Analysis of robust innate immune response after transplantation in the absence of adaptive immunity

The role of efferocytosis and transplant rejection: Strategies in promoting transplantation tolerance using apoptotic cell therapy and/or synthetic particles

Recently, efforts have been made to recognize the precise reason(s) for transplant failure and the process of rejection utilizing the molecular signature. Most transplant recipients do not appreciate the unknown length of survival of allogeneic grafts with the existing standard of care. Two noteworthy immunological pathways occur during allogeneic transplant rejection. A nonspecific innate immune response predominates in the early stages of the immune reaction, and allogeneic antigens initiate a donor-specific adaptive reaction. Though the adaptive response is the major cause of allograft rejection, earlier pro-inflammatory responses that are part of the innate immune response are also regarded as significant in graft loss. The onset of the innate and adaptive immune response causes chronic and acute transplant rejection. Currently employed immunosuppressive medications have shown little or no influence on chronic rejection and, as a result, on overall long-term transplant survival. Furthermore, long-term pharmaceutical immunosuppression is associated with side effects, toxicity, and an increased risk of developing diseases, both infectious and metabolic. As a result, there is a need for the development of innovative donor-specific immunosuppressive medications to regulate the allorecognition pathways that induce graft loss and to reduce the side effects of immunosuppression. Efferocytosis is an immunomodulatory mechanism with fast and efficient clearance of apoptotic cells (ACs). As such, AC therapy strategies have been suggested to limit transplant-related sequelae. Efferocytosis-based medicines/treatments can also decrease the use of immunosuppressive drugs and have no detrimental side effects. Thus, this review aims to investigate the impact of efferocytosis on transplant rejection/tolerance and identify approaches using AC clearance to increase transplant viability.

Blocking hyaluronan synthesis alleviates acute lung allograft rejection

Lung allograft rejection results in the accumulation of low–molecular weight hyaluronic acid (LMW-HA), which further propagates inflammation and tissue injury. We have previously shown that therapeutic lymphangiogenesis in a murine model of lung allograft rejection reduced tissue LMW-HA and was associated with improved transplant outcomes. Herein, we investigated the use of 4-Methylumbelliferone (4MU), a known inhibitor of HA synthesis, to alleviate acute allograft rejection in a murine model of lung transplantation. We found that treating mice with 4MU from days 20 to 30 after transplant was sufficient to significantly improve outcomes, characterized by a reduction in T cell–mediated lung inflammation and LMW-HA content and in improved pathology scores. In vitro, 4MU directly attenuated activation, proliferation, and differentiation of naive CD4⁺ T cells into Th1 cells. As 4MU has already been demonstrated to be safe for human use, we believe examining 4MU for the treatment of acute lung allograft rejection may be of clinical significance.

Humanization of Immunodeficient Animals for the Modeling of Transplantation, Graft Versus Host Disease, and Regenerative Medicine

The humanization of animals is a powerful tool for the exploration of human disease pathogenesis in biomedical research, as well as for the development of therapeutic interventions with enhanced translational potential. Humanized models enable us to overcome biologic differences that exist between humans and other species, while giving us a platform to study human processes in vivo. To become humanized, an immune-deficient recipient is engrafted with cells, tissues, or organoids. The mouse is the most well studied of these hosts, with a variety of immunodeficient strains available for various specific uses. More recently, efforts have turned to the humanization of other animal species such as the rat, which offers some technical and immunologic advantages over mice. These advances, together with ongoing developments in the incorporation of human transgenes and additional mutations in humanized mouse models, have expanded our opportunities to replicate aspects of human allotransplantation and to assist in the development of immunotherapies. In this review, the immune and tissue humanization of various species is presented with an emphasis on their potential for use as models for allotransplantation, graft versus host disease, and regenerative medicine.

GGTA1/iGb3S Double Knockout Mice: Immunological Properties and Immunogenicity Response to Xenogeneic Bone Matrix

Background

Animal tissues and tissue-derived biomaterials are widely used in the field of xenotransplantation and regenerative medicine. A potential immunogenic risk that affects the safety and effectiveness of xenografts is the presence of remnant α-Gal antigen (synthesized by GGTA1 or/and iGb3S). GGTA1 knockout mice have been developed as a suitable model for the analysis of anti-Gal antibody-mediated immunogenicity. However, we are yet to establish whether GGTA1/iGb3S double knockout (G/i DKO) mice are sensitive to Gal antigen-positive xenoimplants.

Methods

α-Gal antigen expression in the main organs of G/i DKO mice or bovine bone substitutes was detected via a standardized ELISA inhibition assay. Serum anti-α-Gal antibody titers of G/i DKO mice after immunization with rabbit red blood cells (RRBC) and implantation of raw lyophilized bone substitutes (Gal antigen content was 8.14 ± 3.17 × 10¹²/mg) or Guanhao Biotech bone substitutes (50% decrease in Gal antigen relative to the raw material) were assessed. The evaluation of total serum antibody, inflammatory cytokine, and splenic lymphocyte subtype populations and the histological analysis of implants and thymus were performed to systematically assess the immune response caused by bovine bone substitutes and bone substitute grafts in G/i DKO mice.

Results

α-Gal epitope expression was reduced by 100% in the main organs of G/i DKO mice, compared with their wild-type counterparts. Following immunization with RRBC, serum anti-Gal antibody titers of G/i DKO mice increased from 80- to 180-fold. After subcutaneous implantation of raw lyophilized bone substitutes and Guanhao Biotech bone substitutes into G/i DKO mice, specific anti-α-Gal IgG, anti-α-Gal IgM, and related inflammatory factors (IFN-γ and IL-6) were significantly increased in the raw lyophilized bone substitute group but showed limited changes in the Guanhao Biotech bone substitute group, compared with the control.

Conclusion

G/i DKO mice are sensitive to Gal antigen-positive xenogeneic grafts and can be effectively utilized for evaluating the α-Gal-mediated immunogenic risk of xenogeneic grafts.

