CD28/CTLA-4/B7 and CD40/CD40L costimulation and activation of regulatory T cells

Costimulatory signals are crucial for T cell activation. Attempts to block costimulatory pathways have been effective in preventing unwanted immune reactions. In particular, blocking the CD28/cytotoxic T lymphocyte antigen(CTLA)-4/B7 interaction(using CTLA-4Ig) and the CD40/CD40 L interaction(using anti-CD40 L antibodies) prevents T cell mediated autoimmune diseases, transplant rejection and graft vs host disease in experimental models. Moreover, CTLA-4Ig is in clinical use to treat rheumatoid arthritis(abatacept) and to prevent rejection of renal transplants(belatacept). Under certain experimental conditions, this treatment can even result in tolerance. Surprisingly, the underlying mechanisms of immune modulation are still not completely understood. We here discuss the evidence that costimulation blockade differentially affects effector T cells(Teff) and regulatory T cells(Treg). The latter are required to control inappropriate and unwanted immune responses, and their activity often contributes to tolerance induction and maintenance. Unfortunately, our knowledge on the costimulatory requirements of Treg cells is very limited. We therefore summarize the current understanding ofthe costimulatory requirements of Treg cells, and elaborate on the effect of anti-CD40 L antibody and CTLA-4Ig treatment on Treg cell activity. In this context, we point out that the outcome of a treatment aiming at blocking the CD28/CTLA-4/B7 costimulatory interaction can vary with dosing, timing and underlying immunopathology.

Intracellular Signals of T Cell Costimulation

Ligation of T cell receptor （TCR） alone is insufficient to induce full activation of T lymphocytes. Additional ligand-receptor interactions （costimulation） on antigen presenting cells （APCs） and T cells are required. T cell costimulation has been shown to be essential for eliciting efficient T cell responses, involving all phases during T cell development. However, the mechanisms by which costimulation affects the function of T cells still need to be elucidated. In recent years, advances have been made in studies of costimulation as potential therapies in cancer, infectious disease as well as autoimmune disease. In this review, we discussed intracellular costimulation signals that regulate T cell proliferation, cell cycle progression, cytokine production, survival, and memory development. In general, the pathway of phosphoinositide-3 kinase （PI3K）/protein kinase B （PKB, also known as Akt）/nuclear factor κB （NF-κB） might be central to many costimulatory effects. Through these pathways, costimulation controls T-cell expansion and proliferation by maintenance of survivin and aurora B expression, and sustains long-term T-cell survival and memory development by regulating the expression of bcl-2 family members. Cellular ＆ Molecular Immunology. 2008;5（4）：239-247.

Costimulatory blockade:A novel approach to the treatment of glomerular disease?

Costimulatory pathways(Cluster of differentiation 28,tumor necrosis factor-related,adhesion and T Cell Ig-and mucin-domain molecules) regulating the interactions between receptors on the T cells andtheir ligands expressed on several cell types,have a key role in controlling many immunological and non immunological processes.Indeed,accumulating evidence indicate that these molecules are involved in the pathogenesis of numerous conditions,such as allograft rejection,atherosclerosis,rheumatoid arthritis,psoriasis and renal diseases,including glomerulonephritis.Primary or secondary(i.e.,associated with infections,drugs or systemic diseases,such as systemic lupus erythematosus,diabetes,etc.) glomerulonephritis represent a group of heterogeneous diseases with different pathogenic mechanisms.Since costimulatory molecules,in particular CD80 and CD40,have been found to be expressed on podocytes in the course of different experimental and clinical glomerulonephritis,costimulation has been thought as a new therapeutic target for patients with glomerular diseases.However,although experimental data suggested that the blockade of costimulatory pathways is effective and safe in the prevention and treatment of glomerular diseases,clinical trials reported contrasting results.So,at this moment,there is not a strong evidence for the general use of costimulatory blockade as an alternative treatment strategy in patients with primary or secondary glomerulonephritis.Here,we critically discuss the current data and the main issues regarding the development of this innovative therapeutic approach.

