Immune Checkpoint-Related Gene Polymorphisms Are Associated With Primary Immune Thrombocytopenia.

Cancer immunotherapy by immune checkpoint blockade has been effective in the treatment of certain tumors. However, the association between immune checkpoints and autoimmune diseases remains elusive and requires urgent investigation. Primary immune thrombocytopenia (ITP), characterized by reduced platelet count and a consequent increased risk of bleeding, is an autoimmune disorder with a hyper-activated T cell response. Here, we investigated the contribution of immune checkpoint-related single-nucleotide polymorphisms (SNPs), including CD28, ICOS, PD1, TNFSF4, DNAM1, TIM3, CTLA4, and LAG3 to the susceptibility and therapeutic effects of ITP. In this case-control study, 307 ITP patients and 295 age-matched healthy participants were recruited. We used the MassARRAY system for genotyping immune checkpoint-related SNPs. Our results revealed that rs1980422 in CD28 was associated with an increased risk of ITP after false discovery rate correction (codominant, CT vs. TT, OR = 1.788, 95% CI = 1.178-2.713, p = 0.006). In addition, CD28 expression at both the mRNA and protein levels was significantly higher in patients with CT than in those with the TT genotype (p = 0.028 and p = 0.001, respectively). Furthermore, the T allele of PD1 rs36084323 was a risk factor for ITP severity and the T allele of DNAM1 rs763361 for corticosteroid-resistance. In contrast, the T allele of LAG3 rs870849 was a protective factor for ITP severity, and the T allele of ICOS rs6726035 was protective against corticosteroid-resistance. The TT/CT genotypes of PD1 rs36084323 also showed an 8.889-fold increase in the risk of developing refractory ITP. This study indicates that immune checkpoint-related SNPs, especially CD28 rs1980422, may be genetic factors associated with the development and treatment of ITP patients. Our results shed new light on prognosis prediction, disease severity, and discovering new therapeutic targets.

Clinical Implications of Peripheral CD3+CD69+ T-Cell And CD8+CD28+ T-Cell Proportions in Patients Prior to Radical Prostatectomy.

PURPOSE: To investigate the clinical implications of CD3+CD69+ T-cells and CD8+CD28+ T-cells in the peripheral blood of patients prior to radical prostatectomy. MATERIALS AND METHODS: A total of 91 prostate cancer (PCa) patients and 50 benign prostatic hyperplasia (BPH) patients were enrolled from January 2016 to December 2017. The proportions of CD3+CD69+ T-cells and CD8+CD28+ T-cells in the peripheral blood of PCa and BPH patients were detected by flow cytometry, and the association of these T-cell populations with pathological Grade Group and pathological TNM classification was evaluated. Data analysis was performed with SAS version 9.4 software. RESULTS: The proportions of CD3+CD69+ and CD8+CD28+ T-cells in peripheral blood were higher in PCa patients than those in BPH patients. Multivariate analysis identified a higher CD3+CD69+ T-cell proportion as a risk factor for PCa (odds ratio (OR) = 4.783, P = 0.0013), but the diagnostic efficacy of the CD3+CD69+ T-cell proportion (area under the curve (AUC)=0.6833, P = 0.0003) for PCa was still inferior to that of the tPSA level (AUC=0.7531, P < 0.0001). The AUCs for CD3+CD69+ T-cell and CD8+CD28+ T-cell proportions for PCa were 0.6959 (P = 0.0372) and 0.6935 (P = 0.0395), respectively, among men with tPSA levels of 4.0-10.0 ng/mL. A lower CD3+CD69+ T-cell proportion was associated with higher pathological Grade Group (P=0.0074). CONCLUSION: The proportions of CD3+CD69+ T-cells and CD8+CD28+ T-cells in peripheral blood are potential diagnostic indicators for PCa. The preoperative proportion of CD3+CD69+ T-cells in peripheral blood may have prognostic value in terms of the pathological Grade Group in PCa.

Six Cases of CD20-Positive Adult T-Cell Leukemia.

