Interferon-gamma acts directly on rejecting renal allografts to prevent graft necrosis

The transcriptional repressor B cell lymphoma 6 regulates CXCR3 chemokine and human leukocyte antigen II expression in endothelial cells

Interferon gamma (IFN-γ) induces an endothelial proimmunogenic phenotype through the JAK/STAT1 pathway, which can shape the activation of alloreactive leukocytes in transplant rejection. In immune cells, the DNA-binding protein B cell lymphoma 6 (BCL6) controls the transcription of inflammatory genes. This study tested if BCL6 modulates IFN-γ-induced gene expression in endothelial cells. In vitro, BCL6 was IFN-γ-inducible in primary human endothelium, along with CXCR3 chemokines and human leukocyte antigen (HLA). BCL6, HLA II, and CXCL9 were also increased in human cardiac transplants during acute rejection. Knockdown of BCL6 augmented, whereas overexpression and BTB domain inhibitors (BCL6-BTBi) suppressed, HLA II and CXCR3 chemokine expression but not HLA I. Further, BCL6 had a greater effect on HLA-DR and DP but was less involved in regulating HLA-DQ expression. The effect correlated with BCL6 binding motifs in or near affected genes. The BCL6 DNA recognition sequence was highly similar to that of STAT1, and BTBi reduced STAT1's transcriptional activity in vitro. Our results show for the first time that BCL6 selectively controls IFN-γ-induced endothelial gene expression, advancing our understanding of the endogenous mechanisms regulating donor immunogenicity.

Dynamic immune recovery process after liver transplantation revealed by single-cell multi-omics analysis

Elucidating the temporal process of immune remodeling under immunosuppressive treatment after liver transplantation (LT) is critical for precise clinical management strategies. Here, we performed a single-cell multi-omics analysis of peripheral blood mononuclear cells (PBMCs) collected from LT patients (with and without acute cellular rejection [ACR]) at 13 time points. Validation was performed in two independent cohorts with additional LT patients and healthy controls. Our study revealed a four-phase recovery process after LT and delineated changes in immune cell composition, expression programs, and interactions along this process. The intensity of the immune response differs between the ACR and non-ACR patients. Notably, the newly identified inflamed NK cells, CD14+RNASE2+ monocytes, and FOS-expressing monocytes emerged as predictive indicators of ACR. This study illuminates the longitudinal evolution of the immune cell landscape under tacrolimus-based immunosuppressive treatment during LT recovery, providing a four-phase framework that aids the clinical management of LT patients.

JAKinibs prevent persistent, IFNγ-autonomous endothelial cell inflammation and immunogenicity

The adhesion and subsequent activation of T cells is a critical step in local inflammatory responses, particularly of alloreactive leukocytes in rejection of transplanted donor tissue. Interferon (IFN)γ is an adaptive cytokine that promotes endothelial cell (EC) expression of pro-adhesive factors and costimulatory molecules. We recently reported that IFNγ-induced endothelial cell antigen-presenting capacity was protracted after cytokine withdrawal. This study sought to determine what intracellular signaling mediates this chronic endothelial activation by IFNγ. The durability of interferon signaling in human aortic endothelial activation was tested. Pro-adhesive and costimulatory gene expression, phenotype, secretome, and Janus kinase (JAK)/STAT phosphorylation in human primary endothelial cells were measured under chronic and transient IFNγ stimulation, with various JAK inhibitors. IFNγ reporter cells were tested for STAT1 transcriptional activity with JAK inhibition and suppressors of cytokine signaling (SOCS) overexpression, under continuous and priming conditions. The consequences of even short exposure to IFNγ were long-lasting and broad, with sustained elevation of adhesion molecules and chemokines up to 48 h later. JAK/STAT and interferon response factor expression were likewise durable, dependent on new transcription but autonomous of continuous IFNγ. Persistent STAT new transcription and JAK signaling in the endothelium was required to maintain a pro-adhesive and proimmunogenic phenotype after IFNγ withdrawal since both could be prevented by cycloheximide but only by JAKinibs with potency against JAK2. Finally, the suppressor of cytokine signaling SOCS1 failed to emerge in primed endothelial cells, which likely accounted for prolonged inflammatory gene expression. The results reveal a sustained JAK-dependent perturbation of endothelial function and suggest that JAKinibs may have therapeutic benefits in dampening vascular inflammation and allogeneic leukocyte activation.NEW & NOTEWORTHY The central question investigated in this study is why vascular endothelium remains inflamed and what underlying signaling is responsible. The new results show that the resolution of endothelial-controlled inflammation may be impaired or delayed because Janus kinase (JAK)/STAT activation is maintained autonomous of interferon (IFN)γ presence, and the late phase negative regulator suppressors of cytokine signaling (SOCS)1 fails to be induced.

New insights into maladaptive vascular responses to donor specific HLA antibodies in organ transplantation

Transplant vasculopathy (TV) causes thickening of donor blood vessels in transplanted organs, and is a significant cause of graft loss and mortality in allograft recipients. It is known that patients with repeated acute rejection and/or donor specific antibodies are predisposed to TV. Nevertheless, the exact molecular mechanisms by which alloimmune injury culminates in this disease have not been fully delineated. As a result of this incomplete knowledge, there is currently a lack of effective therapies for this disease. The immediate intracellular signaling and the acute effects elicited by anti-donor HLA antibodies are well-described and continuing to be revealed in deeper detail. Further, advances in rejection diagnostics, including intragraft gene expression, provide clues to the inflammatory changes within allografts. However, mechanisms linking these events with long-term outcomes, particularly the maladaptive vascular remodeling seen in transplant vasculopathy, are still being delineated. New evidence demonstrates alterations in non-coding RNA profiles and the occurrence of endothelial to mesenchymal transition (EndMT) during acute antibody-mediated graft injury. EndMT is also readily apparent in numerous settings of non-transplant intimal hyperplasia, and lessons can be learned from advances in those fields. This review will provide an update on these recent developments and remaining questions in our understanding of HLA antibody-induced vascular damage, framed within a broader consideration of manifestations and implications across transplanted organ types.

Uncovering a novel role of focal adhesion and interferon-gamma in cellular rejection of kidney allografts at single cell resolution

Background

Kidney transplant recipients are currently treated with nonspecific immunosuppressants that cause severe systemic side effects. Current immunosuppressants were developed based on their effect on T-cell activation rather than the underlying mechanisms driving alloimmune responses. Thus, understanding the role of the intragraft microenvironment will help us identify more directed therapies with lower side effects.

Methods

To understand the role of the alloimmune response and the intragraft microenvironment in cellular rejection progression, we conducted a Single nucleus RNA sequencing (snRNA-seq) on one human non-rejecting kidney allograft sample, one borderline sample, and T-cell mediated rejection (TCMR) sample (Banff IIa). We studied the differential gene expression and enriched pathways in different conditions, in addition to ligand-receptor (L-R) interactions.

Results

Pathway analysis of T-cells in borderline sample showed enrichment for allograft rejection pathway, suggesting that the borderline sample reflects an early rejection. Hence, this allows for studying the early stages of cellular rejection. Moreover, we showed that focal adhesion (FA), IFNg pathways, and endomucin (EMCN) were significantly upregulated in endothelial cell clusters (ECs) of borderline compared to ECs TCMR. Furthermore, we found that pericytes in TCMR seem to favor endothelial permeability compared to borderline. Similarly, T-cells interaction with ECs in borderline differs from TCMR by involving DAMPS-TLRs interactions.

Conclusion

Our data revealed novel roles of T-cells, ECs, and pericytes in cellular rejection progression, providing new clues on the pathophysiology of allograft rejection.

Beyond GWAS-Could Genetic Differentiation within the Allograft Rejection Pathway Shape Natural Immunity to COVID-19?

