Accommodation

Hormesis as an adaptive response to infection

Hormesis is a phenomenon whereby low-level stress can improve cellular, organ, or organismal fitness in response to a subsequent similar or other stress insult. Whereas hormesis is thought to contribute to the fitness benefits arising from symbiotic host-microbe interactions, the putative benefits of hormesis in host-pathogen interactions have yet to be explored. Hormetic responses have nonetheless been reported in experimental models of infection, a common feature of which is regulation of host mitochondrial function. We propose that these mitohormetic responses could be harnessed therapeutically to limit the severity of infectious diseases.

Vascular Signaling in Allogenic Solid Organ Transplantation - The Role of Endothelial Cells

Graft rejection remains the major obstacle after vascularized solid organ transplantation. Endothelial cells, which form the interface between the transplanted graft and the host’s immunity, are the first target for host immune cells. During acute cellular rejection endothelial cells are directly attacked by HLA I and II-recognizing NK cells, macrophages, and T cells, and activation of the complement system leads to endothelial cell lysis. The established forms of immunosuppressive therapy provide effective treatment options, but the treatment of chronic rejection of solid organs remains challenging. Chronic rejection is mainly based on production of donor-specific antibodies that induce endothelial cell activation—a condition which phenotypically resembles chronic inflammation. Activated endothelial cells produce chemokines, and expression of adhesion molecules increases. Due to this pro-inflammatory microenvironment, leukocytes are recruited and transmigrate from the bloodstream across the endothelial monolayer into the vessel wall. This mononuclear infiltrate is a hallmark of transplant vasculopathy. Furthermore, expression profiles of different cytokines serve as clinical markers for the patient’s outcome. Besides their effects on immune cells, activated endothelial cells support the migration and proliferation of vascular smooth muscle cells. In turn, muscle cell recruitment leads to neointima formation followed by reduction in organ perfusion and eventually results in tissue injury. Activation of endothelial cells involves antibody ligation to the surface of endothelial cells. Subsequently, intracellular signaling pathways are initiated. These signaling cascades may serve as targets to prevent or treat adverse effects in antibody-activated endothelial cells. Preventive or therapeutic strategies for chronic rejection can be investigated in sophisticated mouse models of transplant vasculopathy, mimicking interactions between immune cells and endothelium.

Molecular events contributing to successful pediatric cardiac transplantation in HLA sensitized recipients

Antibodies to HLA resulting in positive cytotoxicity crossmatch are generally considered a contraindication for cardiac transplantation. However, cardiac transplantations have been performed in children by reducing the Abs and modifying immunosuppression. To identify mechanisms leading to allograft acceptance in the presence of Abs to donor HLA, we analyzed priming events in endothelial cells (EC) by incubating with sera containing low levels of anti-HLA followed by saturating concentration of anti-HLA. Pre-transplant sera were obtained from children with low levels of Abs to HLA who underwent transplantation. EC were selected for donor HLA and exposed to sera for 72 h (priming), followed by saturating concentrations of anti-HLA (challenge). Priming of EC with sera induced the phosphatidylinositol 3-kinase/Akt mediated by the BMP4/WNT pathway and subsequent challenge with panel reactive antibody sera increased survival genes Bcl2 and Heme oxygenase-1, decreased adhesion molecules, induced complement inhibitory proteins and reduced pro-inflammatory cytokines. In contrast, EC which did not express donor HLA showed decreased anti-apoptotic genes. Primed EC, upon challenge with anti-HLA, results in increased survival genes, decreased adhesion molecules, induction of complement inhibitory proteins, and downregulation of pro-inflammatory cytokines which may result in accommodation of pediatric cardiac allografts despite HLA sensitization.

Disease Tolerance as an Inherent Component of Immunity

Pathogenic organisms exert a negative impact on host health, revealed by the clinical signs of infectious diseases. Immunity limits the severity of infectious diseases through resistance mechanisms that sense and target pathogens for containment, killing, or expulsion. These resistance mechanisms are viewed as the prevailing function of immunity. Under pathophysiologic conditions, however, immunity arises in response to infections that carry health and fitness costs to the host. Therefore, additional defense mechanisms are required to limit these costs, before immunity becomes operational as well as thereafter to avoid immunopathology. These are tissue damage control mechanisms that adjust the metabolic output of host tissues to different forms of stress and damage associated with infection. Disease tolerance is the term used to define this defense strategy, which does not exert a direct impact on pathogens but is essential to limit the health and fitness costs of infection. Under this argument, we propose that disease tolerance is an inherent component of immunity.

B cells with regulatory properties in transplantation tolerance

Induction of tolerance remains a major goal in transplantation. Indeed, despite potent immunosuppression, chronic rejection is still a real problem in transplantation. The humoral response is an important mediator of chronic rejection, and numerous strategies have been developed to target either B cells or plasma cells. However, the use of anti-CD20 therapy has highlighted the beneficial role of subpopulation of B cells, termed regulatory B cells. These cells have been characterized mainly in mice models of auto-immune diseases but emerging literature suggests their role in graft tolerance in transplantation. Regulatory B cells seem to be induced following inflammation to restrain excessive response. Different phenotypes of regulatory B cells have been described and are functional at various differentiation steps from immature to plasma cells. These cells act by multiple mechanisms such as secretion of immuno-suppressive cytokines interleukin-10 (IL-10) or IL-35, cytotoxicity, expression of inhibitory receptors or by secretion of non-inflammatory antibodies. Better characterization of the development, phenotype and mode of action of these cells seems urgent to develop novel approaches to manipulate the different B cell subsets and the response to the graft in a clinical setting.

Tissue damage control in disease tolerance

Immune-driven resistance mechanisms are the prevailing host defense strategy against infection. By contrast, disease tolerance mechanisms limit disease severity by preventing tissue damage or ameliorating tissue function without interfering with pathogen load. We propose here that tissue damage control underlies many of the protective effects of disease tolerance. We explore the mechanisms of cellular adaptation that underlie tissue damage control in response to infection as well as sterile inflammation, integrating both stress and damage responses. Finally, we discuss the potential impact of targeting these mechanisms in the treatment of disease.

Over-expression of heme oxygenase-1 does not protect porcine endothelial cells from human xenoantibodies and complement-mediated lysis

Accommodated organs can survive in the presence of anti-organ antibodies and complement. Heme oxygenase-1 (HO-1) is essential to ensure accommodation in concordant xenotransplant models. However, whether induction of HO-1 over-expression could protect porcine endothelial cells (PECs) against human xenoantibodies and complement-mediated lysis and induce an in vitro accommodation is still unknown. The SV40-immortalized porcine aorta-derived endothelial cell line (iPEC) was pre-incubated with 20, 50, or 80 μmol/L of cobalt-protoporphyrins IX (CoPPIX) for 24 h, and the HO-1 expression in iPECs was analyzed by using Western blotting. CoPPIX-treated or untreated iPECs were incubated with normal human AB sera, and complement-dependent cytotoxicity (CDC) was measured by both flow cytometry and lactate dehydrogenase (LDH) release assay. In vitro treatment with CoPPIX significantly increased the expression of HO-1 in iPECs in a dose-dependent manner. Over-expression of HO-1 was successfully achieved by incubation of iPECs with either 50 or 80 μmol/L of CoPPIX. However, HO-1 over-expression did not show any protective effects on iPECs against normal human sera-mediated cell lysis. In conclusion, induction of HO-1 over-expression alone is not enough to protect PECs from human xenoantibodies and complement-mediated humoral injury. Additionally, use of other protective strategies is needed to achieve accommodation in pig-to-primate xenotransplantation.