Adult T-cell leukaemia/lymphoma (ATLL) is a neoplasm originating in mature CD4+ peripheral T cells. However, rare cases of CD20+ ATLL have been reported. Here, we describe six cases of CD20+ ATLL diagnosed in our department. The median age was 79 years (range, 54-90 years); two patients were men, and four were women. Elevated lactate dehydrogenase was observed in four cases. All cases were lymphoma type and positive for human T-lymphotropic virus-1 (HTLV-1). HTLV-1 proviral DNA was detected in four cases. The Ann Arbor stage was I, II, or IV in one patient each and III in three patients. The clinical course was poor in almost all cases. Tumour cells were large in all cases, and flow cytometry revealed CD20+ lymphoma cells in five of six cases. Immunohistochemistry revealed lymphoma cells positive for CD20, CD3, CD4, and CCR4 and negative for CD8, CD79a, and PAX5 in all cases. CD20 expression was lower than that in normal B cells. One case was initially misdiagnosed as diffuse large B-cell lymphoma. Thus, combined use of an antibody panel and molecular genetic studies is important to avoid misdiagnosing ATLL as B-cell lymphoma.

BAFF upregulates CD28/B7 and CD40/CD154 expression and promotes mouse T and B cell interaction in vitro via BAFF receptor.

AIM: B cell-activating factor belonging to the TNF family (BAFF) is a member of TNF family and required for peripheral B cell survival and homeostasis. BAFF has been shown to promote the proliferation of T and B cells. In this study we examined whether and how BAFF mediated the interaction between mouse T and B cells in vitro. METHODS: BAFF-stimulated B or T cells were co-cultured with T or B cells. The interactions between T and B cells were analyzed by measuring the expression of co-stimulatory molecules (CD28/CD80 or CD40/CD154), the proliferation and secretion of T and B cells and other factors. Two siRNAs against the transmembrane activator and calcium modulator and cyclophilin ligand interactor (TACI) and BAFF receptor (BAFF-R) were used to identify the receptors responsible for the actions of BAFF. RESULTS: BAFF-stimulated B cells significantly promoted the proliferation and activity of co-cultured T cells, and increased the percentages of CD4(+)CD28(+) and CD4(+)CD154(+) T cells. Similarly, BAFF-stimulated T cells significantly promoted the proliferation and activity of co-cultured B cells, and increased CD19(+)CD80(+) and CD19(+)CD40(+)B cell subpopulations. BAFF-R siRNA-silenced B cells showed significantly lower expression of CD40 and CD80 than the control B cells. When the BAFF-R siRNA-silenced B cells were stimulated with BAFF, then co-cultured with T cells, the expression of CD28 and CD154 on T cells was not increased. TACI siRNA-silenced B cells exhibited higher expression of CD40 and CD80 than the control B cells. When the TACI siRNA-silenced B cells were stimulated with BAFF, then co-cultured with T cells, the expression of CD28 and CD154 on T cells was significantly increased. CONCLUSION: BAFF upregulates CD28/B7 and CD40/CD154 expression, and promotes the interactions between T and B cells in a BAFF-R-dependent manner.

Tumor CTLA-4 overexpression predicts poor survival in patients with nasopharyngeal carcinoma.

The expression levels of CTLA-4 and CD28 were analyzed in 191 nasopharyngeal carcinoma (NPC) patients diagnosed and treated at our hospital between January 2010 and November 2011. The 3-year overall survival (OS) rate (91.4% vs. 81.2%,p = 0.043), failure-free survival (FFS) rate (82.8% vs. 68.0%, p = 0.009) and distant failure-free survival (D-FFS) rate (85.8% vs. 72.3%, p = 0.006) in the low tumor CTLA-4 expression group was higher than in the high tumor CTLA-4 group. There were no differences between the locoregional failure-free survival (LR-FFS) rates in the high and low tumor CTLA-4 expression groups. Moreover, no differences in the OS, FFS, D-FFS, or LR-FFS were observed between the groups with high and low lymphocyte CTLA-4 levels, high and low tumor CD28 levels, or high and low lymphocyte CD28 levels. Cox regression analysis confirmed the prognostic value of tumor CTLA-4 expression, particularly for D-FFS, in NPC patients (p = 0.044). NPC patients with high tumor CTLA-4 expression had a poorer prognosis than those with low expression.

Structural Design of Engineered Costimulation Determines Tumor Rejection Kinetics and Persistence of CAR T Cells.

