Role of STAT4 and STAT6 signaling in allograft rejection and CTLA4-Ig-mediated tolerance

STAT6 Pathway Is Critical for the Induction and Function of Regulatory T Cells Induced by Mucosal B Cells

B cells could convert naïve T cells into regulatory T cells (so-called Treg-of-B cells) which have the ability to treat animal models of inflammatory diseases, including allergic asthma, collagen-induced arthritis and colitis; however, the mechanisms of Treg-of-B cell generation remain unclear. In this study, we investigated the role of STAT6 in the generation of Treg-of-B (P) cells, which Treg cells were generated by Peyer’s patch B cells (P stands for Peyer’s patch). CD4+CD25- T cells from wild type, STAT6 knockout and IL-4 knockout mice were cocultured with wild type Peyer’s patch B cells for Treg-of-B (P) cell generation. A murine asthmatic model was used to analyze the in vivo regulatory function of Treg-of-B (P) cells. The data demonstrated that STAT6 played a critical role in the generation of Treg-of-B (P) cells, which confirmed with STAT6-deficient T cells and the STAT6 inhibitor AS1517499. When STAT6 was lacking, Treg-of-B (P) cells exerted impaired suppressive ability with decreased LAG3 expression. Furthermore, Peyer’s patch B cells played an essential role in regulatory T cell generation. In the absence of Peyer’s patch B cells, T cells expressed decreased phosphorylated STAT6, which was followed by decreased LAG3 expression and impaired suppressive ability, suggesting that Peyer’s patch B cells provided the critical signal to activate STAT6 phosphorylation in T cells. Moreover, STAT6 deficient Treg-of-B (P) cells could not alleviate inflammation in an animal model of asthma in vivo. IL-4 was downstream of phosphorylated STAT6 and maintained Treg-of-B (P) cell survival with increased expression of Bcl-2 and Bcl_XL. We reported a novel finding that the STAT6-LAG3 signaling axis is important for the induction and function of Treg-of-B (P) cells.

Programmed T cell differentiation: Implications for transplantation

While T cells play a critical role in protective immunity against infection, they are also responsible for graft rejection in the setting of transplantation. T cell differentiation is regulated by both intrinsic transcriptional pathways as well as extrinsic factors such as antigen encounter and the cytokine milieu. Herein, we review recent discoveries in the transcriptional regulation of T cell differentiation and their impact on the field of transplantation. Recent studies uncovering context-dependent differentiation programs that differ in the setting of infection or transplantation will also be discussed. Understanding the key transcriptional pathways that underlie T cell responses in transplantation has important clinical implications, including development of novel therapeutic agents to mitigate graft rejection.

TIM‑4 blockade of KCs combined with exogenous TGF‑β injection helps to reverse acute rejection and prolong the survival rate of mice receiving liver allografts

An acute reaction response (AR) following liver transplantation (LT) is caused by immune responses that are primarily mediated by T lymphocytes. Kupffer cells (KCs) are the largest antigen presenting cell (APC) group in vivo and are the primary modulators of the inflammatory or tolerogenic immune response in liver tissues. T cell immunoglobulin-domain and mucin-domain-4 (TIM-4), the only TIM protein not expressed on T cells, is expressed on APCs; suggesting that it mediates the various immune responses. However, to the best of our knowledge, the role of TIM-4 expressed by KCs in LT injury remains unknown. The present study aimed to explore whether and how TIM-4 expressed by KCs is involved in the AR of liver allografts. Orthotopic liver transplantation (OLT) was performed in mice to establish a model of AR and results demonstrated that LT may lead to the augmented expression of TIM-4 in activated KCs. It was also revealed that TIM-4 blockade markedly attenuated AR injury in vivo via the nuclear factor-κB (NF-κB) and p38 mitogen-activated protein kinase (p38 MAPK) signaling pathways. In addition, levels of transforming growth factor-β (TGF-β) were increased following TIM-4 blockade. Furthermore, in a KC/cluster of differentiation (CD)4⁺ T cell co-culture system, blocking TIM-4 inhibited T helper 2 (Th2) differentiation, stimulated the conversion of naive (CD)4⁺ T cells into CD4⁺CD25⁺Forkhead box protein p3⁺ T regulatory cells and suppressed interleukin-4/signal transducer and activator of transcription 6/transcription factor gata3 signaling. These effects were enhanced following the addition of TGF-β. It was also demonstrated that LT mouse models treated with TIM-4 blockade in combination with exogenous TGF-β injections, increased the survival times of mice and enhanced the amelioration of AR in LT. These results indicate that blocking the expression of TIM-4 by KCs via exogenous TGF-β injection may be an effective therapeutic strategy to inhibit the AR of liver allografts.

