Recent advances in the immunology of chronic rejection

Intercellular transfer of MHC molecules in T cell alloimmunity and allotransplantation

After transplantation of allogeneic tissues and organs, recognition by recipient T cells of donor MHC molecules initiates the pro-inflammatory adaptive immune response leading to allograft rejection. T cell allorecognition has long been known to be mediated via two distinct pathways: the direct pathway in which T cells recognize intact allogeneic MHC molecules displayed on donor cells and the indirect pathway whereby T cells recognize donor MHC peptides processed and presented by recipient antigen-presenting cells (APCs). It is believed that direct allorecognition is the driving force behind early acute allograft rejection while indirect allorecognition is involved in chronic allograft rejection, a progressive condition characterized by graft vasculopathy and tissue fibrosis. Recently, we and others have reported that after transplantation of allogeneic skin and organs, donor MHC molecules are transferred from donor cells to the host's APCs via trogocytosis or extracellular vesicles. Recipient APCs having captured donor MHC molecules can either present them to T cells in their intact form on their surface (semi-direct pathway) or the form of peptides bound to self-MHC molecules (indirect pathway). The present article provides an overview of recent studies evaluating the role of intercellular exchange of MHC molecules in T cell alloimmunity and its contribution to allograft rejection and tolerance.

Pathways of Antigen Recognition by T Cells in Allograft Rejection

The adaptive immune response leading to the rejection of allogeneic transplants is initiated and orchestrated by recipient T cells recognizing donor antigens. T-cell allorecognition is mediated via 3 distinct mechanisms: the direct pathway in which T cells recognize allogeneic major histocompatibility complex (MHC) molecules on donor cells, the indirect pathway through which T cells interact with donor peptides bound with self-MHC molecules on recipient antigen-presenting cells, and the recently described semidirect pathway whereby T cells recognize donor MHC proteins on recipient antigen-presenting cells. In this article, we present a description of each of these allorecognition pathways and discuss their role in acute and chronic rejection of allogeneic transplants.

Properties of Poly (Lactic-co-Glycolic Acid) and Progress of Poly (Lactic-co-Glycolic Acid)-Based Biodegradable Materials in Biomedical Research

In recent years, biodegradable polymers have gained the attention of many researchers for their promising applications, especially in drug delivery, due to their good biocompatibility and designable degradation time. Poly (lactic-co-glycolic acid) (PLGA) is a biodegradable functional polymer made from the polymerization of lactic acid (LA) and glycolic acid (GA) and is widely used in pharmaceuticals and medical engineering materials because of its biocompatibility, non-toxicity, and good plasticity. The aim of this review is to illustrate the progress of research on PLGA in biomedical applications, as well as its shortcomings, to provide some assistance for its future research development.

Pattern of organ remodeling in chronic non-communicable diseases is due to endogenous regulations and falls under the category of Kauffman's self-organization: A case of arterial neointimal pathology

