Targeted CTLA-4 engagement induces CD4+CD25+CTLA-4high T regulatory cells with target (allo)antigen specificity

Activation of T cell checkpoint pathways during β-cell antigen presentation by engineered dendritic cells promotes protection from type 1 diabetes

Defective immune regulation has been recognized in type 1 diabetes (T1D). Immune regulatory T cell check-point receptors, which are generally upregulated on activated T cells, have been the molecules of attention as therapeutic targets for enhancing immune response in tumor therapy. Here, we show that pancreatic β-cell antigen (BcAg) presentation by engineered tolerogenic dendritic cells (tDCs) that express CTLA4 selective ligand (B7.1wa) or a combination of CTLA4, PD1 and BTLA selective ligands (B7.1wa, PD-L1, and HVEM-CRD1 respectively; multiligand-DCs) causes an increase in regulatory cytokine and T cell (Treg) responses and suppression of the effector T cell function as compared to engineered control-DCs. Non-obese diabetic (NOD) mice treated with BcAg-pulsed CTLA4-ligand-DCs and multiligand-DCs at pre-diabetic and early-hyperglycemic stages showed significantly lower degree of insulitis, higher frequencies of insulin-positive islets, profound delay in, and reversal of, hyperglycemia for a significant duration. Immune cells from the tDC treated mice not only produced lower amounts of IFNγ and higher amounts of IL10 and TGFβ1 upon BcAg challenge, but also failed to induce hyperglycemia upon adoptive transfer. While both CTLA4-ligand-DCs and multiligand-DCs were effective in inducing tolerance, multiligand-DC treatment produced an overall higher suppressive effect on effector T cell function and disease outcome. These studies show that enhanced engagement of T cell checkpoint receptors during BcAg presentation can modulate T cell function and suppress autoimmunity and progression of the disease in T1D.

Costimulation Blockade in Transplantation

T cells play a pivotal role in orchestrating immune responses directed against a foreign (allogeneic) graft. For T cells to become fully activated, the T-cell receptor (TCR) must interact with the major histocompatibility complex (MHC) plus peptide complex on antigen-presenting cells (APCs), followed by a second "positive" costimulatory signal. In the absence of this second signal, T cells become anergic or undergo deletion. By blocking positive costimulatory signaling, T-cell allo-responses can be aborted, thus preventing graft rejection and promoting long-term allograft survival and possibly tolerance (Alegre ML, Najafian N, Curr Mol Med 6:843-857, 2006; Li XC, Rothstein DM, Sayegh MH, Immunol Rev 229:271-293, 2009). In addition, costimulatory molecules can provide negative "coinhibitory" signals that inhibit T-cell activation and terminate immune responses; strategies to promote these pathways can also lead to graft tolerance (Boenisch O, Sayegh MH, Najafian N, Curr Opin Organ Transplant 13:373-378, 2008). However, T-cell costimulation involves an incredibly complex array of interactions that may act simultaneously or at different times in the immune response and whose relative importance varies depending on the different T-cell subsets and activation status. In transplantation, the presence of foreign alloantigen incites not only destructive T effector cells but also protective regulatory T cells, the balance of which ultimately determines the fate of the allograft (Lechler RI, Garden OA, Turka LA, Nat Rev Immunol 3:147-158, 2003). Since the processes of alloantigen-specific rejection and regulation both require activation of T cells, costimulatory interactions may have opposing or synergistic roles depending on the cell being targeted. Such complexities present both challenges and opportunities in targeting T-cell costimulatory pathways for therapeutic purposes. In this chapter, we summarize our current knowledge of the various costimulatory pathways in transplantation and review the current state and challenges of harnessing these pathways to promote graft tolerance (summarized in Table 10.1).

Engineered Dendritic Cell-Directed Concurrent Activation of Multiple T cell Inhibitory Pathways Induces Robust Immune Tolerance

Inhibitory/repressor-receptors are upregulated significantly on activated T cells, and have been the molecules of attention as targets for inducing immune tolerance. Induction of effective antigen specific tolerance depends on concurrent engagement of the TCR and one or more of these inhibitory receptors. Here, we show, for the first time that dendritic cells (DCs) can be efficiently engineered to express multiple T cell inhibitory ligands, and enhanced engagement of T cell inhibitory receptors, upon antigen presentation, by these DCs can induce effective CD4+ T cell tolerance and suppress autoimmunity. Compared to control DCs, antigen presentation by DCs that ectopically express CTLA4, PD1 and BTLA selective ligands (B7.1wa, PD-L1, and HVEM-CRD1 respectively) individually (mono-ligand DCs) or in combination (multi-ligand DCs) causes an inhibition of CD4+ T cell proliferation and pro-inflammatory cytokine response, as well as increase in Foxp3+ Treg frequency and immune regulatory cytokine production. Administration of self-antigen (mouse thyroglobulin; mTg) loaded multi-ligand DCs caused hyporesponsiveness to mTg challenge, suppression of autoantibody production, and amelioration of experimental autoimmune thyroiditis. Overall, this study shows that engineered DC-directed enhanced concurrent activation of multiple T cell coinhibitory pathways is an effective way to induce self-antigen specific T cell tolerance to suppress ongoing autoimmunity.

Selective CD28 Inhibition Modulates Alloimmunity and Cardiac Allograft Vasculopathy in Anti-CD154-Treated Monkeys

BACKGROUND

Selective CD28 inhibition is actively pursued as an alternative to B7 blockade using cytotoxic T lymphocyte antigen 4 Ig based on the hypothesis that the checkpoint immune regulators cytotoxic T lymphocyte antigen 4 and programmed death ligand 1 will induce tolerogenic immune signals. We previously showed that blocking CD28 using a monovalent nonactivating reagent (single-chain anti-CD28 Fv fragment linked to alpha-1 antitrypsin [sc28AT]) synergizes with calcineurin inhibitors in nonhuman primate (NHP) kidney and heart transplantation. Here, we explored the efficacy of combining a 3-week "induction" sc28AT treatment with prolonged CD154 blockade.

METHODS

Cynomolgus monkey heterotopic cardiac allograft recipients received sc28AT (10 mg/kg, d0-20, n = 3), hu5C8 (10-30 mg/kg, d0-84, n = 4), or combination (n = 6). Graft survival was monitored by telemetry. Protocol biopsies and graft explants were analyzed for International Society of Heart and Lung Transplantation acute rejection grade and cardiac allograft vasculopathy score. Alloantibody, T-cell phenotype and regulatory T cells were analyzed by flow cytometry. Immunochemistry and gene expression (NanoString) characterized intra-graft cellular infiltration.

RESULTS

Relative to modest prolongation of median graft survival time with sc28AT alone (34 days), hu5C8 (133 days), and sc28AT + hu5C8 (141 days) prolonged survival to a similar extent. CD28 blockade at induction, added to hu5C8, significantly attenuated the severity of acute rejection and cardiac allograft vasculopathy during the first 3 months after transplantation relative to hu5C8 alone. These findings were associated with decreased proportions of circulating CD8 and CD3CD28 T cells, and modulation of inflammatory gene expression within allografts.

CONCLUSIONS

Induction with sc28AT promotes early cardiac allograft protection in hu5C8-treated NHPs. These results support further investigation of prolonged selective CD28 inhibition with CD40/CD154 blockade in NHP transplants.

Prognostic value of circulating regulatory T cell subsets in untreated non-small cell lung cancer patients

The role of the different circulating regulatory T-cells (Treg) subsets, as well as their correlation with clinical outcome of non-small cell lung cancer (NSCLC) patients is poorly understood. Peripheral blood from 156 stage III/IV chemotherapy-naive NSCLC patients and 31 healthy donors (HD) was analyzed with flow cytometry for the presence and functionality of CD4⁺ Treg subsets (naive, effector and terminal effector). Their frequencies were correlated with the clinical outcome. All CD4⁺ Treg subsets exhibited highly suppressive activity by TGF-β and IL-10 production. The percentages of naive Treg were found elevated in NSCLC patients compared to HD and were associated with poor clinical outcome, whereas the percentage of terminal effector Treg was lower compared to HD and higher levels were correlated with improved clinical response. At baseline, normal levels of naive and effector Treg were associated with longer overall survival (OS) compared to high levels, while the high frequency of the terminal effector Treg was correlated with longer Progression-Free Survival and OS. It is demonstrated, for first time, that particular CD4⁺ Treg subtypes are elevated in NSCLC patients and their levels are associated to the clinical outcome. The blocking of their migration to the tumor site may be an effective therapeutic strategy.

