Induction of long-term cardiac allograft survival by heme oxygenase-1 gene transfer

Advances in Genetic Reprogramming: Prospects from Developmental Biology to Regenerative Medicine

The foundations of cell reprogramming were laid by Yamanaka and co-workers, who showed that somatic cells can be reprogrammed into pluripotent cells (induced pluripotency). Since this discovery, the field of regenerative medicine has seen advancements. For example, because they can differentiate into multiple cell types, pluripotent stem cells are considered vital components in regenerative medicine aimed at the functional restoration of damaged tissue. Despite years of research, both replacement and restoration of failed organs/ tissues have remained elusive scientific feats. However, with the inception of cell engineering and nuclear reprogramming, useful solutions have been identified to counter the need for compatible and sustainable organs. By combining the science underlying genetic engineering and nuclear reprogramming with regenerative medicine, scientists have engineered cells to make gene and stem cell therapies applicable and effective. These approaches have enabled the targeting of various pathways to reprogramme cells, i.e., make them behave in beneficial ways in a patient-specific manner. Technological advancements have clearly supported the concept and realization of regenerative medicine. Genetic engineering is used for tissue engineering and nuclear reprogramming and has led to advances in regenerative medicine. Targeted therapies and replacement of traumatized , damaged, or aged organs can be realized through genetic engineering. Furthermore, the success of these therapies has been validated through thousands of clinical trials. Scientists are currently evaluating induced tissue-specific stem cells (iTSCs), which may lead to tumour-free applications of pluripotency induction. In this review, we present state-of-the-art genetic engineering that has been used in regenerative medicine. We also focus on ways that genetic engineering and nuclear reprogramming have transformed regenerative medicine and have become unique therapeutic niches.

Porcine genome engineering for xenotransplantation

The extreme shortage of human donor organs for treatment of patients with end-stage organ failures is well known. Xenotransplantation, which might provide unlimited organ supply, is a most promising strategy to solve this problem. Domestic pigs are regarded as ideal organ-source animals owing to similarity in anatomy, physiology and organ size to humans as well as high reproductive capacity and low maintenance cost. However, several barriers, which include immune rejection, inflammation and coagulative dysfunctions, as well as the cross-species transmission risk of porcine endogenous retrovirus, blocked the pig-to-human xenotransplantation. With the rapid development of genome engineering technologies and the potent immunosuppressive medications in recent years, these barriers could be eliminated through genetic modification of pig genome together with the administration of effective immunosuppressants. A number of candidate genes involved in the regulation of immune response, inflammation and coagulation have been explored to optimize porcine xenograft survival in non-human primate recipients. PERV inactivation in pigs has also been accomplished to firmly address the safety issue in pig-to-human xenotransplantation. Many encouraging preclinical milestones have been achieved with some organs surviving for years. Therefore, the clinical trials of some promising organs, such as islet, kidney and heart, are aimed to be launched in the near future.

Genetic Restoration of Heme Oxygenase-1 Expression Protects from Type 1 Diabetes in NOD Mice

Antigen-presenting cells (APCs) including dendritic cells (DCs) play a critical role in the development of autoimmune diseases by presenting self-antigen to T-cells. Different signals modulate the ability of APCs to activate or tolerize autoreactive T-cells. Since the expression of heme oxygenase-1 (HO-1) by APCs has been associated with the tolerization of autoreactive T-cells, we hypothesized that HO-1 expression might be altered in APCs from autoimmune-prone non-obese diabetic (NOD) mice. We found that, compared to control mice, NOD mice exhibited a lower percentage of HO-1-expressing cells among the splenic DCs, suggesting an impairment of their tolerogenic functions. To investigate whether restored expression of HO-1 in APCs could alter the development of diabetes in NOD mice, we generated a transgenic mouse strain in which HO-1 expression can be specifically induced in DCs using a tetracycline-controlled transcriptional activation system. Mice in which HO-1 expression was induced in DCs exhibited a lower Type 1 Diabetes (T1D) incidence and a reduced insulitis compared to non-induced mice. Upregulation of HO-1 in DCs also prevented further increase of glycemia in recently diabetic NOD mice. Altogether, our data demonstrated the potential of induction of HO-1 expression in DCs as a preventative treatment, and potential as a curative approach for T1D.

Effects of carbon monoxide on early dysfunction and microangiopathy following GalT-KO porcine pulmonary xenotransplantation in cynomolgus monkeys

BACKGROUND

Despite progress in the current genetic manipulation of donor pigs, most non-human primates were lost within a day of receiving porcine lung transplants. We previously reported that carbon monoxide (CO) treatment improved pulmonary function in an allogeneic lung transplant (LTx) model using miniature swine. In this study, we evaluated whether the perioperative treatment with low-dose inhalation of CO has beneficial effects on porcine lung xenografts in cynomolgus monkeys (cynos).

METHODS

Eight cynos received orthotopic left LTx using either α-1,3-galactosyltransferase knockout (GalT-KO; n = 2) or GalT-KO with human decay accelerating factor (hDAF) (GalT-KO/hDAF; n = 6) swine donors. These eight animals were divided into three groups. In Group 1 (n = 2), neither donor nor recipients received CO therapy. In Group 2 (n = 4), donors were treated with inhaled CO for 180-minute. In Group 3 (n = 2), both donors and recipients were treated with CO (donor: 180-minute; recipient: 360-minute). Concentration of inhaled CO was adjusted based on measured levels of carboxyhemoglobin in the blood (15%-20%).

RESULTS

Two recipients survived for 3 days; 75 hours (no-CO) and 80 hours (CO in both the donor and the recipient), respectively. Histology showed less inflammatory cell infiltrates, intravascular thrombi, and hemorrhage in the 80-hour survivor with the CO treatment than the 75-hours non-CO treatment. Anti-non-Gal cytotoxicity levels did not affect the early loss of the grafts. Although CO treatment did not prolong overall xeno lung graft survival, the recipient/donor CO treatment helped to maintain platelet counts and inhibit TNF-α and IL-6 secretion at 2 hours after revascularization of grafts. In addition, lung xenografts that were received recipient/donor CO therapy demonstrated fewer macrophage and neutrophil infiltrates. Infiltrating macrophages as well as alveolar epithelial cells in the CO-treated graft expressed heme oxygenase-1.

CONCLUSION

Although further investigation is required, CO treatment may provide a beneficial strategy for pulmonary xenografts.

Heme oxygenase-1-transduced bone marrow mesenchymal stem cells in reducing acute rejection and improving small bowel transplantation outcomes in rats

Background

We determined whether bone marrow mesenchymal stem cells (BMMSCs) transduced with heme oxygenase-1 (HO-1), a cytoprotective and immune-protective factor, could improve outcomes for small bowel transplantation (SBTx) in rats.

