T cell costimulatory blockade: new therapies for transplant rejection

T-cell Exhaustion in Organ Transplantation

Exhaustion of T cells occurs in response to long-term exposure to self and foreign antigens. It limits T cell capacity to proliferate and produce cytokines, leading to an impaired ability to clear chronic infections or eradicate tumors. T-cell exhaustion is associated with a specific transcriptional, epigenetic, and metabolic program and characteristic cell surface markers' expression. Recent studies have begun to elucidate the role of T-cell exhaustion in transplant. Higher levels of exhausted T cells have been associated with better graft function in kidney transplant recipients. In contrast, reinvigorating exhausted T cells by immune checkpoint blockade therapies, while promoting tumor clearance, increases the risk of acute rejection. Lymphocyte depletion and high alloantigen load have been identified as major drivers of T-cell exhaustion. This could account, at least in part, for the reduced rates of acute rejection in organ transplant recipients induced with thymoglobulin and for the pro-tolerogenic effects of a large organ such as the liver. Among the drugs that are widely used for maintenance immunosuppression, calcineurin inhibitors have a contrasting inhibitory effect on exhaustion of T cells, while the influence of mTOR inhibitors is still unclear. Harnessing or encouraging the natural processes of exhaustion may provide a novel strategy to promote graft survival and transplantation tolerance.

Blockade of tumor necrosis factor superfamily members CD30 and OX40 abrogates disease activity in murine immune-mediated glomerulonephritis

Co-stimulation is a prerequisite for pathogenic activity in T cell-mediated diseases and has been demonstrated to achieve tolerance in organ-specific autoimmunity as a therapeutic target. Here, we evaluated the involvement of the tumor necrosis factor family members CD30 and OX40 in immune-complex mediated kidney disease. In vitro stimulation and proliferation studies were performed with CD4⁺ cells from wild type and CD30/OX40 double knock-out (CD30OX40^-/-) mice. In vivo studies were performed by induction of nephrotoxic serum nephritis in wild type, CD30OX40^{- /-} , CD30^-/-, OX40^-/-, reconstituted Rag1^-/- and C57Bl/6J mice treated with αCD30L αOX40L antibodies. CD30, OX40 and their ligands were upregulated on various leukocytes in nephrotoxic serum nephritis. CD30OX40^-/- mice, but not CD30^-/- or OX40^-/- mice were protected from nephrotoxic serum nephritis. Similar protection was found in Rag1^-/- mice injected with CD4⁺ T cells from CD30OX40^-/- mice compared to Rag1^-/- mice injected with CD4⁺ T cells from wild type mice. Furthermore, CD4⁺ T cells deficient in CD30OX40^-/- displayed decreased expression of CCR6 in vivo. CD30OX40^-/- cells were fully capable of differentiating into disease mediating T helper cell subsets, but showed significantly decreased levels of proliferation in vivo and in vitro compared to wild type cells. Blocking antibodies against CD30L and OX40L ameliorated nephrotoxic serum nephritis without affecting pan-effector or memory T cell populations. Thus, our results indicate disease promotion via CD30 and OX40 signaling due to facilitation of exaggerated T cell proliferation and migration of T helper 17 cells in nephrotoxic serum nephritis. Hence, co-stimulation blockade targeting the CD30 and OX40 signaling pathways may provide a novel therapeutic strategy in autoimmune kidney disease.

Tea Polyphenol Inhibits Allostimulation in Mixed Lymphocyte Culture

Green tea polyphenols are known to protect allogenic donor tissues from acute rejection by their recipients. This immunosuppressive effect may be generated by a unique chemical property of the major component, epigallocatechin-o-gallate (EGCG), which can block specific cell surface molecules of the donor tissues. To test this hypothesis, we examined the effects of EGCG on the murine mixed lymphocyte reactions. EGCG treatment of stimulator cells significantly attenuated the proliferation of responder T cells. The proliferation did not recover upon the secondary stimulations by fresh untreated cells or exogenous IL-2. Flow cytometric analyses showed that EGCG treatment decreased the staining intensities of various cell surface molecules including MHC II, which plays a major role in antigen presentation, and B7.1, B7.2, and their ligand, CD28, which are required for costimulatory signals in T-cell activation. These results suggest that an anergic state of alloreactive T cells may be induced by either weakening of antigen signaling or blockage of costimulatory signals with EGCG. Other possible mechanisms behind the immunosuppressive effect and a potential use of EGCG treatment of donor tissues in transplantation medicine are discussed.

Human Chorionic Villous Mesenchymal Stem Cells Modify the Functions of Human Dendritic Cells, and Induce an Anti-Inflammatory Phenotype in CD1+ Dendritic Cells

BACKGROUND

Mesenchymal stem cells derived from the chorionic villi of human term placenta (pMSCs) have drawn considerable interest because of their multipotent differentiation potential and their immunomodulatory capacity. These properties are the foundation for their clinical application in the fields of stem cell transplantation and regenerative medicine. Previously, we showed that pMSCs induce an anti-inflammatory phenotype in human macrophages. In this study, we determined whether pMSCs modify the differentiation and maturation of human monocytes into dendritic cells (DCs). The consequences on dendritic function and on T cell proliferation were also investigated.

METHODS

Interleukin-4 (IL-4) and granulocyte-macrophage colony stimulating factor (GM-CSF) were used to stimulate the differentiation of monocytes into immature dendritic cells (iDCs), which were subsequently co-cultured with pMSCs. Lipopolysaccharide (LPS) was used to induce maturation of iDCs into mature dendritic cells (mDCs). Flow cytometry and enzyme-linked immunosorbent assays (ELISA) were used to quantify the effect pMSC co-culturing on DC differentiation using CD1a, a distinctive marker of DCs, as well as other molecules important in the immune functions of DCs. The phagocytic activity of iDCs co-cultured with pMSCs, and the effects of iDCs and mDC stimulation on T cell proliferation, were also investigated.

RESULTS

Monocyte differentiation into iDCs was inhibited when co-cultured with pMSCs and maturation of iDCs by LPS treatment was also prevented in the presence of pMSCs as demonstrated by reduced expression of CD1a and CD83, respectively. The inhibitory effect of pMSCs on iDC differentiation was dose dependent. In addition, pMSC co-culture with iDCs and mDCs resulted in both phenotypic and functional changes as shown by reduced expression of costimulatory molecules (CD40, CD80, CD83 and CD86) and reduced capacity to stimulate CD4(+) T cell proliferation. In addition, pMSC co-culture increased the surface expression of major histocompatibility complex (MHC-II) molecules on iDCs but decreased MHC-II expression on mDCs. Moreover, pMSC co-culture with iDCs or mDCs increased the expression of immunosuppressive molecules [B7H3, B7H4, CD273, CD274 and indoleamine-pyrrole 2,3-dioxygenase (IDO). Additionally, the secretion of IL-12 and IL-23 by iDCs and mDCs co-cultured with pMSCs was decreased. Furthermore, pMSC co-culture with mDCs decreased the secretion of IL-12 and INF-γ whilst increasing the secretion of IL-10 in a T cell proliferation experiment. Finally, pMSC co-culture with iDCs induced the phagocytic activity of iDCs.

