Blockade of the interaction between PD-1 and PD-L1 accelerates graft arterial disease in cardiac allografts

PD-1/PD-L1 Provides Protective Role in Hypoxia-Induced Pulmonary Vascular Remodeling

BACKGROUND

Hypoxia-induced pulmonary hypertension (HPH) is a T helper 17 cell response-driven disease, and PD-1 (programmed cell death 1)/PD-L1 (programmed cell death-ligand 1) inhibitor-associated pulmonary hypertension has been reported recently. This study is designed to explore whether the PD-1/PD-L1 pathway participates in HPH via regulating endothelial dysfunction and T helper 17 cell response.

METHODS

Lung tissue samples were obtained from eligible patients. Western blotting, immunohistochemistry, and immunofluorescence techniques were used to assess protein expression, while immunoprecipitation was utilized to detect ubiquitination. HPH models were established in C57BL/6 WT (wild-type) and PD-1-/- mice, followed by treatment with PD-L1 recombinant protein. Adeno-associated virus vector delivery was used to upregulate PD-L1 in the endothelial cells. Endothelial cell function was assessed through assays for cell angiogenesis and adhesion.

RESULTS

Expression of the PD-1/PD-L1 pathway was downregulated in patients with HPH and mouse models, with a notable decrease in PD-L1 expression in endothelial cells compared with the normoxia group. In comparison to WT mice, PD-1-/- mice exhibited a more severe HPH phenotype following exposure to hypoxia, However, administration of PD-L1 recombinant protein and overexpression of PD-L1 in lung endothelial cells mitigated HPH. In vitro, blockade of PD-L1 with a neutralizing antibody promoted endothelial cell angiogenesis, adhesion, and pyroptosis. Mechanistically, hypoxia downregulated PD-L1 protein expression through ubiquitination. Additionally, both in vivo and in vitro, PD-L1 inhibited T helper 17 cell response through the PI3K (phosphoinositide 3-kinase)/AKT (protein kinase B)/mTOR (mammalian target of rapamycin) pathway in HPH.

CONCLUSIONS

PD-1/PD-L1 plays a role in ameliorating HPH development by inhibiting T helper 17 cell response through the PI3K/AKT/mTOR pathway and improving endothelial dysfunction, suggesting a novel therapeutic indication for PD-1/PD-L1-based immunomodulatory therapies in the treatment of HPH.

Androgen aggravates aortic aneurysms via suppression of PD-1 in mice

Androgen has long been recognized for its pivotal role in the sexual dimorphism of cardiovascular diseases, including aortic aneurysms (AAs), a devastating vascular disease with a higher prevalence and fatality rate in men than in women. However, the mechanism by which androgen mediates AAs is largely unknown. Here, we found that male, not female, mice developed AAs when exposed to aldosterone and high salt (Aldo-salt). We revealed that androgen and androgen receptors (ARs) were crucial for this sexually dimorphic response to Aldo-salt. We identified programmed cell death protein 1 (PD-1), an immune checkpoint, as a key link between androgen and AAs. Furthermore, we demonstrated that administration of anti-PD-1 Ab and adoptive PD-1-deficient T cell transfer reinstated Aldo-salt-induced AAs in orchiectomized mice and that genetic deletion of PD-1 exacerbated AAs induced by a high-fat diet and angiotensin II (Ang II) in nonorchiectomized mice. Mechanistically, we discovered that the AR bound to the PD-1 promoter to suppress the expression of PD-1 in the spleen. Thus, our study unveils a mechanism by which androgen aggravates AAs by suppressing PD-1 expression in T cells. Moreover, our study suggests that some patients with cancer might benefit from screenings for AAs during immune checkpoint therapy.

Cellular Alterations in Immune Checkpoint Inhibitor Therapy-Related Cardiac Dysfunction

PURPOSE OF REVIEW

Immune checkpoint inhibitor (ICI) therapy has emerged as a pivotal advancement in cancer treatment, but the widespread adoption has given rise to a growing number of reports detailing significant cardiovascular toxicity. This review concentrates on elucidating the mechanisms behind ICI-related cardiovascular complications, emphasizing preclinical and mechanistic data.

RECENT FINDINGS

Accumulating evidence indicates a more significant role of immune checkpoints in maintaining cardiac integrity than previously understood, and new key scientific data are available to improve our understanding of ICI-related cardiovascular toxicity, including hidden cardiotoxicity. New avenues for innovative concepts are hypothesized, and opportunities to leverage the knowledge from ICI-therapy for pioneering approaches in related scientific domains can be derived from the latest scientific projects. Cardiotoxicity from ICI therapy is a paramount challenge for cardio-oncology. Understanding the underlying effects builds the foundation for tailored cardioprotective approaches in the growing collective at risk for severe cardiovascular complications.

Immune Checkpoints in Solid Organ Transplantation

Allogenic graft acceptance is only achieved by life-long immunosuppression, which comes at the cost of significant toxicity. Clinicians face the challenge of adapting the patients' treatments over long periods to lower the risks associated with these toxicities, permanently leveraging the risk of excessive versus insufficient immunosuppression. A major goal and challenge in the field of solid organ transplantation (SOT) is to attain a state of stable immune tolerance specifically towards the grafted organ. The immune system is equipped with a set of inhibitory co-receptors known as immune checkpoints (ICs), which physiologically regulate numerous effector functions. Insufficient regulation through these ICs can lead to autoimmunity and/or immune-mediated toxicity, while excessive expression of ICs induces stable hypo-responsiveness, especially in T cells, a state sometimes referred to as exhaustion. IC blockade has emerged in the last decade as a powerful therapeutic tool against cancer. The opposite action, i.e., subverting IC for the benefit of establishing a state of specific hypo-responsiveness against auto- or allo-antigens, is still in its infancy. In this review, we will summarize the available literature on the role of ICs in SOT and the relevance of ICs with graft acceptance. We will also discuss the possible influence of current immunosuppressive medications on IC functions.

Immune Checkpoint Inhibitors in Solid Organ Transplant Recipients With Advanced Skin Cancers-Emerging Strategies for Clinical Management

Use of immune checkpoint inhibitors (ICIs) in solid organ transplant recipients (SOTRs) with advanced skin cancers presents a significant clinical management dilemma. SOTRs and other immunosuppressed patients have been routinely excluded from ICI clinical trials with good reason: immune checkpoints play an important role in self- and allograft-tolerance and risk of acute allograft rejection reported in retrospective studies affects 10% to 65% of cases. These reports also confirm that cutaneous squamous cell carcinoma and melanoma respond to ICI therapy, although response rates are generally lower than those observed in immunocompetent populations. Prospective trials are now of critical importance in further establishing ICI efficacy and safety. However, based on current knowledge, we recommend that ICIs should be offered to kidney transplant recipients with advanced cutaneous squamous cell carcinoma, melanoma, or Merkel cell carcinoma if surgery and/or radiotherapy have failed. For kidney transplant recipients, this should be first line ahead of chemotherapy and targeted therapies. In SOTRs, the use of ICIs should be carefully considered with the benefits of ICIs versus risks of allograft rejection weighed up on a case-by-case basis as part of shared decision-making with patients. In all cases, parallel management of immunosuppression may be key to ICI responsiveness. We recommend maintaining immunosuppression before ICI initiation with a dual immunosuppressive regimen combining mammalian target of rapamycin inhibitors and either corticosteroids or calcineurin inhibitors. Such modification of immunosuppression must be considered in the context of allograft risk (both rejection and also its subsequent treatment) and risk of tumor progression. Ultimately, a multidisciplinary approach should underpin all clinical decision-making in this challenging scenario.

