Antibody-mediated Transplant Rejection Research Articles

Morphologic and Molecular Features of Antibody-Mediated Transplant Rejection: Pivotal Role of Molecular Injury as an Independent Predictor of Renal Allograft Functional Decline.

Current knowledge about the factors correlating with functional decline and subsequent failure of kidney allografts in antibody-mediated rejection (ABMR) is limited. We conducted a cohort study involving 75 renal allograft recipients diagnosed with late ABMR occurring at least 6months after transplantation. The study aimed to examine the correlation of molecular and histologic features with estimated glomerular filtration rate (eGFR) trajectories and death-censored graft survival. We focused on sum scores reflecting histologic ABMR activity versus chronicity and molecular scores of ABMR probability (ABMRProb), injury-repair response (IRRAT) and fibrosis (ciprob). In multivariable Cox analysis, a Banff lesion-based chronicity index (ci+ct+cg[x2]; hazard ratio per interquartile range [IQR]: 1.97 [95% confidence interval: 0.97 to 3.99]) and IRRAT (1.93 [0.96 to 3.89]) showed the strongest associations with graft failure. Among biopsy variables, IRRAT exhibited the highest relative variable importance and emerged as the sole independent predictor of eGFR slope (change per IQR: -4.2 [-7.8 to -0.6] mL/min/1.73m2/year). In contrast, morphologic chronicity associated with baseline eGFR only. We conclude that the extent of molecular injury is a robust predictor of renal function decline. Transcriptome analysis has the potential to improve outcome prediction and possibly identify modifiable injury, guiding targeted therapeutic interventions.

Chimeric HLA antibody receptor T cells for targeted therapy of antibody-mediated rejection in transplantation.

The presence of donor-specific antibodies (DSA), mainly against HLA, increases the risk of allograft rejection. Moreover, antibody-mediated rejection (ABMR) remains an important barrier to optimal long-term outcomes after solid organ transplantation. The development of chimeric autoantibody receptor T lymphocytes has been postulated for targeted therapy of autoimmune diseases. We aimed to develop a targeted therapy for DSA desensitization and ABMR, generating T cells with a chimeric HLA antibody receptor (CHAR) that specifically eliminates DSA-producing B cells. We have genetically engineered an HLA-A2-specific CHAR (A2-CHAR) and transduced it into human T cells. Then, we have performed in vitro experiments such as cytokine measurement, effector cell activation, and cytotoxicity against anti-HLA-A2 antibody-expressing target cells. In addition, we have performed A2-CHAR-Tc cytotoxic assays in an immunodeficient mouse model. A2-CHAR expressing T cells could selectively eliminate HLA-A2 antibody-producing B cells in vitro. The cytotoxic capacity of A2-CHAR expressing T cells mainly depended on Granzyme B release. In the NSG mouse model, A2-CHAR-T cells could identify and eradicate HLA-A2 antibody-producing B cells even when those cells are localized in the bone marrow. This ability is effector:target ratio dependent. CHAR technology generates potent and functional human cytotoxic T cells to target alloreactive HLA class I antibody-producing B cells. Thus, we consider that CHAR technology may be used as a selective desensitization protocol or an ABMR therapy in transplantation.