COVID-19 infections pose a serious global health concern so it is crucial to identify the biomarkers for the susceptibility to and resistance against this disease that could help in a rapid risk assessment and reliable decisions being made on patients' treatment and their potential hospitalisation. Several studies investigated the factors associated with severe COVID-19 outcomes that can be either environmental, population based, or genetic. It was demonstrated that the genetics of the host plays an important role in the various immune responses and, therefore, there are different clinical presentations of COVID-19 infection. In this study, we aimed to use variant descriptive statistics from GWAS (Genome-Wide Association Study) and variant genomic annotations to identify metabolic pathways that are associated with a severe COVID-19 infection as well as pathways related to resistance to COVID-19. For this purpose, we applied a custom-designed mixed linear model implemented into custom-written software. Our analysis of more than 12.5 million SNPs did not indicate any pathway that was significant for a severe COVID-19 infection. However, the Allograft rejection pathway (hsa05330) was significant (p = 0.01087) for resistance to the infection. The majority of the 27 SNP marking genes constituting the Allograft rejection pathway were located on chromosome 6 (19 SNPs) and the remainder were mapped to chromosomes 2, 3, 10, 12, 20, and X. This pathway comprises several immune system components crucial for the self versus non-self recognition, but also the components of antiviral immunity. Our study demonstrated that not only single variants are important for resistance to COVID-19, but also the cumulative impact of several SNPs within the same pathway matters.

Histologic and Molecular Patterns in Responders and Non-responders With Chronic-Active Antibody-Mediated Rejection in Kidney Transplants

Introduction

There is no proven therapy for chronic-active antibody-mediated rejection (caABMR), the major cause of late kidney allograft failure. Histological and molecular patterns associated with possible therapy responsiveness are not known.

Methods

Based on rigorous selection criteria this single center, retrospective study identified 16 out of 1027 consecutive kidney transplant biopsies taken between 2008 and 2016 with pure, unquestionable caABMR, without other pathologic features. The change in estimated GFR pre- and post-biopsy/treatment were utilized to differentiate subjects into responders and non-responders. Gene sets reflecting active immune processes of caABMR were defined a priori, including endothelial, inflammatory, cellular, interferon gamma (IFNg) and calcineurin inhibitor (CNI) related-genes based on the literature. Transcript measurements were performed in RNA extracted from stored, formalin-fixed, paraffin-embedded (FFPE) samples using NanoString™ technology. Histology and gene expression patterns of responders and non-responders were compared.

Results

A reductionist approach applying very tight criteria to identify caABMR and treatment response excluded the vast majority of clinical ABMR cases. Only 16 out of 139 cases with a written diagnosis of chronic rejection fulfilled the caABMR criteria. Histological associations with therapy response included a lower peritubular capillaritis score (p = 0.028) along with less glomerulitis. In contrast, no single gene discriminated responders from non-responders. Activated genes associated with NK cells and endothelial cells suggested lack of treatment response.

Conclusion

In caABMR active microvascular injury, in particular peritubular capillaritis, differentiates treatment responders from non-responders. Transcriptome changes in NK cell and endothelial cell associated genes may further help to identify treatment response. Future prospective studies will be needed which include more subjects, who receive standardized treatment protocols to identify biomarkers for treatment response.

Clinical Trial Registration

[ClinicalTrials.gov], identifier [NCT03430414].

Single-Cell RNA Sequencing Reveals the Immunological Profiles of Renal Allograft Rejection in Mice

Allograft rejection is a common immunological feature in renal transplantation and is associated with reduced graft survival. A mouse renal allograft rejection model was induced and single-cell RNA sequencing (scRNA-seq) data of CD45+ leukocytes in kidney allografts on days 7 (D7) and 15 (D15) after operation was analyzed to reveal a full immunological profiling. We identified 20 immune cell types among 10,921 leukocytes. Macrophages and CD8+ T cells constituted the main populations on both timepoints. In the process from acute rejection (AR) towards chronic rejection (CR), the proportion of proliferating and naïve CD8+ T cells dropped significantly. Both B cells and neutrophils decreased by about 3 folds. On the contrary, the proportion of macrophages and dendritic cells (DCs) increased significantly, especially by about a 4.5-fold increase in Ly6cloMrc1+ macrophages and 2.6 folds increase in Ly6cloEar2+ macrophages. Moreover, myeloid cells harbored the richest ligand and receptor (LR) pairs with other cells, particularly for chemokine ligands such as Cxcl9, Cxcl10, Cxcl16 and Yars. However, macrophages with weak response to interferon gamma (IFNg) contributed to rejection chronicization. To conclude, reduction in CD8 T cells, B cells and neutrophils while increasing in Ly6cloMrc1+ macrophages and Ly6cloEar2+ macrophages, may contribute significantly to the progress from AR towards CR.

Targeting the mTOR pathway uncouples the efficacy and toxicity of PD-1 blockade in renal transplantation

Immune checkpoint inhibitor (ICI) use remains a challenge in patients with solid organ allografts as most would undergo rejection. In a melanoma patient in whom programmed-death 1 (PD-1) blockade resulted in organ rejection and colitis, the addition of the mTOR inhibitor sirolimus resulted in ongoing anti-tumor efficacy while promoting allograft tolerance. Strong granzyme B⁺, interferon (IFN)-γ⁺ CD8⁺ cytotoxic T cell and circulating regulatory T (T_reg) cell responses were noted during allograft rejection, along with significant eosinophilia and elevated serum IL-5 and eotaxin levels. Co-treatment with sirolimus abated cytotoxic T cell numbers and eosinophilia, while elevated T_reg cell numbers in the peripheral blood were maintained. Interestingly, numbers of IFN-γ⁺ CD4⁺ T cells and serum IFN-γ levels increased with the addition of sirolimus treatment likely promoting ongoing anti-PD-1 efficacy. Thus, our results indicate that sirolimus has the potential to uncouple anti-PD-1 therapy toxicity and efficacy.

The use of immune checkpoint inhibitors (ICI) in cancer patients with solid organ allografts is hampered due to potential organ rejection. Here, the authors present a case report of a patient with kidney allograft and show that treatment with the mTOR inhibitor sirolimus preserves peripheral tolerance and anti-tumour efficacy of ICI therapy.

Interferon-γ converts human microvascular pericytes into negative regulators of alloimmunity through induction of indoleamine 2,3-dioxygenase 1

Early acute rejection of human allografts is mediated by circulating alloreactive host effector memory T cells (TEM). TEM infiltration typically occurs across graft postcapillary venules and involves sequential interactions with graft-derived endothelial cells (ECs) and pericytes (PCs). While the role of ECs in allograft rejection has been extensively studied, contributions of PCs to this process are largely unknown. This study aimed to characterize the effects and mechanisms of interactions between human PCs and allogeneic TEM. We report that unstimulated PCs, like ECs, can directly present alloantigen to TEM, but while IFN-γ-activated ECs (γ-ECs) show increased ability to stimulate alloreactive T cells, IFN-γ-activated PCs (γ-PCs) instead suppress TEM proliferation but not cytokine production or signaling. RNA sequencing analysis of PCs, γ-PCs, ECs, and γ-ECs reveal induction of indoleamine 2,3-dioxygenase 1 (IDO1) in γ-PCs to significantly higher levels than in γ-ECs that correlates with tryptophan depletion in vitro. Consistently, shRNA knockdown of IDO1 markedly reduces γ-PC-mediated immunoregulatory effects. Furthermore, human PCs express IDO1 in a skin allograft rejection humanized mouse model and in human renal allografts with acute T cell-mediated rejection. We conclude that immunosuppressive properties of human PCs are not intrinsic but instead result from IFN-γ-induced IDO1-mediated tryptophan depletion.

An Overview of Pathways of Regulated Necrosis in Acute Kidney Injury

Necrosis is the predominant form of regulated cell death in acute kidney injury (AKI) and represents results in the formation of casts that appear in the urine sedimentation, referred to as muddy brown casts, which are part of the diagnosis of AKI. Pathologists referred to this typical feature as acute tubular necrosis. We are only beginning to understand the dynamics and the molecular pathways that underlie such typical necrotic morphology. In this review, we provide an overview of candidate pathways and summarize the emerging evidence for the relative contribution of these pathways of regulated necrosis, such as necroptosis, ferroptosis, mitochondrial permeability transition-mediated regulated necrosis, parthanatos, and pyroptosis. Inhibitors of each of these pathways are available, and clinical trials may be started after the detection of the most promising drug targets, which will be discussed here. With the global burden of AKI in mind, inhibitiors of regulated necrosis represent promising means to prevent this disease.

