A rendezvous before rejection: where do T cells meet transplant antigens?

Basic Understanding of Liver Transplant Immunology

The liver is a specialized organ and plays an important role in our immune system. The liver constitutes parenchymal cells which are hepatocytes and cholangiocytes (60-80%) and non-parenchymal cells like liver sinusoidal endothelial cells (LSECs), hepatic satellite/Ito cells, Kupffer cells, neutrophils, mononuclear cells, T and B lymphocytes (conventional and non-conventional), natural killer cells, and natural killer T (NKT) cells. The liver mounts a rapid and strong immune response, under unfavorable conditions and acts as an immune tolerance to a variety of non-pathogenic antigens. This delicate and dynamic interaction between different kinds of immune cells in the liver maintains a balance between immune screening and immune tolerance. The liver allografts are privileged immunologically; however, allograft rejection is not uncommon and is classified as cell or antibody-mediated. Advancements in transplant immunology help in the prevention of allografts rejection by immune reactions of the host thus leading to better graft and host survival. Fewer patients may not require immunosuppression due to systemic donor-specific T-cell tolerance. The liver tolerance mechanism is poorly studied, and LSEC and unconventional lymphocytes play an important role that dampens T cell response either by inducing apoptosis of cells or inhibiting co-stimulatory pathways. Newer cell-based therapy based on Treg, dendritic cells, and mesenchymal stromal cells will probably change the future of immunosuppression. Various invasive and non-invasive biomarkers and artificial intelligence have also been investigated to predict graft survival, post-transplant complications, and immunotolerance in the future.

T, NK, then macrophages: Recent advances and challenges in adaptive immunotherapy from human pluripotent stem cells

Adaptive cellular immunotherapy, especially chimeric antigen receptor-T (CAR-T) cell therapy, has advanced the treatment of hematological malignancy. However, major limitations still remain in the source of cells comes from the patients themselves. The use of human pluripotent stem cells to differentiate into immune cells, such as T cells, NK cells, and macrophages, then arm with chimeric antigen receptor (CAR) to enhance tumor killing has gained major attention. It is expected to solve the low number of immune cells recovery from patients, long waiting periods, and ethical issues(reprogramming somatic cells to produce induced pluripotent stem cells (iPS cells) avoids the ethical issues unique to embryonic stem cells (Lo and Parham, 2009). However, there are still major challenges to be further solved. This review summarizes the progress, challenges, and future direction in human pluripotent stem cell-based immunotherapy.

Immune complexome analysis of antigens in circulating immune complexes from patients with acute cellular rejection after living donor liver transplantation

Liver transplantation is a life-saving procedure for many end-stage liver diseases; however, rejection after transplantation is still occurs in some recipients. The most common form of rejection is T cell-related acute cellular rejection (ACR). To understand the mechanism of rejection, it is necessary to identify immune targets. Since the development of B cell immunity depends upon concordant T cell immunity, we hypothesized that rejection-specific antigens in circulating immune complexes (CICs) may be present in the sera of recipients experiencing rejection, and as such, may be useful as diagnostic biomarkers for ACR. The purpose of this study was to investigate rejection-specific antigens in CICs (CIC-antigens) in serum of ACR patients. We applied immune complexome analysis, in which CICs are separated from whole serum and then subjected to direct tryptic digestion and identification of CIC-antigens by nano-liquid chromatography-tandem mass spectrometry, to sera of 32 living donor liver transplant recipients (10 recipients experienced ACR and the others did not experience). CIC-antigens were compared between rejection and non-rejection groups to elucidate those that were only detected in the rejection group. We identified 11 CIC-antigens that were only detected in patients who experienced rejection, 4 of which (thrombospondin-1, apolipoprotein E, apolipoprotein C-III, and complement factor H) were only detected during ACR.

Exosomal miR-142-3p is increased during cardiac allograft rejection and augments vascular permeability through down-regulation of endothelial RAB11FIP2 expression

Aims

Exosome-mediated microRNA transfer is a recently discovered mode of cell-to-cell communication, in which microRNAs act as paracrine molecules, exerting their regulatory effects in recipient cells. T cells and endothelial cells are two main players in the mechanism of acute cellular cardiac rejection. The aim of this study was to investigate the role of exosomal microRNAs in the crosstalk between T cells and endothelial cells and its implications for the molecular mechanisms that drive acute cellular rejection in heart transplantation.

Methods and results

Exosomes isolated from serum samples of heart transplant patients with and without acute cardiac allograft rejection were profiled and showed enrichment of miR-142-3p, miR-92a-3p, miR-339-3p and miR-21-5p. Treatment of endothelial cells with the respected serum exosomes resulted the increased of miR-142-3p level in endothelial cells. Using T cells isolated from healthy donors and activated with either anti-CD3/CD28 antibody or IL-2/PHA, we could show that miR-142-3p is released from activated cells, is contained in exosomes and can be transferred to human vascular endothelial cells in vitro. Transcriptome analysis of endothelial cells treated with activated T cell supernatant with or without exosomes was used to identify mRNA targets of transferred miR-142-3-p. Overexpression of miR-142-3p in endothelial cells resulted in a significant down-regulation of RAB11FIP2, and interaction of miR-142-3p with its predicted target site was confirmed with a reporter assay. Moreover, treatment of endothelial cells with serum exosomes from heart transplant patients with acute cellular rejection resulted in down-regulation of RAB11FIP2 expression and increase in vascular endothelial permeability.

Conclusion

We have identified a novel mechanism whereby miR-142-3p, a microRNA enriched in exosomes during acute cellular rejection, is transferred to endothelial cells and compromises endothelial barrier function via down-regulation of RAB11FIP2. This study sheds new light on the interaction between host immune system and cardiac allograft endothelium during acute cellular rejection.

Effects of 6 months yoga program on renal functions and quality of life in patients suffering from chronic kidney disease

Aim:

To study the effect of 6 months yoga program in patients suffering from chronic kidney disease (CKD).

Materials and Methods:

Fifty-four patients with CKD were studied and divided into two groups (yoga group and control group) to see the effect of yoga in CKD. Patients in the yoga group were offered yoga therapy along with other conventional treatment modalities, while the control group was only on conventional treatment. Subjects in yoga group were trained to perform specific yogic asanas for at least 5 days a week for 40–60 min a day. Regular monitoring of blood pressure, renal function, requirement of a number of dialysis, and quality of life (QOL) indicators were done. Fifty patients (yoga – 25; control-25) completed 6 months follow-up.

Results:

In yoga group, a significant reduction of systolic and diastolic blood pressure, significant reduction in blood urea and serum creatinine levels, and significant improvement in physical and psychological domain of the World Health Organization QOL (as assessed by BREF QOL scores) were seen after 6 months. In control group, rise of blood pressure, deterioration of renal function, and QOL were observed. Poststudy comparison between the two groups showed a statistically significant reduction of blood pressure, nonsignificant reduction in blood urea and serum creatinine, and significant improvement in physical and psychological domain of QOL in yoga group as compared to control group. For subjects in yoga group, the need for dialysis was less when compared to control group although this difference was statistically insignificant. Except for inability of some patients to perform certain yogic asanas no adverse effect was found in the study.

