Acute Antibody-mediated Rejection Research Articles

Rigetto anticorpo-mediato nel trapianto di rene: fisiopatologia, clinica e terapia

Introduction. Over the past two decades, our thinking has changed from considering rejection as primarily a T-cell mediated process to the realization that insufficient control of the humoral arm of a recipient’s immune system is the factor primarily responsible for the allograft dysfunction and loss. Acute Antibody Mediated Rejection (ABMR) in kidney transplantation is a severe complication that frequently occurs after transplantation and is due either to pre-transplant Donor Specific Antibodies (DSAs) or to de novo DSAs. New techniques to detect DSAs in the recipient serum and advances in the assessment of graft pathology have allowed us to recognize this entity in recent years.
 Methods. The treatment of ABMR is a multistep process consisting in the desensitization of the patients with preformed antibodies to prevent acute ABMR: in case of acute ABMR, the antibodies are removed from the serum and anti-B cells immunosuppressants are used.
 Results and Discussion. Along with our knowledge on acute ABMR, a distinct entity has been recognized: the chronic AMBR. Chronic ABMR is a frequent cause of late graft dysfunction and is characterized by a typical histopathologic feature. The treatment is often difficult and new drugs are now tested to control the disease.

S1638 An Unexpected Cause of Colitis in a Cardiac Transplant Patient

INTRODUCTION: Mycophenolate induced colitis is an unexpected complication of the immunosuppression medication. CASE DESCRIPTION/METHODS: A 36 year-old-female with a history of Epstein’s anomaly underwent repeat orthotropic heart transplant in 2020 due to primary graft failure of the first transplant in 2019. Mycophenolate had been changed to Myfortic for abdominal complaints prior to retransplant. She had early mild allograft dysfunction despite unremarkable prospective crossmatch and first surveillance right ventricular biopsy (RVB). She was empirically treated with rituximab, high dose intravenous steroids, serial plasmapheresis, and IVIG. Despite improving cardiac function, she developed acute hypoxic respiratory failure, acute on subacute renal failure, and worsening anemia. Repeat RVB revealed acute antibody and T-cell mediated rejection; the Myfortic dose was increased. Two weeks later the patient developed abdominal pain and loose maroon-colored bloody stool. Lab data showed a white blood cell count of 3.61k/ul and hemoglobin of 9.1g/dl. Elevated liver tests: Alk Phos 143U/L and ALT 111U/L. The CRP was normal however the fecal calprotectin was greater than 1250 ug/g. The SARS-CoV-2 and stool studies including clostridioides difficile, serum CMV IgG yielded negative results. A CT scan showed distension of the colon with an average amount of retained stool and gas. No bowel inflammation was noted. Colonoscopy showed diffuse edematous folds, loss of vascularity, and friable mucosa with dispersed aphthous ulcers and erosions from cecum to the sigmoid colon (Figure 1a, 1b, and 1c). The mucosa was biopsied with concern for inflammatory bowel disease, viral etiology, or undiagnosed inflammatory bowel disease. On histology, the colon mucosa was noted to have interstitial edema, abortive mitosis, eosinophilia, and scattered dilated irregular shaped crypts, most consistent with Mycophenolate related colitis (Figure 2). There was no evidence of viral inclusion bodies. Myfortic was replaced with renal dosing of Azathioprine. There was a dramatic improvement in appetite, nausea, energy, and renal function with no subsequent bloody stools or abdominal pain. DISCUSSION: There are very few reported cases of Mycophenolate induced colitis. Our patient developed bloody stools, acute kidney injury and abdominal pain as was the case in other reports. An elevated fecal calprotectin and the above biopsy findings helped clinch the diagnosis. New-onset colitis can be noted even if the patient was previously on Mycophenolate.Figure 1.: Colonoscopy images.Figure 2.: Histopathological features.

