Anti-vimentin Antibodies Present at the Time of Transplantation May Predict Early Development of Interstitial Fibrosis/Tubular Atrophy

BSHI and BTS UK guideline on the detection of alloantibodies in solid organ (and islet) transplantation

Solid organ transplantation represents the best (and in many cases only) treatment option for patients with end-stage organ failure. The effectiveness and functioning life of these transplants has improved each decade due to surgical and clinical advances, and accurate histocompatibility assessment. Patient exposure to alloantigen from another individual is a common occurrence and takes place through pregnancies, blood transfusions or previous transplantation. Such exposure to alloantigen's can lead to the formation of circulating alloreactive antibodies which can be deleterious to solid organ transplant outcome. The purpose of these guidelines is to update to the previous BSHI/BTS guidelines 2016 on the relevance, assessment, and management of alloantibodies within solid organ transplantation.

Non-HLA Antibodies in Kidney Transplantation: Immunity and Genetic Insights

The polymorphic human leukocyte antigen (HLA) system has been considered the main target for alloimmunity, but the non-HLA antibodies and autoimmunity have gained importance in kidney transplantation (KT). Apart from the endothelial injury, secondary self-antigen exposure and the presence of polymorphic alloantigens, respectively, auto- and allo- non-HLA antibodies shared common steps in their development, such as: antigen recognition via indirect pathway by recipient antigen presenting cells, autoreactive T cell activation, autoreactive B cell activation, T helper 17 cell differentiation, loss of self-tolerance and epitope spreading phenomena. Both alloimmunity and autoimmunity play a synergic role in the formation of non-HLA antibodies, and the emergence of transcriptomics and genome-wide evaluation techniques has led to important progress in understanding the mechanistic features. Among them, non-HLA mismatches between donors and recipients provide valuable information regarding the role of genetics in non-HLA antibody immunity and development.

Set Up for Failure: Pre-Existing Autoantibodies in Lung Transplant

Lung transplant patients have the lowest long-term survival rates compared to other solid organ transplants. The complications after lung transplantation such as primary graft dysfunction (PGD) and ultimately chronic lung allograft dysfunction (CLAD) are the main reasons for this limited survival. In recent years, lung-specific autoantibodies that recognize non-HLA antigens have been hypothesized to contribute to graft injury and have been correlated with PGD, CLAD, and survival. Mounting evidence suggests that autoantibodies can develop during pulmonary disease progression before lung transplant, termed pre-existing autoantibodies, and may participate in allograft injury after transplantation. In this review, we summarize what is known about pulmonary disease autoantibodies, the relationship between pre-existing autoantibodies and lung transplantation, and potential mechanisms through which pre-existing autoantibodies contribute to graft injury and rejection.

A Comprehensive Overview of the Clinical Relevance and Treatment Options for Antibody-mediated Rejection Associated With Non-HLA Antibodies

Although solid organ transplant results have improved significantly in recent decades, a pivotal cause of impaired long-term outcome is the development of antibody-mediated rejection (AMR), a condition characterized by the presence of donor-specific antibodies to HLA or non-HLA antigens. Highly HLA-sensitized recipients are treated with desensitization protocols to rescue the transplantation. These and other therapies are also applied for the treatment of AMR. Therapeutic protocols include removal of antibodies, depletion of plasma and B cells, inhibition of the complement cascade, and suppression of the T-cell-dependent antibody response. As mounting evidence illustrates the importance of non-HLA antibodies in transplant outcome, there is a need to evaluate the efficacy of treatment protocols on non-HLA antibody levels and graft function. Many reviews have been recently published that provide an overview of the literature describing the association of non-HLA antibodies with rejection in transplantation, whereas an overview of the treatment options for non-HLA AMR is still lacking. In this review, we will therefore provide such an overview. Most reports showed positive effects of non-HLA antibody clearance on graft function. However, monitoring non-HLA antibody levels after treatment along with standardization of therapies is needed to optimally treat solid organ transplant recipients.