Conclusion:

Six months yoga program is safe and effective as an adjuvant therapy in improving renal functions and QOL of CKD patients.

The intragraft microenvironment as a central determinant of chronic rejection or local immunoregulation/tolerance

PURPOSE OF REVIEW

Chronic rejection is associated with persistent mononuclear cell recruitment, endothelial activation and proliferation, local tissue hypoxia and related biology that enhance effector immune responses. In contrast, the tumor microenvironment elicits signals/factors that inhibit effector T cell responses and rather promote immunoregulation locally within the tissue itself. The identification of immunoregulatory check points and/or secreted factors that are deficient within allografts is of great importance in the understanding and prevention of chronic rejection.

RECENT FINDINGS

The relative deficiency of immunomodulatory molecules (cell surface and secreted) on microvascular endothelial cells within the intragraft microenvironment, is of functional importance in shaping the phenotype of rejection. These regulatory molecules include coinhibitory and/or intracellular regulatory signals/factors that enhance local activation of T regulatory cells. For example, semaphorins may interact with endothelial cells and CD4 T cells to promote local tolerance. Additionally, metabolites and electrolytes within the allograft microenvironment may regulate local effector and regulatory cell responses.

SUMMARY

Multiple factors within allografts shape the microenvironment either towards local immunoregulation or proinflammation. Promoting the expression of intragraft cell surface or secreted molecules that support immunoregulation will be critical for long-term graft survival and/or alloimmune tolerance.

[Immunology and immunosuppression in kidney transplantation. ABO and HLA incompatible kidney transplantation]

OBJECTIVES

To perform a state of the art about immunological features in renal transplantation, immunosuppressive drugs and their mechanisms of action and immunologically high risk transplantations such as ABO and HLA-incompatible transplantation.

MATERIAL AND METHODS

An exhaustive systematic review of the scientific literature was performed in the Medline database (http://www.ncbi.nlm.nih.gov) and Embase (http://www.embase.com) using different associations of the following keywords (MESH): "allogenic response; allograft; immunosuppression; ABO incompatible transplantation; donor specific antibodies; HLA incompatible; desensitization; kidney transplantation". Publications obtained were selected based on methodology, language, date of publication (last 10 years) and relevance. Prospective and retrospective studies, in English or French, review articles; meta-analysis and guidelines were selected and analyzed. This search found 4717 articles. After reading titles and abstracts, 141 were included in the text, based on their relevance.

RESULTS

The considerable step in comprehension and knowledge allogeneic response this last few years allowed a better used of immunosuppression and the discover of news immunosuppressive drugs. In the first part of this article, the allogeneic response will be described. The different classes of immunosuppressive drugs will be presented and the actual management of immunosuppression will be discussed. Eventually, the modalities and results of immunologically high-risk transplantations such as ABO and HLA incompatible transplantations will be reported.

CONCLUSIONS

The knowledge and the control of allogeneic response to allogeneic graft allowed the development of renal transplantation.

Recombinant HLA-G as Tolerogenic Immunomodulant in Experimental Small Bowel Transplantation

The non-classical MHC I paralogue HLA-G is expressed by cytotrophoblast cells and implicated with fetomaternal tolerance by downregulating the maternal adaptive and innate immune response against the fetus. HLA-G expression correlates with favorable graft outcome in humans and recently promising immunosuppressive effects of therapeutic HLA-G in experimental transplantation (skin allograft acceptance) were shown. Consequently, we examined this novel therapeutic approach in solid organ transplantation. In this study, therapeutic recombinant HLA-G5 was evaluated for the first time in a solid organ model of acute rejection (ACR) after orthotopic intestinal transplantation (ITX). Allogenic ITX was performed in rats (Brown Norway to Lewis) with and without HLA-G treatment. It was found that HLA-G treatment significantly reduced histologically proven ACR at both an early and late postoperative timepoint (POD 4/7), concomitant to a functionally preserved graft contractility at POD 7. Interestingly, graft infiltration by myeloperoxidase+ cells was significantly reduced at POD7 by HLA-G treatment. Moreover, HLA-G treatment showed an effect on the allogenic T-cell immune response as assessed by flow cytometry: The influx of recipient-derived CD8⁺ T-cells into the graft mesenteric lymphnodes at POD7 was significantly reduced while CD4⁺ populations were not affected. As a potential mechanism of action, an induction of T-reg populations in the mesenteric lymphnodes was postulated, but flow cytometric analysis of classical CD4⁺/CD25⁺/FoxP3⁺T_reg-cells showed no significant alteration by HLA-G treatment. The novel therapeutic approach using recombinant HLA-G5 reported herein demonstrates a significant immunosuppressive effect in this model of allogenic experimental intestinal transplantation. This effect may be mediated via inhibition of recipient-derived CD8⁺ T-cell populations either directly or by induction of non-classical T_reg populations.

Kidney Graft Survival in Italy and Factors Influencing it

Purpose

National registry data are often a suitable basis for examination of transplant outcomes. Using data supplied by the Italian National Transplant Registry, established in 1995, we performed the first nationwide analysis of this kind.

Methods

A retrospective analysis of 4893 recipients of cadaveric kidneys transplanted in all Italian centers from 1995 through 2000 was done to study 5-year graft survival. The association between some donor and recipient variables and outcomes in renal transplantation was analyzed. Graft survival was 93% at 3 months, 89% at 1 year, 82% at 3 years, and 80% at 5 years after transplantation.

Results

A significant association between graft survival and donor age (old vs young, relative risk [RR] = 1.62, 95% CI 1.27–2.06) and recipient age (old vs young, RR = 1.25, 95% CI 1.02–1.53). Graft survival was also associated with cold ischemia time (24–36 hours, RR=1.39, 95% CI 1.05–1.85 and >36 hours, RR=1.94, 95% CI 1.32–2.86 vs 0–24 hours) and donor/recipient sex mismatch (female/male vs male/male, RR=1.50, 95% CI 1.17–1.93).

Conclusion

The quality of kidney transplantation in Italy is satisfactory and is comparable to that in other developed countries. Furthermore, our experience confirms that both donor and recipient factors are major determinants of renal allograft function.

The tryptophan metabolite 3-hydroxyanthranilic acid suppresses T cell responses by inhibiting dendritic cell activation

The generation of tryptophan (Trp) metabolites by indoleamine 2,3-dioxygenase (IDO) is an effective mechanism for T cell suppression. However, the effect of Trp metabolites on dendritic cells (DCs) remains unclear. Here, we investigated whether the tryptophan metabolite 3-hydroxyanthranilic acid (3-HAA) directly inhibits DC activation and is responsible for T cell suppression. We found that 3-HAA treatment significantly reduced IL-12, IL-6, and TNF-α production in bone marrow-derived DCs (BMDCs) stimulated with LPS. Maturation markers CD40, CD80, CD86, and I-A were also significantly reduced. Moreover, treatment with 3-HAA decreased the ability of DCs to stimulate T cell activation and differentiation in vitro and in vivo. Finally, we observed that phospho-JNK and phospho-38 levels were reduced in 3-HAA-treated DC2.4 cells and BMDCs. These results suggest that the tryptophan metabolite 3-HAA suppresses T cell responses by inhibiting DC activation.