Comprehensive Analysis of Transcript Changes Associated With Allograft Rejection: Combining Universal and Selective Features

We annotated the top transcripts associated with kidney transplant rejection by p-value, either universal for all rejection or selective for T cell-mediated rejection (TCMR) or antibody-mediated rejection (ABMR; ClinicalTrials.gov NCT01299168). We used eight class-comparison algorithms to interrogate microarray results from 703 biopsies, 205 with rejection. The positive comparators were all rejection, TCMR, or ABMR; the negative comparators varied from normal biopsies to all nonrejecting biopsies, including other diseases. The universal algorithm, rejection versus all nonrejection, identified transcripts mainly inducible by interferon γ. Selectivity for ABMR or TCMR required the other rejection class as well as nonrejection biopsies in the comparator to avoid selecting universal transcripts. Direct comparison of ABMR versus TCMR yielded only transcripts related to TCMR, the stronger signal. Transcripts highly associated with rejection were never completely specific for rejection: Many were increased in biopsies without rejection, reflecting sharing between rejection and injury-induced innate immunity. Union of the top 200 transcripts from universal and selective algorithms yielded 454 transcripts that permitted unsupervised analysis of biopsies in principal component analysis: PC1 was rejection, and PC2 was separation of TCMR from ABMR. Appreciating rejection-associated molecular changes requires a diverse case mix, accurate histologic classification (including C4d-negative ABMR), and both selective and universal algorithms.

Bioengineered gold nanoparticles targeted to mesenchymal cells from patients with bronchiolitis obliterans syndrome does not rise the inflammatory response and can be safely inhaled by rodents

The use of gold nanoparticles (GNPs) as drug delivery system represents a promising issue for diseases without effective pharmacological treatment due to insufficient local drug accumulation and excessive systemic toxicity. Bronchiolitis obliterans syndrome (BOS) represents about 70% of cases of chronic lung allograft dysfunction, the main challenge to long-term lung transplantation. It is believed that due to repeated insults to epithelial bronchiolar cells local inflammatory response creates a milieu that favors epithelial-mesenchymal transition and activation of local mesenchymal cells (MCs) leading to airway fibro-obliteration. In a previous work, we engineered GNPs loaded with the mammalian target of rapamycin inhibitor everolimus, specifically decorated with an antibody against CD44, a surface receptor expressed by primary MCs isolated from bronchoalveolar lavage of BOS patients. We proved in vitro that these GNPs (GNP-HCe) were able to specifically inhibit primary MCs without affecting the bronchial epithelial cell. In the present work, we investigated the effect of these bioengineered nanoconstructs on inflammatory cells, given that a stimulating effect on macrophages, neutrophils or lymphocytes is strongly unwanted in graft airways since it would foster fibrogenesis. In addition, we administered GNP-HCe by the inhalatory route to normal mice for a preliminary assessment of their pulmonary and peripheral (liver, spleen and kidney) uptake. By these experiments, an evaluation of tissue toxicity was also performed. The present study proves that our bioengineered nanotools do not rise an inflammatory response and, under the tested inhalatory conditions that were used, are non-toxic.

Do Natural T Regulatory Cells become Activated to Antigen Specific T Regulatory Cells in Transplantation and in Autoimmunity?

Antigen specific T regulatory cells (T_reg) are often CD4⁺CD25⁺FoxP3⁺ T cells, with a phenotype similar to natural T_reg (nT_reg). It is assumed that nT_reg cannot develop into an antigen specific T_reg as repeated culture with IL-2 and a specific antigen does not increase the capacity or potency of nT_reg to promote immune tolerance or suppress in vitro. This has led to an assumption that antigen specific T_reg mainly develop from CD4⁺CD25⁻FoxP3⁻ T cells, by activation with antigen and TGF-β in the absence of inflammatory cytokines such as IL-6 and IL-1β. Our studies on antigen specific CD4⁺CD25⁺ T cells from animals with tolerance to an allograft, identified that the antigen specific and T_reg are dividing, and need continuous stimulation with specific antigen T cell derived cytokines. We identified that a variety of cytokines, especially IL-5 and IFN-γ but not IL-2 or IL-4 promoted survival of antigen specific CD4⁺CD25⁺FoxP3⁺ T_reg. To examine if nT_reg could be activated to antigen specific T_reg, we activated nT_reg in culture with either IL-2 or IL-4. Within 3 days, antigen specific T_reg are activated and there is induction of new cytokine receptors on these cells. Specifically nT_reg activated by IL-2 and antigen express the interferon-γ receptor (IFNGR) and IL-12p70 (IL-12Rβ2) receptor but not the IL-5 receptor (IL-5Rα). These cells were responsive to IFN-γ or IL-12p70. nT_reg activated by IL-4 and alloantigen express IL-5Rα not IFNGR or IL-12p70Rβ2 and become responsive to IL-5. These early activated antigen specific T_reg, were respectively named Ts1 and Ts2 cells, as they depend on Th1 or Th2 responses. Further culture of Ts1 cells with IL-12p70 induced Th1-like T_reg, expressing IFN-γ, and T-bet as well as FoxP3. Our studies suggest that activation of nT_reg with Th1 or Th2 responses induced separate lineages of antigen specific T_reg, that are dependent on late Th1 and Th2 cytokines, not the early cytokines IL-2 and IL-4.

Systematic review of mouse kidney transplantation

A mouse model of kidney transplantation was first described in 1973 by Skoskiewicz et al. Although the mouse model is technically difficult, it is attractive for several reasons: the mouse genome has been characterized and in many aspects is similar to man and there is a greater diversity of experimental reagents and techniques available for mouse studies than other experimental models. We reviewed the literature on all studies of mouse kidney transplantation to report the donor and recipient strain combinations that have been investigated and the resultant survival and histological outcomes. Some models of kidney transplantation have used the transplanted kidney as a life-supporting organ, however, in many studies the recipient mouse's native kidney has been left in situ. Several different combinations of inbred mouse strains have been reported, with varying degrees of injury, survival or tolerance because of haplotype differences. This model has been exceptionally useful as an investigational tool to understand multiple aspects of transplantation including acute rejection, cellular and humoral rejection mechanisms and their treatment. Furthermore, this model has been used to investigate disease mechanisms beyond transplant rejection including intrinsic renal disease and infection-associated pathology.

Inhibition of innate co-receptor TREM-1 signaling reduces CD4(+) T cell activation and prolongs cardiac allograft survival

The innate receptor "triggering-receptor-expressed-on-myeloid-cells-1" (TREM-1) enhances downstream signaling of "pattern recognition receptor" (PRR) molecules implicated in inflammatory responses. However the mechanistic role of TREM-1 in chronic heart rejection has yet to be elucidated. We examined the effect of TREM-1(+) antigen-presenting cells (APC) on alloreactive CD4(+) lymphocytes. Bm12 donor hearts were transplanted into wild-type MHC-class-II-mismatched C57BL/6J recipient mice. Progressive allograft rejection of bm12-donor hearts with decreased organ function, severe vasculopathy and allograft fibrosis was evident within 4 weeks. TREM-1(+) CD11b(+) MHC-II(+) F4/80(+) CCR2(+) APC and IFNγ-producing CD4(+) cells were detected during chronic rejection. Peptide inhibition of TREM-1 attenuated graft vasculopathy, reduced graft-infiltrating leukocytes and prolonged allograft survival, while being accompanied by sustained low levels of CD4(+) and CD8(+) cell infiltration. Remarkably, temporary inhibition of TREM-1 during early immune activation was sufficient for long-term allograft survival. Mechanistically, TREM-1 inhibition leads to reduced differentiation and proliferation of IFNγ-producing Th1 cells. In conclusion, TREM-1 influences chronic heart rejection by regulating the infiltration and differentiation of CD4(+) lymphocytes.