STAT4 gene polymorphism in patients after renal allograft transplantation

Introduction

STAT4 (signal transducer and activator of transcription 4) is involved in the regulation of innate and adaptive immune responses. Some studies have suggested that STAT4 may be involved in the immune response after graft transplantation. Several polymorphisms in the STAT4 gene have been identified. The most commonly studied polymorphism in the STAT4 gene is rs7574865. In our study, we examined whether this polymorphism is associated with the early and late functions of renal allografts.

Material and methods

A total of 270 recipients of first renal transplants were included in the study. Single nucleotide polymorphisms (SNPs) within the STAT4 gene were genotyped using TaqMan genotyping assays.

Results

There were no statistically significant associations between the STAT4 gene rs7574865 polymorphism and delayed graft function, acute rejection, chronic allograft dysfunction, post-transplant diabetes mellitus, or creatinine serum concentrations after transplantation.

Conclusions

Our results suggest a lack of association between the STAT4 rs7574865 SNP and kidney allograft function in the Polish population.

Intestine immune homeostasis after alcohol and burn injury

Traumatic injury remains one of the most prevalent reasons for patients to be hospitalized. Burn injury accounts for 40,000 hospitalizations in the United States annually, resulting in a large burden on both the health and economic system and costing millions of dollars every year. The complications associated with postburn care can quickly cause life-threatening conditions including sepsis and multiple organ dysfunction and failure. In addition, alcohol intoxication at the time of burn injury has been shown to exacerbate these problems. One of the biggest reasons for the onset of these complications is the global suppression of the host immune system and increased susceptibility to infection. It has been hypothesized that infections after burn and other traumatic injury may stem from pathogenic bacteria from within the host's gastrointestinal tract. The intestine is the major reservoir of bacteria within the host, and many studies have demonstrated perturbations of the intestinal barrier after burn injury. This article reviews the findings of these studies as they pertain to changes in the intestinal immune system after alcohol and burn injury.

Human cytokines activate JAK-STAT signaling pathway in porcine ocular tissue

Background

The JAK/STAT (Janus Tyrosine Kinase, Signal Transducers and Activators of Transcription) pathway is associated with cytokine or growth factor receptors and it is critical for growth control, developmental regulation and homeostasis. The use of porcine ocular cells as putative xenotransplants appears theoretically possible. The aim of this study was to investigate the response of various porcine ocular cells in vitro to human cytokines in regard to the activation of JAK-STAT signaling pathways.

Methods

Porcine lens epithelial cells, pigmented iris epithelial cells and pigmented ciliary body cells were used in this study. These cells were isolated from freshly enucleated porcine eyes by enzymatic digestion. Cultured cells between passages 3–8 were used in all experiments. Electromobility shift assay (EMSA), proliferation assay, immunofluorescence staining and flow cytometry were used to evaluate the JAK-STAT signaling pathway in these cells.

Results

JAK/STAT signaling pathways could be activated in porcine pigmented epithelial ciliary body cells, in pigmented iris epithelial cells and in lens epithelial cells in response to porcine and human interferons and cytokines. All cells showed very strong STAT1 activation upon stimulation with porcine interferon-gamma. Porcine ocular cells also respond to human cytokines; IFN-alpha induced strong activation of STAT1 in EMSA, flow cytometry and immunofluorescence experiments whereas activation of STAT3 was less strong in EMSA, but strong in flow cytometry and immunofluorescence. Human recombinant IL-6 activated STAT3 and human IL-4 activated STAT6. With the help of immunofluorescence assay and flow cytometry we observed nuclear localization of STAT proteins after activation of porcine ocular cells with cytokines and interferons. Human IFN-α had an inhibitory effect on porcine ocular cells in proliferation assays.