The difficulty in defining extended donor criteria for liver grafts: the Eurotransplant experience

Donor criteria for liver grafts have been expanded because of organ shortage. Currently, no exact definitions for extended donor grafts have been established. The aim of this study was to analyze the impact of donor-specific risk factors, independent of recipient characteristics. In collaboration with Eurotransplant and European Liver Transplant Register, solely donor-specific parameters were correlated with 1-year survival following liver transplantation. Analyses of 4701 donors between 2000 and 2005 resulted in the development of a nomogram to estimate graft survival for available grafts. Predictions by nomogram were compared to those by Donor Risk Index (DRI). In the multivariate analysis, cold ischemic time (CIT), highest sodium, cause of donor death, γ-glutamyl transferase (γ-GT), and donor sex (female) were statistically significant factors for 3 months; CIT, γ-GT, and cause of donor death for 12-month survival. The median DRI of this study population was 1.45 (Q1: 1.17; Q3: 1.67). The agreement between the nomogram and DRI was weak (kappa = 0.23). Several donor-specific risk factors were identified for early survival after liver transplantation. The provided nomogram will support quick organ quality assessment. Nevertheless, this study showed the difficulties of determining an exact definition of extended criteria donors.

Endothelial cell activation and proliferation modulate NKG2D activity by regulating MICA expression and shedding

MICA are major histocompatibility complex class I-related molecules, expressed by endothelial cells (ECs), that may be targets for alloantibodies and NKG2D-expressing natural killer (NK) and T effector cells in organ allografts. This study shows that basal levels of MICA expressed on vascular ECs is sufficient to functionally modulate the expression and activity of the immunoreceptor NKG2D in allogeneic NK cells. We found that MICA expression is differentially regulated at the EC surface in response to cytokines. TNFα upregulates MICA while IFNγ significantly decreases MICA at the EC surface. Both cytokines induce the release of soluble MICA by ECs. Modulation of NKG2D correlates with the MICA level on the EC surface. Glycosylation and metalloproteinase activities account for major post-transcriptional mechanisms controlling MICA level and the function in ECs. Our results indicate that, in addition to the NFκB pathway, the mitogen-activated protein kinase pathways JNK, ERK1/2 and p38 are key signaling pathways in the control of MICA by the cytokines. Finally, we show that EC proliferation mediated by FGF-2 or wound healing increases the MICA level. Together, our data suggest that inflammation and proliferation regulate endothelial MICA expression and shedding, enabling ECs to modulate NKG2D activity on effector NK and T cells, and provide further evidence of a role for ECs in immunoregulation.

What is the significance of HLA-DR antigen expression in the extraglomerular mesangium in glomerulonephritis?

INTRODUCTION AND AIMS

The HLA-DR antigen is a HLA class II molecule involved in the presentation of antigenic peptides to the T cell receptor, thus regulating the immune response. Renal expression of the HLA-DR antigen may indicate specific sites of immunologically-mediated kidney injury in glomerulonephritis (GN). The aim of our study was to assess the presence of the HLA-DR antigen along the nephron including the extraglomerular mesangium in GN.

METHODS

A cross-sectional study of 22 patients with glomerulonephritis, mean age: 46.59±10.77 years, 14 male and 8 female, was conducted. Conventional stains, as well as immunohistochemistry for the HLA-DR Antigen Alpha-Chain were employed on kidney biopsies. Immunohistochemistry was assessed using a semi-quantitative score: 0-absent, 1-mild, 2-moderate, 3-intense. Statistical analysis was performed using SPSS17.

RESULTS

Four patients presented Focal and Segmental Glomerulosclerosis (FSGS), 5 patients: membranoproliferative GN, 7 patients: membranous nephropathy, 3 patients: mesangial proliferative GN, 2 patients: minimal change disease (MCD), and 1 patient: crescentic GN. Regarding the percentage of cases with HLA-DR positive cells along the nephron out of 22 patients: glomerular endothelial cells were 100% positive, intraglomerular mesangium cells were 81.8% positive, podocytes were 36.4% positive, extraglomerular mesangium cells were 31.8% positive, proximal tubule cells were 95.5% positive, distal tubule cells were 68.2% positive, interstitial capillaries were 77.3% positive, and cells of interstitial infiltrates were 27.3% positive. The percentage of cases staining positively for the HLA-DR antigen in the extraglomerular mesangium was 25% in FSGS, 60% in membranoproliferative GN, 0% in membranous nephropathy, 33.3% in mesangial proliferative GN, 100% in minimal change disease and 0% in crescentic GN.

CONCLUSIONS

A prominent HLA-DR antigen distribution was found on glomerular endothelial cells, intraglomerular mesangium cells and proximal and distal tubular cells. Extraglomerular mesangium cells and podocytes stained variably for the HLA-DR antigen, as did the cells of the interstitial infiltrates. The extraglomerular mesangium which serves as a portal of entry into the intraglomerular mesangium is endowed with antigen-presenting capabilities and is a region where induction of immune reactions could take place.

Targeting the intragraft microenvironment and the development of chronic allograft rejection

In this review, we discuss a paradigm whereby changes in the intragraft microenvironment promote or sustain the development of chronic allograft rejection. A key feature of this model involves the microvasculature including (a) endothelial cell (EC) destruction, and (b) EC proliferation, both of which result from alloimmune leukocyte- and/or alloantibody-induced responses. These changes in the microvasculature likely create abnormal blood flow patterns and thus promote local tissue hypoxia. Another feature of the chronic rejection microenvironment involves the overexpression of vascular endothelial growth factor (VEGF). VEGF stimulates EC activation and proliferation and it has potential to sustain inflammation via direct interactions with leukocytes. In this manner, VEGF may promote ongoing tissue injury. Finally, we review how these events can be targeted therapeutically using mTOR inhibitors. EC activation and proliferation as well as VEGF-VEGFR interactions require PI-3K/Akt/mTOR intracellular signaling. Thus, agents that inhibit this signaling pathway within the graft may also target the progression of chronic rejection and thus promote long-term graft survival.

Differential activation of human T cells to allogeneic endothelial cells, epithelial cells and fibroblasts in vitro

BACKGROUND

In the direct pathway, T cells recognize intact donor major histocompatability complexes and allogeneic peptide on the surface of donor antigen presenting cells (APCs). Indirect allorecognition results from the recognition of processed alloantigen by self MHC complexes on self APCs. In this study, we wished to evaluate the relative contribution of different intragraft cells to the alloactivation of nave and memory T cells though the direct and the indirect pathway of allorecognition.

METHODS

The processing of membrane fragments from IFN-treated single donor endothelial cells (EC), fibroblasts or renal epithelial cells (RPTEC) was evaluated by DiOC labeling of each cell type and flow cytometry following interaction with PBMC. Direct pathway activation of nave CD45RA+ or memory CD45RO+ CD4+ T cells was evaluated following coculture with IFN-treated and MHC class II-expressing EC, fibroblasts or RPTEC. Indirect pathway activation was assessed using CD45RA+ or CD45RO+ CD4+ T cells cocultured with autologous irradiated APCs in the absence or presence of sonicates derived from IFN-treated allogeneic EC, fibroblasts or RPTEC. Activation of T cells was assessed by [3H]thymidine incorporation and by ELISpot assays.