Blockage of heme oxygenase-1 abrogates the protective effect of regulatory T cells on murine pregnancy and promotes the maturation of dendritic cells

Regulatory T cells (Treg) play an important role in fetal protection. They expand during normal pregnancy and protect fetal antigens from maternal effector cells. Their effect is associated with the up-regulation of tolerance-associated molecules at the fetal-maternal interface. Among these, Heme Oxygenase-1 (HO-1, coded by Hmox1) is of special importance as its blockage correlates with increased abortion rates and its up-regulation positively affects pregnancy outcome. Here, we aimed to investigate whether the protective effect of Treg is mediated by HO-1 in a mouse model. HO-1 blockage by Zinc Protoporhyrin (ZnPPIX) abrogated the protective effect of Treg transfer. We found that HO-1 is important in maintaining maternal dendritic cells (DCs) in an immature state, which contributes to the expansion of the peripheral Treg population. This brings to light one essential pathway through which Treg mediates the semi-allogeneic fetus tolerance.

Intragraft gene expression in positive crossmatch kidney allografts: ongoing inflammation mediates chronic antibody-mediated injury

We studied intragraft gene expression profiles of positive crossmatch (+XM) kidney transplant recipients who develop transplant glomerulopathy (TG) and those who do not. Whole genome microarray analysis and quantitative rt-PCR were performed on RNA from protocol renal allograft biopsies in three groups: (1) +XM/TG+ biopsies before and after TG; (2) +XM/NoTG; and (3) negative crossmatch kidney transplants (control). Microarray comparisons showed few differentially expressed genes between paired biopsies from +XM/TG+ recipients before and after the diagnosis of TG. Comparing +XM/TG+ and control groups, significantly altered expression was seen for 2447 genes (18%) and 3200 genes (24%) at early and late time points, respectively. Canonical pathway analyses of differentially expressed genes showed inflammatory genes associated with innate and adaptive immune responses. Comparing +XM/TG+ and +XM/NoTG groups, 3718 probe sets were differentially expressed but these were over-represented in only four pathways. A classic accommodation phenotype was not identified. Using rt-PCR, the expression of inflammatory genes was significantly increased in +XM/TG+ recipients compared to the +XM/NoTG and control groups. In conclusion, pretransplant donor-specific anti-HLA antibodies results in a gene expression profile characterized by inflammation and cellular infiltration and the majority of +XM grafts are exposed to chronic injury.

Heme cytotoxicity and the pathogenesis of immune-mediated inflammatory diseases

Heme, iron (Fe) protoporphyrin IX, functions as a prosthetic group in a range of hemoproteins essential to support life under aerobic conditions. The Fe contained within the prosthetic heme groups of these hemoproteins can catalyze the production of reactive oxygen species. Presumably for this reason, heme must be sequestered within those hemoproteins, thereby shielding the reactivity of its Fe-heme. However, under pathologic conditions associated with oxidative stress, some hemoproteins can release their prosthetic heme groups. While this heme is not necessarily damaging per se, it becomes highly cytotoxic in the presence of a range of inflammatory mediators such as tumor necrosis factor. This can lead to tissue damage and, as such, exacerbate the pathologic outcome of several immune-mediated inflammatory conditions. Presumably, targeting “free heme” may be used as a therapeutic intervention against these diseases.

Mechanism of accommodation in a sensitized human leukocyte antigen transgenic murine cardiac transplant model

BACKGROUND

Presence of donor-specific antibodies (Abs) is detrimental to posttransplant allograft function. Some sensitized recipients have successfully undergone transplantation after pretransplant conditioning regimen using plasmapheresis and/or intravenous immunoglobulin therapy, but underlying mechanisms that confer such allograft protection are undefined.

METHODS

We developed a single human leukocyte antigen (HLA)-mismatched heterotopic murine heart transplant model (HLA-A2 into HLA-A2-sensitized-C57BL/6) to determine whether pretreatment of donors with low concentration of HLA class I (W6/32) or control Ab (C1.18.4) will confer protection. Expression levels of survival genes, Bcl-2 and heme oxygenase-1, were analyzed by gene array analysis and quantitative real-time polymerase chain reaction. Expression levels of cytokine panel were analyzed by Luminex. Role of Bcl-2 in the induction of allograft protection was analyzed by silencing the Bcl-2 expression in the donor hearts using a small hairpin (shRNA) specific for Bcl-2.

RESULTS

Control Ab-pretreated hearts were rejected in less than 5 days demonstrating hemorrhage, Ab, and C4 deposition. In contrast, W6/32-pretreated hearts were rejected at 15 days (P<0.05) that was prolonged to 25 days with antilymphocyte serum treatment. W6/32-pretreated hearts on day 5 exhibited increased expression of Bcl-2 (5.5-folds), Bcl-xl (5.5-folds), and heme oxygenase-1 (4.4-folds); decreased expression of ICAM-1, VCAM-1 (3.2-fold), along with reduced levels of cytokines interleukin (IL)-1β (4.4-folds), tumor necrosis factor α (3.7-folds), IL-6 (7.5-folds), IL-12 (2.3-folds) and chemokines monocyte chemotactic protein 1 (4.5-folds), MIG (4.4-folds), MIP-1α (3.4-folds), and IL-8 (3.1-folds). Silencing of Bcl-2 in accommodated hearts before transplant resulted in loss of protection with rejection (9±3 vs. 15±2days, P<0.05).

CONCLUSION

Pretreatment of hearts with low levels of anti-HLA Abs increases expression of antiapoptotic genes that inhibits caspases, leading to decreased inflammatory cytokines and chemokines, which promote allograft survival.

Complement inhibition enables renal allograft accommodation and long-term engraftment in presensitized nonhuman primates

Protection against humoral injury mediated by donor-specific antibodies (DSA), also known as accommodation, may allow for long-term allograft survival in presensitized recipients. In the present study, we determined the role of complement in renal allograft accommodation in donor skin-presensitized nonhuman primates under conventional immunosuppression. Donor skin allografts were transplanted to presensitized recipients 14 days prior to renal transplantation. Renal allografts not receiving any immunosuppressive treatment developed accelerated rejection with predominantly humoral injury, which was not prevented using conventional cyclosporine (CsA) triple therapy. Inhibition of complement activation with the Yunnan-cobra venom factor (Y-CVF) successfully prevented accelerated antibody-mediated rejection and resulted in successful accommodation and long-term renal allograft survival in most presensitized recipients. Accommodation in this model was associated with the prevention of the early antibody responses induced against donor antigens by complement inhibition. Some antiapoptotic proteins and complement regulatory proteins, including Bcl-2, CD59, CD46 and clusterin, were upregulated in the surviving renal allografts. These results suggest that the complement inhibition-based strategy may be valuable alternative in future clinical cross-match positive or ABO-incompatible transplantation.