Conclusion

Our study demonstrated that some types of human cytokines and interferon activate intracellular JAK-STAT signaling pathways in porcine ocular cells. We hypothesize that direct stimulation of the JAK-STAT pathway in porcine cells in response to human cytokines will lead to complications or failure, if pig-to-human ocular tissue xenotransplantation were to be carried out. For successful xenotransplantation among other obstacles there must be new approaches developed to regulate signaling pathways.

Interruption of dendritic cell-mediated TIM-4 signaling induces regulatory T cells and promotes skin allograft survival

Dendritic cells (DCs) are the central architects of the immune response, inducing inflammatory or tolerogenic immunity, dependent on their activation status. As such, DCs are highly attractive therapeutic targets and may hold the potential to control detrimental immune responses. TIM-4, expressed on APCs, has complex functions in vivo, acting both as a costimulatory molecule and a phosphatidylserine receptor. The effect of TIM-4 costimulation on T cell activation remains unclear. In this study, we demonstrate that Ab blockade of DC-expressed TIM-4 leads to increased induction of induced regulatory T cells (iTregs) from naive CD4(+) T cells, both in vitro and in vivo. iTreg induction occurs through suppression of IL-4/STAT6/Gata3-induced Th2 differentiation. In addition, blockade of TIM-4 on previously activated DCs still leads to increased iTreg induction. iTregs induced under TIM-4 blockade have equivalent potency to control and, upon adoptive transfer, significantly prolong skin allograft survival in vivo. In RAG(-/-) recipients of skin allografts adoptively transferred with CD4(+) T cells, we show that TIM-4 blockade in vivo is associated with a 3-fold prolongation in allograft survival. Furthermore, in this mouse model of skin transplantation, increased induction of allospecific iTregs and a reduction in T effector responses were observed, with decreased Th1 and Th2 responses. This enhanced allograft survival and protolerogenic skewing of the alloresponse is critically dependent on conversion of naive CD4(+) to Tregs in vivo. Collectively, these studies identify blockade of DC-expressed TIM-4 as a novel strategy that holds the capacity to induce regulatory immunity in vivo.

Anti-STAT6 CTL activity in Stat6 (-/-) mice: A cautionary tale

The generation of germline gene mutations in mice has been an invaluable tool for experimental biology. However, studying immune responses that develop in the absence of a specific protein that could alter thymic selection complicates experimental interpretations. We observed that CD8⁺ T cells from Stat6^−/− mice displayed “autoreactivity” to STAT6-expressing cells, associated with specific STAT6 peptides binding to MHC class I molecules. These results suggest caution in interpreting experiments where STAT6-expressing cells are transferred into Stat6^−/− mice, or where adoptive transfer of Stat6^−/− lymphocytes is performed. Our results further highlight additional considerations when studying immune responses involving cell transfer into gene-deficient mice.

Live-cell imaging of the association of STAT6-GFP with mitochondria

The transcription factor STAT3 has been previously reported to be associated with mitochondria. However, we have been unable to visualize an association of STAT3-GFP, STAT3-DsRed or STAT3-Flag with mitochondria in human Hep3B hepatocytes thus far even though an association of these molecules with other cytoplasmic organelles (endosomes) was readily demonstrable. We then addressed the broader question of a possible association of other STAT-family of proteins with mitochondria by first using immunolocalization assays in Hep3B and human pulmonary arterial endothelial and smooth muscle cells. Strong anti-STAT6-immunolocalization with mitochondria was apparent in fluorescence and electron microscopy assays of cells first washed with a digitonin-sucrose buffer to remove bulk soluble STAT proteins. In live-cell imaging studies, STAT6-GFP, but not N1-GFP, was observed to constitutively colocalize with MitoTracker- and tetramethylrhodamine ethyl ester (TMRE)-positive mitochondria, and with mitochondrial F1-ATPase when assayed by immunofluorescence after fixation. This association was Tyr-phosphorylation independent in that a STAT6 truncated protein (STAT6^1-459-GFP) which lacked the SH2 domain (517–632) and the cytokine-activated Y641 phosphorylation site also accumulated in MitoTracker-positive mitochondria. This was consistent with the unexpected discovery that anti-STAT6-immunofluoresence also associated with mitochondria in mouse embryo fibroblasts (MEFs) from both wild-type and the STAT6^SH2-/SH2- mouse. MEFs from the latter mouse, which had been engineered in 1996 to be deleted in the STAT6 SH2 domain (amino acids 505–584) expressed an immune-specific ∼50 kDa protein detectable in whole cell and mitochondria-enriched fractions. Taken together, the present data provide the first definitive evidence of the association of any STAT-protein family member with mitochondria - that of STAT6.