Evaluation of PLGA containing anti-CTLA4 inhibited endometriosis progression by regulating CD4+CD25+Treg cells in peritoneal fluid of mouse endometriosis model

Our study investigated poly(lactic-co-glycolic acid) (PLGA) as protein delivery vehicles encapsulate CTLA-4-antibody (anti-CTLA-4) which is essential for CD4+CD25+Treg cells suppressive function exposing superior potential for inhibiting endometriosis progress in mouse model than single anti-CTLA-4. Anti-CTLA-4 loaded PLGA combined to ligands CTLA-4 in surface of CD4+CD25+Treg cells which distributed in peritoneal fluid of mouse endometriosis model. The particle size, zeta potential of the anti-CTLA-4 loaded nanoparticles was detected by dynamic light scattering. Morphology of nanoparticles was evaluated by transmission electron microscopy (TEM). Confocal laser scanning microscopy (CLSM) indicated distribution of anti-CTLA-4 with PLGA or without in peritoneal fluid. Cumulative anti-CTLA-4 release from nanoparticles was evaluated by Micro BCA assay. The percentage of CD4+CD25+Treg cells in peritoneal fluid was demonstrated by flow cytometer. In vitro experiment we co-culture ectopic endometrial cells (EEC) with isolated CD4+CD25+Treg cells in peritoneal fluid (PF), proliferation and invasion of ectopic endometrial cells (EEC) was measured by BrdU ELISA assay and Matrigel invasion assay. In comparison with anti-CTLA-4 without nanoparticles, the bioconjugates PLGA/anti-CTLA-4 were tolerated in peritoneal fluid with a controlled release of anti-CTLA-4 in 3, 7, 14days. Moreover, PLGA/anti-CTLA-4 had superior protective regulation ability to reduce level of CD4+CD25+Treg cells in peritoneal fluid. Most strikingly, in vitro experiment, PLGA/anti-CTLA-4 exhibited better ability in inhibiting proliferation and invasion of ectopic endometrial cells in co-culture system compared with anti-CTLA-4. Progressively, PLGA/anti-CTLA-4 had better suppressive activity to inhibited IL-10 and TGF-beta secreted by CD4+CD25+Treg cells which indicating that PLGA/anti-CTLA-4 suppressed cells proliferation and invasion through reduced IL-10 and TGF-beta production. Thus, PLGA/anti-CTLA-4 may be a potential strategy for endometriosis therapy.

T cells and costimulation in cancer

Optimal T cell response is dependent not only on T cell receptor activation, but also on additional signaling from coreceptors. The main coreceptors include B7 and tumor necrosis factor family members. They exert costimulatory or coinhibitory effects, and their balance determines the fate of T cell response. In normal conditions, costimulators facilitate the development of protective immune response, whereas coinhibitors dampen inflammation to avoid organ/tissue damage from excessive immune reaction. In the tumor microenvironment, the balance is garbled: inhibitory pathways predominate, and T cell response is impaired. The importance of cosignaling in the tumor immune response has been experimentally and clinically demonstrated. New therapeutic strategies targeting T cell cosignaling, especially coinhibitory molecules, are under active experimental and clinical investigation. This review summarizes the functions of main T cell cosignaling axes and discusses their clinical application.

A novel pancreatic β-cell targeting bispecific-antibody (BsAb) can prevent the development of type 1 diabetes in NOD mice

To prepare a novel Bispecific Antibody (BsAb) as a potential targeted therapy for T1D, we produced a "functionally inert" monoclonal antibody (mAb) against Glucose transporter-2 (GLUT-2) expressed on β-cells to serve as an anchoring antibody. The therapeutic arm is an agonistic mAb against Cytotoxic T-Lymphocyte Antigen 4 (CTLA-4), a negative regulator of T-cell activation expressed on activated CD4+ T-cells. A BsAb was prepared by chemically coupling an anti-GLUT2 mAb to an agonistic anti-CTLA-4 mAb. This BsAb was able to bind to GLUT2 and CTLA-4 in vitro, and to pancreatic islets, both in vitro and in vivo. We tested the safety and efficacy of this BsAb by treating Non-Obese Diabetes (NOD) mice and found that it could delay the onset of diabetes with no apparent undesirable side effects. Thus, engagement of CTLA-4 on activated T cells from target tissue can be an effective way to treat type-1 diabetes.

Alternative splice forms of CTLA-4 induced by antisense mediated splice-switching influences autoimmune diabetes susceptibility in NOD mice

Activated and regulatory T cells express the negative co-stimulatory molecule cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4) that binds B7 on antigen-presenting cells to mediate cellular responses. Single nucleotide polymorphisms in the CTLA-4 gene have been found to affect alternative splicing and are linked to autoimmune disease susceptibility or resistance. Increased expression of a soluble splice form (sCTLA-4), lacking the transmembrane domain encoded by exon 3, has been shown to accelerate autoimmune pathology. In contrast, an exon 2-deficient form lacking the B7 ligand binding domain (liCTLA-4), expressed by diabetes resistant mouse strains has been shown to be protective when expressed as a transgene in diabetes susceptible non-obese diabetic (NOD) mice. We sought to employ an antisense-targeted splice-switching approach to independently produce these CTLA-4 splice forms in NOD mouse T cells and observe their relative impact on spontaneous autoimmune diabetes susceptibility. In vitro antisense targeting of the splice acceptor site for exon 2 produced liCTLA-4 while targeting exon 3 produced the sCTLA-4 form in NOD T cells. The liCTLA-4 expressing T cells exhibited reduced activation, proliferation and increased adhesion to intercellular adhesion molecule-1 (ICAM-1) similar to treatment with agonist α-CTLA-4. Mice treated to produce liCTLA-4 at the time of elevated blood glucose levels exhibited a significant reduction in the incidence of insulitis and diabetes, whereas a marked increase in the incidence of both was observed in animals treated to produce sCTLA-4. These findings provide further support that alternative splice forms of CTLA-4 affects diabetes susceptibility in NOD mice and demonstrates the therapeutic utility of antisense mediated splice-switching for modulating immune responses.

Targeting CD28 to prevent transplant rejection

INTRODUCTION

The pivotal role of costimulatory pathways in regulating T-cell activation versus tolerance has stimulated tremendous interest in their manipulation for therapeutic purposes. Of these, the CD28-B7 pathway is arguably the most important and best studied. Therapeutic targets of CD28 are currently used in the treatment of melanoma, autoimmune diseases and in transplantation.

AREAS COVERED

In this review, we summarize our current knowledge of CD28 and cytotoxic T-lymphocyte antigen-4 (CTLA-4) signaling, and review the current state and challenges of harnessing them to promote transplant tolerance.

EXPERT OPINION

Despite the success of belatacept, a first-in-class CTLA-4 fusion protein now clinically used in transplantation, it is apparent that we have only scratched the surface in understanding the complexities of how costimulatory pathways modulate the immune system. Our initial assumption that positive costimulators activate effector T cells and prevent tolerance, while negative costimulators inhibit effector T cells and promote tolerance, is clearly an oversimplified view. Indeed, belatacept is not only capable of blocking deleterious CD28-B7 interactions that promote effector T-cell responses but can also have undesired effects on tolerogenic regulatory T-cell populations.

Effect of cytotoxic T-lymphocyte-associated protein 4 on CD4(+)CD25(+) regulatory T cells in murine schistosomiasis japonica

In a previous study we demonstrated that CD4(+)CD25(+) regulatory T cells (Tregs) contributed to the escape of Schistosoma japonicum (S. japonicum) from the host's immune responses. In this paper, we studied the effect of cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) on CD4(+)CD25(+) Tregs in murine Schistosomiasis japonica and its corresponding role in the immune evasion of S. japonicum in mice. The results showed substantial reductions of worm burden and egg production in worm groups treated with anti-CD25 or anti-CTLA-4 monoclonal antibodies (mAb) compared to an infected but untreated control. The reduction effect was even enhanced in an experimental group co-treated with both mAbs. Compared to the control group, the percentage of CD4(+)CD25(+) Tregs was very much lower in the anti-CD25 mAb group as determined by FACS analyses and higher in the anti-CTLA-4 mAb group. ELISA analyses showed that both the anti-CTLA-4 mAb and the co-treated groups had higher levels of cytokines compared to the control group as well as larger egg granuloma sizes as determined by microscopical analyses of liver sections of infected mice. These results suggest that treatment with an anti-CTLA-4 mAb allows the host to clear S. japonicum, but at the cost of elevated pathological damage. The latter indicated a role of CTLA-4 in granuloma formation. Moreover, CD4(+)CD25(+) Tregs and CTLA-4 may exert synergistic effects during immune evasion processes by enhancing Th1-type immune response.