T cell engineering is a powerful means to rapidly generate anti-tumor T cells. The costimulatory properties of second-generation chimeric antigen receptors (CARs) determine the overall potency of adoptively transferred T cells. Using an in vivo "stress test" to challenge CD19-targeted T cells, we studied the functionality and persistence imparted by seven different CAR structures providing CD28 and/or 4-1BB costimulation. One configuration, which uses two signaling domains (CD28 and CD3ζ) and the 4-1BB ligand, provided the highest therapeutic efficacy, showing balanced tumoricidal function and increased T cell persistence accompanied by an elevated CD8/CD4 ratio and decreased exhaustion. Remarkably, induction of the IRF7/IFNß pathway was required for optimal anti-tumor activity. Thus, 1928z-41BBL T cells possess strikingly potent intrinsic and immunomodulatory qualities.

The suppressive function of human CD8(+) iTregs is inhibited by IL-1ß and TNFα.

CD8(+) Tregs display an immunoregulatory activity and may play an essential role in the immunopathology of several diseases. Therefore, their therapeutic potential is exquisite and further studies on their differentiation and function are essential. The aim of this study was to evaluate the role of the innate immune system in CD8(+) iTreg differentiation and function. Naive human CD8(+) CD25(-) CD45RA(+) T cells were cultured in Treg-inducing conditions with or without IL-1ß, TNFα or monocyte-derived dendritic cells (DCs). The differentiation of CD8(+) CD127(-) CD25(hi) FoxP3(hi) -induced Tregs (CD8(+) iTregs) is dependent on TGF-ß1 and IL-2, which had synergistic effect upon their differentiation. CD8(+) iTregs were also induced in a coculture with allogeneic mature DCs (mDCs). The CD8(+) iTregs suppressive function was confirmed, which was diminished in the presence of IL-1ß and TNFα. The IL-1ß-prevented suppressive function was associated with reduced secretion of IL-10 and IFNγ, whereas the presence of TNFα did not affect their secretion. Furthermore, the presence of TNFα reduced IL-10 and TGF-ß1 secretion by CD8(+) iTregs, whereas only IL-10 secretion was decreased by IL-1ß. Together, these results suggest that IL-1ß and TNFα prevent IL-2- and TGF-ß1-driven CD8(+) iTregs suppressive function in human T cells. Such pro-inflammatory innate immune response possibly mediates its negative tolerogenic effect through reduced IFNγ-, IL-10- and TGF-ß1-driven mechanism.

CD45RA-Foxp3(low) non-regulatory T cells in the CCR7-CD45RA-CD27+CD28+ effector memory subset are increased in synovial fluid from patients with rheumatoid arthritis.

Increased numbers of regulatory T (Treg) cells are found in synovial fluid from patients with rheumatoid arthritis (RASF) compared with peripheral blood. However, Treg cells in RASF have been shown to have a decreased capacity to suppress T cells. Here we phenotypically classified CD4+ T cells in RASF into six subsets based on the expression of CD45RA, CCR7, CD27 and CD28, and demonstrated that the CCR7-CD45RA-CD27+CD28+ TEM subset was significantly increased in synovial fluid compared with peripheral blood. In addition, the proportion of Foxp3+ Treg cells in the CCR7-CD45RA-CD27+CD28+ TEM subset was significantly increased in RASF. Furthermore, most of the Foxp3+ Treg cells in RASF were non-suppressive CD45RA-Foxp3(low) non-Treg cells, and the frequency of the non-Treg cells in the CCR7-CD45RA-CD27+CD28+ TEM subset was significantly increased in RASF. Our findings suggest that the pro-inflammatory environment in RA joints may induce the increase of CD45RA-Foxp3(low) non-Treg cells in synovial fluid.

Infectious versus non-infectious loosening of implants: activation of T lymphocytes differentiates between the two entities.

PURPOSE: Loosening of implants occurs mainly for two reasons: bacterial infection of the implant or "aseptic loosening" presumably due to wear particles derived from the implant. To gain further insight into the pathomechanism, we analysed activation of the T cell response in these patients. METHODS: Activation of peripheral T lymphocytes was determined by cytofluorometry as down-regulation of CD28 and up-regulation of CD11b. In addition, tissue samples obtained during surgery were analysed by quantitative RT-PCR for gene expression of CD3, CD14 and cathepsin K, as markers for T cells, monocytes/macrophages or osteoclasts, respectively. RESULTS: Activated T lymphocytes were detected in patients with infection but not in patients with aseptic loosening. Gene expression of CD3 was significantly enhanced in tissues of patients with infection compared to those with aseptic loosening. Expression of CD14 and of cathepsin K did not differ between the two groups. CONCLUSION: Implant-associated infection and aseptic loosening are associated with a local inflammatory response, which eventually results in osteoclastogenesis and bone resorption. Systemic T cell activation, in contrast, occurs only in patients with implant-associated infection, and hence analysis of T cell activation markers could serve as a diagnostic tool to differentiate between the two entities.