Allogenicity of human cardiac stem/progenitor cells orchestrated by programmed death ligand 1

RATIONALE

Transplantation of allogeneic cardiac stem/progenitor cells (CPC) in experimental myocardial infarction promoted cardiac regeneration and improved heart function. Although this has enhanced prospects of using allogeneic CPC for cardiac repair, the mechanisms regulating the behavior of these allogeneic cells, which are central to clinical applications, remain poorly understood.

OBJECTIVE

T cells orchestrate the allogeneic adaptive immune response. Therefore, to provide insight into the mechanisms regulating the immunologic behavior of human CPC (hCPC), we investigated the allogeneic T-cell response elicited by cryopreserved c-kit-selected hCPC.

METHODS AND RESULTS

By using an experimental model of allogeneic stimulation, we demonstrate that, whether under inflammatory conditions or not, hCPC do not trigger conventional allogeneic Th1 or Th2 type responses but instead induce proliferation and selective expansion of suppressive CD25(high)CD127(low)human leukocyte antigen-DR(+)FoxP3(high) effector regulatory T cells. The regulatory T-cell proliferation and amplification were dependent on the interaction with the B7 family member programmed death ligand 1 (PD-L1), which is substantially expressed on hCPC and increased under inflammatory conditions. Thus, hCPC in allogeneic settings acquire the capacity to downregulate an ongoing immune response, which was dependent on PD-L1.

CONCLUSIONS

Collectively, these data reveal that hCPC in allogeneic settings have a tolerogenic immune behavior, promoting a contact PD-L1-dependent regulatory response and a PD-L1-dependent allogeneic-driven immunomodulation. Our study attributes an important role for PD-L1 in the immune behavior of allogeneic hCPC and raises the possibility of using PD-L1 expression as a marker to identify and select low-risk high-benefit allogeneic cardiac repair cells.

Human endothelial cells generate Th17 and regulatory T cells under inflammatory conditions

Organ transplantation represents a unique therapeutic option for irreparable organ dysfunction and rejection of transplants results from a breakdown in operational tolerance. Although endothelial cells (ECs) are the first target in graft rejection following kidney transplantation, their capacity to alloactivate and generate particular T lymphocyte subsets that could intervene in this process remains unknown. By using an experimental model of microvascular endothelium, we demonstrate that, under inflammatory conditions, human ECs induced proliferation of memory CD4(+)CD45RA(-) T cells and selectively amplified proinflammatory Th17 and suppressive CD45RA(-)HLA-DR(+)FoxP3(bright) regulatory CD4(+) T lymphocytes (Tregs). Although HLA-DR expression on resting microvascular ECs was sufficient to induce proliferation of memory CD4(+) T cells, Treg amplification was dependent on the interaction with CD54, highly expressed only under inflammatory conditions. Moreover, expansion of Th17 cells was dependent on IL-6 and STAT-3, and inhibition of either specifically impaired Th17, without altering Treg expansion. Collectively these data reveal that the HLA-DR(+) ECs regulate the local inflammatory allogeneic response, promoting either an IL-6/STAT-3-dependent Th17 response or a contact-CD54-dependent regulatory response according to the cytokine environment. Finally, these data open therapeutic perspectives in human organ transplantation based on targeting the IL-6/STAT-3 pathway and/or promoting CD54 dependent Treg proliferation.

Functional genomic analysis of peripheral blood during early acute renal allograft rejection

BACKGROUND

Acute graft rejection is an important clinical problem in renal transplantation and an adverse predictor for long-term graft survival. Peripheral blood biomarkers that provide evidence of early graft rejection may offer an important option for posttransplant monitoring, optimize the utility of graft biopsy, and permit timely and effective therapeutic intervention to minimize the graft damage.

METHODS

In this feasibility study (n=58), we have used gene expression profiling in a case-control design to compare whole blood samples between normal subjects (n=20) and patients with (n=11) or without (n=22) biopsy-confirmed acute rejection (BCAR) or borderline changes (n=5).