Protective role of heme oxygenase-1 in Listeria monocytogenes-induced abortion

It is well-known fact that various pathogens, including bacteria, virus, and protozoa, induce abortion in humans and animals. However the mechanisms of infectious abortion are little known. In this study, we demonstrated that Listeria monocytogenes infection in trophoblast giant cells decreased heme oxygenase (HO)-1 and B-cell lymphoma-extra large (Bcl-XL) expression, and that their overexpression inhibited cell death induced by the infection. Furthermore, HO-1 and Bcl-XL expression levels were also decreased by L. monocytogenes in pregnant mice. Treatment with cobalt protoporphyrin, which is known to induce HO-1, inhibited infectious abortion. Taken together, our study indicates that L. monocytogenes infection decreases HO-1 and Bcl-XL expression and induces cell death in placenta, leading to infectious abortion.

The adaptor Lnk (SH2B3): an emerging regulator in vascular cells and a link between immune and inflammatory signaling

A better knowledge of the process by which inflammatory extracellular signals are relayed from the plasma membrane to specific intracellular sites is a key step to understand how inflammation develops and how it is regulated. This review focuses on Lnk (SH2B3) a member, with SH2B1 and SH2B2, of the SH2B family of adaptor proteins that influences a variety of signaling pathways mediated by Janus kinase and receptor tyrosine kinases. SH2B adaptor proteins contain conserved dimerization, pleckstrin homology, and SH2 domains. Initially described as a regulator of hematopoiesis and lymphocyte differentiation, Lnk now emerges as a key regulator in hematopoeitic and non hematopoeitic cells such as endothelial cells (EC) moderating growth factor and cytokine receptor-mediated signaling. In EC, Lnk is a negative regulator of TNF signaling that reduce proinflammatory phenotype and prevent EC from apoptosis. Lnk is a modulator in integrin signaling and actin cytoskeleton organization in both platelets and EC with an impact on cell adhesion, migration and thrombosis. In this review, we discuss some recent insights proposing Lnk as a key regulator of bone marrow-endothelial progenitor cell kinetics, including the ability to cell growth, endothelial commitment, mobilization, and recruitment for vascular regeneration. Finally, novel findings also provided evidences that mutations in Lnk gene are strongly linked to myeloproliferative disorders but also autoimmune and inflammatory syndromes where both immune and vascular cells display a role. Overall, these studies emphasize the importance of the Lnk adaptor molecule not only as prognostic marker but also as potential therapeutic target.

Regulation of vulnerable plaque development by the heme oxygenase/carbon monoxide system

Plaque rupture and luminal thrombosis is the most common cause of coronary occlusion that leads to acute coronary syndromes. High-risk plaques, or vulnerable plaques, are defined as lesions that are prone to rupture, also known as thin cap fibroatheroma (TCFA), or lesions prone to erosion or with calcified cores. This review will focus mainly on the vulnerable plaque, which is thought to be the precursor of the thrombogenic or ruptured plaque. Heme oxygenase 1 (HO-1) protein expression is specifically increased in lesions with a vulnerable plaque phenotype resembling TCFAs and correlates with a rise in expression levels of intimal proinflammatory markers. Data from several human and animal studies imply an important function for HO-1 in the genetic regulation of early, as well as late atherogenesis, and plaque destabilization toward a vulnerable phenotype. Although a direct association between HO-1, vulnerable plaque development, and clinical outcome is for now missing, the correlations that have been reported for HO-1 and coronary artery disease point to a possible link.

Accommodation in renal transplantation: unanswered questions

PURPOSE OF REVIEW

Accommodation, an acquired resistance of an organ to immune-mediated damage, has been recognized as an outcome of renal transplantation for more than 20 years. Accommodation was originally identified in blood group-incompatible kidney transplants that survived and functioned normally in recipients with high titers of antiblood group antibodies directed against antigens in the grafts. The most compelling questions today include how often and by which mechanisms accommodation occurs, and what might be the biological implications of accommodation. This communication summarizes recent advances in addressing these questions.

RECENT FINDINGS

Because its diagnosis has depended on identification of antidonor antibodies in serum, the prevalence of accommodation has been considered low. Recent research in animal models and clinical subjects may challenge that view. This research also suggests that sublethal graft injury of various types induces accommodation and that accommodation may be a dynamic condition, eventuating into tolerance on the one hand and chronic graft injury on the other.

SUMMARY

Burgeoning lines of investigation into accommodation now portray a condition of greater prevalence than once thought, exposing pathways that may contribute to the understanding of a range of responses to transplantation.

Intrasplenic preconditioning: a model for the study of xenostimuli accommodation

BACKGROUND

Discordant xenotransplantation, the grafting of organs from one phylogenic species to another, results in hyper-acute rejection (HAR). HAR is associated with the deposition of recipient preformed xenoreactive natural antibodies and complement on the endothelium of the donor organ, leading to activation and apoptosis of the endothelium, an event associated with xenograft rejection. Endothelial resistance to HAR, termed "accommodation," an active protection of graft endothelium, may be achieved by previous stimulation of endothelial cells by discordant xenoantibodies.

MATERIALS AND METHODS

Forty-eight male Wistar rats were used to evaluate HAR induction in an isolated, dually perfused in-situ rat liver transfused with human blood. This ex-vivo model served to mimic rat-to-human liver xenotransplantation. Preconditioning of the liver endothelium was induced by rat intrasplenic injection of human blood (n=8) or effluent of previously xenotransfused rat liver (n=8), i.e., high versus low xenoantibody solution, each undertaken 1d before liver xenotransfusion. Two other groups were not preconditioned. Preconditioned and non-preconditioned rats were perfused directly with human blood, and eight rats were used as controls (non-preconditioned Krebs-perfused). Eight rats were perfused directly with human blood, and eight rats were used as controls. The effluent that exited these first-line livers was used to perfuse the second-line livers.

RESULTS

Portal and hepatic artery perfusion pressures, resistances, rates of oxygen extraction, lactic acid and pH, and wet-to-dry weight ratio values were significantly increased in livers xenotransfused with blood indicating HAR, compared with unchanged values in livers perfused with Krebs solution. Portal pressure and resistance were best protected from HAR by the blood preconditioning in the blood perfused group, while the hepatic artery perfusion system was better protected by the perfusate precondition-blood perfused group. The physiologic effects of HAR were attenuated in most second-line livers.

CONCLUSIONS

Attenuation of HAR in rats' livers is achieved by preconditioning with xenoantibodies and/or by "filtering out" xenoantibodies present in the circulation, and is suggestive of accommodation. This novel method may be useful in future studies aimed at refining methods for accommodating xenotransplantation.

Endothelial cells in allograft rejection

In organ transplantation, blood borne cells and macromolecules (e.g., antibodies) of the host immune system are brought into direct contact with the endothelial cell lining of graft vessels. In this location, graft endothelial cells play several roles in allograft rejection, including the initiation of rejection responses by presentation of alloantigen to circulating T cells; the development of inflammation and thrombosis; and as targets of injury and agents of repair.

Endothelial cells in allograft rejection

In organ transplantation, blood borne cells and macromolecules (e.g., antibodies) of the host immune system are brought into direct contact with the endothelial cell lining of graft vessels. In this location, graft endothelial cells play several roles in allograft rejection, including the initiation of rejection responses by presentation of alloantigen to circulating T cells; the development of inflammation and thrombosis; and as targets of injury and agents of repair.

Accommodation and antibodies

Accommodation refers to the condition in which an organ transplant functions normally by acquiring resistance to immune-mediated injury (especially), despite the presence of anti-transplant antibodies in the recipient. This status is associated with several modifications in the recipient as well as in the graft, such as previous depletion of anti-graft antibodies and their slow return once the graft is placed; expression of several protective genes in the graft; a Th2 immune response in the recipient; and inhibition of the membrane attack complex of complement.

