ig during DC/T cell co-culture resulted in the expected inhibition of proliferation. C57BL/6 splenic or BMDCs exposed to CTLA4-Ig did not display IDO activity. We conclude that CTLA4-Ig immunosuppressive activity does not depend on a DC regulatory phenotype but on its presence during DC/T cell interaction.
► CTLA4-Ig binding to CD80/86 on murine DC surface is short lived. ► CTLA4-Ig does not confer a DC regulatory phenotype ► CTLA4-Ig does not induce IDO ► CTLA4-Ig mediates immune inhibition by affecting DC/T cell interaction
CTLA4-Ig; Abatacept; IFN-γ; IDO; Reverse signaling
Cytotoxic T lymphocyte associated antigen-4 (CTLA-4) is a costimulatory receptor transducing a potent inhibitory signal. Increasing evidence showed that CTLA-4 gene is an important susceptibility locus for autoimmune disorders. Alternatively spliced mRNA generates a soluble form, called sCTLA-4. Whereas low levels of sCTLA-4 are detected in normal human serum, increased/high serum levels are observed in several autoimmune diseases. The biological significance of increased sCTLA-4 serum level is not fully clarified yet. It can be envisaged that sCTLA-4 specifically inhibits the early T-cell activation by blocking the interaction of CD80/CD86 with the costimulatory receptor CD28. On the other hand, higher levels of sCTLA-4 could contend the binding of the membrane form of CTLA-4 with CD80/CD86, in later activation phase, causing a reduction of inhibitory signalling. We showed that sCTLA-4 from sera of patients with different autoimmune diseases is able to display functional activities on an in vitro system acting on the proliferation capability and modulating the secretion of cytokines. We observed a dual effect of sCTLA-4: inhibiting the secretion of IFN-γ, IL-2, IL-7, and IL-13 and activating the secretion of TGF-β and IL-10. This study underlines the role of sCTLA-4 in modulating the immune response and its relevance in autoimmune disease pathogenesis.
CTLA-4, initially described as a membranebound molecule, is a costimulatory receptor transducing a potent inhibitory signal. Increasing evidence shows the CTLA-4 gene to be an important susceptibility locus for autoimmune endocrinopathies and other autoimmune disorders. A soluble form of cytotoxic T-lymphocyte-associated antigen-4 (sCTLA-4) has been established and shown to possess CD80/CD86 binding activity and in vitro immunoregulatory functions. sCTLA-4 is generated by alternatively spliced mRNA. Whereas low levels of sCTLA-4 are detected in normal human serum, increased serum levels are observed in several autoimmune diseases (e.g. Graves’ disease, myasthenia gravis, systemic lupus erythematosus, type 1 diabetes, systemic sclerosis, coeliac disease, autoimmune pancreatitis and primary biliary cirrhosis). The biological significance of increased sCTLA-4 serum levels is not fully clarified yet. On the one hand, it can be envisaged that sCTLA-4 specifically inhibits early T-cell activation by blocking the interaction of CD80/CD86 with the costimulatory receptor CD28. On the other hand, higher levels of sCTLA-4 could compete for the binding of the membrane form of CTLA-4 with CD80/CD86 in the later phases of T-lymphocyte activation, causing a reduction in inhibitory signalling. This double-edged nature of sCTLA-4 to block the binding of CD28 to CD80/CD86 may result in different outcomes during the clinical course of an autoimmune disease.
CTLA-4; Immunoregulation; Autoimmune disease; T-cell activation
The critical role of cytotoxic lymphocyte antigen 4 (CTLA-4) in inhibiting antigen-driven T cell responses upon engagement with its ligands, B7-1 and B7-2, and its importance for peripheral T cell tolerance and T cell homeostasis has been studied intensively. The CTLA-4 splice variant, li-CTLA-4 is expressed in naïve and activated T cells and can actively alter T cell signaling despite its lack of a B7 binding domain. To study the effect of li-CTLA-4 in regulating T cell responses in the context of autoimmunity, we engineered a B6.CTLA-4 (floxed-Exon2)-BAC-transgene, resulting in selective expression of li-CTLA-4 upon Cre-mediated deletion of Exon 2. Introducing the B6.BAC into the NOD background, which is genetically deficient for li-CTLA-4, restores mRNA levels of li-CTLA-4 to those observed in B6 mice. Further, re-expressing this ligand non-binding isoform in NOD mice reduced IFN-γ-production in T effector cells accompanied by a significant decrease in insulitis and T1D frequency. However, selective expression of li-CTLA-4 could not fully rescue the CTLA-4KO disease phenotype when bred onto NOD.BDC2.5.CTLA-4KO background due to the requirement of the full-length, B7-binding CTLA-4 molecule on T effector cells. Thus, the li-CTLA-4 form, when expressed at physiologic levels in the CTLA-4 sufficient NOD background can suppress autoimmunity, however, the functionality of the li-CTLA-4 isoform depends on the presence of the full-length molecule to alter effector T cell signaling.