Allograft outcomes in outbred mice

Inbreeding depression and lack of genetic diversity in inbred mice could mask unappreciated causes of graft failure or remove barriers to tolerance induction. To test these possibilities, we performed heart transplantation between outbred or inbred mice. Unlike untreated inbred mice in which all allografts were rejected acutely (6-16 days posttransplantation), untreated outbred mice had heterogeneous outcomes, with grafts failing early (<4 days posttransplantation), acutely (6-24 days) or undergoing chronic rejection (>75 days). Blocking T cell costimulation induced long-term graft acceptance in both inbred and outbred mice, but did not prevent the early graft failure observed in the latter. Further investigation of this early phenotype established that it is dependent on the donor, and not the recipient, being outbred and that it is characterized by hemorrhagic necrosis and neutrophilic vasculitis in the graft without preformed, high titer antidonor antibodies in the recipient. Complement or neutrophil depletion prevented early failure of outbred grafts, whereas transplanting CD73-deficient inbred hearts, which are highly susceptible to ischemia-reperfusion injury, recapitulated the early phenotype. Therefore, outbred mice could provide broader insight into donor and recipient determinants of allograft outcomes but their hybrid vigor and genetic diversity do not constitute a uniform barrier to tolerance induction.

Dynamic Changes of IFN-γ-producing Cells, TGF-β and Their Preidctive Value in Early Outcomees of Renal Transplantation

BACKGROUND

A growing body of evidence demonstrated an immune etiology as well as nonimmune mechanisms for episodes of clinical acute rejection and long-term allograft dysfunction.

OBJECTIVE

To investigate the correlation of IFN-γ-producing cells and TGF-β with incidence of clinical acute rejection in living-related and unrelated kidney allogarft recipients during the first post-transplant year.

METHODS

This multi-center study was performed on 57 kidney allograft recipients from living-related (n=20) and unrelated (n=37) donors between April 2011 and September 2012 and who were followed prospectively for a mean period of one year. Peripheral blood samples were collected from all patients pre-transplantation and at days 14, 30 and 90 after transplantation; PBMCs were used as responding cells in enzyme-linked immunosorbent spot (ELISPOT) assay to measure the frequency of IFN-γ-producing cells after stimulation with donor lymphocytes. Additionally, TGF-β levels were measured in cell culture supernatants of ELISPOT assay.

RESULTS

During the follow-up period, 45 (79%) patients were diagnosed with stable graft function (group A); 12 (21%) experienced clinical acute rejection episodes (group B). The frequency of IFN-γ-producing cells was significantly (p<0.001) higher in the rejection group in all three times after transplantation. Also, post-transplantation comparison for TGF-β showed a significantly (p<0.001) higher contents in group A vs. group B. Comparing the post-transplantation levels of TGF-β and mean numbers of IFN-γ- producing cells between groups A and B demonstrated a continuous increment in TGF-β and decreasing frequencies of IFN-γ-producing cells in group A vs. group B.

CONCLUSION

Serial post-transplantation monitoring of IFN-γ-producing donor reactive cells during the first months is a clinically feasible approach for identification of kidney allogarft recipients at risk for ongoing immune-mediated graft damage and later graft loss.

Renal allograft recipients fail to increase interferon-γ during invasive fungal diseases

Invasive fungal diseases are a major cause of death in renal allograft recipients. We previously reported that adjunctive recombinant human interferon-γ therapy has clinical utility for invasive fungal diseases after renal transplantation. We have now developed a rapid peripheral blood-based quantitative real-time PCR assay that enables accurate profiling of cytokine imbalances. Our preliminary studies in renal transplant patients with invasive fungal diseases suggest that they fail to mount an adequate interferon-γ response to the fungal infection. In addition, they have reduced IL-10 and increased TNF-α when compared to stable renal transplant patients. These preliminary cytokine profiling-based observations provide a possible explanation for the therapeutic benefit of adjunctive human interferon-γ therapy in renal allograft recipients with invasive fungal diseases.

Immunotherapy for fungal infections

Invasive fungal infections have become a major cause of mortality in immunocompromised individuals. Despite the current availability of number of highly active antifungal agents, overall mortality remains around 40%. Importantly, it is clear that a failure to restore host immunity leads to worse outcomes. These observations provide clear rationale for the development of novel immunotherapies to improve outcomes in immunocompromised individuals with invasive fungal infections. In this article we summarise the key advances that have been made in the field of immunotherapy for fungal infections in recent years, with a particular focus on clinical studies of interferon-γ therapy, adoptive T cell therapy, and gene therapy for chronic granulomatous disorder. In addition a number of pre-clinical approaches are reviewed.

Genetic predisposition of donors affects the allograft outcome in kidney transplantation; polymorphisms of stromal-derived factor-1 and CXC receptor 4

Genetic interaction between donor and recipient may dictate the impending responses after transplantation. In this study, we evaluated the role of the genetic predispositions of stromal-derived factor-1 (SDF1) [rs1801157 (G>A)] and CXC receptor 4 (CXCR4) [rs2228014 (C>T)] on renal allograft outcomes. A total of 335 pairs of recipients and donors were enrolled. Biopsy-proven acute rejection (BPAR) and long-term graft survival were traced. Despite similar allele frequencies between donors and recipients, minor allele of SDF1 rs1801157 (GA+AA) from donor, not from recipients, has a protective effect on the development of BPAR compared to wild type donor (GG) (P = 0.005). Adjustment for multiple covariates did not affect this result (odds ratio 0.39, 95% C.I 0.20–0.76, P = 0.006). CXCR4 rs2228014 polymorphisms from donor or recipient did not affect the incidence of acute rejection. SDF1 was differentially expressed in renal tubular epithelium with acute rejection according to genetic variations of donor rs1801157 showing higher expressions in the grafts from GG donors. Contrary to the development of BPAR, the presence of minor allele rs1801157 A, especially homozygocity, predisposed poor graft survival (P = 0.001). This association was significant after adjusting for several risk factors (hazard ratio 3.01; 95% C.I = 1.19–7.60; P = 0.020). The allelic variation of recipients, however, was not associated with graft loss. A donor-derived genetic polymorphism of SDF1 has influenced the graft outcome. Thus, the genetic predisposition of donor should be carefully considered in transplantation.

T cell-mediated rejection of kidney transplants: a personal viewpoint

In kidney allografts, T cell mediated rejection (TCMR) is characterized by infiltration of the interstitium by T cells and macrophages, intense IFNG and TGFB effects, and epithelial deterioration. Recent experimental and clinical studies provide the basis for a provisional model for TCMR. The model proposes that the major unit of cognate recognition in TCMR is effector T cells engaging donor antigen on macrophages. This event creates the inflammatory compartment that recruits effector and effector memory CD4 and CD8 T cells, both cognate and noncognate, and macrophage precursors. Cognate T cells cross the donor microcirculation to enter the interstitium but spare the microcirculation. Local inflammation triggers dedifferentiation of the adjacent epithelium (e.g. loss of transporters and expression of embryonic genes) rather than cell death, via mechanisms that do not require known T-cell cytotoxic mechanisms or direct contact of T cells with the epithelium. Local epithelial changes trigger a response of the entire nephron and a second wave of dedifferentiation. The dedifferentiated epithelium is unable to exclude T cells, which enter to produce tubulitis lesions. Thus TCMR is a cognate recognition-based process that creates local inflammation and epithelial dedifferentiation, stereotyped nephron responses, and tubulitis, and if untreated causes irreversible nephron loss.

IFN-gamma-receptor signaling ameliorates transplant vasculopathy through attenuation of CD8+ T-cell-mediated injury of vascular endothelial cells

Occlusive transplant vasculopathy (TV) is the major cause for chronic graft rejection. Since endothelial cells (EC) are the first graft cells encountered by activated host lymphocytes, it is important to delineate the molecular mechanisms that coordinate the interaction of EC with activated T cells. Here, the interaction of CD8(+) T cells with Ag-presenting EC in vivo was examined using a transgenic heart transplantation model with beta-galactosidase (beta-gal) expression exclusively in EC (Tie2-LacZ hearts). We found that priming with beta-gal peptide-loaded DC failed to generate a strong systemic IFN-gamma response, but elicited pronounced TV in both IFN-gamma receptor (IFNGR)-competent, and ifngr(-/-) Tie2-LacZ hearts. In contrast, stimulation of EC-specific CD8(+) T cells with beta-gal-recombinant mouse cytomegalovirus (MCMV-LacZ) in recipients of ifngr(+/+) Tie2-LacZ hearts did not precipitate significant TV. However, MCMV-LacZ infection of recipients of ifngr(-/-) Tie2-LacZ hearts led to massive activation of beta-gal-specific CD8 T cells, and led to development of fulminant TV. Further analyses revealed that the strong systemic IFN-gamma "storm" associated with MCMV infection induced upregulation of programmed death-1 ligand 1 (PD-L1) on EC, and subsequent attenuation of programmed death-1 (PD-1)-expressing EC-specific CD8(+) T cells. Thus, IFNGR signaling in ECs activates a potent peripheral negative feedback circuit that protects vascularized grafts from occlusive TV.