Vascular endothelium and graft-versus-host disease

Vascular endothelial cells are an exposed target tissue for immune-mediated injury during graft-versus-host disease (GVHD). However, widespread endothelial death resulting in multi-organ failure similar to that in hyperacute solid-organ transplant rejection is not observed during GVHD. The rather mild endothelial injury seen in histological samples from affected skin biopsies contrasts with severe epithelial injury observed sometimes simultaneously. The elucidation of the mechanisms that influence endothelial susceptibility to immune-mediated injury would explain this paradox and may help to separate GVHD from the beneficial graft-versus-leukaemia effect. Transplant-associated microangiopathy, veno-occlusive disease and accelerated arteriosclerosis are vascular injury syndromes that occur after allogeneic stem-cell transplantation. Biomarkers are needed to identify individuals at risk of developing these complications. Treatments that have been found to be particularly effective for these specific endothelial injury syndromes need to be tested in larger clinical trials.

Four stages and lack of stable accommodation in chronic alloantibody-mediated renal allograft rejection in Cynomolgus monkeys

The etiology of immunologically mediated chronic renal allograft failure is unclear. One cause is thought to be alloantibodies. Previously in Cynomolgus monkeys, we observed a relationship among donor-specific alloantibodies (DSA), C4d staining, allograft glomerulopathy, allograft arteriopathy and progressive renal failure. To define the natural history of chronic antibody-mediated rejection and its effect on renal allograft survival, we now extend this report to include 417 specimens from 143 Cynomolgus monkeys with renal allografts. A subset of animals with long-term renal allografts made DSA (48%), were C4d positive (29%), developed transplant glomerulopathy (TG) (22%) and chronic allograft arteriopathy (CAA) (19%). These four features were highly correlated and associated with statistically significant shortened allograft survival. Acute cellular rejection, either Banff type 1 or 2, did not correlate with alloantibodies, C4d deposition or TG. However, endarteritis (Banff type 2) correlated with later CAA. Sequential analysis identified four progressive stages of chronic antibody-mediated rejection: (1) DSA, (2) deposition of C4d, (3) TG and (4) rising creatinine/renal failure. These new findings provide strong evidence that chronic antibody-mediated rejection develops without enduring stable accommodation, progresses through four defined clinical pathological stages and shortens renal allograft survival.

Expression of heme oxygenase-1 is associated with abortion caused by Brucella abortus infection in pregnant mice

Brucella abortus is a facultative intracellular pathogen that can survive inside macrophages and trophoblast giant (TG) cells, and the causative agent of brucellosis. In the present study, we found that expression of heme oxygenase-1 (HO-1) in TG cells is correlated with abortion induced by B. abortus infection in pregnant mice. Expression of HO-1 in the placenta was decreased by B. abortus infection and treatment with cobalt-protoporphyrin (Co-PP), which is known to up-regulate HO-1 expression, inhibited abortion due to the bacterial infection. In TG cells, treatment with Co-PP was shown to up-regulate HO-1, whereas its expression was decreased by B. abortus infection. Such down-regulation of HO-1 in the TG cells was enhanced by IFN-gamma treatment. HO-1 down-regulation in TG cells due to knockdown or IFN-gamma treatment served to induce cell death caused by B. abortus infection. These results suggest that down-regulation of HO-1 in TG cells due to B. abortus infection is an important event in infectious abortion.

CCR5 Blockade Modulates Inflammation and Alloimmunity in Primates

Pharmacologic antagonism of CCR5, a chemokine receptor expressed on macrophages and activated T cells, is an effective antiviral therapy in patients with macrophage-tropic HIV infection, but its efficacy in modulating inflammation and immunity is only just beginning to be investigated. In this regard, the recruitment of CCR5-bearing cells into clinical allografts is a hallmark of acute rejection and may anticipate chronic rejection, whereas conventionally immunosuppressed renal transplant patients homozygous for a nonfunctional Delta32 CCR5 receptor rarely exhibit late graft loss. Therefore, we explored the effects of a potent, highly selective CCR5 antagonist, Merck's compound 167 (CMPD 167), in an established cynomolgus monkey cardiac allograft model. Although perioperative stress responses (fever, diminished activity) and the recruitment of CCR5-bearing leukocytes into the graft were markedly attenuated, anti-CCR5 monotherapy only marginally prolonged allograft survival. In contrast, relative to cyclosporine A monotherapy, CMPD 167 with cyclosporine A delayed alloantibody production, suppressed cardiac allograft vasculopathy, and tended to further prolong graft survival. CCR5 therefore represents an attractive therapeutic target for attenuating postsurgical stress responses and favorably modulating pathogenic alloimmunity in primates, including man.

ABO blood group and related antigens, natural antibodies and transplantation

The current success rate of transplant surgery and immunosuppression has led to a demand for organs that has outstripped the supply. This has required investigation of alternate strategies. Therefore, allotransplantation across the ABO blood group barrier has commenced, and pig-to-human xenotransplantation is under consideration. The first immunological barrier to both these types of transplantation is the prevention of the antibody-mediated rejection. This rejection is a result of natural preformed antibodies circulating in the serum of the recipient binding to either ABO (for allo) or alpha-galactose (alpha-Gal) (for xeno) antigens expressed on the donor tissue. These antibodies recognise antigens that are, in both cases, carbohydrate molecules with the characteristic feature that the nonreducing terminal carbohydrate is either a Gal or N-acetlygalactosamine residue in an alpha1,3 linkage. These epitopes are synthesised by closely related members of a single family of glycosyltransferases. This review discusses the carbohydrate antigens, the enzymes involved in their synthesis and the consequences of natural antibodies binding these antigens.

Inhaled Carbon Monoxide Prevents Graft-Induced Intimal Hyperplasia in Swine

BACKGROUND

Arteriovenous grafts often fail due to stenosis caused by venous anastomotic intimal hyperplasia (IH) and vascular smooth muscle cell (VSMC) proliferation. We examined the effects of inhaled carbon monoxide (CO), a product of heme-oxygenase-1 degradation of heme, on IH in a porcine arteriovenous graft model.

MATERIALS AND METHODS

Eighteen Yorkshire pigs were divided into three groups (N = 6/group): (1) CO 100 ppm preoperatively for 1 h; (2) CO 250 ppm preoperatively for 1 h and intraoperatively; and (3) air-treated controls. Animals underwent end-to-side placement of polytetrafluoroethylene grafts connecting the common femoral artery and vein in both groins. Intimal thickness of the venous anastomosis at 30 days was measured blinded. The effect of CO on pig VSMC proliferation was studied in cell culture using [(3)H]thymidine incorporation.

RESULTS

Pigs in the group receiving CO 250 ppm showed significantly less IH compared to animals in the group receiving 100 ppm and the air-treated group (267.5 +/- 21.4, 824 +/- 145.8, and 914.8 +/- 133.7 pixels, respectively, P < 0.0001). This effect was not observed when comparing the 100 ppm group to the air-treated group. COHb levels were significantly elevated in the 100 ppm and 250 ppm compared to air-treated pigs (5.8 +/- 0.47, 13.2 +/- 1.0 versus 2.3 +/- 0.11%, respectively, P < 0.001). Oxygen saturation, respiratory rate, and hemodynamics were not significantly different between the groups. CO induced VSMC growth arrest compared to air in vitro (11.9 +/- 4 versus 20.3 +/- 5 10(3) counts/min/well, P < 0.01).