#4178 HYPERCHLOREMIC METABOLIC ACIDOSIS AFTER PLASMAPHERESIS IN A PATIENT WITH RENAL TRANSPLANT REJECTION: A CASE REPORT

Abstract Background and Aims Plasmapheresis is an effective therapeutic intervention for several renal disorders, including renal transplant rejection. However, repeated plasmapheresis can cause various side effects and complications. Method We present a 61-year-old male with a medical history of type 2 diabetes, hypertension, successfully treated multiple myeloma and a post-mortem kidney transplantation 7 months ago. The patient was hospitalized because of rapid deterioration of his renal function (eGFR CKD-EPI 15 ml/min/1.73m2). Renal biopsy of the transplanted kidney confirmed the diagnosis of antibody-mediated transplant rejection. Treatment with methylprednisolone, plasmapheresis with a 40 g/L albumin solution as a replacement fluid and intravenous immunoglobulins was initiated. After 4 plasmapheresis treatments, the patient developed gastrointestinal complaints and muscle weakness. Despite the patient's use of 3 grams of oral sodium bicarbonate supplements a day, laboratory tests revealed a hyperchloremic metabolic acidosis: bicarbonate 11.7 mmol/L, chloride 111 mmol/L, sodium 138 mmol/L. Metabolic acidosis due to citrate accumulation was ruled out with a normal total-to-ionized calcium ratio. After treatment with intravenous bicarbonate supplementation, the symptoms disappeared. Analysis of the albumin plasmapheresis solution showed a chloride concentration of 132 mmol/L. Results This is the first case that describes metabolic acidosis after albumin plasmapheresis in a patient with impaired renal function. The observed hyperchloremic metabolic acidosis is most likely the result of the administration of large volumes (3.5 litres per session) of a 4% albumin solution with high chloride concentrations. We hypothesize that patients with renal impairment are more prone to develop metabolic acidosis after plasmapheresis with albumin-saline replacement fluids due to their reduced renal capacity to excrete excess acid and chloride. Conclusion Special attention should be paid to the acid-base balance during plasmapheresis in patients with impaired renal function. Future research should investigate the incidence of hyperchloremic metabolic acidosis during albumin plasmapheresis in different eGFR categories.

In vivo PK/PD assessment of invisibilized IgG cleaving protease for chronic treatment of autoimmune diseases

Abstract Pathogenic autoantibodies are key effectors of inflammation, promoting complement cascade activation, immune cell response, and the consequent tissue damage in autoimmune disease and transplant rejection. Proteases that cleave IgG antibodies present a novel therapeutic opportunity to treat autoimmune diseases and antibody mediated transplant rejection. Using our IMPACT platform leveraging machine learning, we engineered IgG proteases with reduced immunogenicity for acute and chronic treatment of antibody-mediated diseases. In addition, the invisibilized protease was fused to a Fc to extend its half-life. To evaluate these IgG proteases in vivowe developed a pharmacokinetics and pharmacodynamics (PK/PD) model. C57BL6 mice were dosed with intravenous immunoglobulin (IVIg) at different time points after protease treatment. Protease and IgG levels were quantified by MSD 15 minutes before and two hours after IVIg injection, respectively. IgG cleavage was detected at early time points which correlated with higher systemic drug levels. Additionally, the Fc-fused protease was detected at later time points with increased systemic enzymatic activity, as compared to the enzyme domain only. Finally, we evaluated the potential of the Fc-protease to cleave antigen bound IgG at the tissue level in a mouse anti–glomerular basement membrane (GBM) induced nephritis model. In summary, our in vivo studies established a PK/PD relationship between exposure and cleaved IgG while showing the benefit of fusing the protease domain to a Fc.

Sugar and spice: Fc glycosylation in antibody-mediated transplant rejection

Bharadwaj etal.1 demonstrate that anti-donor HLA antibodies display low levels of Fc fucosylation. This signature was associated with potent provocation of NK cell effector functions and was discriminative for active antibody-mediated rejection among patients with donor specific HLA antibodies.