Risk Factors and Outcomes of Acute and Refractory Antibody-Mediated Rejection

Risk Factors and Outcomes of Acute and Refractory Antibody-Mediated Rejection

SUCCESSFUL CALCINEURIN-INHIBITOR-FREE IMMUNOSUPPRESSION REGIMEN WITH SIROLIMUS AND PREDNISONE IN LUNG TRANSPLANT RECIPIENTS: A CASE SERIES

SESSION TITLE: Fellows Transplantation Posters SESSION TYPE: Fellow Case Report Posters PRESENTED ON: October 18-21, 2020 INTRODUCTION: The current standard of care for immunosuppression after lung transplantation is the use of triple agents with a calcineurin inhibitor (CNI), cell cycle inhibitor (CCI), and corticosteroids (CS) with the calcineurin inhibitor (CNI) being the backbone of the regimen. However, the use of immunosuppressant drugs is frequently complicated by the development of malignancy, nephrotoxicity, cytopenias, and infection, usually requiring a reduction in immunosuppression. In cases where both CCIs and CNIs must be stopped, mTOR inhibitors are frequently used in an effort to maintain sufficient immunosuppression. A definitive role for mTOR inhibitors for immunosuppression post-lung transplant, however, remains unclear although there have been some studies in renal transplant recipients. There are challenges with transitioning to mTOR inhibitors due to concerns over wound healing in the first year, potential pulmonary toxicities, as well as the lack of data on efficacy. To our knowledge, there is no data on the outcomes of lung transplant patients maintained on dual immunosuppression with mTOR inhibitors and steroids alone. CASE PRESENTATION: We present a series of three lung transplant patients maintained on an immunosuppressant regimen of sirolimus and prednisone. All three patients remained free of acute cellular rejection and antibody-mediated rejection. Of the three patients, two remain alive and one patient died from multi-system organ failure secondary to sepsis. DISCUSSION: This small case series highlights the successful use of dual immunosuppression with mTOR inhibitors and corticosteroids in patients with contraindications to both calcineurin inhibitors and cell cycle inhibitors. CONCLUSIONS: More data is required to determine how mTOR-CS dual immunosuppression compares to traditional CCI-CNI-CS triple immunosuppression in regards to transplant rejection and the safest way to transition to this regimen when necessary. Reference #1: Ivulich S, Westall G, Dooley M, Snell G. The Evolution of Lung Transplant Immunosuppression. Drugs. 2018;78(10):965-982. doi:10.1007/s40265-018-0930-6 DISCLOSURES: No relevant relationships by Shambhu Aryal, source=Web Response No relevant relationships by Adam Cochrane, source=Web Response No relevant relationships by Margaret Fregoso, source=Web Response No relevant relationships by Vikramjit Khangoora, source=Web Response Consultant relationship with Veracyte Please note: $1001 - $5000 Added 04/03/2020 by Steven Nathan, source=Web Response, value=Honoraria Consultant relationship with United Therapeutics Please note: $5001 - $20000 Added 05/27/2020 by Steven Nathan, source=Web Response, value=Consulting fee Consultant relationship with Bellerophon Please note: $5001 - $20000 Added 05/27/2020 by Steven Nathan, source=Web Response, value=Consulting fee Speaker/Speaker's Bureau relationship with Roche-Genentech Please note: $5001 - $20000 Added 05/27/2020 by Steven Nathan, source=Web Response, value=Honoraria Speaker/Speaker's Bureau relationship with Boerhinger-Ingelheim Please note: $20001 - $100000 Added 05/27/2020 by Steven Nathan, source=Web Response, value=Honoraria

Urinary Biomarkers for Diagnosis and Prediction of Acute Kidney Allograft Rejection: A Systematic Review.

Noninvasive tools for diagnosis or prediction of acute kidney allograft rejection have been extensively investigated in recent years. Biochemical and molecular analyses of blood and urine provide a liquid biopsy that could offer new possibilities for rejection prevention, monitoring, and therefore, treatment. Nevertheless, these tools are not yet available for routine use in clinical practice. In this systematic review, MEDLINE was searched for articles assessing urinary biomarkers for diagnosis or prediction of kidney allograft acute rejection published in the last five years (from 1 January 2015 to 31 May 2020). This review follows the Preferred Reporting Items for Systematic Reviews and Meta-analysis (PRISMA) guidelines. Articles providing targeted or unbiased urine sample analysis for the diagnosis or prediction of both acute cellular and antibody-mediated kidney allograft rejection were included, analyzed, and graded for methodological quality with a particular focus on study design and diagnostic test accuracy measures. Urinary C-X-C motif chemokine ligands were the most promising and frequently studied biomarkers. The combination of precise diagnostic reference in training sets with accurate validation in real-life cohorts provided the most relevant results and exciting groundwork for future studies.