The effect of autoimmune arthritis treatment strategies on regulatory T-cell dynamics

PURPOSE OF REVIEW

Since their discovery over 15 years ago, intensive research has focused on the presence, phenotype and function of FOXP3(+) regulatory T cells (Treg) in autoimmune diseases such as rheumatoid arthritis (RA). The questions of whether Treg deficiencies underlie autoimmune pathology and whether or how Treg-related therapeutic approaches might be successful are still a subject of a vivid debate. In this review we give an overview of how current therapies influence Treg numbers and function in RA and juvenile idiopathic arthritis (JIA) and discuss these findings in the light of new Treg-based intervention strategies for autoimmune arthritis.

RECENT FINDINGS

The attempt to relate rheumatic diseases like rheumatoid arthritis and juvenile idiopathic arthritis to Treg has led to somewhat heterogeneous observations. So far, no clear defects in Treg numbers or function have been identified in autoimmune arthritis. The current standard therapies, that is methotrexate and biologicals, are generally effective, but the exact mechanism of action and their effect on Treg is not fully known. Nevertheless, the majority of in-vitro and ex-vivo data point towards a positive influence of these treatments on Treg number and function. These observations are not all consistent, however, and it is not known whether the observed effects on Treg are primary or secondary effects. To safely conduct targeted regulatory T-cell therapy in rheumatic diseases more knowledge about regulatory T-cell function in an inflammatory environment is needed that coincides with the initiative to elucidate the exact mechanism of current therapies.

Correlation of increased blood levels of GITR and GITRL with disease severity in patients with primary Sjögren's syndrome

Glucocorticoid-induced tumor necrosis factor receptor family-related protein (GITR) is a type I transmembrane protein belonging to the TNFR superfamily. After activated by its ligand GITRL, GITR could influence the activity of effector and regulatory T cells, participating in the development of several autoimmune and inflammatory diseases included rheumatoid arthritis and autoimmune thyroid disease. We previously reported that serum GITRL levels are increased in systemic lupus erythematosus (SLE) patients compared with healthy controls (HC). Here, we tested serum soluble GITR (sGITR) and GITRL levels in 41 primary Sjögren's syndrome (pSS) patients and 29 HC by ELISA and correlated sGITR and GITRL levels with clinical and laboratory variables. GITR and GITRL expression in labial salivary glands was detected by immunohistochemistry. pSS patients had significantly increased serum levels of sGITR and GITRL compared with controls (GITR: 5.66 ± 3.56 ng/mL versus 0.50 ± 0.31 ng/mL; P < 0.0001; GITRL: 6.17 ± 7.10 ng/mL versus 0.36 ± 0.28 ng/mL; P < 0.0001). Serum sGITR and GITRL levels were positively correlated with IgG (GITRL: r = 0.6084, P < 0.0001; sGITR: r = 0.6820, P < 0.0001) and ESR (GITRL: r = 0.8315, P < 0.0001; sGITR: r = 0.7448, P < 0.0001). Moreover, GITR and GITRL are readily detected in the lymphocytic foci and periductal areas of the LSGs. In contrast, the LSGs of HC subjects did not express GITR or GITRL. Our findings indicate the possible involvement of GITR-GITRL pathway in the pathogenesis of pSS. Further studies may facilitate the development of targeting this molecule pathway for the treatment of pSS.

Jacalin regulates IgA production by peripheral blood mononuclear cells

AIMS

In IgA nephropathy, circulating immune complexes containing IgA1 are deposited on the glomerular mesangium, causing mesangial cell proliferation and acceleration of extracellular matrix production. The suppressive effect of jacalin, a galactose-binding lectin, on IgA production in vitro was determined.

MATERIALS & METHODS

Normal human peripheral blood mononuclear cells were stimulated with plate-bound anti-CD3 and Th2 stimulation, with or without jacalin. Regulatory and effector cell subsets were determined by flow cytometry, and immunoglobulin production by ELISA.

RESULTS

Jacalin increased the ratio of CD4(+)CD25(+)CD152(+) Tregs:effector T cells in peripheral blood mononuclear cell cultures 60-fold. This CD4(+)CD25(+)CD152(+) Treg increase may have inhibited Th2-stimulated IgA production by B cells.

CONCLUSION

Immune tolerance induced by jacalin can suppress IgA production.

CTLA-4 blockade and the renaissance of cancer immunotherapy

Cytotoxic T-lymphocyte associated antigen 4 (CTLA-4) plays a key role in restraining the adaptive immune response of T-cells towards a variety of antigens including tumor associated antigens (TAAs). The blockade of this immune checkpoint elicits an effective anticancer immune response in a range of preclinical models, suggesting that naturally occurring (or therapeutically induced) TAA specific lymphocytes need to be "unleashed" in order to properly fight against malignant cells. Therefore, investigators have tested this therapeutic hypothesis also in humans: the favorable results obtained with this strategy in patients with advanced cutaneous melanoma are revolutionizing the management of this highly aggressive disease and are fueling new enthusiasm on cancer immunotherapy in general. Here we summarize the biology of CTLA-4, overview the experimental data supporting the rational for targeting CTLA-4 to treat cancer and review the main clinical findings on this novel anticancer approach. Moreover, we critically discuss the current challenges and potential developments of this promising field of cancer immunotherapy.

CTLA-4 promotes Foxp3 induction and regulatory T cell accumulation in the intestinal lamina propria

Thymic induction of CD4(+)Foxp3(+) regulatory T (Treg) cells relies on CD28 costimulation and high-affinity T-cell receptor (TCR) signals, whereas Foxp3 (forkhead box P3) induction on activated peripheral CD4(+) T cells is inhibited by these signals. Accordingly, the inhibitory molecule CTLA-4 (cytotoxic T-lymphocyte antigen 4) promoted, but was not essential for CD4(+) T-cell Foxp3 induction in vitro. We show that CTLA-4-deficient cells are equivalent to wild-type cells in the thymic induction of Foxp3 and maintenance of Foxp3 populations in the spleen and mesenteric lymph nodes, but their accumulation in the colon, where Treg cells specific for commensal bacteria accumulate, is impaired. In a T cell-transfer model of colitis, the two known CTLA-4 ligands, B7-1 and B7-2, had largely redundant roles in inducing inflammation and promoting Treg cell function. However, B7-2 proved more efficient than B7-1 in inducing Foxp3 in vitro and in vivo. Our data reveal an unappreciated role for CTLA-4 in establishing the Foxp3(+) compartment in the intestine.

Coinhibitory molecules in cancer biology and therapy

The adaptive immune response is controlled by checkpoints represented by coinhibitory molecules, which are crucial for maintaining self-tolerance and minimizing collateral tissue damage under physiological conditions. A growing body of preclinical evidence supports the hypothesis that unleashing this immunological break might be therapeutically beneficial in the fight against cancer, as it would elicit an effective antitumor immune response. Remarkably, recent clinical trials have demonstrated that this novel strategy can be highly effective in the treatment of patients with cancer, as shown by the paradigmatic case of ipilimumab (a monoclonal antibody blocking the coinhibitory molecule cytotoxic T lymphocyte associated antigen-4 [CTLA4]) that is opening a new era in the therapeutic approach to a chemoresistant tumor such as cutaneous melanoma. In this review we summarize the biology of coinhibitory molecules, overview the experimental and clinical attempts to interfere with these immune checkpoints to treat cancer and critically discuss the challenges posed by such a promising antitumor modality.

CD4+ CD25+ Foxp3+ IFNγ+ CD178+ human induced Treg (iTreg) contribute to suppression of alloresponses by apoptosis of responder cells

Induced Treg with the phenotype CD4(+)CD25(+)Foxp3(+)IFNγ(+) were shown to be associated with good long-term graft outcome in renal transplant recipients and inhibition of allogeneic T-cell responses in vitro. In the present study, we investigated whether apoptosis and Fas/FasL-dependent pathways contribute to the inhibition of T-cell activation. Early apoptosis and necrosis rates as well as co-expression of immunostimulatory and immunosuppressive proteins in/on CD4(+)CD25(+)Foxp3(+), CD4(+)IFNγ(+)Foxp3(+) and CD4(+)CD25(+)IFNγ(+) PBL were analyzed using cells from healthy controls and four-color flow cytometry, PMA/Ionomycin-stimulated PBL, and MLC. Sixteen hours PMA/Ionomycin stimulation induced iTreg subsets with the phenotype CD4(+)CD25(+)Foxp3(+), CD4(+)IFNγ(+)Foxp3(+) and CD4(+)CD25(+)IFNγ(+) co-expressing CD95, CD152, CD178, CD279, Granzyme A, Granzyme B, Perforin, IL-10, and TGFβ(1). CD178(+) iTreg increased within 3h after PMA/Ionomycin stimulation in parallel to early apoptotic Annexin(+)/PI(-) PBL, suggesting CD178-mediated apoptosis of responder cells by CD4(+)CD25(+)Foxp3(+)IFNγ(+)CD178(+) iTreg. CD4(+)CD25(+)IFNγ(+) and CD4(+)CD25(+)CD178(+) PBL separated from primary cell cultures and added to autologous PMA/Ionomycin stimulated secondary cell cultures induced apoptosis immediately. Early apoptosis was not antigen-specific as shown in secondary MLC with separated CD4(+)CD25(+)IFNγ(+) and CD4(+)CD25(+)CD178(+) PBL and third-party cells as stimulator. CD4(+)CD25(+)Foxp3(+)IFNγ(+)CD178(+) iTreg differentiate after cell stimulation and induce antigen-unspecific apoptosis of activated CD95(+) responder/effector cells in vitro that might contribute to iTreg-mediated inhibition of T-cell activation.

