A Novel Missense Variant in CTLA4 Associated with Immune Dysregulation

The new quest in CTLA-4 insufficiency: How to immune modulate effectively?

Targeted treatment of immune thrombocytopenia in CTLA-4 insufficiency: a case report.

Testimony from the Bedside: From Coley's Toxins to Targeted Immunotherapy

Background: The diagnostic yield of next-generation sequencing (NGS) technologies in the diagnosis of monogenic inborn errors of immunity (IEI) remains limited, rarely exceeding 30%. Monoallelic pathogenic germline variants in cytotoxic T lymphocyte-associated antigen-4 (CTLA-4) result in variable immunodeficiency and immune dysregulation. The genetic diagnosis of CTLA-4 insufficiency can affect follow-up procedures and may lead to consideration of treatment with CTLA-4-Ig. Objectives: The aim of the study was to identify the genetic cause of familial immunodeficiency and immune dysregulation in cases where single nucleotide variant analysis of short-read NGS data yielded no diagnostic result. Methods: Analysis of copy number variants (CNVs) was applied on short-read NGS data. Results: We identified a novel monoallelic deletion-insertion variant in CTLA-4 (c.445_568-544delinsTTTGCGATTG) resulting in familial autoimmunity. This is the second larger scale variant in CTLA-4, which despite consistently reduced expression of CTLA-4 displayed variable expressivity, ranging from typical juvenile idiopathic arthritis to common variable immunodeficiency-like immunodeficiency. Conclusions: Our report suggests the significance of integration of CNV analysis in routine evaluation of NGS, which may increase its diagnostic yield in IEI.

Background: Cytotoxic T lymphocyte-associated antigen-4 (CTLA4) haploinsufficiency is characterized by a variety of phenotypes, ranging from autoimmune disorders, enteropathy, fatal combined immunodeficiency, as well as lymphoproliferation and malignancy. Aim: To broaden the genotypic spectrum and clinical presentations of patients with CTLA4 variants. Methods: We evaluated a female patient with autoimmunity and lymphopenia. Immune workup and whole exome sequencing (WES) were performed. Results: The proband presented at 11 years of age with hypothyroidism and later developed Evans syndrome, alopecia, eczema, and lymphocytic interstitial pneumonia. Immune evaluation revealed T, B, and NK lymphopenia with normal humoral immunity. Following a negative genetic panel for autoimmune lymphoproliferative syndrome (ALPS), WES analysis identified a novel heterozygous intronic variant predicted in-silico to cause skipping of exon 2 of the CTLA4 gene. Conclusion: A novel heterozygous mutation in CTLA4 caused variable presentations of immune dysregulation, one of the hallmarks of CTLA4 haploinsufficiency. Statement of Novelty: We herein report a novel mutation in CTLA4 resulting in various features of autoimmunity.

Objective: To investigate the survival and death risk factors of mesothelioma cases stratified by the expression levels of CD8 and cytotoxic T lymphocyte-associated antigen-4 (CTLA-4) , providing new clue to evaluate disease progression and clinical outcome. Methods: This was a retrospective case report, which included 47 clinically and pathologically confirmed mesothelioma cases on November 2016. Their clinical and pathological information, asbestos exposure history and survival data were collected. Infiltrated lymphocyte, 5-methylcytosine (5-mC) , CTLA-4, CD8 and Ki-67 antigen were detected using hematoxylin-eosin staining and immunohistochemistry. Survival time and death risk factors of mesothelioma patients with different CD8 and CTLA-4 protein expression characteristics were analyzed. And analyze the influence of Ki-67 expression on the survival of patients with different CD8 and CTLA-4 protein and gene expression characteristics. Results: Among the 47 cases, 63.8% (30/47) had low/medium level of infiltrated lymphocyte. The immunohistochemistry scores of CTLA-4, CD8, 5-mC and Ki-67 were 92.97 (54.95, 120.65) , 72.41 (36.62, 89.82) , 11.09 (3.40, 52.89) and 5.88 (2.41, 11.48) , respectively. Patients with CD8(high) CTLA-4(high) had higher 5-mC level than those with CD8(high) CTLA-4(low) (P<0.01) . The median survival time of 27 cases was 0.83±0.29 year. The median survival times of those with CD8(high) CTLA-4(high) and CD8(high) CTLA-4(low) were 0.58±0.51 year and 0.83±0.30 year, respectively (P=0.521) . The immunohistochemistry score of Ki-67 ≥5.88 was an independent death risk factor for patients with CD8(high) CTLA-4(low) (HR=8.40, P=0.01) . Under different CD8 and CTLA-4 protein expression characteristics, in the patients with CD8(high) CTLA-4(low), the median survival times of those with high and low Ki-67 expression were 0.57±0.11 years and 2.31±0.46 years, respectively (P<0.01) . Under different CD8 and CTLA-4 mRNA expression characteristics, in the patients with CD8(high) CTLA-4(low), the median survival times of those with high and low Ki-67 mRNA expression were 1.20±0.36 years and 3.38±0.43 years, respectively (P=0.018) . Conclusion: Mesothelioma case with high CD8 but low CTLA-4 content might coexist DNA hypomethylation. In the presence of high Ki-67 expression, their survival time appears to be shortened with increased death risk.