The Inhibition of Complement System in Formal and Emerging Indications: Results from Parallel One-Stage Pairwise and Network Meta-Analyses of Clinical Trials and Real-Life Data Studies

This manuscript presents quantitative findings on the actual effectiveness of terminal complement component 5 (C5) inhibitors and complement component 1 (C1) esterase inhibitors through their formal and common “off-label” (compassionate) indications. The results emanated from pairwise and network meta-analyses to present evidence until September 2019. Clinical trials (CT) and real-life non-randomized studies of the effects of interventions (NRSI) are consistent on the benefits of C5 inhibitors and of the absence of effects of C1 esterase inhibitors (n = 7484): Mathematically, eculizumab (surface under the cumulative ranking area (SUCRA) >0.6) and ravulizumab (SUCRA ≥ 0.7) were similar in terms of their protective effect on hemolysis in paroxysmal nocturnal hemoglobinuria (PNH), thrombotic microangiopathy (TMA) in atypical hemolytic uremic syndrome (aHUS), and acute kidney injury (AKI) in aHUS, in comparison to pre-/off-treatment state and/or placebo (SUCRA < 0.01), and eculizumab was efficacious on thrombotic events in PNH (odds ratio (OR)/95% confidence interval (95% CI) in CT and real-life NRSI, 0.07/0.03 to 0.19, 0.24/0.17 to 0.33) and chronic kidney disease (CKD) occurrence/progression in PNH (0.31/0.10 to 0.97, 0.66/0.44 to 0.98). In addition, meta-analysis on clinical trials shows that eculizumab mitigates a refractory generalized myasthenia gravis (rgMG) crisis (0.29/0.13 to 0.61) and prevents new acute antibody-mediated rejection (AMR) episodes in kidney transplant recipients (0.25/0.13 to 0.49). The update of findings from this meta-analysis will be useful to promote a better use of complement inhibitors, and to achieve personalization of treatments with this class of drugs.

Acute Rejection Following Kidney Transplantation: State-of-the-Art and Future Perspectives.

Although acute renal graft rejection rate has declined in the last years, and because an adequate therapy can improve graft outcome, its therapy remains as one of the most significant challenges for pharmacists and physicians taking care of transplant patients. Due to the lack of evidence highlighted by the available metaanalyses, we performed a narrative review focused on the basic mechanisms and current and future therapies of acute rejection in kidney transplantation. According to Kidney Disease/Improving Global Outcomes (KDIGO) guidelines, both clinical and subclinical acute rejection episodes should be treated. Usually, high dose steroids and basal immunosuppression optimization are the first line of therapy in treating acute cellular rejection. Rabbit antithymocytic polyclonal globulins are used as rescue therapy for recurrent or steroid-resistant cellular rejection episodes. Current standard-of-care (SOC) therapy for acute antibody-mediated rejection (AbMR) is the combination of plasma exchange with intravenous immunoglobulin (IVIG). Since a significant rate of AbMR does not respond to SOC, different studies have analyzed the role of new drugs such as Rituximab, Bortezomib, Eculizumab and C1 inhibitors. Lack of randomized controlled trials and heterogenicity among performed studies limit obtaining definite conclusions. Data about new direct and indirect B cell and plasma cell depleting agents, proximal and terminal complement blockers, IL-6/IL-6R pathway inhibitors and antibody removal agents, among other promising drugs, are reviewed.