Cinchonine exerts anti-tumor and immunotherapy sensitizing effects in lung cancer by impairing autophagic-lysosomal degradation

Currently, there are several treatments approaches available for lung cancer; however, patients who develop drug resistance or have poor survival rates urgently require new therapeutic strategies for lung cancer. In autophagy, damaged proteins or organelles are enclosed within autophagic vesicles with a bilayer membrane structure and transported to the lysosomes for degradation and recirculation. Autophagy is a crucial pathway involved in the clearance of reactive oxygen species (ROS) and damaged mitochondria. Meanwhile, inhibiting autophagy is a promising strategy for cancer treatment. In this study, we found for the first time that Cinchonine (Cin) can act as an autophagy suppressor and exert anti-tumor effects. Cin significantly inhibited the proliferation, migration, and invasion of cancer cells in vitro and the tumor growth and metastasis in vivo, without obvious toxic effects. We found that Cin suppressed the autophagic process by blocking autophagosome degradation through the inhibition of the maturation of lysosomal hydrolases. Cin-mediated autophagy inhibition resulted in the elevated ROS level and the accumulation of damaged mitochondria, which in turn promoted apoptosis. N-acetylcysteine, a potential ROS scavenger, significantly suppressed Cin-induced apoptosis. Additionally, Cin upregulated programmed death-ligand 1 (PD-L1) expression in lung cancer cells by inhibiting autophagy. Compared with monotherapy and control group, the combined administration of anti-PD-L1 antibody and Cin significantly reduced tumor growth. These results suggest that Cin exerts anti-tumor effects by inhibiting autophagy, and that the combination of Cin and PD-L1 blockade has synergistic anti-tumor effects. The data demonstrates the significant clinical potential of Cin in lung cancer treatment.

Immune-related adverse effects of checkpoint immunotherapy and implications for the treatment of patients with cancer and autoimmune diseases

During the past decade, there has been a revolution in cancer therapeutics by the emergence of antibody-based immunotherapies that modulate immune responses against tumors. These therapies have offered treatment options to patients who are no longer responding to classic anti-cancer therapies. By blocking inhibitory signals mediated by surface receptors that are naturally upregulated during activation of antigen-presenting cells (APC) and T cells, predominantly PD-1 and its ligand PD-L1, as well as CTLA-4, such blocking agents have revolutionized cancer treatment. However, breaking these inhibitory signals cannot be selectively targeted to the tumor microenvironment (TME). Since the physiologic role of these inhibitory receptors, known as immune checkpoints (IC) is to maintain peripheral tolerance by preventing the activation of autoreactive immune cells, IC inhibitors (ICI) induce multiple types of immune-related adverse effects (irAEs). These irAEs, together with the natural properties of ICs as gatekeepers of self-tolerance, have precluded the use of ICI in patients with pre-existing autoimmune diseases (ADs). However, currently accumulating data indicates that ICI might be safely administered to such patients. In this review, we discuss mechanisms of well established and newly recognized irAEs and evolving knowledge from the application of ICI therapies in patients with cancer and pre-existing ADs.

An integrative review of nonobvious puzzles of cellular and molecular cardiooncology

Oncologic patients are subjected to four major treatment types: surgery, radiotherapy, chemotherapy, and immunotherapy. All nonsurgical forms of cancer management are known to potentially violate the structural and functional integrity of the cardiovascular system. The prevalence and severity of cardiotoxicity and vascular abnormalities led to the emergence of a clinical subdiscipline, called cardiooncology. This relatively new, but rapidly expanding area of knowledge, primarily focuses on clinical observations linking the adverse effects of cancer therapy with deteriorated quality of life of cancer survivors and their increased morbidity and mortality. Cellular and molecular determinants of these relations are far less understood, mainly because of several unsolved paths and contradicting findings in the literature. In this article, we provide a comprehensive view of the cellular and molecular etiology of cardiooncology. We pay particular attention to various intracellular processes that arise in cardiomyocytes, vascular endothelial cells, and smooth muscle cells treated in experimentally-controlled conditions in vitro and in vivo with ionizing radiation and drugs representing diverse modes of anti-cancer activity.

Blocking of programmed cell death-ligand 1 (PD-L1) expressed on endothelial cells promoted the recruitment of CD8+IFN-γ+ T cells in atherosclerosis

BACKGROUND

Programmed death ligand-1 (PD-L1) is involved in the negative regulation of immune responses in a variety of diseases. We evaluated the contribution of PD-L1 to the activation of immune cells that promote atherosclerotic lesion formation and inflammation.

METHODS AND RESULTS

Compared to ApoE^-/- mice that were provided a high-cholesterol diet in combination with anti-PD-L1 antibody developed a larger lipid burden with more abundant CD8⁺ T cells. The anti-PD-L1 antibody increased the abundance of CD3⁺PD-1⁺, CD8 + PD-1⁺,CD3⁺IFN-γ⁺ and CD8⁺IFN-γ⁺ T cell under high-cholesterol diet, as well as the serum tumor necrosis factor-α (TNF-a), IFN-γ, PF, GNLY, Gzms B and LTA. Interestingly, the anti-PD-L1 antibody increased the serum level of sPD-L1. In vitro, blocking of PD-L1 on the surface of mouse aortic endothelial cells with anti-PD-L1 antibody stimulated the activation and secretion of cytokines, including IFN-γ, PF, GNLY, Gzms B and LTA, from cytolytic CD8⁺IFN-γ⁺ T cell. However, the concentration of sPD-L1 was lower after treatment of the MAECs with anti-PD-L1 antibody.

CONCLUSIONS

Our findings highlighted that blocking of PD-L1 promoted up-regulation of CD8 + IFN-γ + T cell-mediated immune responses, leading to the secretion of inflammatory cytokine that exacerbated the atherosclerotic burden and promoted inflammation. However, further studies are needed to gain insight into whether PD-L1 activation could be a novel immunotherapy strategy for atherosclerosis.

Androgen aggravates aortic aneurysms via suppressing PD-1 in mice

Androgen has long been recognized for its pivotal role in the sexual dimorphism of cardiovascular diseases, including aortic aneurysms, a devastating vascular disease with a higher prevalence and mortality rate in men than women. However, the molecular mechanism by which androgen mediates aortic aneurysms is largely unknown. Here, we report that male but not female mice develop aortic aneurysms in response to aldosterone and high salt (Aldo-salt). We demonstrate that both androgen and androgen receptors (AR) are crucial for the sexually dimorphic response to Aldo-salt. We identify T cells expressing programmed cell death protein 1 (PD-1), an immune checkpoint molecule important in immunity and cancer immunotherapy, as a key link between androgen and aortic aneurysms. We show that intraperitoneal injection of anti-PD-1 antibody reinstates Aldo-salt-induced aortic aneurysms in orchiectomized mice. Mechanistically, we demonstrate that AR binds to the PD-1 promoter to suppress its expression in the spleen. Hence, our study reveals an important but unexplored mechanism by which androgen contributes to aortic aneurysms by suppressing PD-1 expression in T cells. Our study also suggests that cancer patients predisposed to the risk factors of aortic aneurysms may be advised to screen for aortic aneurysms during immune checkpoint therapy.