QUILTY LESION FOXP3+ AND TGF-BETA+ REGULATORY T-CELLS ARE ASSOCIATED WITH ACCEPTANCE OF HEART ALLOGRAFTS

To evaluate the cellular composition of Quilty lesions in heart transplant biopsies and their association with acceptance or rejection of cardiac allografts. In this study we included a cohort of cardiac transplant biopsies with Quilty lesions for which a final diagnosis had already been rendered for treatment purposes. Serial sections from 42 specimens were stained immunohistochemically for CD4, CD8, FoxP3 (as surrogate marker of innate regulatory T cells) and TGF-beta-1 (as surrogate marker of adaptive regulatory immune cells). The relative abundance of cells positive for each of these four markers was evaluated both in the Quilty lesion itself and in the uninvolved, surrounding myocardium using semi-quantitative methods. Correlations were then made, using chi-square and Pearson analysis, between these measures and allograft acceptance. FoxP3+ (OR 1.33, p<0.05) and TGF-beta+ cells (OR 1.4) in the quilty lesions are associated with higher allograft acceptance. Of note, no FoxP3+ cells were seen in myocardium. However, the presence of CD8+ cells in the myocardium is associated with greater degrees of both acute cellular (p<0.02) and antibody-mediated transplant rejection (p<0.04). High numbers of CD4+ cells in the myocardium are also associated with a greater degree of acute cellular rejection (p<0.04). However, the presence of either CD4+ or CD8+ T-cells in Quilty lesions are not associated with rejection. Interestingly, greater numbers of TGF-beta-positive cells in the myocardium are associated with a greater degree of antibody-mediated rejection. Quilty lesions previously have been associated with mild to moderate acute cellular rejection, but their precise function remains unclear: it has yet to be determined whether they might participate in immune-mediated tissue destruction or may represent an immune-mediated tissue salvage mechanism. In this study, both FoxP3+ innate and TGF-beta+ adaptive regulatory cells are associated with increased allograft acceptance in biopsies when localize? in quilty lesions. Myocardial effector CD4+ and CD8+ T-cells are associated with increased rejection. However, their presence in quilty lesions has no effect in rejection or acceptance or the transplant. Therefore, quilty lesions may rather represent intragraft tertiary lymphoid tissue to prevent allograft rejection, and assist in acceptance of the organ transplant. Drs. George and Anne Race Distinguished Professor of Pathology Endowment Fund (Dr. Jose Torrealba).

Transplant Antibody-Mediated Rejection: Guiding Effective Treatments

Transplant Antibody-Mediated Rejection: Guiding Effective Treatments

Cell-based Assays for Antibody-mediated Transplant Rejection

Cell-based Assays for Antibody-mediated Transplant Rejection

Parameter Identification for a Model of Neonatal Fc Receptor-Mediated Recycling of Endogenous Immunoglobulin G in Humans.

Salvage of endogenous immunoglobulin G (IgG) by the neonatal Fc receptor (FcRn) is implicated in many clinical areas, including therapeutic monoclonal antibody kinetics, patient monitoring in IgG multiple myeloma, and antibody-mediated transplant rejection. There is a clear clinical need for a fully parameterized model of FcRn-mediated recycling of endogenous IgG to allow for predictive modeling, with the potential for optimizing therapeutic regimens for better patient outcomes. In this paper we study a mechanism-based model incorporating nonlinear FcRn-IgG binding kinetics. The aim of this study is to determine whether parameter values can be estimated using the limited in vivo human data, available in the literature, from studies of the kinetics of radiolabeled IgG in humans. We derive mathematical descriptions of the experimental observations—timecourse data and fractional catabolic rate (FCR) data—based on the underlying physiological model. Structural identifiability analyses are performed to determine which, if any, of the parameters are unique with respect to the observations. Structurally identifiable parameters are then estimated from the data. It is found that parameter values estimated from timecourse data are not robust, suggesting that the model complexity is not supported by the available data. Based upon the structural identifiability analyses, a new expression for the FCR is derived. This expression is fitted to the FCR data to estimate unknown parameter values. Using these parameter estimates, the plasma IgG response is simulated under clinical conditions. Finally a suggestion is made for a reduced-order model based upon the newly derived expression for the FCR. The reduced-order model is used to predict the plasma IgG response, which is compared with the original four-compartment model, showing good agreement. This paper shows how techniques for compartmental model analysis—structural identifiability analysis, linearization, and reparameterization—can be used to ensure robust parameter identification.

HLA Class II–Triggered Signaling Cascades Cause Endothelial Cell Proliferation and Migration: Relevance to Antibody-Mediated Transplant Rejection