CONCLUSIONS

We have shown that pMSCs have an inhibitory effect on the differentiation, maturation and function of DCs, as well as on the proliferation of T cells, suggesting that pMSCs can control the immune responses at multiple levels.

Influence of immune responses in gene/stem cell therapies for muscular dystrophies

Muscular dystrophies (MDs) are a heterogeneous group of diseases, caused by mutations in different components of sarcolemma, extracellular matrix, or enzymes. Inflammation and innate or adaptive immune response activation are prominent features of MDs. Various therapies under development are directed toward rescuing the dystrophic muscle damage using gene transfer or cell therapy. Here we discussed current knowledge about involvement of immune system responses to experimental therapies in MDs.

A phase 1, randomized ascending single-dose study of antagonist anti-human CD40 ASKP1240 in healthy subjects

This first-in-human, phase I study evaluated the safety, tolerability, pharmacokinetic and pharmacodynamic profile of ASKP1240 in healthy subjects. Twelve sequential groups (each 6 active and 3 placebo) were randomly assigned to placebo or single ascending doses of intravenous ASKP1240 (0.00003-10 mg/kg). ASKP1240 exhibited nonlinear pharmacokinetics, with mean maximal serum concentrations and area under the serum concentration-time curves ranging from 0.7 to 251.6 μg/mL and 6.5 to 55409.6 h·μg/mL following doses 0.1 mg/kg-10 mg/kg, respectively. CD40 receptor occupancy by ASKP1240, which was dose-dependent, reached a maximum at doses above 0.01 mg/kg. ASKP1240 was well tolerated, with no evidence of cytokine release syndrome or thromboembolic events. Treatment emergent antibodies to ASKP1240 were detected in 5/70 (7.1%) ASKP1240 recipients. In conclusion, antagonism of the CD40/CD154 interaction with ASKP1240 was safe and well tolerated at the doses tested.

Lymphotoxin-beta receptor blockade induces inflammation and fibrosis in tolerized cardiac allografts

The lymphotoxin system (LT) regulates interactions between lymphocytes and stromal cells to maintain lymphoid microenvironmental homeostasis. Soluble LT beta-receptor-Ig (LTβRIg) blocks lymphocyte LTα1β2-stromal cell LTβR signaling. In a murine cardiac allograft model, LTbRIg treatment reversed the tolerance induced by anti-CD40L antibody leading to graft inflammation and fibrosis. LTβRIg treatment decreased PD-L1 expression by blood endothelial cells, and decreased VCAM-1 while increasing CXCL1, CXCL2, CXCL12, CCL5, CCL21 and IL-6 expression in fibroblastic reticular cells. In secondary lymphoid organs these effects caused T- and B cell zone disruption, loss of CD35(+) follicular dendritic cells and abnormal recruitment of CD11b(+) Ly6G(+) neutrophils. These disruptions correlated with increased numbers of CD8(+) T cells and CD11b(+) Ly6G(+) neutrophils, and decreased numbers of CD4(+) T cells and Foxp3(+) regulatory T cells in the grafts. Depleting neutrophils or blocking neutrophil-attracting chemokines restored normal histology in lymph node, spleen and grafts. Taken together, LTβRIg treatment altered stromal subset, particularly fibroblastic reticular cell, production of cytokines and chemokines, resulting in changes in neutrophil recruitment in spleen, lymph node and grafts, and inflammation and fibrosis associated with decreased Foxp3(+) regulatory T cells and increased CD8(+) T cell infiltration of grafts.

Attenuation of Murine Graft-Versus-Host Disease by a Tea Polyphenol

Since donor T-cells' allorecognition of host antigens is a prerequisite for the onset of graft-versus-host disease (GVHD), blocking their cellular signaling pathways can decrease the severity of GVHD. We hypothesized that epigallocatechin-3-gallate (EGCG), due to its strong affinity to macromolecules, would adhere to surface molecules of donor T cells, inhibit their allorecognition, and attenuate GVHD in the recipient. We tested the hypothesis by treating donor splenocytes with EGCG in both in vitro and in vivo murine GVHD models. EGCG treatment decreased the proliferation of donor cells in MLR cultures and secretion of IL-2 and INF-γ. It also reduced the epitope detection of CD3∊, CD4, and CD28 but did not downregulate the protein expression of these molecules, suggesting blockage of cell surface stimulatory signals. Similarly, EGCG treatment did not decrease mRNA expression for some of these molecules but decreased mitogen-induced cell proliferation, indicating that EGCG did not interfere the transcription of these genes but affected cell proliferation pathways. Furthermore, EGCG-treated donor splenocytes, when transplanted into immunocompromized recipient mice, decreased of proliferation, and the treatment extended the recipients' survival at least during the early stage of GVHD. These results strongly suggest that EGCG attenuates GVHD by both blocking specific cell surface molecules and affecting the donor T-cell proliferation pathways.

Cell-dose-dependent increases in circulating levels of immune effector cells in rhesus macaques following intracranial injection of allogeneic MSCs

OBJECTIVE

Mesenchymal stem cells (MSCs) possess potent immunomodulatory activity, but whether they evade immune surveillance in an allogeneic transplant setting remains controversial. Herein we evaluated whether administration of major histocompatibility complex (MHC) class I-mismatched MSCs induce an immune response in rhesus macaques.

MATERIALS AND METHODS

MSCs from a male donor were injected intracranially at two different doses into eight immunocompetent female infant rhesus macaques. Blood cell counts and circulating levels of lymphocyte subpopulations were quantified prior to surgery and at 10, 30, and 90 to 180 days postsurgery by flow cytometry. Immunoreactivity of recipient peripheral blood mononuclear cells to donor MSCs was evaluated in vitro and alloantibody production in vivo was determined by enzyme-linked immunosorbent assay and flow cytometry.

RESULTS

MSC transplantation induced transient but significant increases in circulating white blood cells, lymphocytes, and neutrophils in most transplant recipients, but not sham-operated control animals. Flow cytometric analysis revealed a strong correlation between expansion of CD8(+), CD16(+), and CD8(+)/CD16(+) lymphocyte subpopulations in peripheral blood, the dose of administered MSCs, and degree of antigenic mismatch between donor and recipient. MSC-specific alloantibodies were also detected in several transplant recipients. However, peripheral blood mononuclear cells harvested from transplant recipients postsurgery exhibited no lytic activity against donor MSCs in vitro upon rechallenge.

CONCLUSIONS

MSCs induced an allograft response in rhesus macaques that involved principally CD8(+), CD16(+), and CD8(+)/CD16(+) lymphocyte subpopulations and was cell-dose- and haplotype-dependent. This study demonstrates that MSCs are weakly immunogenic in vivo when transplanted across MHC class I barriers.

Allergen-specific subcutaneous immunotherapy in allergic asthma: immunologic mechanisms and improvement

Allergic asthma is a disease characterized by persistent allergen-driven airway inflammation, remodeling, and airway hyperresponsiveness. CD4(+) T-cells, especially T-helper type 2 cells, play a critical role in orchestrating the disease process through the release of the cytokines IL-4, IL-5, and IL-13. Allergen-specific immunotherapy (SIT) is currently the only treatment with a long-term effect via modifying the natural course of allergy by interfering with the underlying immunological mechanisms. However, although SIT is effective in allergic rhinitis and insect venom allergy, in allergic asthma it seldom results in complete alleviation of the symptoms. Improvement of SIT is needed to enhance its efficacy in asthmatic patients. Herein, the immunoregulatory mechanisms underlying the beneficial effects of SIT are discussed with the ultimate aim to improve its treatment efficacy.