CONCLUSION

A single exposure to a low concentration of inhaled CO (250 ppm) confers protection against intimal proliferation of VSMCs when given perioperatively in a clinically relevant model of arteriovenous grafts. These data are the first to suggest, in a clinically relevant model, the potential role for CO in clinical applications.

Induction of Accommodation Model by Combined RNA Interference Targeting 1,3-Galactosyltransferase Gene and Low-Dose GS-IB4 Lectin In Vitro

OBJECTIVE

This study sought to mimic the interaction of xenograft endothelial cells and human serum in vitro after successfully silencing the expression of porcine alpha1,3-galactosyltransferase (alpha1,3GT) gene by RNA interference (RNAi), and to investigate the possibility of inducing accommodation in vitro by stimulation of alpha-Gal-specific binding lectin, Griffonia simplicifolia isolectin B4 (GS-IB4) and RNAi.

MATERIALS AND METHODS

Various alpha-Gal expression patterns on a pig endothelial cell immortalized line (PED) was achieved by serial doses of small interfering RNA (siRNA) targeting porcinc alpha1,3GT gene. alpha1,3GT-siRNA transfected PEDs were exposed to increasing doses of GS-IB4 lectin (0.5, 2, and 8 microg/mL) for 4 hours before incubation with normal human serum (NHS). Accommodation phenomenon of PEDs in NHS was observed by 51Cr release and antibody/complement binding assays.

RESULTS

With combined RNAi and low-dose GS-IB4 stimulation, PEDs remarkably inhibited complement-mediated cytotoxicity, which showed a better protective effect than using RNAi alone. At a concentration of 2 mug/mL, GS-IB4 exhibited the maximum protective effect. The expression of E-selectin on alpha1,3GT-siRNA transfected PEDs did not differ from that on parental PEDs with heat-inactivated NHS (HINHS) stimulation. Combined with GS-IB4 stimulation, however, it inhibited expression of E-selectin, which was GS-IB4 dose dependent, resulting in mean fluorescence intensity values of 98.5, 42.0, and 36.3 at 0.5, 2, and 8 microg/mL. The mRNA expression of the protective gene HO-1 was significantly up-regulated after treatment with RNAi and low-dose of GS-IB4.

CONCLUSIONS

Combined RNAi and low-dose GS-IB4 induced pig endothelial cell accommodation in vitro. The level of alpha-Gal expression played an important role in the induction of accommodation.

ABO-histo blood group incompatibility in hematopoietic stem cell and solid organ transplantation

In contrast to solid organ transplantation (SOT), ABO-histo blood group incompatibility is of minor importance for hematopoietic stem cell transplantation (HSCT). Patients receiving ABO-incompatible HSCT are at an increased risk for immune-mediated hematological complications including immediate and delayed hemolysis, late red blood cell engraftment and pure red cell aplasia, but seem not to have a worse overall survival or increased transplant-related mortality. This review gives an overview of the immunological mechanisms leading to complications associated with ABO-incompatible HSCT and describes approaches to prevent them. The current organ shortage in SOT stimulates the exploration of new strategies to expand the donor pool including ABO-incompatible SOT and xenotransplantation. Here, we discuss the hypothesis that ABO-incompatible transplantation may be viewed as a human in vivo model for the humoral immune mechanisms of antigen-mismatched transplantation. ABO-incompatible HSCT and SOT provide excellent possibilities to analyze graft accommodation and transplantation tolerance. Understanding the underlying mechanisms of graft survival in ABO-incompatible transplantation may facilitate new strategies to overcome the immunological barriers in SOT and xenotransplantation.

Xenotransplantation and ABO incompatible transplantation: The similarities they share

Transplantation of kidney allografts across the ABO barrier has been feasible with the development of technologies for removal of anti-blood group antibodies from the circulation of the recipent. The recipients of ABO incompatible grafts display tolerance, accommodation or rejection of the graft. Understanding the factors that determine the outcome of the immune response against incompatible blood group antigens has required the study of an appropriate experimental animal model. The model used is that of knockout (KO) mice for the alpha1,3galactosyltransferase gene, lacking the alpha-gal epitopes and transplanted with wild type mouse heart expressing the alpha-gal epitope. The alpha-gal epitope (Galalpha1-3Galbeta1-(3)4GlcNAc-R) is one of the most abundant carbohydrate epitopes on cells of non-primate mammals and New World monkeys, where it is synthesized by the glycosylation enzyme alpha1,3galactosyltransferase. In humans, apes and Old World monkeys, this epitope is absent due to an evolutionary event that led to the inactivation of the alpha1,3galactosyltransferase gene in ancestral Old World primates. Instead, humans, apes and Old World monkeys produce a natural antibody, the anti-Gal antibody, that is the most abundant natural antibody in humans (approximately 1% of circulating immunoglobulins) and which specifically interacts with alpha-gal epitopes. The interaction between anti-Gal and alpha-gal epitopes is a major immunologic barrier in xenotransplantation, preventing transplantation of pig organs or tissues (i.e. xenografts) into humans. Anti-Gal antibodies also comprise a large proportion of anti-blood group B activity in A and O individuals. Moreover, in recipients of ABO incompatible grafts, much of the elicited anti-A and anti-B antibodies are in fact anti-Gal antibodies capable of binding also to the incompatible blood group antigens. Since the alpha-gal epitope is very similar in its structure to blood groups A and B, understanding anti-Gal response to alpha-gal epitopes is likely to provide information on the immune response to ABO incompatible antigens. Studies on the immune response to alpha-gal epitopes in KO mice have indicated that this epitope can not activate T cells. Anti-Gal B cells engaging alpha-gal epitopes on transplated wild type mouse heart can be activated to produce their antibodies only if they receive help from T cells that are activated by allogeneic or xenogeneic peptides. If T cell help is not available for several days the B cells are induced to differentiate into cells capable of producing accommodating antibodies. Accommodating anti-Gal antibodies bind to the incompatible carbohydrate antigen but do not induce rejection. Prolonged exposure of anti-Gal B cells to the incompatible alpha-gal epitope on the wild type mouse heart graft induces tolerance due to the deletion of these B cells. These studies imply that similar variation in the availability of T cell help in recipients of ABO incompatible grafts result in rejection, accommodation or tolerance, to the blood group antigen. The studies on immune response to incompatible alpha-gal epitopes have further indicated that tolerance to incompatible blood group antigens can be achieved by gene therapy with autologous bone marrow cells or autologous lymphocytes engineered to express the incompatible blood group antigen. Studies in the mouse model suggest that administration into the patient such autologous cells engineered to express the incompatible transplantation carbohydrate antigen induces deletion of anti-blood group B cells and induction of tolerance, provided that the anti-blood group antibodies are removed. Such tolerance is perpetuated indefinitely by the subsequent transplantation of the organ expressing the incompatible blood group antigen.