RESULTS

A total of 183 probe sets representing 160 genes were differentially expressed (false discovery rate [FDR] <0.01) between subjects with or without BCAR, from which linear discriminant analysis and cross-validation identified an initial gene signature of 24 probe sets, and a more refined set of 11 probe sets found to classify subject samples correctly. Cross-validation suggested an out-of-sample sensitivity of 73% and specificity of 91% for identification of samples with or without BCAR. An increase in classifier gene expression correlated closely with acute rejection during the first 3 months posttransplant. Biological evaluation indicated that the differentially expressed genes encompassed processes related to immune response, signal transduction, and cytoskeletal reorganization.

CONCLUSION

Preliminary evidence indicates that gene expression in the peripheral blood may yield a relevant measure for the occurrence of BCAR and offer a potential tool for immunologic monitoring. These results now require confirmation in a larger cohort.

TLR signals promote IL-6/IL-17-dependent transplant rejection

Acute allograft rejection has often been correlated with Th1 differentiation, whereas transplantation tolerance is frequently associated with induction of regulation. The discovery of the Th17 phenotype has prompted its scrutiny in transplant rejection. Although IL-17 has recently been observed in settings of acute allograft rejection and drives rejection in T-bet-deficient mice that have impaired type 1 T cell responses, there is little evidence of its requirement during acute rejection in wild-type animals. We and others have previously shown that TLR9 signaling by exogenous CpG at the time of transplantation is sufficient to abrogate anti-CD154-mediated acceptance of fully mismatched cardiac allografts. In this study, we investigated the mechanism by which acute rejection occurs in this inflammatory context. Our results indicate that CpG targets recipient hemopoietic cells and that its pro-rejection effects correlate both with prevention of anti-CD154-mediated conversion of conventional CD4(+) T cells into induced regulatory T cells and with the expression of IFN-gamma and IL-17 by intragraft CD4(+) T cells. Moreover, the combined elimination of IL-6 and IL-17 signaling abrogated the ability of CpG to promote acute cardiac allograft rejection. Thus, proinflammatory signals at the time of transplantation can change the quality of the effector immune response and reveal a pathogenic function for IL-6 and IL-17 in wild-type recipients.

A novel role of CD4 Th17 cells in mediating cardiac allograft rejection and vasculopathy

T-bet plays a crucial role in Th1 development. We investigated the role of T-bet in the development of allograft rejection in an established MHC class II–mismatched (bm12 into B6) model of chronic allograft vasculopathy (CAV). Intriguingly, and in contrast to IFN-γ^−/− mice that are protected from CAV, T-bet^−/− recipients develop markedly accelerated allograft rejection accompanied by early severe vascular inflammation and vasculopathy, and infiltration by predominantly IL-17–producing CD4 T cells. Concurrently, T-bet^−/− mice exhibit a T helper type 1 (Th1)–deficient environment characterized by profound IFN-γ deficiency, a Th2 switch characterized by increased production of interleukin (IL) 4, IL-5, IL-10, and IL-13 cytokines, as well as increased production of the proinflammatory cytokines IL-6, IL-12p40, and IL-17. Neutralization of IL-17 inhibits accelerated allograft rejection and vasculopathy in T-bet^−/− mice. Interestingly, CD4 but not CD8 T cell deficiency in T-bet^−/− mice affords dramatic protection from vasculopathy and facilitates long-term graft acceptance. This is the first study establishing that in the absence of Th1-mediated alloimmune responses, CD4 Th17 cells mediate an aggressive proinflammatory response culminating in severe accelerated allograft rejection and vasculopathy. These results have important implications for the development of novel therapies to target this intractable problem in clinical solid organ transplantation.

G6b-B cell surface inhibitory receptor expression is highly restricted to CD4+ T-cells and induced by interleukin-4–activated STAT6 pathway

