Learning from rejection: What transplantation teaches us about (other) vascular pathologies

Circulating de novo Donor Specific Antibodies and Carotid Intima-media Thickness in Pediatric Kidney Transplant Recipients, A Pilot Study

Background: The presence of circulating de novo donor specific anti-HLA antibodies (dnDSA) has been implicated in an immune-mediated form of accelerated systemic arteriosclerosis in adult heart and kidney transplant recipients, however this has not been previously investigated in pediatric kidney transplant recipients. Carotid intima-media thickness (CIMT) is a reliable method for detection of arteriosclerosis. We hypothesized that children who develop dnDSA after kidney transplant would have increased CIMT compared with those who remain dnDSA negative. Methods: A prospective, controlled pilot cohort study of 38 transplant patients and 20 healthy controls was conducted to investigate the association between CIMT and development of dnDSA after kidney transplant. CIMT, anthropometrics, blood pressure and lipid panel were measured at 1, 18, and 30 months post-transplant. DSA was checked at 6, 12, 18, 24 and 30 months post-transplant. CIMT of DSA positive transplant recipients was compared to DSA negative and controls. Results: Of the 38 transplant recipients, 7 patients developed dnDSA by 18-30 months post-transplant. Among 5 dnDSA positive patients who did not receive treatment for DSA prior to CIMT measurement (n=6 observations), the median CIMT was 0.505 mm (95% CI 0.454-0.560 mm) at 18-30 months post-transplant, compared to 0.455 mm (95% CI 0.440-0.470) in DSA negative transplant recipients (n = 54 observations of 30 patients) and 0.450 mm (95% CI 0.436-0.460) in the healthy controls (20 observations of 20 patients). Presence of dnDSA was independently associated with a 7.8% increase in CIMT compared to those without dnDSA (p=0.006), after adjusting for race, hypertension, dyslipidemia, and abdominal obesity. Conclusions: Development of dnDSA was associated with increased CIMT, an indicator of arteriosclerosis, in a cohort of dnDSA positive pediatric kidney transplant recipients. The association between dnDSA and CIMT was independent of traditional CV risk factors, including hypertension, dyslipidemia, and abdominal obesity.

Investigation of the expressions of MMPs and TIMPs between isogeneic and allogeneic rat aortic transplantation

The present study investigated the effects of matrix metalloproteinases (MMPs) and tissue inhibitor of metalloproteinases (TIMPs) in transplantation-associated arteriosclerosis by observing their expression in transplanted aortas in rats. Allogenic and isogenic abdominal aortic transplantations were performed and grafts were removed from the recipients at the designated time points (day 7, 14, 28 and 56 post transplantation). Hematoxylin and eosin staining, immunohistochemistry, immunofluorescence and western blot analysis were used to evaluate the grafts. Significant proliferation of the intima was observed in the allogenic transplantation groups (P<0.05). The expressions of MMPs and TIMPs in the allografts were significantly increased compared with the isografts, and the suppression of MMP2 in allografts reduced injury after transplantation. The present study concluded that the imbalance of MMPs and TIMPs led to the disturbance of synthesis and the degradation of the extracellular matrix and it may represent a key cause of chronic rejection.

Prolonged Cold Ischemia Time Results in Local and Remote Organ Dysfunction in a Murine Model of Vascularized Composite Transplantation

Vascularized composite allotransplantation (VCA) is a viable reconstructive option for complex tissue defects. Although grafts with a large muscular component may be uniquely susceptible to ischemia-reperfusion (I/R) syndrome, the safe cold ischemia time in VCA has not been established. We investigated the effects of cold ischemia on innate immune response and recipient survival in a murine orthotopic hindlimb transplantation model. Surprisingly, mice receiving grafts exposed to 6 h or longer of cold storage demonstrated reduced survival and massive elevations in serum creatinine, blood urea nitrogen, and creatine kinase, compared with 1 h of cold storage recipients. This was accompanied by progressive increase in macrophage and neutrophil cell infiltration in muscle biopsy specimens, altered platelet endothelial cell adhesion molecule-1 expression, and ultimate renal injury. Multiplex immunoassay analysis identified 21 cytokines in serum and 18 cytokines in muscle biopsy specimens that are likely essential in the complex response to I/R-triggered injury in VCA. In conclusion, this study, in a mouse model of orthotopic hindlimb transplantation, is the first to document that prolonged cold ischemia triggers progressive I/R injury with vascular endothelial damage and may lead to irrecoverable local and remote organ damage. These experimental findings are important in guiding future therapies for human VCA recipients.

Immunobiology in VCA

Transplantation of vascularized composite tissue is a relatively new field that is an amalgamation of experience in solid organ transplantation and reconstructive plastic and orthopedic surgery. What is novel about the immunobiology of VCA is the addition of tissues with unique immunologic characteristics such as skin and vascularized bone, and the nature of VCA grafts, with direct exposure to the environment, and external forces of trauma. VCAs are distinguished from solid organ transplants by the requirement of rigorous physical therapy for optimal outcomes and the fact that these procedures are not lifesaving in most cases. In this review, we will discuss the immunobiology of these systems and how the interplay can result in pathology unique to VCA as well as provide potential targets for therapy.

Gene expression profile in cardiovascular disease and preeclampsia: a meta-analysis of the transcriptome based on raw data from human studies deposited in Gene Expression Omnibus

INTRODUCTION

Cardiovascular disease (CVD) and preeclampsia (PE) share common clinical features. We aimed to identify common transcriptomic signatures involved in CVD and PE in humans.