THE ROLE OF VCAM-1/VLA-4 IN THE ACTIVATION OF ALLOGENIC T CELLS BY MURINE MACROPHAGES

This work was supported by grants from the National Natural Science Foundation of China.No. (39730420). ** To whom requests for reprints should be addressed.This is one of papers of the special issue on gene therapy research (Chin J Cancer Res Vol. 9 No. 4 December, 1997). Vascular cell adhesion molecule 1 (VCAM 1) is a member of immunoglobulin superfamily. The principal ligand for VCAM 1 is integrin α4β1/VLA 4 (very late antigen 4). It was reported that VCAM 1 was expressed on macrophages and dendritic cells, but little is known about its function on these professional antigen pre senting cells (APC). The present study was performed to investigate the expression of VCAM 1 on macrophages and the role of VCAM 1/VLA 4 in the activation of allogenic T cells by murine macrophages. We analyzed VCAM 1 expression on peritoneal macrophages and macrophage cell line J774A.1 by fluorescence activated cell sorting (FACS). Using neutralizing antibodies, we further analyzed the role of VCAM 1/VLA 4 interaction in macrophage and allogenic T cell mixed lymphocyte reaction (MLR). We found that VCAM 1 was consti tutively expressed on macrophages and its expression level was upregulated by soluble tumor associated antigen (freeze thaw lysates of FBL 3 leukemia cells) and TNF α. In MLR assays, we observed that blocking VCAM 1/VLA 4 interaction with anti VCAM 1 or anti VLA 4 mAbs caused significant inhibition of the proliferative response and IL 2 production. These results suggest that VCAM 1on macrophages not only facilitates the cell to cell contact through adhesive interaction but also plays a role in the costimulation of T cells via its interaction with VLA 4 on the T cells.

Establishment of hepatocarcinoma cell line transfected by the B7 gene and its biocharacteristics

OBJECTIVE: To study the function of costimulation sign in tumor immunology and construct the new cell line B7^+ Smmc7721. METHODS: The B7 gene was transfected into the hepatocarcinoma cell Smmc7721 by liposma. Polymerase chain reaction (PCR) and reverse transcriptase-PCR (RT-PCR) were applied to test the result. MTT colorimetric assay was used to value the killing effect of lymphokine activated killer cells (LAK) activated by IL-2 on the transfected cell line and the original line. RESULT: B7^+ Smmc7721 was improved to be steadily expressed B7 molecule and LAK cells could more effectively act on the B7^+ Smmc7721 cells. CONCLUSION: The B7 gene can be transfected to hepatocarcinoma cells and can be expressed steadily in vitro, thus increasing the efficiency of LAK cells activated by IL-2 on them.

Immunological Intolerance and Tolerance by Antigenic Co-Stimulation

The plasticity and dynamism in the immune responses to both self and environmental stimulation promote the maintenance and adaptation of a system that tends to harmoniously survive and evolve. Fluctuating antigenic forces coexist within the immune system and oscillate between order and chaos to the equilibrium. Thus, when mounting a response to internal or environmental antigens, the main host responses can be divided into two immunological categories. The first, a well-adapted mechanism of complex multi-cellular organisms classically known as tolerance, promotes persistent immunological responses. In the second, opposite way, the modulation of inflammatory immune responses occurs, which we call “intolerance”. Tolerance and intolerance can be mediated by humoral molecules, such as inflammatory compounds, complement, and antibodies, and by different cell types, such as sentinel cells, antigen-presenting cells, and cells that orchestrate the immune response. Tolerogenesis is important in vertebrates because it predisposes species to adapt to self and environmental negative-selective forces. This process depends, in large part, on antigenic co-stimulation (AgCS), which operates as a multi-integrated network formed by all immune and non-immune cells of the body that establishes tolerant immunoregulatory interactions from cells to cells and from cells to the environment. Antigenic distribution, quantity, nature, route of administration, and antigenic convergence on co-stimulatory pathways, and concurrent infections, and the presence of microorganisms (commensals and pathogens) in more than one site are important factors for activating AgCS. To conclude, the AgCS route is a natural immune response generated by heterogeneous APC profile with centralized regulation that promote the counterbalance between intolerant e tolerant status, which can have several applications in the medical and biological fields.

Ribavirin contributes to eradicate hepatitis C virus through polarization of T helper 1/2 cell balance into T helper 1 dominance

The mechanism of action of ribavirin(RBV) as an immunomodulatory and antiviral agent and its clinical significance in the future treatment of patients with hepatitis C virus(HCV) infection are reviewed.RBV up-regulates type 1 and/or 2 cytokines to modulate the T helper(Th) 1/2 cell balance to Th1 dominance.Examination of co-stimulatory signaling indicated that RBV down-modulates inducible co-stimulator on Th cells,which contributes to differentiating na?ve Th cells into Th2 cells while reducing their interleukin-10 production.The effects on T-regulatory(Treg) cells were also investigated,and RBV inhibited the differentiation of na?ve Th cells into adaptive Treg cells by downmodulating forkhead box-P3.These findings indicate that RBV mainly down-regulates the activity of Th2 cells,resulting in the maintenance of Th1 activity that contributes to abrogating HCV-infected hepatocytes.Although an interferon-free treatment regimen exhibits almost the same efficacy without serious complications,regimens with RBV will be still be used because of their ability to facilitate the cellular immune response,which may contribute to reducing the development of hepatocellular carcinogenesis in patients infected with HCV.

