CTLA4Ig Research Articles

Selective CD28 blockade attenuates CTLA-4-dependent CD8+ memory T cell effector function and prolongs graft survival.

Memory T cells pose a significant problem to successful therapeutic control of unwanted immune responses during autoimmunity and transplantation, as they are differentially controlled by cosignaling receptors such as CD28 and CTLA-4. Treatment with abatacept and belatacept impede CD28 signaling by binding to CD80 and CD86, but they also have the unintended consequence of blocking the ligands for CTLA-4, a process that may inadvertently boost effector responses. Here, we show that a potentially novel anti-CD28 domain antibody (dAb) that selectively blocks CD28 but preserves CTLA-4 coinhibition confers improved allograft survival in sensitized recipients as compared with CTLA-4 Ig. However, both CTLA-4 Ig and anti-CD28 dAb similarly and significantly reduced the accumulation of donor-reactive CD8+ memory T cells, demonstrating that regulation of the expansion of CD8+ memory T cell populations is controlled in part by CD28 signals and is not significantly impacted by CTLA-4. In contrast, selective CD28 blockade was superior to CTLA-4 Ig in inhibiting IFN-γ, TNF, and IL-2 production by CD8+ memory T cells, which in turn resulted in reduced recruitment of innate CD11b+ monocytes into allografts. Importantly, this superiority was CTLA-4 dependent, demonstrating that effector function of CD8+ memory T cells is regulated by the balance of CD28 and CTLA-4 signaling.

Low energy X-ray (grenz ray) treatment of purified islets prior to allotransplant markedly decreases passenger leukocyte populations

ABSTRACTGrenz rays, or minimally penetrating X-rays, are known to be an effective treatment of certain recalcitrant immune-mediated skin diseases, but their use in modulating allograft rejection has not been tested. We examined the capacity of grenz ray treatment to minimize islet immunogenicity and extend allograft survival in a mouse model. In a preliminary experiment, 1 of 3 immunologically intact animals demonstrated long-term acceptance of their grenz ray treated islet allograft. Further experiments revealed that 28.6% (2 of 7) grenz ray treated islet allografts survived >60 d. A low dose of 20Gy, was important; a 4-fold increase in radiation resulted in rapid graft failure, and transplanting a higher islet mass did not alter this outcome. To determine whether increased islet allograft survival after grenz treatment would be masked by immunosuppression, we treated the recipients with CTLA-4 Ig, and found an additive effect, whereby 17.5% more animals accepted the graft long-term versus those with CTLA-4 Ig alone. Cell viability assays verified that islet integrity was maintained after treatment with 20Gy. As well, through splenocyte infiltration analysis, donor CD4+ T cell populations 24-hours after transplant were decreased by more than16-fold in recipients receiving irradiated islets compared with control. Donor CD8+ T cell populations, although less prevalent, decreased in all treatment groups compared with control. Our results suggest that brief treatment of isolated islets with low energy grenz rays before allotransplantation can significantly reduce passenger leukocytes and promote graft survival, possibly by inducing donor dendritic cells to differentiate toward a tolerogenic phenotype.

IL-2-Mediated In Vivo Expansion of Regulatory T Cells Combined with CD154-CD40 Co-Stimulation Blockade but Not CTLA-4 Ig Prolongs Allograft Survival in Naive and Sensitized Mice.

In recent years, regulatory T cells (Treg)-based immunotherapy has emerged as a promising strategy to promote operational tolerance after solid organ transplantation (SOT). However, a main hurdle for the therapeutic use of Treg in transplantation is their low frequency, particularly in non-lymphopenic hosts. We aimed to expand Treg directly in vivo and determine their efficacy in promoting donor-specific tolerance, using a stringent experimental model. Administration of the IL-2/JES6-1 immune complex at the time of transplantation resulted in significant expansion of donor-specific Treg, which suppressed alloreactive T cells. IL-2-mediated Treg expansion in combination with short-term CD154–CD40 co-stimulation blockade, but not CTLA-4 Ig or rapamycin, led to tolerance to MHC-mismatched skin grafts in non-lymphopenic mice, mainly by hindering alloreactive CD8+ effector T cells and the production of alloantibodies. Importantly, this treatment also allowed prolonged survival of allografts in the presence of either donor-specific or cross-reactive memory cells. However, late rejection occurred in sensitized hosts, partly mediated by activated B cells. Overall, these data illustrate the potential but also some important limitations of Treg-based therapy in clinical SOT as well as the importance of concomitant immunomodulatory strategies in particular in sensitized hosts.