RESULTS

We find that CD14+ APCs readily acquire membrane fragments from fibroblasts and RPTEC, but fail to acquire membrane fragments from intact EC. However, APCs process membranes from EC undergoing apoptosis.There was a notable direct pathway alloproliferative response of CD45RO+ CD4+ T cells to IFN-treated EC, but not to fibroblasts or RPTEC. Also, there was a minimal direct pathway response of CD45RA+ CD4+ T cells to all cell types. In contrast, we found that both CD45RA+ and CD45RO+ CD4+ T cells proliferated following coculture with autologous APCs in the presence of sonicates derived from IFN-treated EC, fibroblasts or RPTEC. By ELISpot, we found that these T cells stimulated via the indirect pathway also produced the cytokines IFN, IL-2, IL-4 and IL-5.

CONCLUSIONS

Recipient APCs may readily process membrane fragments from allogeneic intragraft cells, but not from EC unless they are undergoing apoptosis. This processing is sufficient for indirect pathway alloactivation of both CD45RA+ and CD45RO+ CD4+ T cells. Only graft vascular EC mediate direct pathway reactivation of CD4+ T cells.

Key Features of the Intragraft Microenvironment that Determine Long-Term Survival Following Transplantation

In this review, we discuss how changes in the intragraft microenvironment serve to promote or sustain the development of chronic allograft rejection. We propose two key elements within the microenvironment that contribute to the rejection process. The first is endothelial cell proliferation and angiogenesis that serve to create abnormal microvascular blood flow patterns as well as local tissue hypoxia, and precedes endothelial-to-mesenchymal transition. The second is the overexpression of local cytokines and growth factors that serve to sustain inflammation and, in turn, function to promote a leukocyte-induced angiogenesis reaction. Central to both events is overexpression of vascular endothelial growth factor (VEGF), which is both pro-inflammatory and pro-angiogenic, and thus drives progression of the chronic rejection microenvironment. In our discussion, we focus on how inflammation results in angiogenesis and how leukocyte-induced angiogenesis is pathological. We also discuss how VEGF is a master control factor that fosters the development of the chronic rejection microenvironment. Overall, this review provides insight into the intragraft microenvironment as an important paradigm for future direction in the field.

Roles of vascular endothelial growth factor in acute rejection reaction following liver transplantation

The presently known cytokines that participate in acute rejection of organ transplantation include four categories by order of function: inflammatory cytokines, immunospecific cytokines, inflammatory cell activating cytokines and growth cytokines. Of them, growth cytokines that directly induce division, proliferation and migration of endothelial cells mainly include the vascular endothelial growth factor (VEGF) family and the fibroblast growth factor (FGF) family [1]. Recent studies [2] showed that interactions and time overlap of inflammatory cell infiltration and angiogenesis are the main mechanisms that induce acute rejection (AR) following organ transplantation, which has been demonstrated by the clinical fact that AR symptoms after liver transplantation could only be relieved by combination use of drugs for improving micro vessels and those for improving micro bile ducts. This article is a review of VEGF that mediates inflammatory cell infiltration and angiogenesis in the portal area [3].

Requirements for prolongation of allograft survival with regulatory T cell infusion in lymphosufficient hosts

BACKGROUND

For the clinical applicability of regulatory T cells (Tregs) in transplantation, it is critical to determine if donor antigen specificity is required for their immunosuppressive function. We developed an allospecific CD4(+) T cell receptor transgenic (TCR-tg) mouse as a source for large numbers of Tregs with defined allospecificity and tested whether they are more effective than polyclonal Tregs at suppressing allograft rejection.

MATERIALS AND METHODS

CD4(+)CD25(+)CD62L(hi) T cells were sorted from the spleen and peripheral lymph nodes of wild-type (WT-Tregs) and TCR-tg (Allo-Tregs) mice, and expanded using IL-2 and anti-CD3/anti-CD28 conjugated magnetic beads. Tregs were tested for their ability to suppress the proliferation and cytokine production of alloreactive CD4(+)CD25(-) T cells in mixed leukocyte assays. Syngeneic WT hosts were adoptively transferred 5 × 10(6) Tregs and transplanted with allogeneic hearts.

RESULTS

Using anti-CD3/anti-CD28 conjugated beads, Tregs were expanded in vitro 100-fold and maintained their suppressor phenotype and function. Allo-Tregs were 6-8 times more potent on a cell-for-cell basis than WT-Tregs in suppressing allospecific proliferation in vitro. Allo-Tregs were unable to suppress in the absence of allo-antigen. Adoptive transfer of expanded Allo-Tregs into WT recipients prolonged the graft survival in a F1 heart transplant model compared with WT-Treg or no treatment [20.0 ± 4.4 d (n = 6) versus 10.4 ± 1.2 (n = 8) and 9.7 ± 1.6 d (n = 6)].

CONCLUSIONS

Unlike polyclonal Tregs, allospecific Tregs are able to prolong allograft survival. However, large numbers of Allo-Tregs were unable to induce tolerance, suggesting that Treg therapy in immunocompetent recipients will require conditioning and/or additional immunomodulation for the induction of tolerance.

Regulation of human dendritic cells by a novel specific nuclear factor-kappaB inhibitor, dehydroxymethylepoxyquinomicin

Regulation of antigen-presenting cells (APC) is crucial in controlling allograft rejection. Dendritic cells (DC) are the most potent APC and must mature to present antigens to T-cell receptors. During DC maturation, nuclear factor-kappaB (NF-kappaB) is a key transcriptional factor. We synthesized dehydroxymethylepoxyquinomicin (DHMEQ), which specifically inhibits the final step of nuclear translocation of activated NF-kappaB proteins and examined its immunoregulatory effects on human monocyte-derived DC (Mo-DC). Regulatory Mo-DC were generated by pretreatment with DHMEQ before LPS stimulation, which were termed dl-DC. DHMEQ pretreatment (5 microg/ml) completely inhibited nuclear translocation of activated NF-kappaB. DHMEQ significantly inhibited DC production of proinflammatory cytokines (IL-6, TNF-alpha, and IL-12 p70) in a dose-dependent manner. IL-12 was most potently inhibited. However, IL-10 production by dl-DC was only moderately affected by DHMEQ. Although CD40 and the expression of HLA-DR (HLA-DR) expression on dl-DC was downregulated, CD80 and CD86 expression was moderately upregulated. Induction of T helper 1 cell responses was efficiently impaired by dl-DC. This confirmed that DHMEQ-treated Mo-DC exhibited immunoregulatory effects. These findings suggest that DHMEQ has potential as an immunosuppressive drug for human immune cells.