Translating costimulation blockade to the clinic: lessons learned from three pathways

SUMMARY

As the recognition that costimulatory signals are critical for optimal T-cell activation, proliferation, and differentiation, there has been an explosion in the study of costimulatory molecules and their roles in enhancing anti-donor T-cell responses following transplantation. Here, we focus on the bench-to-beside translation of blocking agents designed to target three critical costimulatory pathways: the CD28/CD80/CD86 pathway, the CD154/CD40 pathway, and the lymphocyte function associated antigen-1/intercellular adhesion molecule pathway. While blockade of each of these pathways proved promising in inhibiting donor-reactive T-cell responses and promoting long-term graft survival in murine models of transplantation, the progression of development of therapeutic agents to block these pathways has each taken a slightly different course. Both logistical and biological pitfalls have accompanied the translation of blockers of all three pathways into clinically applicable therapies, and the development of costimulatory blockade as a substitute for current standard-of-care calcineurin inhibitors has by no means reached completion. Collaboration between both the basic and clinical arenas will further propel the development of costimulation blockers currently in the pipeline, as well as of novel methods to target these critical pathways during transplantation.

IFN-gamma dictates allograft fate via opposing effects on the graft and on recipient CD8 T cell responses

CD8 T cells are necessary for costimulation blockade-resistant rejection. However, the mechanism by which CD8 T cells mediate rejection in the absence of major costimulatory signals is poorly understood. IFN-gamma promotes CD8 T cell-mediated immune responses, but IFN-gamma-deficient mice show early graft loss despite costimulation blockade. In contrast, we found that IFN-gamma receptor knockout mice show dramatically prolonged graft survival under costimulation blockade. To investigate this paradox, we addressed the effects of IFN-gamma on T cell alloresponses in vivo independent of the effects of IFN-gamma on graft survival. We identified a donor-specific CD8 T cell breakthrough response temporally correlated with costimulation blockade-resistant rejection. Neither IFN-gamma receptor knockout recipients nor IFN-gamma-deficient recipients showed a CD8 breakthrough response. Graft death on IFN-gamma-deficient recipients despite costimulation blockade could be explained by the lack of IFN-gamma available to act on the graft. Indeed, the presence of IFN-gamma was necessary for graft survival on IFN-gamma receptor knockout recipients, as either IFN-gamma neutralization or the lack of the IFN-gamma receptor on the graft precipitated early graft loss. Thus, IFN-gamma is required both for the recipient to mount a donor-specific CD8 T cell response under costimulation blockade as well as for the graft to survive after allotransplantation.

Monitoring of human liver and kidney allograft tolerance: a tissue/histopathology perspective

Several factors acting together have recently enabled clinicians to seriously consider whether chronic immunosuppression is needed in all solid organ allograft recipients. This has prompted a dozen or so centers throughout the world to prospectively wean immunosuppression from conventionally treated liver allograft recipients. The goal is to lessen the impact of chronic immunosuppression and empirically identify occasional recipients who show operational tolerance, defined as gross phenotype of tolerance in the presence of an immune response and/or immune deficit that has little or no significant clinical impact. Rare operationally tolerant kidney allograft recipients have also been identified, usually by single case reports, but only a couple of prospective weaning trials in conventionally treated kidney allograft recipients have been attempted and reported. Pre- and postweaning allograft biopsy monitoring of recipients adds a critical dimension to these trials, not only for patient safety but also for determining whether events in the allografts can contribute to a mechanistic understanding of allograft acceptance. The following is based on a literature review and personal experience regarding the practical and scientific aspects of biopsy monitoring of potential or actual operationally tolerant human liver and kidney allograft recipients where the goal, intended or attained, was complete withdrawal of immunosuppression.

Kidney transplantation: mechanisms of rejection and acceptance

We describe the molecular and cellular mechanisms believed to be responsible for the rejection of renal allografts, including acute T cell-mediated rejection, acute antibody-mediated (humoral) rejection, rejection mediated by the innate immune system, and chronic rejection. We present mechanisms of graft acceptance, including accommodation, regulation, and tolerance. Studies in animals have replicated many pathologic features of acute and chronic rejection. We illuminate the pathogenesis of human pathology by reflection from experimental models.

The effects of tolerance on allograft damage caused by the innate immune system

BACKGROUND

It is not known whether tolerance can be induced in a strong proinflammatory milieu or whether the induction of tolerance can prevent interferon (IFN)-gamma-associated graft injury. To address these questions, we studied the effects of rIFN-gamma infusion on porcine cardiac allograft survival.

METHODS

Recombinant interferon (rIFN)-gamma was continuously infused into the left anterior descending artery of hearts transplanted into major histocompatibility complex-inbred miniature swine treated with a 12-day course of cyclosporine A. Group 1 recipients received a nearly syngeneic heart, group 2 recipients received a class I disparate heart, and group 3 recipients were cotransplanted with a class I-disparate heart and kidney, a procedure demonstrated to induce tolerance to both grafts. A fourth group of animals were not transplanted but received intracoronary rIFN-gamma infusion into the native heart.

RESULTS

rIFN-gamma perfusion not only accelerated the acute rejection of class I-disparate hearts (mean survival time, 19+/-7.21 vs. 38+/-8.19; P=0.025) but caused near-syngeneic heart transplants, which otherwise survived indefinitely, to reject within 35 days. In contrast, rIFN-gamma perfusion had no demonstrable effects on hearts grafts in tolerant recipients or on autologous hearts.

CONCLUSIONS

These results suggest that tolerance induction can occur in the presence of IFN-gamma-mediated inflammation, and that tolerance induction can prevent the tissue injury caused by the overproduction of IFN-gamma. This suggests that the beneficial effects of tolerance may include protection from nonspecific inflammatory responses, such as those produced by ischemia-reperfusion injury and brain death.

Interferon-gamma and donor MHC class I control alternative macrophage activation and activin expression in rejecting kidney allografts: a shift in the Th1-Th2 paradigm

Organ allografts deficient in interferon-gamma (Ifng) or major histocompatibility complex (MHC) class I products develop accelerated necrosis when rejection develops, depending on perforin and granzymes. Thus Ifng-induced donor class I products deliver inhibitory signals to host inflammatory cells. We used microarrays to investigate whether Ifng-induced donor class I products also control inflammation patterns in mouse kidney allografts. Compared to wild-type (WT) allografts, many transcripts were increased in both Ifng-deficient allografts (Ifng-suppressed transcripts [GSTs]) and class I-deficient allografts (class I-suppressed transcripts [CISTs]), with 73% overlap between GSTs and CISTs. Some GSTs and CISTs reflected increased necrosis, including known injury-induced transcripts. However, many GSTs and CISTs were independent of perforin, granzymes and necrosis, and were associated with alternative macrophage activation (AMA) (e.g. arginase I [Arg1], macrophage elastase [Mmp12] and macrophage mannose receptor 1 [Mrc1]). AMA transcripts were induced despite absence of host interleukin (IL)4 and IL13 receptors. The AMA inducer may be activins, whose genes (inhibin A [InhbA] and inhibin B [InhbB]) were increased in all allografts with AMA. We conclude that in allograft rejection, Ifng acts via donor Ifng receptors (Ifngr) to induce donor class Ia and Ib products, which engage host inflammatory cells to limit perforin-granzyme-mediated damage and prevent AMA associated with inhibition of activin expression. Thus, Ifng may control T helper type 2 (Th2) cell inflammation by induction of class I products.