Both anti-TNF and CTLA4 Ig treatments attenuate the disease severity of staphylococcal dermatitis in mice.

BackgroundRA patients being treated with biologics are known to have an increased risk of infections. We recently demonstrated that both CTLA4 Ig and anti-TNF treatment aggravate systemic Staphylococcus aureus (S. aureus) infection in mice, but with distinct clinical manifestations. However, the effects of CTLA4 Ig and anti-TNF treatments on a local S. aureus infection (e.g., skin infection) might differ from their effects on a systemic infection.AimsThe aim of this study was to examine the differential effects of anti-TNF versus CTLA4 Ig treatment on S. aureus skin infections in mice.MethodAbatacept (CTLA4 Ig), etanercept (anti-TNF treatment) or PBS was given to NMRI mice subcutaneously inoculated with S. aureus strain SH1000. The clinical signs of dermatitis, along with histopathological changes due to skin infection, were compared between the groups.ResultsBoth CTLA4 Ig and anti-TNF treatment resulted in less severe skin infections and smaller post-infectious hyperpigmentation compared with controls. Consistent with the clinical signs of dermatitis, smaller lesion size, more epithelial hyperplasia and more granulation were found in skin biopsies from mice receiving anti-TNF compared with PBS controls. However, both CTLA4 Ig and anti-TNF therapy tended to prolong the healing time, although this finding was not statistically significant. Serum MCP-1 levels were elevated in the anti-TNF group relative to the CTLA4 Ig and PBS groups, whereas IL-6 levels were higher in PBS controls than in the other two groups. Both anti-TNF and CTLA4 Ig treatments tended to down-regulate the necrosis/apoptosis ratio in the locally infected skin tissue. Importantly, no tangible difference was found in the bacterial burden among groups.ConclusionBoth CTLA4 Ig and anti-TNF therapies attenuate disease severity but may prolong the healing time required for S. aureus skin infections. Neither treatment has an impact on bacterial clearance in skin tissues.

Long term treatment with abatacept or tocilizumab does not increase Epstein-Barr virus load in patients with rheumatoid arthritis - A three years retrospective study.

BackgroundEpstein-Barr Virus (EBV) is a widely disseminated lymphotropic herpes virus implicated in benign and malignant disorders. In transplant patients, immunosuppressive drugs (cyclosporine) diminish control of EBV replication, potentially leading to lymphoproliferative disorders (LPD). Rheumatoid arthritis (RA) patients have impaired control of EBV infection and have EBV load ten times higher than controls. As post transplant patients, patients with RA have increased risk of developing lymphomas. Immunosuppressive drugs used to treat RA (conventional disease modifying drugs cDMARDs or biologics bDMARDs) could enhance the risk of developing LPD in RA patients. We have previously shown that long term treatment with Methotrexate and/or TNF alpha antagonists does not increase EBV load in RA. Our objective was to monitor the Epstein-Barr Virus load in RA patients treated with Abatacept (CTLA4 Ig), a T cell coactivation inhibitor, and Tocilizumab, an anti IL6 receptor antibody.MethodsEBV load in the peripheral blood mononuclear cells (PBMCs) of 55 patients under Abatacept (in 34% associated with Methotrexate) and 35 patients under Tocilizumab (in 37% associated with Methotrexate) was monitored for durations ranging from 6 months to 3 years by real time PCR. The influences of treatment duration and disease activity score 28 (DAS28) index on EBV load were analyzed.ResultsAbatacept did not significantly modify EBV load over time. Tocilizumab significantly diminished EBV load over time. No patient (of 90) developed EBV associated lymphoma.ConclusionLong term treatment with Abatacept or Tocilizumab does not increase EBV load in the PBMNCs of patients with RA.

Renal Allograft Survival in Nonhuman Primates Infused With Donor Antigen-Pulsed Autologous Regulatory Dendritic Cells.