Renal ischemia-reperfusion leads to long term infiltration of activated and effector-memory T lymphocytes

It is well-established that significant ischemia-reperfusion injury during kidney transplantation results in increased incidence of long-term fibrosis and rejection. To test for a role of T cell infiltration and activation following ischemic injury, we induced both bilateral and unilateral renal ischemia in mice, followed by reperfusion, and then isolated mononuclear cells. Analysis of these cells by flow cytometry showed that 2 weeks after bilateral ischemia there was a significant increase of CD8(+) T cells. Furthermore, both CD4(+) and CD8(+) T cells infiltrated the injured kidney 6 weeks after unilateral ischemia. These T cells had increased expression of CD69(+) and CD44(hi)CD62L(-), markers of activation and effector-memory, respectively. CD4(+)NK1.1(+) and CD19(+) B cells were decreased in percentage both 6 and 11 weeks after bilateral or unilateral injury. There was a significant upregulation of IL-1beta, IL-6, TNF-alpha, IFN-gamma, MIP-2, and RANTES expression, measured by real-time PCR, 6 weeks after unilateral renal ischemia, further indicating T cell activation. Depletion of CD4(+) and CD8(+) T cells before ischemia caused less medullary damage and reduced kidney IFN-gamma expression, whereas their depletion following ischemia increased kidney IL-1beta; however, depletion of these cells had no effect on histological damage to the kidney. Our study demonstrates that moderate or severe kidney ischemia induces long-term T lymphocyte infiltration and cytokine/chemokine upregulation, leading to kidney structural changes.

Transplantation immunology: what the clinician needs to know for immunotherapy

The liver is unique among transplanted organs with respect to its interaction with the host immune system. There is evidence, both anecdotal and documented, that some liver recipients who cease taking immunosuppressive drugs maintain allograft function, suggesting robust tolerance is in place. Moreover, recipients of human liver allografts require less immunosuppression than do other organ recipients, and liver transplants confer protection on other organ grafts from the same donor. Hence, the liver shows features of immune privilege. Still, the liver can display destructive immunologic processes such as rejection in approximately one quarter of patients. The understanding of the cellular and molecular mechanisms operant in tolerance vs allograft rejection is important for developing new agents to improve long-term outcome, minimize infectious complications (including recurrence of hepatotropic viruses), and deliver immunosuppression without long-term toxicity. This review describes the unique aspects of the hepatic immune response, the pathways involved in T-cell activation and alloantigen recognition, effector cells and pathways mediating liver allograft rejection, the role of regulatory T cells, and targets of current and future immunosuppressive agents.

[Simultaneous pancreas-kidney transplantation. Influence of donor and recipient gender]

BACKGROUND

Differences in graft survival due to gender have been reported after transplantation of the kidney, liver, and heart. However, little is known about the role of donor and recipient gender in simultaneous pancreas-kidney transplantation.

METHODS

Single-centre analysis was performed of first simultaneous pancreas-kidney transplantations performed between 1994 and 2005 at the Bochum Transplant Center in Germany (n=218).

RESULTS

Recipients of female donor organs exhibited acute organ rejections earlier and more frequently (P<0.05). Male recipients of organs from male donors had a lower risk of acute rejection than recipients of female donor organs (P<0.05). In addition to female donor gender, higher donor age and early kidney dysfunction were risk factors for perioperative rejection (P<0.05). Long-term kidney and pancreas function was best in male-donor-to-female-recipient transplants over the time periods of 7 and 3 years, respectively (P<0.05). Risk factors of long-term organ failure were: the need of revision laparotomy, organ rejection, and early postoperative organ dysfunction (P<0.05).

CONCLUSION

This is the first report of graft function after simultaneous pancreas-kidney transplantation looking specifically at gender differences with respect to donor and recipient. There was an increased risk of organ rejection of female donor organs.

PDL1 is required for peripheral transplantation tolerance and protection from chronic allograft rejection

The PD-1:PDL pathway plays an important role in regulating alloimmune responses but its role in transplantation tolerance is unknown. We investigated the role of PD-1:PDL costimulatory pathway in peripheral and a well established model of central transplantation tolerance. Early as well as delayed blockade of PDL1 but not PDL2 abrogated tolerance induced by CTLA4Ig in a fully MHC-mismatched cardiac allograft model. Accelerated rejection was associated with a significant increase in the frequency of IFN-gamma-producing alloreactive T cells and expansion of effector CD8(+) T cells in the periphery, and a decline in the percentage of Foxp3(+) graft infiltrating cells. Similarly, studies using PDL1/L2-deficient recipients confirmed the results with Ab blockade. Interestingly, while PDL1-deficient donor allografts were accepted by wild-type recipients treated with CTLA4Ig, the grafts developed severe chronic rejection and vasculopathy when compared with wild-type grafts. Finally, in a model of central tolerance induced by mixed allogeneic chimerism, engraftment was not abrogated by PDL1/L2 blockade. These novel data demonstrate the critical role of PDL1 for induction and maintenance of peripheral transplantation tolerance by its ability to alter the balance between pathogenic and regulatory T cells. Expression of PDL1 in donor tissue is critical for prevention of in situ graft pathology and chronic rejection.

Initial steroid bolus injection promotes vigorous CD8+ alloreactive responses toward early graft acceptance immediately after liver transplantation in humans

We have found that steroid bolus withdrawal prior to graft reperfusion increased the incidence of acute cellular rejection (ACR). This study aims to clarify how initial steroid bolus (ISB) injection at reperfusion influences the kinetics of CD8(+) alloreactive immune responses immediately after living donor liver transplantation (LDLT). A total of 49 hepatitis C virus (HCV)-infected recipients were classified into 3 groups according to hierarchical clustering by preoperative CD8(+)CD45 isoforms. The naive T cell proportion was considerably higher in Group I than in Groups II and III, whereas Group II recipients had the highest effector memory (EM) T cells and Group III the highest effector T cells. The frequency of ACR was significantly higher in recipients without ISB than in those with ISB. In particular, the ACR rates were the highest in Group II without ISB. Following ISB, the proportion of effector T cells was promptly upregulated within 6 hours after graft reperfusion, simultaneously with the upregulation of CD27(-)CD28(-) subsets, interferon-gamma (IFN-gamma), tumor necrosis factor-alpha and perforin expression, which significantly correlated with increasing interleukin (IL)-12 receptor beta 1 cells. These were then downregulated to below preoperative levels by tacrolimus (Tac) administered at 24 hours. These changes did not occur in the absence of ISB. In Group II without ISB, the downregulation of IL-12Rbeta1(+) cells was the greatest, consistent with the highest rates of ACR and mortality (60%). In conclusion, ISB must be done in place, especially in Group II with preexisting high EM T cells, to enable the development of early allograft acceptance.

Organ-Specific Differences in the Function of MCP-1 and CXCR3 During Cardiac and Skin Allograft Rejection

BACKGROUND

Chemokines are well-established to function in the recruitment of leukocytes into allografts in the course of rejection. Moreover, some studies have indicated that there are organ-specific differences in chemokine function, but the mechanism accounting for this difference is not known.

METHODS

Fully major histocompatibility complex-mismatched vascularized cardiac transplants or skin transplants were performed using BALB/c (H-2d), C57BL/6 (H-2b), MCP-1-/- (H-2b) and CXCR3-/- (H-2b) mice as donors or recipients. Also, skin grafts (H-2b) were placed onto SCID mice (H-2d) that received BALB/c splenocytes (H-2d) by adoptive transfer either at the time of transplantation, or after a period of 28 days.