Methods

We performed heterotopic SBTx from Brown Norway rats to Lewis rats, before infusing Ad/HO-1-transduced BMMSCs (Ad/HO-1/BMMSCs) through the superficial dorsal veins of the penis. Respective infusions with Ad/BMMSCs, BMMSCs, and normal saline served as controls. The animals were sacrificed after 1, 5, 7, or 10 days. At each time point, we measured small bowel histology and apoptosis, HO-1 protein and mRNA expression, natural killer (NK) cell activity, cytokine concentrations in serum and intestinal graft, and levels of regulatory T (Treg) cells.

Results

The saline-treated control group showed aggravated acute cellular rejection over time, with mucosal destruction, increased apoptosis, NK cell activation, and upregulation of proinflammatory and immune-related mediators. Both the Ad/BMMSC-treated group and the BMMSC-treated group exhibited attenuated acute cellular rejection at an early stage, but the effects receded 7 days after transplantation. Strikingly, the Ad/HO-1/BMMSC-treated group demonstrated significantly attenuated acute cellular rejection, reduced apoptosis and NK cell activity, and suppressed concentrations of inflammation and immune-related cytokines, and upregulated expression of anti-inflammatory cytokine mediators and increased Treg cell levels.

Conclusion

Our data suggest that Ad/HO-1-transduced BMMSCs have a reinforced effect on reducing acute rejection and protecting the outcome of SBTx in rats.

Modulation of antigen processing by haem-oxygenase 1. Implications on inflammation and tolerance

Haem-oxygenase-1 (HO-1) is an enzyme responsible for the degradation of haem that can suppress inflammation, through the production of carbon monoxide (CO). It has been shown in several experimental models that genetic and pharmacological induction of HO-1, as well as non-toxic administration of CO, can reduce inflammatory diseases, such as endotoxic shock, type 1 diabetes and graft rejection. Recently, it was shown that the HO-1/CO system can alter the function of antigen-presenting cells (APCs) and reduce T-cell priming, which can be beneficial during immune-driven inflammatory diseases. The molecular mechanisms by which the HO-1 and CO reduce both APC- and T-cell-driven immunity are just beginning to be elucidated. In this article we discuss recent findings related to the immune regulatory capacity of HO-1 and CO at the level of recognition of pathogen-associated molecular patterns and T-cell priming by APCs. Finally, we propose a possible regulatory role for HO-1 and CO over the recently described mitochondria-dependent immunity. These concepts could contribute to the design of new therapeutic tools for inflammation-based diseases.

Insights into Myeloid-Derived Suppressor Cells in Inflammatory Diseases

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of cells involved in immune regulation. This population subdivides into granulocytic MDSCs and monocytic MDSCs, which regulate immune responses via the production of various molecules including reactive oxygen species, nitric oxide, arginase-1, interleukin-10, and transforming growth factor-β. Most studies of MDSCs focused on their role in tumors. MDSCs protect tumor cells from immune responses, and thus the frequency of MDSCs associates with poor prognosis. Many recent studies reported an important role for MDSCs in inflammatory diseases via the regulation of immune cells. In addition, the utilization of MDSCs by infectious pathogens suggests an immune evasion mechanism. Thus, MDSCs are important immune regulators in inflammatory diseases, as well as in tumors. This review focuses on the role of MDSCs in the regulation of inflammation in non-tumor settings.

Monocyte-Derived Suppressor Cells in Transplantation

Myeloid-derived suppressor cells (MDSC) are cells of myeloid origin with enhanced suppressive function. They are negative regulators of the immune responses and comprise a heterogeneous mixture of immunosuppressive cells of monocytic (M-MDSC) and granulocytic (G-MDSC) origin. A more recent nomenclature proposes the term "suppressive monocyte derived cells" (suppressive MCs) to define CSF1/CSF2-dependent mouse suppressor cells that develop from common monocyte progenitors (cMoPs) after birth. Here, we review the literature about monocytic-derived cells with demonstrated suppressor function in vitro and in vivo within the context of solid organ transplantation.

New insights into intracellular locations and functions of heme oxygenase-1

SIGNIFICANCE

Heme oxygenase-1 (HMOX1) plays a critical role in the protection of cells, and the inducible enzyme is implicated in a spectrum of human diseases. The increasing prevalence of cardiovascular and metabolic morbidities, for which current treatment approaches are not optimal, emphasizes the necessity to better understand key players such as HMOX1 that may be therapeutic targets.

RECENT ADVANCES

HMOX1 is a dynamic protein that can undergo post-translational and structural modifications which modulate HMOX1 function. Moreover, trafficking from the endoplasmic reticulum to other cellular compartments, including the nucleus, highlights that HMOX1 may play roles other than the catabolism of heme.

CRITICAL ISSUES

The ability of HMOX1 to be induced by a variety of stressors, in an equally wide variety of tissues and cell types, represents an obstacle for the therapeutic exploitation of the enzyme. Any capacity to modulate HMOX1 in cardiovascular and metabolic diseases should be tempered with an appreciation that HMOX1 may have an impact on cancer. Moreover, the potential for heme catabolism end products, such as carbon monoxide, to amplify the HMOX1 stress response should be considered.

FUTURE DIRECTIONS

A more complete understanding of HMOX1 modifications and the properties that they impart is necessary. Delineating these parameters will provide a clearer picture of the opportunities to modulate HMOX1 in human disease.

Genomics of liver transplant injury and regeneration

While improved surgical techniques, post-operative care, and immunosuppression regimens have reduced morbidity and mortality associated with orthotopic liver transplantation (OLT), further improvement of outcomes requires personalized treatment and a better understanding of genomic mechanisms involved. Gene expression profiles of ischemia/reperfusion (I/R) injury, regeneration, and rejection, may suggest mechanisms for development of better predictive tools and treatments. The liver is unique in its regenerative potential, recovering lost mass and function after injury from ischemia, resection, and rejection. I/R injury, an inevitable consequence of perfusion cessation, cold storage, and reperfusion, is regulated by the interaction of the immune system, inflammatory cytokines, and reduced microcirculatory blood flow in the liver. Rejection, a common post-operative complication, is mediated by the recipient's immune system through T-cell-dependent responses activating proinflammatory and apoptotic pathways. Characterizing distinctive gene expression signatures for these events can identify therapies to reduce injury, promote regeneration, and improve outcomes. While certain markers of liver injury and regeneration have been observed in animals, many of these are unverified in human studies. Further investigation of these genomic signatures and mechanisms through new technology offers promise, but continues to pose a significant challenge. An overview of the current fund of knowledge in this area is reviewed.

