Immunological function of the endothelial cell within the setting of organ transplantation

Inflammation Determines the Capacity of Allogenic Endothelial Cells to Regulate Human Treg Expansion

During allotransplantation, the endothelium acts as semi-professional antigen-presenting cells with the ability to activate proliferation and to promote differentiation of CD4⁺-T subsets. These abilities are dependent on the luminal expression of HLA class II antigens by microvascular endothelial cells, which is regulated by inflammatory cytokines. The upregulation of HLA-DR and HLA-DQ during rejection implies significant intragraft inflammation. Furthermore, the microvascular inflammation is an independent determinant for renal allograft failure. In this study, the potential of inflammation to modify endothelial regulation of peripheral CD4⁺ Treg cells was examined. Microvascular endothelial cells were exposed to pro-inflammatory cytokines for varying durations before co-culture with PBMC from non-HLA matched donors. Proliferation and expansion of CD4⁺Treg and soluble factor secretion was determined. Early interactions were detected by phosphorylation of Akt. Video microscopy was used to examine spatial and temporal endothelial-CD4⁺T interactions. Highly inflammatory conditions led to increased endothelial expression of HLA-DR, the adhesion molecule ICAM-1, the costimulatory molecule PD-L1 and de novo expression of HLA-DQ. Treg differentiation was impaired by exposure of endothelial cells to a high level of inflammation. Neither IL-6, IL-2 nor TGFβ were implicated in reducing Treg numbers. High PD-L1 expression interfered with early endothelial cell interactions with CD4⁺T lymphocytes and led to modified TCR signaling. Blocking endothelial PD-L1 resulted in a partial restoration of Treg. The allogenic endothelial cell-mediated expansion of Treg depends on a critical threshold of inflammation. Manipulation of the PD-L1/PD-1 pathway or endothelial activation post-transplantation may promote or interfere with this intrinsic mechanism of allospecific Treg expansion.

Advanced in vitro Research Models to Study the Role of Endothelial Cells in Solid Organ Transplantation

The endothelium plays a key role in acute and chronic rejection of solid organ transplants. During both processes the endothelium is damaged often with major consequences for organ function. Also, endothelial cells (EC) have antigen-presenting properties and can in this manner initiate and enhance alloreactive immune responses. For decades, knowledge about these roles of EC have been obtained by studying both in vitro and in vivo models. These experimental models poorly imitate the immune response in patients and might explain why the discovery and development of agents that control EC responses is hampered. In recent years, various innovative human 3D in vitro models mimicking in vivo organ structure and function have been developed. These models will extend the knowledge about the diverse roles of EC in allograft rejection and will hopefully lead to discoveries of new targets that are involved in the interactions between the donor organ EC and the recipient's immune system. Moreover, these models can be used to gain a better insight in the mode of action of the currently prescribed immunosuppression and will enhance the development of novel therapeutics aiming to reduce allograft rejection and prolong graft survival.

Composite tissue allotransplantation: opportunities and challenges

Vascularized composite allotransplants (VCAs) have unique properties because of diverse tissue components transplanted en mass as a single unit. In addition to surgery, this type of transplant also faces enormous immunological challenges that demand a detailed analysis of all aspects of alloimmune responses, organ preservation, and injury, as well as the immunogenicity of various tissues within the VCA grafts to further improve graft and patient outcomes. Moreover, the side effects of long-term immunosuppression for VCA patients need to be carefully balanced with the potential benefit of a non-life-saving procedure. In this review article, we provide a comprehensive update on limb and face transplantation, with a specific emphasis on the alloimmune responses to VCA, established and novel immunosuppressive treatments, and patient outcomes.

HLA class II antibodies induce necrotic cell death in human endothelial cells via a lysosomal membrane permeabilization-mediated pathway