EFFECT OF PRETRANSPLANT RITUXIMAB ADMINISTRATION ON LIVING KIDNEY RECIPIENTS WITH SENSITIZATION HISTORY WITHOUT PREFORMED DONOR-SPECIFIC HLA ANTIBODY

Introduction: In transplant recipients, donor-reactive alloimmune memory cells can arise from prior exposure to foreign HLA by sensitization history. It is reported that recipients with sensitization history have higher incidence of antibody-mediated rejection (ABMR), even without positive crossmatch and positive preformed donor-specific antibody (DSA). We investigated the effect of preoperative rituximab administration on the living kidney recipients with sensitization history without preformed DSA. Materials and Methods: A total of 310 living kidney recipients who had negative crossmatch and preformed DSA was administered rituximab before kidney transplantation. We divided them into the following three groups: control group (n=186) without a history of sensitization, transfusion group (n = 74) with a history of transfusion only, and pregnancy group (n = 50) with a history of pregnancy only. The DSA was measured using the Luminex single bead method before transplantation. We investigated the incidence of ABMR among the three groups. Results: There was no significant difference between the three groups in terms of functioning graft, overall death, no death-censored graft failure, and death-censored graft failure. The Kaplan–Meier cumulative death-censored graft survival in recipients who were negative for preformed DSA at 1, 5, and 10 years after living kidney transplantation was 98.9%, 96.2%, and 92.3% in the control group, 98.6%,96.5%, and 96.5% in the transfusion group, and 100%, 97.0%, and % 80.8% in the pregnancy group, respectively, showing no significant difference (Log-rank test = 0.703). There was no significant difference in graft function between the three groups. The incidence of acute ABMR was higher in the pregnancy group than in the transfusion and control groups (18.0%, 8.1%, and 5.9%, respectively, p = 0.024) The acute ABMR-free rate in recipients negative for preformed DSA at 1, 3, and 5 years after living kidney transplantation was 96.2%, 95.1%, and 93.7% in the control group, 94.6%, 94.6%, and 91.5% in the transfusion group, and 86.0%, 84.0%, and 81.4% in the pregnancy group, respectively (Log-rank test = 0.021). The pregnancy group had a higher incidence of chronic ABMR than the Control and Transfusion groups (14.0%, 8.1%, and 6.8%, respectively), but with no significant difference (p = 0.331). The chronic ABMR free rate at 10 years after living kidney transplantation was 91.5% in the control group, 93.0% in the transfusion group, and 84.4% in the pregnancy group, respectively, showing no significant difference (Log-rank test = 0.529). The incidence of complication including infection was similar among the three groups. Conclusions: The incidence of acute and chronic ABMR was still high in the recipients with pregnant history without preformed DSA even after rituximab administration.

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).

Plasma volume treated with double filtration plasmapheresis and outcomes of acute antibody-mediated rejection in kidney transplant recipients: A retrospective cohort study.

A retrospective cohort study was conducted to evaluate the association between the plasma volume treated by double filtration plasmapheresis and allograft outcomes for the treatment of acute antibody-mediated rejection in kidney transplant recipients. Patients were divided into two groups: group 1, plasma volume treated between 1 and <1.3 total plasma volume and group 2, plasma volume treated ≥1.3 total plasma volume. Primary outcome was ≥50% reduction of serum creatinine rising from baseline value at 1 month. A total of 32 courses (146 sessions) of double filtration plasmapheresis were performed; 17 and 15 courses in group 1 and group 2, respectively. Primary outcome occurred in 41% of group 1 and 40% of group 2 (adjusted risk ratio 1.15 [95%CI, 0.48-2.76]). Graft loss at 1 year did not differ between the two groups (adjusted hazard ratio 0.65 [95%CI, 0.23-1.87]). Infection tendency seemed to be higher in group 2 (40% vs 18%, P = .243).

Mechanism of Graft Damage Caused by NTPDase1-activated Macrophages in Acute Antibody-Mediated Rejection