Belatacept for maintenance immunosuppression in cardiothoracic transplantation: The potential frontier

Current immunosuppressive regimens with calcineurin inhibitors have improved the management of patients after transplantation. However, their adverse effects are linked to increased morbidity and limit the long-term survival of heart and lung transplant recipients. Belatacept, a costimulation inhibitor interfering with the interaction between CD28 on T cells and the B7 ligands on antigen presenting cells, has shown success and is currently approved for use in renal transplant recipients. Furthermore, it lacks many of the cardiovascular, metabolic, neurologic, and renal adverse of effects of calcineurin inhibitors that have the largest impact on long-term survival in cardiothoracic transplant. Additionally, it requires no therapeutic drug monitoring and is only administered once a month. Limitations to belatacept use have been observed that must be considered when comparing immunosuppression options. Despite this, maintenance immunosuppression with belatacept has the potential to improve outcomes in cardiothoracic transplant recipients, as it has with kidney transplant recipients. However, no large clinical trials investigating belatacept for maintenance immunosuppression in heart and lung transplant recipients exist. There is a large need for focused research of belatacept in cardiothoracic transplantation. Belatacept is a viable treatment option for maintenance immunosuppression, and it is reasonable to pursue more evidence in cardiothoracic transplant recipients.

Ectopic expression of recipient CD47 inhibits mouse macrophage-mediated immune rejection against human stem cell transplants

Like conventional transplants, immunosuppression is required to facilitate survival and function of human embryonic stem cell (hESC) derivatives after implantation into xenogeneic recipients. We have previously reported that T cells alone are sufficient to reject allogeneic murine ESC derivatives; and strategies that inhibit T-cell activation, including coreceptor and costimulation blockade, prevent hESC derivatives from being rejected. This study aimed to investigate, in addition to T cells, whether macrophages contribute to transplant rejection of hESC xenografts with nonobese diabetic (NOD)/SCID mice that lack functional T and B cells but have macrophages. We show that acute rejection against hESC-derived endothelial cells (hESC-ECs) was mediated, to some degree, by infiltrating macrophages that phagocytosed them. Transgenic expression of murine CD47 on cell surface of hESC-ECs mitigates macrophage-mediated phagocytosis and improves their survival after transplantation. Our results highlight that innate immune cells, such as macrophages, can reject hESC derivatives, raising concern against the use of NOD/SCID as transplant recipients for testing in vivo function of hESC-derived tissues. Augmenting CD47 signaling promotes survival and function of hESC derivatives after xenogeneic transplantation.-Leung, C. S., Li, J., Xu, F., Wong, A. S. L., Lui, K. O. Ectopic expression of recipient CD47 inhibits mouse macrophage-mediated immune rejection against human stem cell transplants.

Combining Theoretical and Experimental Techniques to Study Murine Heart Transplant Rejection

The quality of life of organ transplant recipients is compromised by complications associated with life-long immunosuppression, such as hypertension, diabetes, opportunistic infections, and cancer. Moreover, the absence of established tolerance to the transplanted tissues causes limited long-term graft survival rates. Thus, there is a great medical need to understand the complex immune system interactions that lead to transplant rejection so that novel and effective strategies of intervention that redirect the system toward transplant acceptance (while preserving overall immune competence) can be identified. This study implements a systems biology approach in which an experimentally based mathematical model is used to predict how alterations in the immune response influence the rejection of mouse heart transplants. Five stages of conventional mouse heart transplantation are modeled using a system of 13 ordinary differential equations that tracks populations of both innate and adaptive immunity as well as proxies for pro- and anti-inflammatory factors within the graft and a representative draining lymph node. The model correctly reproduces known experimental outcomes, such as indefinite survival of the graft in the absence of CD4⁺ T cells and quick rejection in the absence of CD8⁺ T cells. The model predicts that decreasing the translocation rate of effector cells from the lymph node to the graft delays transplant rejection. Increasing the starting number of quiescent regulatory T cells in the model yields a significant but somewhat limited protective effect on graft survival. Surprisingly, the model shows that a delayed appearance of alloreactive T cells has an impact on graft survival that does not correlate linearly with the time delay. This computational model represents one of the first comprehensive approaches toward simulating the many interacting components of the immune system. Despite some limitations, the model provides important suggestions of experimental investigations that could improve the understanding of rejection. Overall, the systems biology approach used here is a first step in predicting treatments and interventions that can induce transplant tolerance while preserving the capacity of the immune system to protect against legitimate pathogens.

[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.

[Role of innate immunity in tolerance induction]

This review considers the role of innate immunity in mechanisms of transplant tolerance and rejection, analyse the role of innate immunity cells (dendritic cells-DC, NK, must and other cells) in these processes, and the pathes of creation of tolerogenic DC for transplant rejection therapy and tolerance.

Longitudinal Analysis of Whole Blood Transcriptomes to Explore Molecular Signatures Associated with Acute Renal Allograft Rejection

In this study, we explored a time course of peripheral whole blood transcriptomes from kidney transplantation patients who either experienced an acute rejection episode or did not in order to better delineate the immunological and biological processes measureable in blood leukocytes that are associated with acute renal allograft rejection. Using microarrays, we generated gene expression data from 24 acute rejectors and 24 nonrejectors. We filtered the data to obtain the most unambiguous and robustly expressing probe sets and selected a subset of patients with the clearest phenotype. We then performed a data-driven exploratory analysis using data reduction and differential gene expression analysis tools in order to reveal gene expression signatures associated with acute allograft rejection. Using a template-matching algorithm, we then expanded our analysis to include time course data, identifying genes whose expression is modulated leading up to acute rejection. We have identified molecular phenotypes associated with acute renal allograft rejection, including a significantly upregulated signature of neutrophil activation and accumulation following transplant surgery that is common to both acute rejectors and nonrejectors. Our analysis shows that this expression signature appears to stabilize over time in nonrejectors but persists in patients who go on to reject the transplanted organ. In addition, we describe an expression signature characteristic of lymphocyte activity and proliferation. This lymphocyte signature is significantly downregulated in both acute rejectors and nonrejectors following surgery; however, patients who go on to reject the organ show a persistent downregulation of this signature relative to the neutrophil signature.