IFN-gamma prevents early perforin-granzyme-mediated destruction of kidney allografts by inducing donor class I products in the kidney

Interferon-gamma (Ifng) protects organ allografts: mouse kidney allografts lacking Ifng receptors rapidly fail with massive ischemic necrosis around days 5 to 7, reflecting microcirculation failure. We hypothesized that Ifng protects the graft by preventing perforin-granzyme-mediated cytotoxic damage to the microcirculation by inducing class Ia and/or Ib products. We transplanted kidney allografts lacking Ifng receptors into various knockout hosts. The necrosis/congestion phenotype did not require host B cells or IL-4 and IL-13 receptors, but required the T-cell alloresponse: it did not occur if the hosts were syngeneic or T-cell deficient. However, host perforin-granzyme mechanisms were required: no necrosis developed if hosts lacked either perforin or granzymes A and B. The ability of Ifng to protect the allograft required donor class I products: allografts lacking class I products due to Tap1 or beta2 microglobulin deficiency developed a similar necrosis-congestion phenotype at day 7 despite Ifng receptors being present. Thus when host cytotoxic T cells infiltrate organ allografts, Ifng prevents their perforin-granzyme mechanism from compromising the microcirculation by a mechanism requiring donor class Ia or Ib products. We propose that donor class Ia or Ib products are needed to trigger inhibitory receptors on effector T cells.

Renal Allograft Immune Response Is Influenced by Patient and Donor Cytokine Genotypes

This study investigated the impact of specific cytokine genotypes on the incidence of acute rejection episodes (ARE), chronic graft dysfunction (CGD), and anti-HLA donor-specific antibody (DS-Ab) production in 86 renal transplant recipients and 70 cadaveric donors. A PCR-SSP method was performed for the analysis of polymorphisms in TNF-alpha, IL-6, TGF-beta, IL-10, and IFN-gamma cytokines. DS-Ab monitoring of sera was performed using a FCXM analysis. Observed cytokine frequencies for patients and donors were not significantly different from the expected frequencies under Hardy-Weinberg equilibrium conditions. The evaluation in recipients revealed a higher frequency of DS-Ab-positive patients among the TNF-alpha high (50.0% vs 25.7%), and for the IL-10 cytokine a greater incidence of ARE-positive patients (35.8% vs 18.2%) with the high + intermediate, compared with the low genotype. The combined effect of these 2 genotypes predisposed to DS-Abs (71.4% vs 25.3%; P = 0.02; odds ratio [OR] = 7.37). As for the TGF-beta1 cytokine, we observed a higher number of CGD-positive patients among high compared with intermediate producers (14.3% vs 0%; P = .050). The analysis of donors revealed a significantly lower incidence of ARE-positive patients among recipients whose donors were carriers of the high IL-6 G/G-genotype compared with the G/C+C/C-genotypes (16.7% vs 41.2%; P = .03), suggesting a protective effect of the G/G genotype on ARE and a predisposing role of donor (-174)allele C. In addition, we noted an association between the IFN-gamma low A/A-genotype and a higher incidence of ARE (42.1% vs 0%; P = .002) and DS-Ab production (47.4% vs 12.5%; P = .02) compared with high producers.

Interleukin-12p70 Prolongs Allograft Survival by Induction of Interferon Gamma and Nitric Oxide Production

BACKGROUND

Interleukin (IL)-12p70, a heterodimeric cytokine has been considered central to induction of Th1 responses with the assistance of IL-18 and IL-27. It was predicted IL-12p70 treatment would promote allograft rejection. In these studies, IL-12p70 delayed rejection.

METHODS

We compared Piebald Virol Glaxo (PVG) neonatal heart graft survival in fully allogeneic Dark Agoutti (DA) rats treated with IL-12p70 alone or in combination with other cytokines. The mechanism by which IL-12p70 induced delayed rejection was examined by reverse transcription polymerase chain reaction of cytokine mRNA and studying the role of interferon (IFN)-gamma and inducible nitric oxide synthase (iNOS) that were induced by IL-12.

RESULTS

IL-12p70 treatment significantly delayed PVG neonatal heart graft rejection compared to normal rejection control and other control groups treated with supernatant from Chinese hamster ovary (CHO)-K1 cells transfected with IL-12p35, IL-12p40, or no cytokine gene. IL-12p70 had no effect on alloantibody response. IFN-gamma and iNOS mRNA expression was increased in heart graft and regional lymph node compared to normal rejection and other treatment groups, consistent with Th1 response induction. IL-12p35 mRNA expression decreased in IL-12p70 treated rats but there was no difference in IL-12p40, Th2, or Tr1 cytokine mRNA expression. Coadministration of an iNOS inhibitor, L-NIL, or a monoclonal antibody (mAb) that blocks IFN-gamma, inhibited IL-12p70's ability to prolong allograft survival; as did co-treatment with IL-4 but not IL-13.

CONCLUSIONS

IL-12p70 treatment may inhibit rejection by hyperinduction of Th1 responses, especially production of IFN-gamma and nitric oxide. These effects may be by enhancing regulatory T-cell responses or by the activation of iNOS in macrophages to produce excessive nitric oxide that in turn inhibits alloimmune responses.

In situ assays demonstrate that interferon-gamma suppresses infection-stimulated hepatic fibrin deposition by promoting fibrinolysis

BACKGROUND

Inflammatory cytokines potently impact hemostatic pathways during infection, but the tissue-specific regulation of coagulation and fibrinolysis complicates studies of the underlying mechanisms.

METHODS AND RESULTS

Here, we describe assays that quantitatively measuring prothrombinase (PTase), protein C-ase (PCase) and plasminogen activator (PA) activities in situ, thereby facilitating studies of tissue-specific hemostasis. Using these assays, we investigate the mechanisms regulating hepatic fibrin deposition during murine toxoplasmosis and the means by which interferon-gamma (IFN-gamma) suppresses infection-stimulated fibrin deposition. We demonstrate that Toxoplasma infection upregulates hepatic PTase, PCase, and PA activity. Wild type and gene-targeted IFN-gamma-deficient mice exhibit similar levels of infection-stimulated PTase activity. By contrast, IFN-gamma-deficiency is associated with increased PCase activity and reduced PA activity during infection. Parallel analyses of hepatic gene expression reveal that IFN-gamma-deficiency is associated with increased expression of thrombomodulin (TM), a key component of the PCase, increased expression of thrombin-activatable fibrinolysis inhibitor (TAFI), a PC substrate, and reduced expression of urokinase PA (u-PA).

CONCLUSIONS

These findings suggest that IFN-gamma suppresses infection-stimulated hepatic fibrin deposition by suppressing TM-mediated activation of TAFI, thereby destabilizing fibrin deposits, and concomitantly increasing hepatic u-PA activity, thereby promoting fibrinolysis. We anticipate that further application of these in situ assays will improve our understanding of tissue-specific hemostasis, its regulation by cytokines, and its dysregulation during coagulopathy.

Changes in the transcriptome in allograft rejection: IFN-gamma-induced transcripts in mouse kidney allografts

We used Affymetrix Microarrays to define interferon-gamma (IFN-gamma)-dependent, rejection-induced transcripts (GRITs) in mouse kidney allografts. The algorithm included inducibility by recombinant IFN-gamma in kidneys of three normal mouse strains, increase in kidney allografts in three strain combinations and less induction in IFN-gamma-deficient allografts. We identified 40 transcripts, which were highly IFN-gamma inducible (e.g. Cxcl9, ubiquitin D, MHC), and 168 less sensitive to IFN-gamma in normal kidney. In allografts, expression of GRITs was intense and consistent at all time points (day 3 through 42). These transcripts were partially dependent on donor IFN-gamma receptors (IFN-gammars): receptor-deficient allografts manifested up to 76% less expression, but some transcripts were highly dependent (ubiquitin D) and others relatively independent (Cxcl9). Kidneys of hosts rejecting allografts showed expression similar to that observed with IFN-gamma injections. Many GRITs showed transient IFN-gamma-dependent increase in isografts, peaking at day 4-5. GRITs were increased in heart allografts, indicating them as generalized feature of alloresponse. Thus, expression of rejection-induced transcripts is robust and consistent in allografts, reflecting the IFN-gamma produced by the alloresponse locally and systemically, acting via host and donor IFN-gammar, as well as local IFN-gamma production induced by post-operative stress.