Heme oxygenase-1 protects regulatory T cells from hypoxia-induced cellular stress in an experimental mouse brain tumor model

Two characteristic features of malignant gliomas (MG) are the presence of hypoxia and accumulation of regulatory T cells (Tregs). Heme-oxygenase-1 (HO1) is a cytoprotective enzyme expressed in high level by Tregs in glioma. In this study, we show that higher HO1 expression in Tregs is associated with increased survival under hypoxic conditions and that HO1 inhibitor, tin protoporphyrin (SnPP), abrogates the survival benefits. Moreover, SnPP preferentially eliminates Tregs and treatment with SnPP of tumor bearing mice significantly increases survival (23 to 31days (p<0.05)). Thus HO1 inhibition provides another alternative way of therapeutically targeting Tregs in MG.

Carbon monoxide decreases endosome-lysosome fusion and inhibits soluble antigen presentation by dendritic cells to T cells

Heme oxygenase-1 (HO-1) inhibits immune responses and inflammatory reactions via the catabolism of heme into carbon monoxide (CO), Fe(2+) , and biliverdin. We have previously shown that either induction of HO-1 or treatment with exogenous CO inhibits LPS-induced maturation of dendritic cells (DCs) and protects in vivo and in vitro antigen-specific inflammation. Here, we evaluated the capacity of HO-1 and CO to regulate antigen presentation on MHC class I and MHC class II molecules by LPS-treated DCs. We observed that HO-1 and CO treatment significantly inhibited the capacity of DCs to present soluble antigens to T cells. Inhibition was restricted to soluble OVA protein, as no inhibition was observed for antigenic OVA-derived peptides, bead-bound OVA protein, or OVA as an endogenous antigen. Inhibition of soluble antigen presentation was not due to reduced antigen uptake by DCs, as endocytosis remained functional after HO-1 induction and CO treatment. On the contrary, CO significantly reduced the efficiency of fusion between late endosomes and lysosomes and not by phagosomes and lysosomes. These data suggest that HO-1 and CO can inhibit the ability of LPS-treated DCs to present exogenous soluble antigens to naïve T cells by blocking antigen trafficking at the level of late endosome-lysosome fusion.

Expression of heme oxygenase-1 in neural stem/progenitor cells as a potential mechanism to evade host immune response

Besides their therapeutic benefit as cell source, neural stem/progenitor cells (NSPCs) exhibit immunosuppressive properties of great interest for modulating immune response in the central nervous system. To decipher the mechanisms of NSPC-mediated immunosuppression, activated T cells were exposed to NSPCs isolated from fetal rat brains. Analyses revealed that NSPCs inhibited T-cell proliferation and interferon-gamma production in a dose-dependent manner. A higher proportion of helper T cells (CD4+ T cells) was found in the presence of NSPCs, but analyses of FoxP3 population indicated that T-cell suppression was not secondary to an induction of suppressive regulatory T cells (FoxP3+ CD4+ CD25+). Conversely, induction of the high affinity interleukin-2 (IL-2) receptor (CD25) and the inability of IL-2 to rescue T-cell proliferation suggest that NSPCs display immunosuppressive activity without affecting T-cell activation. Cultures in Transwell chambers or addition of NSPC-conditioned medium to activated T cells indicated that part of the suppressive activity was not contact dependent. We therefore searched for soluble factors that mediate NSPC immunosuppression. We found that NSPCs express several immunosuppressive molecules, but the ability of these cells to inhibit T-cell proliferation was only counteracted by heme oxygenase (HO) inhibitors in association or not with nitric oxide synthase inhibitors. Taken together, our findings highlight a dynamic crosstalk between NSPCs and T lymphocytes and provide the first evidence of an implication of HO-1 in mediating the immunosuppressive effects of the NSPCs.

Carbon monoxide-treated dendritic cells decrease β1-integrin induction on CD8⁺ T cells and protect from type 1 diabetes

Carbon monoxide (CO) treatment improves pathogenic outcome of autoimmune diseases by promoting tolerance. However, the mechanism behind this protective tolerance is not yet defined. Here, we show in a transgenic mouse model for autoimmune diabetes that ex vivo gaseous CO (gCO)-treated DCs loaded with pancreatic β-cell peptides protect mice from disease. This protection is peptide-restricted, independent of IL-10 secretion by DCs and of CD4(+) T cells. Although no differences were observed in autoreactive CD8(+) T-cell function from gCO-treated versus untreated DC-immunized groups, gCO-treated DCs strongly inhibited accumulation of autoreactive CD8(+) T cells in the pancreas. Interestingly, induction of β1-integrin was curtailed when CD8(+) T cells were primed with gCO-treated DCs, and the capacity of these CD8(+) T cells to lyse isolated islet was dramatically impaired. Thus, immunotherapy using CO-treated DCs appears to be an original strategy to control autoimmune disease.

The social network of carbon monoxide in medicine

Networking between cells is critical for proper functioning of the cellular milieu and is mediated by cascades of highly regulated and overlapping signaling molecules. The enzyme heme oxygenase-1 (HO-1) generates three separate signaling molecules through the catalysis of heme - carbon monoxide (CO), biliverdin, and iron - each of which acts via distinct molecular targets to influence cell function, both proximally and distally. This review focuses on state-of-the art developments and insights into the impact of HO-1 and CO on the innate immune response, the effects of which are responsible for an ensemble of functions that help regulate complex immunological responses to bacterial sepsis and ischemia/reperfusion injury. HO-1 exemplifies an evolutionarily conserved system necessary for the cellular milieu to adapt appropriately, function properly, and ensure survival of the organism.

Gene transfer of heme oxygenase-1 using an adeno-associated virus serotype 6 vector prolongs cardiac allograft survival

Introduction. Allograft survival can be prolonged by overexpression of cytoprotective genes such as heme oxygenase-1 (HO-1). Modifications in vector design and delivery have provided new opportunities to safely and effectively administer HO-1 into the heart prior to transplantation to improve long-term graft outcome. Methods. HO-1 was delivered to the donor heart using an adeno-associated virus vector (AAV) with a pseudotype 6 capsid and vascular endothelial growth factor (VEGF) to enhance myocardial tropism and microvascular permeability. Survival of mouse cardiac allografts, fully or partially mismatched at the MHC, was determined with and without cyclosporine A. Intragraft cytokine gene expression was examined by PCR. Results. The use of AAV6 to deliver HO-1 to the donor heart, combined with immunosuppression, prolonged allograft survival by 55.3% when donor and recipient were completely mismatched at the MHC and by 94.6% if partially mismatched. The combination of gene therapy and immunosuppression was more beneficial than treatment with either AAV6-HO-1 or CsA alone. IL-17a, b, e and f were induced in the heart at rejection. Conclusions. Pretreatment of cardiac allografts with AAV6-HO-1 plus cyclosporine A prolonged graft survival. HO-1 gene therapy represents a beneficial adjunct to immunosuppressive therapy in cardiac transplantation.