Longitudinal analysis of whole blood transcriptomes to explore molecular signatures associated with acute renal allograft rejection

In this study, we explored a time course of peripheral whole blood transcriptomes from kidney transplantation patients who either experienced an acute rejection episode or did not in order to better delineate the immunological and biological processes measureable in blood leukocytes that are associated with acute renal allograft rejection. Using microarrays, we generated gene expression data from 24 acute rejectors and 24 nonrejectors. We filtered the data to obtain the most unambiguous and robustly expressing probe sets and selected a subset of patients with the clearest phenotype. We then performed a data-driven exploratory analysis using data reduction and differential gene expression analysis tools in order to reveal gene expression signatures associated with acute allograft rejection. Using a template-matching algorithm, we then expanded our analysis to include time course data, identifying genes whose expression is modulated leading up to acute rejection. We have identified molecular phenotypes associated with acute renal allograft rejection, including a significantly upregulated signature of neutrophil activation and accumulation following transplant surgery that is common to both acute rejectors and nonrejectors. Our analysis shows that this expression signature appears to stabilize over time in nonrejectors but persists in patients who go on to reject the transplanted organ. In addition, we describe an expression signature characteristic of lymphocyte activity and proliferation. This lymphocyte signature is significantly downregulated in both acute rejectors and nonrejectors following surgery; however, patients who go on to reject the organ show a persistent downregulation of this signature relative to the neutrophil signature.

Effector mechanisms of rejection

Organ transplantation appears today to be the best alternative to replace the loss of vital organs induced by various diseases. Transplants can, however, also be rejected by the recipient. In this review, we provide an overview of the mechanisms and the cells/molecules involved in acute and chronic rejections. T cells and B cells mainly control the antigen-specific rejection and act either as effector, regulatory, or memory cells. On the other hand, nonspecific cells such as endothelial cells, NK cells, macrophages, or polymorphonuclear cells are also crucial actors of transplant rejection. Last, beyond cells, the high contribution of antibodies, chemokines, and complement molecules in graft rejection is discussed in this article. The understanding of the different components involved in graft rejection is essential as some of them are used in the clinic as biomarkers to detect and quantify the level of rejection.

Toll-like receptor 4 in experimental kidney transplantation: early mediator of endogenous danger signals

The role of toll-like receptors (TLRs) has been described in the pathogenesis of renal ischemia/reperfusion injury, but data on the expression and function of TLR4 during renal allograft damage are still scarce. We analyzed the expression of TLR4 in an experimental rat model 6 and 28 days after allogeneic kidney transplantation in comparison to control rats and rats after syngeneic transplantation. On day 6, a significant induction in TLR4 expression--restricted to the glomerular compartment--was found in acute rejecting allografts only. TLR4 expression strongly correlated with renal function, and TLR4 induction was accompanied by a significant increase in CC chemokine expression within the graft as well as in urinary CC chemokine excretion. TLR4 induction may be caused by an influx of macrophages as well as TLR4-expressing intrinsic renal cells. Fibrinogen deposition in renal allografts correlated with renal TLR4 expression and may act as a potent stimulator of chemokine release via TLR4 activation. This study provides, for the first time, data about the precise intrarenal localization and TLR4 induction after experimental kidney transplantation. It supports the hypothesis that local TLR4 activation by endogenous ligands may be one pathological link from unspecific primary allograft damage to subsequent chemokine release, infiltration and activation of immune cells leading to deterioration of renal function and induction of renal fibrosis.

Ectonucleotidases in solid organ and allogeneic hematopoietic cell transplantation

Extracellular nucleotides are ubiquitous signalling molecules which modulate distinct physiological and pathological processes. Nucleotide concentrations in the extracellular space are strictly regulated by cell surface enzymes, called ectonucleotidases, which hydrolyze nucleotides to the respective nucleosides. Recent studies suggest that ectonucleotidases play a significant role in inflammation by adjusting the balance between ATP, a widely distributed proinflammatory danger signal, and the anti-inflammatory mediator adenosine. There is increasing evidence for a central role of adenosine in alloantigen-mediated diseases such as solid organ graft rejection and acute graft-versus-host disease (GvHD). Solid organ and hematopoietic cell transplantation are established treatment modalities for a broad spectrum of benign and malignant diseases. Immunological complications based on the recognition of nonself-antigens between donor and recipient like transplant rejection and GvHD are still major challenges which limit the long-term success of transplantation. Studies in the past two decades indicate that purinergic signalling influences the severity of alloimmune responses. This paper focuses on the impact of ectonucleotidases, in particular, NTPDase1/CD39 and ecto-5'-nucleotidase/CD73, on allograft rejection, acute GvHD, and graft-versus-leukemia effect, and on possible clinical implications for the modulation of purinergic signalling after transplantation.

Graft rejection - endogenous or allogeneic?

The presence and persistence of alloantigen is necessary for graft-specific T-cell-mediated immunity. However, specificity comprises only a single facet of an extremely complex process. Evidence is accruing to suggest that immunogenicity could be manipulated by endogenous ligands released during tissue injury. Stress molecules are significantly up-regulated following transplantation and stimulate conserved receptors on a range of leucocytes, including dendritic cells (DCs). The DCs are essential for co-stimulation and the induction of adaptive immunity. Stress signals can act as an adjuvant leading to DC maturation and activation. DCs stimulated by endogens exhibit enhanced alloantigen presentation, co-stimulation and production of pro-inflammatory cytokines, such as interleukin-1β (IL-1β) and IL-18. Inflammasomes have a major role in IL-1β/IL-18 production and secretion, and can be stimulated by endogens. Importantly, the polarization toward inflammatory T helper type 17 cells as opposed to regulatory T cells is dependent upon, among other factors, IL-1β. This highlights an important differentiation pathway that may be influenced by endogenous signals. Minimizing graft damage and stress expression should hypothetically be advantageous, and we feel that this area warrants further research, and may provide novel treatment modalities with potential clinical benefit.