Transplant recipients developing donor-specific HLA class II (HLA-II) Abs are at higher risk for Ab-mediated rejection (AMR) and transplant vasculopathy. To understand how HLA-II Abs cause AMR and transplant vasculopathy, we determined the signaling events triggered in vascular endothelial cells (EC) following Ab ligation of HLA-II molecules. HLA-II expression in EC was induced by adenoviral vector expression of CIITA or by pretreatment with TNF-α/IFN-γ. Ab ligation of class II stimulated EC proliferation and migration. Class II Ab also induced activation of key signaling nodes Src, focal adhesion kinase, PI3K, and ERK that regulated downstream targets of the mammalian target of rapamycin (mTOR) pathway Akt, p70 ribosomal S6 kinase, and S6 ribosomal protein. Pharmacological inhibitors and small interfering RNA showed the protein kinases Src, focal adhesion kinase, PI3K/Akt, and MEK/ERK regulate class II Ab-stimulated cell proliferation and migration. Treatment with rapalogs for 2 h did not affect HLA-II Ab-induced phosphorylation of ERK; instead, mTOR complex (mTORC)1 targets were dependent on activation of ERK. Importantly, suppression of mTORC2 for 24 h with rapamycin or everolimus or treatment with mTOR active-site inhibitors enhanced HLA-II Ab-stimulated phosphorylation of ERK. Furthermore, knockdown of Rictor with small interfering RNA caused overactivation of ERK while abolishing phosphorylation of Akt Ser473 induced by class II Ab. These data are different from HLA class I Ab-induced activation of ERK, which is mTORC2-dependent. Our results identify a complex signaling network triggered by HLA-II Ab in EC and indicate that combined ERK and mTORC2 inhibitors may be required to achieve optimal efficacy in controlling HLA-II Ab-mediated AMR.

Targeting B Cells and Plasma Cells in Glomerular Diseases: Translational Perspectives.

The unique contributions of memory B cells and plasma cells in kidney diseases remain unclear. In this review, we evaluate the clinical experience with treatments directed at B cells, such as rituximab, and at plasma cells, such as proteasome inhibition, to shed light on the role of these two B lineage compartments in glomerular diseases. Specifically, analysis of these targeted interventions in diseases such as ANCA-associated vasculitis, SLE, and antibody-mediated transplant rejection permits insight into the pathogenetic effect of these cells. Notwithstanding the limitations of preclinical models and clinical studies (heterogeneous populations, among others), the data suggest that memory B and plasma cells represent two engines of autoimmunity, with variable involvement in these diseases. Whereas memory B cells and plasma cells appear to be key in ANCA-associated vasculitis and antibody-mediated transplant rejection, respectively, SLE seems likely to be driven by both autoimmune compartments. These conclusions have implications for the future development of targeted therapeutics in immune-mediated renal disease.

Outside-in HLA class I signaling regulates ICAM-1 clustering and endothelial cell-monocyte interactions via mTOR in transplant antibody-mediated rejection.

Antibody-mediated rejection (AMR) resulting in transplant allograft vasculopathy (TAV) is the major obstacle for long-term survival of solid organ transplants. AMR is caused by donor-specific antibodies to HLA, which contribute to TAV by initiating outside-in signaling transduction pathways that elicit monocyte recruitment to activated endothelium. Mechanistic target of rapamycin (mTOR) inhibitors can attenuate TAV; therefore, we sought to understand the mechanistic underpinnings of mTOR signaling in HLA class I Ab-mediated endothelial cell activation and monocyte recruitment. We used an in vitro model to assess monocyte binding to HLA I Ab-activated endothelial cells and found mTOR inhibition reduced ezrin/radixin/moesin (ERM) phosphorylation, intercellular adhesion molecule 1 (ICAM-1) clustering, and monocyte firm adhesion to HLA I Ab-activated endothelium. Further, in a mouse model of AMR, in which C57BL/6. RAG1-/- recipients of BALB/c cardiac allografts were passively transferred with donor-specific MHC I antibodies, mTOR inhibition significantly reduced vascular injury, ERM phosphorylation, and macrophage infiltration of the allograft. Taken together, these studies indicate mTOR inhibition suppresses ERM phosphorylation in endothelial cells, which impedes ICAM-1 clustering in response to HLA class I Ab and prevents macrophage infiltration into cardiac allografts. These findings indicate a novel therapeutic application for mTOR inhibitors to disrupt endothelial cell-monocyte interactions during AMR.