Viral persistence is associated with hierarchical antiviral CD8 T cell exhaustion with increased programmed death-1 (PD-1) expression. In HCV persistence, HCV-specific CD8 T cells from the liver (the site of viral replication) display increased PD-1 expression and a profound functional impairment that is not reversed by PD-1 blockade alone. Here, we report that the inhibitory receptor cytotoxic T lymphocyte-associated antigen-4 (CTLA-4) is preferentially upregulated in PD-1+ T cells from the liver but not blood of chronically HCV-infected patients. PD-1/CTLA-4 co-expression in intrahepatic T cells was associated with a profound HCV-specific effector dysfunction that was synergistically reversed by combined PD-1/CTLA-4 blockade in vitro, but not by blocking PD-1 or CTLA-4 alone. A similar effect was observed in circulating HCV-specific CD8 T cells with increased PD-1/CTLA-4 co-expression during acute hepatitis C. The functional response to combined blockade was directly associated with CTLA-4 expression, lost with CD28-depletion and CD4-independent (including CD4+FoxP3+ Tregs). We conclude that PD-1 and CTLA-4 pathways both contribute to virus-specific T cell exhaustion at the site of viral replication by a redundant mechanism that requires combined PD-1/CTLA-4 blockade to reverse. These findings provide new insights into the mechanisms of virus-specific T cell dysfunction, and suggest that the synergistic effect by combined inhibitory receptor blockade might have a therapeutic application against chronic viral infection in vivo, provided that it does not induce autoimmunity.
Hepatitis C virus (HCV) is an important human pathogen with a high rate of persistence associated with chronic liver disease that can progress to cirrhosis and hepatocellular carcinoma. Chronic HCV infection occurs in the setting of impaired antiviral T cells that over-express an inhibitory receptor PD-1 (programmed death-1 receptor). Recent studies showed that in vitro inhibition of the PD-1 pathway via an inhibitory antibody can reverse the functional impairment in HCV-specific CD8 T cells from blood but not the liver (the site of viral infection and disease progression). In this study, we show that a second co-inhibitory receptor, CTLA-4, is upregulated in HCV-specific CD8 T cells from the liver and that combined PD-1/CTLA-4 blockade (but not single blockade of PD-1 or CTLA-4) can synergistically enhance their function. This functional enhancement was CD28-dependent but CD4-independent. This effect also differed between viruses, tissue compartments (liver vs. periphery) and clinical status (acute vs. chronic). We conclude that PD-1, CTLA-4, and CD28 expression profiles define a novel hierarchy in HCV-specific CD8 T cell exhaustion than can be synergistically reversed by combined inhibitory receptor blockade. These findings have potential immunotherapeutic applications, provided that no autoimmunity is induced.
Spondylarthropathies (SpA) are characterized by abnormal immune responses including T cell activation. Cytotoxic T lymphocyte associated molecule-4 (CTLA-4) is involved in down-regulating immune responses. A soluble form of CTLA-4 (sCTLA-4), resulting from an alternative splicing, has been identified and was found increased in several autoimmune diseases. Here, we evaluated circulating levels of sCTLA-4 as a marker of immune dysregulation in SpA. Intracellular CTLA-4 and levels of CTLA-4 transcript expression in peripheral blood lymphocytes (PBL) were also studied.
Sera from 165 patients with SpA were evaluated for sCTLA-4 measurements. Results were compared with those from 71 patients with rheumatoid arthritis (RA) and 88 healthy subjects. In 32 patients with SpA, 22 patients with RA and 15 healthy controls, we analyzed the intracellular CTLA-4 expression in CD4+ T cells, CD8+ T cells, activated (HLA-DR+Foxp3-) CD4+ T cells, CD4+ regulatory (CD25+Foxp3+) T cells and in CD3 negative cells by flow cytometry. Expression of the full length (coding for membrane CTLA-4) and spliced form (coding for sCTLA-4) of CTLA-4 transcripts in PBL were analyzed by quantitative real-time polymerase chain reaction (QRT-PCR).
High levels of sCTLA-4 were found in the SpA group compared to the RA group and healthy controls (P < 0.0001). Soluble CTLA-4 serum levels strongly correlated with clinical index of disease activity BASDAI (r = 0.42, P < 0.0001) and C-reactive protein (CRP) levels (r = 0.17, P = 0.037). In contrast to RA patients, SpA patients did not exhibit changes in intracellular CTLA-4 expression in the different PBL subsets tested. Finally, the SpA group showed a preferential expression of the spliced CTLA-4 mRNA (P = 0.0014) in PBL.
SpA patients exhibit high levels of circulating sCTLA-4 that may result from an alternative splicing of CTLA-4 transcripts. This may influence immune activation and regulation in SpA.
Juvenile idiopathic arthritis (JIA) is an autoimmune disorder mediated by Th1-immune responses. Cytotoxic T-lymphocyte Antigen 4 (CTLA4), expressed on the T-cell surface, plays a negative role in regulating T-cell activation. Single nucleotide polymorphisms (SNPs) in CTLA4 have been implicated in susceptibility to several autoimmune disorders, including JIA. Our objective was to test three functional CTLA4 variants for association with JIA.
Families of 531 children with JIA were genotyped for SNPs located in the promoter region (C-318T), exon-1 (A49G), and the 3’ untranslated region (CT60) of CTLA4 by PCR amplification and digestion. Family-based association test (FBAT) was used to test CTLA4 SNPs and haplotypes for association with JIA. A second independent cohort of more than 300 children with JIA and 500 controls were genotyped for case-control analyses. Case-control analyses of the combined cohorts, as well as meta-analyses of published association studies between CTLA4 and JIA, were performed.
There were no deviations of transmission of any of the CTLA4 variants to children with JIA, or JIA subtypes, by FBAT. There were also no significant associations between CTLA4 C-318T or A49G SNPs in 650 JIA cases and 350 controls. Similarly, there were also no significant associations between CT60 variants with over 800 JIA cases and 500 controls. The meta-analysis also failed to confirm an association between JIA and CTLA4 variants.