Inhibition of TLR2 promotes graft function in a murine model of renal transplant ischemia-reperfusion injury

Toll-like receptors (TLRs) are important molecules involved in the activation of innate and subsequent development of adaptive immunity. TLRs are ligated by exogenous ligands from pathogens and by endogenous ligands released in inflammatory diseases. Activation of TLR leads to activation of NF-κB and release of proinflammatory cytokines, such as IL-6 and TNF-α. TLRs play an important role in the pathogenesis of renal diseases. Increased expression of TLRs have been associated with ischemic kidney damage, acute kidney injury, end-stage renal failure, acute renal transplant rejection, and delayed allograft function. OPN301 is a mouse anti-human TLR2 antibody that cross-reacts with mouse TLR2. We show that inhibition of TLR2 promotes graft function in an isograft model of renal transplantation. Recipient mice were treated intravenously with OPN301 before reperfusion of the transplanted kidney that had been subjected to 30 min of cold ischemia. After 5 d, the residual native kidney was removed, and renal transplant function was assessed 24 h later by measurement of blood urea nitrogen. Renal function in both saline- and isotype-treated mice was similar, with significant improvement in OPN301-treated mice (isotype-treated vs. OPN301-treated: 33.9±3.2 vs. 19.8±1.9 μM; P<0.01). The histopathological appearance corresponded with renal functional results. In OPN301-treated recipients, renal structure was well preserved, whereas in the saline-treated group, tubular injury was severe, with marked tubular thinning, epithelial shedding, cast formation and necrosis. Inhibition of TLR2 also leads to a decrease in C3d deposition, although it is unclear whether this is due directly to TLR2 inhibition or a decrease in renal inflammation. This study shows that inhibition of TLR2 with a therapeutic agent (OPN301) provides significant protection from ischemia/reperfusion injury in a model of kidney transplantation.

Proteomic analysis reveals innate immune activity in intestinal transplant dysfunction

BACKGROUND

Many patients with intestinal failure require intestinal transplantation (ITx) to survive. Acute cellular rejection poses a challenge in ITx because its biologic components are incompletely understood. New methodologies for its integrative and longitudinal analysis are needed.

METHODS

In this study, we characterized episodes of acute cellular rejection in ITx recipients using a noninvasive proteomic analysis. Ostomy effluent was obtained from all patients undergoing ITx at University of California, Los Angeles from July 2008 to September 2009 during surveillance endoscopies in the first 8 weeks post-ITx. Effluent was analyzed using 17-plex Luminex technology and matrix-assisted laser desorption/ionization proteomics.

RESULTS

Of 56 ostomy effluent samples from 17 ITx recipients, 14% developed biopsy-proven rejection at a median of 25 days post-ITx. Six had mild rejection, two were indeterminate for rejection, and no graft loss was seen in the first 3 months posttransplantation. Effluent levels of five innate immune cytokines were elevated in the posttransplantation phase: granulocyte colony-stimulating factor, interleukin-8, tissue necrosis factor-α, interleukin-1β, and interferon-γ. Proteomic analysis revealed 17 protein features differentially seen in rejection, two identified as human neutrophil peptide 1 and 2. This was confirmed by the presence of human neutrophil peptide-positive lamina propria neutrophils in biopsy tissue samples.

CONCLUSIONS

Proteomic and cytokine analysis of ostomy effluents suggests an early and unappreciated role of innate immune activation during rejection.

Loss of tolerance to self after transplant

Organ transplantation is the widely accepted treatment for end-stage organ failure. Since the first successful kidney transplant from an identical twin donor in 1954, researchers have been studying the effects of the immune system on transplantation outcomes. Although the surgery is technically successful, the majority of grafts from genetically disparate donors are rejected due to a number of factors that stimulate recipient immune responses, ultimately resulting in graft loss despite the chronic use of immunosuppressive (IS) drugs. Unfortunately, while short-term success has greatly improved with the development of novel IS drugs, the long-term graft survival of solid organs has not improved significantly over the last few decades. The problem of late graft loss is mainly attributed to development of chronic rejection. Therefore, understanding all of the immune mechanisms involved in transplant rejection is important to prevent graft dysfunction, and eventually, graft loss. In this review, we will give an overview of allograft rejection, the progression from acute to chronic rejection, and in addition, the recent discovery of a critical role for loss of self-tolerance and development of IL-17-dependent autoimmunity in chronic rejection.

Impact of Toll-like receptor 2 expression in renal allograft rejection

BACKGROUND

An important role of TLR2 has been shown in various experimental models of renal ischaemia/reperfusion injury. To study the expression of TLR2 in renal allograft rejection systematically, we established an experimental rat transplantation model.

METHODS

TLR2 expression was analysed in 99 human renal allograft biopsies, and in rat allografts at Day 6 and 28 after experimental renal transplantation. To discriminate whether regulation of TLR2 was following immunological processes after allogeneic transplantation or was a consequence from ischaemia/reperfusion injury, control animals subjected to syngeneic transplantation or to ischaemia/reperfusion damage were also investigated.

RESULTS

TLR2 mRNA was significantly elevated in rat allografts with acute rejection on Day 6 and decreased spontaneously towards Day 28. TLR2 induction correlated with renal function and TLR2 excretion in the urine of transplanted rats. TLR2 staining was also significantly increased in human allografts with acute rejection. TLR2 protein could be localized in tubular epithelial cells and vascular endothelial cells, and in CD68- and CD4-positive infiltrating cells.

CONCLUSIONS

TLR2 is markedly up-regulated in both experimental and human acute renal allograft rejection. Our data suggest a role for TLR2 during allogen-dependent graft damage after renal transplantation.

Genome-wide transcription profile of endothelial cells after cardiac transplantation in the rat

Transcriptome analyses of organ transplants have until now usually focused on whole tissue samples containing activation profiles from different cell populations. Here, we enriched endothelial cells from rat cardiac allografts and isografts, establishing their activation profile at baseline and on days 2, 3 and 4 after transplantation. Modulated transcripts were assigned to three categories based on their regulation profile in allografts and isografts. Categories A and B contained the majority of transcripts and showed similar regulation in both graft types, appearing to represent responses to surgical trauma. By contrast, category C contained transcripts that were partly allograft-specific and to a large extent associated with interferon-gamma-responsiveness. Several transcripts were verified by immunohistochemical analysis of graft lesions, among them the matricellular protein periostin, which was one of the most highly upregulated transcripts but has not been associated with transplantation previously. In conclusion, the majority of the differentially expressed genes in graft endothelial cells are affected by the transplantation procedure whereas relatively few are associated with allograft rejection.