Impact of Precision Medicine in Oncology: Immuno-oncology

ABSTRACT

Cancer treatment has dramatically changed over the last decade with the development of immunotherapy. Therapies including immune cytokines, immune checkpoint inhibition, intratumoral therapies, and cellular therapies are already widely used in the oncology clinic. Active development continues in these areas and in the development of vaccines, bispecific therapies, and more refined cellular therapies. In this review, we will examine the role that immune therapy has in cancer treatment and explore areas of future development.

Atherosclerosis: The Involvement of Immunity, Cytokines and Cells in Pathogenesis, and Potential Novel Therapeutics

As a leading contributor to coronary artery disease (CAD) and stroke, atherosclerosis has become one of the major cardiovascular diseases (CVD) negatively impacting patients worldwide. The endothelial injury is considered to be the initial step of the development of atherosclerosis, resulting in immune cell migration and activation as well as inflammatory factor secretion, which further leads to acute and chronic inflammation. In addition, the inflammation and lipid accumulation at the lesions stimulate specific responses from different types of cells, contributing to the pathological progression of atherosclerosis. As a result, recent studies have focused on using molecular biological approaches such as gene editing and nanotechnology to mediate cellular response during atherosclerotic development for therapeutic purposes. In this review, we systematically discuss inflammatory pathogenesis during the development of atherosclerosis from a cellular level with a focus on the blood cells, including all types of immune cells, together with crucial cells within the blood vessel, such as smooth muscle cells and endothelial cells. In addition, the latest progression of molecular-cellular based therapy for atherosclerosis is also discussed. We hope this review article could be beneficial for the clinical management of atherosclerosis.

Expression and Significance of Programmed Death-1 and Its Ligands in the Accelerated Formation of Atherosclerosis in an Induced Murine Lupus Model

Atherosclerosis (AS) is a chronic inflammatory disease that occurs in artery walls, which seriously affects the survival and prognosis of patients with systemic lupus erythematosus (SLE). Immune and inflammatory responses have notable effects on all stages of AS. In this study, we modeled SLE combined with AS in vivo via intraperitoneal injection of pristane (2,6,10,14-tetramethylpentadecane) into apolipoprotein E-knockout (ApoE-/- ) mice that had accelerated atherosclerotic lesions compared with wild-type (WT) ApoE-/- mice. In pristane-induced ApoE-/- mice, expression of programmed death-1 (PD-1) and programmed death-ligand 1 (PD-L1) in peripheral blood and on the surfaces of atherosclerotic lesions significantly increased, and levels of proinflammatory cytokines, namely, interferon-gamma (IFN-γ) and tumor necrosis factor alpha (TNF-α) in peripheral blood were elevated. We did not detect expression of programmed death-ligand 2 (PD-L2) in the arterial plaques of either pristane-induced or WT ApoE-/- mice, nor did we observe any significant difference in PD-L2 expression in peripheral blood between the two groups. Taken together, these results suggested that PD-1/PD-L1 signaling pathway might play an important regulatory role in the progression of AS in an induced murine lupus model which implies a potential target for treatment of AS in SLE.

Overexpression of PD-1 on T cells promotes tolerance in cardiac transplantation via an ICOS-dependent mechanism

The programmed death 1/programmed death ligand 1 (PD-1/PD-L1) pathway is a potent inhibitory pathway involved in immune regulation and is a potential therapeutic target in transplantation. In this study, we show that overexpression of PD-1 on T cells (PD-1 Tg) promotes allograft tolerance in a fully MHC-mismatched cardiac transplant model when combined with costimulation blockade with CTLA-4–Ig. PD-1 overexpression on T cells also protected against chronic rejection in a single MHC II–mismatched cardiac transplant model, whereas the overexpression still allowed the generation of an effective immune response against an influenza A virus. Notably, Tregs from PD-1 Tg mice were required for tolerance induction and presented greater ICOS expression than those from WT mice. The survival benefit of PD-1 Tg recipients required ICOS signaling and donor PD-L1 expression. These results indicate that modulation of PD-1 expression, in combination with a costimulation blockade, is a promising therapeutic target to promote transplant tolerance.

PD-1/PD-L1 immune checkpoints: Tumor vs atherosclerotic progression

Immunotherapy has become one of the most attraction cancer therapy strategies. The PD-1/PD-L1 pathway plays key roles in immune responses and autoimmunity by regulating T cell activity. Overactivation of this pathway dampens T cell and immune function, which allows tumor cells immune escape. Antibody or inhibitors of PD-1/PD-L1 immune targets have been implicated in clinic anti-cancer therapy and gain great clinic outcoming for their high efficiency. However, recent studies showed that the PD-1/PD-L1 immunotherapy in some tumor patients was found to accelerate T cell-driven inflammatory and the progression of atherosclerotic lesions. This article reviews the research progression of PD-1/PD-L1 in tumors and atherosclerosis, and the possible mechanisms of anti-PD-1/PD-L1 immunotherapy increasing the risk of atherosclerotic lesions.

PD-1 and PD-L1 expression in cardiac transplantation

Programmed death-ligand 1 (PD-L1), a transmembrane protein and member of the CD28 T cell family is associated with lymphocyte activation.¹ PD-L1 expression is upregulated on activated antigen presenting cells such as monocytes, myeloid and dendritic cells.² When bound to its cognate receptor programmed cell death (PD-1), inhibition of immune responses including downregulation of T cell proliferation occurs.³ Mechanistically, such inhibition would be hypothetically favorable in the setting of a transplanted organ undergoing allograft rejection. However, there is a paucity of data addressing the role of PD-L1 and PD-1 expression in the human transplanted heart.

Up-Regulation of Donor Dendritic Cell PD-L1 Expression Reduced Recipient Lymphocyte Activation and Proliferation In Vitro

OBJECTIVE

To observe the effects of dendritic cells (DC) in donor C57BL/6 (H-2^b) micetransfected with recombinant adenovirus vector Ad-PD-L1 on proliferation and activation of lymphocytes in recipient DBA/2 (H-2^d) mice.

METHODS

The pSport 1-mSD274 plasmid containing the full-length PD-L1 cDNA of the mouse was digested and subcloned to the shuttle plasmid pShuttle-GFP-CMV(-), and then the adenovirus skeleton plasmid pAdxsi-GFP-CMV-PD-L1 was constructed by enzymolysis and ligation, transformed into DH5α sensitive bacteria, and screened for positive clones. After enzyme digestion, sequencing, and identification, 293 cells were transfected with liposome after linearization for packaging and amplification, and the virus was purified by cesium chloride density gradient centrifugation. DC of donor C57BL/6 mice were isolated, cultured, and divided into the following 3 groups: group A, adenovirus vector Ad-PD-L1 transfection group; group B, empty vector transfection group; and group C, control group. Western blot was used to detect the expression of PD-L1 in each group of cells after transfection. Isolate lymphocytes from recipient DBA/2 mice were labeled with carboxyfluorescein diacetate succinimidyl ester (CFSE) and mixed with DC of donor C57BL/6 mice with lymphocytes of recipient DBA/2 mice. Flow cytometry was performed to observe the proliferation of lymphocytes.