Correlation of circulating glucocorticoid-induced TNFR-related protein ligand levels with disease activity in patients with systemic lupus erythematosus

The aim of this paper is to investigate the correlation of glucocorticoid-induced tumor necrosis factor receptor- (TNFR-) related protein ligand (GITRL) with disease activity and organ involvement in patients with systemic lupus erythematosus (SLE). Serum GITRL levels were measured in 58 patients with SLE and 30 healthy controls matched for age and sex. Patients were assessed for clinical and laboratory variables. Correlations of serum GITRL levels with SLEDAI, laboratory values, and clinical manifestations were assessed. Serum GITRL levels were determined by ELISA. Serum GITRL levels were markedly increased in patients with SLE compared with healthy controls (mean 401.3 ng/mL and 36.59 ng/mL, resp.; P < 0.0001). SLE patients with active disease showed higher serum GITRL levels compared to those with inactive disease (mean 403.3 ng/mL and 136.3 ng/mL, resp; P = 0.0043) as well as normal controls (36.59 ng/mL; P < 0.0001). Serum GITRL levels were positively correlated with SLEDAI, titers of anti-dsDNA antibody, erythrocyte sedimentation rate (ESR), and IgM and negatively correlated with complement3 (C3). Serum GITRL levels were higher in SLE patients with renal involvement and vasculitis compared with patients without the above-mentioned manifestations.

Preclinical efficacy and immunological safety of FR104, an antagonist anti-CD28 monovalent Fab' antibody

Antagonist anti-CD28 antibodies prevent T cell costimulation and differentiate from CTLA4Ig since they cannot block CTLA-4 and PDL-1 coinhibitory signals. They demonstrated efficacy in suppressing effector T cells while enhancing regulatory T cells function and immune tolerance. However, anti-CD28 antibodies devoid of immunotoxicity and with a good pharmacokinetic profile have not yet been developed. Here, we describe FR104, a novel humanized pegylated anti-CD28 Fab' antibody fragment presenting a long elimination half-life in monkeys. In vitro, FR104 failed to induce human T cell proliferation and cytokines secretion, even in the presence of anti-CD3 antibodies or when cross-linked with secondary antibodies. Furthermore, in humanized NOD/SCID mice adoptively transferred with human PBMC, whereas superagonist and divalent antibodies elicited rapid cytokines secretion and human T cell activation, FR104 did not. These humanized mice developed a florid graft-versus-host disease, which was prevented by administration of FR104 in a CTLA4-dependent manner. Interestingly, administration of high doses of CTLA4-Ig was ineffective to prevent GVHD, whereas administration of low doses was partially effective. In conclusion, we demonstrated that FR104 is devoid of agonist activity on human T cells and thus compatible with a clinical development that might lead to higher therapeutic indexes, by sparing CTLA-4, as compared to CD80/CD86 antagonists.

CD28-specific immunomodulating antibodies: what can be learned from experimental models?

Tolerance induction to alloantigens remains a major challenge in transplant immunology. Progress in the last decade of our understanding of T-cell activation has led to the development of new immunotherapeutic strategies to replace conventional immunosuppression which inhibits the immune system in a nonspecific way. In particular, positive and negative costimulatory molecules of the CD28 family have been consistently demonstrated to be critical for the development of productive immune responses as well as the establishment and maintenance of peripheral tolerance. However, recent discoveries of novel costimulatory interactions confer a novel dimension to the immunoregulatory interactions within the B7:CD28 family and compels a revised view within a "quintet" of costimulatory molecules: CD28/B7/CTLA-4/PD-L1/ICOSL. Complexity introduced in this more detailed costimulatory pathway has important implications in therapeutic interventions against human immunological diseases and, especially, highlight the fundamental differences in selectively targeting CD28 molecules instead of B7 counterparts. In this review, we discuss these differences and emphasize different CD28-specific immunomodulating strategies evaluated in experimental models of transplantation and autoimmune diseases.

The role of coinhibitory signaling pathways in transplantation and tolerance

Negative costimulatory molecules, acting through so-called inhibitory pathways, play a crucial role in the control of T cell responses. This negative “second signal” opposes T cell receptor activation and leads to downregulation of T cell proliferation and promotes antigen specific tolerance. Much interest has focused upon these pathways in recent years as a method to control detrimental alloresponses and promote allograft tolerance. However, recent experimental data highlights the complexity of negative costimulatory pathways in alloimmunity. Varying effects are observed from molecules expressed on donor and recipient tissues and also depending upon the activation status of immune cells involved. There appears to be significant overlap and redundancy within these systems, rendering this a challenging area to understand and exploit therapeutically. In this article, we will review the literature at the current time regarding the major negative costimulation pathways including CTLA-4:B7, PD-1:PD-L1/PD-L2 and PD-L1:B7-1, B7-H3, B7-H4, HVEM:BTLA/CD160, and TIM-3:Galectin-9. We aim to outline the role of these pathways in alloimmunity and discuss their potential applications for tolerance induction in transplantation.

Ligation of cytotoxic T lymphocyte antigen-4 to T cell receptor inhibits T cell activation and directs differentiation into Foxp3+ regulatory T cells

Cross-linking of ligand-engaged cytotoxic T lymphocyte antigen-4 (CTLA-4) to the T cell receptor (TCR) during the early phase of T cell activation attenuates TCR signaling, leading to T cell inhibition. To promote this event, a bispecific fusion protein comprising a mutant mouse CD80 (CD80w88a) and lymphocyte activation antigen-3 was engineered to concurrently engage CTLA-4 and cross-link it to the TCR. Cross-linking is expected to be attained via ligation of CTLA-4 first to MHCII and then indirectly to the TCR, generating a CTLA-4-MHCII-TCR trimolecular complex that forms between T cells and antigen-presenting cells during T cell activation. Treating T cells with this bispecific fusion protein inhibited T cell activation. In addition, it induced the production of IL-10 and TGF-β and attenuated AKT and mTOR signaling. Intriguingly, treatment with the bispecific fusion protein also directed early T cell differentiation into Foxp3-positive regulatory T cells (Tregs). This process was dependent on the endogenous production of TGF-β. Thus, bispecific fusion proteins that engage CTLA-4 and co-ligate it to the TCR during the early phase of T cell activation can negatively regulate the T cell response. Bispecific biologics with such dual functions may therefore represent a novel class of therapeutics for immune modulation. These findings presented here also reveal a potential new role for CTLA-4 in Treg differentiation.

Aberrant expression of costimulatory molecules in splenocytes of the mevalonate kinase-deficient mouse model of human hyper-IgD syndrome (HIDS)

OBJECTIVE

We sought to determine the activation status and proliferative capacities of splenic lymphocyte populations from a mevalonate kinase-deficient mouse model of hyper-IgD syndrome (HIDS). We previously reported that murine mevalonate kinase gene ablation was embryonic lethal for homozygous mutants while heterozygotes (Mvk (+/-)) demonstrated several phenotypic features of human HIDS including increased serum levels of IgD, IgA, and TNFα, temperature dysregulation, hematological abnormalities, and splenomegaly.

METHODS AND RESULTS

Flow cytometric analysis of cell surface activation markers on T and B lymphocytes, and macrophage populations, demonstrated aberrant expression of B7 glycoproteins in all splenic cell types studied. Differences in expression levels between Mvk (+/-) and Mvk (+/+) littermate controls were observed in both the basal state (unstimulated) and after Concanavalin A (Con-A) stimulation in vitro of whole splenocyte cultures. In Mvk (+/-) CD4 and CD8 T cells, alterations in expression of CD25, CD80, CD152, and CD28 were observed. Mvk (+/-) splenic macrophages expressed altered levels of CD80, CD86, CD40, and CD11c while Mvk (+/-) B lymphocytes had differential expression of CD40, CD80, and CD86. Mvk (+/-) splenocyte subpopulations also exhibited altered proliferative capacities in response to in vitro stimulation.