Cytotoxic T lymphocyte-associated antigen 4 (CTLA4) plays a critical role in down-regulating T cell responses. A number of autoimmune diseases have shown genetic linkage to the CTLA4 locus. We have cloned and expressed an alternatively spliced form of CTLA4 that has genetic linkage with type 1 diabetes in NOD mice. This splice variant of CTLA4, named ligand-independent CTLA4 (liCTLA4), lacks exon 2 including the MYPPPY motif essential for binding to the costimulatory ligands B7-1 and B7-2. liCTLA4 is expressed as a protein in primary T cells and strongly inhibits T cell responses by binding and dephosphorylating the TcRzeta chain. Expression of liCTLA4, but not full length CTLA4 (flCTLA4), was higher in memory/regulatory T cells from diabetes resistant NOD congenic mice compared to susceptible NOD mice. Transgenic expression of liCTLA4 in autoimmune prone Ctla4 -/- mice inhibited spontaneous T cell activation and prevented early lethality in the Ctla4 -/- mice. Thus, increased expression and negative signalling delivered by the liCTLA4 may play a critical role in regulating the development of T cell-mediated autoimmune diseases.

Recently, systemic administration of a human monoclonal antibody directed against cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) expressed on circulating T cells in patients with chronic lymphocytic leukaemia (CLL) has been considered. Also, CLL cells have been shown to express CTLA-4, increased levels of which in the leukaemic compartment are a predictor of good clinical outcome. Since both CLL and Treg microenvironment cells can be targeted by the CTLA-4 blocking antibody in this immunotherapy approach, the investigation of the functional effect of CTLA-4 blockade on CLL cells might be of potential clinical relevance. The main aim of this study was to examine the effect of CTLA-4 blockade on proliferation activity and apoptosis of CLL cells in patients with low and high CTLA-4 expression. We found that in the high CTLA-4-expressing CLL group, CTLA-4 blockade on the CLL cell surface resulted in a significant increase in the median percentages of Ki67+ cells and a tendency to decrease in the proportion of apoptotic cells. In contrast, in the low CTLA-4 expressors, CTLA-4 blockade did not affect the proliferation activity or the frequency of apoptosis. This study reports for the first time the different effect of CTLA-4 blockade on CLL cells in CLL patients depending on the levels of CTLA-4 expression. CTLA-4 blockade seems to induce pro-survival signals in leukaemic cells from CLL patients exhibiting high CTLA-4 expression, suggesting that an immunotherapy approach based on the systemic use of monoclonal anti-CTLA-4 antibodies could be an unfavourable strategy for some CLL patients.

Virus-specific cluster of differentiation 8 (CD8+) cytotoxic T cells (CTL) recognize viral antigens presented on major histocompatibility complex (MHC) class I chains on infected hepatocytes, with help from CD4+ T cells. However, this CTL response is frequently weak or undetectable in patients with chronic hepatitis B virus (HBV) and hepatitis C virus (HCV) infection. Programmed cell death 1 (PD-1) and cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) are receptors in the CD28 family of costimulatory molecules, providing inhibitory signals to T cells. The overexpressions of PD-1 and CTLA-4 in patients with viral infection have been shown to associate with functional impairment of virus-specific T cells. In acute viral hepatitis, PD-1 and CTLA-4 are up-regulated during the symptomatic phase, and then down-regulated after recovery. These findings suggest that PD-1 and CTLA-4 have protective effects as inhibitory molecules to suppress cytotoxic T cells which induce harmful destruction of viral infected hepatocytes in self-limited viral hepatitis. In chronic viral hepatitis, the extended upregulations of PD-1 and CTLA-4 are associated with T cell exhaustion and persistent viral infection, suggesting positive correlations between expression of immune inhibitory factors and the chronicity of viral disease. In this review, we summarize recent literature relating to PD-1, CTLA-4, and other inhibitory receptors in antigen-specific T cell exhaustion in viral hepatitis, including hepatitis A, B, C, and others.