The G6b-B gene encodes a novel cell surface receptor of the immunoglobulin superfamily that activates inhibitory signaling pathways by triggering SHP-1/SHP-2 via immunoreceptor tyrosine-based inhibitory motifs (ITIM) in its cytoplasmic domain. We previously identified decreased G6b-B expression in peripheral blood mononuclear cells (PBMC) during acute cellular cardiac allograft rejection. We studied the expression of G6b-B in different human mononuclear cell populations and its regulation. Real-time polymerase chain reaction (PCR) revealed that G6b-B mRNA is higher in CD4+ T cells or monocytes, but is not different between CD25+ CD4+ T cells and CD25- CD4+ T cells. G6b-B mRNA was increased in CD4+ T cells in presence of interleukin-4 in dose- and time-dependent manners. To understand the regulatory mechanism, we analyzed a 1.9-kb 5'-flanking region of the G6b-B translation start site and found a putative cis-acting element for Signal Transducer and Activator of Transcription (STAT)-6. Luciferase-reporter-gene-assay and electrophoretic mobility shift assays identified the STAT6 site as necessary for the induction of G6b-B by IL-4. Our study demonstrates that G6b-B expression is highly restricted to peripheral CD4+ T cells and up-regulated by the IL-4-induced STAT6 pathway, strongly suggesting that G6b-B is involved in regulation of the immune response by CD4+ T cell-mediated and IL-4 induced regulatory mechanisms.

STAT4: a critical regulator of inflammation in vivo

Signal transducer and activator of transcription 4 (STAT4) is a central mediator in generating inflammation during protective immune responses and immune-mediated diseases. In the 8 yr since their first description, STAT4-deficient mice have defined the role of STAT4 in a variety of in vivo model systems. Despite the extensive study and use of these mice, the exact role of STAT4 in vivo is still unclear. In this review, I focus on describing the phenotypes of STAT4-deficient immune responses to pathogens and in diseases. Comparing the effects of STAT4 deficiency among numerous model systems will further enhance the development of a systemic model of STAT4 function in vivo.

Signaling by IL-12 and IL-23 and the immunoregulatory roles of STAT4

Produced in response to a variety of pathogenic organisms, interleukin (IL)-12 and IL-23 are key immunoregulatory cytokines that coordinate innate and adaptive immune responses. These dimeric cytokines share a subunit, designated p40, and bind to a common receptor chain, IL-12R beta 1. The receptor for IL-12 is composed of IL-12R beta 1 and IL-12R beta 2, whereas IL-23 binds to a receptor composed of IL-12R beta 1 and IL-23R. Both cytokines activate the Janus kinases Tyk2 and Jak2, the transcription factor signal transducer and activator of transcription 4 (STAT4), as well as other STATs. A major action of IL-12 is to promote the differentiation of naive CD4+ T cells into T-helper (Th) 1 cells, which produce interferon (IFN)-gamma, and deficiency of IL-12, IL-12R subunits or STAT4 is similar in many respects. In contrast, IL-23 promotes end-stage inflammation. Targeting IL-12, IL-23, and their downstream signaling elements would therefore be logical strategies for the treatment of immune-mediated diseases.

Modulating co-stimulation: a rational strategy in the treatment of rheumatoid arthritis?

Rheumatoid arthritis (RA) is a common destructive inflammatory disease that affects 0.5-1% of the population in many countries. Even though several new treatments have been introduced for patients with RA, a considerable proportion of patients do not benefit from these, and the need for alternative treatment strategies is clear. This review explores the potential for a therapy targeting the adaptive immune system by modulating co-stimulation of T cells with a CTLA4-Ig fusion protein (abatacept).

RNA interference: a potent tool for gene-specific therapeutics

RNA interference (RNAi) is a process through which double-stranded RNA induces the activation of cellular pathways, leading to potent and selective silencing of genes with homology to the double strand. Much excitement surrounding small interfering RNA (siRNA)-mediated therapeutics arises from the fact that this approach overcomes many of the shortcomings previously experienced with approaches such as antibodies, antisense oligonucleotides and pharmacological inhibitors. Induction of RNAi through administration of siRNA has been successfully used in treatment of hepatitis, viral infections, and cancer. In this review we will present a brief history of RNAi, methods of inducing RNAi, application of RNAi in the therapeutic setting, and the possibilities of using this highly promising approach in the context of transplantation.

Analysis of cytokine functions in graft rejection by gene expression profiles

BACKGROUND

The function of interferon (IFN)gamma in the regulation of the immune response after allogeneic transplantation is still poorly understood. Previous studies have suggested that IFNgamma can promote rejection and be important in tolerance induction.