Systemic administration of autologous regulatory dendritic cells (DCreg; unpulsed or pulsed with donor antigen [Ag]), prolongs allograft survival and promotes transplant tolerance in rodents. Here, we demonstrate that nonhuman primate (NHP) monocyte-derived DCreg preloaded with cell membrane vesicles from allogeneic peripheral blood mononuclear cells induce T cell hyporesponsiveness to donor alloantigen (alloAg) in vitro. These donor alloAg-pulsed autologous DCreg (1.4-3.6 × 106 /kg) were administered intravenously, 1 day before MHC-mismatched renal transplantation to rhesus monkeys treated with costimulation blockade (cytotoxic T lymphocyte Ag 4 immunoglobulin [CTLA4] Ig) and tapered rapamycin. Prolongation of graft median survival time from 39.5 days (no DCreg infusion; n = 6 historical controls) and 29 days with control unpulsed DCreg (n = 2), to 56 days with donor Ag-pulsed DCreg (n = 5) was associated with evidence of modulated host CD4+ and CD8+ T cell responses to donor Ag and attenuation of systemic IL-17 production. Circulating anti-donor antibody (Ab) was not detected until CTLA4 Ig withdrawal. One monkey treated with donor Ag-pulsed DCreg rejected its graft in association with progressively elevated anti-donor Ab, 525 days posttransplant (160 days after withdrawal of immunosuppression). These findings indicate a modest but not statistically significant beneficial effect of donor Ag-pulsed autologous DCreg infusion on NHP graft survival when administered with a minimal immunosuppressive drug regimen.

Costimulation Blockade in Autoimmunity and Transplantation: The CD28 Pathway.

T cell activation is a complex process that requires multiple cell signaling pathways, including a primary recognition signal and additional costimulatory signals. TCR signaling in the absence of costimulatory signals can lead to an abortive attempt at activation and subsequent anergy. One of the best-characterized costimulatory pathways includes the Ig superfamily members CD28 and CTLA-4 and their ligands CD80 and CD86. The development of the fusion protein CTLA-4-Ig as an experimental and subsequent therapeutic tool is one of the major success stories in modern immunology. Abatacept and belatacept are clinically approved agents for the treatment of rheumatoid arthritis and renal transplantation, respectively. Future interventions may include selective CD28 blockade to block the costimulatory potential of CD28 while exploiting the coinhibitory effects of CTLA-4.

Reparixin, a CXCR1/2 inhibitor in islet allotransplantation

ABSTRACTQuality of life in Type 1 diabetic patients may be improved with islet transplantation, but lifelong immunosuppression is required to prevent rejection. Allo-immune response is a key player in graft dysfunction and although the adaptive immune response is well characterized, the effect of the innate immune reaction after transplantation is only recently becoming appreciated. In this study, we address how the innate response affects long-term outcomes in a murine islet allotransplant model. CTLA-4 Ig treatment is known to significantly prolong kidney subcapsular islet allograft survival and enhance glucose tolerance. The combination of CTLA-4 Ig with reparixin, which blocks against inflammatory neutrophil infiltration, yielded no long-term graft survival in an intrahepatic allotransplant model but had similar long-term graft survival in the kidney subcapsular model. Seven days after transplant, serum blood IFN-γ levels were significantly lower in the CTLA-4 Ig with reparixin treatment group compared to controls. IL-12p70 cytokine levels were increased with combination treatment, a positive modulation of the inflammatory response to the allograft. Furthermore, KC GRO, also known as CXCL1, was decreased in serum 7 d after transplant. Histologically, we found that immune cell infiltrate, CD4+ and CD8+ T cell populations along with both CXCR1+ and CXCR2+ cell populations were decreased within the CTLA-4 Ig and reparixin islet transplant graft. Overall these data provide insight into the down regulation of T-cell recruitment by CTLA-4 Ig and decreased neutrophil activation and recruitment with reparixin after long-term islet graft survival.

The Limits of Linked Suppression for Regulatory T Cells.