CD4^(+)T cells produce IFN-I to license cDC1s for induction of cytotoxic T-cell activity in human tumors

CD4^(+)T cells can"help"or"license" conventional type 1 dendritic cells(cDC1s)to induce CD8^(+)cytotoxic T lymphocyte(CTL)anticancer responses,as proven in mouse models.We recently identified cDC1s with a transcriptomic imprint of CD4^(+)T-cell help,specifically in T-cell-infiltrated human cancers,and these cells were associated with a good prognosis and response to PD-1-targeting immunotherapy.Here,we delineate the mechanism of cDC1 licensing by CD4^(+)T cells in humans.Activated CD4^(+)T cells produce IFNβvia the STING pathway,which promotes MHC-I antigen(cross-)presentation by cDC1s and thereby improves their ability to induce CTL anticancer responses.In cooperation with CD40 ligand(L),IFNβalso optimizes the costimulatory and other functions of cDC1s required for CTL response induction.IFN-I-producing CD4^(+)T cells are present in diverse T-cell-infiltrated cancers and likely deliver“help”signals to CTLs locally,according to their transcriptomic profile and colocalization with“helped/licensed”cDCs and tumor-reactive CD8^(+)T cells.In agreement with this scenario,the presence of IFN-I-producing CD4^(+)T cells in the TME is associated with overall survival and the response to PD-1 checkpoint blockade in cancer patients.

Understanding the development and function of T follicular helper cells

A fundamental function of T helper(Th)cells is to regulate B-cell proliferation and immunoglobulin class switching,especially in the germinal centers.Th1 and Th2 lineages of CD41 T cells have long been considered to play an essential role in helping B cells by promoting the production immunoglobulin G2a(IgG2a)and IgG1/IgE,respectively.Recently,it has become clear that a subset CD41 T cells,named T follicular helper(Tfh)cells,is critical to B-cell response induction.In this review,we summarize the latest advances in our understanding of the regulation of Tfh cell differentiation,the relationship of Tfh cells to other CD41 T-cell lineages,and the role of Tfh cells in health and disease.

T Lymphocyte Co-Signaling Pathways of the B7-CD28 Family

The past years have witnessed significant advance in our understanding of critical roles of T cell co-signals in B7-CD28 family molecules in regulating T cell activation and tolerance.New co-signaling molecules have been identified and their functions have been delineated.These co-signaling pathways play overlapping and distinct regulatory roles at various stages of a T cell response.By expressing in appropriate time and location,these pathways have different regulatory functions through independent receptors or on different subsets of lymphocytes.Precise understanding of these pathways will allow the development of novel approaches to treatment of human diseases such as cancer,viral infection,autoimmune diseases and transplantation rejection. Cellular & Molecular Immunology.2004;1(1):37-42.

Keratinocytes costimulate naive human T cells via CD2: a potential target to prevent the development of proinflammatory Th1 cells in the skin

The interplay between keratinocytes and immune cells,especially T cells,plays an important role in the pathogenesis of chronic inflammatory skin diseases.During psoriasis,keratinocytes attract T cells by releasing chemokines,while skin-infiltrating selfreactive T cells secrete proinflammatory cytokines,e.g.,IFN γand IL-17A,that cause epidermal hyperplasia.Similarly,in chronic graftversus-host disease,allogenic IFN γ-producing Th1/Tc1 and IL-17-producing Th17/Tc17 cells are recruited by keratinocyte-derived chemokines and accumulate in the skin.However,whether keratinocytes act as nonprofessional antigen-presenting cells to directly activate naive human T cells in the epidermis remains unknown.Here,we demonstrate that under proinflammatory conditions,primary human keratinocytes indeed activate naive human T cells.This activation required cell contact and costimulatory signaling via CD58/CD2 and CD54/LFA-1.Naive T cells costimulated by keratinocytes selectively differentiated into Th1 and Th17 cells.In particular,keratinocyte-initiated Th1 differentiation was dependent on costimulation through CD58/CD2.The latter molecule initiated STAT1 signaling and IFN γproduction in T cells.Costimulation of T cells by keratinocytes resulting in Th1 and Th17 differentiation represents a new explanation for the local enrichment of Th1 and Th17 cells in the skin of patients with a chronic inflammatory skin disease.Consequently,local interference with T cell–keratinocyte interactions may represent a novel strategy for the treatment of Th1 and Th17 cell-driven skin diseases.