Antibody-mediated rejection (AMR) is the major cause of allograft loss after solid organ transplantation. Circulating donor-specific antibodies against human leukocyte antigen (HLA), in particular HLA class II antibodies are critical for the pathogenesis of AMR via interactions with endothelial cells (ECs). To investigate the effects of HLA class II antibody ligation to the graft endothelium, a model of HLA-DR antibody-dependent stimulation was utilized in primary human ECs. Antibody ligation of HLA class II molecules in interferon-γ-treated ECs caused necrotic cell death without complement via a pathway that was independent of apoptosis and necroptosis. HLA-DR-mediated cell death was blocked by specific neutralization of antibody ligation with recombinant HLA class II protein and by lentiviral knockdown of HLA-DR in ECs. Importantly, HLA class II-mediated cytotoxicity was also induced by relevant native allele-specific antibodies from human allosera. Necrosis of ECs in response to HLA-DR ligation was mediated via hyperactivation of lysosomes, lysosomal membrane permeabilization (LMP), and release of cathepsins. Notably, LMP was caused by reorganization of the actin cytoskeleton. This was indicated by the finding that LMP and actin stress fiber formation by HLA-DR antibodies were both downregulated by the actin polymerization inhibitor cytochalasin D and inhibition of Rho GTPases, respectively. Finally, HLA-DR-dependent actin stress fiber formation and LMP led to mitochondrial stress, which was revealed by decreased mitochondrial membrane potential and generation of reactive oxygen species in ECs. Taken together, ligation of HLA class II antibodies to ECs induces necrotic cell death independent of apoptosis and necroptosis via a LMP-mediated pathway. These findings may enable novel therapeutic approaches for the treatment of AMR in solid organ transplantation.

Technical, Immunological, and Ethical Similarities and Differences Between Vascularized Composite Allotransplantation and Solid Organ Transplantation in Current Practice

Solid organ transplantation (SOT) is a surgical method used as the gold standard in end-term organ failure. Following SOT, successful results have also been achieved in vascularized composite tissue transplantation, which improves the quality of life with the success of solid organ transplants and the development of modern immunosuppressive regimens. This review discusses the preoperative, operative, postoperative, and immunological differences between vascularized tissue transplantation and SOT.

Luminex Solid-Phase Crossmatch for De Novo Donor-Specific Antibodies in Living-Donor Related Transplants

OBJECTIVES

There are no reports of de novo donor-specific antibody monitoring by a low-cost solid-phase crossmatch assay using donor lysate after renal transplant.

MATERIALS AND METHODS

We prospectively evaluated 121 complement-dependant cytotoxicity crossmatch-negative living-donor kidney transplant recipients for development of de novo donor-specific antibodies (class I and II HLA) by solid-phase crossmatch Luminex assay after transplant.

RESULTS

Of 121 recipients in our study group, 26 (21.5%) developed de novo donor-specific antibody within 3 months after transplant. Fifteen (58%) of these 26 recipients developed class II de novo donor-specific antibody, 8 patients (30%) developed class I, and 3 (12%) developed both class I and class II. Of the remaining 95 patients (79%) who did not develop de novo donor-specific antibody, 6 (33.3%) had antibody-mediated rejection with glomerulitis (2 with C4d-positive disease). Donor-specific antibody was detected by Luminex solid-phase crossmatch in 18 patients (5 with class I, 11 with class II, and 2 with both class I and II), all with no evidence of clinical rejection. Development of de novo donor-specific antibody detected by solid-phase crossmatch was associated with more acute rejection (31% in de novo donor-specific antibody-positive group versus 19% in the negative group). The positive group had more antibody-mediated rejection (75% of acute rejections), whereas only 33.3% of acute rejections in the negative group were antibody-mediated rejection. Of 12 patients with antibody-mediated rejection, 9 were C4d negative (75%) and were diagnosed by donor-specific antibody positivity detected by solid-phase cros?match testing and histologic findings. The use of donor lysate in solid-phase crossmatch assays is more economical than the single-antigen bead Luminex assay (per test cost of US $45.20 vs $403.20).

Underlying Mechanisms of Protection Involved in Immunocloak

BACKGROUND

We have previously reported on a novel organ-specific immunomodifying therapy that provides protection from early allograft rejection in the absence of systemic immunosuppressive drugs. This novel therapy is a nanobarrier membrane called ImmunoCloak, consisting of a matrix of laminin, proteoglycans, fibronectin, and collagens. The membrane "immunocloaks" the luminal surfaces within the renal vasculature by covering the point of contact between donor vascular endothelial cells and the recipient's immune cells, without adversely affecting renal function. The resulting nonthrombogenic and nonimmunogenic apical surface significantly delays the onset of rejection fivefold over untreated controls. Currently, our focus is to elucidate the mechanisms of protection provided by placement of the membrane.