We have previously found that CD4(+)CD25(+) regulatory T cells (Tregs) can adoptively transfer tolerance after its induction with costimulatory blockade in a mouse model of murine cardiac allograft transplantation. In these experiments, we tested an hypothesis with three components: (1) the Tregs that transfer tolerance have the capacity for linked suppression, (2) the determinants that stimulate the Tregs are expressed by the indirect pathway, and (3) the donor peptides contributing to these indirect determinants are derived from donor major histocompatibility complex (MHC) antigens (Ags). First heart transplants were performed from the indicated donor strain to B10.D2 recipients along with costimulatory blockade treatment (250 μg i.p. injection of MR1 on day 0 and 250 μg i.p. injection of CTLA-4 Ig on day 2). At least 8 weeks later, a second heart transplant was performed to a new B10.D2 recipient who had been irradiated with 450 cGy. This recipient was given 40 × 106 naive B10.D2 spleen cells + 40 × 106 B10.D2 spleen cells from the first (tolerant) recipient. We performed three different types of heart transplants using various donors. (1) Tregs suppress the graft rejection in an Ag-specific manner. (2) Tregs generated in the face of MHC disparities suppress the rejection of grafts expressing third party MHC along with tolerant MHC. The limits of linkage appear to be quantitative and not universally determined by either the indirect pathway or by peptides of donor MHC Ags.

Inhibition of Donor-Reactive CD8+ T Cell Responses by Selective CD28 Blockade Is Independent of Reduced ICOS Expression.

Programmed T cell differentiation is critically influenced by the complement of costimulatory and coinhibitory signals transmitted during initial antigen encounter. We previously showed that selective CD28 blockade with novel domain antibodies that leave CTLA-4-mediated coinhibitory signaling intact resulted in more profound attenuation of donor-reactive T cell responses and improved graft survival in a murine transplant model. Selective CD28 blockade was also associated with decreased ICOS expression on donor-reactive CD8+ T cell responses as compared to CTLA-4 Ig, but the functional importance of this reduced ICOS expression was not known. In this study, we created retrogenic donor-reactive CD8+ T cells that overexpress ICOS in order to determine whether reduced ICOS expression mechanistically underlies the increased efficacy of selective CD28 blockade in controlling graft-specific T cell responses as compared to conventional costimulation blockade with CTLA-4 Ig. Results indicated that the ability of selective CD28 blockade to blunt donor-reactive CD8+ T cell expansion following transplantation was independent of its ability to inhibit ICOS expression. Furthermore, we have previously published that 2B4 coinhibitory signals are functionally important for controlling graft-specific CD8+ T cell responses in mice treated with CD28 blockade. Here we used a co-adoptive transfer approach to determine that 2B4 coinhibitory signals on antigen-specific CD8+ T cells function in a cell-intrinsic manner to limit ICOS expression in the setting of selective CD28 blockade.

Immunological potential of cytotoxic T lymphocyte antigen 4 immunoglobulin in murine autoimmune cholangitis.

Cytotoxic T lymphocyte antigen 4 (CTLA-4) immunoglobulin (Ig) is an important regulator of T cell activation and a fusion protein directed at CD80 and CD86; it blocks co-stimulatory signalling and T cell activation. We have taken advantage of a murine model of human primary biliary cirrhosis (PBC), mice expressing a transforming growth factor (TGF)-β receptor II dominant negative (dnTGF-βRII) transgene to address the potential therapeutic efficacy of CTLA-4 Ig. To mimic patients with PBC at different stages or duration of disease, we treated mice with either CTLA-4 Ig or control IgG three times weekly from 3 to 12 or 24 weeks of age, or from 12 to 24 weeks of age. CTLA-4 Ig treatment from 3 weeks of age significantly reduced liver inflammation to 12 weeks of age. Treatment initiated at 12 weeks of age also ameliorated the autoimmune cholangitis at 24 weeks of age. However, in mice treated at 3 weeks of age, suppression of liver inflammation was not sustained and colitis was aggravated when treatment was extended to 24 weeks of age. Our data indicate that, in dnTGF-βRII mice, CTLA-4 Ig treatment has short-term beneficial effects on autoimmune cholangitis, but the effect varies according to duration of treatment and the time in which therapy was initiated. Further dissection of the events that lead to the reduction in therapeutic effectiveness of CTLA-4 Ig will be critical to determining whether such efforts can be applied to human PBC.

Blockade of the activation of T cells around β-cell by the targeted CTLA-4 Ig at the surface of β-cell.