ObjectivesTo investigate the effect and mechanism of macrophage activation and graft damage caused by nucleoside triphosphate diphosphohydrolase 1 (NTPDase1) in acute antibody-mediated rejection (AMR). MethodsAcute AMR was induced in different skin-grafted nude mouse models with wild-type NTPDase1 expression, transgene-enhanced NTPDase1 expression, or NTPDase1 gene knockout. Several methods (eg, real-time fluorescence quantitative polymerase chain reaction, high-performance liquid chromatography [HPLC], immunofluorescence, flow cytometry, and luciferin/luciferase assays) were used to study (at the histologic and molecular levels) the extracellular adenosine diphosphate (ADP) concentration, macrophage proliferation, major histocompatibility complex (MHC) class II antigen expression on the surface of macrophages, B-cell activating factor (BAFF) expression in the peripheral blood serum, and the total number of SmIg-positive B cells during acute AMR. The relative activity of NTPDase1 in B cells and epithelial cells, pathologic changes, and the incidence of positive C4d deposition around the capillaries of skin grafts on the different nude mice were studied. ResultsMacrophages proliferated significantly when acute AMR occurred. The higher the NTPDase1 expression level, the lower the extracellular ADP concentration, the expression of MHC class II antigens on the surface of macrophages, the expression of BAFF in the peripheral blood serum, and the total number of SmIg-positive B cells, indicating negative correlations. The relative activity of NTPDase1 in B cells and epithelial cells of the skin graft was different among the different mice. The higher the NTPDase1 expression level, the lower the degree of pathologic damage to the skin graft. ConclusionsImbalance in extracellular ADP degradation by NTPDase1 may promote macrophage activation, and activated macrophages may be an important cause of graft damage.

Atrase B, a novel metalloprotease with anti-complement and anti-coagulant activity, significantly delays discordant cardiac xenograft rejection.

Both the complement and the coagulation systems play important roles in the development of hyperacute or acute antibody-mediated xenograft rejection. Atrase B is a novel metalloproteinase isolated from the venom of Naja atra. In this study, we investigated the inhibitory effects of atrase B on complement activation and coagulation, as well as the effect on xenograft survival in a discordant xenotransplantation model. The in vitro anti-complement activity of atrase B was evaluated using a normal human serum (NHS)-mediated complement-dependent cytotoxicity model with an immortalized porcine aortic endothelial cell line (iPEC) as the target. The in vivo inhibitory effects on complement activity and coagulation function were measured in rats after the administration of atrase B. Guinea pig hearts were transplanted heterotopically into Wistar rats with or without atrase B pre-treatment. Pre-treatment of the NHS with atrase B inhibited the cell lysis of iPECs in a dose-dependent manner. FACS analysis showed that atrase B potently suppressed the deposition of C5b-9, but not C3c and C4c, on iPECs. In vivo, atrase B-treated rats showed a significant reduction in serum complement activity; markedly prolonged PT, APTT, and TT; and a decreased plasma level of fibrinogen. When compared to PBS treatment evaluated at study endpoint, atrase B treatment significantly delayed xenograft rejection and attenuated pathologic damage, the formation of platelet microthrombi, and the deposition of fibrin and C5b-9. The dual activities of anti-complement and anti-coagulation make atrase B a potential adjuvant therapeutic drug for use in xenotransplantation.

TO007PLASMA EXTRACELLULAR VESICLES MEDIATE ENDOTHELIAL TO MESENCHYMAL TRANSITION AND TUBULAR SENESCENCE IN RENAL ANTIBODY MEDIATED REJECTION BY COMPLEMENT ACTIVATION