CONCLUSION

We postulate that imbalances in the expression of cell surface proteins necessary for activation, proliferation, and regulation of the intensity and duration of an immune response may result in defective T cell activation, proliferation, and effector functions in our model and potentially in human HIDS.

FOXP3+ regulatory T cells: from suppression of rejection to induction of renal allograft tolerance

Naturally occurring and induced regulatory T cells (Tregs) can become hyporesponsive and anergic to antigen stimulation in autoimmune diseases and allograft rejection. The mechanisms of suppression of effector T cells by Tregs remain unclear, but there are in vitro and in vivo evidences showing that these cells are able to suppress antigen-specific responses via direct cell-to-cell contact, secrete anti-inflammatory cytokines such as TGF-β and IL-10, and inhibit the generation of memory T cells, among others. The transcription factor FOXP3 is a specific marker of Tregs and its deficiency is associated with autoimmune diseases and inflammation. During acute rejection of kidney allografts, an augmented FOXP3 gene expression as well as increased CD4(+)CD25(+)FOXP3(+) and other cell populations are observed in graft biopsies. However, it is not clear whether Tregs migrate into the graft and are retained there to suppress the inflammatory process, or whether they are directly associated with more complex mechanisms to induce immune tolerance. FOXP3(+) Tregs may direct the immune response toward a graft acceptance program, potentially affecting the long-term survival of transplanted organs and tissues. Immunosuppressive drugs modulate the number and function of circulating Tregs and FOXP3 expression. Experimental and clinical studies have shown that mTOR inhibitors have positive and calcineurin inhibitors negative effects on Tregs, but it is difficult to set apart the effect of multiple other factors known to be associated with short- and long-term renal graft outcomes. This review aimed to describe the functions of Tregs and its transcription factor FOXP3 in suppression of immune response during rejection and in induction of kidney graft tolerance, as well as to review the individual effects of immunosuppressive drugs on Tregs.

Effect of CD4(+)CD25(+) regulatory T cells in the development of anterior chamber-associated immune deviation

AIM

To investigate whether CD4(+)CD25(+) regulatory T (Treg) cells play a role in the development of anterior chamber-associated immune deviation (ACAID).

METHODS

The dynamic changes in the frequency of CD4(+)CD25(+) T cells, CD4(+)CD25(+) FoxP3(+) T cells and CD4(+)CD25(+) PD-1(+) T cells from spleens of mice with ACAID were analyzed by flow cytometry. Foxp3 mRNA expression in purified CD4(+)CD25(+) T cells was analyzed using real-time PCR. The suppressive effect of purified CD4(+)CD25(+) T cells on the proliferation of CD4(+)CD25(-) T cells was evaluated by [(3)H] thymidine incorporation. A blocking experiment was performed to further address the role of CD4(+)CD25(+) T cells in ACAID. The expression of IL-10 in purified CD4(+)CD25(+) T cells was evaluated by ELISA.

RESULTS

Increased frequencies of CD4(+)CD25(+) T cells, CD4(+)CD25(+) FoxP3(+) T cells and CD4(+)CD25(+) PD-1(+) T cells were observed in ACAID. The CD4(+)CD25(+) T cells from mice with ACAID showed enhanced suppressive effect on the proliferation of CD4(+)CD25(-) T cells. Treatment of BALB/c mice with anti-CD25 antibody after injection of OVA into the anterior chamber significantly inhibited the induction of ACAID. Furthermore, purified CD4(+)CD25(+) T cells from ACAID mice secreted IL-10.

CONCLUSION

Our results demonstrate that Treg cells are induced in the mice undergoing ACAID. These Treg cells may play a role in the development of ACAID.

The effects of Foxp3-expressing regulatory T cells expanded with CD28 superagonist antibody in DSS-induced mice colitis

Regulatory T (Treg) cells play an important role in the pathogenesis of inflammatory bowel disease (IBD). In the present study, we found that a superagonistic CD28-specific monoclonal antibody (supCD28mAb, D665) could preferentially stimulate expansion of CD4+Foxp3+ Treg cells. Foxp3(EGFP) mice were orally administrated with 3.5% DSS for 5days, and intraperitoneally injected supCD28mAb 1mg/mice in treated group. All of the mice were sacrificed on day 8, and both clinical and histological parameters showed that the severity of colitis was significantly reduced in treated group compared to controls. In treated group, the proportion of CD103, CD152 and CD62L expression on Foxp3+Treg cells in the spleen and mesenteric lymph node were higher than controls. Furthermore, qRT-PCR analysis showed that expression of anti-inflammatory cytokines such as IL-10, TGF-β was significantly increased in treated group. Taken together, our data demonstrated that supCD28mAb targets CD4+Foxp3+Treg cells expansion in vivo, maintains and enhances their regulatory functions, to reduce the damage of colon in dextran sulfate sodium (DSS)-induced mouse colitis by secreting a large amount of IL-10. It represents a major advance towards the therapeutic use of polyclonally activated Treg cells as cellular therapy for treatment of IBD.

3G11 expression in CD4+ T cell-mediated autoimmunity and immune tolerance

3G11 is a sialylated carbohydrate epitope of the disialoganglioside molecule expressed on mouse CD4(+) T cells. Recent research showed that 3G11 expression is related to the modulation of T cell function, i.e., 3G11(-) T cells exhibit anergic/Treg characteristics and efficiently inhibit autoimmunity in the central nervous system. The relationship between 3G11 expression and immune tolerance is summarized in this literature review.

Dendritic cell-directed CTLA-4 engagement during pancreatic beta cell antigen presentation delays type 1 diabetes

The levels of expression of alternatively spliced variants of CTLA-4 and insufficient CTLA-4 signaling have been implicated in type 1 diabetes. Hence, we hypothesized that increasing CTLA-4-specific ligand strength on autoantigen-presenting dendritic cells (DCs) can enhance ligation of CTLA-4 on T cells and lead to modulation of autoreactive T cell response. In this study, we show that DC-directed enhanced CTLA-4 engagement upon pancreatic beta cell Ag presentation results in the suppression of autoreactive T cell response in NOD mice. The T cells from prediabetic NOD mice treated with an agonistic anti-CTLA-4 Ab-coated DC (anti-CTLA-4-Ab DC) showed significantly less proliferative response and enhanced IL-10 and TGF-beta1 production upon exposure to beta cell Ags. Furthermore, these mice showed increased frequency of Foxp3+ and IL-10+ T cells, less severe insulitis, and a significant delay in the onset of hyperglycemia compared with mice treated with control Ab-coated DCs. Further analyses showed that diabetogenic T cell function was modulated primarily through the induction of Foxp3 and IL-10 expression upon Ag presentation by anti-CTLA-4-Ab DCs. The induction of Foxp3 and IL-10 expression appeared to be a consequence of increased TGF-beta1 production by T cells activated using anti-CTLA-4-Ab DCs, and this effect could be enhanced by the addition of exogenous IL-2 or TGF-beta1. Collectively, this study demonstrates the potential of a DC-directed CTLA-4 engagement approach not only in treating autoimmunity in type 1 diabetes, but also in altering diabetogenic T cell function ex vivo for therapy.

Regulatory T cells and their molecular markers in peripheral blood of the patients with systemic lupus erythematosus

CD4(+)CD25(+) regulatory T cells (Tregs) and the expression of their molecular markers (GITR, Foxp3) in peripheral blood of the patients with systemic lupus erythematosus (SLE) were investigated in order to reveal the pathogenesis of SLE on the cellular and molecular levels. The level of Tregs in peripheral blood was detected by flow cytometry. The expression levels of GITR and Foxp3 mRNA in peripheral blood mononuclear cells (PBMCs) were assayed by reverse transcriptase-polymerase chain reaction (RT-PCR). The level of IL-6 in the plasma was measured by ELISA. Comparisons were made among 3 groups: the active SLE group, the inactive SLE group, and normal control group. The level of Tregs in the active SLE group and the inactive SLE group was significantly lower than in the normal control group (P<0.01). The level of Tregs in the active group was lower than in the inactive group with the difference being not significant (P>0.05). The level of Tregs in SLE patients was significantly negatively correlated with the disease active index in SLE (SLEDAI) (r=-0.81, P<0.01). The expression levels of GITR mRNA in PBMCs of the active SLE group and the inactive SLE group were significantly higher than in the normal control group (P<0.05), and those of Foxp3 mRNA in SLE patients of both active and inactive SLE groups were significantly lower than in the normal control group (P<0.05). There was no significant difference in the expression of GITR and Foxp3 mRNA between the active SLE group and inactive SLE group (P>0.05). The plasma levels of IL-6 in both the inactive SLE group and active SLE group were significantly higher than in the normal control group (P<0.01). The plasma level of IL-6 in the active SLE group was significantly increased as compared with that in the inactive SLE group (P<0.05), and the plasma level of IL-6 in SLE was significantly positively correlated with SLEDAI scores (r=0.58, P<0.01) and significantly negatively correlated with the ratio of CD4(+)CD25(+) cells/CD4(+) cells (r=-0.389, P<0.05). It was concluded that the levels of Tregs and Foxp3 mRNA in peripheral blood of SLE patients were decreased and the levels of GITR mRNA and plasma IL-6 were increased. The Tregs and their molecular markers GITR, Foxp3 as well as the plasma IL-6 might play an important role in the pathogenesis of SLE.