Clinical diagnosis is based on analysis of pathologic findings that may result in perceived patterns. The same is true for diagnostic pathology: Pattern analysis is a foundation of the histopathology-based diagnostic system and, in conjunction with clinical and laboratory findings, forms a basis for the classification of diseases. Any histopathology diagnosis is based on the explicit assumption that the same diseased condition should result in formation of the same (or highly similar) morphologic patterns in different individuals; it is a standard approach in microscopic pathology, including that of non-communicable chronic diseases with organ remodeling. During fifty years of examining diseased tissues under microscopy, I keep asking the same question: Why is a similarity of patterns expected for chronic organ remodeling? For infection diseases, xenobiotic toxicity and deficiencies forming an identical pathologic pattern in different individuals is understandable and logical: The same infection, xenobiotic, or deficiency strikes the same target, which results in identical pathology. The same is true for Mendelian diseases: The same mutations lead to the same altered gene expressions and the same pathologic pattern. But why does this regularity hold true for chronic diseases with organ remodeling? Presumable causes (or risk factors) for a particular chronic disease differ in magnitude and duration between individuals, which should result in various series of transformations. Yet, mysteriously enough, pathological remodeling in a particular chronic disease always falls into a main dominating pattern, perpetuating and progressing in a similar fashion in different patients. Furthermore, some chronic diseases of different etiologies and dissimilar causes/risk factors manifest as identical or highly similar patterns of pathologic remodeling. HYPOTHESIS: I hypothesize that regulations governing a particular organ's chronic remodeling were selected in evolution as the safest response to various insults and physiologic stress conditions. This hypothesis implies that regulations directing diseased chronic remodeling always preexist but normally are controlled; this control can be disrupted by a diverse range of non-specific signals, liberating the pathway for identical pathologic remodeling. This hypothesis was tested in an analysis of arterial neointimal formation, the identical pathology occurring in different diseases and pathological conditions: graft vascular disease in organ transplantation, in-stent restenosis, peripheral arterial diseases, idiopathic intimal hyperplasia, Kawasaki disease, coronary atherosclerosis and as reaction to drugs. The hypothesis suggests that arterial intimal cells are poised between only two alternative pathways: the pathway with controlled intimal cell proliferation or the pathway where such control is disrupted, ultimately leading to the progressive neointimal pathology. By this property the arterial neointimal formation constitutes a special case of Kauffman's self-organization. This new hypothesis gives a parsimonious explanation for identical pathological patterns of arterial remodeling (neointimal formation), which occurs in diseases of different etiologies and due to dissimilar causes/risk factors, or without any etiology and causes/risk factors at all. This new hypothesis also suggests that regulation facilitating intimal cell proliferation cannot be overwritten or annulled because this feature is vital for arterial differentiation, cell renewal, and integrity. This hypothesis suggests that studying numerous, and likely interchangeable, non-specific signals that disrupt regulation controlling intimal cell proliferation is unproductive; instead, a study of the controlling regulation(s) itself should be a priority of our research.

Application of PLGA nano/microparticle delivery systems for immunomodulation and prevention of allotransplant rejection

INTRODUCTION

Allograft transplantation is an effective end-point therapy to replace the function of an impaired organ. The main problem associated with allotransplantation is the induction of immune responses that results in acute and chronic graft rejection. To modulate the response of the immune system, transplant recipients generally take high dose immunosuppressant drugs for life. These drugs are associated with serious side effects such as infection with opportunistic pathogens and the development of neoplasia.

AREAS COVERED

We reviewed the obstacles to successful transplantation and PLGA-based strategies to reduce immune-mediated allograft rejection.

EXPERT OPINION

Biomaterial-based approaches using micro- and nanoparticles such as poly (lactic-co-glycolic acid) (PLGA) can be used to achieve controlled release of drugs. This approach decreases the required effective dose of drugs and enables local delivery of these agents to specific tissues and cells, whilst decreasing systemic effects.

Endothelial nitric oxide synthase (eNOS) gene polymorphism in early term chronic allograft nephropathy

Chronic allograft nephropathy (CAN) is a complex phenomenon caused by underlying kidney disease with superimposed enviromental and genetic factors. CAN development begins with progressive renal microvascular injury. Endothelial cells play key roles in the regulation of vascular tone, permeability, and remodeling. A reduction in basal nitric oxide (NO) release as a result of genetic variation in endothelial NO synthase (eNOS) function may predispose to hypertension, thrombosis, vasospasm, and atherosclerosis, all contributing to the development of CAN. We analyzed the G894T mutation at exon 7 of the eNOS gene in relationship to CAN among 81 children with renal transplantations. The 20 patients who developed CAN underwent renal biopsies for histological confirmation. Proteinuria and hypertension were observed in CAN. We selected 173 healthy reference subjects. The G894T polymorphism of the eNOS gene was determined by PCR-restriction fragment-length polymorphism analysis. The group included 33 male and 48 female subjects who received 32 living-related grafts and 49 from deceased donors (DD) donors. Donor age (y) was 32.7 +/- 13.7 and the HLA A,B,DR mismatch number of the cadaveric cases was 3.5 +/- 0.79. The distribution of the genotypes were ENOS GG/GT/TT 48%, 33%, 19%, respectively. G-alleles frequency was 64.8%; T-allele frequency was 35.2%. ENOS G894T gene polymorphism did not seem to influence long-term renal allograft outcome. Recipient ENOS G894T gene polymorphism did not alter the risk of chronic allograft failure. Even if NO synthesis and bioactivity are influenced by this polymorphism, many vasoactive factors may have roles to suppress the advantageous effects of NO.