METHODS

Meta-analysis of individual raw microarray data deposited in GEO, obtained from blood samples of patients with CVD versus controls and placental samples from women with PE versus healthy women with uncomplicated pregnancies. Annotation of cases versus control samples was taken directly from the microarray documentation. Genes that showed a significant differential expression in the majority of experiments were selected for subsequent analysis. Hypergeometric gene list analysis was performed using Bioconductor GOstats package. Bioinformatic analysis was performed in PANTHER.

RESULTS

Seven studies in CVD and 5 studies in PE were eligible for meta-analysis. A total of 181 genes were found to be differentially expressed in microarray studies investigating gene expression in blood samples obtained from patients with CVD compared to controls and 925 genes were differentially expressed between preeclamptic and healthy placentas. Among these differentially expressed genes, 22 were common between CVD and PE.

DISCUSSION

Bioinformatic analysis of these genes revealed oxidative stress, p-53 pathway feedback, inflammation mediated by chemokines and cytokines, interleukin signaling, B-cell activation, PDGF signaling, Wnt signaling, integrin signaling and Alzheimer disease pathways to be involved in the pathophysiology of both CVD and PE. Metabolism, development, response to stimulus, immune response and cell communication were the associated biologic processes in both conditions. Gene set enrichment analysis showed the following overlapping pathways between CVD and PE: TGF-β-signaling, apoptosis, graft-versus-host disease, allograft rejection, chemokine signaling, steroid hormone synthesis, type I and II diabetes mellitus, VEGF signaling, pathways in cancer, GNRH signaling, Huntingtons disease and Notch signaling.

CONCLUSION

CVD and PE share same common traits in their gene expression profile indicating common pathways in their pathophysiology.

Engineering of synthetic cellular microenvironments: implications for immunity

In this article, we discuss novel synthetic approaches for studying the interactions of cells with their microenvironment. Notably, critical cellular processes such as growth, differentiation, migration, and fate determination, are tightly regulated by interactions with neighboring cells, and the surrounding extracellular matrix. Given the huge complexity of natural cellular environments, and their rich molecular and physical diversity, the mission of understanding "environmental signaling" at a molecular-mechanistic level appears to be extremely challenging. To meet these challenges, attempts have been made in recent years to design synthetic matrices with defined chemical and physical properties, which, artificial though they may be, could reveal basic "design principles" underlying the physiological processes. Here, we summarize recent developments in the characterization of the chemical and physical properties of cell sensing and adhesion, as well as the design and use of engineered, micro- to nanoscale patterned and confined environments, for systematic, comprehensive modulation of the cells' environment. The power of these biomimetic surfaces to highlight environmental signaling events in cells, and in immune cells in particular, will be discussed.

Graft microvascular disease in solid organ transplantation

Alloimmune inflammation damages the microvasculature of solid organ transplants during acute rejection. Although immunosuppressive drugs diminish the inflammatory response, they do not directly promote vascular repair. Repetitive microvascular injury with insufficient regeneration results in prolonged tissue hypoxia and fibrotic remodeling. While clinical studies show that a loss of the microvascular circulation precedes and may act as an initiating factor for the development of chronic rejection, preclinical studies demonstrate that improved microvascular perfusion during acute rejection delays and attenuates tissue fibrosis. Therefore, preservation of a functional microvasculature may represent an effective therapeutic strategy for preventing chronic rejection. Here, we review recent advances in our understanding of the role of the microvasculature in the long-term survival of transplanted solid organs. We also highlight microvessel-centered therapeutic strategies for prolonging the survival of solid organ transplants.

Coronary cardiac allograft vasculopathy versus native atherosclerosis: difficulties in classification

Cardiac allograft vasculopathy is regarded as a progressive and diffuse intimal hyperplastic lesion of arteries and veins that leads to insidious vessel narrowing and to allograft ischemic disease, such as acute myocardial infarction or sudden cardiac death. The coronary lesions in transplanted hearts are considered as a particular type of arteriosclerosis with many similarities but also significant differences compared to native coronary atherosclerosis. It is particularly difficult for pathologists to systematically classify the lesions and to elucidate their origins, since over time, the allograft immune responses cause vascular pathology characterized by not only the onset of de novo fibrocellular lesions but also remodeling of already-existing native atherosclerotic lesions in the donor heart. Intraplaque hemorrhages, which result from newly formed leaky microvessels, may cause rapid increase of stenosis and generate a substrate for plaque destabilization. Comparing cardiac allograft vasculopathy from explanted hearts at autopsy with native coronary atherosclerosis from hearts removed at transplantation has revealed that ongoing intraplaque hemorrhages are also an important feature of cardiac allograft vasculopathy and may be important factors in the rapid progression of cardiac allograft vasculopathy.

Macrophages in solid organ transplantation

Macrophages are highly plastic hematopoietic cells with diversified functions related to their anatomic location and differentiation states. A number of recent studies have examined the role of macrophages in solid organ transplantation. These studies show that macrophages can induce allograft injury but, conversely, can also promote tissue repair in ischemia-reperfusion injury and acute rejection. Therapeutic strategies that target macrophages to improve outcomes in solid organ transplant recipients are being examined in preclinical and clinical models. In this review, we discuss the role of macrophages in different types of injury and rejection, with a focus on macrophage-mediated tissue injury, specifically vascular injury, repair and remodeling. We also discuss emerging macrophage-centered therapeutic opportunities in solid organ transplantation.