Anti-HIV designer T cells progressively eradicate a latently infected cell line by sequentially inducing HIV reactivation then killing the newly gp120-positive cells.

The current antiretroviral therapy (ART) can effectively reduce plasma HIV loads to undetectable levels, but cannot eliminate latently infected resting memory CD4 T cells that persist for the lifetime of infected patients. Therefore, designing new therapeutic approaches to eliminate these latently infected cells or the cells that produce HIV upon reactivation from latency is a priority in the ART era in order to progress to a cure of HIV. Here, we show that "designer" T cells expressing chimeric antigen receptor (CAR), CD4-CD28-CD3ζ, can target and kill HIV Env-expressing cells. Further, they secrete effector cytokines upon contact with HIV Env+ target cells that can reactivate latent HIV in a cell line model, thereby exposing those cells to recognition and killing by anti-HIV CAR+ T cells. Taken to the limit, this process could form the basis for an eventual functional or sterilizing cure for HIV in patients.

Gene therapy of malignant solid tumors by targeting erbB2 receptors and by activating T cells.

One of the strategies to improve the outcome of anti-erbB2-mediated immunotherapy is to combine anti-erbB2 antibodies with T-cell-based adoptive immunotherapy, which can be achieved by expressing anti-erbB2 mAb on the surface of T cells. A single-chain variable fragment (scFv) from an anti-erbB2 mAb has been expressed on T cell surface to bind to erbB2-positive cells, and CD3ζ has been expressed as a fusion partner at C terminus of this scFv to transduce signals. T cells grafted with this chimeric scFv/CD3ζ were able to specifically attack target tumor cells with no MHC/Ag restriction. To test the effects of CD28 signal on cellular activation and antitumor effectiveness of chimeric scFv/CD3ζ-modified T cells, we constructed a recombinant anti-erbB2 scFv/Fc/CD28/CD3ζ gene in a retroviral vector. T cells expressing anti-erbB2 scFv/Fc/CD28/CD3ζ specifically lyzed erbB2-positive target tumor cells and secreted not only interferon-γ (IFN-γ) but also IL-2 after binding to their target cells. Our data indicate that CD3 and CD28 signaling can be delivered in one molecule, which is sufficient for complete T cell activation without exogenous B7/CD28 co-stimulation.

CD28-B7 interaction modulates short- and long-lived plasma cell function.

The interaction of CD28, which is constitutively expressed on T cells, with B7.1/B7.2 expressed on APCs is critical for T cell activation. CD28 is also expressed on murine and human plasma cells but its function on these cells remains unclear. There are two types of plasma cells: short-lived ones that appear in the secondary lymphoid tissue shortly after Ag exposure, and long-lived plasma cells that mainly reside in the bone marrow. We demonstrate that CD28-deficient murine short- and long-lived plasma cells produce significantly higher levels of Abs than do their wild-type counterparts. This was owing to both increased frequencies of plasma cells as well as increased Ab production per plasma cell. Plasma cells also express the ligand for CD28, B7.1, and B7.2. Surprisingly, deficiency of B7.1 and B7.2 in B cells also led to higher Ab levels, analogous to Cd28(-/-) plasma cells. Collectively, our results suggest that the CD28-B7 interaction operates as a key modulator of plasma cell function.

Cytomegalovirus exposure, immune exhaustion and cancer occurrence in renal transplant recipients.