RESULTS

Digestion and sequencing confirmed that the recombinant adenovirus vector Ad-PD-L1 containing PD-L1 was successfully constructed. After transfection with DC of donor C57BL/6 mice, the expression of PD-L1 increased by 37% (P < .05), and the PD-L1 transfected DC and recipient DBA/2. Mouse lymphocytes were cocultured. Compared with the control group, the increased expression of PD-L1 significantly inhibited the proliferation and activation of lymphocytes. The lymphocyte proliferation of DBA/2 mice decreased by 41% (P < .01).

CONCLUSION

The recombinant adenovirus vector Ad-PD-L1 containing the mouse PD-L1 gene was successfully constructed. After transfection with dendritic cells of donor C57BL/6 mice, PD-1/PD-L1 inhibited lymphocytes proliferation and activation of recipient DBA/2 mice through costimulatory pathway.

Delicate Role of PD-L1/PD-1 Axis in Blood Vessel Inflammatory Diseases: Current Insight and Future Significance

Immune checkpoint molecules are the antigen-independent generator of secondary signals that aid in maintaining the homeostasis of the immune system. The programmed death ligand-1 (PD-L1)/PD-1 axis is one among the most extensively studied immune-inhibitory checkpoint molecules, which delivers a negative signal for T cell activation by binding to the PD-1 receptor. The general attributes of PD-L1's immune-suppressive qualities and novel mechanisms on the barrier functions of vascular endothelium to regulate blood vessel-related inflammatory diseases are concisely reviewed. Though targeting the PD-1/PD-L1 axis has received immense recognition-the Nobel Prize in clinical oncology was awarded in the year 2018 for this discovery-the use of therapeutic modulating strategies for the PD-L1/PD-1 pathway in chronic inflammatory blood vessel diseases is still limited to experimental models. However, studies using clinical specimens that support the role of PD-1 and PD-L1 in patients with underlying atherosclerosis are also detailed. Of note, delicate balances in the expression levels of PD-L1 that are needed to preserve T cell immunity and to curtail acute as well as chronic infections in underlying blood vessel diseases are discussed. A significant link exists between altered lipid and glucose metabolism in different cells and the expression of PD-1/PD-L1 molecules, and its possible implications on vascular inflammation are justified. This review summarizes the most recent insights concerning the role of the PD-L1/PD-1 axis in vascular inflammation and, in addition, provides an overview exploring the novel therapeutic approaches and challenges of manipulating these immune checkpoint proteins, PD-1 and PD-L1, for suppressing blood vessel inflammation.

Immune Checkpoint Therapies for Melanoma

Immunotherapy with immune checkpoint inhibition has dramatically changed the treatment of melanoma. Immune checkpoint inhibitors targeting cytotoxic T-lymphocyte-associated protein 4 and programmed cell death protein 1 are approved for the treatment of advanced melanoma alone and in combination. In addition, these agents are approved for use in high-risk resected stage III melanoma in the adjuvant setting. Clinical trials testing the combination of immune checkpoint inhibition with other therapies and novel immunotherapies continue. This article reviews the current literature on approved uses of immune checkpoint inhibition in melanoma and discusses ongoing trials and future directions.

Vascular toxic effects of cancer therapies

Cancer therapies can lead to a broad spectrum of cardiovascular complications. Among these, cardiotoxicities remain of prime concern, but vascular toxicities have emerged as the second most common group. The range of cancer therapies with a vascular toxicity profile and the clinical spectrum of vascular toxic effects are quite broad. Historically, venous thromboembolism has received the greatest attention but, over the past decade, the arterial toxic effects, which can present as acute vasospasm, acute thrombosis and accelerated atherosclerosis, of cancer therapies have gained greater recognition. This Review focuses on these types of cancer therapy-related arterial toxicity, including their mechanisms, and provides an update on venous thromboembolism and pulmonary hypertension associated with cancer therapies. Recommendations for the screening, treatment and prevention of vascular toxic effects of cancer therapies are outlined in the context of available evidence and society guidelines and consensus statements. The shift towards greater awareness of the vascular toxic effects of cancer therapies has further unveiled the urgent needs in this area in terms of defining best clinical practices. Well-designed and well-conducted clinical studies and registries are needed to more precisely define the incidence rates, risk factors, primary and secondary modes of prevention, and best treatment modalities for vascular toxicities related to cancer therapies. These efforts should be complemented by preclinical studies to outline the pathophysiological concepts that can be translated into the clinic and to identify drugs with vascular toxicity potential even before their widespread clinical use.

PD-1/PD-L1 in cardiovascular disease

The PD-1/PD-L1 coinhibitory pathway has critical roles in the immune response and autoimmunity via the regulation of T cell activity. Excessive activity and high expression of this pathway suppresses the function of T cells and immunity. Recent research has indicated that tumour cells express high levels of PD-L1, which has an immunosuppressive effect and can result in treatment failure. Anti-PD-L1 or anti-PD-1 agents have well-established beneficial effects on mortality and quality of life in cancer patients. Based on the regulatory effects and therapeutic value of the PD-1/PD-L1 pathway in malignant disorders, we propose that it also regulates cell immunity and in CHD and atherosclerosis. Low expression level of PD-1/ PD-L1 or anti-PD-1/PD-L1 therapy accelerates the immune processes in CHD and aggravates disease according to numerous studies. A few studies have provided strong evidence that changes in the expression levels of PD-1 or PD-L1 can alter the degree of inflammation and the state of coronary plaques in atherosclerosis. In this review, we summarise the alterations of the PD-1/PD-L1 pathway and discuss its role in CHD.

Immunotherapy Toxicity

The development of immunotherapy to target cancer has led to improved treatment of many types of malignancy. The immune checkpoint inhibitors are a class of medications that block cell signaling and allow the immune system to recognize and attack cancer cells. CTLA-4, PD-1, and PD-L1 inhibitors have been approved as treatment options in many different types of localized and advanced malignancies. Immune checkpoint inhibitors can be associated with unique side effects known as immune-related adverse events. Side effects most commonly occur in the skin, gastrointestinal tract, lung, and endocrine glands but can affect other organ systems as well.

Arterial events in cancer patients-the case of acute coronary thrombosis

Patients with cancer are at high risk for both venous and arterial thrombotic complications. A variety of factors account for the greater thrombotic risk, including the underlying malignancy and numerous cancer-directed therapies. The occurrence of an acute thrombotic event in patients with cancer is associated with substantial morbidity and mortality. Acute coronary syndrome (ACS) represents a particularly important cardiovascular complication in cancer patients. With cardio-vascular risk factors becoming more prevalent in an aging cancer population that is surviving longer, questions pertaining to the appropriate management of vascular toxicity are likely to assume even greater value in the coming years. In this article, we review the current understanding of ACS in patients with cancer. The predisposition to thrombosis in a malignant host and the cancer treatments most commonly associated with vascular toxicity are reviewed. Risk prediction and management strategies are discussed, and discrepancies in the clinical evidence are highlighted.