STAT-1 decoy oligodeoxynucleotide inhibition of acute rejection in mouse heart transplants

During acute rejection of cardiac transplants endothelial cell-leukocyte interaction fueled by co-stimulatory molecules like CD40/CD154 may ultimately lead to graft loss. One key player in up-regulating the expression of such pro-inflammatory gene products is the interferon-gamma-dependent transcription factor STAT-1. Hence down-regulating interferon-gamma-stimulated pro-inflammatory gene expression in the graft endothelial cells by employing a decoy oligodeoxynucleotide (dODN) neutralising STAT-1 may protect the graft. To verify this hypothesis, heterotopic mouse heart transplantation was performed in the allogeneic B10.A(2R) to C57BL/6 and syngeneic C57BL/6 to C57BL/6 strain combination without immunosuppression. Graft vessels were pre-treated with STAT-1 dODN, mutant control ODN (10 muM each) or vehicle (Ringer solution). Cellular rejection (vascular and interstitial component) was graded histologically and CD40, ICAM-1, VCAM-1, MCP-1, E-selectin and RANTES expression in the graft monitored by real time PCR 24 h and 9 days post-transplantation. Nine days after transplantation both rejection scores were significantly diminished by 85 and 70%, respectively, in STAT-1 dODN-treated allografts as compared to mutant control ODN-treated allografts. According to immunohistochemistry analysis, this was accompanied by a reduced infiltration of monocyte/macrophages and T cells into the graft myocardium. In addition, pro-inflammatory gene expression was strongly impaired by more than 80% in STAT-1 dODN-treated allografts 24 h post-transplantation but not in mutant control ODN or vehicle-treated allografts. This inhibitory effect on pro-inflammatory gene expression was no longer detectable 9 days post-transplantation. Single periprocedural treatment with a STAT-1 dODN thus effectively reduces cellular rejection in mouse heart allografts. This effect is associated both with an early decline in pro-inflammatory gene expression and a later drop in mononuclear cell infiltration.

Comparative Analysis of Polymer and Linker Chemistries on the Efficacy of Immunocamouflage of Murine Leukocytes

Membrane grafting of methoxypoly(ethylene glycol) [mPEG] to allogeneic leukocytes attenuates allorecognition and significantly reduces the risk of graft-versus-host disease in mice. To optimize the immunological efficacy of polymer grafting, murine splenocytes were modified using three differing linker chemistries: CmPEG (5 kDa), BTCmPEG (5 and 20 kDa) and TmPEG (5 kDa). In vitro immunocamouflage efficacy was examined by flow cytometic analysis of leukocyte markers and mixed lymphocyte reactions (MLR). In contrast to CmPEG and BTCmPEG, TmPEG exerted significant cellular toxicity. Flow cytometric analysis demonstrated that both CmPEG and BTCmPEG were highly effective at camouflaging cell surface markers while TmPEG was ineffective. Furthermore, CmPEG and BTCmPEG dramatically blocked MLR allorecognition and cellular proliferation. Polymer length was the most critical factor in the immunocamouflage of cells with the BTCmPEG 20 kDa being the most effective. In contrast to other immunomodulatory approaches, immunocamouflage of leukocytes yields a multivalent effect globally interfering with attachment, allorecognition, presentation and costimulation pathways.

Microarrays: monitoring for transplant tolerance and mechanistic insights

With recent advances in immunology and a growing understanding of transplantation biology, the development of reliable assays that may be used for identification and prediction of the current state of an immune response (rejection and tolerance) are urgently needed to allow us to predict the development of immunologic graft injury, individualize immunosuppression, rationally minimize immunosuppressive drug toxicity, promote a better understanding of the mechanisms underlying stable graft acceptance, and aid in the design of tolerance-inducing clinical transplantation trials. Microarrays can provide nonbiased, simultaneous global expression patterns for more than 40,000 human genes across different experiments. High throughput microarray technology offers a means to study disease-specific transcriptional changes in tissue biopsy, peripheral blood, and biofluids.

CD28 downregulation on CD4+ T cells is associated with age of kidney transplant recipient

There is a growing body of evidence showing that the intensity of rejection is weaker in older kidney allograft recipients while chronic complications, but not rejection, are the main causes of graft loss. To investigate whether the age of the recipient is a factor affecting the expressions of the CD28, CTLA-4, and CD40L costimulatory molecules on CD4+ T cells. Their expression levels were determined in 78 kidney transplant recipients aged 17-68 years. The expression was assessed on unstimulated and anti-CD3 antibody + IL-2-stimulated CD4+ T cells. Median time after transplantation was 20 months and median serum creatinine was 1.5 mg/dl. Significant correlations between age and CD28 expression (r = -0.4, P = 0.0004) on CD4+ T cells and between age and CTLA-4 expression after stimulation (r = 0.34, P = 0.008) were found. CD40L expression on CD4+ T cells was not affected by recipient age. The decreased expression of CD28 and enhanced expression of CTLA-4 (after stimulation) associated with age may be helpful in transplant acceptance.

Immunologic approaches to composite tissue allograft

This article discusses the immunologic principles and the most promising immunologic approaches for composite tissue allograft tolerance. We have previously reviewed some of the pharmacologic approaches for composite tissue allo-transplantation. In this review, we will summarize the range of options that may address the challenge of transplantation in reconstructive surgery.

Frontiers in nephrology: immune tolerance to allografts in humans

Vascularized allografts are rejected unless some indefinite modification to the recipient's immune system is made. This modification is typically achieved through the long-term administration of immunosuppressive drugs. Patients thus trade their end-stage organ failure for dependence on daily drug therapy and the accompanying chronic condition of immunodeficiency. However, it is clear from studies in experimental animals that rejection can be prevented through the use of several therapeutic approaches, including donor hematopoietic cell infusion, chimerism, T cell depletion, and/or co-stimulation blockade. Successfully treated animals avoid rejection beyond the period of therapy without a phenotype of chronic immunosuppression and are thus considered to be tolerant of their grafts. Although intriguing, this success in animals has yet to be reproducibly translated to the clinic, and human transplant recipients remain tethered to immunosuppressive drugs with rare exceptions. This article provides an overview of the existing, largely anecdotal, clinical experience with organ allograft tolerance. It reviews the various approaches that are being applied in pilot human trials and suggests avenues for future clinical investigation.