Role of Flow Cytometry to Define Unacceptable HLA Antigens in Lung Transplant Recipients with HLA-Specific Antibodies

BACKGROUND

Antidonor HLA-specific antibodies have been associated with hyperacute rejection and primary graft failure in lung transplant recipients. Thus, transplant candidates with HLA-specific antibodies generally undergo prospective crossmatching to exclude donors with unacceptable HLA antigens. However, the need to perform a prospective crossmatch limits the donor pool and is associated with increased waiting list times and mortality. A virtual crossmatch strategy using flow cytometry, which enables precise determination of HLA-specific antibody specificity, was compared to prospective crossmatching in sensitized lung transplant candidates.

METHODS

In all, 341 lung transplant recipients were analyzed retrospectively (April 1992 to July 2003). Sixteen patients with HLA-specific antibodies underwent transplantation based on flow cytometric determination of antibody specificity and 10 underwent prospective crossmatching.

RESULTS

Freedom from bronchiolitis obliterans syndrome (BOS) at three years was similar in those undergoing a virtual crossmatch, those undergoing prospective crossmatching, and those without HLA-specific antibodies (80.4% +/- 13.4, 85.7% +/- 13.2, and 73.8% +/- 2.8, respectively, P = 0.88). Three-year survival was also comparable (87.5% +/- 8.3, 70.0% +/- 14.5, and 78.5% +/- 2.4, respectively, P = 0.31). Elimination of prospective crossmatching for sensitized patients was associated with a significant decrease in time on the waiting list (P < 0.01) and in waiting list mortality (P < 0.05). All 16 patients undergoing a virtual crossmatch had negative retrospective crossmatches.

CONCLUSIONS

By carefully determining the specificity of HLA-specific antibodies, flow cytometry methodologies enable the prediction of negative crossmatch results with up to 100% accuracy, enabling the determination of appropriateness of donors. Using this virtual crossmatch strategy, crossmatching can be safely omitted prior to lung transplantation, thereby decreasing waiting list time and mortality rates for candidates with HLA-specific antibodies.

Heme oxygenase-1 is essential for and promotes tolerance to transplanted organs

This investigation focused on obtaining a further understanding of the role of heme oxygenase-1 (HO-1) in tolerance induction. Hearts from C57BL/6 (H-2b) mice survived long-term when transplanted into BALB/c (H-2d) recipients treated with the tolerance-inducing regimen of anti-CD40L antibody (MR-1) plus donor-specific transfusion (DST). Grafts did not, however, survive long-term in (HO-1-/-) recipients given the same treatment. Similarly, long-term survival induced by DST was ablated when HO-1 activity was blocked by zinc protoporphyrin IX (ZnPPIX). We further asked whether modulation of HO-1 expression/activity could be used to promote the induction of graft tolerance. DST alone (day 0) failed to promote any prolongation of survival of DBA/2 (H-2d) hearts transplanted into B6AF1 (H-2(b,k/d)) recipients. However, long-term survival and (dominant peripheral) tolerance were readily induced when DST was combined with induction of HO-1 expression by cobalt protoporphyrin IX (CoPPIX). HO-1 induction plus DST led to a significant up-regulation of Foxp3, TGF-beta, IL-10, and CTLA4, which suggests a prominent role for CD4+CD25+ regulatory T cells (Tregs). In fact, the tolerogenic effect of HO-1 plus DST was dependent on CD4+CD25+ Tregs as suggested by adoptively transferring these cells into irradiated recipients under various regimens. Taken together, these findings show that expression of HO-1 in a graft recipient can be essential for long-term graft survival and for induction of tolerance and that modulation of HO-1 expression/activity can be used therapeutically to synergize in the generation of graft tolerance.

Over-expression of heme oxygenase-1 by adenoviral gene transfer improves pregnancy outcome in a murine model of abortion

Mammalian pregnancy is a complex phenomenon allowing the maternal immune system to support its allogeneic fetus. Physiological pathways protecting the fetus from rejection are thought to be comparable with those leading to allograft acceptance. Heme oxygenase (HO)-1 is known to protect locally against rejection in transplantation models due to its anti-oxidant, anti-inflammatory and cytoprotective functions. Based on previous data on low HO-1 levels in placenta from mice undergoing abortion, we hypothesized that an up-regulation of HO-1 during pregnancy would avoid fetal rejection in the murine abortion combination CBA/J x DBA/2J, using BALB/c-mated CBA/J as normal controls. We injected pregnant mice undergoing abortion with 1 x 10(5) PFU of an adenoviral vector containing HO-1 and GFP (AdHO-1/GFP), and compared the pregnancy outcome with PBS- or 1 x 10(5) AdEGFP-treated abortion-prone mice and with PBS-treated normal pregnant mice. The abortion rate diminished significantly after adenoviral gene transfer of AdHO-1/GFP. The systemic and local IL-4/IFN-gamma ratio was augmented in AdHO-1-treated mice compared to abortion-prone mice. Interestingly, the HO-1 treatment up-regulated the ratio IL-10/TNF-alpha in spleen but not in decidual lymphocytes. HO-1-treated mice further showed diminished apoptosis rate and increased Bag-1 mRNA levels at the materno-fetal interface. Thus, we propose HO-1 as a key regulator of pregnancy success. HO-1 would exert its action by locally up-regulating the Th2/Th1 cytokine ratio and by further protecting tissues from apoptosis.

Protection from abortion by heme oxygenase-1 up-regulation is associated with increased levels of Bag-1 and neuropilin-1 at the fetal-maternal interface

Tolerance mechanisms allowing pregnancy success resemble those involved in allograft acceptance. Heme oxygenase (HO) is a tissue-protective molecule, which allows graft acceptance and is known to have antiapoptotic effects on several cell types. We previously reported down-regulated levels of HO-1 and HO-2 in placenta from allopregnant mice undergoing abortion. In this study, we analyzed whether the up-regulation of HO-1 by cobalt-protoporphyrin (Co-PP) during implantation window can rescue mice from abortion. Induction of HO-1 by Co-PP treatment prevented fetal rejection, whereas the down-regulation of HOs by zinc-protoporphyrin application boosted abortion. The beneficial effect of HO-1 induction was not related to a local shift to Th2-profile or to a change in the NO system. Interestingly, the expression of the antiapoptotic/cytoprotective molecule Bag-1 as well as the levels of neuropilin-1, a novel marker for T regulatory cells, were up-regulated after Co-PP treatment. Our data strongly support a very important role for HO-1 in fetal allotolerance and suggest that HO-1 might be protective by up-regulating tissue protective molecules, i.e., Bag-1, and by activating T regulatory cells rather than by changing the local cytokine profile.

HLA class I antibody mediated accommodation of endothelial cells via the activation of PI3K/cAMP dependent PKA pathway

Allografts transplanted across ABO incompatibility or human leucocyte antigen (HLA)-sensitization undergoes antibody (Ab) mediated hyperacute rejection. Depleting anti-graft Ab from the recipient by plasmapheresis prior to transplantation can prevent this Ab-mediated rejection. Under these conditions, allografts have been shown to function even when the Ab rebound in the recipients. We have developed an in vitro model using human aortic endothelial cells (EC) and elucidated the ability of W6/32 HLA class I monoclonal Ab to provide signals following binding to MHC class I molecules. Using this model, we show that ECs undergo caspase 3-dependent cell death by apoptosis upon exposure to saturating concentrations of W6/32 and complement. In contrast, exposure of ECs to sub-saturating concentrations of W6/32 conferred resistance towards Ab/complement-mediated lysis that has been termed accommodation. Accommodated ECs exhibited a significant increase in the expression of anti-apoptotic genes Bcl-xL, Bcl-2 and Heme Oxygenase-1 and the induction of Phosphatidylinositol 3 kinase (PI3K) and cyclic adenosine monophosphate (cAMP) dependent protein kinase A activities that facilitate the phosphorylation of Bad at positions Ser(136) and Ser(112). In conclusion, exposure of sub-saturating concentrations of HLA class I Ab results in the induction of signals downstream that confers resistance to endothelial cells against Ab-complement mediated cell death. Together, the observations made in this study will provide the basis for delineating the molecular mechanisms involved in mediating accommodation and developing strategies to induce accommodation in grafts prior to transplantation in highly sensitized patients.