Abstract Background and Aims EVs (Extracellular vesicles) are circulating microparticles able to mediate cell-to cell communication by carrying proteins, DNA, RNA or antibodies on their surface. EV are emerging as pivotal in renal Antibody-mediated rejection (AMR), one of the major causes of transplant failure associated to a massive complement activation. AMR is characterized by endothelial to mesenchymal transition (EndMT) and the occurrence of tubular accelerated senescence process, known as graft “Inflammaging”. However, the potential role of EVs in accelerating the renal aging and graft fibrosis after AMR is not well understood. Method Plasma EVs were isolated from 10 Acute AMR (AAMR), 10 Chronic AMR (CAMR) patients, 5 stable graft transplanted patients and 5 healthy volunteers. EVs were isolated by ultracentrifugation at 100.000 g for 1h at 4°C, quantified by Nanoparticle Tracking Analysis (Nanosight, NTA EV/ml) and characterized by FACS (Attune Nxt). RPTEC and endothelial cell culture were incubated with EVs (5e+4 EVs/cells target for 24h. MTT test was performed to assess cell viability. Cellular senescence was investigated by qPCR for p21, p53, Klotho and CYP1B1 and SA-β-gal staining were performed. To assess EndMT analysis for CD31, VE-cadherin, Vimentin, Collagen I was performed by FACS. mRNA level of C3 and CFH were also measured by qPCR and C4d deposits were evaluated in endothelial cell colture by IF. Renal biopsies were then analyzed for inflammaging (p16INK4a) and EndMT markers (CD31/αSMA) by IHC and IF. Results The Nanosight analysis showed significant differences in the amount of-EVs count per ml of plasma in AMR patients compared to healthy subjects. EVs appeared to be significantly augmented in acute AMR, in a higher manner than chronic AMR (NTA, p=0.0154). By cytofluorimetric analysis, the endothelial markers CD31 and VE- cadherin appeared to be significantly increased compared of healthy control, indicating a predominant endothelial EV origin (p&amp;lt;0.05). Furthermore, an increase for CD3, CD4, CD8, CD40 and CD40L lymphocyte/monocytes markers was found. In vitro, the exposure of RPTEC and endothelial cells to AMR-derived EVs did not induce the loss of cell proliferation. However, AMR-derived EVs induced senescence in RPTEC, as observed by increase in SA-β-gal positive cells, upregulation of p21, p53, CYP1B1 and downregulated KL gene expression (p&amp;lt;0.05). EVs induced the EndMT as observed by FACS with the downregulation of CD31, VE-cadherin (CD144) and increase of Vimentin and Collagen I (p=0.025). To evaluate the contribution of EVs to local complement activation, C3 and CFH qPCR analysis were performed. EVs from AMR patients induced a significant increase in C3 gene expression with concomitant downregulation in CFH in RPTEC. EV exposition induced the classical and lectin pathway activation in endothelial culture medium, and C4d deposition. These data support the hypothesis that circulating EVs can amplify local complement activation in systemic endothelial and tubular cells during AMR, therefore leading to accelerated senescence and fibrosis as later effects. Finally, renal AMR biopsies showed significant tubular senescence as indicated by p16 expression; p16 was significantly upregulated in Chronic compared with Acute AMR biopsies (p&amp;lt;0.05). The AMR biopsies showed positivity for EndMT, as indicated by CD31 decrease and interstitial αSMA upregulation (p&amp;lt;0.05). Conclusion These results suggest a putative role for circulating AMR derived-EVs in inducing the tubular inflammaging by local complement activation and early fibrosis by EndMT. The EVs cargo characterization that is ongoing might highlight novel targets for therapeutic intervention.

Mechanisms of organ transplant injury mediated by B cells and antibodies: Implications for antibody-mediated rejection.

Recent adjustments to the histological diagnosis and the introduction of molecular classification are providing renewed support for the paradigm that antibody-mediated rejection (ABMR) is an important clinical problem for which there is an urgent need for better therapies. Acute ABMR is observed when the graft is exposed to rapid increases in high-titer donor-specific antibodies (DSA) that are most often generated as anamnestic responses in sensitized recipients or de novo responses in nonsensitized patients who are nonadherent. Chronic ABMR is associated with slower increases in DSA, which may be high or low titer and transient or persistent. These DSA elicit cycles of injury and repair that manifest as multilamination of the peritubular capillary basement membrane or arteriopathy manifesting as intimal fibrosis. Mitigating the problem of AMBR requires the anamnestic and de novo DSA responses to be prevented and established DSA responses to be reversed. To this end, a better understanding of the immunobiology of DSA production is necessary and also the development of assays capable of detecting early humoral immune responses.Recent advances in understanding the immunobiology of B cells and areas requiring further investigation that might lead to new therapies or better diagnosis are discussed in this review.