These results suggest that C-318T, A49G or CT60 or haplotypes tagged by these CTLA4 SNPs are not associated with JIA or major JIA subtypes.
CTLA4; JRA; genetics; autoimmune; association; juvenile idiopathic arthritis
Cytotoxic T lymphocyte antigen 4 (CTLA4) appears to negatively regulate T cell activation.
One mechanism by which CTLA4 might antagonize T cell function is through inhibition of
CD28 signaling by competing for their shared ligands B7-1 and B7-2. In addition, CTLA4 ligation could initiate a signaling cascade that inhibits T cell activation. To address whether
CTLA4 could inhibit immune responses in the absence of CD28, rejection of heart allografts
was studied in CD28-deficient mice. H-2q hearts were transplanted into allogeneic wild-type
or CD28-deficient mice (H-2b). Graft rejection was delayed in CD28-deficient compared with
wild-type mice. Treatment of wild-type recipients with CTLA4-immunoglobulin (Ig), or with
anti–B7-1 plus anti–B7-2 mAbs significantly prolonged allograft survival. In contrast, treatment
of CD28-deficient mice with CTLA4-Ig, anti–B7-1 plus anti–B7-2 mAbs, or a blocking anti-CTLA4 mAb induced acceleration of allograft rejection. This increased rate of graft rejection
was associated with more severe mononuclear cell infiltration and enhanced levels of IFN-γ
and IL-6 transcripts in donor hearts of untreated wild-type and CTLA4-Ig– or anti-CTLA4
mAb–treated CD28-deficient mice. Thus, the negative regulatory role of CTLA4 extends beyond its potential ability to prevent CD28 activation through ligand competition. Even in the
absence of CD28, CTLA4 plays an inhibitory role in the regulation of allograft rejection.
cytotoxic T lymphocyte antigen 4; CD28-deficient; cytotoxic T lymphocyte
antigen 4–immunoglobulin; transplantation; T lymphocyte
Co-stimulatory signal B7(CD80/CD86):CD28 is needed in order to activate T cells in immune response. Cytotoxic T lymphocyte-associated antigen-4-immunoglobulin (CTLA4-Ig) binding to the B7 molecules on antigen-presenting cells downregulates this activation and represents a recent biological treatment in rheumatoid arthritis (RA). Objectives of the study were to investigate the presence of the B7.2 (CD86) molecule and its masking by CTLA4-Ig on cultures of both RA synovial macrophages (RA SM), and of macrophages differentiated from THP-1 cells (M). In addition, the anti-inflammatory effects of CTLA4-Ig on co-cultures of RA SM and M with activated T cells were tested.
All macrophages were co-cultured for 24 hours with activated T cells, without or with CTLA4-Ig (10, 100, 500 μg/ml for 1 hour, 3 hours and overnight, respectively). Immunofluorescence (IF) staining for B7.2, and an analysis of inflammatory cytokine expression (interleukin (IL) -6, tumor necrosis factor (TNF) α, IL-1β, transforming growth factor (TGF) β) by immunocytochemistry (ICC), western blot (WB) and reverse transcriptase-polymerase chain reaction (RT-PCR) were performed.
Macrophages showed intense B7.2 expression. CTLA4-Ig/B7.2 masking was evident for all macrophages, even after only 1 hour of cell culture (range from 10 to 100 μg/ml). ICC of co-cultures showed a dose-dependent decrease in inflammatory cytokines (P < 0.001 for IL-6, TNFα, IL-1β and TGFβ). Data were confirmed by WB and RT-PCR analysis.
Optimal concentrations of CTLA4-Ig for the CTLA4-Ig/B7.2 masking on activated macrophages were identified and were found to induce significant downregulation in the cell production of IL-6, TNFα, IL1-β and TGFβ. In conclusion, macrophages would appear to be a sensitive target for CTLA4-Ig treatment in RA.
Cytotoxic T lymphocyte antigen-4 (CTLA-4) is a major negative regulatory molecule for T cell activation with a complex biology and function. CTLA-4 is known to regulate homeostatic lymphoproliferation as well as tolerance induction and has been proposed to be an important effector molecule by which regulatory T cells suppress immunity. The immunoregulatory properties of CTLA-4 are primarily mediated by competition with the co-stimulator CD28 for ligand-binding but also by delivering negative signals to T cells through its cytoplasmic tail. In this study, we addressed the effect of directly mutating the amino acid residue, Tyrosine 201 (Tyr201), of the intracellular domain of CTLA-4 in situ and its implications in T cell function in the context of autoimmunity. Therefore a novel CTLA-4 knock-in mouse (Y201V KI) was generated, in which Tyr201 was replaced by a valine that could not be phosphorylated. Mice expressing the CTLA-4 mutant molecule were generally healthy and did not show signs of disruption of T cell homeostasis under steady state conditions seen in CTLA-4 deficient mice. However, T cells isolated from Y201V KI mice expressed higher levels of CTLA-4 on the cell surface and displayed a Th2 biased phenotype following TCR stimulation. Furthermore, Y201V KI mice developed exacerbated disease as compared to wild-type upon antigen-specific T cell activation in an in vivo model of experimental autoimmune encephalomyelitis (EAE). Importantly, the Y201V mutation resulted in impaired suppressive activity of T regulatory cells (Treg) while T effector function remained intact. These data suggest that effects associated with and mediated through Tyr201 of CTLA-4s intracellular domain are critical for Treg function.