Tumor necrosis factor alpha and gamma interferon, but not hemorrhage or pathogen burden, dictate levels of protective fibrin deposition during infection

While coagulation often causes pathology during infectious disease, we recently demonstrated that fibrin, a product of the coagulation pathway, performs a critical protective function during acute toxoplasmosis (L. L. Johnson, K. N. Berggren, F. M. Szaba, W. Chen, and S. T. Smiley, J. Exp. Med. 197:801-806, 2003). Here, we investigate the mechanisms regulating the formation of this protective fibrin. Through comparisons of Toxoplasma-infected wild-type and cytokine-deficient mice we dissociate, for the first time, the relative fibrin-regulating capacities of pathogen products, host cytokines, and infection-stimulated hemorrhage. Remarkably, neither the pathogen burden nor hemorrhage is a primary regulator of fibrin levels. Rather, two type 1 cytokines exert dominant and counterregulatory roles: tumor necrosis factor alpha (TNF-alpha), acting via the type 1 TNF-alpha receptor, promotes fibrin deposition, while gamma interferon (IFN-gamma), acting via STAT1 and IFN-gamma receptors expressed on radioresistant cells, suppresses fibrin deposition. These findings have important clinical implications, as they establish that cytokines known to regulate pathological coagulation also dictate levels of protective fibrin deposition. We present a novel model depicting mechanisms by which the immune system can destroy infected tissue while independently restraining hemorrhage and promoting tissue repair through the deliberate deposition of protective fibrin.

Pluripotent allospecific CD8+ effector T cells traffic to lung in murine obliterative airway disease

Long-term success in lung transplantation is limited by obliterative bronchiolitis, whereas T cell effector mechanisms in this process remain incompletely understood. Using the mouse heterotopic allogeneic airway transplant model, we studied T cell effector responses during obliterative airways disease (OAD). Allospecific CD8+ IFN-gamma+ T cells were detected in airway allografts, with significant coexpression of TNF-alpha and granzyme B. Therefore, using IFN-gamma as a surrogate marker, we assessed the distribution and kinetics of extragraft allo-specific T cells during OAD. Robust allospecific IFN-gamma was produced by draining the lymph nodes, spleen, and lung mononuclear cells from allograft, but not isograft recipients by Day 14, and significantly decreased by Day 28. Although the majority of allospecific T cells were CD8+, allospecific CD4+ T cells were also detected in these compartments, with each employing distinct allorecognition pathways. An influx of pluripotent CD8+ effector cells with a memory phenotype were detected in the lung during OAD similar to those seen in the allografts and secondary lymphoid tissue. Antibody depletion of CD8+ T cells markedly reduced airway lumen obliteration and fibrosis at Day 28. Together, these data demonstrate that allospecific CD8+ effector T cells play an important role in OAD and traffic to the lung after heterotopic airway transplant, suggesting that the lung is an important immunologic site, and perhaps a reservoir, for effector cells during the rejection process.

Expression of CTL associated transcripts precedes the development of tubulitis in T-cell mediated kidney graft rejection

The usual phenotype of clinical kidney allograft rejection is infiltration by lymphocytes and macrophages and evolution of histologic Banff lesions, particularly tubulitis, which indicate parenchymal injury. Using Affymetrix microarrays, we evaluated the relationship between the evolution of pathologic lesions and the transcriptome. We studied CBA/J into C57Bl/6 mouse kidney allografts in which one host kidney is left in place to permit observation of lesion development. Histology was dominated by early infiltration by mononuclear cells from day 3 and slower evolution of tubulitis after day 7. We defined a set of cytotoxic T lymphocyte-associated transcripts (CATs) on the basis of expression in purified cytotoxic T lymphocytes (CTL) and in a mixed lymphocyte culture, and absence in normal kidney. CATs were detectable by day 3 and highly expressed by day 5 in rejecting kidneys, with a median signal 14% of that in CTL, compared to 4% in isografts and normal kidneys, and persisted through day 42. Lack of mature B cells had little effect on CAT expression, confirming that CATs reflect T-cell-mediated rejection. Expression of CATs was established before diagnostic lesions and remained remarkably consistent through day 42 despite massive alterations in the pathology, and probably reflects T cells recruited to the graft.

IFN-gamma decreases CTL generation by limiting IL-2 production: A feedback loop controlling effector cell production

IFN-gamma is produced by cytotoxic T lymphocytes (CTL) but can also decrease CTL generation. We used IFN-gamma-R1-deficient (GRKO) and IFN-gamma-deficient (GKO) mice to study the effects of IFN-gamma in MLC on the generation of CTL activity and CTL number, IL-2 production and cell proliferation. CTL activity was increased in MLC when GRKO responders or GKO stimulators and responders were used, compared to wild-type (WT) MLC. The number of cells displaying the CTL phenotype (CD3+, CD8+, CD25+) was also increased, accompanied by increased IL-2 production and proliferation. Combinations of WT or GRKO CD4+ T cells with WT or GRKO CD8+ T cells as responders showed that IFN-gamma mostly affects CD4+ T cells to limit CTL generation. Intracellular staining indicated that IL-2 production was largely by CD4+ T cells. Moreover, addition of IL-2 to WT responders mimicked GKO CTL generation and activity, whereas neutralizing IL-2 decreased CTL activity in GRKO and WT responders. Thus IFN-gamma reduces CTL generation in alloimmune responses largely by limiting proliferation of IL-2 producing CD4+ T cells. This creates a feedback loop in which effectors produce IFN-gamma that limits IL-2 production which in turn limits CTL generation.

Donor genomics influence graft events: the effect of donor polymorphisms on acute rejection and chronic allograft nephropathy

BACKGROUND

Organs procured from deceased donors emanate from individuals with diverse genetic backgrounds. Donor organs, therefore, may vary in their response to injury and immune stimuli in a genetically determined manner. We assessed polymorphisms from 244 renal allograft donors to better understand the impact of donor polymorphisms on selected transplant outcomes.

METHODS

Donor genomic DNA restriction fragment length polymorphisms were assayed for evidence of common cytokine [interleukin (IL)-2, IL-6, IL-10, tumor necrosis factor (TNF)-alpha, TGF-beta, interferon (IFN)-gamma] and chemokine (CCR2, CCR5) polymorphisms. Associations between donor polymorphisms and graft events were determined using chi-square, linear regression, and Kaplan-Meier analyses.

RESULTS

Several genotypic polymorphisms demonstrated a modest association with acute rejection, including the transforming growth factor (TGF)-beta T/C codon 10 (P= 0.027) and the CCR5 G/A 59029 (P= 0.039) genes by chi-square analysis. Notably, the presence of the T allele in the IFN-gamma gene (+874) demonstrated a highly significant association with biopsy-proven chronic allograft nephropathy (P < 0.008). This association remained highly significant in a multiple linear regression model that incorporated biopsy-proven acute rejection as a covariate.

CONCLUSION

These data suggest that many of the donor polymorphisms studied in this analysis may influence a recipient's immune response to a renal allograft. However, their greatest impact may be demonstrated in long-term outcomes.

Molecular diagnosis of renal-allograft rejection: correlation with histopathologic evaluation and antirejection-therapy resistance

BACKGROUND

Because histopathologic criteria cannot always predict the pathogenesis and response to curative antirejection therapy, new hope derives from the molecular analysis of intragraft immunologic markers. We studied whether the cutoff of intragraft expression level of T-cell activation markers may define subgroups of acute rejection differing either in type of rejection or clinical outcome.

METHODS

Forty-three human renal-allograft biopsies were quantified for mRNA expression of granzyme B, Fas ligand, interferon (IFN)gamma, interleukin (IL)-4, and IL-6 with a reverse-transcriptase real-time quantitative polymerase chain reaction (RT-PCR) method. Expression levels were correlated with the histopathologic rejection type according to the Banff 1997 classification criteria, and with the sensitivity to the antirejection immunosuppressive therapy, by means of receiver operating-characteristic (ROC) curves.