Analysis of arterial intimal hyperplasia: review and hypothesis

BACKGROUND

Despite a prodigious investment of funds, we cannot treat or prevent arteriosclerosis and restenosis, particularly its major pathology, arterial intimal hyperplasia. A cornerstone question lies behind all approaches to the disease: what causes the pathology?

HYPOTHESIS

I argue that the question itself is misplaced because it implies that intimal hyperplasia is a novel pathological phenomenon caused by new mechanisms. A simple inquiry into arterial morphology shows the opposite is true. The normal multi-layer cellular organization of the tunica intima is identical to that of diseased hyperplasia; it is the standard arterial system design in all placentals at least as large as rabbits, including humans. Formed initially as one-layer endothelium lining, this phenotype can either be maintained or differentiate into a normal multi-layer cellular lining, so striking in its resemblance to diseased hyperplasia that we have to name it "benign intimal hyperplasia". However, normal or "benign" intimal hyperplasia, although microscopically identical to pathology, is a controllable phenotype that rarely compromises blood supply. It is remarkable that each human heart has coronary arteries in which a single-layer endothelium differentiates early in life to form a multi-layer intimal hyperplasia and then continues to self-renew in a controlled manner throughout life, relatively rarely compromising the blood supply to the heart, causing complications requiring intervention only in a small fraction of the population, while all humans are carriers of benign hyperplasia. Unfortunately, this fundamental fact has not been widely appreciated in arteriosclerosis research and medical education, which continue to operate on the assumption that the normal arterial intima is always an "ideal" single-layer endothelium. As a result, the disease is perceived and studied as a new pathological event caused by new mechanisms. The discovery that normal coronary arteries are morphologically indistinguishable from deadly coronary arteriosclerosis continues to elicit surprise.

CONCLUSION

Two questions should inform the priorities of our research: (1) what controls switch the single cell-layer intimal phenotype into normal hyperplasia? (2) how is normal (benign) hyperplasia maintained? We would be hard-pressed to gain practical insights without scrutinizing our premises.

Elevated serum interleukin-6 (IL-6) in solid-organ transplant recipients is positively associated with tissue destruction and IL-6 gene expression in the periodontium

BACKGROUND

The number of transplanted solid organs and life expectancy after transplantation are steadily rising worldwide. Inflammation is widely recognized as playing a pivotal role in transplant rejection, and several studies have shown that serum interleukin-6 (IL-6) levels can identify individuals who are at greater risk for rejection. Given the known association between IL-6 and chronic periodontitis, the aim of our study was to assess the periodontal status of solid-organ transplant subjects compared to systemically healthy controls, to quantify the IL-6 levels in the serum and periodontal tissues, and to explore their association.

METHODS

Forty-seven heart and kidney transplant and 18 systemically healthy age-matched individuals were recruited. Subjects received a complete periodontal examination, and blood and periodontal tissue samples were collected for quantification of IL-6 protein and mRNA levels, respectively.

RESULTS

Transplant subjects had significantly higher serum IL-6 levels and slightly but statistically significantly increased mean probing depths than healthy controls. Multivariable linear regression analysis adjusting for gender, diabetes, smoking, and immunosuppressant dose showed that the mean probing depth, number of missing teeth, and mean percentage of sites with > or =4 mm attachment loss were independent predictors for elevated serum IL-6 levels. Transplant subjects with chronic periodontitis had higher mean serum IL-6 levels than those without chronic periodontitis, and there was a positive correlation between periodontal IL-6 gene expression levels and serum IL-6 protein levels.

CONCLUSIONS

Periodontal tissue destruction and local IL-6 synthesis are associated with elevated serum IL-6 levels in transplant recipients. This may have serious implications in solid-organ transplant deterioration and chronic rejection.

