Transplant-associated Thrombotic Microangiopathy Research Articles

Endothelial Complications of Hematopoietic Cell Transplantation for Sickle Cell Disease

Introduction Hematopoietic cell transplantation (HCT) is a curative therapy for sickle cell disease (SCD), with especially favorable outcomes in young patients from HLA-identical donors. Unfortunately, HCT is associated with endothelial injury syndromes (EIS), including veno-occlusive disease/sinusoidal obstruction syndrome (VOD/SOS), transplant-associated thrombotic microangiopathy (TA-TMA), and also acute graft-versus-host disease (GVHD), that increase transplant risk. This is further complicated by hemolysis-mediated endothelial dysfunction in patients with SCD. The impact of EIS in this population is not certain. We thus sought to better evaluate endothelial complications of HCT for SCD in a large, international registry. Methods We examined de-identified records of HCT for SCD that were retrieved from data on patients transplanted between 1991 and 2020 in the United States submitted to the Center for International Blood and Marrow Transplant Research (CIBMTR) obtained through curesickle.org. Patients were followed longitudinally until death, loss to follow-up, or last contact through June 2021 at 3, 6, 12, and 24 months after HCT, and then every 2 years. Donors included HLA-matched siblings, haploidentical relatives, and HLA-matched and HLA-mismatched unrelated donors. We examined overall survival, event-free survival, and acute and chronic GVHD. Cox regression models were used to examine for risk factors associated with TMA and VOD. In addition, one-factor (univariate) analysis was used to identify factors associated with higher risk complications. Results A total of 1641 unique patients underwent a first allogeneic HCT between 1991 and 2020, with a median year of HCT of 2014. Of HCT recipients, 67.7% were below the age of 18 years at HCT and 74.7% had Karnofsky performance score ≥ 90. Acute GVHD grades II-IV developed in 18.3% and 22.3% developed chronic GVHD. Graft failure was reported in 17.6% following HCT, which was from an HLA-identical sibling in 61.5%, mismatched relative in 17.6%, matched unrelated donor in 10.2%, and mismatched unrelated donor in 10.7%. Conditioning regimen was myeloablative (50.8%), reduced intensity (23%), or non-myeloablative (22.3%). Patients were followed for a median of 47.8 months (0.3 - 312.9), with 3-year overall survival 91.2% and 3-year event-free survival 85.2%. Median time to death was 9.6 months for 152 patients. Estimated hazard ratio (HR) of death in 7/8 vs. 8/8 HLA matching was 1.5 (95% CI: 0.752, 2.445), which was not statistically significant. However, HR of death for ≤ 6/8 vs. 8/8 HLA matching was 1.7 (95% CI: 1.215, 2.445), indicating a statistically significant increased risk of death. TA-TMA was reported in 27 patients at a median of 2.8 months post-HCT. Univariate analysis of risk factors for TA-TMA indicated increasing incidence with the year of HCT. Age at HCT, HLA matching, and conditioning regimen intensity were not significantly associated. VOD was reported in 24 cases; Cox proportional hazards analysis indicated decreasing incidence with year of HCT. Estimated HR for VOD of patients who developed grade II-IV AGVHD group was 2.965, (95% C.I. 1.089, 8.074). Age at HCT, conditioning intensity, and donor type were not significant. Acute and chronic GVHD were associated with recipient age > 10 years and donors other than HLA-matched siblings; non-myeloablative conditioning was protective against GHVD development. Conclusion Incidence of endothelial complications following HCT for SCD is low, although TA-TMA has been increasingly recognized in recent years. VOD has been observed less frequently over time and correlates with acute GVHD. Donor type, recipient age, and conditioning intensity have the greatest impact on GVHD development.

Complement Activation Is Associated with Endothelial Damage in Hematopoietic Stem Cell Transplant Associated-Thrombotic Microangiopathy