STAT-1 decoy oligonucleotide improves microcirculation and reduces acute rejection in allogeneic rat small bowel transplants

During acute rejection leukocyte-endothelial cell interaction fuelled by costimulatory molecules such as the CD40/CD154 receptor/ligand dyad disrupts microcirculation of the small bowel. Downregulating endothelial CD40 expression by employing a decoy oligonucleotide (dODN) neutralizing the transcription factor signal transducer and activator of transcription-1 (STAT-1) may protect the graft. Therefore allogenic small bowel transplantation was performed in the Brown Norway to Lewis rat model. Graft vessels were pretreated with STAT-1 dODN, mutant control ODN (20 microM) or vehicle (n=8). CD40 antisense ODN and scrambled control ODN-treated transplants served as target control (n=3 each). Intravital microscopy, histology, immunohistochemistry and Western blot analyses were performed 7 days later. Functional capillary density, red blood cell velocity and perfusion index in STAT-1 dODN and CD40 antisense ODN-treated transplants were improved whereas stasis index was reduced. Leukocyte-endothelial cell interaction showed no difference. Histological parameters of rejection, infiltrating CD3-positive cells and apoptotic bodies were also reduced in STAT-1 dODN and CD40 antisense ODN-treated transplants 7 days post-transplantation. CD40 protein abundance was reduced to less than 10% of control in STAT-1 dODN-treated grafts. STAT-1 dODN blockade of CD40 expression improves mucosal perfusion, reduces graft rejection, T-cell infiltration and apoptosis in rat small bowel allografts during acute rejection.

The impact of memory T cells on rejection and the induction of tolerance

Accumulating evidence suggests that alloreactive memory T cells (Tm) may be generated in transplant recipients that have not previously been exposed to alloantigen through mechanisms such as cross-reactivity and homeostatic proliferation. The presence of Tm correlates with both acute and chronic rejection episodes and, furthermore, may be responsible for the failure to induce tolerance in large animal and clinical settings. A clearer understanding of how Tm function and their requirements to mount an effective response to alloantigen will be key to further attempts to translate tolerance induction protocols from the experimental setting to the clinic.

CD40L, CD28, and CTLA-4 expression on CD4+ T cells in kidney graft recipients: A relationship with post-transplantation clinical course

BACKGROUND

Experimental studies have demonstrated that the intensity of alloreactivity against a transplanted organ results from an interaction of positive (CD40/CD40L and B.7/CD28) and inhibitory (B.7/CTLA-4) signals between antigen-presenting cells (APCs) and T lymphocytes.

METHODS

We examined the CD40L, CD28, and both surface (s) and intracellular (i) CTLA-4 expressions on freshly drawn and anti-CD3+rIL-2-stimulated peripheral blood CD4+ T cells in groups of kidney transplant recipients in relation to distinct clinical course using the tri-color immunofluorescence method.

RESULTS

The median proportions of freshly isolated CD3+/CD4+/CTLA-4+ and CD3+/CD4+/CD40L+ cells in all groups of graft recipients were higher than in control subjects. In patients with stable graft function (SGF), non-significantly higher sCTLA-4, significantly higher iCTLA-4 expression, and significantly lower CD40L expression on freshly drawn CD4+ T cells compared with recipients with chronic allograft nephropathy (CAN) were found. Moreover, CD4+ T cells from SGF patients showed a higher potential to express sCTLA-4 and CD40L molecules and to down-regulate the CD28 molecule in response to ex vivo stimulation than those from patients with CAN. In patients without acute graft rejection (NAGR), a markedly higher proportion of freshly drawn CD3+/CD4+/iCTLA-4+ cells compared with patients with acute graft rejection (AGR) and an up-regulation of the median percentage of CD3+/CD4+/CD40L+ cells after ex vivo stimulation was found.

CONCLUSIONS

In patients with SGF, peripheral blood CD4+ T cells exhibited a higher potential to express surface CTLA-4 and CD40L and to down-regulate CD28 costimulatory molecules in response to ex vivo stimulation, indicating a relationship between the expression patterns of both costimulatory and inhibitory molecules in CD4+ T cells and clinical course after renal transplantation.

A new look at blockade of T-cell costimulation: a therapeutic strategy for long-term maintenance immunosuppression

Activated T cells orchestrate the immune response that results in graft rejection; therefore, a common goal among current immunosuppressive therapies is to block T-cell activation, proliferation and function. Current immunosuppressive regimens that inhibit T cells and immune cells have greatly reduced the incidence of acute rejection following solid-organ transplant. However, the expected improvements in long-term outcomes have not been realized. This may be related to the non-immune side effects of current maintenance immunosuppressants, which target ubiquitously expressed molecules. The focus in transplantation research is shifting in search of maintenance immunosuppressive regimens that might offer improved long-term outcomes by providing efficacy in prevention of acute rejection combined with reduced toxicities. An emerging therapeutic strategy involves an immunoselective maintenance immunosuppressant that inhibits full T-cell activation by blocking the interaction between costimulatory receptor-ligand pairs. This review describes costimulatory pathways and the development of molecules, which inhibit them in the context of transplantation research. Recent clinical data using the selective costimulation blocker, belatacept (LEA29Y), as a part of a CNI-free maintenance immunosuppressive regimen in renal transplantation is highlighted.

Genetic association of interleukin-1β and receptor antagonist (IL-1Ra) gene polymorphism with allograft function in renal transplant patients

Cytokines are known to be important mediators during renal graft outcome. The present study was therefore, conducted to determine the impact of IL-1beta and its receptor antagonist polymorphism on allograft outcome. We evaluated single nucleotide polymorphism (SNPs) in interleukin-1 gene cluster, IL-1beta (promoter region -511 and exon-5 +3954) and IL-1Ra (86-bp VNTR) in 136 renal transplant recipients and 150 normal healthy controls by polymerase chain restriction based (PCR-RFLP) analysis. Recipients were HLA matched and clinically characterized including delayed graft function (DGF), rejection episode (RE) and stable graft function (SGF). Haplotypes and linkage disequilibrium (LD) were determined using SNPAnalyzer software. Significant difference was observed for the frequency distribution of the three sites of IL-1 gene among patients and controls (p<0.001, 0.022 and <0.001 respectively). When RE and DGF were compared to SGF, only IL-1Ra showed significant differences among RE and SGF (p=0.014) and DGF and SGF (p=0.020). The presence of 1/2 genotype showed 18 folds risk in RE and 10 folds in DGF (OR=18.000 and OR=10.667 respectively). The majority of recipients with SGF had 1-4 HLA mismatch whereas RE had 5-8 mismatches. Risk for rejection increased >6 folds (OR=6.571; p<0.01) for 5-8 mismatches. Haplotypes constructed with the combination of three polymorphisms in IL-1 gene cluster showed significant difference between RE and SGF group. LD value for IL-1beta (promoter region) and IL-1Ra and IL-1beta promoter and exon-5 gene in the control group indicated strong association among the variants (D'=0.37, p<0.0001 and D'=0.29, p=0.002). Our study demonstrate that genetically determined low production of IL-1Ra may be a risk factor for RE and DGF and that IL-1beta/IL-1Ra haplotype influences the impact of allograft outcome. These findings may significantly abet in better perception of the survival of the graft.