Influence of immunosuppression on alloresponse, inflammation and contractile function of graft after intestinal transplantation

In small bowel transplantation (SBTx), graft manipulation, ischemia/reperfusion injury and acute rejection initiate a severe cellular and molecular inflammatory response in the muscularis propria leading to impaired motility of the graft. This study examined and compared the effect of tacrolimus and sirolimus on inflammation in graft muscularis. After allogeneic orthotopic SBTx, recipient rats were treated with tacrolimus or sirolimus. Tacrolimus and sirolimus attenuated neutrophilic, macrophage and T-cell infiltration in graft muscularis, which was associated with reduced apoptotic cell death. Nonspecific inflammatory mediators (IL-6, MCP-1) and T-cell activation markers (IL-2, IFN-gamma) were highly upregulated in allogeneic control graft muscularis 24 h and 7 days after SBTx, and tacrolimus and sirolimus significantly suppressed upregulation of these mediators. In vitro organ bath method demonstrated a severe decrease in graft smooth muscle contractility in allogeneic control (22% of normal control). Correlating with attenuated upregulation of iNOS, tacrolimus and sirolimus treatment significantly improved contractility (64% and 72%, respectively). Although sirolimus reduced cellular and molecular inflammatory response more efficiently after 24 h, contrary tacrolimus prevented acute rejection more efficiently. In conclusion, tacrolimus and sirolimus attenuate cellular and molecular inflammatory response in graft muscularis and subsequent dysmotility of the graft after allogeneic SBTx.

Superior myocardial preservation with HTK solution over Celsior in rat hearts with prolonged cold ischemia

BACKGROUND

Increasing allograft ischemic time is a significant risk factor for mortality following heart transplantation (HTx). The purpose of this study was to evaluate the protective effects of histidine-tryptophan-ketoglutarate (HTK) and Celsior (CEL) using a rat HTx model with prolonged cold storage.

METHODS

The hearts were excised from donor rats, stored in cold preservation solution for either 6 or 18 hours, and heterotopically transplanted into syngeneic recipients. Serum creatine phosphokinase (CPK), serum troponin I, graft-infiltrating cells, graft mRNA levels for inflammatory mediators, and tissue adenosine triphosphate (ATP) levels were analyzed, as markers of graft injury.

RESULTS

The recipients of grafts stored in HTK for 18 hours of prolonged cold ischemia had lower levels of serum CPK and tissue malondialdehyde, less upregulation of the mRNAs for IL-6 and inducible nitric oxide synthase, less apoptosis, and higher ATP levels than those receiving grafts stored in CEL and Saline. Cardiac contraction 3 hours after reperfusion was observed in 43% of the cardiac grafts stored in HTK for 18 hours, while no cardiac wall movement was seen in grafts stored in either saline or CEL.

CONCLUSION

Cold storage in HTK exhibited superior protective effects against prolonged cold ischemia in a syngeneic rat transplantation model.

Mechanisms of Toll-like receptor 4 (TLR4)-mediated inflammation after cold ischemia/reperfusion in the heart

BACKGROUND

Toll-Like Receptor 4 (TLR4) signaling mediates early inflammation after cold ischemia-reperfusion (I/R). We hypothesized that the TLR4 coreceptor CD14, the intracellular adaptor proteins myeloid differentiation factor 88 (MyD88) and TIR domain-containing-adaptor inducing IFNbeta (TRIF) would be required for cold I/R induced inflammation. High mobility group box 1 (HMGB1) is a putative endogenous activator of TLR4. Therefore, we also assessed the contribution of HMGB1 in cold I/R induced inflammation.

METHODS

Syngeneic heart transplants were performed in mice deficient in CD14, MyD88, TRIF, or wild-type mice. In other experiments, anti-HMGB1 neutralizing antibody or control IgG was administered at reperfusion. Donor hearts were subjected to 2 hr of cold ischemia and retrieved after 3 hr of reperfusion.

RESULTS

After cold I/R, grafts revealed striking translocation of HMGB1 out of the nucleus in cardiac myocytes. Administration of an anti-HMGB1 neutralizing antibody resulted in reduced systemic interleukin (IL)-6, tumor necrosis factor alpha (TNFalpha), and intercellular adhesion molecule-1 (ICAM-1) messenger RNA (mRNA) levels (P< or =0.05). Compared with controls, CD14 knock-out (KO) mice exhibited significantly lower (P< or =0.05) systemic IL-6 and JE/monocyte chemotractant protein-1 levels after cold I/R. Intragraft TNFalpha and IL-1beta mRNA levels were also significantly lower (P< or =0.05) in CD14 KO grafts. MyD88 KO mice exhibited significantly lower (P< or=0.05) systemic IL-6 levels compared with control mice after cold I/R. Intragraft TNFalpha, IL-6, and ICAM-1 mRNA levels were also significantly lower (P< or =0.05) in MyD88 KO grafts. Significantly lower levels (P< or =0.05) of serum IL-6, monocyte chemotractant protein-1 as well as intragraft TNFalpha, IL-6, IL-1beta, and ICAM-1 were observed after cold I/R in TRIF deficient animals compared with controls.

CONCLUSIONS

CD14, MyD88, TRIF, and HMGB1 contribute to the inflammatory response that occurs after cold I/R. These results provide insight into the mechanisms of TLR4-mediated inflammation after cold I/R.