CTLA-4; T regulatory cells; autoimmunity; EAE/MS
Coreceptors CD28 and cytotoxic T lymphocyte antigen (CTLA)-4 have opposing effects on TcR/CD3 activation of T cells. While CD28 enhances and CTLA-4 inhibits activation, the underlying molecular basis of these effects has yet to be established. In this context, ganglioside and cholesterol enriched membrane microdomains (rafts, GEMs) serve as centers of signaling in T cells. Although CD28 can promote TcR/raft colocalization, evidence is lacking on whether the surface expression of membrane rafts can be targeted by CTLA-4 in its modulation of T cell responses. In this study, we demonstrate that both CD28 and CTLA-4 profoundly alter the surface expression of membrane rafts during T cell activation. While CD28 increased expression and the number of peripheral T cells induced to express surface rafts in response to TcR ligation, CTLA-4 potently inhibited both TcR and TcR × CD28 induced raft expression on the surface of T cells. Consistent with this, CD28 increased the presence of the linker of activated T cells (LAT) in purified membrane rafts, while CTLA-4 coligation effectively blocked this increase. Further, the reversal of the CTLA-4 block with CD3/CD28 ligation was accompanied by an increase in surface raft expression and associated LAT. Our observations demonstrate for the first time that CTLA-4 targets the release of rafts to the surface of T cells, and provides a mechanism for the opposing effects of CD28 and CTLA-4 on costimulation.
T cell function; CD28; CTLA-4; lipid rafts; LAT
Various phenotype and functional T-cell abnormalities are observed in multiple myeloma (MM) patients. The aim of this study was to investigate the association between polymorphisms in the gene encoding cytotoxic T-lymphocyte antigen-4 (CTLA-4), a negative regulator of the T-lymphocyte immune response and susceptibility to multiple myeloma in a Polish population. Two hundred MM patients and 380 healthy subjects were genotyped for the following polymorphisms: CTLA-4c.49A>G, CTLA-4g.319C>T, CTLA-4g.*642AT(8_33), CT60 (CTLA-4g.*6230G>A), Jo31 (CTLA-4g.*10223G>T). Our study is the largest and most comprehensive evaluation to date of the association between genetic polymorphisms in the CTLA-4 molecule and multiple myeloma. It was found that CTLA-4c.49A>G[G], CT60[G], and Jo31[G] alleles were more frequently observed in MM patients than in controls (0.50 vs. 0.44, p = 0.03, 0.65 vs. 0.58, p = 0.04, and 0.63 vs. 0.57, p = 0.03, respectively). Moreover, the haplotype CTLA-4c.49A>G[G], CTLA-4g.319C>T[C], CTLA-4g.*642AT(8_33) , CT60[G], Jo31[G] including all susceptibility alleles increases the risk of MM about fourfold (OR: 3.79, 95%CI: 2.08–6.89, p = 0.00001). These findings indicate that genetic variations in the CTLA-4 gene play role in susceptibility to multiple myeloma and warrant further investigation through replication studies.
CTLA-4; Gene polymorphisms; MM
CTLA-4 (Cytotoxic T lymphocyte antigen-4) is traditionally known as a negative regulator of T cell activation. The blocking of CTLA-4 using human monoclonal antibodies, such as Ipilimumab, is currently used to relieve CTLA-4-mediated inhibition of anti-tumor immune response in metastatic melanoma. Herein, we have analyzed CTLA-4 expression and Ipilimumab reactivity on melanoma cell lines and tumor tissues from cutaneous melanoma patients. Then, we investigated whether Ipilimumab can trigger innate immunity in terms of antibody dependent cellular cytotoxicity (ADCC) or Tumor Necrosis Factor (TNF)-α release. Finally, a xenograft murine model was set up to determine in vivo the effects of Ipilimumab and NK cells on melanoma.
CTLA-4 expression and Ipilimumab reactivity were analyzed on 17 melanoma cell lines (14 primary and 3 long-term cell lines) by cytofluorimetry and on 33 melanoma tissues by immunohistochemistry. CTLA-4 transcripts were analyzed by quantitative RT-PCR. Soluble CTLA-4 and TNF-α were tested by ELISA. Peripheral blood mononuclear cells (PBMC), NK and γδT cells were tested in ADCC assay with Ipilimumab and melanoma cell lines. TNF-α release was analyzed in NK-melanoma cell co-cultures in the presence of ipilimumab. In vivo experiments of xenotransplantation were carried out in NOD/SCID mice. Results were analyzed using unpaired Student’s t-test.
All melanoma cell lines expressed mRNA and cytoplasmic CTLA-4 but surface reactivity with Ipilimumab was quite heterogeneous. Accordingly, about 2/3 of melanoma specimens expressed CTLA-4 at different level of intensity.
Ipilimumab triggered, via FcγReceptorIIIA (CD16), ex vivo NK cells as well as PBMC, IL-2 activated NK and γδT cells to ADCC of CTLA-4+ melanoma cells. No ADCC was detected upon interaction with CTLA-4- FO-1 melanoma cell line. TNF-α was released upon interaction of NK cells with CTLA-4+ melanoma cell lines. Remarkably, Ipilimumab neither affected proliferation and viability nor triggered ADCC of CTLA-4+ T lymphocytes. In a chimeric murine xenograft model, the co-engraftment of Ipilimumab-treated melanoma cells with human allogeneic NK cells delayed and significantly reduced tumor growth, as compared to mice receiving control xenografts.
Our studies demonstrate that Ipilimumab triggers effector lymphocytes to cytotoxicity and TNF-α release. These findings suggest that Ipilimumab, besides blocking CTLA-4, can directly activate the elimination of CTLA-4+ melanomas.