METHODS

The mechanisms underlying the protective effect of the ImmunoCloak treatment was evaluated using human peripheral blood mononuclear cells and by testing for antigen presentation by cytokine/chemokine analysis using the Luminex platform, T cell allogeneic responses were measured by flow cytometry, and diapedesis was assessed using transwell plates.

RESULTS

We now report that ImmunoCloak interrupts antigen presentation thereby preventing early T cell activation and interferes with diapedesis. There was significant inhibition in the synthesis of proinflammatory cytokines with a concordant blockade of T cell-mediated responses. The placement of the ImmunoCloak also significantly reduced leukocyte migration through the endothelial cell layer by 93%.

CONCLUSIONS

Eliminating the need for nephrotoxic immunosuppressive drugs during the early posttransplant period could help to ameliorate the severity of delayed graft function and could provide a path to using more ischemically damaged renal allografts.

Vascularized composite allograft-specific characteristics of immune responses

Vascularized composite allograft (VCA) transplantation, or reconstructive transplantation, has revolutionized the treatment of complex tissue and functional defects. Despite arriving during an age in which the immunology of solid organ transplant rejection has been investigated in much detail, these transplants have offered new perspectives from which to explore the immunobiology of transplantation. VCAs have a number of unique molecular, cellular, and architectural features which alter the character and intensity of the rejection response. While much is yet to be clarified, an understanding of these distinct mechanisms affords new possibilities for the control of immune responses in an effort to improve outcomes after VCA transplantation.

Heme Oxygenase-1 Inhibits HLA Class I Antibody-Dependent Endothelial Cell Activation

Antibody-mediated rejection (AMR) is a key limiting factor for long-term graft survival in solid organ transplantation. Human leukocyte antigen (HLA) class I (HLA I) antibodies (Abs) play a major role in the pathogenesis of AMR via their interactions with HLA molecules on vascular endothelial cells (ECs). The antioxidant enzyme heme oxygenase (HO)-1 has anti-inflammatory functions in the endothelium. As complement-independent effects of HLA I Abs can activate ECs, it was the goal of the current study to investigate the role of HO-1 on activation of human ECs by HLA I Abs. In cell cultures of various primary human macro- and microvascular ECs treatment with monoclonal pan- and allele-specific HLA I Abs up-regulated the expression of inducible proinflammatory adhesion molecules and chemokines (vascular cell adhesion molecule-1 [VCAM-1], intercellular cell adhesion molecule-1 [ICAM-1], interleukin-8 [IL-8] and monocyte chemotactic protein 1 [MCP-1]). Pharmacological induction of HO-1 with cobalt-protoporphyrin IX reduced, whereas inhibition of HO-1 with either zinc-protoporphyrin IX or siRNA-mediated knockdown increased HLA I Ab-dependent up-regulation of VCAM-1. Treatment with two carbon monoxide (CO)-releasing molecules, which liberate the gaseous HO product CO, blocked HLA I Ab-dependent EC activation. Finally, in an in vitro adhesion assay exposure of ECs to HLA I Abs led to increased monocyte binding, which was counteracted by up-regulation of HO-1. In conclusion, HLA I Ab-dependent EC activation is modulated by endothelial HO-1 and targeted induction of this enzyme may be a novel therapeutic approach for the treatment of AMR in solid organ transplantation.

Sialylation of antibodies in kidney recipients with de novo donor specific antibody, with or without antibody mediated rejection

BACKGROUND

DSA are associated with reduced long-term transplant function and increased prevalence of chronic rejection in some patients, whereas others do not: our goal was to determine whether the sialylation of IgG and DSA could help to explain in these last cases their "non-aggressive" and/or "protective" biological activity.

METHODS

The sialylation level of total IgG in blood from two groups of kidney-transplant patients with de novo DSA, one with an AMR (DSA⁺AMR⁺), and the other without were studied.

RESULTS

In the DSA⁺AMR^- patients total IgG were more sialylated at time of transplant, and at the first detection of DSA, class I DSA were 2.6-fold more sialylated (mean 9.943±1.801 versus 3.898±2.475, p=0.058); DSA⁺AMR⁺ patients exhibited higher levels of class II DSA.

CONCLUSIONS

In our study, higher levels of sialylated IgG are detectable on day of transplant in patients who do not develop AMR, they have higher sialylated class I DSA at the initial detection of DSA, whereas class II DSA are significantly higher in patients who develop AMR. This is the first report suggesting that transplant outcome, and particularly AMR, is associated with levels of sialylated IgG antibodies. Our data suggest that DSA are functionally heterogeneous and that further studies with an enlarged cohort may improve our understanding of their clinical impact.