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.

Protective effect of heme oxygenase-1 induction against hepatic injury in alcoholic steatotic liver exposed to cold ischemia/reperfusion

AIMS

The purpose of this study was to investigate the cytoprotective role of heme oxygenase-1 (HO-1) induction in hepatic injury in alcoholic steatotic liver exposed to cold ischemia/reperfusion (I/R).

MAIN METHODS

Animals were fed an ethanol liquid diet or isocaloric control diet for 5 weeks. Isolated perfused rat livers were preserved in Histidine-Tryptophan-Ketoglutarate at 4 °C. After 24 h of storage, livers were subjected to 120 min of reperfusion with Krebs-Henseleit bicarbonate buffer at 37 °C. Animals were pretreated with cobalt protoporphyrin (CoPP, 5 mg/kg, i.p.) or zinc protoporphyrin (ZnPP, 25 mg/kg, i.p.), HO-1 inducer and antagonist, respectively.

KEY FINDINGS

In the model of ischemia/isolated perfusion, endogenous HO-1 was downregulated in the livers fed with ethanol diet (ED I/R). In ED I/R group, portal pressure and lactate dehydrogenase release were significantly increased, while bile output and hyaluronic acid clearance decreased compared to rats fed on control diet (CD I/R). Furthermore, hepatic glutathione content decreased and lipid peroxidation increased in the ED I/R group compared to the CD I/R group. These alterations were attenuated by upregulation of HO-1 with CoPP pretreatment.

SIGNIFICANCE

Our results suggest that chronic ethanol consumption aggravates hepatic injury during cold I/R and it is likely due to downregulation of endogenous HO-1. Prior induction of HO-1 expression may provide a new strategy to protect livers against hepatic I/R injury or to increase the donor transplant pool through modulation of marginal alcoholic steatotic livers.

Heme oxygenase and carbon monoxide as an immunotherapeutic approach in transplantation and cancer

Heme oxygenases (HOs) are the rate-limiting intracellular enzymes that degrade heme into carbon monoxide (CO), biliverdin and free divalent iron. Among HOs, HO-1 is the only isoform that is highly inducible in response to numerous stress factors and proinflammatory cytokines. This enzyme has shown cytoprotective, antioxidant and anti-inflammatory properties. Moreover, HO-1 and, in particular, CO also have tolerogenic actions in adaptive immune responses. HO-1 can provide immunosuppression through its expression by regulatory T cells or antigen-presenting cells. The physiological importance of HO-1 has been demonstrated in both mice and humans, and modulation of HO-1 expression has therapeutic effects in a variety of disorders involving inflammation and immune responses, including organ transplantation and cancer. Consistently, upregulation of the HO-1 pathway has a significant protective effect against spontaneous or induced autoimmune diseases, allergy and can be beneficial to graft survival. However, HO-1 may also play a role in tumorigenesis by lowering antitumor innate immune responses that control tumor growth or reduce tumor expansion. Thus, controlling HO-1 expression may be of great interest in immune intervention protocols where tolerance is desirable, such as in transplantation, or where enhanced immunogenicity is needed in the case of cancer.

Taurine chloramine protects RAW 264.7 macrophages against hydrogen peroxide-induced apoptosis by increasing antioxidants

Taurine chloramine is the major chloramine generated in activated neutrophils via the reaction between the overproduced hypochlorous acid and the stored taurine. Taurine chloramine has anti-inflammatory and cytoprotective effects in inflamed tissues by inhibiting the production of inflammatory mediators. Taurine chloramine increases heme oxygenase activity and also protects against hydrogen peroxide (H₂O₂)-derived necrosis in macrophages. In this study, we examined further whether taurine chloramine could protect RAW 264.7 macrophages from apoptosis caused by H₂O₂. Macrophages treated with 0.4 mM H₂O₂ underwent apoptosis without showing immediate signs of necrosis, and the cells pretreated with taurine chloramine were protected from the H₂O₂-derived apoptosis. Taurine chloramine increased heme oxygenase-1 expression and heme oxygenase activity. The taurine chloramine-derived upregulation of heme oxygenase-1 expression was blocked by inhibition of ERK phosphorylation. Taurine chloramine decreased cellular glutathione (GSH) levels initially, but the GSH level increased above the control level by 10 h. Taurine chloramine also increased catalase expression and protected macrophages from the apoptotic effect of H₂O₂. Combined, these results indicate that the taurine chloramine, produced and released endogenously by the activated neutrophils, can protect the macrophages in inflamed tissues from the H₂O₂-derived apoptosis not only by increasing the expression of cytoprotective enzymes like heme oxygenase-1 and catalase, but also by increasing the intracellular antioxidant GSH level.

Immunoregulatory properties of heme oxygenase-1

Heme oxygenase-1 (HO-1) is one of the three isoforms of the heme oxygenase enzyme that catabolyzes the degradation of heme into biliverdin with the production of free iron and CO. HO-1 is induced by its substrate and by other stimuli, including agents involved in oxidative stress and proinflammatory cytokines as well as several anti-inflammatory stimuli. A growing body of evidence points toward the capacity of this molecule to inhibit immune reactions and the pivotal role of HO-1 in inflammatory diseases. We will first review the physiological role of HO-1 as determined by the analysis of HO-1-deficient individuals. This will be followed by an examination of the effect of HO-1 within immunopathological contexts such as immune disorders (autoimmunity and allergy) or infections. A section will be devoted to the use of an HO-1 inducer as an immunosuppressive molecule in transplantation. Finally, we will review the molecular basis of HO-1 actions on different immune cells.

Pregnancy: tolerance and suppression of immune responses

Presence of foreign tissue in a host's body would immediately lead to a strong immune response directed to destroy the alloantigens present in fetus and placenta. However, during pregnancy, the semiallogeneic fetus is allowed to grow within the maternal uterus due to multiple mechanisms of immune tolerance, which are discussed in this chapter.

Role of heme oxygenase-1 in transplantation

Heme oxygenase-1 (HO-1) is the rate-limiting enzyme in heme catabolism that converts heme to Fe++, carbon monoxide and biliverdin. HO-1 acts anti-inflammatory and modulates apoptosis in many pathological conditions. In transplantation, HO-1 is overexpressed in organs during brain death, when undergoing ischemic damage and rejection. However, intentionally induced, it ameliorates pathological processes like ischemia reperfusion injury, allograft, xenograft or islet rejection, facilitates donor specific tolerance and alleviates chronic allograft changes. We herein consistently summarize the huge amount of data on HO-1 and transplantation that have been generated in multiple laboratories during the last 15years and suggest possible clinical implications and applications for the near future.