Cytotoxic T-lymphocyte-associated protein-4 (CTLA-4) was first discovered in 1987 and confirmed to be a protein that is mainly expressed on the surface of activated lymphocytes. CTLA-4 is expressed on the surface of T cells and binds to B7 expressed on antigen presenting cells(APCs) to potentially play a role in inhibiting lymphocyte proliferation. Inhibitors of CTLA-4 were developed to promote the anti-tumor effects of T cells and inhibit tumor growth. CTLA-4, as an immune checkpoint, has been realized as an important therapeutic target in bladder cancer. Two main CTLA-4 inhibitors are currently used: ipilimumab is a first-generation IgG1 monoclonal antibody that targets CTLA-4, and it is completely synthetic; tremelimumab, representing another class of CTLA-4 inhibitors, is a monoclonal antibody against CTLA-4 that acts similarly to ipilimumab and binds specifically to CTLA-4. The two types of CTLA-4 inhibitors were found to improve the treatment effect in patients with bladder cancer in comparison to conventional agents. To review this topic, we searched recently published related articles.

Cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) is an important surface molecule of activated T cells that has a strong affinity with the B7 molecule on the surface of antigen-presenting cells. Among these molecules, the CTLA-4 extracellular region (CTLA-4 IgV) may be used as a novel immune adjuvant molecule for delivering antigens and inducing strong humoral and cellular immune responses. In this study, bioinformatics analysis was performed to determine and clone the extracellular region of Xinjiang sheep CTLA-4 (NM_001009214). The CTLA-4 IgV gene was amplified and ligated into the pMD19-T vector, and the positive bacteria were screened by blue-white spots for sequencing and comparison. The correctly sequenced CTLA-4 IgV was digested and then ligated into the prokaryotic expression vector pET-30a(+). The plasmid pET30a-CTLA-4 IgV was constructed to induce the expression of the recombinant protein CTLA-4 IgV. Thereafter, CTLA-4 IgV was identified. Clustal X multiple sequence alignment revealed that the protein sequence of Xinjiang sheep CTLA-4 IgV was different from that of the known CTLA-4 extracellular region. The 3D protein structure of Xinjiang sheep CTLA-4 IgV was constructed via the bioinformatics method. Subsequently, molecular docking between the Xinjiang sheep CTLA-4 IgV protein and the B7 molecule was conducted. Results revealed multiple binding sites in the extracellular region of Xinjiang sheep CTLA-4, and two multiple interactions ensured stable binding after docking. The functionality of the Xinjiang sheep CTLA-4 IgV protein was further verified by fusing the CTLA-4 extracellular V region with EgG1Y162, a protective protein from Echinococcus granulosa, and the purified recombinant protein CTLA-4 IgV-EgG1Y162 was expressed with the mouse bone marrow-derived. The addition of the Xinjiang sheep CTLA-4 IgV protein at the amino terminus promoted the binding of EgG1Y162 to dendritic cells (DCs) and increased the maturation rate of these cells, further indicating that the protein could effectively improve the antigen presentation ability of DCs. The CTLA-4 extracellular domain protein of Xinjiang sheep is unique and has the potential to promote the presentation of the fusion protein by DCs as an adjuvant. The cloning and expression of this gene provide new measures and ideas for the preparation of the Xinjiang sheep vaccine to prevent zoonotic diseases.