RESULTS

Cardiac allografts in MCP-1-/- recipients survived significantly longer (P<0.0005) than wild-type (WT) controls. However, there was no prolongation of survival when MCP-1-/- grafts were used a donors in WT mice. In contrast, the absence of donor but not recipient MCP-1 prolonged skin allograft survival. WT donor cardiac grafts in CXCR3-/- recipients had a modest prolongation of survival (P<0.0005), whereas CXCR3-/- donor cardiac grafts in WT recipients were rejected similar to controls. Also, while recipient CXCR3 had no effect on the rejection of skin, CXCR3-/- donor skin grafts survived significantly longer than WT controls. This survival advantage was lost when vascularized CXCR3-/- skin grafts were used as donors in the SCID model of rejection.

CONCLUSION

Recipient derived MCP-1 and CXCR3 are functional in the rejection of vascularized, but not nonvascularized, allografts. In contrast, donor-derived MCP-1 and CXCR3 are functional in nonvascularized, but not vascularized grafts.

Immunobiology of Rejection and Adaptation

Transplantation is an acceptable therapy for failing organs, however, the balance between prevention of acute rejection and immunosuppressant-induced toxicity remains elusive. Organ transplantation from a genetically disparate donor induces an immune response toward donor antigens in the recipient. An uncontrolled cumulative effect of these responses may jeopardize the recipient's life and destroy the grafted tissue. The donor antigen in the form of passenger leukocytes from the allograft migrating to the organized lymphoid collection is a prerequisite for initiation of acute rejection. In the host lymphoid tissue donor-specific dendritic cells primed with donor peptide activate naïve CD4 helper T cells which in turn activate effector CD8 T-cell clones through the release of cytokines. Activated effector CD8 cells return to the graft and augment destructive activity with the help of adhesive molecules and perforin. This seems to be the mechanism of adaptive immunity to destroy viral pathogens; the pattern of allograft injury is not much different. Adaptation and tolerance are based on the principle of exhaustion of donor-specific immune responses by an activation-deletion-exhaustion pathway.

Human Leukocyte Antigen and Its Role in Transplantation Biology

Human leukocyte antigens (HLA), the human version of the major histocompatibility complex (MHC), an integral part of maintenance of immune surveillance, have been widely studied for their roles in transplantation biology. A donor with an identical HLA system can donate tissue more successfully than the one who is not matched. The MHC is divided into class I, II, and III antigens; class I and II play important roles in transplantation immunology. HLA is codominantly expressed on chromosome 6 in every individual; HLA-A, -B, and -DR is known as the "haplo-type." There are two sets of HLA antigens in each individual. Thus a child can inherit four different haplo-type combinations from parents. There is a 25% chance of totally matched or mismatched siblings and a 50% chance of half-matched siblings among a family with parents being a 50% match. The main purpose of HLA typing and lymphocyte crossmatching (LCM) in transplantation is to assess donor-recipient immune compatibility and identify the presence of preformed donor-specific cytotoxic alloantibodies in the recipient. It can be tested by serology or molecular techniques. We studied 8462 individuals for HLA typing by serology supplemented with molecular techniques (sequence-specific primers with low resolution). The common alleles were HLA-A19 (9.4%), -A1 (7.7%), -A2 (7.2%), -B5 (10.2%), -B35 (6.6%), -B40 (5.3%), -DR2 (10.2%), -DR5 (7.5%), and -DR7 (5.1%). HLA typing and LCM testing support successful transplantation.

Expression and release of soluble HLA-E is an immunoregulatory feature of endothelial cell activation

Human leukocyte antigen (HLA)-E belongs, with HLA-G and HLA-F, to the non-classic major histocompatibility complex (MHC) class I (Ib) molecules, broadly defined by a limited polymorphism and a restricted pattern of cellular expression. In contrast to HLA-G, the expression and function of HLA-E and HLA-F in physiologic and pathologic processes remain poorly established. In the present study, we show that HLA-E protein expression in normal human nonlymphoid organs is mainly restricted to endothelial cells (ECs). HLA-E is also basally expressed by B and T lymphocytes, natural killer (NK) cells and by macrophages. We demonstrate that tumor necrosis factor alpha (TNFalpha), interleukin-1beta (IL-1beta), and interferon gamma (IFNgamma) up-regulate the cell-surface expression of HLA-E on ECs in vitro and induce the release of soluble HLA-E (sHLA-E). HLA-E up-regulation protects IFN-gamma-activated ECs from NK-mediated cell lysis, while sHLA-E protects bystander cells. Finally, sHLA-E is not detected in normal sera, and increased serum levels correlate with disease activity in patients with antineutrophil cytoplasmic antibody-associated systemic vasculitis. Thus, HLA-E expression and release of sHLA-E are features of EC activation and emphasize immunoregulatory functions of the endothelium. The present identification of soluble HLA-E molecules may have important implications in understanding the pathogenesis of immune-mediated vascular diseases and for the diagnosis and monitoring of patients.

A microsurgical approach to hepatic and extrahepatic antigen presentation and its effects on the migration pattern of activated CD8+ T cells

CD8+T lymphocytes activated in peripheral lymphoid organs are believed to preferentially localize to the hepatic sinusoids, but the role of antigen in the process has been difficult to define. To create experimental mice in which the liver was unique in lacking the ability to present antigen, we adopted a novel microsurgical approach, in which the site of antigen presentation was restricted by orthotopic mouse liver transplantation of MHC Class I-disparate livers. We used two related mouse strains, of which the wild-type strain could present an injectable model antigen, while a mutant strain could not. By transplanting mutant-strain livers into wild type recipients, we were able to evaluate the absence of intrahepatic parenchymal antigen presentation on CD8+ T cell activation, differentiation, and migration. This illustrates that orthotopic liver transplantation is a powerful technique for addressing issues of antigen presentation.

Phenotypic and Functional Characterization of Kidney-Infiltrating Lymphocytes in Renal Ischemia Reperfusion Injury

T and B lymphocytes have been implicated in the pathogenesis of renal ischemia reperfusion injury (IRI). The trafficking of lymphocytes into kidneys during IRI has been postulated to underlie this effect, but has not been rigorously studied. We therefore characterized the lymphocyte populations infiltrating into mouse kidneys 3 and 24 h after renal IRI. Immunohistochemistry and flow cytometry staining of kidney lymphocytes showed increased trafficking of CD3+ T cells and CD19+ B cells in both sham-operated and IRI mice 3 h after renal IRI. In the IRI mice, increased infiltration of NK1.1+ and CD4+ NK1.1+ cells compared with normal and sham-operated mice was observed 3 and 24 h after renal IRI, respectively. After 24 h of renal IRI, the decreased percentages of CD3+, CD19+, and NK1.1+ populations in the IRI mice compared with control groups were observed. Increased TNF-alpha and IFN-gamma production of kidney infiltration CD3+ T cells in IRI mice but not sham-operated mice was found. Unexpectedly, isolation and transfer of kidney-infiltrating lymphocytes 24 h after renal IRI into T cell-deficient mice reduced their functional and histological injury after renal IRI, suggesting that kidney-infiltrating lymphocytes could have a protective function. These quantitative, qualitative, and functional changes in kidney lymphocytes provide mechanistic insight into how lymphocytes modulate IRI, as well as demonstrating that abdominal surgery alone leads to lymphocyte changes in kidney.