Preferential costimulation by CD80 results in IL-10-dependent TGF-beta1(+) -adaptive regulatory T cell generation

Costimulatory ligands CD80 and CD86 have different binding preferences and affinities to their receptors, CD28 and CTLA-4. Earlier, we demonstrated that CD80 binds to CTLA-4 with higher affinity and has a role in suppressing T cell response. The current study demonstrates that not only did blockade of CD86 upon Ag presentation by bone marrow-derived dendritic cells (DC) to OVA-specific T cells result in induction of hyporesponsive T cells but also that these T cells could suppress the proliferative response of effector T cells. These T cells showed TGF-beta1 on their surface and secreted TGF-beta1 and IL-10 upon restimulation. Although blockade of CTLA-4 and neutralization of IL-10 profoundly inhibited the induction of these TGF-beta1(+) T cells, their ability to suppress the effector T cell proliferation was abrogated by neutralization of TGF-beta1 alone. Induction of TGF-beta1(+) and IL-10(+) T cells was found to be independent of natural CD4(+)CD25(+) regulatory T cells, demonstrating that preferential ligation of CTLA-4 by CD80 induced IL-10 production by effector T cells, which in turn promoted the secretion of TGF-beta1. Treatment of prediabetic NOD mice with islet beta cell Ag-pulsed CD86(-/-) DCs, but not CD80(-/-) DCs, resulted in the induction of TGF-beta1- and IL-10-producing cells, significant suppression of insulitis, and delay of the onset of hyperglycemia. These observations demonstrate not only that CD80 preferentially binds to CTLA-4 but also that interaction during Ag presentation can result in IL-10-dependent TGF-beta1(+) regulatory T cell induction, reinstating the potential of approaches to preferentially engage CTLA-4 through CD80 during self-Ag presentation in suppressing autoimmunity.

Enhanced engagement of CTLA-4 induces antigen-specific CD4+CD25+Foxp3+ and CD4+CD25- TGF-beta 1+ adaptive regulatory T cells

CTLA-4 is a critical negative regulator of T cell response and is instrumental in maintaining immunological tolerance. In this article, we report that enhanced selective engagement of CTLA-4 on T cells by Ag-presenting dendritic cells resulted in the induction of Ag-specific CD4(+)CD25(+)Foxp3(+) and CD4(+)CD25(-)TGF-beta1(+) adaptive Tregs. These cells were CD62L(low) and hyporesponsive to stimulation with cognate Ag but demonstrated a superior ability to suppress Ag-specific effector T cell response compared with their CD62L(high) counterparts. Importantly, treatment of mice with autoimmune thyroiditis using mouse thyroglobulin (mTg)-pulsed anti-CTLA-4 agonistic Ab-coated DCs, which results in a dominant engagement of CTLA-4 upon self-Ag presentation, not only suppressed thyroiditis but also prevented reemergence of the disease upon rechallenge with mTg. Further, the disease suppression was associated with significantly reduced mTg-specific T cell and Ab responses. Collectively, our results showed an important role for selective CTLA-4 signaling in the induction of adaptive Tregs and suggested that approaches that allow dominant CTLA-4 engagement concomitant with Ag-specific TCR ligation can be used for targeted therapy.

Heme oxygenase-1 attenuates ovalbumin-induced airway inflammation by up-regulation of foxp3 T-regulatory cells, interleukin-10, and membrane-bound transforming growth factor- 1

Cumulative evidence suggests the up-regulation of interleukin (IL)-10 and T-regulatory (Treg) cells is implicated in anti-inflammatory effect of heme oxygenase-1 (HO-1). Thus, we postulated that induction of HO-1 could augment IL-10 and transforming growth factor (TGF)-beta production and foxp3+CD4+CD25+ Treg cell function, thereby leading to attenuation of airway inflammation. In this study, CD4+CD25+ Treg cells isolated from mouse spleen were either transfected with a HO-1 expression vector (pcDNA3HO-1) or treated with a HO-1 inducer (hemin). Up-regulation of HO-1 enhanced foxp3 expression and IL-10 secretion in the Treg cells in vitro. Next, BALB/c, C57/B6.129, and IL-10-deficient B6.129P2-Il10tm1Cgn/J mice were challenged by ovalbumin to induce airway inflammation. Consistent with in vitro findings, hemin treatment resulted in induction of HO-1 and foxp3 and production of IL-10 and membrane-bound TGF-beta1 in vivo. This was further correlated with decrease of ovalbumin-specific immunoglobulin E level and eosinophil infiltration in bronchial alveolar lavage fluid from the asthmatic mice. Furthermore, hemin significantly enhanced the biological activity of CD4+CD25+ Treg cells. This protective effect was specifically blocked by Sn-protoporphyrin, a HO-1 enzymatic inhibitor. Finally, hemin failed to up-regulate the function of CD4+CD25+ Treg cells from IL-10-deficient mice. Our study indicates that HO-1 exerts its protective effect on asthma through a mechanism mediated by foxp3+CD4+CD25+ Treg cells, IL-10, and membrane-bound TGF-beta1.

CTLA-4 and CD4+ CD25+ regulatory T cells inhibit protective immunity to filarial parasites in vivo

The T cell coinhibitory receptor CTLA-4 has been implicated in the down-regulation of T cell function that is a quintessential feature of chronic human filarial infections. In a laboratory model of filariasis, Litomosoides sigmodontis infection of susceptible BALB/c mice, we have previously shown that susceptibility is linked both to a CD4+ CD25+ regulatory T (Treg) cell response, and to the development of hyporesponsive CD4+ T cells at the infection site, the pleural cavity. We now provide evidence that L. sigmodontis infection drives the proliferation and activation of CD4+ Foxp3+ Treg cells in vivo, demonstrated by increased uptake of BrdU and increased expression of CTLA-4, Foxp3, GITR, and CD25 compared with naive controls. The greatest increases in CTLA-4 expression were, however, seen in the CD4+ Foxp3- effector T cell population which contained 78% of all CD4+ CTLA-4+ cells in the pleural cavity. Depletion of CD25+ cells from the pleural CD4+ T cell population did not increase their Ag-specific proliferative response in vitro, suggesting that their hyporesponsive phenotype is not directly mediated by CD4+ CD25+ Treg cells. Once infection had established, killing of adult parasites could be enhanced by neutralization of CTLA-4 in vivo, but only if performed in combination with the depletion of CD25+ Treg cells. This work suggests that during filarial infection CTLA-4 coinhibition and CD4+ CD25+ Treg cells form complementary components of immune regulation that inhibit protective immunity in vivo.

Prognostic factors related to clinical response in patients with metastatic melanoma treated by CTL-associated antigen-4 blockade

PURPOSE

CTL-associated antigen 4 (CTLA-4) can inhibit T-cell activation and helps maintain peripheral self-tolerance. Previously, we showed immune-related adverse events (IRAE) and objective, durable clinical responses in patients with metastatic melanoma treated with CTLA-4 blockade. We have now treated 139 patients in two trials and have sufficient follow-up to examine factors associated with clinical response.

EXPERIMENTAL DESIGN

A total of 139 patients with metastatic melanoma were treated: 54 patients received ipilimumab in conjunction with peptide vaccinations and 85 patients were treated with intra-patient dose escalation of ipilimumab and randomized to receive peptides in accordance with HLA-A*0201 status.

RESULTS

Three patients achieved complete responses (CR; ongoing at 29+, 52+, and 53+ months); an additional 20 patients achieved partial responses (PR) for an overall objective response rate of 17%. The majority of patients (62%, 86 of 139) developed some form of IRAE, which was associated with a greater probability of objective antitumor response (P = 0.0004); all patients with CR had more severe IRAEs. Prior therapy with IFNalpha-2b was a negative prognostic factor, whereas prior high-dose interleukin-2 did not significantly affect the probability of response. There were no significant differences in the rate of clinical response or development of IRAEs between the two trials. The duration of tumor response was not affected by the use of high-dose steroids for abrogation of treatment-related toxicities (P = 0.23). There were no treatment-related deaths.

CONCLUSION

In patients with metastatic melanoma, ipilimumab can induce durable objective clinical responses, which are related to the induction of IRAEs.