Heme oxygenase as a therapeutic target in immunological pregnancy complications

The allogeneic fetus has been considered to be an allograft and the tolerance mechanisms involved in pregnancy maintenance resemble those leading to graft acceptance. Up-regulation of Heme Oxygenase-1 (HO-1) promotes graft acceptance. Additionally, HO-1 has been proposed to have tissue-protective properties. Previous studies reported the presence of HO-1 and HO-2 in mammalian placenta and postulated a protective role for HO during pregnancy. Here, we analyze HO-1 and HO-2 expression at the feto-maternal interface from normal pregnant and abortion mice and correlate these findings with inducible nitric oxide synthase (iNOS) and endothelial nitric oxide synthase (eNOS) expression as well as with Th1/Th2 cytokine production by immune cells. DBA/2-mated CBA/J females undergoing abortion and BALB/c-mated CBA/J females having normal pregnancies were included in our study. The mice received no treatment. On day 14 of pregnancy, the mice were sacrificed, the abortion rate was calculated and the ex vivo Th1/Th2 production by decidual immune cells was analyzed by flow cytometry. The expression of HO-1 and HO-2, iNOS and eNOS was analyzed by immunohistochemistry (IHC) and Western blot in placenta samples. The Th1/Th2 cytokines ratio was augmented in decidua from abortion mice. We further observed a significant down-regulation of HO-1, HO-2, iNOS and eNOS molecules in placental tissue from mice undergoing abortion when compared to normal pregnant mice. Since we found diminished HOs and nitric oxide synthase (NOS) levels at the feto-maternal interface from abortion mice when compared to normal pregnant mice, which were further associated with increased Th1/Th2 cytokine production, we propose HO as a putative therapeutic target in immunological abortions. Up-regulation of HO-1 or HO-2 would favour the Th2-cytokine production, which could avoid abortion onset.

Nonhuman primate models in type 1 diabetes research

The recent success of "steroid-free" immunosuppressive protocols and improvements in islet preparation techniques have proven that pancreatic islet transplantation (PIT) is a valid therapeutic approach for patients with type 1 diabetes. However, there are major obstacles to overcome before PIT can become a routine therapeutic procedure, such as the need for chronic immunosuppression, the loss of functional islet mass after transplantation requiring multiple islet infusion to achieve euglycemia without exogenous administration of insulin, and the shortage of human tissue for transplantation. With reference to the first obstacle, stable islet allograft function without immunosuppressive therapy has been achieved after tolerance was induced in diabetic primates. With reference to the second obstacle, different strategies, including gene transfer of antiapoptotic genes, have been used to protect isolated islets before and after transplantation. With reference to the third obstacle, pigs are an attractive islet source because they breed rapidly, there is a long history of porcine insulin use in humans, and there is the potential for genetic engineering. To accomplish islet transplantation, experimental opportunities must be balanced by complementary characteristics of basic mouse and rat models and preclinical large animal models. Well-designed preclinical studies in primates can provide the quality of information required to translate islet transplant research safely into clinical transplantation.

Targeted deletion of Fgl-2/fibroleukin in the donor modulates immunologic response and acute vascular rejection in cardiac xenografts

BACKGROUND

Xenografts ultimately fail as a result of acute vascular rejection (AVR), a process characterized by intravascular thrombosis, fibrin deposition, and endothelial cell activation.

METHODS AND RESULTS

We studied whether targeted deletion of Fgl-2, an inducible endothelial cell procoagulant, (Fgl-2-/-) in the donor prevents AVR in a mouse-to-rat cardiac xenotransplantation model. By 3 days after transplant, Fgl-2+/+ grafts developed typical features of AVR associated with increased levels of donor Fgl-2 mRNA. Grafts from Fgl-2-/- mice had reduced fibrin deposition but developed cellular rejection. Treatment with a short course of cobra venom factor and maintenance cyclosporine resulted in long-term acceptance of both Fgl-2+/+ and Fgl-2-/- grafts. On withdrawal of cyclosporine, Fgl-2+/+ grafts developed features of AVR; in contrast, Fgl-2-/- grafts again developed acute cellular rejection. Rejecting Fgl-2+/+ hearts stained positively for IgG, IgM, C3, and C5b-9, whereas rejecting Fgl-2-/- hearts had minimal Ig and complement deposition despite xenoantibodies in the serum. Furthermore, serum containing xenoantibodies failed to stain Fgl-2-/- long-term treated hearts but did stain wild-type heart tissues. Treatment of Fgl-2-/- xenografts with mycophenolate mofetil and tacrolimus, a clinically relevant immune suppression protocol, led to long-term graft acceptance.

CONCLUSIONS

Deletion of Fgl-2 ameliorates AVR by downregulation of xenoantigens and may facilitate successful clinical heart xenotransplantation.

Alpha Gal ligation of pig endothelial cells induces protection from complement and apoptosis independently of NF-kappa B and inflammatory changes

Cytoprotection of endothelial cells (EC) is important in EC biology and pathophysiology, including graft rejection. Using porcine aortic EC and human complement as an in vitro model of xenotransplantation, we have reported that ligation of EC Gal alpha (1-3)Gal epitopes (alpha Gal) with antibodies or lectins BS-I and IB4 induces EC resistance to injury by complement. However, before the protective response is observed, alpha Gal ligation induces an early, proinflammatory response. Using a similar model, we now investigated whether the early inflammatory response, as well as NF-kappa B activation, is required for induction of cytoprotection. Despite up-regulation of EC mRNA for many inflammatory cytokines rapidly after BS-I stimulation, recombinant cytokines or conditioned media from EC incubated with BS-I failed to induce protection when used to stimulate EC. While the lectin-induced inflammatory response was markedly reduced by inhibition of NF-kappa B, the protection from complement and apoptosis was unaffected. The lectins caused up-regulation of mRNA for protective genes A20, porcine inhibitor of apoptosis protein and hemoxygenase-1, which was not modified by NF-kappa B inhibition. These findings suggest that induction of cytoprotection in porcine EC by alpha Gal ligation results from activation of pathways that are largely independent of those that elicit NF-kappaB activation and the inflammatory response.

Heme oxygenase-1 (HO-1), a protective gene that prevents chronic graft dysfunction

Heme oxygenase-1 (HO-1) is a stress-responsive enzyme that acts during inflammatory reactions as the rate-limiting step in the catabolism of heme, yielding equimolar amounts of iron (Fe), biliverdin, and the gas carbon monoxide (CO). Expression of HO-1 regulates inflammatory and immune responses, such as those involved in the rejection of transplanted organs. We will discuss here accumulating evidence supporting the notion that expression of HO-1 in a transplanted organ can prevent its rejection. We will argue that the protective effects exerted by HO-1 are mediated to a large extent by the end products that it generates via the catabolism of heme. Better knowledge of how to enhance these protective effects is likely to help create new therapeutic strategies to improve the outcome of transplanted organs.