CTLA-4; Melanoma; Ipilimumab; ADCC; NK/γδ T cell activation
Cytotoxic T lymphocyte-associated antigen-4 (CTLA-4) targeted therapy by anti-CTLA-4 monoclonal antibody (mAb) is highly effective in cancer patients. However, it is extremely expensive and potentially produces autoimmune-related adverse effects. Therefore, the development of a method to evaluate CTLA-4 expression prior to CTLA-4-targeted therapy is expected to open doors to evidence-based and cost-efficient medical care and to avoid adverse effects brought about by ineffective therapy. In this study, we aimed to develop a molecular imaging probe for CTLA-4 visualization in tumor. First, we examined CTLA-4 expression in normal colon tissues, cultured CT26 cells, and CT26 tumor tissues from tumor-bearing BALB/c mice and BALB/c nude mice by reverse transcription polymerase chain reaction (RT-PCR) analysis and confirmed whether CTLA-4 is strongly expressed in CT26 tumor tissues. Second, we newly synthesized 64Cu-1,4,7,10-tetraazacyclododecane-N,N′,N″,N‴-tetraacetic acid-anti-mouse CTLA-4 mAb (64Cu-DOTA-anti-CTLA-4 mAb) and evaluated its usefulness in positron emission tomography (PET) and ex-vivo biodistribution analysis in CT26-bearing BALB/c mice. High CTLA-4 expression was confirmed in the CT26 tumor tissues of tumor-bearing BALB/c mice. However, CTLA-4 expression was extremely low in the cultured CT26 cells and the CT26 tumor tissues of tumor-bearing BALB/c nude mice. The results suggested that T cells were responsible for the high CTLA-4 expression. Furthermore, 64Cu-DOTA-anti-CTLA-4 mAb displayed significantly high accumulation in the CT26 tumor, thereby realizing non-invasive CTLA-4 visualization in the tumor. Together, the results indicate that 64Cu-DOTA-anti-CTLA-4 mAb would be useful for the evaluation of CTLA-4 expression in tumor.
Our goal was to identify genes regulated by Wnt/β-catenin signaling in melanoma cells, as this pathway has been implicated in melanocyte development and in melanoma biology. We therefore undertook transcriptional profiling of UACC 1273 human melanoma cells following treatment with recombinant Wnt-3a and found that cytotoxic T-lymphocyte antigen-4 (CTLA-4) was the most highly induced gene. We observed CTLA-4 expression in human epidermal melanocytes and in patient-derived primary melanoma tumors and found that Wnt/β-catenin signaling elevates CTLA-4 expression in two cultured melanoma cell lines. CTLA-4 is likely a direct target of Wnt/β-catenin signaling, as the β-catenin responsiveness of a 1.7 kb region of the CTLA-4 promoter requires a T-cell factor-1/lymphoid enhancing factor-1 consensus site present at −114 to −119 bp from the transcriptional start site. These findings are the initial demonstration that CTLA-4 is a direct target of Wnt/β-catenin signaling and the first report of its expression in primary melanoma tumors and melanocytes. Given the described role of CTLA-4 in inhibiting the immune response, these findings may shed light on the role of Wnt/β catenin signaling in melanoma and on the mechanism of action of human anti-CTLA-4 antibody, currently in phase III clinical trials for the treatment of melanoma.
CTLA-4 encodes cytotoxic T lymphocyte-associated antigen-4, a cell-surface molecule providing a negative signal for T-cell activation. CTLA-4 gene polymorphisms have been widely studied in connection with genetic susceptibility to various autoimmune diseases, but studies have led to contradictory results in different populations. This case-control study sought to investigate whether CTLA-4 CT60 and/or +49A/G polymorphisms were involved in the genetic predisposition to primary Sjögren syndrome (pSS). We analysed CTLA-4 CT60 and +49A/G polymorphisms in a first cohort of 142 patients with pSS (cohort 1) and 241 controls, all of Caucasian origin. A replication study was performed on a second cohort of 139 patients with pSS (cohort 2). In cohort 1, the CTLA-4 +49A/G*A allele was found on 73% of chromosomes in patients with pSS, compared with 66% in controls (p = 0.036; odds ratio (OR) 1.41, 95% confidence interval (CI) 1.02 to 1.95). No difference in CTLA-4 CT60 allelic or genotypic distribution was observed between patients (n = 142) and controls (n = 241). In the replication cohort, the CTLA-4 +49A/G*A allele was found on 62% of chromosomes in patients with pSS, compared with 66% in controls (p = 0.30; OR 0.85, 95% CI 0.63 to 1.16). Thus, the CTLA-4 +49A/G*A allele excess among patients from cohort 1 was counterbalanced by its under-representation in cohort 2. When the results from the patients in both cohorts were pooled (n = 281), there was no difference in CTLA-4 +49A/G allelic or genotypic distribution in comparison with controls. Our results demonstrate a lack of association between CTLA-4 CT60 or +49A/G polymorphisms and pSS. Premature conclusions might have been made if a replication study had not been performed. These results illustrate the importance of case-control studies performed on a large number of patients. In fact, sampling bias may account for some contradictory results previously reported for CTLA-4 association studies in autoimmune diseases.