Pathophysiology and therapy of pruritus in allergic and atopic diseases

Pruritus (itch) is a major characteristic and one of the most debilitating symptoms in allergic and atopic diseases and the diagnostic hallmark of atopic dermatitis. Pruritus is regularly defined as an unpleasant sensation provoking the desire to scratch. Although we achieved rather good knowledge about certain inducers of itch such as neuropeptides, amines, mu-opioids, cytokines and proteases, for example, less is known about the pathophysiological specifities among the different diseases, and the therapeutic consequences which may derive thereoff. This review dissects the role of mediators, receptors and itch inhibitors on peripheral nerve endings, dorsal root ganglia, the spinal cord and the CNS leading to the amplification or - vice versa - suppression of pruritus. As the treatment of pruritus in allergic and atopic skin disease is still not satisfactory, knowing these pathways and mechanisms may lead to novel therapeutic approaches against this frequently encountered skin symptom.

Anti-inflammatory treatment strategies for ischemia/reperfusion injury in transplantation

Inflammatory reactions in the graft have a pivotal influence on acute as well as long-term graft function. The main reasons for an inflammatory reaction of the graft tissue are rejection episodes, infections as well as ischemia/reperfusion (I/R) injury. The latter is of particular interest as it affects every solid organ during the process of transplantation. I/R injury impairs acute as well as long-term graft function and is associated with an increased number of acute rejection episodes that again affect long-term graft outcome.

I/R injury is the result of ATP depletion during prolonged hypoxia. Further tissue damage results from the reperfusion of the tissue after the ischemic insult. Adaptive cellular responses activate the innate immune system with its Toll-like receptors and the complement system as well as the adaptive immune system. This results in a profound inflammatory tissue reaction with immune cells infiltrating the tissue. The damage is mediated by various cytokines, chemokines, adhesion molecules, and compounds of the extracellular matrix. The expression of these factors is regulated by specific transcription factors with NF-κB being one of the key modulators of inflammation.

Strategies to prevent or treat I/R injury include blockade of cytokines/chemokines, adhesion molecules, NF-κB, specific MAP kinases, metalloproteinases, induction of protective genes, and modulation of the innate immune system. Furthermore, preconditioning of the donor is an area of intense research. Here pharmacological treatment as well as new additives to conventional cold storage solutions have been analyzed together with new techniques for the perfusion of grafts, or methods of normothermic storage that would avoid the problem of cold damage and graft ischemia.

However, the number of clinical trials in the field of I/R injury is limited as compared to the large body of experimental knowledge that accumulated during recent years in the field of I/R injury. Future activities in the treatment of I/R injury should focus on the translation of experimental protocols into clinical trials in order to reduce I/R injury and, thus, improve short- as well as long-term graft outcome.

Induction of indoleamine 2,3-dioxygenase expression via heme oxygenase-1-dependant pathway during murine dendritic cell maturation

Heme oxygenase (HO)-1 is expressed in a variety of conditions involved in the regulation of immune responses. In this study, we examined the role of HO-1 in dendritic cell (DC) maturation and expression of indoleamine 2,3-dioxygenase (IDO), a key enzyme that catalyzes the initial, rate-limiting step in tryptophan degradation. IDO deficiency led to diminished phenotypic and functional maturation of DCs in vitro and in vivo. IDO expression and DC maturation was abrogated by the HO inhibitor zinc protoporphrin, but increased by hemin, a potent inducer of HO-1. Moreover, LPS-induced HO-1 expression was mediated by an NF-kappaB-dependent pathway. Our findings provide additional insight into the immunological functions of IDO and HO-1, and suggest possible therapeutic adjuvants for the treatment of DC-related acute and chronic diseases.

Pivotal Advance: Heme oxygenase 1 expression by human CD4+ T cells is not sufficient for their development of immunoregulatory capacity

HO-1 is the only inducible one of three isoenzymes that catalyzes the oxidative degradation of heme. HO-1 is inducible by various cellular stress factors and exerts cytoprotective and immunomodulatory effects. Recent publications demonstrated that HO-1 is constitutively expressed by CD4(+)CD25(+) T(regs) and induced in CD4(+)CD25(-) T cells upon FoxP3 transfection. Here, we investigated whether HO-1 was essential and sufficient for human T(regs) to exert immunosuppression in vitro. PGJ(2) induced pronounced expression of HO-1 in CD4(+)CD25(-) T cells without accompanying FoxP3 induction. Treatment of CD4(+)CD25(-) T cells with PGJ(2) decreased their proliferation, whereas the HO-1 inhibitor SnPP enhanced the proliferation of HO-1-expressing T(regs), suggesting that HO-1 may modulate the proliferative capacity of T lymphocytes. HO-1 modulation by SnPP treatment of T(regs) or PGJ(2) treatment of CD4(+)CD25(-) T cells neither suppressed nor induced immune-modulatory function in these cells, respectively, as measured by responder-cell proliferation and/or IL-2 production. In summary, these data suggest that HO-1 expression by T(regs) might contribute to their typical reluctance to proliferate but does not account independently for their suppressive functions.

Endotoxin-induced myeloid-derived suppressor cells inhibit alloimmune responses via heme oxygenase-1

Inflammation and cancer are associated with impairment of T-cell responses by a heterogeneous population of myeloid-derived suppressor cells (MDSCs) coexpressing CD11b and GR-1 antigens. MDSCs have been recently implicated in costimulation blockade-induced transplantation tolerance in rats, which was under the control of inducible NO synthase (iNOS). Herein, we describe CD11b+GR-1+MDSC-compatible cells appearing after repetitive injections of lipopolysaccharide (LPS) using a unique mechanism of suppression. These cells suppressed T-cell proliferation and Th1 and Th2 cytokine production in both mixed lymphocyte reaction and polyclonal stimulation assays. Transfer of CD11b+ cells from LPS-treated mice in untreated recipients significantly prolonged skin allograft survival. They produced large amounts of IL-10 and expressed heme oxygenase-1 (HO-1), a stress-responsive enzyme endowed with immunoregulatory and cytoprotective properties not previously associated with MDSC activity. HO-1 inhibition by the specific inhibitor, SnPP, completely abolished T-cell suppression and IL-10 production. In contrast, neither iNOS nor arginase 1 inhibition did affect suppression. Importantly, HO-1 inhibition before CD11b+ cell transfer prevented the delay of allograft rejection revealing a new MDSC-associated suppressor mechanism relevant for transplantation.