METHODS

To analyze the various IFNgamma-dependent functions in terms of T helpers 1 and 2 responses during rejection, we investigated mice deficient in the transcription factors (signal transducer of activated T cells [STAT]4 and 6) and IFNgamma in fully major histocompatibility complex-mismatched vascularized cardiac transplants. Serum levels of the cytokines tumor necrosis factor-alpha, IFNgamma, and interleukin (IL)-1beta were evaluated by enzyme-linked immunosorbent assay, and the graft-infiltrating cells were examined by immunohistochemical staining. To analyze a large panel of immune parameters, we determined the expression of chemokines, chemokine receptors, and clusters of differentiation markers by RNAase protection assays. The data were analyzed with algorithms that generated hierarchic clustering dendrograms. Also, the expression profiles of individual genes were determined with self-organizing maps.

RESULTS

Our data show that both the STAT4- and STAT6-deficient groups have statistically prolonged graft survival (P<0.04 and P<0.01). Despite the absence of prolongation of graft survival in the IFNgamma-deficient group, our analysis of variance data show that more genes (18) were modulated in the IFNgamma-deficient group compared with the other two STAT4- and STAT6-deficient groups (five each).

CONCLUSIONS

Our results indicate that IFNgamma plays a distinct role in the modulation of gene expression that includes STAT4-independent mechanisms. Our study identifies eight genes (IL-1beta, IL-1RA, macrophage inflammatory protein-1beta, monocyte chemoattractant protein-1, CC-chemokine receptor (CCR)-1, CCR2, CCR5, and F4/80) that are highly expressed in all of our experimental groups. Thus, these genes become candidates for essential functions during rejection.

Impaired NF-kappaB activation in T cells permits tolerance to primary heart allografts and to secondary donor skin grafts

T-cell activation is essential for acute allograft rejection. However, the biochemical signaling pathways used by T cells mediating rejection have not been extensively investigated. In vitro, T-cell activation is associated with nuclear translocation of specific transcription factors that regulate expression of genes critical for T-cell function. Given the central role of NF-kappaB in T-cell activation In vitro, we examined its role in the acute rejection of skin and cardiac allografts using mice with defective NF-kappaB translocation in T cells due to the presence of a super repressor IkappaBalpha transgene. T-cell-intrinsic NF-kappaB activation was required for cardiac but not skin allograft rejection, suggesting differential T-cell priming by the two tissues. Strikingly, priming with heart allografts induced complete acceptance of subsequently transplanted donor skin grafts, indicating that impaired NF-kappaB activation in T cells facilitates the induction of donor-specific tolerance to highly immunogenic tissues. These data suggest the biochemical pathways necessary for allograft rejection vary, based on the antigen and the context in which it is presented, and that inhibition of T-cell-intrinsic NF-kappaB activation during allogeneic priming may represent a novel strategy whereby tolerance to transplanted organs can be achieved.

Interferon-gamma is not a universal requirement for islet allograft survival

BACKGROUND

Although many transplantation studies have implicated a graft-destructive role for T helper (Th)1 cytokines and a graft-protective role for Th2 cytokines, more recent studies have challenged this paradigm by showing that long-term allograft survival can actually require the presence of Th1 cytokines, such as interleukin 2 and interferon (IFN)-gamma. The purpose of this study was to examine the requirement for IFN-gamma in the induction of islet allograft acceptance after monoclonal antibody therapy targeting conceptually distinct molecular pathways: the costimulatory molecule CD154, the CD4 coreceptor, or the beta2 integrin lymphocyte function-associated antigen (LFA)-1 (CD11a).

METHODS

Diabetic C57Bl/6 (B6; H2b) mice were grafted with fully MHC mismatched BALB/c (H2d) islets, or reciprocally, diabetic BALB/c mice underwent transplantation with B6 islets and were treated with anti-CD154, anti-CD4, or anti-LFA-1.

RESULTS

When IFN-gamma gene knockout mice were used as graft recipients, the requirement for IFN-gamma in allograft survival was found to be highly conditional, depending on both the host strain and the induction therapy used. In both strain combinations studied, anti-CD154 was effective in the presence or absence of IFN-gamma, whereas anti-CD4 lost therapeutic potential in the absence of this cytokine. Alternatively, the requirement for IFN-gamma for allograft prolongation by anti-LFA-1 therapy was noted only in B6 transplant recipients.

CONCLUSIONS

IFN-gamma is not always requisite in islet allograft survival but rather varies according to the molecular target of induction therapy and the genetic background of the transplant recipient.