Cytotoxic T lymphocyte-associated antigen 4 (CTLA4) is an important negative regulator of T-cell response and its genetic association with type 1 diabetes (T1D) has recently been demonstrated. The frequent co-association of autoimmune diseases (AID) and the implication from multiple genome scans that the CTLA4 gene region is a general autoimmune region, led us to study the role of CTLA4 in independent cohorts of T1D, coeliac disease (CD) and rheumatoid arthritis (RA) patients. We present independent data that confirm the association of CTLA4 in Dutch patients with juvenile onset T1D and show differential association of CTLA4 with CD and RA. The CTLA4 gene polymorphisms were tested for association in 350 T1D, 310 CD, 520 RA patients and 900 controls. In addition, 218 families were tested by the transmission disequilibrium test (TDT). T1D patients showed the highest association with the MH30*G: -1147*C: +49*G: CT60*G: JO37_3*G (haplotype 2) in both a case/control cohort (P=0.002, OR=1.42) and by TDT (P=0.02, OR=1.43). In contrast, this haplotype showed no association in the RA and CD cohorts. However, we observed an increased frequency of the MH30*G: -1147*T: +49*A: CT60*G: JO37_3*A (haplotype 3) in the CD patients diagnosed at a young age (OR=1.6, P=0.026, P (c)=0.052). Furthermore, when T1D and CD patients were stratified based on the HLA risk, the T1D susceptible CTLA4 haplotype 2 was over-represented in the high HLA-risk T1D and CD groups. In conclusion, we confirmed association between CTLA4 haplotype 2 and T1D in the Dutch population. Association with another CTLA4 haplotype (haplotype 3) was confirmed for CD, but only in those patients who had an early age of expression. No effect was found between RA and CTLA4. The association of the CTLA4 haplotype 2 with the high-risk HLA genotype in T1D and CD, which share DQ2 as the one of high-risk alleles, might provide a clue to understanding the common genetic background of AID.

The recurrence rate of lymphoma is very high, and tumor stem cells may be an important mechanism. Cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) can inhibit antitumor immunity and promote cancer progression, but its role and mechanism in lymphoma are still unclear. Here we collected lymphoma tissue and peripheral blood from patients with diffuse large B-cell lymphoma (DLBCL). Results showed that CTLA-4 expression and CD44+ cell in the high-risk group were significantly higher than that in the low-risk group. Correlation analysis showed that CTLA-4 expression positively correlated with CD44+ cell in lymphoma tissue and regulatory T (Treg) cells in lymphocytes. In vitro experiment showed that CTLA-4 increased the ratio of lymphoma stem cells, and proliferation and invasion of lymphoma cells through TGF-β pathway. Moreover, CTLA-4 enhanced the proliferation of Treg cells induced by lymphoma cells. Animal experiments showed that CTLA-4 can promote transplanted lymphoma growth. Immunohistochemistry results showed that both Ki-67 and CD44+ cells increased significantly in the CTLA-4 group. TGF-β neutralization can significantly block these effects of CTLA-4. In conclusion, CTLA-4 promoted DLBCL progression through lymphoma stem cell enrichment and immunosuppression.

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Cytotoxic T lymphocyte-associated antigen-4 (CTLA-4) is an immune checkpoint expressed in regulatory T (Treg) cells and activated T lymphocytes. Despite its potential as a treatment strategy for melanoma, CTLA-4 inhibition has limited efficacy. Using data from The Cancer Genome Atlas (TCGA) melanoma database and another dataset, we found that decreased CTLA4 mRNA was associated with a poorer prognosis in metastatic melanoma. To investigate further, we measured blood CTLA4 mRNA in 273 whole-blood samples from an Australian cohort and found that it was lower in metastatic melanoma than in healthy controls and associated with worse patient survival. We confirmed these findings using Cox proportional hazards model analysis and another cohort from the US. Fractionated blood analysis revealed that Treg cells were responsible for the downregulated CTLA4 in metastatic melanoma patients, which was confirmed by further analysis of published data showing downregulated CTLA-4 surface protein expression in Treg cells of metastatic melanoma compared to healthy donors. Mechanistically, we found that secretomes from human metastatic melanoma cells downregulate CTLA4 mRNA at the post-transcriptional level through miR-155 while upregulating FOXP3 expression in human Treg cells. Functionally, we demonstrated that CTLA4 expression inhibits the proliferation and suppressive function of human Treg cells. Finally, miR-155 was found to be upregulated in Treg cells from metastatic melanoma patients compared to healthy donors. Our study provides new insights into the underlying mechanisms of reduced CTLA4 expression observed in melanoma patients, demonstrating that post-transcriptional silencing of CTLA4 by miRNA-155 in Treg cells may play a critical role. Since CTLA-4 expression is downregulated in non-responder melanoma patients to anti-PD-1 immunotherapy, targeting miRNA-155 or other factors involved in regulating CTLA4 expression in Treg cells without affecting T cells could be a potential strategy to improve the efficacy of immunotherapy in melanoma. Further research is needed to understand the molecular mechanisms regulating CTLA4 expression in Treg cells and identify potential therapeutic targets for enhancing immune-based therapies.