Induction of long-term graft acceptance by a combination treatment of donor splenocytes and CTLA4Ig in a high responder rat liver transplantation model

The CTLA4Ig has led to an improved survival rate in various allograft transplantation models. We investigated in a high responder rat model (Dark Agouti to Lewis) of orthotopic liver transplantation (ORLT), whether an additional adoptive cell transfer can enhance the effect of CTLA4Ig. After transplantation, recipients (n = 13/group) were treated with donor or third-party splenocytes alone or in combination with CTLA4Ig. Administration of splenocytes alone had no significant effect on survival (median 13 days, range 9-14) compared with untreated controls (median 10 days, range 8-12). CTLA4Ig monotherapy prolonged survival to a median of 30 days (range 11-150) but resulted in long-term graft rejection. The additional administration of third-party splenocytes showed no significant improvement over CTLA4Ig monotherapy. Only the combination of donor splenocytes with CTLA4Ig led to long-term graft acceptance (>150 days) without clinical and/or histological signs of rejection. A higher rate of apoptosis could be detected in livers at early time-points in long-term survivors receiving CTLA4Ig and donor splenocytes. Analysis of cytokine mRNA expression revealed a decrease of interleukin-2 at early time-points in all groups receiving CTLA4Ig; whereas, interferon-gamma was increased in long-term survivors receiving CTLA4Ig and donor cells or donor cells alone. The combination of CTLA4Ig and donor derived splenocytes is potent to induce long-term survival and graft acceptance. The mechanisms appear to involve the induction of an early inflammatory impulse and apoptosis.

Absence of inducible costimulator on alloreactive T cells reduces graft versus host disease and induces Th2 deviation

Inducible costimulator (ICOS) is expressed on activated and memory T cells and is involved in the regulation of cytokine production. We studied the role of ICOS on alloreactive T cells in graft versus host disease (GVHD) and determined that ICOS expression was up-regulated on alloreactive T cells in recipients of an allogeneic hematopoietic stem cell transplantation (allo-HSCT) with GVHD. We compared ICOS-/- T cells with wild-type (WT) T cells in 2 GVHD models. In both models, recipients of ICOS-/- T cells demonstrated significantly less GVHD morbidity and mortality, which was associated with less intestinal and hepatic GVHD but increased cutaneous GVHD. In addition, recipients of ICOS-/- donor T cells displayed a slight decrease in graft versus leukemia (GVL) activity. Further analysis of alloreactive ICOS-/- T cells showed no defect in activation, proliferation, cytotoxicity, and target organ infiltration. Recipients of ICOS-/- T cells had decreased serum levels of interferon-gamma (IFN-gamma), while interleukin-4 (IL-4) and IL-10 levels were increased, suggesting that alloreactive ICOS-/- T cells are skewed toward T helper-2 (Th2) differentiation. These data suggest a novel role for ICOS in the regulation of Th1/Th2 development of activated T cells. In conclusion, alloreactive ICOS-/- donor T cells induce less GVHD due to a Th2 immune deviation while GVL activity is slightly diminished.

CD40 ligand increases complement C3 secretion by proximal tubular epithelial cells

Interstitial leukocyte infiltration is a major finding in tubulointerstitial damage (TID). Infiltrating lymphocytes interact with proximal tubular epithelial cells (PTEC) by means of secreted soluble factors and/or cell contact mechanisms. CD40 expressed onto PTEC can be engaged by CD40L present on T cells. PTEC are able to locally secrete complement C3, which may most likely promote TID. The aim of the study was to investigate the putative action of CD40 ligation on enhancement of C3 secretion by PTEC. Primary human PTEC and stabilized HK-2 cells were used in culture experiments. Cells were stimulated by soluble factors IL-1beta, IFN-gamma, and/or CD40L-expressing murine fibroblast L cells. Analysis of C3 gene expression was evaluated by reverse-transcription PCR and Northern blot. Secreted C3 was assayed by ELISA and a functional hemolytic test on supernatants. Intracellular events were explored by the NF-kappaB-specific inhibitor caffeic acid phenetyl ester (CAPE). Among soluble factors, IL-1beta and IFN-gamma increased C3 gene expression and secretion (two-fold to three-fold versus basal) on both HK-2 and PTEC. CD40 engagement by CD40L upregulated HK-2 C3 secretion by four-fold. IL-1beta did not further increase CD40-induced C3 secretion, whereas IFN-gamma associated with CD40L was the strongest stimulus (30-fold increase). Inhibition of NF-kappaB offset CD40L-induced C3 secretion by 70%. CD40 ligation is able to enhance C3 secretion by PTEC. This cell contact mechanism is in synergism with a T cell-derived soluble factor (IFN-gamma). C3 secretion induced by CD40L may represent a mechanism of amplification of TID associated with lymphocyte infiltration.

Tolerizing Effects of Co-stimulation Blockade Rest on Functional Dominance of CD4+CD25+ Regulatory T Cells

BACKGROUND

Clinical tolerance is the net result of regulatory and effector functions. In this article, the authors show that tolerance induction by co-stimulation blockade preferentially works through CD4CD25 regulatory T-cell-mediated suppression that is effectively achieved by selective reduction of the effector T-cell load. Anti-CD86 and anti-CD40L monoclonal antibody treatment during in vitro mixed lymphocyte reaction (MLR) typically results in the induction of a suppressive polyclonal T-cell population. This induced suppressive capacity was found to be dependent on the presence of CD4CD25 T cells at the start of MLR.

METHODS

Using a CFSE-based strategy, the authors show that within the polyclonal T-cell population, the suppressive effect was exerted by a nondividing CD4CD25 T-cell subset.

RESULTS

The cells exclusively originated from preexisting CD4CD25 regulatory T cells and proved anergic and highly suppressive on isolation. They carried the CD45RB and CD62L phenotype and expressed GITR. There was no indication of de novo induction of regulatory T cells by co-stimulation blockers. Instead, the authors observed, both in vitro and in vivo, that co-stimulation blockade shifted the ratio between alloreactive effectors and regulatory T cells in favor of the latter.

CONCLUSION

The authors therefore conclude that co-stimulation blockade contributes to functional dominance of regulatory T cells by preventing expansion of alloreactive effector T cells. Tolerance-inducing protocols should ideally facilitate this phenomenon.

Synergistic effect of triptolide and tacrolimus on rat cardiac allotransplantation

Recent studies have shown that triptolide inhibits T cell activation through mechanisms different from those of cyclosporine A and tacrolimus and we postulated that triptolide might have a synergistic effect with tacrolimus to enhance immunosuppression. Using a F344 donor-to-Lewis recipient rat combination, we investigated the immunosuppressive effects of triptolide alone or in combination with tacrolimus on the survival of cardiac allografts. Recipients were treated with placebo, triptolide, tacrolimus, and triptolide in combination with tacrolimus at different doses. The median survival time (MST) was 8 days for placebo; 9.5, 11, 14 and 19 days for triptolide monotherapy at doses of 0.04, 0.08, 0.16, and 0.32 mg/kg/day, respectively, and 11, 13.5, and 52 days for tacrolimus monotherapy at doses of 0.025, 0.05, and 0.1 mg/kg/day, respectively. Tacrolimus 0.025 mg/kg/day combined with triptolide 0.08 and 0.16 mg/kg/day prolonged the MST to 17.5 and 20 days, respectively; while tacrolimus 0.05 mg/kg/day combined with triptolide 0.04, 0.08, and 0.16 mg/kg/day prolonged the MST to 21, 23, and 23 days, respectively. These results suggest that triptolide is a moderately effective immunosuppressive agent. Triptolide combined with a subtherapeutic dose of tacrolimus produced a synergistic effect in prolonging rat cardiac allograft survival.