A murine model of falciparum-malaria by in vivo selection of competent strains in non-myelodepleted mice engrafted with human erythrocytes

To counter the global threat caused by Plasmodium falciparum malaria, new drugs and vaccines are urgently needed. However, there are no practical animal models because P. falciparum infects human erythrocytes almost exclusively. Here we describe a reliable falciparum murine model of malaria by generating strains of P. falciparum in vivo that can infect immunodeficient mice engrafted with human erythrocytes. We infected NOD(scid/beta2m-/-) mice engrafted with human erythrocytes with P. falciparum obtained from in vitro cultures. After apparent clearance, we obtained isolates of P. falciparum able to grow in peripheral blood of engrafted NOD(scid/beta2m-/-) mice. Of the isolates obtained, we expanded in vivo and established the isolate Pf3D7(0087/N9) as a reference strain for model development. Pf3D7(0087/N9) caused productive persistent infections in 100% of engrafted mice infected intravenously. The infection caused a relative anemia due to selective elimination of human erythrocytes by a mechanism dependent on parasite density in peripheral blood. Using this model, we implemented and validated a reproducible assay of antimalarial activity useful for drug discovery. Thus, our results demonstrate that P. falciparum contains clones able to grow reproducibly in mice engrafted with human erythrocytes without the use of myeloablative methods.

Toll-like receptor 4 mediates the early inflammatory response after cold ischemia/reperfusion

BACKGROUND

Ischemia/reperfusion (I/R) injury leads to graft dysfunction and may contribute to alloimmune responses posttransplantation. The molecular mechanisms of cold I/R injury are only partially characterized but may involve toll-like receptor (TLR)-4 activation by endogenous ligands. We tested the hypothesis that TLR4 mediates the early inflammatory response in the setting of cold I/R in a murine cardiac transplant model.

METHODS

Syngeneic heart transplants were performed in mutant mice deficient in TLR4 signaling (C3H/HeJ) and wild-type mice (C3H/HeOuJ). Transplants were also performed between the strains (mutant hearts into wild-type recipients and the converse). Donor hearts were subjected to 2 hr of cold ischemia. The grafts were retrieved at 3 and 24 hr after reperfusion. Serum samples were collected for cytokine analysis. Reverse-transcription polymerase chain reaction and histologic analysis were used to assess intra-graft inflammation.

RESULTS

After transplant, serum tumor necrosis factor (TNF), interleukin (IL)-6, JE/monocyte chemotractant protein (MCP)-1, IL-1beta, and troponin I levels, as well as intragraft TNF, IL-1beta, IL-6, early growth response (EGR)-1, intercellular adhesion molecule (ICAM)-1, and inducible nitric oxide synthase (iNOS) mRNA levels, were significantly lower in the mutant-->mutant group compared to the wild-type-->wild-type group (P< or =0.05). Intermediate levels of serum IL-6, JE/MCP-1, as well as intragraft TNF, IL-1beta, IL-6, and ICAM-1 mRNA were observed after transplants in the mutant-->wild-type and wild-type-->mutant groups. Immunohistochemistry revealed less myocardial nuclear factor-kappaB nuclear translocation at and less neutrophil infiltration in the mutant-->mutant group compared to the wild-type-->wild-type group.

CONCLUSIONS

These findings demonstrate that TLR4 signaling is central to both the systemic and intragraft inflammatory responses that occur after cold I/R in the setting of organ transplantation and that TLR4 signaling on both donor and recipient cells contributes to this response.

Graft Produced Interleukin-6 Functions as a Danger Signal and Promotes Rejection After Transplantation

BACKGROUND

Interleukin (IL)-6 is a pleiotropic cytokine that functions in both the innate and adaptive immune responses. However, the role of IL-6 in allograft rejection remains poorly understood.

METHODS

In this study, we demonstrate a critical role for graft-produced IL-6 in allograft rejection in a murine model of cardiac allograft transplantation.

RESULTS

The results show that IL-6-deficient grafts transplanted into allogeneic wild-type recipients have significantly prolonged survival, approximately three times the survival time of wild-type controls. In contrast, allogeneic cardiac transplants into IL-6-deficient recipients do not have prolonged graft survival, indicating that donor graft cells are the relevant source of IL-6. Our investigation of potential mechanisms shows that graft-produced IL-6 promotes the activation of peripheral CD4 and CD8 T cells. Furthermore, we show that IL-6 deficiency prolongs graft survival only in the presence of CD25+ T cells that have a phenotype consistent with regulatory T cells. Interestingly, IL-6 production by the graft is triggered by antigen-independent innate immune mechanisms.

CONCLUSIONS

Thus, our results suggest the paradigm that graft rejection versus tolerance is determined by a balance between the activation of effector T cells versus immune suppression by regulatory T cells, and that after transplantation, IL-6 functions as a systemic danger signal that overcomes constitutive immune suppression mediated by regulatory T cells and promotes the activation of effector T cells.

The innate immune system in allograft rejection and tolerance

As T cells alone are both necessary and sufficient for the rejection of virtually all allogeneic tissues, much of transplantation immunology has focused on cells of the adaptive immune system. During the past decade, advances in our understanding of innate responses to pathogen-associated molecules have spurred a "rediscovery" of innate immunity. Fueled by this, an increasing body of literature has emerged in which the role of the innate immune system in allograft rejection and tolerance has been examined more closely. This review will give an overview of recent studies and emerging concepts of how the cellular components of the innate immune system participate in the immune response to solid organ transplantation. These important studies highlight the complex interplay between diverse cells of the immune response and provide the basis for optimal strategies of tolerance induction.

Microarray analysis of gene expression in murine cardiac graft infiltrating cells

Microarray technology can rapidly generate large databases of gene expression profiles. Our laboratory has applied these techniques to analyze differential gene expression in cardiac tissue and cells based on mouse heart transplantation. We have analyzed the different gene expression profiles such as stress or injury including ischemia following transplantation. We also have investigated the role of infiltrating inflammatory cells during graft rejection by purifying subsets of infiltrating cells using GFP transgenic mice and detailed all technical experiences and issues. The purpose of this study is to assist researchers to simplify the process of analyzing large database using microarray technology.