P1755EFFICACY AND SAFETY ECULIZUMAB FOR THE TREATMENT OF ANTIBODY MEDIATED REJECTION FOLLOWING RENAL TRANSPLANTATION

Abstract Background and Aims : We evaluated the efficacy and safety of eculizumab in comparison with plasmapheresis (PP) and intravenous immunoglobulin (IVIG) therapy in renal transplant recipients diagnosed with antibody-mediated rejection (AMR). Methods This was a multi-center, open-label, prospective, randomized analysis. The patients were randomized as to therapy type (eculizumab infusions or standard of care, SOC: PP/IVIG). The patients (eculizumab arm: 7 patients, SOC arm: 4 patient) were evaluated for the continuing presence of donor-specific antibodies (DSAs) and C4d (staining on biopsy), as well as histological evidence, using repeat renal biopsies after treatment. Results The allograft biopsies revealed that eculizumab did not prevent the progression to transplant glomerulopathy. Only 2 patients in the SOC arm experienced rejection reversal, and no graft losses occurred in either group. Following AMR treatment, the DSA titers generally decreased compared to titers taken at the time of AMR diagnosis. There were no serious adverse effects in the eculizumab arm. Conclusion Eculizumab alone is not sufficient to treat AMR and does not prevent acute AMR from progressing to chronic AMR or to transplant glomerulopathy. However, it should be considered as a potential alternative therapy because it may be associated with decreased DSA levels.

Favorable Short-Term Outcome of Living Donor Kidney Transplantations in Flow Cytometry Crossmatch Positive Cases by Pretransplant Splenectomy: A Case Report

BackgroundThe introduction of rituximab has contributed to successful living donor kidney transplantations in ABO-incompatible recipients and has replaced splenectomy for desensitization. However, several reports still suggest that postoperative splenectomy may be effective in preventing graft failure in patients with acute antibody-mediated kidney transplant rejection (AAMR) in kidney transplantation. Therefore, we aim to assess if preoperative splenectomy also could be an alternative practical choice to avoid AAMR in high-risk rejection cases such as flow cytometry crossmatch (FCXM)-positive cases. Material and methodWe carried out 4 living donor kidney transplantations in FCXM-positive cases: 3 underwent pretransplant splenectomy, and 1 did not. ResultsAll 3 cases in whom pretransplant splenectomy was performed were discharged without rejection. On the contrary, in the case where pretransplant splenectomy was not performed, there was graft rejection and additional desensitization therapies were needed. ConclusionWhile larger clinical studies with longer observation periods are needed, our report suggested that pretransplant splenectomy may lead to successful short-term kidney transplantation outcomes in FCXM-positive cases.

Early Steroid Withdrawal Protocol With Basiliximab and Rituximab in ABO-Incompatible Kidney Transplant Recipients

ObjectivesCorticosteroids remain an important component of immunosuppressive regimens in high-risk kidney transplants. In this study, we investigated the efficacy of early steroid withdrawal with basiliximab and rituximab in ABO–blood type incompatible (ABO-i) recipients of kidney transplants. MethodsBetween 2008 and 2019, 15 patients underwent ABO-i kidney transplantation. Seven of the 15 patients were treated with a steroid maintenance protocol and the remaining 8 with an early steroid withdrawal protocol. The immunosuppressive protocol consisted of tacrolimus, mycophenolate mofetil, and methylprednisolone (MP), with basiliximab administered as induction therapy. Rituximab was administered as a single 200-mg dose 1 to 4 weeks before kidney transplantation. Two to 4 sessions of either double-filtration plasmapheresis or regular plasmapheresis or both were performed to remove anti-AB antibodies before transplantation. During surgery, MP was administered at a dose of 500 mg; thereafter, the dosage was tapered rapidly, and the drug was discontinued on day 14 post transplant. ResultsIn the steroid maintenance group, 2 patients experienced acute antibody-mediated rejection (AMR). One patient with severe AMR had graft loss on postoperative day 4. Patient and graft survival rates in the steroid maintenance group were 100% and 86%, respectively. MP was successfully withdrawn in the steroid withdrawal group. In this group, there was no biopsy-proven rejection. Patient and graft survival rates were 100%, and when last measured, serum creatinine level ± SD was 1.6 ± 0.8 mg/dL. ConclusionsOur protocol successfully enabled the early withdrawal of steroids in recipients of ABO-i grafts; however, further follow-up is necessary to confirm our results.

Intravenous immunoglobulin significantly reduces exposure of concomitantly administered anti-C5 monoclonal antibody tesidolumab.