Identification of heme oxygenase-1-specific regulatory CD8+ T cells in cancer patients

Treg deficiencies are associated with autoimmunity. Conversely, CD4+ and CD8+ Tregs accumulate in the tumor microenvironment and are associated with prevention of antitumor immunity and anticancer immunotherapy. Recently, CD4+ Tregs have been much studied, but little is known about CD8+ Tregs and the antigens they recognize. Here, we describe what we believe to be the first natural target for CD8+ Tregs. Naturally occurring HLA-A2-restricted CD8+ T cells specific for the antiinflammatory molecule heme oxygenase-1 (HO-1) were able to suppress cellular immune responses with outstanding efficacy. HO-1-specific CD8+ T cells were detected ex vivo and in situ among T cells from cancer patients. HO-1-specific T cells isolated from the peripheral blood of cancer patients inhibited cytokine release, proliferation, and cytotoxicity of other immune cells. Notably, the inhibitory effect of HO-1-specific T cells was far more pronounced than that of conventional CD4+CD25+CD127- Tregs. The inhibitory activity of HO-1-specific T cells seemed at least partly to be mediated by soluble factors. Our data link the cellular stress response to the regulation of adaptive immunity, expand the role of HO-1 in T cell-mediated immunoregulation, and establish a role for peptide-specific CD8+ T cells in regulating cellular immune responses. Identification of potent antigen-specific CD8+ Tregs may open new avenues for therapeutic interventions in both autoimmune diseases and cancer.

Gene therapy in transplantation

Gene therapy is an exciting and novel technology that offers the prospect of improving transplant outcomes beyond those achievable with current clinical protocols. This review explores both the candidate genes and ways in which they have been deployed to overcome both immune and non-immune barriers to transplantation success in experimental models. Finally, the major obstacles to implementing gene therapy in the clinic are considered.

Tumor-specific regulatory T cells in cancer patients

A large body of evidence indicates that the presence of regulatory T cells (Tregs) in tumors is associated with a dampened tumor-specific immune response and a clear negative impact on survival. Many different subsets of Tregs have been identified, which all act through similar or distinct pathways to suppress tumor-specific effector cells. The observation that tumor-infiltrating Tregs are able to recognize tumor-derived antigens and can be expanded by vaccines that primarily aim at reinforcing the effector arm of the antitumor response stresses the need to study Tregs for each type of cancer targeted by immunotherapy. Current protocols enable us to isolate and culture tumor-infiltrating Tregs. Ultimately, this will not only lead to a full comprehension of the specificity and working mechanisms of Tregs but also facilitate the development of successful interventions strategies for the immunotherapy of cancer.

Heme oxygenase 1: does it have a role in renal cytoprotection?

Heme oxygenase (HO) was first identified as the rate-limiting enzyme in the degradative pathway of heme, but is now recognized to be involved in diverse biological processes. Different isoforms of HO exist; HO-1 (HMOX1) is ubiquitously present in mammalian tissue with low constitutive expression under physiological conditions, but is upregulated in response to a variety of potentially noxious stimuli. HO-1, an integral component of an important cytoprotective mechanism, mediates its action through removal of heme, the generation of heme breakdown reaction products (biliverdin, free iron, and carbon monoxide), and modulation of key cellular molecules. Data from experimental models in which HO-1 was induced or inhibited, together with observations in genetically modified animals, showed a beneficial effect of HO-1 in several pathways leading to kidney injury. The discovery of a functional guanosine thymine tandem repeat polymorphism in the promoter region of the human HO-1 gene has stimulated clinical investigations in a variety of diseases. However, despite theoretical and experimental support for an important pathophysiological role for HO-1, the relevance of this polymorphism in native kidney or renal transplant function is equivocal. This article reviews the molecular genetics of HO-1, its myriad cytoprotective effects allied to how these are mediated, and relates these findings to experimental and clinical evidence of HO-1 involvement in renal disease.

Anti-CD28 antibodies modify regulatory mechanisms and reinforce tolerance in CD40Ig-treated heart allograft recipients

Blockade of CD40-CD40 ligand (CD40L) costimulation has been shown to synergize with that of CTLA4/CD28-B7 to promote transplant tolerance. To date, however, CD28-B7 interactions have been prevented using B7-blocking reagents like CTLA4-Ig that inhibit CD28-B7 together with CTLA4-B7 interactions. In this study, we have tested anti-CD28 Abs to prevent selectively CD28-B7 interactions while preserving CTLA4-B7 in addition to CD40-CD40L blockade. In the LEW.1W to LEW.1A rat combination, interfering with CD40-CD40L interactions by CD40Ig administration through gene transfer resulted in indefinite heart allograft survival due to the appearance of clonotypic CD8+CD45RClow regulatory T cells that were capable of transferring the tolerant state to naive animals. However, cardiac transplants in these recipients systematically developed chronic rejection lesions. Whereas anti-CD28 Ab monotherapy only delayed acute rejection and failed to induce tolerance, coadministration of anti-CD28 Abs and CD40Ig resulted in the long-term acceptation of allografts without chronic rejection lesions in 60% of the recipients, reduced the level of intragraft mRNA transcripts for cytokines and immune factors, and fully abrogated alloantibody production. In addition, the nature of regulatory cells was modified: the CD8+CD45RClow clonotypic T cells described in the CD40Ig-treated animals could not be found in cotreated animals, and the other CD8+CD45RClow cells had no regulatory activity and a different cytokine expression profile. Instead, in cotreated recipients we found IDO-dependent non-T cells with regulatory activity in vitro. Thus, the addition of a short-term anti-CD28 treatment with CD40Ig resulted in decreased heart allograft chronic rejection lesions, complete inhibition of Ab production, and modified regulatory mechanisms.

Lentivirus mediated HO-1 gene transfer enhances myogenic precursor cell survival after autologous transplantation in pig

Cell therapy for Duchenne muscular dystrophy and other muscle diseases is limited by a massive early cell death following injections. In this study, we explored the potential benefit of heme oxygenase-1 (HO-1) expression in the survival of porcine myogenic precursor cells (MPCs) transplanted in pig skeletal muscle. Increased HO-1 expression was assessed either by transient hyperthermia or by HO-1 lentiviral infection. One day after the thermic shock, we observed a fourfold and a threefold increase in HSP70/72 and HO-1 levels, respectively. This treatment protected 30% of cells from staurosporine-induced apoptosis in vitro. When porcine MPC were heat-shocked prior to grafting, we improved cell survival by threefold at 5 days after autologous transplantation (26.3 +/- 5.5% surviving cells). After HO-1 lentiviral transduction, almost 60% of cells expressed the transgene and kept their myogenic properties to proliferate and fuse in vitro. Apoptosis of HO-1 transduced cells was reduced by 50% in vitro after staurosporine induction. Finally, a fivefold enhancement in cell survival was observed after transplantation of HO-1-group (47.5 +/- 9.1% surviving cells) as compared to the nls-LacZ-group or control group. These results identify HO-1 as a protective gene against early MPC death post-transplantation.