The emerging field of non-human leukocyte antigen antibodies in transplant medicine and beyond

The major medical advances in our knowledge of the human leukocyte antigen (HLA) system have allowed us to uncover several gaps in our understanding of alloimmunity. Although the non-HLA system has long sparked the interest of the transplant community, recognition of the role of immunity to non-HLA antigenic targets has only emerged recently. In this review, we will provide a comprehensive summary of the paradigm-changing concept of immunity to the non-HLA angiotensin II type 1 receptor (AT1R), discovered by Duška Dragun et al., that began from careful bedside clinical observations, to validated detection of anti-AT1R antibodies and lead to clinical intervention. This scientific approach has also allowed the recognition of broader pathogenicity of anti-AT1R antibodies across multiple organ transplants and in other human diseases, the integration of both non-HLA and HLA systems to understand their immunologic effects on organ allografts, and the identification of future directions for therapeutic intervention to modulate immunity to AT1R. Rationally designed successful interventions to target AT1R system provide an exemplar for other non-HLA antibodies to cross borders between medical specialties, will generate new avenues in translational research beyond transplantation, and will foster the development of new and reliable tools to improve our understanding of non-HLA immunity and ultimately allow us to improve patient care.

Non-HLA Abs in Solid Organ Transplantation

The role of anti-HLA antibodies in solid organ rejection is well established and these antibodies are routinely monitored both in patients in the waiting list and in the post-transplant setting. More recently, the presence of other antibodies directed towards non-HLA antigens, or the so-called minor histocompatibility antigens, has drawn the attention of the transplant community; however, their possible involvement in the graft outcome remains uncertain. These antibodies have been described to possibly have a role in rejection and allograft failure. This review focuses on the most studied non-HLA antibodies and their association with different clinical outcomes considered in solid organ transplantation with the aim of clarifying their clinical implication and potential relevance for routine testing.

Anti-vimentin antibodies in transplant and disease

Non-HLA antibodies are recognized as a potential source of antibody mediated rejection following transplantation. The epitopes which lead to production of these antibodies are a result of tissue disruption, specifically endothelium, secondary to inflammation and injury. Vimentin is a cytoskeletal protein involved in many aspects of cellular organization, signaling, and proliferation. Recently, antivimentin antibodies have been shown to be important not only for rheumatological autoimmune diseases, but also cardiac and renal transplant dysfunction. In cardiac transplant recipients, antivimentin antibodies are associated with coronary artery vasculopathy and chronic graft loss. In renal transplantation, antivimentin antibodies are detected prior to transplantation and are also correlated with chronic graft dysfunction. In renal transplant recipients, antivimentin antibodies seen prior to transplantation are thought to be secondary to chronic endothelial injury during hemodialysis and therefore more prevalent prior to renal transplant than cardiac transplantation. In this review, we will examine the generation and pathogenesis of antivimentin antibodies. Given that these antibodies appear to be associated with both post-cardiac and -renal transplant dysfunction, developing standard detection paradigms may be important for risk stratification prior to transplantation. Finally, understanding the pathogenesis of antivimentin antibodies may lead to the development potential therapies in order to improve long-term survival.

Vimentin expression is required for the development of EMT-related renal fibrosis following unilateral ureteral obstruction in mice

Most renal transplants ultimately fail secondary to chronic allograft nephropathy (CAN). Vimentin (vim) is a member of the intermediate filament family of proteins and has been shown to be important in the development of CAN. One of the pathways leading to chronic renal fibrosis after transplant is thought to be epithelial to mesenchymal transition (EMT). Even though vim expression is one of the main steps of EMT, it is unknown whether vim expression is required for EMT leading to renal fibrosis and allograft loss. To this end, the role of vim in renal fibrosis was determined via unilateral ureteral obstruction (UUO) in vim knockout mice (129 svs6 vim -/-). Following UUO, kidneys were recovered and analyzed via Western blotting, immunofluorescence, and transcriptomics. Cultured human proximal renal tubular (HK-2) cells were subjected to lentiviral-driven inhibition of vim expression and then treated with transforming growth factor (TGF)-β to undergo EMT. Immunoblotting as well as wound healing assays were used to determine development of EMT. Western blotting analyses of mice undergoing UUO reveal increased levels of vim soon after UUO. As expected, interstitial collagen deposition increased in control mice following UUO but decreased in vim -/- kidneys. Immunofluorescence analyses also revealed altered localization of β-catenin in vim -/- mice undergoing UUO without significant changes in mRNA levels. However, RNA sequencing revealed a decrease in β-catenin-dependent genes in vim -/- kidneys. Finally, vim-silenced HK-2 cell lines undergoing EMT were shown to have decreased cellular migration during wound healing. We conclude that vim inhibition decreases fibrosis following UUO by possibly altering β-catenin localization and downstream signaling.