The role of Cytomegalovirus (CMV) in carcinogenesis is controversial. We studied whether CMV may contribute to cancer occurrence in renal transplant recipients. We studied a prospective cohort of 455 consecutive patients who received a kidney transplant between January 1995 and December 2006. All cancers and types of cancers were assessed. Lymphocyte phenotype and cytokines production were analysed according to CMV status in a subset population of this cohort. Mean follow-up was 84 ± 29 months. One hundred and nineteen cancers (26.2%) occurred during the study follow-up. There was a higher cumulated incidence of cancers in CMV-exposed patients (30.4% vs. 20%; P=0.018). Mean time to cancer occurrence was shorter in CMV-exposed patients than in CMV-naïve patients (4.7 ± 2.6 vs. 6.7 ± 2.8; P = 0.001). Cox regression analysis revealed that both pretransplant CMV exposure (HR, 1.83; 95% CI, 1.17-2.88; P = 0.009) and post-transplant CMV replication (HR, 2.17; 95% CI, 1.02-4.59; P = 0.044) were risk factors for cancer. Among CD8+ T cells, exhausted T cells assessed as CD57+CD28- were expanded in CMV-exposed patients (26 ± 20 vs. 9 ± 8%; P < 0.0001), whereas CD8+CD57+IL2- cells were more frequent in CMV-exposed patients. Our results highly suggest that CMV increases the risk of cancer after transplantation.

Regulation of CD28 expression on umbilical cord blood and adult peripheral blood CD8+ T cells by interleukin(IL)-15/IL-21.

Interleukin (IL)-15 and IL-21, both belonging to common γ-chain-signaling cytokine family, have an important role to maintain homeostatic proliferation of CD8(+) T cells. CD28, an essential co-stimulatory molecule on T cells, may be a marker of replicative senescence. We investigated the effect of IL-15 and IL-21, alone or in combination, on activation, apoptosis, cytokine production and cytotoxic function of magnetic bead purified umbilical cord blood (UCB) and adult peripheral blood (APB) CD8(+) T cells with regards to their CD28 expression. We established that (1) IL-15-induced CD8(+) T cell proliferation was associated with a preferential expansion of CD28(-) population in UCB, which could be partially counteracted by IL-21; (2) UCB CD8(+) T cells were more readily responsive to IL-15 compared to their adult counterparts in terms of CD69 expression, with the majority of CD69-bearing CD8(+) T cells were CD28(-); (3) IL-21 further promoted interferon-gamma, but not tumor necrosis factor-alpha production from IL-15 treated CD8(+) T cells; (4) IL-21 also synergized with IL-15 to enhance perforin and granzyme B expression of CD8(+) T cells, especially in APB CD8(+)CD28(-) subsets; (5) IL-21 resulted in CD8(+) T cells apoptosis both in APB and UCB cells, mainly in CD8(+)CD28(-) subsets. Taken together, we demonstrate differential IL-15/IL-21 response in UCB CD8(+) T cells with regards to CD28 expression. Our results suggest that combining IL-21 and IL-15 immunotherapy may be better than IL-15 alone to ameliorate graft-versus-host disease while preserving antitumor effect in the post-UCB transplantation period.

Characterization of a new mouse model for peripheral T cell lymphoma in humans.

Peripheral T cell lymphomas (PTCLs) are associated with a poor prognosis due to often advanced disease at the time of diagnosis and due to a lack of efficient therapeutic options. Therefore, appropriate animal models of PTCL are vital to improve clinical management of this disease. Here, we describe a monoclonal CD8(+) CD4(-) αß T cell receptor Vß2(+) CD28(+) T cell lymphoma line, termed T8-28. T8-28 cells were isolated from an un-manipulated adult BALB/c mouse housed under standard pathogen-free conditions. T8-28 cells induced terminal malignancy upon adoptive transfer into syngeneic BALB/c mice. Despite intracellular expression of the cytotoxic T cell differentiation marker granzyme B, T8-28 cells appeared to be defective with respect to cytotoxic activity as read-out in vitro. Among the protocols tested, only addition of interleukin 2 in vitro could partially compensate for the in vivo micro-milieu in promoting growth of the T8-28 lymphoma cells.

Characterization of T-cell memory phenotype after in vitro expansion of tumor-infiltrating lymphocytes from melanoma patients.

Memory T-cell populations in human antitumor tumor-infiltrating lymphocytes (TILs) for adoptive cell transfer have not been fully characterized. Our studies demonstrated that CD62L, CD27 and CD28 positive effector memory T-cells were present in the TIL samples from the tumor tissues of melanoma patients and T-cell expansion led to the significant loss of memory T-cells. CD27- and CD28-positive T-cells had high levels of CD44 expression. T-Cell expansion resulted in significant down-regulation of CD44 expression. Interleukin-2 (IL-2) and anti-CD3 antibody stimulation may be responsible for CD44 down-regulation on CD8(+) T-cells during expansion. Furthermore, CD44 down-regulation using small interfering RNA (siRNA) on TILs dramatically reduced interferon-gamma and IL-2 release upon tumor stimulation. These results suggest that the regulation of CD44 expression in TILs may play an important role in memory T-cell maintenance and antitumor immune response.