Immunocamouflage: prevention of transfusion-induced graft-versus-host disease via polymer grafting of donor cells

Graft-versus-host disease (GVHD) can occur following the transfer of allogeneic lymphocytes into immunosuppressed and, in rare cases, immunocompetent recipients. The initiation of GVHD requires the allorecognition of the recipient's disparate MHC molecules by the donor T lymphocytes (T cell). Currently, GVHD is controlled by cyclosporine administration--a potent, but toxic, T-cell suppressing agent. To determine if the nontoxic grafting of methoxypoly(ethylene glycol) (mPEG) to immunologically foreign lymphocytes could prevent allorecognition and GVHD, in vitro and in vivo murine studies were performed. In vitro studies utilizing mixed lymphocyte reactions (MLRs) demonstrate that mPEG modification effectively prevented allorecognition and subsequent T-cell proliferation. The loss of cellular proliferation was not due to mPEG cytotoxicity but rather to the inhibition of cell-cell interactions. Flow cytometric studies showed that T-cell and antigen-presenting cell adhesion molecules (CD2, CD11a), signaling (CD3epsilon, T-cell receptor), and costimulatory molecules (CD28, CD80) were efficiently immunocamouflaged by mPEG derivatization. Interestingly, upon antigenic stimulation mPEG-modified cells demonstrate enhanced apoptosis as evidenced by DNA laddering. In vivo studies using immunocompetent and immunosuppressed mice established that mPEG modification of donor lymphocytes effectively attenuated the in vivo proliferation of donor cells and the initiation of GVHD.

Requirement for Donor and Recipient CD40 Expression in Cardiac Allograft Rejection: Induction of Th1 Responses and Influence of Donor-Derived Dendritic Cells

Costimulation through the CD40-CD40 ligand (CD40L) pathway is critical to allograft rejection, in that anti-CD40L mAb therapy prolongs allograft survival. However, the majority of studies exploring CD40-CD40L interactions have targeted CD40L. Less is known about the requirement for donor- and/or host-derived CD40 during rejection. This study assessed the relative contributions of donor and recipient CD40 expression to the rejection process. As the effectiveness of costimulatory blockade may be mouse strain dependent, this study explored the requirement for donor and recipient CD40 expression in BALB/c and C57BL/6 mice. Wild-type (WT) and CD40(-/-) BALB/c recipients readily rejected WT and CD40(-/-) C57BL/6 allografts, and rejection was associated with a prominent Th1 response. In contrast, CD40(-/-) C57BL/6 recipients failed to reject WT or CD40(-/-) BALB/c allografts and did not mount Th1 or Th2 responses. However, injection of donor CD40(-/-) dendritic cells induced both Th1 and Th2 responses and allograft rejection in CD40(-/-) C57BL/6 recipients. Finally, WT C57BL/6 mice rejected CD40(-/-) allografts, but this rejection response was associated with muted Th1 responses. These findings demonstrate that 1) CD40 expression by the recipient or the graft may impact on the immune response following transplantation; 2) the requirement for CD40 is influenced by the mouse strain; and 3) the requirement for CD40 in rejection may be bypassed by donor DC. Further, as CD40 is not required for rejection in BALB/c recipients, but anti-CD40L mAb prolongs graft survival in these mice, these results suggest that anti-CD40L therapy functions at a level beyond disruption of CD40-CD40L interactions.

Blocking B7 and CD40 co-stimulatory molecules decreases antiviral T cell activity

Inhibition of co-stimulatory signals for T cells by interrupting CD80/CD86-CD28 and CD40-CD154 interactions is a promising approach to prevent transplant rejection and to induce graft tolerance. However, this tolerizing treatment might affect T cell reactivity towards all the antigens to which the immune system is exposed during treatment. We addressed the question whether such inhibition of co-stimulatory ligands on human antigen presenting cells (APC) would affect T cell reactivity against a virus. This was tested in an in vitro system with freshly isolated human monocytes transduced with adenovirus (ad) containing either murine interferon-gamma (mIFN-gamma) or green fluorescent protein (GFP) as marker transgene. T cells co-cultured with transduced monocytes proliferated and produced cytokines. These 'primed' T cells had strong antiviral activity as they subsequently killed ad/GFP-transduced monocytes and reduced mIFN-gamma accumulation in coculture with ad/mIFN-transduced monocytes. However, if priming had occurred in the presence of blocking anti-CD40/CD80/CD86 MoAbs, generation of this antiviral activity was completely prevented. Moreover, T cells primed in the absence of co-stimulatory cells failed to proliferate upon restimulation with adenovirus-transduced monocytes. The results confirm that co-stimulatory signals from APC are required for efficient induction of antiviral T cell activity and point to a potential infectious risk of blocking co-stimulatory signals.

Fc-dependent depletion of activated T cells occurs through CD40L-specific antibody rather than costimulation blockade

Although the underlying mechanisms are not well understood, it is generally believed that antigen recognition by T cells in the absence of costimulation may alter the immune response, leading to anergy or tolerance. Further support for this concept comes from animal models of autoimmunity and transplantation, where treatments based on costimulation blockade, in particular CD40 ligand (CD40L)-specific antibodies, have been highly effective. We investigated the mechanisms of action of an antibody to CD40L and provide evidence that its effects are dependent on the constant (Fc) region. Prolongation of graft survival is dependent on both complement- and Fc receptor-mediated mechanisms in a major histocompatibility complex (MHC)-mismatched skin transplant model. These data suggest that antibodies to CD40L act through selective depletion of activated T cells, rather than exerting immune modulation by costimulation blockade as currently postulated. This finding opens new avenues for treatment of immune disorders based on selective targeting of activated T cells.

Tolerance and the "Holy Grail" of transplantation

Advances in transplantation biology have greatly improved patient outcomes following transplant surgery. However, generalized immunosuppression remains the Achilles heel of modern transplantation surgery with its associated infectious and neoplastic morbidities. Tolerance remains the ultimate goal for the entire field. Although recent advances in transplant immunology suggest that tolerance may be achievable in the near future, the complex and redundant nature of the human immune system may not allow us to circumvent such a basic function as the recognition of nonself. In this paper, advances in transplant immunology are reviewed and their potential relevance to achieving the "Holy Grail" of transplantation are discussed.

Contrasting alloreactive CD4+ and CD8+ T cells: there's more to it than MHC restriction

Surface expression of CD4 or CD8 is commonly used to identify T-cell subsets that recognize antigen presented by class II MHC or class I MHC, respectively. This holds true for T cells that respond to allogeneic MHC molecules that are directly recognized as foreign, as well as peptides from allogeneic MHC molecules that are indirectly presented by self MHC molecules. CD4 or CD8 expression was initially believed to define cytokine secreting helper T cells or cytotoxic cells, respectively. However, this association of phenotype and function is not absolute, in that CD4+ cells may possess lytic activity and CD8+ cells secrete cytokines, notably IFNgamma. Recently, additional fundamental differences in the immunobiology of these T-cell subsets have been identified. These include differences in costimulatory requirements, cytokine responsiveness, cytokine production, cell survival, and the maintenance of memory. This review will survey these differences, emphasizing alloreactive T-cell responses as well as relevant observations that have been made in other systems.

Triptolide is a potent suppressant of C3, CD40 and B7h expression in activated human proximal tubular epithelial cells

BACKGROUND

Previous studies have shown that triptolide possesses potent immunosuppressive and anti-inflammatory properties. Increasing recognition of the importance of the proximal tubular epithelial cells (PTEC) in renal disease and renal transplantation raises the question of whether triptolide suppresses the pro-inflammatory activity of PTEC.