De-Endothelialized Aortic Homografts: A Promising Scaffold Material for Tissue-Engineered Heart Valves

This study was designed to investigate the feasibility of de-endothelialized aortic homografts as a scaffold for tissue-engineered heart valves. Aortic homografts obtained from donor rabbits were treated either with collagenase to eliminate endotheliocytes or with the enzyme-detergent-nuclease method to remove all cell components. Then biomechanical properties of fresh, de-endothelialized and acellular homografts were investigated comparatively. The inflammation potential and immunogenicity were also assessed after allogenic transplantation. Expression of immune indices and inflammatory infiltration in de-endothelialized and acellular homografts were much weaker than in the controls, and no significant difference was observed between treated groups. However, heat shrinkage temperature, tensile strength and broken extension rate of acellular homografts decreased significantly compared to de-endothelialized ones. It is concluded that both de-endothelialization and thorough decellularization could reduce the immunogenicity and inflammation potential significantly, but the de-endothelialized scaffold retained better structural strength. The de-endothelialized aortic homograft might be a promising scaffold for tissue-engineered heart valves.

Anti-huCD20 antibody therapy for antibody-mediated rejection of renal allografts in a mouse model

We have reported that B6.CCR5(-/-) mice reject renal allografts with high serum donor-specific antibody (DSA) titers and marked C4d deposition in grafts, features consistent with antibody-mediated rejection (AMR). B6.huCD20/CCR5(-/-) mice, where human CD20 expression is restricted to B cells, rejected A/J renal allografts by day 26 posttransplant with DSA first detected in serum on day 5 posttransplant and increased thereafter. Recipient treatment with anti-huCD20 mAb prior to the transplant and weekly up to 7 weeks posttransplant promoted long-term allograft survival (>100 days) with low DSA titers. To investigate the effect of B cell depletion at the time serum DSA was first detected, recipients were treated with anti-huCD20 mAb on days 5, 8, and 12 posttransplant. This regimen significantly reduced DSA titers and graft inflammation on day 15 posttransplant and prolonged allograft survival >60 days. However, DSA returned to the titers observed in control treated recipients by day 30 posttransplant and histological analyses on day 60 posttransplant indicated severe interstitial fibrosis. These results indicate that anti-huCD20 mAb had the greatest effect as a prophylactic treatment and that the distinct kinetics of DSA responses accounts for acute renal allograft failure versus the development of fibrosis.

Vessel rejection secondary to human leucocyte antigen antibodies directed against the arterial conduit following pancreas transplantation from a separate donor

Whole-organ pancreas transplantation is typically carried out using a Y-graft derived from the donor iliac vessels. We describe a case in which a 31-year-old male underwent a simultaneous pancreas-kidney transplant, but in which vessels from a different donor were used for the arterial anastomosis of the pancreas graft. Although initially there was good function, 18 months post-transplant the patient was admitted with diabetic ketoacidosis secondary to pancreas graft failure. Radiological investigations revealed complete occlusion of the vascular Y-graft, and laboratory investigations demonstrated donor-specific human leucocyte antigen (HLA) antibodies directed against HLA mismatches of the vessel donor. This case highlights the risks of using allogeneic vascular material for surgical anastomoses.

Early systemic cellular immune response in children and young adults receiving decellularized fresh allografts for pulmonary valve replacement

OBJECTIVES

The longevity of homografts is determined by the activation of the recipients' immune system resulting from allogenic antigen exposition. Fresh decellularized pulmonary homografts (DPH) have shown promising early results in pulmonary valve replacement in children and young adults and could potentially avoid significant activation of the immune system, as more than 99% of the donor DNA is removed during the decellularization process. While the humoral immune response to decellularized allografts has been studied, detailed information on the more significant cellular immune response is currently lacking.

METHODS AND RESULTS

Peripheral blood samples were obtained from patients undergoing pulmonary valve replacement with DPH before, after, and for approximately 3 years after implantation. Absolute counts and percentages of mature T- (CD3(+)), B- (CD19(+)), and natural killer- (CD16(+)/CD56(+)) cells, as well as T helper- (CD4(+)) and cytotoxic T-cell- (CD8(+)) subsets, were determined by fluorescence-activated cell sorting (FACS). Between May 2009 and September 2013, 199 blood samples taken from 47 patients with a mean age at DPH implantation of 16.6±10.8 years were analyzed. The hemodynamic performance of DPH was excellent in all but one patient, and no valve-related deaths or conduit explantations were observed. The short-term follow up revealed a significant postoperative decrease in cell counts of most subtypes with reconstitution after 3 months. Continued assessment did not show any significant deviations in cell counts from their baseline values.