ABO histo-blood group system-incompatible allografting

Most of the 29 blood group systems known today are not restricted to erythroid tissues hence their more recent identification as histo-blood group systems. Beyond the uncontested importance of the HLA system in human allograft survival, some of the histo-blood group systems might increasingly become recognised to play a role in graft-host interaction and peritransplant transfusion therapy. At least the ABO histo-blood group system has drawn a lot of interest since both, elective ABO-mismatch with living kidney donor/recipient pairs and infant heart recipients have been described as radical, but effective treatments of end-stage organ dysfunction. More recently, at least in part successful efforts to overcome unintentional ABO-mismatched lung and heart grafts spark interest in more precisely avoiding hyperacute transplant rejection due to complement-activating anti-A/B antibodies of the recipients. Such options as to prepare the recipient with plasma exchange and following him up with polyspecific intravenous immunoglobulins, monoclonal antibodies and targeted immunosuppression using mycophenolate, rabbit antithymocyte globulin and anti-CD20 antibody rituximab are bound to efficiently remove anti-A/B antibodies and apparently inhibit their resynthesis. The present contribution overviews recently acquired knowledge on the ABO histo blood group system and the role it plays in solid organ transplantation leant against a patient observed at our institution.

Gene Therapy-Mediated CD40L and CD28 Co-stimulatory Signaling Blockade plus Transient Anti-xenograft Antibody Suppression Induces Long-Term Acceptance of Cardiac Xenografts

BACKGROUND

The authors have previously demonstrated that inhibition of CD28 and CD40 ligand (CD40L) co-stimulatory signals by adenovirus-mediated cytotoxic T-lymphocyte-associated (CTL) antigen 4 (A4) immunoglobulin (Ig) and CD40Ig gene therapies induces tolerance or long-term acceptance in rat liver and heart allograft transplantation. In this study, the authors examined whether co-stimulation blockade with a brief course treatment of FK779, a novel leflunomide derivative, would be an ideal strategy for controlling xenograft rejection.

METHODS

Hamster hearts were transplanted into Lewis rats. Adenovirus vector coding (Ad) CD40Ig, CTLA4Ig, or LacZ gene (1 x 10(9) plaque-forming units) was administered intravenously to recipient rats 2 days before or immediately after xenografting. FK779 (10 mg/kg/day) was administered orally to recipients for 7 days beginning on day -1. Graft survival, graft histology, and xenoreactive antibodies were examined.

RESULTS

: Both untreated and AdLacZ-treated control rats rejected cardiac xenografts, with a median survival time (MST) of 3 days. Co-stimulatory blockade alone by AdCTLA4Ig, AdCD40Ig, or both could not overcome such delayed xenograft rejection (DXR) (MST, 3-4 days). Under a short-course FK779 treatment that suppressed T-cell-independent xenoreactive antibodies, administration of AdCD40Ig (MST, 30.5 days) but not AdCTLA4Ig (MST, 9 days) significantly prolonged xenograft survival as compared with the FK779 monotherapy (MST, 7 days). In contrast, DXR and cellular rejection were controlled successfully and all xenografts were accepted for over 100 days when AdCTLA4Ig and AdCD40Ig were administered under FK779 induction therapy. However, chronic rejection was present in all long-term surviving xenografts.

CONCLUSIONS

: Gene therapy-based co-stimulation blockade with FK779 induction treatment seems to be an attractive strategy with which to control xenograft rejection.

Immune response, accommodation, and tolerance to transplantation carbohydrate antigens

The carbohydrate antigens, blood groups A and B, and the alpha-gal epitope (Galalpha1-3Gal) are major risk factors in transplantation. Transplantation across ABO barriers may result in rejection by elicited anti-blood group antibodies, accommodation where elicited anti-blood group antibodies do not reject the graft, or tolerance where no anti-blood group antibodies are produced and the graft is not rejected. alpha1,3Galactosyltransferase knockout mice that lack alpha-gal epitopes but produce the anti-Gal antibody serve as a model for studying these immune responses. Knockout mice underwent transplantation heterotopically with wild-type mouse heart expressing alpha-gal epitopes and subsequently received lymphocytes including naive and memory anti-Gal B cells. The type of elicited immune response was found to be associated with the period that anti-Gal B cells were exposed to alpha-gal epitopes of the graft in the absence of T-cell help. Immediate T-cell help induced production of cytolytic anti-Gal antibodies that reject the graft, whereas delayed T-cell help induced production of accommodating anti-Gal antibodies. In the absence of T-cell help for prolonged periods, anti-Gal B cells exposed to alpha-gal epitopes were deleted, resulting in tolerance. Similar variations in the extent of T-cell help may determine the B-cell response to incompatible A or B antigens. The experimental model further suggests that active tolerance induction before transplantation may be achieved by gene therapy with autologous bone marrow cells or autologous lymphocytes manipulated to express the incompatible transplantation carbohydrate antigen by introduction of the corresponding glycosyltransferase gene into these cells.

A novel approach to xenotransplantation combining surface engineering and genetic modification of isolated adult porcine islets

BACKGROUND

Effective cytoprotection to xenoislets would circumvent the major tissue limitation for pancreatic islet transplantation (PIT). Cell-surface engineering with poly[ethylene glycol] (PEG) derivatives can successfully prevent antibody binding to the surface antigens. Gene transfer of the antiapoptotic Bcl-2 gene has been shown to decrease cytotoxicity mediated by xenoreactive natural antibodies and complement. In this study, we assessed survival and function of surface-engineered porcine islets genetically modified to overexpress Bcl-2.

METHODS

Incorporation of PEG derivatives into the islet surface and adenovirus-mediated gene transfer of Bcl-2 (AdBcl-2) was accomplished within 24 hours post-isolation. Cytotoxicity induced by human xenoreactive natural antibodies was evaluated by islet intracellular lactate dehydrogenase release and microscopic analysis using membrane-integrity staining. Islet functionality was assessed by static incubation and after intraportal infusion (5000 IEQ) into diabetic NOD-SCID mice reconstituted with human lymphocytes (5 x 10 8 /intraperitoneally/15 days before PIT).

RESULTS

No significant change in islet viability, morphology, and functionality was demonstrated after the incorporation of PEG-mono-succimidyl-succinate (MSPEG), or PEG-di-succimidyl-succinate "end"-capped with albumin (DSPEG) with or without gene transfer of Bcl-2. Islets treated with MSPEG presented a significant reduction in lactate dehydrogenase release compared with controls (41.2 +/- 3 vs 72.1 +/- 7, respectively, P <.05). Further protection was accomplished by DSPEG or AdBcl-2. The maximal cytoprotection was achieved by DSPEG +AdBcl-2 (15.5 +/- 4.9%, P <.001). Nonfasting glucose >200 mg/dL was found in 100% of the animals given control islets (n = 6) within 48 hours post-transplant. In contrast, euglycemia was achieved in 100% of the animals given islets modified with DSPEG + AdBcl-2 during the observation time.

CONCLUSIONS

Surface-engineering with functionalized PEG derivatives in combination with genetic modification with Bcl-2 significantly reduced islet loss after PIT. Application of this novel technology may improve results in xenoislet transplantation.