METHODS

Cultured human PTEC were exposed to tumor necrosis factor-alpha (TNF-alpha) and immunosuppressant (triptolide or CsA or FK506) for 24 hours, followed by RT-PCR, ELISA, flow cytometry and Western blotting analysis for complement C3, CD40, B7h expression.

RESULTS

TNF-alpha up-regulated C3, CD40 and B7h production by PTEC. This up-regulation was inhibited by all three immunosuppressants with different intensity. Firstly, triptolide (4 to 8 ng/mL), CsA (4000 to 6000 ng/mL) and FK506 (2000 ng/mL) inhibited up-regulation of C3 mRNA, but CsA and FK506 had less of an effect than triptolide. Secondly, triptolide (4 to 8 ng/mL) completely inhibited C3 expression at both mRNA and protein levels. In contrast, CsA and FK506 had only slight effects on C3 expression at the protein level. Thirdly, triptolide (4 to 8 ng/mL), CsA (500 to 2500 ng/mL) and FK506 (1250 ng/mL) inhibited up-regulation of CD40 and B7h mRNA, the effect on B7h and CD40 mRNA expression by CsA and FK506 being greater than that on C3 mRNA expression.

CONCLUSION

Triptolide effectively inhibited up-regulation of C3, CD40 and B7h on PTEC. Triptolide was more effective than CsA and FK506 at inhibiting C3 expression. This suggests that triptolide, at non-cytotoxic concentrations, has the potential to reduce the inflammatory and immunostimulatory properties of PTEC, in addition to any of the previously reported actions on T cell or B cell function.

The immunobiology of inductive anti-CD40L therapy in transplantation: allograft acceptance is not dependent upon the deletion of graft-reactive T cells

CD40-CD40L costimulatory interactions are crucial for allograft rejection, in that treatment with anti-CD40L mAb markedly prolongs allograft survival in several systems. Recent reports indicate that costimulatory blockade results in deletion of graft-reactive cells, which leads to allograft tolerance. To assess immunologic parameters that were influenced by inductive CD40-CD40L blockade, cardiac allograft recipients were treated with multiple doses of the anti-CD40L mAb MR1, which was remarkably effective at prolonging allograft survival. Acute allograft rejection responses such as IL-2 producing helper cell priming, Th1 priming, and alloantibody production were abrogated by anti-CD40L treatment. Interestingly, the spleens of mice bearing long-term cardiac allografts following inductive anti-CD40L treatment retained precursor donor alloantigen-reactive CTL, IL-2 producing helper cells, and Th1 in numbers comparable to those observed in naïve mice. These mice retained the ability to reject donor-strain skin allografts, but were incapable of rejecting the original cardiac allograft, or a second donor-strain cardiac allograft. Further, differentiated effector cells were incapable of mediating rejection following adoptive transfer into mice bearing long-term allografts, suggesting that regulatory cell function, rather than effector cell deletion was responsible for long-term graft acceptance. Collectively, these data demonstrate that inductive CD40-CD40L blockade does not result in the deletion of graft-reactive T cells, but induces the maintenance of these cells in a quiescent precursor state. They further point to a tissue specificity of this hyporesponsiveness, suggesting that not all donor alloantigen-reactive cells are subject to this regulation.

Immune response modulation by recombinant peptides expressed in virus-like particles

Aspergillus fumigatus, a ubiquitous fungus, is implicated in the pathogenesis of a number of clinically different allergic diseases in man, including allergic bronchopulmonary aspergillosis. Peptide-based immunotherapy may offer an alternative treatment strategy for the management of allergic disease. The objective of this study was to alter the allergen-specific immune response using dominant T cell epitopes of a major A. fumigatus allergen, Asp f2, expressed in yeast as virus-like particles (VLP). The T cell epitopes of Asp f2, recognized in mice with an H-2d background, were determined by producing T-cell hybridomas. Two dominant T cell epitopes, aa60--71 and aa235--249, were identified and expressed in a yeast VLP system. To induce tolerance VLP-peptides were injected subcutaneously into mice previously immunized with recombinant Asp f2. The T cell immune response was abrogated totally in 3 weeks following a single injection of VLP but was restored 2 months later following intranasal antigen exposure. T-cell depletion resulted in the reduction of 20-30% of all antigen-specific immunoglobulin classes. Thus, recombinant peptides expressed in the VLP system can be used successfully in the modulation of Asp f2-induced immune response in mice, although a single administration is not sufficient to maintain a state of tolerance for a long period of time.

Gene therapy and solid-organ transplantation

Recent developments in transplantation medicine improved the short- and long-term survival of solid-organ transplantation. However, chronic allograft rejection, the side effects of the long-term immunosuppressive treatment, and organ shortage are still the major obstacles to achieving long-term survival. Gene therapy has the potential to meet these challenges and has unique advantages in transplantation. In this review we summarize the studies using gene therapy in solid-organ transplantation.

Xenotransplantation of renal primordia

The limited availability of donor organs restricts the number of kidney transplantations performed per year. One novel solution to this shortage envisions 'growing' new kidneys in situ via xenotransplantation of renal primordia. To be successful, such an approach would require the following criteria to be met: that transplants are 'grown' in a location that renders their subsequent excretory function possible; that developed transplants have normal morphology and function; that transplanted metanephroi become well integrated into the host, in terms of inducing a state of immune tolerance and being vascularized by host vessels; and that source material for metanephros transplants is easy to access. This review summarizes recent work addressing these issues.

Growing kidneys

The number of kidney transplantations performed per year is restricted by the limited availability of donor organs. One possible solution to this shortage is the use of renal xenografts. However, the transplantation of xenografts is complicated by hyperacute and acute rejection. A second possible solution is to 'grow a kidney' from a transplanted renal anlage. It has been postulated that the host immune response might be attenuated after the transplantation of such an anlage (metanephros) instead of a developed kidney. Transplanted metanephroi become chimeric organs in that their blood supply originates, at least partly, from the host. It is possible to transplant a developing metanephros, without the use of immunosuppression, from one rat to another. Transplanted metanephroi grow, differentiate, become vascularized, and function in host rats. 'Growing kidneys' via the transplantation of metanephroi may hold promise as a novel therapeutic approach to the treatment of chronic renal failure.

CD40 ligation enhances IL-15 production by tubular epithelial cells

Interleukin-15 (IL-15) is a potent T-cell growth factor and activator. Acute rejection of kidney allografts strongly correlated with elevated IL-15 mRNA in the graft. A role in the rejection process is also suggested for the interaction between CD40 ligand (CD154) expressed on membranes of activated T cells and its receptor (CD40). The effect of CD40 ligation on IL-15 production in human tubular epithelial cells (TEC) was investigated. TEC were co-cultured with a cell line genetically engineered to express CD154. CD154-expressing cells (CD40L cells) bind to TEC. Addition of the CD40L cells to the TEC culture resulted in elevated IL-15 levels. This enhanced production was not observed with control cells, when anti-CD154 antibody was added, and when direct contact between CD40L-cells and TEC was prevented with the use of a Trans-well system. CD40 activation resulted in a twofold increase of IL-15 mRNA transcripts as measured by reverse transcription-PCR and a concordant elevation in IL-15 protein production as measured by specific enzyme-linked immunosorbent assay. The intensity of activation by CD154 was linearly dependent on cell number, reaching plateau when the effector/target-ratio was 1:1. The increase of IL-15 levels was similar to that produced by stimulation with interferon-gamma (IFN-gamma). Combination of IFN-gamma and activation with CD154 resulted in an additive effect. To conclude, activated T cells may enhance IL-15 expression in two ways: by secreting IFN-gamma and by cell to cell contact using CD154. Each signal alone induces IL-15 in similar magnitudes, and both signals are additive. Because IL-15 is a major T-cell activator, this interaction may contribute to graft rejection.