Primary biliary cirrhosis (PBC) is a chronic autoimmune cholestatic liver disease frequently characterized by anti-mitochondrial autoantibodies (AMA). A minority of patients are AMA-negative. Cytotoxic-T-Lymphocyte-Antigen-4 (CTLA-4) is a surface molecule expressed on activated T-cells delivering a critical negative immunoregulatory signal. A soluble form of CTLA-4 (sCTLA-4) has been detected at high concentrations in several autoimmune diseases, and its possible functional meaning has been suggested. We aimed to evaluate sCTLA-4 concentration in sera of patients with PBC and to correlate it to immunological abnormalities associated with the disease. Blood samples were collected from 82 PBC-patients diagnosed according to international criteria (44 AMA-positive/MIT3-positive and 38 AMA-negative-MIT3-negative), and 65 controls. sCTLA-4 levels were evaluated by ELISA and Western blot. Increased sCTLA-4 concentrations were found in all AMA-positive PBC-patients, but in none of the AMA-negative ones, nor in normal controls or in controls with unrelated liver diseases. sCTLA-4 presence was associated with autoantibodies against MIT3, but not with nuclear autoantibodies (sp100, gp210). This is the first study to demonstrate that levels of sCTLA-4 are elevated in sera of PBC patients. However, they are clearly restricted to patients with AMA positivity, suggesting an immunological difference with respect to AMA-negative ones.
Cytotoxic T-lymphocyte associated protein 4 (CTLA4) is a negative regulator of T-cell proliferation. Polymorphisms in CTLA4 have been inconsistently associated with susceptibility to rheumatoid arthritis (RA) in populations of European ancestry but have not been examined in African Americans. The prevalence of RA in most populations of European and Asian ancestry is ∼1.0%; RA is purportedly less common in black Africans, with little known about its prevalence in African Americans. We sought to determine if CTLA4 polymorphisms are associated with RA in African Americans. We performed a 2-stage analysis of 12 haplotype tagging single nucleotide polymorphisms (SNPs) across CTLA4 in a total of 505 African American RA patients and 712 African American controls using Illumina and TaqMan platforms. The minor allele (G) of the rs231778 SNP was 0.054 in RA patients, compared to 0.209 in controls (4.462×10−26, Fisher's exact). The presence of the G allele was associated with a substantially reduced odds ratio (OR) of having RA (AG+GG genotypes vs. AA genotype, OR 0.19, 95% CI: 0.13–0.26, p = 2.4×10−28, Fisher's exact), suggesting a protective effect. This SNP is polymorphic in the African population (minor allele frequency [MAF] 0.09 in the Yoruba population), but is very rare in other groups (MAF = 0.002 in 530 Caucasians genotyped for this study). Markers associated with RA in populations of European ancestry (rs3087243 [+60C/T] and rs231775 [+49A/G]) were not replicated in African Americans. We found no confounding of association for rs231778 after stratifying for the HLA-DRB1 shared epitope, presence of anti-cyclic citrullinated peptide antibody, or degree of admixture from the European population. An African ancestry-specific genetic variant of CTLA4 appears to be associated with protection from RA in African Americans. This finding may explain, in part, the relatively low prevalence of RA in black African populations.
Rheumatoid arthritis (RA) is a systemic autoimmune condition affecting the synovial membranes of diarthrodial joints. The etiology of RA is unclear but is thought to result from an environmental trigger in the context of genetic predisposition. We report that a single nucleotide polymorphism (SNP) (rs231778) in CTLA4, which encodes a negative regulator of T cell activation, is associated (p = 2.4×10−28) with protection from developing RA among African Americans. rs231778 is only polymorphic in populations of African ancestry. Protective alleles such as this one may contribute to the purported lower prevalence of RA in African Americans. Our finding appears to be independent from confounding by linkage with the HLA-DRB1 shared epitope or by genetic admixture. Furthermore, we did not replicate associations of CTLA4 SNPs with RA or other autoimmune diseases previously reported in Asians and Caucasians, such as rs3087243 (+60C/T) and rs231775 (+49A/G). The associations of different SNPs with RA susceptibility specific to different populations highlight the importance of CTLA4 in the pathogenesis of RA and demonstrate the ethnic-specific genetic background that contributes to its susceptibility.
Background: The cytotoxic T lymphocyteassociated
antigen 4 gene (CTLA-4) encode the
T cell receptor involved in the control of T cell
proliferation and mediates T cell apoptosis.
The receptor protein is a specific T lymphocyte
surface antigen that is detected on cells only
after antigen presentation. Thus, CTLA-4 is
directly involved in both immune and autoimmune
responses and may be involved in the
pathogenesis of multiple T cell-mediated
autoimmune disorders. There is polymorphism
at position 49 in exon 1 of the CTLA-4 gene,
providing an A-G exchange. Moreover, we
assessed the CTLA-4 49 (Thr/Ala) polymorphism
in diabetic patients and first-degree relatives
as compared to control subjects.
Research design and methods: Three loci
(HLA-DQB1, DQA1 and CTLA-4) were analysed in 62 type 1 diabetic patients, 72 firstdegree
relatives and 84 nondiabetic control
subjects by means of PCR-RFLP.
Results: A significant enrichment in DQB1
alleles encoding for an amino acid different
from Asp in position 57 (NA) and DQA1 alleles
encoding for Arg in position 52 was
observed in diabetic subjects and first-degree
relatives as compared to controls. The genotype
and allele frequencies of these polymorphisms
in type 1 diabetic patients and firstdegree
relatives differed significantly from
those of controls (p< 0.001 and 0.05 respectively).
CTLA-49 Ala alleles frequencies were
75.8% in type 1 diabetic patients and 68.1% in
first-degree relatives in comparison to 35.7% in
control subjects. The Ala/Ala genotype conferred
a relative risk of 18.8 (p < 0.001).