Immune-checkpoint inhibitors to treat cancers in specific immunocompromised populations: a critical review

INTRODUCTION

Because of their efficacy against numerous cancers, immune-checkpoint inhibitors (ICIs), anti-cytotoxic T-lymphocyte antigen-4, and anti-programmed cell death monoclonal antibodies are being used ever more often in oncology. However, some patients were excluded from clinical trials because of their comorbidities despite their potentially higher cancer frequencies, as is the case for immunocompromised patients. Areas covered: We analyzed reported preclinical and clinical information and evaluated the risk/benefit ratio for four immunocompromised populations: people living with human immunodeficiency virus (PLHs), solid-organ transplant recipients, recipients of hematopoietic stem-cell allografts, and patients with autoimmune diseases. Expert commentary: Information available in the literature is fragmentary and scarce, making it difficult to evaluate the risk/benefit ratio. It can, nonetheless, be noted that ICI use in PLHs seems possible. For solid-organ transplant recipients, the risk for the graft seems elevated. For the other two populations, it is difficult to conclude at this time.

The Costimulatory Pathways and T Regulatory Cells in Ischemia-Reperfusion Injury: A Strong Arm in the Inflammatory Response?

Costimulatory molecules have been identified as crucial regulators in the inflammatory response in various immunologic disease models. These molecules are classified into four different families depending on their structure. Here, we will focus on various ischemia studies that use costimulatory molecules as a target to reduce the inherent inflammatory status. Furthermore, we will discuss the relevant role of T regulatory cells in these inflammatory mechanisms and the costimulatory pathways in which they are involved.

ATVB Distinguished Scientist Award: How Costimulatory and Coinhibitory Pathways Shape Atherosclerosis

OBJECTIVE

Immune cells play a critical role in atherosclerosis. Costimulatory and coinhibitory molecules of the tumor necrosis factor receptor and CD28 immunoglobulin superfamilies not only shape T-cell and B-cell responses but also have a major effect on antigen-presenting cells and nonimmune cells.

APPROACH AND RESULTS

Pharmacological inhibition or activation of costimulatory and coinhibitory molecules and genetic deletion demonstrated their involvement in atherosclerosis. This review highlights recent advances in understanding how costimulatory and coinhibitory pathways shape the immune response in atherosclerosis.

CONCLUSIONS

Insights gained from costimulatory and coinhibitory molecule function in atherosclerosis may inform future therapeutic approaches.

A Century of Radiation Therapy and Adaptive Immunity

The coming of age for immunotherapy (IT) as a genuine treatment option for cancer patients through the development of new and effective agents, in particular immune checkpoint inhibitors, has led to a huge renaissance of an old idea, namely to harness the power of the immune system to that of radiation therapy (RT). It is not an overstatement to say that the combination of RT with IT has provided a new conceptual platform that has re-energized the field of radiation oncology as a whole. One only has to look at the immense rise in sessions at professional conferences and in grant applications dealing with this topic to see its emergence as a force, while the number of published reviews on the topic is staggering. At the time of writing, over 97 clinical trials have been registered using checkpoint inhibitors with RT to treat almost 7,000 patients, driven in part by strong competition between pharmaceutical products eager to find their market niche. Yet, for the most part, this enthusiasm is based on relatively limited recent data, and on the clinical success of immune checkpoint inhibitors as single agents. A few preclinical studies on RT-IT combinations have added real value to our understanding of these complex interactions, but many assumptions remain. It seems therefore appropriate to go back in time and pull together what actually has been a long history of investigations into radiation and the immune system (Figure 1) in an effort to provide context for this interesting combination of cancer therapies.

The intragraft microenvironment as a central determinant of chronic rejection or local immunoregulation/tolerance

PURPOSE OF REVIEW

Chronic rejection is associated with persistent mononuclear cell recruitment, endothelial activation and proliferation, local tissue hypoxia and related biology that enhance effector immune responses. In contrast, the tumor microenvironment elicits signals/factors that inhibit effector T cell responses and rather promote immunoregulation locally within the tissue itself. The identification of immunoregulatory check points and/or secreted factors that are deficient within allografts is of great importance in the understanding and prevention of chronic rejection.

RECENT FINDINGS

The relative deficiency of immunomodulatory molecules (cell surface and secreted) on microvascular endothelial cells within the intragraft microenvironment, is of functional importance in shaping the phenotype of rejection. These regulatory molecules include coinhibitory and/or intracellular regulatory signals/factors that enhance local activation of T regulatory cells. For example, semaphorins may interact with endothelial cells and CD4 T cells to promote local tolerance. Additionally, metabolites and electrolytes within the allograft microenvironment may regulate local effector and regulatory cell responses.

SUMMARY

Multiple factors within allografts shape the microenvironment either towards local immunoregulation or proinflammation. Promoting the expression of intragraft cell surface or secreted molecules that support immunoregulation will be critical for long-term graft survival and/or alloimmune tolerance.

PD-1/PD-L1 Interaction Maintains Allogeneic Immune Tolerance Induced by Administration of Ultraviolet B-Irradiated Immature Dendritic Cells

Our previous study demonstrated that transfusion of ultraviolet B-irradiated immature dendritic cells (UVB-iDCs) induced alloantigen-specific tolerance between two different strains of mice. Programmed death-1 (PD-1) and programmed death ligand-1 (PD-L1) have been suggested to play an important role in maintaining immune tolerance. In the present study, we seek to address whether PD-1/PD-L1 plays a role in the maintenance of UVB-iDC-induced tolerance. We first observe that the UVB-iDC-induced alloantigen-specific tolerance can be maintained for over 6 weeks. Supporting this, at 6 weeks after tolerance induction completion, alloantigen-specific tolerance is still able to be transferred to syngeneic naïve mice through adoptive transfer of CD4+ T cells. Furthermore, skin transplantation study shows that the survival of allogeneic grafts is prolonged in those tolerant recipients. Further studies show that PD-1/PD-L1 interaction is essential for maintaining the induced tolerance as blockade of PD-1/PD-L1 by anti-PD-L1 antibodies largely breaks the tolerance at both cellular and humoral immunological levels. Importantly, we show that PD-1/PD-L1 interaction in tolerant mice is also essential for controlling alloantigen-responding T cells, which have never experienced alloantigens. The above findings suggest that PD-1/PD-L1 plays a crucial role in maintaining immune tolerance induced by UVB-iDCs, as well as in actively controlling effector T cells specific to alloantigens.

Upregulation of Programmed Death-1 and Its Ligand in Cardiac Injury Models: Interaction with GADD153

Purpose

Programmed Death-1 (PD-1) and its ligand, PD-L1, are regulators of immune/ inflammatory mechanisms. We explored the potential involvement of PD-1/PD-L1 pathway in the inflammatory response and tissue damage in cardiac injury models.

Experimental Design

Ischemic-reperfused and cryoinjured hearts were processed for flow cytometry and immunohistochemical studies for determination of cardiac PD-1 and PD-L1 in the context of assessment of the growth arrest- and DNA damage-inducible protein 153 (GADD153) which regulates both inflammation and cell death. Further, we explored the potential ability of injured cardiac cells to influence proliferation of T lymphocytes.

Results

The isolated ischemic-reperfused hearts displayed marked increases in expression of PD-1 and PD-L1 in cardiomyocytes; however, immunofluorescent studies indicate that PD-1 and PD-L1 are not primarily co-expressed on the same cardiomyocytes. Upregulation of PD-1/PD-L1 was associated with a) marked increases in GADD153 and interleukin (IL)-17 but a mild increase in IL-10 and b) disruption of mitochondrial membrane potential (ψ_m) as well as apoptotic and necrotic cell death. Importantly, while isotype matching treatment did not affect the aforementioned changes, treatment with the PD-L1 blocking antibody reversed those effects in association with marked cardioprotection. Further, ischemic-reperfused cardiac cells reduced proliferation of T lymphocytes, an effect partially reversed by PD-L1 antibody. Subsequent studies using the cryoinjury model of myocardial infarction revealed significant increases in PD-1, PD-L1, GADD153 and IL-17 positive cells in association with significant apoptosis/necrosis.