Immune response to stem cells and strategies to induce tolerance

Although recent progress in cardiovascular tissue engineering has generated great expectations for the exploitation of stem cells to restore cardiac form and function, the prospects of a common mass-produced cell resource for clinically viable engineered tissues and organs remain problematic. The refinement of stem cell culture protocols to increase induction of the cardiomyocyte phenotype and the assembly of transplantable vascularized tissue are areas of intense current research, but the problem of immune rejection of heterologous cell type poses perhaps the most significant hurdle to overcome. This article focuses on the potential advantages and problems encountered with various stem cell sources for reconstruction of the damaged or failing myocardium or heart valves and also discusses the need for integrating advances in developmental and stem cell biology, immunology and tissue engineering to achieve the full potential of cardiac tissue engineering. The ultimate goal is to produce 'off-the-shelf' cells and tissues capable of inducing specific immune tolerance.

Bilirubin oxidation provoked by nitric oxide radicals predicts the progression of acute cardiac allograft rejection

Bilirubin, a strong intrinsic antioxidant, quenches free radicals produced under inflammatory conditions. The oxidized bilirubin metabolites, i.e. biopyrrins, are immediately excreted into urine and can indicate the intensity of oxidation in vivo. Our preliminary studies suggested the involvement of reactive nitrogen species (RNS) in generation of biopyrrins. However, little is known about biological significance of bilirubin oxidation by RNS. Here, we analyzed the correlation between bilirubin oxidation and nitric oxide (NO) radicals during rat acute cardiac allograft rejection. In allograft recipients, urinary biopyrrins steeply increased on day 3 prior to the increase in myocardial tissue damage marker, serum troponin-T. In contrast, no significant changes in urinary biopyrrins were evident in recipients of isografts or cyclosporine-A treated allografts. Urinary nitrotyrosine, a marker of oxidation by NO radicals also increased on day 3, while administration of a NO synthase inhibitor, N(G)-monomethyl-L-arginine apparently diminished the elevation of urinary biopyrrins as well as nitrotyrosine. Immunohistochemistry revealed enhanced local expression of heme oxygenase-1, biopyrrins and nitrotyrosine in allografts in accordance with the cellular infiltrates, suggesting that changes in urinary biopyrrins reflect the bilirubin oxidation in grafts undergoing rejection. These results indicate that locally evoked bilirubin oxidation by NO radicals can predict the progression of rejection.

Heme Oxygenase-1 Expression in Macrophages Plays a Beneficial Role in Atherosclerosis

Heme oxygenase (HO-1) is the rate-limiting enzyme in the catabolism of heme, which leads to the generation of biliverdin, iron, and carbon monoxide. It has been shown to have important antioxidant and antiinflammatory properties that result in a vascular antiatherogenic effect. To determine whether HO-1 expression in macrophages constitutes a significant component of the protective role in atherosclerosis, we evaluated the effect of decreased or absent HO-1 expression in peritoneal macrophages on oxidative stress and inflammation in vitro, and the effect of complete deficiency of HO-1 expression in macrophages in atherosclerotic lesion formation in vivo. We found that compared with HO-1(+/+) controls, peritoneal macrophages from HO-1(-/-) and HO-1(+/-) mice exhibited (1) increased reactive oxygen species (ROS) generation, (2) increased proinflammatory cytokines such as monocyte chemotactic protein 1 (MCP-1) and interleukin 6 (IL-6), and (3) increased foam cell formation when treated with oxLDL, attributable in part to increased expression of scavenger receptor A (SR-A). Bone marrow transplantation experiments performed in lethally irradiated LDL-R null female mice, reconstituted with bone marrow from HO-1(-/-) versus HO-1(+/+) mice, revealed that HO-1(-/-) reconstituted animals exhibited atherosclerotic lesions with a greater macrophage content as evaluated by immunohistochemistry and planimetric assessment. We conclude that HO-1 expression in macrophages constitutes an important component of the antiatherogenic effect by increasing antioxidant protection and decreasing the inflammatory component of atherosclerotic lesions.

CD40Ig treatment results in allograft acceptance mediated by CD8CD45RC T cells, IFN-gamma, and indoleamine 2,3-dioxygenase

Treatment with CD40Ig results in indefinite allograft survival in a complete MHC-mismatched heart allograft model in the rat. Here we show that serial second, third, and fourth adoptive transfers of total splenocytes from CD40Ig-treated recipients into secondary recipients led to indefinite donor-specific allograft acceptance. Purification of splenocyte subpopulations from CD40Ig-treated recipients demonstrated that only the adoptively transferred CD8(+)CD45RC(low) subset resulted in donor-specific long-term survival, whereas CD8(+)CD45RC(low) T cells from naive animals did not. Accepted grafts displayed increased indoleamine 2,3-dioxygenase (IDO) expression restricted in the graft to ECs. Coculture of donor ECs with CD8(+)CD45RC(low) T cells purified from CD40Ig-treated animals resulted in donor-specific IDO expression dependent on IFN-gamma. Neutralization of IFN-gamma or IDO triggered acute allograft rejection in both CD40Ig-treated and adoptively transferred recipients. This study demonstrates for what we believe to be the first time that interference in CD40-CD40 ligand (CD40-CD40L) interactions induces allospecific CD8(+) Tregs that maintain allograft survival. CD8(+)CD45RC(low) T cells act through IFN-gamma production, which in turn induces IDO expression by graft ECs. Thus, donor alloantigen-specific CD8(+) Tregs may promote local graft immune privilege through IDO expression.

Could heme-oxygenase-1 have a role in modulating the recipient immune response to embryonic stem cells?

Pluripotent human embryonic stem cells (hESCs) may provide a potential source of cellular therapies, but as allogeneic cells may require evading the recipient's immune response. Using an NIH-registry hESC line, it was found that undifferentiated hESCs induce a reduced proliferative response compared to PBMC and demonstrate that this diminished response correlates with the activity of heme oxygenase-1 (HO-1). Inhibition of HO-1 significantly increases T cell proliferation against hESC, indicating the potential suppression of these cells during transplantation of allogeneic hESC. These data suggest the hypothesis that HO-1 provides a mechanism for protecting hESCs in vivo.