Heightened CD40 ligand gene expression in peripheral CD4+ T cells from patients with kidney allograft rejection

BACKGROUND

CD40 ligand (CD40L) gene expression is increased in rejecting allograft biopsies. We, therefore, tested the possibility that CD40L gene expression is heightened in peripheral CD4+ T cells during renal allograft rejection.

METHODS

CD40L gene expression in peripheral blood CD4+ T cells from two renal transplant groups was measured by quantitative reverse transcription-polymerase chain reaction (RT-PCR). Group 1: 20 patients with excellent renal transplant function; group 2: 25 patients with findings of acute and/or chronic allograft nephropathy (CAN); and group 3 of 12 normal controls. CD4+ cells were isolated by positive selection. The modifying effect of cyclosporine (CsA) and FK506 on CD40L gene expression was further tested in vitro in CD4+ T lymphocytes separated from pokeweed mitogen- (PWM) activated peripheral blood lymphocytes (PBL) preparations.

RESULTS

Mean+/-SD expressions of CD40L gene, in aM, in groups 1-3 were as follows: 0.0052+/-0.0094; 0.022+/-0.023 (P=0.0038 vs. group 2); and 0.014+/-0.005. Levels of CD40L gene expression correlated significantly with acute rejection Banff 97 score (R2=0.44, P=0.0004) and severity of intertubular capillary changes (ITCC) (R2=0.33, P=0.011). After in vitro activation, CD40L gene expression increased by approximately 4-fold and the addition of CsA or FK506 diminished CD40L gene expression to a base level.

CONCLUSION

Peripheral CD4+ T cell CD40L gene expression increases significantly in acute rejection and CAN and may serve as a non-invasive method to monitor allograft function and determine the biological response to CsA and FK506.

Human allograft acceptance is associated with immune regulation

The ultimate goal of transplantation is drug-free allograft acceptance, which is rarely encountered in transplant recipients. Using a novel human-to-mouse "trans vivo" delayed-type hypersensitivity assay, we assessed donor-reactive cell-mediated immune responses in kidney and liver transplant patients, four of whom discontinued all immunosuppression. One of these subjects (J.B.) rejected his graft after 7 years of stable function, while the others (D.S., R.D., M.L.) continue to have excellent graft function 5, 28, and 4 years after the cessation of immunosuppression. PBMCs from J.B. exhibited strong responses to both donor and recall antigens whereas PBMCs from patients D.S., R.D., and M.L. responded strongly to recall, but not donor, antigens. Furthermore, when donor and recall antigens were colocalized, the recall response in these three patients was inhibited. This donor antigen-linked nonresponsiveness was observed in four other patients who are still maintained on immunosuppression. The weakness of donor-reactive DTH responses in these patients is due to donor alloantigen-triggered regulation that relies on either TGF-beta or IL-10. In D.S., regulation is triggered by a single donor HLA Class I antigen, either in membrane-bound or soluble form. This demonstrates that allograft acceptance in humans is associated with an immune regulation pattern, which may be useful in the diagnosis and/or monitoring of transplant patients for allograft acceptance.

Distinct T cell/renal tubular epithelial cell interactions define differential chemokine production: implications for tubulointerstitial injury in chronic glomerulonephritides

Chemokines can promote interstitial fibrosis that is, in turn, a strong predictor of renal failure in chronic glomerulonephritides (GN). Resident renal cells, including renal tubular epithelial cells (RTEC), represent a prominent source of chemokine expression. Evaluating those factors responsible for sustained chemokine production by RTEC during GN is therefore crucial. The contribution of interstitial T cells to such expression, and in particular the precise nature of their interactions with RTEC, are poorly understood. Activated T cell/RTEC coculture induced production of high levels of monocyte chemoattractant protein-1 (MCP-1), RANTES, and IFN-inducible protein-10 from RTEC. Using double-chamber cultures and activated T cell plasma membrane preparations we demonstrated that both cell contact and soluble factors contributed to RTEC chemokine production. Importantly, different chemokines exhibited distinct activation requirements. Thus, for RANTES cell contact was essential, but not sufficient. In contrast, either soluble factors or cell contact induced MCP-1 and IFN-inducible protein-10 production, although both pathways were required for a maximal response. Neutralization experiments identified critical roles in this process for proinflammatory cytokines such as TNF-alpha, IL-1beta, and IFN-gamma as well as membrane molecules such as LFA-1, CD40 ligand, and membrane bound TNF-alpha. Finally, chemotactic bioassays of T cell/RTEC coculture supernatants demonstrated 80% reduction of monocyte migration following MCP-1 neutralization, indicating a dominant role for this chemokine. In summary, activation of renal tubular cells by infiltrating T cells can amplify and perpetuate local inflammatory responses through chemokine production differentially mediated by soluble and cell contact-dependent factors. Recognition of this regulatory diversity has important implications in the choice of potential therapeutic targets in GN.

Progress in the treatment of proliferative lupus nephritis

Lupus nephritis is often well developed at the time of diagnosis. High-dose corticosteroids are universally accepted as the initial approach to the control of severe inflammation in the kidney. Long-term disease control and the minimization of iatrogenic risk usually require adjunctive therapies that target the more fundamental immunoregulatory disturbances of lymphoid cells. Of the available cytotoxic drugs, cyclophosphamide is currently among the most effective, although it cannot be considered ideal in terms of efficacy or toxicity. New prospects for the treatment of proliferative lupus nephritis include novel immunosuppressive agents (e.g. mycophenolate, cyclosporine, fludarabine), combination chemotherapy (e.g. cyclophosphamide plus fludarabine), and sequential chemotherapy (e.g. cyclophosphamide-azathioprine), immunological reconstitution using intensive cytoreductive chemotherapy (with or without stem cell rescue), co-stimulatory molecule inhibition (e.g. humanized anti-CD154 monoclonal antibody, CTLA4-Ig). Gene therapy remains an attractive prospect, but its feasibility clearly depends on the further definition of lupus-promoting genes and the availability of methods to establish stable expression of disease-corrective genes in the appropriate lymphoid cells.

Blockade of costimulatory pathways of T-cell activation: the solution to acute and chronic rejection?

Understanding of how antigen-specific signals and costimulatory molecules are involved in T-cell activation has resulted in new strategies to interfere with allograft rejection. The present review focuses on the role of two receptor-ligand pairs: CD28 and cytotoxic T lymphocyte associated antigen-4, which interact with the B7 ligands (CD80, CD86); and CD40, which interacts with the CD40L (CD154). On the basis of the extensive tissue distribution of CD40, it is likely that the CD40/CD40L system plays a much broader role.