Vascular endothelial growth factor-induced signaling pathways in endothelial cells that mediate overexpression of the chemokine IFN-gamma-inducible protein of 10 kDa in vitro and in vivo

Vascular endothelial growth factor (VEGF), an angiogenesis factor, has recently been found to have potent proinflammatory properties in vivo. However, the mechanism by which it mediates inflammation is poorly understood. In this study, we have evaluated the function of VEGF on the induced expression and function of the T cell chemoattractant chemokine IFN-gamma-inducible protein of 10 kDa (IP-10). In vitro, we find that VEGF augments the effect of IFN-gamma on the induction of IP-10 mRNA and protein expression in endothelial cells. Moreover, we show that VEGF and IFN-gamma regulate the activation of the IP-10 promoter, and that the kinases PI3K, phosphoinositide-dependent kinase 1, and Akt act as intermediary signaling molecules for cytokine-inducible IP-10 transcriptional activation in endothelial cells. To examine whether VEGF is functional for IP-10 expression in vivo, Chinese hamster ovary cells that were designed to secrete VEGF were injected s.c. into the skin of nude mice and were found to mediate a time-dependent increase in IP-10 mRNA. This response was reduced in animals treated systemically with the PI3K inhibitor wortmannin. When the Chinese hamster ovary cells expressing VEGF plasmid were injected s.c. into C57BL/6 wild-type or CXCR3-/- mice, they elicited an inflammatory reaction in wild-type but not in CXCR3-/- mice. Collectively, these findings indicate that VEGF-induced augmentation of IP-10 expression is a major mechanism underlying its proinflammatory function.

Gender-Specific Issues in Liver and Kidney Failure and Transplantation: A Review

INTRODUCTION

Historically, research has been performed in male animals and extrapolated to the care of females regardless of biological differences. Men and women differ, however, with regard to severity and pathogenesis of disease and healthcare needs and this uniform approach, regardless of gender, is not always in the best interests of the patient. The relationship between sex hormones and immunological processes has been extensively documented but is not yet well understood and these differences will be discussed as they relate to liver and kidney failure and transplantation.

DISCUSSION

Certain forms of organ failure are more common in either men or women and the physiological changes associated with pregnancy present unique challenges to the transplant physician since pregnancy may adversely affect graft function and immunosuppression presents a risk for opportunistic infection in the mother or fetal injury. Donor and recipient gender affect graft and patient survival after transplantation and there is clearly some gender bias in organ donation and transplantation.

CONCLUSIONS

We need to be mindful of these differences in relation to gender-specific diseases, hormonal and immunological differences in designing clinical protocols and treatment pathways in order to improve outcomes in transplantation. Unfortunately, this is difficult in an environment where our practice is largely restricted by a shortage of donor organs and the need to decrease waiting list mortality.

Blood Cyclosporine Level Soon After Kidney Transplantation is a Major Determinant of Rejection: Insights From the Mycophenolate Steroid-Sparing Trial

Target organs express antigens directly recognized by antigen-specific T cells, thereby precipitating rejection. When early T-cell activation is inhibited, there is a low risk of rejection. We sought to determine the predictive values of serial posttransplant blood cyclosporine trough (C(0)) concentrations to minimize the risk for a first rejection episode compared with 2-hour postdose (C(2)) drug concentrations. The final aim of the study was to identify a concentration range for the best predictive pharmacokinetic parameter that should be targeted to reduce the risk of rejection. This possibility was explored in 334 de novo kidney transplant recipients who participated in the prospective, multicenter Mycophenolate Steroid-Sparing Trial. Among measurements performed during the first 6 months postsurgery, cyclosporine C(0) levels measured early after transplantation were the strongest predictor of acute graft rejection. Levels within 300 to 440 ng/mL were associated with the lowest risk of rejection, while patients with levels lower than 300 ng/mL showed a more than double risk. Cyclosporine trough values predicted allograft rejection with an accuracy of 74%, while C(2) levels had no predictive value. These findings underline the need to target cyclosporine therapy early posttransplant to modulate T-cell activation.

Lymph Node Occupancy Is Required for the Peripheral Development of Alloantigen-Specific Foxp3+ Regulatory T Cells

We previously demonstrated that L-selectin (CD62L)-dependent T cell homing to lymph nodes (LN) is required for tolerance induction to alloantigen. To explore the mechanisms of this observation, we analyzed the development and distribution of regulatory T cells (Treg), which play an important protective role against allograft rejection in transplantation tolerance. Alloantigen-specific tolerance was induced using either anti-CD2 plus anti-CD3 mAbs, or anti-CD40L mAbs plus donor-specific transfusion, in fully mismatched (BALB/c donor, C57BL/6 recipient) vascularized cardiac allografts. An expansion of CD4(+)CD25(+)CD62L(high) T cells was observed specifically within the LN of tolerant animals, but not in other anatomic sites or under nontolerizing conditions. These cells exhibited a substantial up-regulation of Foxp3 expression as measured by real-time PCR and by fluorescent immunohistochemistry, and possessed alloantigen-specific suppressor activity. Neither LN nor other lymphoid cells expressed the regulatory phenotype if recipients were treated with anti-CD62L mAbs, which both prevented LN homing and caused early allograft rejection. However, administration of FTY720, a sphingosine 1-phosphate receptor modulator that induces CD62L-independent T cell accumulation in the LNs, restored CD4(+)CD25(+) Treg in the LNs along with graft survival. These data suggest that alloantigen-specific Foxp3(+)CD4(+)CD25(+) Treg develop and are required within the LNs during tolerization, and provide compelling evidence that distinct lymphoid compartments play critical roles in transplantation tolerance.

CD70 Signaling Is Critical for CD28-Independent CD8+T Cell-Mediated Alloimmune Responses In Vivo

The inability to reproducibly induce robust and durable transplant tolerance using CD28-B7 pathway blockade is in part related to the persistence of alloreactive effector/memory CD8(+) T cells that are less dependent on this pathway for their cellular activation. We studied the role of the novel T cell costimulatory pathway, CD27-CD70, in alloimmunity in the presence and absence of CD28-B7 signaling. CD70 blockade prolonged survival of fully mismatched vascularized cardiac allografts in wild-type murine recipients, and in CD28-deficient mice induced long-term survival while significantly preventing the development of chronic allograft vasculopathy. CD70 blockade had little effect on CD4(+) T cell function but prevented CD8(+) T cell-mediated rejection, inhibited the proliferation and activation of effector CD8(+) T cells, and diminished the expansion of effector and memory CD8(+) T cells in vivo. Thus, the CD27-CD70 pathway is critical for CD28-independent effector/memory CD8(+) alloreactive T cell activation in vivo. These novel findings have important implications for the development of transplantation tolerance-inducing strategies in primates and humans, in which CD8(+) T cell depletion is currently mandatory.