Conclusions

The data suggest that upregulation of PD-1/PD-L1 pathway in cardiac injury models mediates tissue damage likely through a paracrine mechanism. Importantly, inhibition of T cell proliferation by ischemic-reperfused cardiac cells is consistent with the negative immunoregulatory role of PD-1/PD-L1 pathway, likely reflecting an endogenous cardiac mechanism to curtail the deleterious impact of infiltrating immune cells to the damaged myocardium. The balance of these countervailing effects determines the extent of cardiac injury.

3-[(dodecylthiocarbonyl)methyl]-glutarimide attenuates graft arterial disease by suppressing alloimmune responses and vascular smooth muscle cell proliferation

BACKGROUND

Graft arterial disease (GAD) is a major cause of late graft loss after organ transplantation. Alloimmune responses and vascular remodeling eventually cause the transplant organ to develop GAD. In this study, we aimed to limit the development of GAD by inhibiting alloimmune responses and vascular smooth muscle cell (VSMC) proliferation with a new compound, 3-[(dodecylthiocarbonyl)methyl]-glutarimide ([DTCM]-glutarimide), in a murine cardiac model of GAD.

METHODS

The hearts from B6.CH-2 mice were transplanted into C57BL/6 mouse recipients to examine the extent of GAD. The recipients were treated with either vehicle or DTCM-glutarimide intraperitoneally (40 mg/kg per day) for 4 weeks.

RESULTS

The administration of DTCM-glutarimide attenuated GAD formation (luminal occlusion: 37.9 ± 5.9% vs 14.8 ± 5.4%, P < 0.05) by inhibiting the number of graft-infiltrating cells and decreasing alloreactive interferon (IFN)-γ production compared with control mice, as measured by the Enzyme-linked ImmunoSpot assay. In vitro, VSMCs proliferated on stimulation with either basic fibroblast growth factor or IFN-γ and splenocytes after transplantation, but the addition of DTCM-glutarimide resulted in the inhibition of VSMC proliferation. Moreover, DTCM-glutarimide suppressed cyclin D1 expression and inhibited cell cycle progression from G1 to S in VSMCs.

CONCLUSIONS

The compound DTCM-glutarimide suppressed GAD development by inhibiting not only alloimmune responses but also VSMC proliferation in the graft.

Acute and chronic rejection: compartmentalization and kinetics of counterbalancing signals in cardiac transplants

Acute and chronic rejection impact distinct compartments of cardiac allografts. Intramyocardial mononuclear cell infiltrates define acute rejection, whereas chronic rejection affects large arteries. Hearts transplanted from male to female C57BL/6 mice undergo acute rejection with interstitial infiltrates at 2 weeks that resolve by 6 weeks when large arteries develop arteriopathy. These processes are dependent on T cells because no infiltrates developed in T cell-deficient mice and transfer of CD4 T cells restored T cell as well as macrophage infiltrates and ultimately neointima formation. Markers of inflammatory macrophages were up-regulated in the interstitium acutely and decreased as markers of wound healing macrophages increased chronically. Programmed cell death protein, a negative costimulator, and its ligand PDL1 were up-regulated in the interstitium during resolution of acute rejection. Blocking PDL1:PD1 interactions in the acute phase increased interstitial T cell infiltrates. Toll-like receptor (TLR) 4 and its endogenous ligand hyaluronan were increased in arteries with neointimal expansion. Injection of hyaluronan fragments increased intragraft production of chemokines. Our data indicate that negative costimulatory pathways are critical for the resolution of acute interstitial infiltrates. In the arterial compartment recognition of endogenous ligands including hyaluronan by the innate TLRs may support the progression of arteriopathy.

Immune-mediated vascular injury and dysfunction in transplant arteriosclerosis

Solid organ transplantation is the only treatment for end-stage organ failure but this life-saving procedure is limited by immune-mediated rejection of most grafts. Blood vessels within transplanted organs are targeted by the immune system and the resultant vascular damage is a main contributor to acute and chronic graft failure. The vasculature is a unique tissue with specific immunological properties. This review discusses the interactions of the immune system with blood vessels in transplanted organs and how these interactions lead to the development of transplant arteriosclerosis, a leading cause of heart transplant failure.

DCs sensitized with mPD-L1-Ig fusion protein improve the effect of heart transplantation in mice by promoting the generation of T-reg cells

PURPOSE

To detect the effects of DCs sensitized by mPD-L1-Ig fusion protein in heart transplantation in mice as well as its mechanisms.

METHOD

The mPD-L1-IgG1 construct was used to build a yeast expression system, and the fusion protein was expressed by secretion after the transfection of the GS115 yeast strain, purified by affinity chromatography and ion exchange chromatography, and assayed by SDS-PAGE and Western blot. The ability of the fusion protein to bind to the acceptor PD-1 was tested by ELISA, and the ability of the fusion protein to inhibit the function of T cells was tested by mixed lymphocyte reaction (MLR).

RESULTS

We used the new PD-L1-IgG1 fusion protein to sensitize imDCs and maintained the immature state of DCs, so as to induce stable and effective immune tolerance to heart transplantation. After the treatment of DCs by mPD-L1-Ig in vitro, the levels of CD80, CD40 and I-Ab expression on DCs are relatively weaker, the ability of DCs to stimulates the proliferation of allogeneic spleen T cells was significantly decreased (P<0.01), and the levels of Th1 (IL-2, IFN-γ) and Th2 (IL-4, IL-10) secreted by induced allogeneic T cells were significantly decreased (P<0.01). An in vivo experiment also revealed that DCs sensitized by mPD-L1-IgG1 could prolong the survival time of a transplanted heart to 17.8±1.12days, and alleviate the pathological change of the cardiac allografts compared with other three groups.

CONCLUSION

DCs sensitized by the yeast-expressed mPD-L1-Ig fusion protein are shown to alleviate the cardiac allograft rejection in mice.

Tubular cell HIV-entry through apoptosed CD4 T cells: a novel pathway

We hypothesized that HIV-1 may enter tubular cells by phagocytosis of apoptotic fragments of HIV-1-infected T cells infiltrating tubular interstitium. The study was designed to evaluate the interaction of programmed death-1 (PD-1) receptors on CD4 T cells and programmed death ligand-1 (PD-L1) on tubular cells (HK2 and HRPTEC, primary tubular cells). Co-cultivation of HIV-1 infected lymphocytes (HIV-LY) with HK2s/HRPTECs resulted in T cell apoptosis, uptake of the apoptosed HIV-LY by HK2s/HRPTECs, tubular cell activation and HIV expression. Cytochalasin-B inhibited tubular cell HIV-LY uptake and anti-PD-L1 antibody inhibited HIV-LY apoptosis and tubular cell HIV-LY uptake, activation and HIV expression. These observations do indicate induction of apoptosis of T cells due to interaction of PD-1 and PD-L1 upon co-cultivation and subsequent phygocytosis of HIV-laden apoptotic bodies by tubular cells and thus the transfer of HIV-1 into tubular cells. These findings identify a novel pathway that facilitates HIV-1 entry into tubular cell.