B-Cell Targets to Treat Antibody-Mediated Rejection in Transplantation

Antibody-mediated rejection (AMR) in allograft transplantation can be defined with a rapid increase in the levels of specific serological parameters after organ transplantation, presence of donor specific antibodies (DSAs) against human leukocyte antigen (HLA) molecules, blood group (ABO) antigens and/or endothelial cell antigens (e.g. MICA, ECA, Vimentin, or ETAR) and also particular histological parameters [1,2]. If the AMR persists or progresses, the treatment to eliminate the humoral component of acute rejection include three sequential steps: (a) steroid pulses, antibody removal (plasma exchange or immuno-adsorption) and high doses of intravenous immunoglobulin-IVIG, (b) Rituximab (anti-CD20) or Bortezomib (anti-proteasome), and finally (c) Eculizumab (anti-C5) and rescue splenectomy.

Inhibition of JAK3 and PKC via Immunosuppressive Drugs Tofacitinib and Sotrastaurin Inhibits Proliferation of Human B Lymphocytes In Vitro

BackgroundAntibody-mediated response in solid organ transplantation is critical for graft dysfunction and loss. The use of immunosuppressive agents partially inhibits the B-lymphocyte response leading to a risk of acute and chronic antibody-mediated rejection. This study evaluated the impact of JAK3 and PKC inhibitors tofacitinib (Tofa) and sotrastaurin (STN), respectively, on B-cell proliferation, apoptosis, and activation in vitro. MethodsHuman B cells isolated from peripheral blood of healthy volunteers were cocultured with CD40 ligand–transfected fibroblasts as feeder cells in the presence of interleukin (IL) 2, IL-10, and IL-21. The cocultures were treated with immunosuppressants Tofa, STN, and rapamycin (as a control), to analyze the proliferation and apoptosis of B cells by means of Cyquant and flow cytometry, respectively. CD27 and IgG staining were applied to evaluate whether treatments modified the activation of B cells. ResultsTofa and STN were able to inhibit B-cell proliferation to the same extent as rapamycin, without inducing cell apoptosis. After 6 days in coculture with feeder cells, all B cells showed CD27 memory B-cell phenotype. None of the immunosuppressive treatments modified the proportion between class-switched and non–class-switched memory B cells observed in nontreated cultures. The high predominance of CD27+CD24+ phenotype was not modified by any immunosuppressive treatment. ConclusionsOur results show that Tofa and STN can suppress B-cell antibody responses to an extent similar to rapamycin, in vitro; therefore these compounds may be a useful therapy against antibody-mediated rejection in transplantation.

The Complement System and Antibody-Mediated Transplant Rejection.

Complement activation is an important cause of tissue injury in patients with Ab-mediated rejection (AMR) of transplanted organs. Complement activation triggers a strong inflammatory response, and it also generates tissue-bound and soluble fragments that are clinically useful markers of inflammation. The detection of complement proteins deposited within transplanted tissues has become an indispensible biomarker of AMR, and several assays have recently been developed to measure complement activation by Abs reactive to specific donor HLA expressed within the transplant. Complement inhibitors have entered clinical use and have shown efficacy for the treatment of AMR. New methods of detecting complement activation within transplanted organs will improve our ability to diagnose and monitor AMR, and they will also help guide the use of complement inhibitory drugs.

Significance of C4d Immunostaining in Placental Chronic Intervillositis

Deposition of the complement split product C4d is a phenomenon studied extensively as a marker for complement activation in antibody-mediated transplant rejection. C4d also is observed in placental disease processes including spontaneous abortion, infarct, and villitis of unknown origins. Massive chronic intervillositis is a rare placental abnormality associated with increased risk of growth restriction, fetal death, and recurrent fetal loss. In this study, we evaluated C4d immunostaining in placentas with accumulation of intervillous monocytes with and without villitis. Archived placentas from Kosair Children's Hospital (Louisville, KY) and Seattle Children's Hospital (Seattle, WA) were selected and divided into 4 groups, 16 cases of intervillositis with complicated pregnancy, 15 cases of uncomplicated intervillositis, 20 cases of complicated villitis, and 13 cases of uncomplicated villitis, all with varying degrees of monocytic cells in the intervillous space. Representative specimen blocks were immunohistochemically stained for C4d. The percentage of positive staining of the microvillous surface of the syncytiotrophoblast was scored by five pathologists, and the following consensus score was determined: 0 = 0% to 5%; 1 = 5% to 25%; 2 = 25% to 75%; and 3 ≥ 75%. C4d immunostain localized to the microvillous border of syncytiotrophoblast in many of the placentas. C4d staining was more strongly associated with intervillositis than with villitis (odds ratio: 6.3; confidence interval: 2.1-18.7; P = 0.001).