Gene expression profiling-based identification of CD28 and PI3K as new biomarkers for chronic graft-versus-host disease.

Chronic graft-versus-host disease (cGVHD) is a major cause of morbidity and mortality after allogeneic hematopoietic stem cell transplantation. Currently, no reliable biomarkers are available to predict the onset or progression of cGVHD. Therefore, in this study, we collected peripheral blood mononuclear cells from four patients with cGVHD and four ones with non-GVHD after hematopoietic stem cell transplantation and employed Affymetrix GeneChip Human U133 Plus 2.0 microarrays to screen the genes differentially expressed in cGVHD versus non-GVHD groups, with the aim to identify potential clinical biomarkers to predict cGVHD risk or progression. Microarray analysis demonstrated that the expression of 3180 genes changed significantly in cGVHD versus non-GVHD, with 879 genes upregulated and 2301 genes downregulated. Among them we chose CD28 and PI3K as candidates for further verification. Flow cytometry and quantitative real-time polymerase chain reaction analysis confirmed the significant upregulation of CD28 and PI3K in samples from patients with cGVHD compared with patients with non-GVHD, respectively. In conclusion, our study suggested that the upregulation of CD28 and PI3K contributed to the onset and progression of cGVHD and provided evidence that CD28 and PI3K may serve as promising biomarkers for cGVHD.

CD4(+) CD28(+) lymphocytes on day 5 after high-dose melphalan for multiple myeloma predict a low risk of infections during severe neutropenia and are associated with the number of reinfused T lymphocytes of the autologous stem cell graft.

BACKGROUND AIMS: Neutropenia following high-dose chemotherapy is associated with a substantial risk of infectious complications. The aim of this study was to identify variables in residual leukocyte subsets during neutropenia that are predictive for neutropenic fever. METHODS: Residual leukocytes in the peripheral blood on day 5 after autologous blood stem cell transplantation were analyzed by three-color flow cytometry in 55 consecutive patients with multiple myeloma. Furthermore, the number of T cells transfused with the autografts was determined. RESULTS: Neutrophil counts at day 5 and neutrophil engraftment were similar in patients with and without neutropenic fever. Low absolute lymphocyte, CD4(+) CD28(+) and CD45RO(+) CD28(+) counts at day 5 were associated with neutropenic fever. T-cell counts at day 5 correlated with the CD3(+) cell number in the graft. CONCLUSIONS: Our data show that the absolute lymphocyte, CD4(+) CD28(+) and CD45RO(+) CD28(+) counts play a role in host defense during severe neutropenia. The T-cell number in the graft may help to identify patients at high risk of neutropenic infections.

The type III histone deacetylase Sirt1 protein suppresses p300-mediated histone H3 lysine 56 acetylation at Bclaf1 promoter to inhibit T cell activation.

The NAD-dependent histone deacetylase Sirt1 is a negative regulator of T cell activation. Here we report that Sirt1 inhibits T cell activation by suppressing the transcription of Bcl2-associated factor 1 (Bclaf1), a protein required for T cell activation. Sirt1-null T cells have increased acetylation of the histone 3 lysine 56 residue (H3K56) at the bclaf1 promoter, as well as increasing Bclaf1 transcription. Sirt1 binds to bclaf1 promoter upon T cell receptor (TCR)/CD28 stimulation by forming a complex with histone acetyltransferase p300 and NF-κB transcription factor Rel-A. The recruitment of Sirt1, but not p300, requires Rel-A because blocking Rel-A nuclear translocation in T cells and siRNA-mediated knockdown of Rel-A can inhibit Sirt1 binding to bclaf1 promoter. Although knockdown of either p300 or GCN5 partially suppressed global H3K56 acetylation, only p300 knockdown specifically attenuated H3K56 acetylation at the bclaf1 promoter. Lastly, knockdown of Bclaf1 suppresses the hyperactivation observed in Sirt1(-/-) T cells, indicated by less IL-2 production in CD4(+) T cells and reduced proliferation. Therefore, Sirt1 negatively regulates T cell activation via H3K56 deacetylation at the promoter region to inhibit transcription of Bclaf1.