Awareness of drug-drug interactions is critical in organ transplant recipient management. However, biologic agents interfering with monoclonal antibodies is not widely considered. We report the effect of high-dose intravenous immunoglobulin (IVIg) on safety, tolerability, pharmacokinetics (PK), and pharmacodynamics (PD) of the human anti-C5 monoclonal antibody tesidolumab (LFG316) in end-stage renal disease patients awaiting kidney transplant. In this single-center, phase 1, open-label, parallel-group study, 8 patients were assigned to receive either single-dose tesidolumab+IVIg or tesidolumab alone, with 56-day follow-up. Within-group PK parameters were consistent. Mean tesidolumab exposure decreased 34%, clearance increased 63%, and half-life decreased 41% comparing tesidolumab+IVIg to tesidolumab alone. IVIg influence on tesidolumab elimination was most evident in the first 3weeks. Complete suppression of both total and alternative complement activities was maintained for 4weeks in the tesidolumab alone group and for 2weeks in the tesidolumab+IVIg group. Tesidolumab was well tolerated. IVIg infused before tesidolumab affected tesidolumab PK and PD, resulting in a shortened period of full complement activity inhibition. These findings suggest a clinically relevant impact of IVIg on monoclonal antibody clearance and indirectly hint at an IVIg mechanism of action in treating autoimmune diseases and allosensitization by accelerating pathogenic IgG antibody degradation. Trial registration number: NCT02878616.

Natural Killer Cells: Critical Effectors During Antibody-mediated Rejection of Solid Organ Allografts.

Antibody-mediated rejection (AMR) is an important cause of graft loss and continues to present a formidable obstacle to successful transplantation. Unresolved problems continue to be the absence of effective strategies to ablate the donor-specific antibody (DSA) response as well as to attenuate the antibody-mediated graft tissue injury. While the properties of DSA that cause greater graft tissue injury and the characteristic microvascular pathology of the graft injury are well documented, the mechanisms underlying the injury mediated by the antibodies remains unclear. Recent transcriptome interrogation of kidney and heart biopsies procured during ongoing AMR has indicated the expression of genes associated with natural killer (NK) cell activation that is absent during T cell-mediated rejection. The expression of NK cell transcripts during AMR correlates with the presence of CD56+ cells in the microcirculation inflammation observed during AMR. Several mouse models have recently demonstrated the role of NK cells in antibody-mediated chronic vasculopathy in heart allografts and the requirement for NK cell activation during acute AMR of kidney allografts. In the latter model, NK cell activation within kidney allografts is regulated by the activation of myeloid cells producing myeloperoxidase. Overall, the studies to date indicate that AMR constitutes a complex series of DSA-induced interactions with components of the innate immune response. The innate immune participants and their expressed effector functions resulting in the rejection are beginning to be identified. The identification of these components should uncover novel targets that can be used to attenuate acute graft tissue injury in the presence of DSA.

Quadritherapy vs standard tritherapy immunosuppressant regimen after heart transplantation: A propensity score-matched cohort analysis.

After heart transplant, adding everolimus (EVL) to standard immunosuppressive regimen mostly relies on converting calcineurin inhibitors (CNIs) into EVL. The aim of this study was to describe the effects of combining low-dose EVL and CNIs in maintenance immunosuppression regimen (quadritherapy) and compare it with standard tritherapy associating standard-dose CNIs, mycophenolate mofetil, and corticosteroids. In the 3-year registry cohort of heart transplanted patients, those who received quadritherapy were compared with those who received tritherapy. EVL was added after 3months posttransplant. Three analyses were performed to control for confounders: propensity score matching, multivariable survival, and inverse probability score weighting analyses. Among 213 patients who were included (75 with quadritherapy), propensity score matching selected 64 unique pairs of patients with similar characteristics. In the matched cohort (n=128), quadritherapy was associated with fewer deaths (3 [4.7%] vs 17 [21.9%], P=.007) and biopsy-proven acute rejections (15 [23.4%] vs 31 [48.4%], P=.002). These results were confirmed in the overall cohort (n=213), after multivariable and inverse probability score weighting analyses. Renal function and donor-specific HLA-antibodies remained similar in both groups. Low-dose combination quadritherapy was associated with fewer deaths and rejections, compared with standard immunosuppression tritherapy.