CONCLUSION

The absence of cellular immune response in patients receiving DPH supports the concept that decellularization can provide a basis for autologous regeneration.

Challenges with sensitized recipients in pediatric heart transplantation

The sensitization of patients to human leukocyte antigens prior to heart transplantation is increasingly being recognized as an important challenge both before and after the transplant, and the effects of sensitization on clinical outcomes are just beginning to be understood. Many patients are listed with the requirement of a negative prospective or virtual crossmatch prior to accepting a donor organ. This strategy has been associated with both longer waitlist times and higher waitlist mortality. An alternative approach is to transplant across a potentially positive crossmatch while utilizing strategies to decrease the significance of the human leukocyte antigen antibodies. This review will examine the challenges and the impact of sensitization on pediatric patients prior to and following heart transplantation.

Exploring the role of short-course cyclosporin a therapy in preventing homograft valve calcification after transplantation

This study was designed to explore the role of short-course cyclosporin A therapy in preventing calcification. Homograft valves heterotopically allografted onto abdominal aorta from SD to Wistar rats. The expression of CD25, CD40L, CD71, calcium content and morphological change were observed. In control group, expression of immune indices got maximal at early stage postoperatively, and then gradually declined, remained at low level 12 weeks afterwards. In test group with Cyclosporin A, the expression of immune indices were lower than that of control group at 2-4 weeks postoperatively, but no significant difference was found 8 weeks afterwards. The calcification began from 4 weeks postoperatively, increased gradually and reached highest level at 12 weeks. In test group calcium content was much lower from 4 to 16 weeks postoperatively. It is concluded that cyclosporine A treatment can prevent calcification of homograft valves because it inhibited immune response at early stage after transplantation.

Endothelial cell preservation at hypothermic to normothermic conditions using clinical and experimental organ preservation solutions

INTRODUCTION

Endothelial barrier function is pivotal for the outcome of organ transplantation. Since hypothermic preservation (gold standard) is associated with cold-induced endothelial damage, endothelial barrier function may benefit from organ preservation at warmer temperatures. We therefore assessed endothelial barrier integrity and viability as function of preservation temperature and perfusion solution, and hypothesized that endothelial cell preservation at subnormothermic conditions using metabolism-supporting solutions constitute optimal preservation conditions.

METHODS

Human umbilical vein endothelial cells (HUVEC) were preserved at 4-37°C for up to 20 h using Ringer's lactate, histidine-tryptophan-ketoglutarate solution, University of Wisconsin (UW) solution, Polysol, or endothelial cell growth medium (ECGM). Following preservation, the monolayer integrity, metabolic capacity, and ATP content were determined as positive parameters of endothelial cell viability. As negative parameters, apoptosis, necrosis, and cell activation were assayed. A viability index was devised on the basis of these parameters.

RESULTS

HUVEC viability and barrier integrity was compromised at 4°C regardless of the preservation solution. At temperatures above 20°C, the cells' metabolic demands outweighed the preservation solutions' supporting capacity. Only UW maintained HUVEC viability up to 20°C. Despite high intracellular ATP content, none of the solutions were capable of sufficiently preserving HUVEC above 20°C except for ECGM.

CONCLUSION

Optimal HUVEC preservation is achieved with UW up to 20°C. Only ECGM maintains HUVEC viability at temperatures above 20°C.

Adult and cord blood endothelial progenitor cells have different gene expression profiles and immunogenic potential

BACKGROUND

Endothelial colony-forming cells (ECFC) are endowed with vascular regenerative ability in vivo and in vitro. In this study we compared the genotypic profile and the immunogenic potential of adult and cord blood ECFC, in order to explore the feasibility of using them as a cell therapy product.

MATERIALS AND METHODS

ECFC were obtained from cord blood samples not suitable for haematopoietic stem cell transplantation and from adult healthy blood donors after informed consent. Genotypes were analysed by commercially available microarray assays and results were confirmed by real-time polymerase chain reaction analysis. HLA antigen expression was evaluated by flow-cytometry. Immunogenic capacity was investigated by evaluating the activation of allogeneic lymphocytes and monocytes in co-cultures with ECFC.