The importance of CTLA-4 polymorphism and human leukocyte antigen genotype for the induction of diabetes-associated cytokine response in healthy school children

BACKGROUND

Type 1 diabetes (T1D) is an autoimmune disease associated with the destruction of pancreatic beta cells and genetically linked to human leukocyte antigen (HLA) class II DR3-DQ2 and DR4-DQ8 haplotypes. The +49A/G polymorphism of the immunoregulatory cytotoxic T-lymphocyte antigen 4 (CTLA-4) gene is also associated with T1D. Genetic and environmental risk factors precede the onset of T1D, which is characterized by a T helper 1 cell-dominating cytokine response to diabetes-related autoantigens.

AIM

To investigate immunological differences between healthy children with and without CTLA-4 +49A/G and HLA genetic susceptibility for T1D.

STUDY DESIGN

Young, 7-15 years of age, healthy subjects (n = 58) were investigated to test whether CTLA-4 +49A/G genotype was associated with enzyme-linked immunospot assay T-cell responses to T1D-related autoantigens. Because T1D is primarily HLA-DQ associated, we stratified the healthy subjects by HLA genotypes associated with the disease.

RESULTS

Peptide of heat shock protein 60 induced a higher interferon-gamma (IFN-gamma) response in subjects with risk-associated CTLA-4 polymorphism (GG genotype) (p = 0.02) while glutamic acid decarboxylase 65-induced interleukin-4 (IL-4) secretion was lower in GG genotype subjects (p = 0.02).

CONCLUSION

The increased IFN-gamma response and lower IL-4 response toward diabetes-related autoantigens shown in CTLA-4 +49 GG risk subjects show a possible mechanism for the association between CTLA-4 and T1D.

Noncanonical NF-kappaB signaling in dendritic cells is required for indoleamine 2,3-dioxygenase (IDO) induction and immune regulation

Ligation of CD40 on dendritic cells (DCs) induces early production of inflammatory mediators via canonical NF-kappaB signaling, as well as late expression of the anti-inflammatory enzyme indoleamine 2,3-dioxygenase (IDO) via unknown signal transduction. By selective blocking of either the canonical NF-kappaB pathway using the NEMO-binding domain peptide or the noncanonical NF-kappaB pathway by small interfering RNA, we demonstrate that IDO expression requires noncanonical NF-kappaB signaling. Also, noncanonical NF-kappaB signaling down-regulates proinflammatory cytokine production in DCs. In addition, selective activation of the noncanonical NF-kappaB pathway results in noninflammatory DCs that suppress T-cell activation and promote the development of T cells with regulatory properties. These findings reveal an important role of the noncanonical NF-kappaB pathway in the regulation of immunity.

Allosuppressive Donor CD4+CD25+ Regulatory T Cells Detach from the Graft and Circulate in Recipients after Liver Transplantation

Organ transplantation (Tx) results in a transfer of donor leukocytes from the graft to the recipient, which can lead to chimerism and may promote tolerance. It remains unclear whether this tolerance involves donor-derived regulatory T cells (Tregs). In this study, we examined the presence and allosuppressive activity of CD4+CD25+Foxp3+ Tregs in perfusates of human liver grafts and monitored the cells presence in the circulation of recipients after liver Tx. Vascular perfusions of 22 liver grafts were performed with University of Wisconsin preservation and albumin solutions. Flow cytometric analysis revealed that perfusate T cells had high LFA-1 integrin expression and had a reversed CD4 to CD8 ratio compared with control blood of healthy individuals. These findings indicate that perfusate cells are of liver origin and not derived from residual donor blood. Further characterization of perfusate mononuclear cells showed an increased proportion of CD4+CD25+CTLA4+ T cells compared with healthy control blood. Increased percentages of Foxp3+ cells, which were negative for CD127, confirmed the enrichment of Tregs in perfusates. In MLR, CD4+CD25+ T cells from perfusates suppressed proliferation and IFN-gamma production of donor and recipient T cells. In vivo within the first weeks after Tx, up to 5% of CD4+CD25+CTLA4+ T cells in recipient blood were derived from the donor liver. In conclusion, a substantial number of donor Tregs detach from the liver graft during perfusion and continue to migrate into the recipient after Tx. These donor Tregs suppress the direct pathway alloresponses and may in vivo contribute to chimerism-associated tolerance early after liver Tx.

Pathological and clinical correlates of FOXP3+ cells in renal allografts during acute rejection

The localization and significance of regulatory T cells (Treg) in allograft rejection is of considerable clinical and immunological interest. We analyzed 80 human renal transplant biopsies (including seven donor biopsies) with a double immunohistochemical marker for the Treg transcription factor FOXP3, combined with a second marker for CD4 or CD8. Quantitative FOXP3 cell counts were performed and analyzed for clinical and pathologic correlates. FOXP3(+) cells were present in the interstitium in acute cellular rejection (ACR) type I and II, at a greater density than in acute humoral rejection or CNI toxicity (p < 0.01). Most FOXP3(+) cells were CD4(+) (96%); a minority expressed CD8. FOXP3(+)CD4(+) cells were concentrated in the tubules (p < 0.001), suggesting a selective attraction or generation at that site. Considering only patients with ACR, a higher density of FOXP3(+) correlated with HLA class II match (p = 0.03), but paradoxically with worse graft survival. We conclude that infiltration of FOXP3(+) cells occurs in ACR to a greater degree than in humoral rejection, however, within the ACR group, no beneficial effect on outcome was evident. Tregs concentrate in tubules, probably contributing to FOXP3 mRNA in urine; the significance and pathogenesis of 'Treg tubulitis' remains to be determined.

Protective Regulatory T Cell Generation in Autoimmune Diabetes by DNA Covaccination with Islet Antigens and a Selective CTLA-4 Ligand

DNA vaccination of autoimmune diabetes-prone NOD mice with unmodified target islet antigens, i.e., preproinsulin (PPIns) or glutamic acid decarboxylase 65 (GAD65), is poorly protective. However, in this study, we demonstrate protection against disease by covaccination with a mutant B7-1 molecule (B7-1wa) that binds the negative T cell regulator CTLA-4 (CD152), but not CD28. Codelivery of plasmids encoding a PPIns-GAD65 fusion construct and B7-1wa protected against both insulitis and diabetes. In vitro, the T cells of covaccinated mice had negative responses to both insulin and GAD65, and this was restored by adding blocking antibodies to transforming growth factor beta1 (TGF-beta1), suggesting a role for this cytokine. Adoptive transfer experiments revealed that DNA vaccination generated protective CD4(+) regulatory T cells (Tr) of either CD25(+) or CD25(-) phenotype. Furthermore, vaccinated mice had increased numbers of T cells with Tr-associated markers, such as CTLA-4, Foxp3, and membrane-bound TGF-beta1. Tr cells inhibited the responses of diabetogenic T cells to islet antigens, and depletion of T cells expressing membrane-bound TGF-beta1 abolished the suppressive effect. Thus, selective engagement of CTLA-4 during islet-antigen DNA vaccination induces Tr cells that protect against this autoimmune disease.

The role of TGF-beta in allergic inflammation

The transforming growth factor beta (TGF-beta) plays a dual role in allergic disease. It is important in suppressing T cells and also mediates repair responses that lead to unwanted remodeling of tissues. Advances in the immunology of allergy indicate that allergens cause overreactions in the lymphocyte compartment because of the lack or decreased number of suppressive, regulatory T cells. TGF-beta was shown to induce regulatory T cells and participate directly in suppression of effector T cells. Therefore, TGF-beta may help return reactivity to allergens to normal subsymptomatic activity. Whether chronic inflammatory diseases such as asthma profit from TGF-beta-mediated suppression of specific immune responses or whether the TGF-beta-mediated tissue remodeling aggravates diseases more than it helps control immune reactions is unclear. This article addresses these issues and future strategies in this field.

Function of tumor necrosis factor receptor family members on regulatory T-cells

Effector cells play a crucial role in the immune system of higher vertebrates in eliminating invading pathogens and transformed cells that could cause disease or death of the individual. To be effective and specific, immune responses have to distinguish between self and nonself. Mechanisms of central and peripheral tolerance have evolved to control effector cells that could respond to autoantigens. Regulatory T-cells (Treg cells) are critical modulators of effector cells in the periphery that suppress autoreactive T-cells but are also involved in modulating immune responses against invading pathogens. Identification of surface markers of Treg cells and the development of in vitro systems to study the suppressive function of Treg cells have revealed distinct phenotypic and functional subsets of Treg cells. Several tumor necrosis factor receptor (TNFR) family members have been shown to play a role in the development, homeostasis, and suppressor function of Treg cells. Recent findings suggest that TNFRs and other cell-surface molecules of Treg cells can be explored for therapeutic strategies targeting autoimmune disorders, cancer, and immune responses against pathogens.