CD4+CD25+ regulatory T cells in transplantation: progress, challenges and prospects

The involvement of CD4(+)CD25(+) regulatory T cells (Treg) in general immune homeostasis and protection from autoimmune syndromes is now well established. Similarly, there has been increasing evidence for Treg involvement in allograft rejection and current immunotherapies. However, despite significant advances in understanding the development, function, and therapeutic efficacy of Treg in certain well-defined rodent models, the relevance of Treg to clinical transplantation remains unclear. In this review, we summarize our current understanding of the role of Treg in immunity and organ transplantation in experimental and clinical settings. In addition, we review advances in using Treg as a form of immune therapy. The goal is to highlight the complexities and opportunities in the field and to provide evidence to support the use of antigen-specific Tregs in the context of transplantation to facilitate a robust and selective state of immune tolerance.

The effect of renal ischemia-reperfusion injury on expression of RAE-1 and H60 in mice kidney

INTRODUCTION

NKG2D, an activating receptor, may trigger NK and CD8+ T cells. Ligands for NKG2D and major histocompability complex class I chain-related antigen (MIC) have been reported to be expressed in rejected human renal allografts. MIC-NKG2D engagement may induce natural killer (NK) cell activation providing T-cell costimulation. We hypothesized that this interaction between innate and adaptive immunity may occur during kidney ischemia-reperfusion injury (IRI).

METHODS

Male C57BL/6 mice after right renal resection were subjected to 35 minutes of left renal ischemia: the ischemic group. Sham-operated mice underwent the same protocol without vascular occlusion. The sham and ischemic kidneys were removed at 2 to 7, 10, 14, or 28 days postoperatively. The normal, sham, and ischemic kidney tissues were collected for reverse-transcriptase polymerase chain reaction, and immunohistochemistry analysis of MIC homologues in mice (Rae-1 and H60).

RESULTS

Compared with no expression in sham control and normal kidneys, IRI caused mRNA expression of Rae-1 from 2 to 10 days postoperatively and protein expression of Rae-1 from 2 to 14 days postoperatively in ischemic kidneys. We observed no expression of H60 mRNA or protein in any kidney.

CONCLUSION

H60 transcripts have been reported to be present in the BALB/c background but not in C57BL/6. We found IRI did not cause H60 mRNA on protein expression in C57BL/6 kidneys. Rae-1 was absent in normal C57BL/6 kidneys. The IRI-induced expression of the NKG2D ligand, Rae-1, might activate NK and CD8+ T cells. Our results suggested that MIC may be an important link between innate and adaptive immunity in kidney IRI.

Modifying graft immunogenicity and immune response prior to transplantation: potential clinical applications of donor and graft treatment

Many studies have shown a strong association between initial graft injury and poor long-term graft outcome. Events initiated by unspecific immune-activating processes including brain death and ischemia/reperfusion injury occurring prior to transplantation reduce graft functionality and amplify the host immune response. These events may be particularly relevant for less than optimal grafts with reduced resistance to unspecific injuries. Several approaches to ameliorate immune activation of the graft by treating the donor or the graft have been studied. While various substances have been shown to have protective effects in experimental transplantation, only a few drugs have been tested clinically and have demonstrated beneficial effects. We review the results of experimental and clinical studies on donor or graft immunomodulation prior to transplantation and analyze the evidence to support clinical application of these strategies.

Toll-like receptors and graft rejection

Innate immunity plays a role in fighting against invading microorganisms. Emerging evidence suggests that in addition to responding to pathogen-associated molecular patterns of microorganisms, Toll-like receptors (TLRs) can be activated by endogenous ligands expressed by mammalian cells. Clinical and laboratory studies have shown that TLRs may participate in organ graft rejection and transplant immune tolerance, which are briefly reviewed in the present manuscript.

The role of macrophages in allograft rejection

Macrophage accumulation has long been recognized as a feature of allograft rejection, yet the role of macrophages in rejection remains underappreciated. Macrophages contribute to both the innate and acquired arms of the alloimmune response and thus may be involved in all aspects of acute and chronic allograft rejection. Recent advances in macrophage biology have allowed a better understanding of the mechanisms of macrophage accumulation, their state of activation and the pleuripotent roles they play in allograft rejection. Therapeutic attention to macrophages, in addition to T lymphocytes, may lead to improved outcomes in organ transplantation.

Innate immunity and organ transplantation: the potential role of toll-like receptors

Traditionally, the recognition and tolerance of transplanted grafts has been considered to be within the realm of the adaptive immune system. Innate immunity, on the other hand, as the first line of host defense, plays a role in fighting against invading microorganisms. Recently, with the discovery of the Toll-like receptors (TLRs), the role of innate immune responses in the control of adaptive immunity has become a new area of interest. Emerging evidence suggests that in addition to responding to pathogen-associated molecular patterns of microorganisms, TLRs can be activated by endogenous ligands, expressed by mammalian cells. These 'danger signals' may participate in ischemia-reperfusion related organ damage and subsequently influence function and survival of transplanted grafts. Furthermore, it has been suggested that adaptive immune responses can enhance the acute inflammatory responses controlled by innate immunity in organ transplantation. This review addresses the potential involvement of TLRs in different stages of organ transplantation. Intriguing and controversial findings are presented and discussed in order to stimulate more attention to this emerging and potentially important area of research in organ transplantation.

Macrophage-derived interleukin-18 in experimental renal allograft rejection

BACKGROUND

Interleukin 18 (IL-18) is primarily a macrophage-derived, pro-inflammatory cytokine. As macrophages can act as effector cells in acute rejection, we examined the role of IL-18 in a rat model of acute renal allograft rejection.

METHODS

Life-sustaining orthotopic DA to Lewis allograft and Lewis-Lewis isograft kidney transplants were performed. In the same model, macrophage-depleted animals, achieved with liposomal-clodronate therapy, were also studied. Macrophage (ED1+) accumulation and IL-18 expression was assessed by immunohistochemistry. CD11b+ cells (macrophages) were isolated from kidney and spleen by micro beads. Real-time PCR was used to assess IL-18 and INF-gamma mRNA expression in tissue and cell isolates.