Effects of immunoglobulin to prevent coronary allograft vasculopathy in heart transplantation

INTRODUCTION

Although 100,000 cardiac transplants have been performed, coronary allograft vasculopathy (CAV), which is a phenomenon of chronic rejection, is still a serious problem.

AREAS COVERED

Several adhesion molecules, cytokines, and chemokines play a critical role in the process. Recent investigations have proved some promising methodologies for preventing or treating rejection. Although immunoglobulins are known to be an effective treatment in many diseases, their effect on cardiac transplantation or CAV is to be elucidated.

EXPERT OPINION

In this review article, we described some promising methodologies that use immunoglobulins to prevent CAV. Immunoglobulins may be used to prevent CAV.

Antibodies against B7-DC with differential binding properties exert opposite effects

Programmed cell death 1 (PD-1) is an immunoregulatory receptor on T cells that binds two ligands, B7-H1 and B7-DC. Although accumulating reports suggest a critical role for the B7-H1:PD-1 pathway in peripheral tolerance, the actual involvement of B7-DC has not been well confirmed. Here, we established a new MAb against mouse B7-DC (MIH37) and compared its functional properties with a previously established anti-B7-DC MAb (TY25). Binding analyses using flow cytometry demonstrated that MIH37 showed an approximately four-fold higher binding affinity to B7-DC and stronger inhibitory effects on B7-DC:PD-1 binding. In contrast to the effects of TY25, treatment with MIH37 at both sensitization and challenge inhibited hapten-induced contact hypersensitivity reactions. Furthermore, the addition of MIH37 inhibited OVA-specific T cell responses in vitro. The inhibitory effects of MIH37 were counteracted by co-blockade with PD-1 and absent in PD-1-deficient mice, suggesting PD-1-dependent action of MIH37. Our present results suggest that greater complexities of PD-1-mediated functions are induced via ligand binding for controlling immunity and tolerance.

Trophoblast debris modulates the expression of immune proteins in macrophages: a key to maternal tolerance of the fetal allograft?

Interactions between maternal immune cells and the placenta are of substantial interest since diseases of pregnancy, such as recurrent miscarriage, villitis of unknown etiology and preeclampsia may arise due to inadequate adaptation of the maternal immune system. During normal pregnancy trophoblast debris is shed from the placenta into the maternal blood in large quantities. This trophoblast debris is then rapidly cleared from the maternal circulation. In this study, we exposed trophoblast debris generated from an in vitro placental explant model to peripheral blood-derived macrophages and quantified a variety of molecules that are important in immune responses by ELISA or flow cytometry. Phagocytosis of trophoblast debris resulted in reduced cell-surface expression of MHC-II molecules, the costimulatory molecules (CD80, CD86, CD40 and B7H3), monocyte chemoattractant protein-1 (MCP-1), inter-cellular adhesion molecule 1 (ICAM-1) and IL-8 receptors in macrophages while the expression of programmed death-1 ligand 1 (PD-L1) was upregulated. In addition, phagocytosis of trophoblast debris induced the secretion of the anti-inflammatory cytokines IL-10, IL6 and IL1Ra and decreased the secretion of pro-inflammatory cytokines IL-1β, IL12p70 and IL-8 by macrophages. Phagocytosis of trophoblast debris also increased macrophage expression of the immunosuppressive enzyme indoleamine 2,3-dioxygenase (IDO). We have shown that phagocytosis of trophoblast debris from normal placentae alters the phenotype of macrophages such that they are likely to deviate maternal immune responses towards tolerance and away from inflammation. This may be one of the mechanisms that allow the human fetal allograft to survive in direct contact with the maternal immune system.

PD-1 protects against inflammation and myocyte damage in T cell-mediated myocarditis

PD-1, a member of the CD28 family of immune regulatory molecules, is expressed on activated T cells, interacts with its ligands, PD-L1/B7-H1 and PD-L2/B7-DC, on other cells, and delivers inhibitory signals to the T cell. We studied the role of this pathway in modulating autoreactive T cell responses in two models of myocarditis. In a CD8(+) T cell-mediated adoptive transfer model, we found that compared with Pd1(+/+) CD8(+) T cells, Pd1(-/-) CD8(+) T cells cause enhanced disease, with increased inflammatory infiltrate, particularly rich in neutrophils. Additionally, we show enhanced proliferation in vivo and enhanced cytotoxic activity of PD-1-deficient T lymphocytes against myocardial endothelial cells in vitro. In experimental autoimmune myocarditis, a disease model dependent on CD4(+) T cells, we show that mice lacking PD-1 develop enhanced disease compared with wild-type mice. PD-1-deficient mice displayed increased inflammation, enhanced serum markers of myocardial damage, and an increased infiltration of inflammatory cells, including CD8(+) T cells. Together, these studies show that PD-1 plays an important role in limiting T cell responses in the heart.

T cell costimulatory and coinhibitory pathways in vascular inflammatory diseases

A broad array of evidence indicates that T lymphocytes make significant contributions to vascular inflammation in the setting of atherosclerotic disease, hypertension, autoimmune vasculitis, and other disorders. Experimental data show that costimulatory and coinhibitory pathways involving molecules of the B7-CD28 and TNF–TNFR families regulate T cell responses that promote vascular disease. Antigen presenting cells (APCs) display both peptide–major histocompatibility complex antigen and costimulators or coinhibitors to T cells. Two major types of APCs, dendritic cells (DCs) and macrophages, are present in significant numbers in the walls of arteries affected by atherosclerosis and arteritis, and some DCs are present in normal arteries. Costimulatory and coinhibitory molecules expressed by these vascular APCs can contribute to the activation or inhibition of effector T cells within the arterial wall. Vascular DCs may also be involved in transport of antigens to secondary lymphoid organs, where they activate or tolerize naïve T cells, depending on the balance of costimulators and coinhibitors they express. Costimulatory blockade is already an approved therapeutic approach to treat autoimmune disease and prevent transplant rejection. Preclinical models suggest that costimulatory blockade may also be effective in treating vascular disease. Experiential data in mice show that DCs pulsed with the appropriate antigens and treated in a way that reduces costimulatory capacity can reduce atherosclerotic disease, presumably by inducing T cell tolerance. Progress in treating vascular disease by immune modulation will require a more complete understanding of the functions of different costimulatory and coinhibitory pathways and the different subsets of vascular APCs involved.

Overexpression of programmed death ligand 1 in dendritic cells inhibits allogeneic lymphocyte activation in mice

BACKGROUND

Co-stimulatory molecules are pivotal for T cell activation. It is increasingly recognized that programmed death ligand 1 (PD-L1) is a novel co-stimulatory molecule, which raises the question as to whether PD-L1 regulates T cell responses. This study aimed to investigate the inhibitory effects of PD-L1 on T cell activation.

MATERIALS AND METHODS

We constructed a transgenic vector containing the complete PD-L1 gene, which interacts with the inhibitory receptor PD-1 in T cell-mediated immune activation. Donor dendritic cells (DCs) derived from C57BL/6 mice were transfected with PD-L1 and mixed with allogeneic, recipient T cells from BALB/c mice. The T cell activation was determined by the MTT assay and T cell proliferation was determined using carboxyfluoroscein succinimidyl ester (CFSE)-labeling following in vitro mixed leukocyte reactions.