Early Progression of Xanthogranulomatous Pyelonephritis in Children Might Be Dependent on Vimentin Expression

BACKGROUND Xanthogranulomatous pyelonephritis (XP) is an extremely rare, severe, atypical form of chronic renal parenchymal inflammation accompanied by hydronephrosis and/or urolithiasis. The pathomechanism of XP is not yet fully understood. Microscopically, XP is indicated by the presence of multinucleated giant cells and lipid-laden macrophages, as well as inflammatory infiltration and intensive renal fibrosis. The lipid accumulation in kidney parenchyma may be secondary to the altered flow of low-density lipoprotein (LDL)-derived cholesterol particles inside the affected cells. Physiologically, the process of LDL-derived cholesterol transport from lysosomes to the sites of its esterification is dependent on vimentin, which is a molecule comprising the cytoskeleton in mesenchymal cells. CASE REPORT A 7-year old girl was hospitalized because of the finding of unexplained kidney lesions on an abdominal ultrasound examination (an enlarged and deformed collecting system of the right kidney with hyperechogenic, solid, staghorn lesions in the calyces). Three months earlier, the patient had experienced recurrent urinary tract infection. Based on the subsequent laboratory and imaging diagnostics, the final diagnosis of XP was established and the girl was qualified for right-sided nephrectomy Microscopic examination revealed numerous foci of granuloma formations with no evident exponents of dysplastic or neoplastic abnormalities. Significant CD68-positive cell infiltrations and scattered foam cells arranging the numerous foci of granuloma inflammation were noticed. Renal parenchyma, adjacent to granuloma lesions, presented a vimentin expression. CONCLUSIONS Vimentin expression in XP may confirm a focal character of chronic granuloma formation and may suggest the complexity of XP pathogenesis involving not only macrophage and fibroblast activation but also local lipid deregulation and fibrosis.

Analysis of Sera of Recipients with Allograft Rejection Indicates That Keratin 1 Is the Target of Anti-Endothelial Antibodies

Anti-endothelial cell antibodies (AECAs) are usually directed against the surface antigens on the vascular endothelial cells. Clinical studies suggest a pathogenic role for nonhuman leukocyte antigen in antibody-mediated rejection; however, the antigens on the donor vascular endothelium that serve as the first-line targets for an immune response during allograft rejection have not been fully identified. Here, we used immunoprecipitation and mass spectrometry to identify antigens from the sera of kidney transplant recipients who were experiencing antibody-mediated rejection. Keratin 1 (KRT1) was identified as a novel antigenic target expressed on endothelial cells. To validate our finding, we produced recombinant proteins representing the three most common alleles of KRT1. The serum used for immunoprecipitation showed a strong reaction to KRT1 recombinants in western blot and ELISA. In the kidney transplant cohort, more AECA-positive recipients than AECA-negative recipients had KRT1 antibodies (32.2% versus 11.9%, p = 0.002). Sera from 255 renal recipients were tested by ELISA. Of the 77 recipients with deteriorating graft function (serum creatinine > 120 μmol/L), 23 had anti-KRT1 antibodies. KRT1-IgG positivity was, therefore, associated with a higher risk of kidney transplant rejection (29.9% (23/77) versus 16.9% (30/178), p = 0.0187). A better understanding of this antigenic target will improve long-term allograft survival.