Diabetes mellitus affects 347 million people worldwide, and over 80 % of diabetes deaths occur in low- and middle-income countries. Type 1 diabetes (T1D) is characterized by the attacks of the body's own immune system on the pancreatic β-cells. In this work, we present a new CTLA-4 Ig targeting at the surface of β-cell and prepare it from Escherichia coli aiming at clearing activated T cells around β-cells and avoiding all-round decline in systematic immunity. This fusion protein is composed of CTLA-4-Ig part and β-cell-targeting part, with properties of the therapeutic effect of CTLA-4-Ig and selective binding to β-cells. In preliminary biological activity assay, our results verified the feasibility of β-cell-targeting strategy and its activity of CTLA-4-Ig part. The fusion protein recognizes and binds specifically to CD80(+) and CD86(+) cells as well as β-cell, but not to control cells, displaying the potential to be used as a feasible and effective treatment of T1D with lessened side effect.

The Combination of Anti-NKG2D and CTLA-4 Ig Therapy Prolongs Islet Allograft Survival in a Murine Model

Islet transplantation is an effective means of treating severe type 1 diabetes in patients with life-threatening hypoglycemia. Improvements in glycemic control with correction of HbA1C enhance quality of life irrespective of insulin independence. By antagonizing the Natural Killer Group 2, member D (NKG2D) receptor expression on NK and CD8+ T cells, in combination with blocking CTLA-4 binding sites, we demonstrate a significant delay of graft rejection in islet allotransplant. Anti-NKG2D combined with CTLA-4 Ig (n = 15) results in prolonged allograft survival, with 84.6 ± 10% of the recipients displaying insulin independence compared to controls (n = 10, p < 0.001). The effect of combination therapy on graft survival is superior to treatments alone (CTLA-4 Ig vs. combination p = 0.024, anti-NKG2D vs. combination p < 0.001) indicating an interaction between these pathways. In addition, combination treatment also improves glucose tolerance when compared to controls (n = 10, p = 0.018). Histologically, NKG2D+ cells were significantly decreased within the allograft after 7 days of combination treatment (n = 6, p = 0.029). T cell proliferation was significantly reduced with anti-NKG2D therapy and CD8+ T cell daughter fractions were also significantly decreased with mAb and combination treatment when measured by in vitro mixed lymphocyte reaction (n = 5, p = 0.015, p = 0.005 and p = 0.048). These results demonstrate that inhibition of NKG2D receptors and costimulatory pathways enhance islet allograft survival.

Anti-CD28 Antagonism Using a Monovalent Fab Antibody for the Prolongation of Human Skin Allograft Survival.

Background. T cells play a principal detrimental role in alloresponses after transplantation. Costimulation through CD28 induces T cells activation, cytokine production, proliferation, and differentiation, whereas the absence of CD28 signalling leads to T cell apoptosis or anergy. Importantly, the development of effector or regulatory responses after initial antigen exposure may be influenced by the balance between CD28 and cytotoxic T lymphocyte antigen 4 (CTLA-4) costimulatory signalling. Influencing this balance by blocking costimulation through CD28 is theoretically advantageous to agonistic signaling through CTLA4 (for example using CTLA4-Ig) as this would not interfere with CTLA4 and PDL-1 co-inhibitory signaling. In the current study we have investigated the hypothesis that a non-activating monovalent anti-CD28 antibody would prevent rejection of human skin allografts in vivo. Methods. Using a humanised mouse system, we treated mice that had received human skin transplants with FR104 (5 mg/kg), CTLA4-Ig (10mg/kg) or vehicle control intravenously twice a week for three weeks. All mice were started on the treatment regimen three weeks post-adoptive transfer of allogeneic human peripheral blood mononuclear cells (PBMCs) to ensure adequate levels of human leukocyte chimerism. Results. FR104 significantly prolonged skin allograft survival in humanised mice compared with CTLA4-Ig (median survival time, MST=63 vs. 31 (p=0.002)) or Saline (MST=31). While FR104 treatment significantly impacted the level of human leukocyte chimerism in the peripheral blood, it remained above the required reconstitution level known to induce skin rejection. The number of graft infiltrating CD4+ (47.8±24.8 vs 83.3±5.1 cells/HPF, P<0.02) and CD8+ (50.0±11.9 vs 111±34.0 cells/HPF, P<0.04) cells was significantly reduced by FR104 treatment as compared to CTLA-4 Ig treatment. No differences were noted in the number of graft infiltrating Foxp3+ cells between FR104 and CTLA4-Ig groups. FR104 significantly suppressed the serum cytokine production of IL-2, IFNγ, TNFα and IL-10. Conclusion. FR104 is an effective immunosuppressant in vivo. By sparing CTLA-4 and PDL-1 coinhibitory signals, FR104 may theoretically lead to improved therapeutic responses compared with CTLA-4-Ig.