OX40 mRNA in peripheral blood as a biomarker of acute renal allograft rejection

Background Acute rejection remains an important cause of renal allograft dysfunction and the need for accurate diagnosis is essential to successfully treat transplant recipients. The purpose of this study was to determine the costimulatory molecules OX40 and OX40L messenger RNA （mRNA） levels in peripheral blood mononuclear cells （PBMCs） to predict acute renal transplant rejection.

The intragraft vascularized bone marrow component plays a critical role in tolerance induction after reconstructive transplantation

The role of the vascularized bone marrow component as a continuous source of donor-derived hematopoietic stem cells that facilitate tolerance induction of vascularized composite allografts is not completely understood.In this study,vascularized composite tissue allograft transplantation outcomes between recipients receiving either conventional bone marrow transplantation(CBMT)or vascularized bone marrow(VBM)transplantation from Balb/c(H2d)to C57BL/6(H2b)mice were compared.Either high-or low-dose CBMT(1.5×10^(8)or 3×10^(7)bone marrow cells,respectively)was applied.In addition,recipients were treated with costimulation blockade(1 mg anti-CD154 and 0.5 mg CTLA4Ig on postoperative days 0 and 2,respectively)and short-term rapamycin(3 mg/kg/day for the first posttransplant week and then every other day for another 3 weeks).Similar to high-dose conventional bone marrow transplantation,5/6 animals in the vascularized bone marrow group demonstrated long-term allograft survival(>120 days).In contrast,significantly shorter median survival was noted in the low-dose CBMT group(~64 days).Consistently high chimerism levels were observed in the VBM transplantation group.Notably,low levels of circulating CD4^(+)and CD8^(+)T cells and a higher ratio of Treg to Teff cells were maintained in VBM transplantation and high-dose CBMT recipients(>30 days)but not in low-dose VBM transplant recipients.Donor-specific hyporesponsiveness was shown in tolerant recipients in vitro.Removal of the vascularized bone marrow component after secondary donor-specific skin transplantation did not affect either primary allograft or secondary skin graft survival.

CD28 ligation increases macrophage suppression of T-cell proliferation

When compared to spleen or lymph node cells, resident peritoneal cavity cells respond poorly to T-cell activation in vitro. The greater proportional representation of macrophages in this cell source has been shown to actively suppress the T-cell response. Peritoneal macrophages exhibit an immature phenotype （MHC class IIlo, B7lo） that reduces their efficacy as antigen-presenting cells. Furthermore, these cells readily express inducible nitric oxide synthase （iNOS）, an enzyme that promotes T-cell tolerance by catabolism of the limiting amino acid arginine. Here, we investigate the ability of exogenous T-cell costimulation to recover the peritoneal T-cell response. We show that CD28 ligation failed to recover the peritoneal T-cell response and actually suppressed responses that had been recovered by inhibiting iNOS. As indicated by cytokine ELISpot and neutralizing monoclonal antibody （mAb） treatment, this ＇cosuppression＇ response was due to CD28 ligation increasing the number of interferon （IFN）-y-secreting cells. Our results illustrate that cellular composition and cytokine milieu influence T-cell costimulation biology.

Responses to LPS boost effector CD8 T-cell accumulation ）utside of signals 1 and 2

Immunization with adjuvant plus antigen induces durable T-cell immunity and is a mainstay of vaccines. Here, the consequence of separating antigen stimulation of T cells from the adjuvant response was studied in a re-transfer model. Effector CD8 T cells in recipient mice were exposed to lipopolysaccharide （LPS）, the Toll-like receptor 4 （TLR4） ligand, which significantly increased persistence. While accumulation in lymphoid and non-lymphoid organs was evident, this result depended upon the timing of LPS administration and the presence of the TLR4 adaptor TRIF in the recipient mice. Interestingly, there was very little impact of the LPS response on subset differentiation, which rather appeared to be programmed by antigen and costimulation. To discern factors that limit accumulation, interleukin 10 （IL-IO） was targeted since it is a product of TLR4 triggering and mitigates inflammation. Blockade of IL-IO increased accumulation even though the effector CD8 T cells were well past the priming phase, but upon recall interferon-y secretion was not affected as would be expected when IL-IO is present during priming. Thus, the adjuvant-altered microenvironment is effective not only in the presence of antigen but also during a window of effector CD8 T-cell stasis, suggesting that pathogen-associated molecular pattern molecules released during co-infection, oT by vaccines, could alter the survival fate of specific effector T cells.