Expression changes in tolerant murine cardiac allografts after gene therapy with a lentiviral vector expressing alpha1,3 galactosyltransferase

Comparison of intragraft gene expression changes in tolerant cardiac allograft models may provide the basis for identifying pathways involved in graft survival. Our laboratory has previously demonstrated that tolerance to the gal alpha1,3 gal epitope, the major target of rejection of wild-type pig hearts in human cardiac transplantation, can be achieved after transplantation with bone marrow transduced with a lentiviral vector expressing alpha1,3 galactosyltransferase. We now present intracardiac gene expression changes associated with long-term tolerance in this model. Biotin-labeled cRNA was hybridized to Affymetrix GeneChip 430 2.0 Mouse Genome Arrays. Data were subjected to functional annotation analysis to identify genes of known function in which expression was increased or decreased by at least 2-fold (t-test, P < .05) in tolerant gal+/+ wild-type hearts as compared to transplanted syngeneic controls. Tolerant hearts demonstrated increased expression of genes associated with the stress response, modulation of immune function and cell survival (HSPa9a, CD56, and Akt1s1), and decreased expression of several immunoregulatory genes (CD209, CD26, and PDE4b). These data suggest that tolerance may be associated with activation of immunomodulatory and survival pathways.

The Heme Catabolic Pathway and its Protective Effects on Oxidative Stress‐Mediated Diseases

Bilirubin, the principal bile pigment, is the end product of heme catabolism. For many years, bilirubin was thought to have no physiological function other than that of a waste product of heme catabolism--useless at best and toxic at worst. Although hyperbilirubinemia in neonates has been shown to be neurotoxic, studies performed during the past decade have found that bilirubin has a number of new and interesting biochemical and biological properties. In addition, there is now a strong body of evidence suggesting that bilirubin may have a beneficial role in preventing oxidative changes in a number of diseases including atherosclerosis and cancer, as well as a number of inflammatory, autoimmune, and degenerative diseases. The results also suggest that activation of the heme oxygenase and heme catabolic pathway may have beneficiary effects on disease prevention either through the action of bilirubin or in conjunction with bilirubin. If so, it may be possible to therapeutically induce heme oxygenase, increase bilirubin concentrations, and lower the risk of oxidative stress-related diseases.

Hepatic ischemia-reperfusion induces renal heme oxygenase-1 via NF-E2-related factor 2 in rats and mice

Hepatic ischemia-reperfusion (IR) results in Kupffer cell activation and subsequent tumor necrosis factor (TNF) alpha release, leading to localized hepatic injury and remote organ dysfunction. Heme oxygenase (HO)-1 is an enzyme that is induced by various stimuli, including proinflammatory cytokines, and exerts antioxidative and anti-inflammatory functions. Up-regulation of HO-1 is known to protect against hepatic IR injury, but the effects of hepatic IR on the kidney are poorly understood. Thus, the purpose of this study was to determine whether hepatic IR and resultant Kupffer cell activation alters renal HO-1 expression. Male Sprague-Dawley rats and wild-type and NF-E2-related factor 2 (Nrf2)-null mice were subjected to 60 min of partial hepatic ischemia, and at various times thereafter, blood, liver, and kidneys were collected. After reperfusion, 1) creatinine clearance decreased; 2) HO-1 mRNA and protein expression in liver and kidney markedly increased; 3) renal NAD(P)H: quinone oxidoreductase 1 mRNA expression was induced; 4) serum TNFalpha levels increased; 5) Nrf2 translocation into the nucleus of renal tissue increased; and 6) renal and urinary 15-deoxy-Delta(12,14)-prostaglandin J2 (15-d-PGJ2) levels increased. Kupffer cell depletion by pretreating with gadolinium chloride 1) attenuated increased mRNA expression of HO-1 in kidney; 2) attenuated the increase in TNFalpha; 3) inhibited the increase in Nrf2 nuclear translocation; and 4) tended to attenuate renal 15-d-PGJ2 levels. Whereas renal HO-1 mRNA expression increased in wild-type mice, it was attenuated in Nrf2-null mice. These results suggest that renal HO-1 is induced via Nrf2 to protect the kidney from remote organ injury after hepatic IR.

Interleukin-10-secreting type 1 regulatory T cells in rodents and humans

Interleukin-10 (IL-10)-secreting T regulatory type 1 (Tr1) cells are defined by their specific cytokine production profile, which includes the secretion of high levels of IL-10 and transforming growth factor-beta(TGF-beta), and by their ability to suppress antigen-specific effector T-cell responses via a cytokine-dependent mechanism. In contrast to the naturally occurring CD4+ CD25+ T regulatory cells (Tregs) that emerge directly from the thymus, Tr1 cells are induced by antigen stimulation via an IL-10-dependent process in vitro and in vivo. Specialized IL-10-producing dendritic cells, such as those in an immature state or those modulated by tolerogenic stimuli, play a key role in this process. We propose to use the term Tr1 cells for all IL-10-producing T-cell populations that are induced by IL-10 and have regulatory activity. The full biological characterization of Tr1 cells has been hampered by the difficulty in generating these cells in vitro and by the lack of specific marker molecules. However, it is clear that Tr1 cells play a key role in regulating adaptive immune responses both in mice and in humans. Further work to delineate the specific molecular signature of Tr1 cells, to determine their relationship with CD4+ CD25+ Tregs, and to elucidate their respective role in maintaining peripheral tolerance is crucial to advance our knowledge on this Treg subset. Furthermore, results from clinical protocols using Tr1 cells to modulate immune responses in vivo in autoimmunity, transplantation, and chronic inflammatory diseases will undoubtedly prove the biological relevance of these cells in immunotolerance.

Ex vivo hypothermic recirculatory adenoviral gene transfer to the transplanted pig heart

BACKGROUND

To facilitate the application of adenoviral gene therapy in clinical heart transplantation, we developed an ex vivo hypothermic recirculatory adenoviral gene transfer method to the transplanted pig heart.

METHODS

Experimental animals were assigned into three groups; controls, 1x10(8) plaque-forming units (pfu)/ml group and 1x10(9) pfu/ml group. During the 30 min gene transfer perfusion, 200 ml of University of Wisconsin solution containing the adenoviral vector was recirculated through the coronary vessels. The myocardial temperature was maintained below 4 degrees C and the perfusion pressure was adjusted at 50 mmHg.

RESULTS

Cardiac myocyte transduction efficiencies in the 1x10(8) pfu/ml group were 0.04% and 0.07%, whereas transduction efficiencies in the 1x10(9) pfu/ml group were widely distributed from 0.45% to 22.62%. The gene transduction efficiency increased with the virus titer. Additionally, no difference in the transduction efficiency was observed between different segments of the left ventricle. The current gene transfer method at 1x10(9) pfu/ml of adenovirus titer enabled homogeneous gene transduction into the transplanted pig heart up to a maximum of 22.62%.

CONCLUSIONS

This model can be applied to a large isolated heart and will greatly facilitate the investigation of gene therapy in large animal models of heart transplantation.