Conclusion: The CTLA-4 49 Ala allele confers
an increased risk of type 1 diabetes, independent
of age and HLA-DQ genetic markers.
As more patient data is cross-referenced with animal models of disease, the primary focus on Th1 auto-reactive effector cell function in autoimmune diseases, such as rheumatoid arthritis and multiple sclerosis, has shifted towards the role of Th17 autoreactive effector cells and the ability of regulatory T cells (Treg) to modulate the pro-inflammatory autoimmune response. Therefore, the currently favored hypothesis is that a delicate balance between Th1/17 effector cells and Treg cell function is critical in the regulation of inflammatory autoimmune disease. An intensive area of research with regard to the Th1/17:Treg cell balance is the utilization of blockade and/ or ligation of various co-stimulatory or co-inhibitory molecules, respectively, during ongoing disease to skew the immune response toward a more tolerogenic/regulatory state. Currently, FDA-approved therapies for multiple sclerosis patients are all aimed at the suppression of immune cell function. The other favored method of treatment is a modulation or deletion of autoreactive immune cells via short-term blockade of activating co-stimulatory receptors via treatment with fusion proteins such as CTLA4-Ig and CTLA4-FasL. Based on the initial success of CTLA4-Ig, there are additional fusion proteins that are currently under development. Examples of the more recently identified B7/CD28 family members are PD-L1, PD-L2, inducible co-stimulatory molecule-ligand (ICOS-L), B7-H3, and B7-H4, all of which may emerge as potential fusion protein therapeutics, each with unique, yet often overlapping functions. The expression of both stimulatory and inhibitory B7 molecules seems to play an essential role in modulating immune cell function through a variety of mechanisms, which is supported by findings that suggest each B7 molecule has developed its own indispensable niche in the immune system. As more data are generated, the diagnostic and therapeutic potential of the above B7 family-member-derived fusion proteins becomes ever more apparent. Besides defining the biology of these B7/CD28 family members in vivo, additional difficulty in the development of these therapies lies in maintaining the normal immune functions of recognition and reaction to non-self-antigens following viral or bacterial infection in the patient. Further complicating the clinical translation of these therapies, the mechanism of action identified for a particular reagent may depend upon the method of immune-cell activation and the subset of immune cells targeted in the study.
The costimulatory molecules B7-1 and B7-2 regulate T lymphocyte activation by delivering activating signals through CD28 and inhibitory signals through cytotoxic T lymphocyte–associated antigen 4 (CTLA-4). The importance of CTLA-4–mediated inhibition was demonstrated by the uncontrolled T cell activation and lymphoproliferative disease that develops in CTLA-4–deficient (−/−) mice. To examine the role of B7 signaling in the activation of CTLA-4–deficient T cells, we bred CTLA-4−/− mice with mice lacking B7-1, B7-2, or both B7 molecules. The CTLA-4/B7-1−/− and the CTLA-4/B7-2−/− mice develop lymphoproliferation and enhanced T cell activation. Mice lacking CTLA-4, B7-1, and B7-2 have a normal life-span, and do not have lymphocytic infiltrates in any organs, or increased T cell activation. Therefore, the two B7 molecules have overlapping functions, since either B7-1 or B7-2 alone can cause the CTLA-4−/− phenotype. Elimination of both B7-1 and B7-2 from the CTLA-4– deficient mouse abrogates the lymphocyte activation and disease, and does not reveal evidence for additional stimulatory CD28 ligands. The CTLA-4−/− phenotype can be reproduced with anti-CD28 antibody in mice lacking CTLA-4, B7-1, and B7-2, but wild-type mice are unaffected by the same treatment. This suggests that the inhibitory function of CTLA-4 can overcome strong CD28-mediated signaling in vivo.
cytotoxic T lymphocyte–associated antigen 4; B7; knockout mouse; costimulation; T lymphocyte
Cytotoxic T lymphocyte–associated antigen (CTLA)-4 can inhibit T-cell responses and is involved in tolerance against self antigens. We previously reported autoimmune manifestations and objective cancer regressions in patients with metastatic melanoma treated with CTLA-4 blockade. The possibility of activating tumor-reactive T cells while removing inhibitory activity with CTLA-4 blockade has stimulated interest in using anti–CTLA-4 antibodies in combination with other cancer immunotherapies to improve clinical outcomes. In this study, we assessed the antitumor activity and autoimmune toxicity of CTLA-4 blockade in combination with an immune-activating stimulus, interleukin (IL)-2, in patients with metastatic melanoma.
Thirty-six patients received anti–CTLA-4 antibody every 3 weeks. Three patients per cohort received doses of .1, .3, 1.0, and 2.0 mg/kg. Twenty-four patients received 3.0 mg/kg. All patients received IL-2 therapy (720,000 IU/kg every 8 hours to a maximum of 15 doses).
Eight patients (22%) experienced objective tumor responses (three complete and five partial), including metastases in the lungs, lymph nodes, mediastinum, and subcutaneous tissues. Six of the eight patients have ongoing objective responses at 11 to 19 months. Five patients (14%) developed grade III/IV autoimmune toxicities secondary to anti–CTLA-4 administration, including four patients with enterocolitis and one with arthritis and uveitis.
There is not evidence to support a synergistic effect of CTLA-4 blockade plus IL-2 administration, because the 22% objective response rate is that expected from the sum of these two agents administered alone. Durable cancer regressions were seen in patients treated with this combination.