Influence of Mismatching of HLA Cross-Reactive Groups on Cadaveric Kidney Transplantation

Finding fully HLA-matched recipients for a given donor is not practical due to the allelic diversity of the loci. Cross-reactive group (CREG) matching has been considered a feasible alternative to HLA matching. However, the true efficacy of CREG matching in cadaveric kidney transplantation is controversial. Using conventional HLA and CREG classifications proposed by Rodey and McKenna, we counted the number of mismatches for 319 patients who received cadaver kidney transplants between 1992 and 2003 at Asan Medical Center in Korea. When we compared transplants with four or fewer HLA-A, -B, and -DR antigen mismatches with those with five or more, we observed a significant difference in 5-year survival rate (88.5% versus 78.6%; P = .0189). Transplants with no or one HLA-DR mismatch had a significantly better 5-year survival rate than those with two HLA-DR mismatches (87.9% versus 80.0%; P = .0469). Among transplants with one or two HLA-DR mismatches, transplants with zero or one CREG mismatch showed better 5-year graft survival rate than those with two or more CREG mismatches (89.4% versus 79.8%; P = .0415) only in McKenna's CREG classification. These results suggest that the impact of CREG mismatches on graft survival may depend on CREG classification and on the distribution of HLA-DR mismatches.

Prolonged cold preservation promotes the recipient's cell participating in neointima formation but delays the later graft arteriosclerosis in rat model

Chronic graft dysfunction is the greatest barrier to long-term graft survival, although the immediate outcome in organ transplantation has been greatly improved. Graft arteriosclerosis is a prominent feature of chronic graft dysfunction. Recipient progenitor cells have been shown to participate in neointimal development in graft arteriosclerosis. The present study investigated the role of recipient endothelial cells in the repair and remodeling after a cold preservation injury in an orthotopic cross-sex abdominal aortic allotransplantation model, namely female Wistar to male Sprague-Dawley rats. Grafts were preserved for 48 hours in 4 degrees C University of Wisconsin (UW) solution for a prolonged cold ischemia (PCI) group or preserved for <1 hour in the control group; or for <1 hour in the presence of feeding with cyclosporine (CyA). A direct in situ polymerase chain reaction (ISPCR) for the SRY gene showed SRY-marked endothelial and smooth muscle-like cells in neointima at 2 weeks in the PCI group, at 4 weeks in the control group, and rarely at 3 months in the CyA group. Staining by H&E showed the aortic graft intima to be thicker in the PCI than in the control group at 4 weeks, but thinning thereafter. The SRY-positive cells correlated with intimal thickness in the PCI and the control group (r = .801 and .825; P < .05 and <.05, respectively), but not in the CyA group (r = .247, P > .5). Our data suggest that prolonged cold preservation promotes recipient cell participation in graft arteriosclerosis after endothelium injury. The early neointimal formation via recipient cells incorporated into arteriosclerotic neointima may delay later intimal thickening. In the aortic allotransplantation model, prolonged cold ischemia may be beneficial for long-term graft survival due to early endothelial replacement. We hypothesize that controlled injury to the graft may serve as a new strategy for treatment of intimal thickening.

Association of the genetic polymorphisms of the renin-angiotensin system and endothelial nitric oxide synthase with chronic renal transplant dysfunction

BACKGROUND

Chronic allograft dysfunction (CAD) is a complex phenomenon caused by underlying kidney disease and superimposed environmental and genetic factors. We investigated the association of polymorphisms in the genes for angiotensin-converting enzyme (ACE), angiotensinogen (AGT), angiotensin II receptor type 1 (ATR1) and type 2 (ATR2), and endothelial nitric oxide synthase (ENOS) with the initiation of CAD.

METHODS

Genotyping was performed in 125 patients who underwent renal transplantation during a 5-year period for the ACE I/D, AGT M235T, ATR1 A1166C, ATR2 C3123A, and ENOS intron 4a/b gene polymorphisms. The following information was collected for each case: date of transplantation, age and sex of donor and recipient, donor type, cold ischemia time, number of human leukocyte antigen mismatches, number of acute rejection episodes, and laboratory findings at discharge from hospital and annual rechecks. Blood pressure was measured at yearly intervals throughout follow-up.