RESULTS

Allografts, but not isografts, developed severe tubulo-interstitial damage and increased serum creatinine by day 5 (P<0.001). Immunohistochemistry revealed a greater ED1+ cell accumulation in day 5 allografts compared with isografts (P<0.001). IL-18 mRNA expression was increased 3-fold in allografts compared to isografts (P<0.001). Accordingly, IL-18 protein was increased in allografts (P<0.001), and was predominantly expressed by ED1+ macrophages. CD11b+ macrophages isolated from allografts had a 6-fold upregulation of IL-18 mRNA expression compared to isograft macrophages (P<0.001). Macrophage depletion resulted in a marked attenuation of allograft rejection, ED1+ and IL-18+ cells were significantly reduced (P<0.05) as was IL-18 mRNA expression (29.28+/-2.85 vs 62.48+/-3.05, P<0.001). INF-gamma mRNA expression (P<0.01) and iNOS (P<0.001) production were also significantly reduced in the macrophage-depleted animals.

CONCLUSION

This study demonstrates that IL-18 is significantly increased during acute rejection and is principally produced by intra-graft macrophages. We hypothesize that IL-18 upregulation may be an important macrophage effector mechanism during the acute rejection process.

Evidence for a role of toll-like receptor 4 in development of chronic allograft rejection after cardiac transplantation

BACKGROUND

Long-term success of cardiac transplantation is limited by various forms of graft rejection. The specific mechanisms initiating and controlling these highly specialized immune processes remain unclear so far.

METHODS

To investigate the role of innate immunity in the development of allograft rejection, we assessed toll-like receptor (TLR)4 expression and typical downstream effects of TLR signaling (B7-1, interleukin [IL]-12, tumor necrosis factor [TNF]-alpha) in circulating CD14+ monocytes in 38 transplant recipients 1 to 3 years and in 10 transplant recipients 6 to 10 years after transplantation and compared them with 20 healthy controls using reverse transcription polymerase chain reaction, flow cytometry, and enzyme-linked immunoadsorbent assay. The results were matched with endothelial function testing as an early clinical indicator of transplant vasculopathy early after transplantation.

RESULTS

Allograft endothelial dysfunction (ED) was defined as a compromised coronary flow reserve (CFVR) to acetylcholine (CFVR<2 in 13 of 38 transplant recipients). In these patients, mRNA transcript levels for TLR4 (P<0.05) and surface expression of TLR4 (P<0.005) and B7-1 (P<0.05) on circulating monocytes as well as secretion of IL-12 (P<0.02) and TNF-alpha (P<0.05) were significantly higher than in the remaining 25 patients without ED. Compared with the controls, recipients late after transplantation did not show significantly elevated levels of TLR4 or dependent mediators. These results were compared with mRNA levels in a mice model of acute and chronic rejection. Rejecting mice exhibited elevated mRNA levels for mTLR4 and mB7-1.

CONCLUSIONS

Our results suggest activation of innate immunity in heart-transplant recipients through TLR4 contributes to the development of chronic rejection after cardiac transplantation.

Pre-transplant elevations of interleukin-12 and interleukin-10 are associated with acute rejection after renal transplantation

BACKGROUND

Methods for predicting patients at higher risk for rejection before transplantation may help improve outcomes. We hypothesized that pre-transplant elevations of serum interleukin-12 (IL-12), a pro-inflammatory cytokine, would predict acute rejection, while pre-transplant IL-10, an immunoregulatory cytokine, would be down-regulated in patients subsequently experiencing acute rejection.

MATERIALS AND METHODS

Thirty patients experiencing acute rejection after cadaveric renal allograft transplantation and a control group of 30 patients, undergoing the same procedure but without the occurrence of rejection, were identified. Serum samples taken before transplantation from each patient were then analyzed quantitatively for IL-12 and IL-10 using ELISA assays.

RESULTS

The mean pre-transplant serum IL-12 level was higher in patients who subsequently underwent acute rejection vs. those who did not (181 +/- 143 pg/mL vs. 81.2 +/- 71.5 pg/mL, respectively, p = 0.007). Unexpectedly, pre-transplant serum IL-10 levels were also elevated in patients who underwent rejection (559 +/- 293 pg/mL vs. 332 +/- 163 pg/mL, respectively, p = 0.002). Multivariate analysis demonstrated that elevations of IL-12 and IL-10 were independent risk factors for rejection when adjusted for confounding variables.

CONCLUSIONS

Pre-transplant elevations of IL-12 and, unexpectedly, IL-10 are associated with acute rejection after cadaveric renal transplantation and may be useful in predicting which patients are at increased immunological risk at the time of transplantation. Further studies are necessary to assess the role of occult systemic inflammation in contributing to poor outcomes after transplantation.

Analysis of the Major Histocompatibility Complex in Graft Rejection Revisited by Gene Expression Profiles

BACKGROUND

The precise role of major histocompatibility complex (MHC) molecules in graft rejection remains incompletely understood. The important role of foreign peptides in the alloimmune response was recently recognized.

METHODS

We performed a comparative study of the functions of minor antigens Class I, Class II, and CD1 in murine cardiac allograft rejection by investigating the expression of a large panel of immune and inflammatory genes. To investigate the role of MHC Class II and I, our protocol analyzed allograft recipients deficient in MHC Class II and b2 microglobulin (b2-M), a critical component of the Class I heterodimer. We also included CD1 deficient recipients to differentiate effects in the beta2-M deficient strain due to CD1 deficiency versus the combined inactivation of CD1 and Class I. The serum cytokines tumor necrosis factor (TNF)-alpha interleukin (IL)-6, interferon (IFN)-gamma and IL-1beta were evaluated posttransplant by ELISA. The intragraft expression of 55 chemokines, chemokine receptors, and CD markers were measured by ribonuclease protection assay. The data were analyzed through hierarchical clustering dendrograms and self-organizing maps.

RESULTS

The analysis indicates that each gene deficiency induces both the upregulation and the downregulation of distinct subsets of genes and that similar kinetics of rejection can be attributed to different molecular mechanisms.

CONCLUSIONS

The study provides novel insights into the role of classical and non-classical MHC molecules in graft rejection.