RESULTS

The expression of PD-L1 protein in PD-L1-transfected DCs was 47.97% ± 1.06%, compared with 4.66% ± 0.76% and 5.30% ± 0.60% in blank and negative controls, respectively (P < 0.05). PD-L1 protein was effectively expressed in DCs. Furthermore, in DCs stably transfected with PD-L1, T cell activation was significantly suppressed and T cell proliferation rate was decreased by 35% compared with untransfected DCs (P < 0.05).

CONCLUSION

PD-L1 delivers an immunoinhibitory signal, suppressing T cell activation. Overexpression of PD-L1 signaling induces tolerance, which presents a promising immunotherapeutic approach for long-term graft acceptance.

Toll-like receptors and macrophage activation in atherosclerosis

Atherosclerosis is a multi-factorial inflammatory disease and is the primary initiator of coronary artery and cerebrovascular disease. Initially believed to be exclusively lipid-driven, recent evidence demonstrates that inflammation is a significant driving force of the disease. Cellular components of innate immunity, for example monocytes and macrophages, play a predominant role in atherosclerosis. Toll-like receptors (TLRs) are the most characterised innate immune receptors and recent evidence demonstrates an important role in atherogenesis. Engagement of TLRs results in the transcription of pro-inflammatory cytokines, foam cell formation and activation of adaptive immunity. Recently they have also been implicated in protection from vascular disease. In this review, we detail the role of the innate immune system, specifically macrophages and TLR signalling, in atherosclerosis and acute cardiovascular complications, and thereby identify the potential of TLRs to act as therapeutic targets.

Effect of adiponectin on cardiac allograft vasculopathy

BACKGROUND

The role of adiponectin (APN), an adipose tissue-specific secretory protein, on chronic rejection after cardiac transplantation in APN-sense transgenic mice (APN-SE) was evaluated.

METHODS AND RESULTS

Heterotopic cardiac transplantation in major histocompatibility complex class II-mismatched mice was performed. B6.C-H-2(bm12)KhEg (Bm12) hearts were transplanted into APN-SE, and allografts were harvested at 8 weeks after transplantation. Quantitative polymerase chain reaction (PCR) and immunohistochemical staining showed that the expression of both AdipoR1 and AdipoR2 was induced in APN-SE recipients. Neointimal hyperplasia was significantly decreased in allografts transplanted into APN-SE (luminal occlusion, 8.9 ± 2.2%) compared to those transplanted into controls (49.4 ± 10.5%; P=0.011). APN-SE showed significantly reduced mRNA levels of interferon (IFN)-γ, tumor necrosis factor (TNF)-α, interleukin (IL)-2, IL-6, and monocyte chemoattractant protein-1 (MCP-1) by quantitative PCR. Western blot analysis revealed that the protein levels of IFN-γ and MCP-1 were reduced in APN-SE recipients. Proliferation of smooth muscle cells stimulated with activated T cells was suppressed by APN addition, and this effect was canceled by treatment with an adenosine monophosphate-activated protein kinase (AMPK) inhibitor.

CONCLUSIONS

APN plays a critical role in the attenuation of chronic rejection by suppressing inflammatory cytokine and chemokine expression and enhancing APN receptor expression. APN plays a beneficial role in reducing the progression of cardiac allograft vasculopathy through the AMPK pathway.

Innate immunity and monocyte-macrophage activation in atherosclerosis

Innate inflammation is a hallmark of both experimental and human atherosclerosis. The predominant innate immune cell in the atherosclerotic plaque is the monocyte-macrophage. The behaviour of this cell type within the plaque is heterogeneous and depends on the recruitment of diverse monocyte subsets. Furthermore, the plaque microenvironment offers polarisation and activation signals which impact on phenotype. Microenvironmental signals are sensed through pattern recognition receptors, including toll-like and NOD-like receptors - the latter of which are components of the inflammasome - thus dictating macrophage behaviour and outcome in atherosclerosis. Recently cholesterol crystals and modified lipoproteins have been recognised as able to directly engage these pattern recognition receptors. The convergent role of such pathways in terms of macrophage activation is discussed in this review.

PPAR-γ signaling and IL-5 inhibition together prevent chronic rejection of MHC Class II-mismatched cardiac grafts

BACKGROUND

Chronic rejection can prevent long-term survival of organ transplants. Although the beneficial effects of peroxisome proliferator-activated receptor-gamma (PPAR-γ) in reducing graft rejection have been reported, the details of the underlying mechanisms remain unclear, especially in the context of modulating cellular infiltration and preventing vasculopathy and interstitial fibrosis.

METHODS

The therapeutic effects of the PPAR-γ agonist, rosiglitazone, combined with anti-interleukin-5 are explored in a mouse model of MHC Class II-histoincompatible cardiac transplantation.

RESULTS

Rosiglitazone treatment alone marginally increased long-term survival and reduced CD8 T-cell infiltration and vasculopathy in the grafts. However, there was no reduction in collagen deposition and interleukin (IL)-4, IL-5 and eosinophil infiltration were increased. Anti-IL-5 antibody treatment alone reduced eosinophil infiltration and collagen deposition, but had no effect on CD8 T-cell infiltration or vasculopathy. Combined treatment with anti-IL-5 antibody and rosiglitazone prevented graft rejection. Furthermore, rosiglitazone treatment increased adiponectin receptor II expression in grafts and on dendritic cells and T cells in vitro. Graft survival correlated with increased expression in grafts of the inhibitory molecule PD-L1.

CONCLUSIONS

The findings obtained increase the knowledge on the mode of action of rosiglitazone in promoting the survival of MHC Class II-mismatched cardiac transplants in which the CD8 T cells and eosinophils play key roles. PPAR-γ signaling combined with IL-5 blockade prevents graft rejection.

Unexpected protective role for Toll-like receptor 3 in the arterial wall

The critical role of Toll-like receptors (TLRs) in mammalian host defense has been extensively explored in recent years. The capacity of about 10 TLRs to recognize conserved patterns on many bacterial and viral pathogens is remarkable. With so few receptors, cross-reactivity with self-tissue components often occurs. Previous studies have frequently assigned detrimental roles to TLRs, in particular to TLR2 and TLR4, in immune and cardiovascular disease. Using human and murine systems, we have investigated the consequence of TLR3 signaling in vascular disease. We compared the responses of human atheroma-derived smooth muscle cells (AthSMC) and control aortic smooth muscle cells (AoSMC) to various TLR ligands. AthSMC exhibited a specific increase in TLR3 expression and TLR3-dependent functional responses. Intriguingly, exposure to dsRNA in vitro and in vivo induced increased expression of both pro- and anti-inflammatory genes in vascular cells and tissues. Therefore, we sought to assess the contribution of TLR3 signaling in vivo in mechanical and hypercholesterolemia-induced arterial injury. Surprisingly, neointima formation in a perivascular collar-induced injury model was reduced by the systemic administration of the dsRNA analog Poly(I:C) in a TLR3-dependent manner. Furthermore, genetic deletion of TLR3 dramatically enhanced the development of elastic lamina damage after collar-induced injury. Accordingly, deficiency of TLR3 accelerated the onset of atherosclerosis in hypercholesterolemic ApoE(-/-) mice. Collectively, our data describe a protective role for TLR signaling in the vessel wall.