2B4 (CD244) Induced By Selective CD28 Blockade Functionally Regulates Allograft-Specific CD8+ T Cell Responses.

Mounting evidence in models of both autoimmunity and chronic viral infection suggests that the outcome of T cell activation is critically impacted by the constellation of costimulatory and coinhibitory receptors expressed on the cells' surface. Here, we identified a critical role for the coinhibitory SLAM family member 2B4 (CD244) in attenuating primary donor-reactive CD8+ T cell responses in the presence of immune modulation with selective CD28 blockade. Our results reveal a specific upregulation of 2B4 on donor-reactive CD8+ T cells in animals in which CD28 signaling was blocked. However, 2B4 upregulation was not observed in animals treated with CTLA-4 Ig (abatacept) or CD28 blockade in the presence of anti-CTLA-4 mAb, indicating that CTLA-4 coinhibitory signals are required for 2B4 upregulation. Skin graft experiments revealed a dramatic prolongation in survival in animals treated with CD28 dAbs, in which CTLA-4 coinhibitory signaling is maintained and 2B4 coinhibitory signaling is induced, as compared to CTLA-4 Ig in both major and minor histocompatibility models. Interestingly, the increased efficacy of CD28 dAbs in attenuating donor-reactive CD8+ T cell responses as compared to CTLA-4 Ig was not an effect of preserved PD-L1/CD80 coinhibitory signals, as blockade of PD-L1 did not abrogate the ability of CD28 dAb to inhibit donor-reactive CD8+ T cell responses or induce 2B4 upregulation. In order to directly assess the functional role of the 2B4 coinhibitory pathway in prolonging allograft survival, we assessed donor-reactive CD8+ T cell responses in 2B4-/- mice. 2B4 upregulation following CD28 blockade was functionally significant, as the inhibitory impact of CD28 blockade was diminished when donor-reactive CD8+ T cells were deficient in 2B4. In contrast, 2B4 deficiency had no effect on CD8+ T cell responses during unmodified rejection or in the presence of CTLA-4 Ig. We conclude that blockade of CD28 signals in the presence of preserved CTLA-4 signals results in the unique upregulation of 2B4 on primary CD8+ effectors, and that this 2B4 expression plays a critical functional role in controlling donor-reactive CD8+ T cell responses during transplantation. DISCLOSURES:Schneeweis, L.: Employee, Bristol Myers-Squibb. Stetsko, D.: Employee, Bristol Myers-Squibb. Suchard, S.: Employee, Bristol Myers-Squibb. Nadler, S.: Employee, Bristol Myers-Squibb.

Costimulatory Blockade With CTLA4 Ig Prevents Rejection of Vascularized Composite Allografts.

Costimulatory Blockade With CTLA4 Ig Prevents Rejection of Vascularized Composite Allografts.

Effect of cytotoxic T lymphocytic associated antigen 4 on acute rejection and CD4 + , CD8 + T cells after liver allotransplantation in rats