Absence of Activation-induced Cytidine Deaminase, a Regulator of Class Switch Recombination and Hypermutation in B Cells, Suppresses Aorta Allograft Vasculopathy in Mice.

Antibody-mediated rejection is caused in part by increasing circulation/production of donor-specific antibody (DSA). Activation-induced cytidine deaminase (AID) is a key regulator of class switch recombination and somatic hypermutation of immunoglobulin in B cells, yet its role in antibody-mediated transplant rejection remains unclear. We show here that AID deficiency in mice enables suppression of allograft vasculopathy (AV) after aorta transplantation, a DSA-mediated process. Splenocytes from C57BL/6 J (B6) AID(−/−) mice were used for determining in vitro proliferation responses, alloreactivity, cell surface marker expression, and antibody production. BALB/c mouse aortas were transplanted into B6 AID(−/−) mice with or without FK506 treatment. Blood and aorta grafts were harvested on day 30 after transplantation and were subjected to DSA, histological, and immunohistological analyses. The AID(−/−) splenocytes were comparable to wild type splenocytes in proliferation responses, alloreactivity, and expression of cell surface markers in vitro. However, they completely failed to produce immunoglobulin G, although they were not impaired in immunoglobulin M production relative to controls. Furthermore, BALB/c aorta grafts from B6 AID(−/−) recipient mice on day 30 after transplantation showed reduced signs of AV compared to the grafts from B6 wild type recipient mice which had severe vascular intimal hyperplasia, interstitial fibrosis, and inflammation. Treatment with FK506 produced a synergistic effect in the grafts from AID(−/−) recipients with further reduction of intimal hyperplasia and fibrosis scores. The AID deficiency inhibits DSA-mediated AV after aorta transplantation in mice. We propose that AID could be a novel molecular target for controlling antibody-mediated rejection in organ transplantation.

Inhibition of the Classical and Lectin Pathway of the Complement System by Recombinant LAIR-2

Activation of complement may cause severe tissue damage in antibody-mediated allograft rejection and other antibody-mediated clinical conditions; therefore, novel potent complement inhibitors are needed. Previously, we described binding of the inhibitory receptor LAIR-1 and its soluble family member LAIR-2 to collagen. Here, we investigated binding of LAIR-1 and LAIR-2 to the complement proteins C1q and MBL, which both have collagen-like domains, and evaluated the effect of this binding on complement function. We demonstrate specific binding of recombinant LAIR proteins to both C1q and MBL. Surface plasmon resonance experiments showed that LAIR-2-Fc protein bound C1q and MBL with the highest affinity compared to LAIR-2-HIS. We, therefore, hypothesized that LAIR-2-Fc is a potent complement inhibitor. Indeed, LAIR-2-Fc inhibited C4 fixation to IgG or mannan, reduced activation of C4 by aggregated IgG in plasma and inhibited iC3b deposition on cells. Finally, LAIR-2-Fc inhibited complement-mediated lysis of cells sensitized with anti-HLA antibodies in an ex vivo model for antibody-mediated transplant rejection. Thus, LAIR-2-Fc is an effective novel complement inhibitor for the treatment and prevention of antibody-mediated allograft rejection and antibody-mediated clinical conditions.

Autoantibodies—epiphenomena or biological clues

The potential roles for autoantibodies in renal transplantation are increasing, as illustrated by a recent report of polyreactive autoantibodies produced by B-cell clones from a kidney transplant recipient that can bind apoptotic cells and activate complement. Such autoantibodies have the potential to amplify microcirculation injury caused by alloantibody in antibody-mediated transplant rejection.

675 CD19 Monitoring after Rituxamab in Patients with Cardiac Transplant Antibody Mediated Rejection (AMR)

675 CD19 Monitoring after Rituxamab in Patients with Cardiac Transplant Antibody Mediated Rejection (AMR)