CTLA-4 blockade decreases TGF-beta, IDO, and viral RNA expression in tissues of SIVmac251-infected macaques

Regulatory T (T(reg)) cells are a subset of CD25(+)CD4(+) T cells that constitutively express high levels of cytotoxic T lymphocyte antigen-4 (CTLA-4) and suppress T-cell activation and effector functions. T(reg) cells are increased in tissues of individuals infected with HIV-1 and macaques infected with simian immunodeficiency virus (SIV(mac251)). In HIV-1 infection, T(reg) cells could exert contrasting effects: they may limit viral replication by decreasing immune activation, or they may increase viral replication by suppressing virusspecific immune response. Thus, the outcome of blocking T(reg) function in HIV/SIV should be empirically tested. Here, we demonstrate that CD25(+) T cells inhibit virus-specific T-cell responses in cultured T cells from blood and lymph nodes of SIV-infected macaques. We investigated the impact of CTLA-4 blockade using the anti-CTLA-4 human antibody MDX-010 in SIV-infected macaques treated with antiretroviral therapy (ART). CTLA-4 blockade decreased expression of the tryptophan-depleting enzyme IDO and the level of the suppressive cytokine transforming growth factor-beta (TGF-beta) in tissues. CTLA-4 blockade was associated with decreased viral RNA levels in lymph nodes and an increase in the effector function of both SIV-specific CD4(+) and CD8(+) T cells. Therefore, blunting T(reg) function in macaques infected with SIV did not have detrimental virologic effects and may provide a valuable approach to complement ART and therapeutic vaccination in the treatment of HIV-1 infection.

TGF-beta requires CTLA-4 early after T cell activation to induce FoxP3 and generate adaptive CD4+CD25+ regulatory cells

Although positive CD28 costimulation is needed for the generation of natural CD4+CD25+ regulatory T cells, we report that negative CTLA-4 costimulation is necessary for generating phenotypically and functionally similar adaptive CD4+CD25+ suppressor cells. TGF-beta could not induce CD4+CD25- cells from CTLA-4(-/-) mice to express normal levels of FoxP3 or to develop suppressor activity. Moreover, blockade of CTLA-4 following activation of wild-type CD4+ cells abolished the ability of TGF-beta to induce FoxP3-expressing mouse suppressor cells. TGF-beta accelerated expression of CTLA-4, and time course studies suggested that CTLA-4 ligation of CD80 shortly after T cell activation enables TGF-beta to induce CD4+CD25- cells to express FoxP3 and develop suppressor activity. TGF-beta also enhanced CD4+ cell expression of CD80. Thus, CTLA-4 has an essential role in the generation of acquired CD4+CD25+ suppressor cells in addition to its other inhibitory effects. Although natural CD4+CD25+ cells develop normally in CTLA-4(-/-) mice, the lack of TGF-beta-induced, peripheral CD4+CD25+ suppressor cells in these mice may contribute to their rapid demise.

Thymocyte/Splenocyte-Derived CD4+CD25+Treg Stimulated by Anti-CD200R2 Derived Dendritic Cells Suppress Mixed Leukocyte Cultures and Skin Graft Rejection

BACKGROUND

CD200 delivers immunoregulatory signals following engagement of its receptor, CD200R. A family of CD200Rs (CD200R1-4) has been described. Spleen expresses cell surface CD200R1, while bone marrow shows predominantly expression of cell surface CD200R2/R3. We showed that dendritic cell precursors (DCp) cultured with anti-CD200R2/3 develop the capacity to induce CD4(+)CD25(+) regulatory T cells (Treg) from peripheral lymphocytes. We now characterize DCs involved in induction of antigen-specific Treg from thymocytes or peripheral T cells, and the properties of Treg cells maintained in long-term culture.

METHODS

Bone marrow DCp (C3H or BL/6 origin) were cultured for 8 days with GMCSF, IL-4 and anti-CD200R2, or with CD200Fc and a previously described peptide inhibitor of CD200R1 to allow preferential engagement of non-CD200R1 receptors by CD200. Mixed leukocyte cultures (MLCs) were initiated with allogeneic responder lymphocytes/thymocytes (BL/6 or C3H) and mitomycin-c treated DCs to induce Treg. Treg cells were maintained by reculture with DCs derived in the same manner and IL-2, cloned at limiting dilution, and tested for their ability to suppress MLCs and skin graft rejection in vivo.

RESULTS

Foxp3(+) CD4(+)CD25(+) Treg were derived from 60-hr thymocyte and splenocyte T cell cultures using both DC populations. Cloned C3H Treg (Foxp3(+)) suppressed both C3H anti-BL/6 reactivity in a fresh MLC and rejection of BL/6 skin allografts in C3H recipients; the converse was true for BL/6 Treg.

CONCLUSIONS

We conclude that CD200 triggering of bone-marrow DCs in the absence of CD200R1 engagement induces CD4(+)CD25(+) Treg, and these cloned antigen-specific Treg may have clinical utility.

New insights into the mechanisms of allergen-specific immunotherapy

PURPOSE OF REVIEW

Specific immunotherapy represents the only curative treatment of a specific allergy, and is therefore of great interest in terms of immunological mechanisms and therapeutic developments.

RECENT FINDINGS

Allergen-specific regulatory T cells are induced after the initiation of specific immunotherapy, and are assumed to suppress effector T cells directly mediating allergic inflammation. Therefore regulatory T cells may play a key role in the re-induction of allergen tolerance. Multiple pathways in many systems are described to promote or enhance regulatory T cells. This review summarizes the current view on immunological mechanisms leading to and coming from regulatory T cells.

SUMMARY

The highlighted mechanisms may not only contribute to improved specific immunotherapy, but also give insight into a clinically relevant therapy targeting regulatory T cells. The approach of addressing endogenous regulatory mechanisms specifically controlling inflammation instead of targeting inflammation itself is relevant for future pharmacological developments.

The role of the FOXP3 transcription factor in the immune regulation of allergic asthma

Unbalanced immune reactions against allergens are caused by Th2 cells, which are the basis of immunoglobulin E (IgE)-mediated symptoms of allergy and asthma. Although Th2 cells are essential for allergy, they are not sufficient to cause disease, because regulatory T cells (Tregs) control their activity and expansion. Therefore, Tregs are assumed to play an important role not only in the sensitization but also in established allergic disease under therapy. A key factor of Tregs is FOXP3, which, upon expression, is sufficient to induce regulatory T-cell phenotypes. The initiation and suppressive function of FOXP3 and Tregs in the context of allergic asthma are discussed in this review.

A mutant B7-1/Ig fusion protein that selectively binds to CTLA-4 ameliorates anti-tumor DNA vaccination and counters regulatory T cell activity

We have shown that a plasmid encoding a B7-1/Ig fusion protein enhanced DNA vaccination against human carcinoembryonic antigen (CEA) more effectively than the plasmid encoding membrane-bound B7-1. However, it was not known if B7-1/Ig acted only by binding CD28 (amplifying a stimulatory signal) or by blocking CTLA-4 on T cells (removing inhibitory signals). Here, we aimed to determine this using a plasmid encoding mutant B7-1/Ig (B7-1wa/Ig), which binds only to CTLA-4 but not to CD28. Our results showed that both the B7-1/Ig and B7-1wa/Ig plasmids, when co-administered with a CEA plasmid, enhanced tumor rejection and the in vitro anti-CEA response. Therefore, B7-1wa/Ig ameliorates DNA vaccination, presumably by binding to CTLA-4. This could result from a number of non-exclusive mechanisms, such as a reduced threshold for T-cell activation, or blockade of CTLA-4/B7-mediated tolerogenic signals in DCs or T cells. We found that, in vitro, a significant fraction of CD3/CD28-activated T cells (in the absence of DCs) expressed CTLA-4 and B7-1. Primed T cells of CTLA-4(+)B7-1(+/-) phenotype acted as regulatory T cells by inhibiting IFNgamma production by re-stimulated CTLA-4(-)B7-1(-) cells, and this was reversed by antibodies against IL-10 or TGF-beta1. Both B7-1wa/Ig and CTLA-4/Ig, which bind to CTLA-4 and B7-1/B7-2 respectively, enhanced IFNgamma production, but not the proliferation or IL-4 release in mixed T-cell populations containing these two cell types. In contrast, CTLA-4(-)B7-1(-) T cells produced IFNgamma which was not affected by B7-1wa/Ig or CTLA-4/Ig. These results suggest that blocking of CTLA-4/B7-1 binding in T cell/T cell interactions blocks negative regulatory signals. This might be the mechanism, at least in part, of the enhancement of anti-tumor immunity by the B7-1wa/Ig and B7-1/Ig plasmids.