Objective To observe the effects of cytotoxic T lymphocytic associated antigen 4 (CTLA4Ig) on CD4 + and CD8 + T cells after orthotopic liver transplantation in rats (ROLT).Methods The ROLT was established.All rats were divided into 2 groups randomly (group A:control group,and group B:study group).CTLA41g was administrated by intraperitoneal injection at a dose of 80 μg.B7 expression was detected.CD4 +/CD8 + T cells were measured.RAI was identified.Results The expression of B7-1 and B7-2 mRNA was decreased significantly on the 2nd,3rd,and 7th day in group B as compared with group A (B7-1:0.166 ± 0.012 vs.0.353 ± 0.043 ; 0.375 ± 0.022 vs.0.503 ± 0.058 ; 0.475 ± 0.023 vs.0.799±0.135;P＜0.01; B7-2:0.170±0.022 vs.0.341 ±0.040; 0.357 ±0.031 vs.0.475±0.041 ; 0.512 ± 0.103 vs.0.829 ± 0.124 ; P ＜ 0.01).The infiltration of CD4 +/CD8 + T cells was decreased significantly on the 2nd,3rd,and 7th day in group B as compared with group A (CD4 +:12.7 ±3.7 vs.21.0±4.4; 15.5 ±3.8 vs.28.2 ±5.2; 18.6 ±4.0 vs.35.0±7.0;P＜0.01; CD8+:9.3±1.5 vs.16.9±2.9; 12.1±2.2 vs.19.9 ±5.3; 17.1±3.7 vs.29.0±5.4;P＜0.01).The RAI was decreased significantly on the 2nd,3rd,and 7th day in group B as compared with group A (1.3 ±0.2 vs.1.9±0.3,P＜0.05; 2.0±0.4 vs.2.6±0.5,P＜0.05; 2.5 ±0.7 vs.4.6±1.1,P＜0.01).Survival period was significantly longer in group B than in group A [(40.9 ± 9.3) d vs.(9.2 ± 2.1) d,P ＜0.01].Conclusion Rat liver allograft immune tolerance can be induced by CTLA4Ig. Key words: Liver transplantation; Cytotoxic T lymphocytic associated antigen 4 ; CD4 + /CD8+ T cells; Acute rejection

Candida-Elicited Murine Th17 Cells Express High CTLA-4 Compared with Th1 Cells and Are Resistant to Costimulation Blockade

Effector and memory T cells may cross-react with allogeneic Ags to mediate graft rejection. Whereas the costimulation properties of Th1 cells are well studied, relatively little is known about the costimulation requirements of microbe-elicited Th17 cells. The costimulation blocker CTLA-4 Ig has been ineffective in the treatment of several Th17-driven autoimmune diseases and is associated with severe acute rejection following renal transplantation, leading us to investigate whether Th17 cells play a role in CD28/CTLA-4 blockade-resistant alloreactivity. We established an Ag-specific model in which Th1 and Th17 cells were elicited via Mycobacterium tuberculosis and Candida albicans immunization, respectively. C. albicans immunization elicited a higher frequency of Th17 cells and conferred resistance to costimulation blockade following transplantation. Compared with the M. tuberculosis group, C. albicans-elicited Th17 cells contained a higher frequency of IL-17(+)IFN-γ(+) producers and a lower frequency of IL-10(+) and IL-10(+)IL-17(+) cells. Importantly, Th17 cells differentially regulated the CD28/CTLA-4 pathway, expressing similarly high CD28 but significantly greater amounts of CTLA-4 compared with Th1 cells. Ex vivo blockade experiments demonstrated that Th17 cells are more sensitive to CTLA-4 coinhibition and therefore less susceptible to CTLA-4 Ig. These novel insights into the differential regulation of CTLA-4 coinhibition on CD4(+) T cells have implications for the immunomodulation of pathologic T cell responses during transplantation and autoimmunity.

2B4 (CD244) induced by selective CD28 blockade functionally regulates allograft-specific CD8+ T cell responses

Mounting evidence in models of both autoimmunity and chronic viral infection suggests that the outcome of T cell activation is critically impacted by the constellation of co-stimulatory and co-inhibitory receptors expressed on the cell surface. Here, we identified a critical role for the co-inhibitory SLAM family member 2B4 (CD244) in attenuating primary antigen-specific CD8(+) T cell responses in the presence of immune modulation with selective CD28 blockade. Our results reveal a specific up-regulation of 2B4 on antigen-specific CD8(+) T cells in animals in which CD28 signaling was blocked. However, 2B4 up-regulation was not observed in animals treated with CTLA-4 Ig (abatacept) or CD28 blockade in the presence of anti-CTLA-4 mAb. 2B4 up-regulation after CD28 blockade was functionally significant, as the inhibitory impact of CD28 blockade was diminished when antigen-specific CD8(+) T cells were deficient in 2B4. In contrast, 2B4 deficiency had no effect on CD8(+) T cell responses during unmodified rejection or in the presence of CTLA-4 Ig. We conclude that blockade of CD28 signals in the presence of preserved CTLA-4 signals results in the unique up-regulation of 2B4 on primary CD8(+) effectors, and that this 2B4 expression plays a critical functional role in controlling antigen-specific CD8(+) T cell responses.

New therapeutics in primary biliary cirrhosis: will there ever be light?

New therapeutics in primary biliary cirrhosis: will there ever be light?