RESULTS

Microarray assays revealed that the genetic profile of cord blood and adult ECFC differed in about 20% of examined genes. We found that cord blood ECFC were characterised by lower pro-inflammatory and pro-thrombotic gene expression as compared to adult ECFC. Furthermore, whereas cord blood and adult ECFCs expressed similar amount of HLA molecules both at baseline and after incubation with γ-interferon, cord blood ECFC elicited a weaker expression of pro-inflammatory cytokine genes. Finally, we observed no differences in the amount of HLA antigens expressed among cord blood ECFC, adult ECFC and mesenchymal cells.

CONCLUSIONS

Our observations suggest that cord blood ECFC have a lower pro-inflammatory and pro-thrombotic profile than adult ECFC. These preliminary data offer level-headed evidence to use cord blood ECFC as a cell therapy product in vascular diseases.

Combined heart and liver transplant attenuates cardiac allograft vasculopathy compared with isolated heart transplantation

BACKGROUND

We evaluated whether combined heart and liver transplant (H+LTx) can protect the heart graft from the development of cardiac allograft vasculopathy using coronary three-dimensional (3D) volumetric intravascular ultrasound (IVUS).

METHODS

From 2004 to 2009, we identified 24 isolated heart transplant (HTx) and 10 H+LTx recipients in whom two coronary 3D IVUS studies were performed 1 year apart. Baseline 3D IVUS was performed at 0.22 (0.17-1.16) years after transplantation, with follow-up 3D IVUS exams performed after baseline exam (0.96 [0.83-1.08]).

RESULTS

Rate of plaque volume and plaque index (plaque volume/vessel volume) progression was attenuated in the H+LTx group (0.3±1.1 vs. 1.5±2.9 mm/mm; P=0.08 and 0.01±0.03 vs. 0.1±0.1; P=0.004, respectively). Rejection burden was much lower in the H+LTx patients. Outcome analysis in 66 consecutive patients (56 HTx and 10 H+LTx) was performed irrespective of performance of second coronary IVUS. H+LTx was associated with reduced rate of cardiac events (P=0.04), which remained significant when adjusted for the difference in the primary etiology for heart disease (P=0.05).

CONCLUSIONS

Our preliminary serial 3D coronary IVUS data show that H+LTx attenuates cardiac allograft vasculopathy by decreasing the rate of plaque volume and plaque index progression and improves coronary-related outcomes. Because of the small numbers and the differences in etiology of heart disease, our data should be interpreted cautiously, and larger clinical trials would be required to recommend H+LTx for improved coronary remodeling.

Donor-specific antibodies to class II antigens are associated with accelerated cardiac allograft vasculopathy: a three-dimensional volumetric intravascular ultrasound study

BACKGROUND

Although a link between donor-specific antibodies against human leukocyte antigens type II (DSA II+) and transplant glomerulopathy has been clearly established, its role in cardiac allograft vasculopathy (CAV) is unclear.

METHODS

Donor-specific antibodies were evaluated using solid-phase single-antigen bead assay before transplantation in 51 heart transplant recipients. Coronary angiography and three-dimensional intravascular ultrasound were performed at baseline and approximately 1 year after the baseline examination.

RESULTS

There were 4 (7.8 %), 11 (21.5%), and 2 (3.9%) patients who had DSA against donor class I (DSA I+), DSA II+, or both, respectively. All patients had negative complement-dependent cytotoxic crossmatch. There was accelerated progression of CAV in the DSA II+ group demonstrated by accelerated progression in plaque index (plaque volume/vessel volume) compared to patients with no DSA II+ antibodies (13.8% [12%] vs. -7.9% [37%], P=0.01). The development of any angiographic CAV was also more common in DSA II+ patients as compared to the DSA- patients at 4 years (100% [0%] vs. 64.2% [10%], P=0.05). All other traditional risk factors for CAV or immunosuppression were similar between the groups (P>0.2 for all).

CONCLUSIONS

This is the first preliminary study demonstrating that heart transplant recipients with preformed class II DSA may be at an increased risk for accelerated CAV as detected by consecutive volumetric three-dimensional intravascular ultrasound.