Pattern of alloimmune response in second same donor allografts after induction of tolerance using CTLA4Ig

BACKGROUND

The pattern of allograft acceptance in the presence of costimulatory blockade is manifested by the sequential appearance of Th1 cells, followed by Th2 cells. The aim of this study was to examine whether this phenomenon repeats itself after second same donor allotransplantation, hoping to determine whether acceptance in this setting provokes a predominance of the Th2 response.

METHODS

Tolerance was achieved by transplantation of CTLA4Ig-transduced ACI liver allografts in Lewis recipients. Recipient long-term survivors received a second transplant, consisting of a cervical heterotopic heart from the same ACI donor strain. Animals were sacrificed at predetermined intervals following the second transplant and the heart and liver were processed for histology and cytokine mRNA expression.

RESULTS

Recipients of CTLA4Ig-transduced livers survived indefinitely. Rechallenge with same donor strain second allograft was manifested by an anergic immune response in the second cardiac allograft, and a very mild transient infiltrate within the first accepted liver graft. Cardiac function was maintained with resolution of all infiltrates. The cytokine cascade was activated within the allografts; however, the pattern of acceptance was not associated with predominance of a specific Th subtype.

CONCLUSIONS

The pattern of acceptance of an allograft following CTLA4Ig-mediated costimulatory blockade is not related to long-term predominance of Th2 cells, a phenomenon that may be unique to the setting of a tolerant liver. It may be likely that the infiltrating lymphocytes that are dominant in the second graft are suppressed by other memory mechanisms.

CD8 T cell-mediated rejection of intestinal allografts is resistant to inhibition of the CD40/CD154 costimulatory pathway

BACKGROUND

Disruption of the CD40/CD154 pathway inhibits rejection in numerous models. The importance of this pathway on intestinal allograft rejection was examined in this study.

METHODS

Intestinal grafts from B6C3F1 mice transplanted into C57BL/6 recipients were assessed histologically for rejection.

RESULTS

The monoclonal antibody to CD154, MR1, failed to inhibit rejection in wild-type mice. Similarly, CD154-/- recipient mice rejected intestinal allografts. MR1 did inhibit early rejection in CD8-/- mice, but had no effect in CD4-/- recipients. All MR1-treated CD8-/- recipients eventually developed rejection. No benefit was observed when blockade of the CD40/CD154 pathway by MR1 was combined with blockade of the CD28/B7 pathway by mCTLA4Ig.

CONCLUSIONS

These data suggest that CD4+ T cells mediating intestinal allograft rejection may be more dependent upon the CD40/CD154 pathway than CD8+ T cells. This finding highlights the importance of identifying agents that suppress CD8+ T cell-mediated rejection.

Analysis of alloreactivity and intragraft cytokine profiles in living donor liver transplant recipients with graft acceptance

Although some previous studies have indicated the possibility of immunosuppression withdrawal in clinical liver transplantation, the mechanism of graft acceptance is not clear. The aim of this study is to elucidate the alloreactivity against the donor and intragraft cytokine profiles in living donor liver transplant (LDLT) recipients with graft acceptance. In October 1999, we had 23 patients who survived without immunosuppression after LDLT with a median drug-free period of 25 months (range: 3-69 months). They consisted of six patients who were electively weaned by an elective weaning protocol and 17 either forcibly or accidentally weaned patients due to various causes but mainly due to infection. We evaluated the alloreactivity against the donor in these patients by a mixed lymphocyte reaction and intragraft cytokine profiles by real-time reverse transcriptase-polymerase chain reaction. The development of donor-specific hyporeactivity was observed in the patients with graft acceptance. The cytokine pattern in the supernatant of the culture medium revealed a down regulation of T helper (Th) 1 cytokine INF gamma against the donor while no significant difference was seen in Th2 cytokine IL-10. Regarding the intragraft cytokine profiles, we could find no amplification of Thl cytokines (IL-2, INF y) and IL-4 while some of the patients revealed a gene expression of IL-10 with no significant difference from that of the normal, untransplanted liver specimen. In addition, no difference was observed in any other cytokines (IL-1beta, IL-8, IL-15, TNFalpha) compared with those of the normal controls. We propose that the down regulation of Th1 cytokine is one possible mechanism of graft acceptance in LDLT recipients.