Cytotoxic T lymphocyte-associated antigen 4; Interleukin 2; Melanoma; Autoimmunity
Co-stimulation blockade can be used to modulate the immune response for induction of organ transplantation tolerance, treatment of autoimmune disease as well as cancer treatment. Cytotoxic T-Lymphocyte Antigen-4 (CTLA-4), also known as CD152, is an important co-stimulatory molecule which serves as a negative regulator for T cell proliferation and differentiation. CTLA-4/CD28-CD80/CD86 pathway is a critical co-stimulatory pathway for adaptive immune response. T cell activation through the T cell receptor and CD28 leads to increased expression of CTLA-4, an inhibitory receptor for CD80 and CD86. MGH MHC-defined miniature swine provide a unique large animal model useful for preclinical studies of transplantation tolerance and immune regulation. In this study, we have expressed the codon-optimized soluble porcine CTLA-4 in the yeast Pichia pastoris system. The secreted porcine CTLA-4 was captured using Ni-Sepharose 6 fast flow resin and further purified using strong anion exchange resin Poros 50HQ. Glycosylation analysis using PNGase F demonstrated the N-linked glycosylation on Pichia pastoris expressed soluble porcine CTLA-4. To improve the expression level and facilitate the downstream purification we mutated the two potential N-linked glycosylation sites with non-polarized alanines by site-directed mutagenesis. Removal of the two N-glycosylation sites significantly improved the production level from ~2 mg/L to ~8 mg/L. Biotinylated glycosylated and non-N-glycosylated soluble porcine CTLA-4 both bind to a porcine CD80-expressing B-cell lymphoma cell line (KD = 13 nM) and competitively inhibit the binding of an anti-CD80 monoclonal antibody. The availability of soluble porcine CTLA-4, especially the non-N-glycosylated CTLA-4, will provide a very valuable tool for assessing co-stimulatory blockade treatment for translational studies in the clinically relevant porcine model.
Porcine CTLA-4; Pichia pastoris expression; purification; porcine CD80; glycosylation
The cytotoxic T lymphocyte antigen 4 (CTLA‐4) gene encodes for a membrane bound (mCTLA‐4) and a soluble (sCTLA‐4) isoform, which are both involved in regulation of T cell function. The CTLA‐4 +49A/G single nucleotide polymorphism (SNP) influences expression of mCTLA‐4; +6230G/A SNP affects the production of sCTLA‐4.
To examine whether these functional SNPs influence the rate of rejection after liver transplantation.
Patients and methods
Liver graft recipients (n = 483) were genotyped for both SNPs, and haplotypes were reconstructed. Association with rejection was tested by the log rank test using the Kaplan‐Meier method with time to the first acute rejection episode as outcome. Multiple analysis of SNPs together with demographic factors was performed by Cox regression.
Three haplotypes were observed in the cohort: +49A/+6230A, +49A/+6230G, and +49G/+6230G. The +49A/+6230G haplotype was significantly and dose dependently associated with acute rejection (p = 0.01). Of the demographic factors tested, only underlying liver disease was significantly associated with rejection. Adjusted for underlying liver disease, each additional +49A/+6230G haplotype allele resulted in a significantly higher risk of acute rejection (risk ratio 1.34 (95% confidence interval 1.04–1.72); p = 0.02). Patients who lacked this haplotype had the lowest, carriers an intermediate, and homozygotes the highest risk of acute rejection.
The CTLA‐4 +49A/+6230G haplotype, which encodes for normal mCTLA‐4 expression but reduced sCTLA‐4 production, is a co‐dominant risk allele for acute rejection after clinical liver transplantation. This implies that even under immunosuppression, CTLA‐4 is critically involved in the regulation of the human immune response to allogeneic grafts.
cytotoxic T lymphocyte antigen 4; liver transplantation; rejection; haplotype; single nucleotide polymorphism
Protection of beta cells from autoimmune destruction potentially cures type 1 diabetes mellitus (T1D). During antigen presentation, interactions between cytotoxic T-lymphocyte antigen-4 (CTLA4) and B7 molecules, or programmed death 1 (PD1) and its ligand PDL1, negatively regulate immune responses in a non-redundant manner. Here, we employed beta cell-targeted adeno-associated virus serotype 8 (AAV8)-based vectors to over-express an artificial PDL1-CTLA4Ig polyprotein or IL10. Beta cell-targeted expression of PDL1-CTLA4Ig or IL10 preserved beta cell mass and protected NOD mice from T1D development. When NOD mice were treated with vectors at early onset of hyperglycemia, PDL1-CTLA4Ig or IL10 alone failed to normalize the early onset of hyperglycemia. When drug-induced diabetic mice received MHC-matched allo-islets, with or without pretreatment of the PDL1-CTLA4Ig-expressing vector, PDL1-CTLA4Ig-expressing islets were protected from rejection for at least 120 days. Similarly, transplantation of PDL1-CTLA4Ig-expressing MHC-matched islets into mice with established T1D resulted in protection of allo-islets from acute rejection, although islet grafts were eventually rejected. Thus, the present study demonstrates the potent immuno-suppressive effects of beta cell-targeted PDL1-CTLA4Ig overexpression against T1D development and allo-islet rejection. The gene-based simultaneous inhibition of PD1 and CTLA4 pathways provides a unique strategy for immunosuppression-free tissue/organ transplantation, especially in the setting of no established autoimmunity.
AAV vector; type 1 diabetes; islet transplant; β-cell regeneration; immune suppression