RESULTS

The proportions of the genotypes were ACE II/ID/DD 12%, 33.6%, 54.4%; AGT MM/MT/TT 33%, 65.2%, 1.9%; ATR1 AA/AC/CC 68.6%, 30.7%, 0.7%; ATR2 CC/CA/AA 57.9%, 27.5%, 14.4%; and ENOS aa/ab/bb 6.4%, 22%, 71.6%, respectively. Statistical analysis of the major risk factors for the initiation of CAD showed that ACE DD genotype, cadaveric donor type, and level of proteinuria at 1 year posttransplantation were associated with poorer renal function. The graft function was not affected by AGT, ATR1, ATR2, and ENOS gene polymorphisms.

CONCLUSIONS

These findings suggest that the DD variant of the ACE gene polymorphism is associated with increased risk of developing CAD.

Renal arterial resistance index and computerized quantification of fibrosis as a combined predictive tool in chronic allograft nephropathy

The renal arterial resistance index (RI) and the PicroSirius-Red stained cortical fractional interstitial fibrosis volume (VintFib) proved to be two independent methods that are reliable predictive factors of poor renal allograft outcome. No data have been published, which define the correlation between ultrasound assessment and quantitative morphologic changes. Renal biopsies were performed in 56 children according to increases in s-creatinine >10%. VintFib was calculated by computerized image analysis. RI was determined in two segmental arteries, 1 yr after transplantation and at the time-point of biopsy. RIs 1 yr after transplantation correlated significantly with RIs at time of biopsy (r = 0.58, p < 0.001). VintFib was higher in children with a RI = 80 than in children with a RI < 80 (mean VintFib = 9.5 +/- 3.2% vs. 5.2 +/- 5.1%, p = 0.004). In children with VintFib > 10%, the mean RI was 77 +/- 5 compared with 69 +/- 6 in patients with VintFib < 10% (p = 0.0002). The highest positive predictive value to detect the risk of decline of GFR at 2 yr after biopsy was 98% when an RI = 80% was associated with a VintFib > 10%. For VintFib > 10% or RI = 80 alone, it was 87% or 67%, respectively. The combined measurement of RI and VintFib is a reliable predictive tool for the risk of developing long-term graft dysfunction after kidney transplantation.

Inhibition of alloresponse by a human trophoblast non-coding RNA suppressing class II transactivator promoter III and major histocompatibility class II expression in murine B-lymphocytes

BACKGROUND

Trophoblasts are a model of natural allograft tolerance. A unique characteristic is the complete lack of expression of all classic major histocompatibility (MHC) antigens. We cloned a human trophoblast non-coding RNA (TncRNA) that suppresses MHC class II expression through inhibition of the class II transactivator (CIITA) promoter. We assessed the functional affects of TncRNA on an alloresponse and dissected the functional domain on CIITA promoter III.

METHODS

Murine B-cell line A20 was transfected with TncRNA. Class II suppressed clones were selected and characterized by flow cytometry and Northern analysis. The clones were then subjected to lymphocyte proliferation assay to assess the stimulation of T-lymphocytes. CIITA promoter III-luciferase reporter plasmids were used with TncRNA plasmids in co-transfection assays; 5'-end deletion plasmids were used to dissect the promoter.

RESULTS

Significant suppression of I-Ad expression was seen. Northern blot scans demonstrated 84% to 93% suppression of class II transcripts. Lymphocyte proliferation assay demonstrated a 50% and 64% inhibition of lymphocyte stimulation in the 2 clones, compared to A20 wild type. Dissection of promoter III indicated that an area between bp -152 to -107 contains the functional site of TncRNA.

CONCLUSION

Human TncRNA is active across species lines and significantly inhibits allogenic response to B-cells. There is concurrent suppression of constitutive class II expression in TncRNA clones mediated through a defined region of CIITA promoter III.