RESULTS

Granzyme B and Fas ligand mRNA expression up-regulation correlated with all allograft rejection types (P<0.01 for all). Moreover, granzyme B showed the highest sensitivity (90%) and specificity (78%) for the potential detection of histologic borderline changes that will require immunosuppressive therapy (area under the curve [AUC]=0.856, P<0.01). Curative antirejection-therapy resistance of overt, acute-rejection episode was significantly associated with higher Fas ligand gene expression (AUC=0.764, P<0.01, sensitivity [71%], specificity [99.5%]).

CONCLUSIONS

Real-time RT-PCR quantification of the over-expression of the granzyme B gene in kidney-graft biopsies has proved to be as reliable in detecting acute rejection as histologic assessment. Furthermore, we demonstrate that the simultaneous measurement of the mRNA up-regulation of Fas ligand might represent an efficient new tool for the prediction of pejorative outcome of acute rejection.

Preconditioning Strategies to Limit Graft Immunogenicity and Cold Ischemic Organ Injury

During the transplant process, the graft is exposed to numerous events, which may enhance its immunogenicity. In particular, factors related to brain death, such as hemodynamic instability and systemic release of cytokines, cold preservation on harvesting, and reperfusion injury, are known to accumulate in harm, conveying a proinflammatory state to the graft before transplant. Alloimmune reactivity is initiated when the host immune system detects non–self-antigens in the context of “danger signals.” Eliminating these danger signals by modifying the graft before transplant has the potential to attenuate the alloimmune response. The molecules, which mediate danger signals, have not yet been fully identified. Free oxygen radicals and interferon-γ are important candidates. One of the most important protective mechanisms against oxidative stress is the heme oxygenase 1 system. Up-regulation of heme oxygenase 1 in grafts has been shown to prevent ischemia-reperfusion damage and improve long-term graft survival in various transplant models. The benefit of blocking the action of interferon-γ in kidney transplants is less clear because the compound plays such a complex and pivotal role in the immune response, and experimental data with interferon-γ receptor knockout mice are conflicting. It has recently become clear that catecholamines are important graft-modifying agents. Dopamine is capable of stimulating the induction of protective enzymes like heme oxygenase-1 (HO-1) rendering the organ more resistant to the insult of ischemia/reperfusion and inflammation. Retrospective clinical data suggest that treatment of brain-dead organ donors with catecholamines is associated with less rejection and a better long-term graft survival of kidneys transplanted from these donors. Catecholamines can also modulate cytokine production and prevent cold-induced damage. Other substances, such as proteoglycans and phosphatidylethanolamine-bound hyaluronic acid, may interfere with the actions of interferon-γ. Further studies of these compounds in experimental animal models and in prospective randomized clinical trials will help establish their efficacy in donor pretreatment. It is important to underscore that donor pretreatment will have great advantages for the recipient because an improved long-term graft survival could thus be achieved cost-efficiently and without great effort or side effects.

Lesions of T-cell-mediated kidney allograft rejection in mice do not require perforin or granzymes A and B

Organ allograft rejection is strongly associated with the presence of alloreactive cytotoxic T cells but the role of cytotoxicity in the pathologic lesions is unclear. Previous studies showed that the principal lesions of kidney rejection - interstitial infiltration, tubulitis, and endothelial arteritis - are T-cell-dependent and antibody-independent. We studied the role of cytotoxic granule components perforin and granzymes A and B in the evolution of the T-cell-mediated lesions of mouse kidney transplant rejection. By real-time RT-PCR, allografts rejecting in wild-type hosts at days 5, 7, 21, and 42 showed massively elevated and persistent expression of perforin and granzymes A and B, but evolution of tubulitis and arteritis did not correlate with increasing granzyme or perforin expression. Allografts transplanted into hosts with disrupted genes for perforin or granzymes A and B showed no change in tubulitis, arteritis, or MHC induction. Thus the development of the histologic lesions diagnostic of T-cell-mediated kidney transplant rejection are associated with but not mediated by perforin or granzyme A or B. Together with previous graft survival studies, these results indicate that the granule-associated cytotoxic mechanisms of T cells are not the effectors of T-cell-mediated allograft rejection.

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.

Temperature-sensitive polymer-conjugated IFN-? induces the expression of IDO mRNA and activity by fibroblasts populated in collagen gel (FPCG)

Indoleamine 2,3-dioxygenase (IDO) is an intracellular tryptophan-catabolizing enzyme possessing various immunosuppressive properties. Here, we report the use of this enzyme to suppress the proliferation of peripheral blood mononuclear cells (PBMC) co-cultured with IDO-expressing fibroblasts of an allogeneic skin substitute in vitro. Fetal foreskin fibroblasts populated within collagen gel (FPCG) were treated with interferon-gamma (IFN-gamma) conjugated with a temperature-sensitive polymer to induce the expression of IDO mRNA and protein. SDS-PAGE showed successful conjugation of IFN-gamma with the temperature-sensitive polymer. Expression of IDO mRNA was evaluated by Northern analysis. IDO enzyme activity was evaluated by the measurement of kynurenine levels. The results of Northern blot analysis showed an induction of IDO mRNA expression when treated with polymer-conjugated IFN-gamma. Kynurenine levels, as a measure of IDO bioactivity, were significantly higher in IFN-gamma-treated fibroblasts than in controls (P < 0.001). In a lasting effect experiment, the expression of IDO mRNA in FPCG treated with polymer-conjugated IFN-gamma was significantly longer than in those treated with free (non-conjugated) IFN-gamma (P < 0.001). IFN-gamma radiolabeling showed a prolonged retention of IFN-gamma within collagen gel in its polymer-conjugated form, compared to its free form. Presence of IDO protein in FPCG was demonstrated by Western analysis even 16 days after removal of the conditioned medium (containing released IFN-gamma). To demonstrate the immunosuppressive effects of IDO on the proliferation of PBMC, IDO-expressing FPCG treated with polymer-conjugated IFN-gamma were co-cultured with PBMC for a period of 5 days. The results showed a significant reduction in proliferation of PBMC co-cultured with IFN-gamma-treated IDO-expressing fibroblasts, compared to those co-cultured with non-IDO-expressing fibroblasts (P < 0.001). The addition of an IDO inhibitor (1-methyl-D-tryptophan) reversed the suppressive effects of IDO on PBMC proliferation. In conclusion, IDO expression in FPCG suppresses the proliferation of immune cells in vitro. The use of a temperature-sensitive polymer further prolongs the effect of IFN-gamma on the expression of IDO. Therefore, modulating IDO levels in situ might be an alternative for prolonging the survival of skin allografts.

Heterogeneity in the evolution and mechanisms of the lesions of kidney allograft rejection in mice

The natural history and pathogenesis of the pathologic lesions that define rejection of kidney transplants have not been well characterized. We studied the evolution of the pathology of rejection in mouse kidney allografts, using four strain combinations across full major histocompatibility complex (MHC) plus nonMHC disparities, to permit more general conclusions. Interstitial infiltrate, MHC induction, and venulitis appeared by day 5, peaked at day 7-10, then stabilized or regressed by day 21. In contrast, tubulitis, arteritis, and glomerulitis were absent or mild at days 5 and 7, but progressed through day 21, indicating separate regulation and homeostatic control of these lesions. Edema, hemorrhage, and necrosis also increased through day 21. All lesions were T-dependent, failing to develop in T-cell-deficient hosts. Allografts into immunoglobulin-deficient hosts manifested typical infiltration, MHC induction, and tubulitis at days 7 and 21, indicating that these lesions are alloantibody-independent. However at day 21 kidneys rejecting in immunoglobulin-deficient hosts showed decreased edema, arteritis, venulitis, and necrosis. Thus the three groups of lesions are: T-cell-mediated interstitial infiltration, MHC induction, and venulitis, which develops rapidly then stabilizes; slower but progressive T-cell-mediated tubulitis and arteritis; and late antibody-mediated endothelial injury, which contributes to late edema, arteritis, and venulitis.