The role of nitric oxide in renal transplantation

This review discusses the concept that nitric oxide synthase (NOS) may orchestrate both the inflammatory response to the renal allograft and anti-inflammatory defense in the graft itself. NO is produced by endothelial, epithelial, as well as inflammatory cells. In the setting of transplantation, the endothelium is the first lining to be subjected to the early response to injury. In turn, activated endothelial cells facilitate leukocyte recruitment, immune-mediated injury, and angiogenesis. On activation by inflammatory stimuli, endothelial cells up-regulate multiple vasoactive substances, oxygen radicals, cytokines, chemokines, and growth factors. Therefore, endothelial integrity, especially the expression of protecting vasoactive agents, such as NO, may be a key factor in resistance or sensitivity to transplantation-mediated injury. Thus, evaluating the mechanisms by which NO is involved in either protecting or injuring the transplanted allogeneic kidney is important for our understanding of renal allograft rejection. This review focuses on the role of NO in the inflammatory endothelial-leukocyte interactions, which are implicated in acute and chronic rejection of the transplanted kidney.

TNP-470, an angiogenesis inhibitor, attenuates the development of allograft vasculopathy

Fischer 344 rat recipients of Lewis allografts were treated with TNP-470, a synthetic fumagillin derivative and a well-established angiogenesis inhibitor. TNP-470 alone resulted in some prolongation of graft survival as compared with untreated recipients, but all grafts ultimately failed. In contrast, treatment with cyclosporine (CsA) from day 0 to 30 resulted in prolonged graft survival and marked cardiac allograft vasculopathy (CAV) by histology (mean score 2.28+/-0.2). There were many neovessels within the intima of CAV lesions. When TNP-470 was administered in combination with CsA from day 0 to 30, the degree of CAV was similar to that with CsA alone (mean score 2.22+/-0.26). However, when TNP-470 was administered from day 30 to 120 after discontinuation of CsA, there was a marked reduction in the degree of CAV (mean score 1.08+/-0.11). Therefore, TNP-470 interrupts the progression of CAV when given late but does not prevent its development when given immediately posttransplantation.

CROSS-REACTIVITY OF CYTOMEGALOVIRUS-SPECIFIC CD8+ T CELLS TO ALLO-MAJOR HISTOCOMPATIBILITY COMPLEX CLASS I MOLECULES

BACKGROUND

In transplantation settings, cytomegalovirus (CMV) infection is a common complication. CMV infection is associated with a higher incidence of graft rejection in solid organ transplantation and graft-versus-host disease in bone marrow transplantation. The underlying mechanism of this association could be the generation of CMV-specific CD8 T cells capable of cross-reacting with alloantigens present on graft and host, respectively.

METHODS

Whereas as to date, no direct ex vivo analysis can be performed of the CD8 T-cell repertoire directed at allo-major histocompatibility complex (MHC) class I molecules, virus-specific cells can be readily enumerated by use of MHC-peptide tetrameric complexes. In this study, the authors used this technique to analyze potential overlapping CD8 T-cell repertoires between self-MHC-viral peptide and allo-MHC complexes by stimulating CMV-specific CD8 T cells with alloantigens. RESULTS.: The authors found that CMV-specific CD8 T cells are activated and proliferate on stimulation with alloantigens.

CONCLUSIONS

Although these cells are cytotoxic against CMV-peptide pulsed target cells, no cytotoxicity of CMV-specific cells to alloantigens could be detected, inferring that there are other mechanisms of graft damage by alloantigen-stimulated virus-specific CTL.

In renal transplantation blood cyclosporine levels soon after surgery act as a major determinant of rejection: Insights from the MY.S.S. Trial

BACKGROUND

Target organs express antigens recognized directly by antigen-specific T cells, and their recognition is crucial to precipitate rejection. Then, the earliest T-cell activation is inhibited by cyclosporine A (CsA), the lowest would be the risk of rejection. Here, we aimed to assess this possibility in a large cohort of de novo kidney transplant recipients participating in an ongoing clinical trial, the Mycophenolate Steroid-Sparing (MY.S.S.) Trial.

METHODS

Three-hundred-thirty-four patients entered the prospective, multicenter MY.S.S. trial. The main aim of the study was to assess the predictive value of serial evaluation of blood CsA trough concentration (C0) and 2-hour postdose drug (C2) levels alone or in combination, and to identify which is the critical posttransplant measurement to target CsA therapy in order to minimize the risk of acute rejection. A very large number of CsA trough (N= 2236) and C2 (N= 2128) measurements during the first 6 months postsurgery were available for analysis. Patients with delayed graft function were excluded.

RESULTS

CsA trough levels measured at day 2 posttransplant were the strongest predictor of acute graft rejection over 6-month follow-up. Levels within 300 to 440 ng/mL were associated with the lowest risk of rejection, while for levels lower than 300 ng/mL, the risk of acute rejection was more than doubled. Higher levels failed to provide any further protection from graft rejection. CsA trough values predicted allograft rejection with an accuracy of 74%, while C2 levels considered alone had no predictive values at all.

CONCLUSION

Findings that among serial daily measurements posttransplant those taken as early as at day 2 have by far the highest capacity to predict rejection episodes, underline the need of targeting CsA therapy very early posttransplant with the goal to modulate early enough T-cell activation at the interface between the recipient's blood and the graft where alloimmune response actually initiates.

Proinflammatory functions of vascular endothelial growth factor in alloimmunity

Vascular endothelial growth factor (VEGF), an established angiogenesis factor, is expressed in allografts undergoing rejection, but its function in the rejection process has not been defined. Here, we initially determined that VEGF is functional in the trafficking of human T cells into skin allografts in vivo in the humanized SCID mouse. In vitro, we found that VEGF enhanced endothelial cell expression of the chemokines monocyte chemoattractant protein 1 and IL-8, and in combination with IFN-gamma synergistically induced endothelial cell production of the potent T cell chemoattractant IFN-inducible protein-10 (IP-10). Treatment of BALB/c (H-2d) recipients of fully MHC-mismatched C57BL/6 (H-2b) donor hearts with anti-VEGF markedly inhibited T cell infiltration of allografts and acute rejection. Anti-VEGF failed to inhibit T cell activation responses in vivo, but inhibited intragraft expression of several endothelial cell adhesion molecules and chemokines, including IP-10. In addition, whereas VEGF expression was increased, neovascularization was not associated with acute rejection, and treatment of allograft recipients with the angiogenesis inhibitor endostatin failed to inhibit leukocyte infiltration of the grafts. Thus, VEGF appears to be functional in acute allograft rejection via its effects on leukocyte trafficking. Together, these observations provide mechanistic insight into the proinflammatory function of VEGF in immunity.

New frontiers: the 2002 FASEB Summer Research Conference in Transplant Immunology

The first Federation of American Societies for Experimental Biology (FASEB) summer research conference on transplantation immunology was organized by Angus Thomson (University of Pittsburgh), Robert Lechler (Imperial College London), Laurence Turka (University of Pennsylvania) and Megan Sykes (Massachusetts General Hospital). Over the past four decades, patient and graft survival rates for solid organ transplant recipients have improved dramatically; however, chronic rejection and the untoward effects of potent immunosuppressive drugs continue to loom. This symposium is a testament to the importance of bringing investigators from diverse biological backgrounds together in a single forum to discuss the fundamental issues of immune biology and advance the goal of transplant-specific tolerance.