Concise review: immunologic lessons from solid organ transplantation for stem cell-based therapies

Clinical organ transplantation became possible only after powerful immunosuppressive drugs became available to suppress the alloimmune response. After decades of solid organ transplantation, organ rejection is still a major challenge. However, significant insight into allorecognition has emerged from this vast experience and should be used to inform future stem cell-based therapies. For this reason, we review the current understanding of selected topics in transplant immunology that have not been prominent in the stem cell literature, including immune responses to ischemia/reperfusion injuries, natural killer cells, the adaptive immune response, some unresolved issues in T-cell allorecognition, costimulatory molecules, and the anticipated role of regulatory T cells in graft tolerance.

Contrasting effects of IFNα on MHC class II expression in professional vs. nonprofessional APCs: Role of CIITA type IV promoter

We previously demonstrated that, in ex vivo cultures, IFNα downregulates the expression of MHC class II (MHCII) genes in human non-professional APCs associated with pancreatic islets. IFNα has an opposing effect on MHCII expression in professional APCs. In this study, we found that the mechanism responsible for the IFNα-mediated MHCII's downregulation in human MHCII-positive non-professional antigen presenting human non-hematopoietic cell lines is the result of the negative feedback system that regulates cytokine signal transduction, which eventually inhibits promoters III and IV of CIITA gene. Because the CIITA-PIV isoform is mostly responsible for the constitutive expression of MHCII genes in non-professional APCs, we pursued and achieved the specific knockdown of CIITA-PIV mRNA in our in vitro system, obtaining a partial silencing of MHCII molecules similar to that obtained by IFNα. We believe that our results offer a new understanding of the potential significance of CIITA-PIV as a therapeutic target for interventional strategies that can manage autoimmune disease and allograft rejection with little interference on the function of professional APCs of the immune system.

Antibody-mediated rejection of single class I MHC-disparate cardiac allografts

Murine CCR5(-/-) recipients produce high titers of antibody to complete MHC-mismatched heart and renal allografts. To study mechanisms of class I MHC antibody-mediated allograft injury, we tested the rejection of heart allografts transgenically expressing a single class I MHC disparity in wild-type C57BL/6 (H-2(b)) and B6.CCR5(-/-) recipients. Donor-specific antibody titers in CCR5(-/-) recipients were 30-fold higher than in wild-type recipients. B6.K(d) allografts survived longer than 60 days in wild-type recipients whereas CCR5(-/-) recipients rejected all allografts within 14 days. Rejection was accompanied by infiltration of CD8 T cells, neutrophils and macrophages, and C4d deposition in the graft capillaries. B6.K(d) allografts were rejected by CD8(-/-)/CCR5(-/-), but not μMT(-/-)/CCR5(-/-), recipients indicating the need for antibody but not CD8 T cells. Grafts recovered at day 10 from CCR5(-/-) and CD8(-/-)/CCR5(-/-) recipients and from RAG-1(-/-) allograft recipients injected with anti-K(d) antibodies expressed high levels of perforin, myeloperoxidase and CCL5 mRNA. These studies indicate that the continual production of antidonor class I MHC antibody can mediate allograft rejection, that donor-reactive CD8 T cells synergize with the antibody to contribute to rejection, and that expression of three biomarkers during rejection can occur in the absence of this CD8 T cell activity.

Intimal hyperplasia: slow but deadly

Intimal hyperplasia is the leading cause of long-term failure in coronary artery bypass vein grafting, coronary artery stenting, angioplasty, arteriovenous fistula for dialysis, and allograft transplantation. Intimal hyperplasia is a product of vascular smooth muscle cell proliferation, migration through the internal elastic lamina, and deposition of extracellular matrix proteins driven by growth factors in the vasculature. This vascular pathology results in a progressive diminution of the vessel lumen and serves as a site for thrombosis and atherosclerotic lesions. A key cell type in the initiation of intimal hyperplasia is the vascular endothelial cell, which appears to have down-stream effects on the vascular smooth muscle proliferation and migration. Currently, the only means available for prevention of intimal hyperplasia is through inhibition of mammalian target of rapamycin (mTOR) with the immunosuppressant rapamycin. mTOR integrates up-stream signals from growth factors such as IL-2 and senses the cellular nutrient and energy levels and redox status. This presentation will discuss the potential means of preserving the vascular endothelial cell and, thereby, reducing the development of intimal hyperplasia in our open-heart surgical patients.