Chronic activation of 4-1BB signaling induces granuloma development in tumor-draining lymph nodes that is detrimental to subsequent CD8^(+)T cell responses

The antitumor capabilities of agonistic anti-4-1BB mAbs have made them an attractive target for tumor immunotherapy.However,the adverse side effects associated with agonist antibodies have hindered their clinical development.Here,we aimed to study the immune-related adverse events of repeated doses and long-term use of agonistic anti-4-1BB mAbs.We show that chronic activation of 4-1BB signals induced the accumulation of IFN-γ-producing PD-1^(+)CD8^(+)T cells in the secondary lymphoid organs of tumor-bearing mice by increasing the number of dividing CD8^(+)T cells,which was beneficial for suppressing tumor growth in the early phase of anti-4-1BB induction.However,repeated exposure to anti-4-1BB mAbs led to granuloma development in tumor-draining lymph nodes(TDLNs)of mice due to recruitment and accumulation of macrophages via the CD8^(+)T cell-IFN-γaxis.This was accompanied by excessive lymph node swelling,which impaired the sequential activation of CD8^(+)T cells.Our data provide insights into the immune-related adverse events of long-term agonist 4-1BB antibody dosing,which should be considered during the clinical development of immunomodulating therapy.

Repressor of GATA-3 can negatively regulate the expression of T cell cytokines through modulation on inducible costimulator

Background The transcription factor, repressor of GATA-3 （ROG）, can simultaneously suppress the expression of T helper cells （Thl and Th2） cytokines. Since the suppression of Th2 cytokines by GATA-3 is well understood, it is postulated that there are other molecular targets of ROG that can suppress the expression of the Thl cytokines. We hypothesized that ROG might suppress the stimulators of T lymphocyte cytokines such as CD3, CD28, and inducible costimulator （ICOS）, or indirectly enhance the expression of cytokine suppressors such as T lymphocyte-associated antigen-4 （CTLA-4） and CD45. The objective of this study was to clarify the molecular targets of ROG involved in suppressing Thl or Th2 cytokines. Methods Real-time quantitative PCR （RT-PCR） and Western blotting were performed to evaluate the mRNA and protein levels of CD3, CD28, ICOS, CTLA-4, and CD45 in Thl and Th2 cells during various levels of ROG expression. Enzyme-linked immunosorbent assay （ELISA） was used to measure the levels of interferon-y （IFN-y） and intedeukin （IL）-4 in culture media of Thl and Th2 cells. Results The results showed that the mRNA and protein levels of ROG were relatively low in Thl and Th2 cells （P 〈0.01）. After ROG-pcDNA3.1 transfection, the mRNA and protein level of ROG was significantly elevated, while the expression of ICOS, IFN-y, and IL-4 was markedly down-regulated （P 〈0.01）. Conversely, transfection of ROG-siRNA led to inhibition of ROG expression and up-regulation of ICOS, IFN-y and IL-4 （P 〈0.01）. However, the expression levels of CD3, CD28, CTLA-4 and CD45 did not change in either ROG-pcDNA3.1 or ROG-siRNA-transfected Thl and Th2 cells （P 〉0.05）. Conclusion It is concluded that ROG can inhibit the expression of Thl and Th2 cytokines by down-regulating the expression of ICOS, which might be a potential molecular target for asthma treatment.

The Inhibitory Effects of Mouse ICOS-Ig Gene-Modified Mouse Dendritic Cells on T Cells

The main approach to reduce graft rejection has been focused on the development of immunosuppressive agents at present.Although these strategies have reportedly reduced graft rejection,there has been a reciprocal increase in more severe immunosuppression and lethal infections,as well as severe side effects.Blockade of costimulatory T cell response has been proved as one of useful strategies to reduce graft rejection.Furthermore, it has been shown that infusion of dendritic cells(DCs)with a potent negative regulatory ability for T cells could prolong allograft survival.In this study mouse DCs(mDCs)were transfected with the recombinant plasmid pcDNA3.0 containing mouse inducible costimulator-Ig(mICOS-Ig) cDNA by electroporation.The transient expression of mICOS-Ig in mDC could be detected by ELISA and SDS-PAGE.Mouse ICOS-Ig fusion protein expressed in mDC and mICOS-Ig gene-modified mDC could inhibit lymphocyte proliferation in mixed lymphocyte culture(MLC)in vitro.Furthermore,mICOS-Ig gene-modified mDC could inhibit lymphocyte proliferation in recipient mice.These results suggested that mICOS-Ig gene-modified mDC exerted inhibitory effects on T cells,and might be suitable for treatment or prevention of graft rejection and immunopathologic diseases.Cellular & Molecular Immunology.2004;1(2):153-157.