Introduction: Hematopoietic stem cell transplant-associated thrombotic microangiopathy (HSCT-TMA) is a life-threatening complication of HSCT. Identification of at-risk patients is challenging, leading to delays in diagnosis and poor outcomes. Degradation of the glycocalyx and dysregulated complement activation are integral to the pathophysiology. The glycocalyx components thrombomodulin (TM) and syndecan-1 (SYND1) are shed during cell damage, and detection in patient plasma may serve as biomarkers of endothelial cell (EC) dysfunction. Therapeutic intervention to preserve glycocalyx integrity may protect the endothelium and also improve the clinical outcome during HSCT-TMA. Additionally, plasma Ba, an alternative complement pathway (AP) activation product, has been identified as a prognostic biomarker of HSCT-TMA. Our objective was to explore the link between excessive AP activation and endothelial damage in the context of HSCT-TMA and to potentially identify biomarkers to aid in its diagnosis. Methods: Biomarker levels of soluble TM, SYND1, and Ba were measured in plasma of pediatric HSCT patients with and without (controls) TMA obtained from Texas Children's Hospital. Sample acquisition was approved by Baylor College of Medicine Institutional Review Board. Biomarkers were also measured in a pre-clinical in vivo model of inflammation-mediated complement activation similar to HSCT-TMA, in which C57BL/6J mice were injected with lipopolysaccharide (LPS) to induce complement activation, followed by treatment with AP (anti-fB IgG) and terminal complement pathway (anti-C5 IgG) inhibitors or an IgG isotype control. Finally, as the immunosuppressant cyclosporin A (CsA) is a known trigger of HSCT-TMA, the role of complement in CsA-mediated damage in human ECs (HMEC-1 cells and HUVECs) was assessed in vitro. ECs were incubated with CsA followed by normal human serum (NHS) in the presence or absence of the C5 complement inhibitor eculizumab. TM was then measured by fluorescent staining on the cell surface and quantified using mean fluorescence intensity (MFI). Results: HSCT-TMA patients (n=11), compared to HSCT control patients (n=7), had significantly elevated levels of biomarkers of glycocalyx damage (TM: 18.3 ± 10.9 ng/mL and 6.6 ± 2.9 ng/mL, respectively; P<0.01; SYND1: 175.3 ± 177.0 ng/mL and 35.8 ± 18.9, respectively; P<0.05). A strong positive correlation between TM and SYND1 was observed (Pearson r=0.89). Plasma Ba was also significantly elevated in patients with TMA compared to those without (1790.0 ± 1262.0 ng/mL and 652.1 ± 233.5 ng/mL, respectively; P<0.05), and correlated positively with both TM and SYND1 levels (Pearson r=0.72 and 0.50, respectively). We have previously shown in an in vivo model of inflammation-mediated complement activation that LPS-injected mice, compared to saline-injected control mice, had significantly increased plasma Ba levels. Here we demonstrated LPS-injected mice (which also received IgG isotype control) had higher circulating levels of TM than untreated mice (35.1 ± 5.8 ng/mL [n=6] and 10.9 ± 1.6 ng/mL [n=6], respectively; P<0.0001). Inhibition of alternative (anti-fB IgG) and terminal (anti-C5 IgG) pathways of complement significantly attenuated TM levels (compared to isotype control [35.1 ± 5.8 ng/mL]; anti-FB: 25.2 ± 5.3 ng/mL, P<0.01; anti-C5: 26.2 ± 4.9 ng/mL, P<0.05, Fig. 1). TM was positively correlated with Ba (Pearson r=0.68). In vitro treatment of HMEC-1 cells with CsA led to deposition of iC3b and C5b-9, and C5 inhibition with eculizumab significantly reduced C5b-9 deposition (P< 0.0001) but had no effect on iC3b deposition. Treatment of HUVECs with CsA also reduced surface expression of TM (P<0.0001), and TM loss was partially restored by eculizumab (P<0.05, Fig 2). Conclusion: Plasma biomarkers of endothelial damage were elevated in patients with HSCT-TMA and in mice with inflammatory-mediated complement activation. Furthermore, AP activation positively correlated with biomarkers of endothelial damage. Blockade of complement activation significantly reduced markers of endothelial damage in both in vivo and in vitro models. These results provide further evidence linking complement activation and endothelial damage in HSCT-TMA and suggest that the use of these biomarkers may aid in the diagnosis of HSCT-TMA. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Trial in Progress: An Open-Label, Multi-Center Phase 2 Study Evaluating Efficacy and Safety of the Masp-2 Inhibitor Narsoplimab in Pediatric Patients with High-Risk Hematopoietic Stem Cell Transplant-Associated Thrombotic Microangiopathy (HSCT-TMA)

Background: Hematopoietic stem cell transplant-associated thrombotic microangiopathy (HSCT-TMA; also known as TA-TMA) is a potentially life-threatening complication associated with multi-organ injury and significant morbidity and mortality. HSCT-TMA incidence rates of up to 39% have been reported in both pediatric and adult allogeneic HSCT (alloHSCT) recipients; high-risk pediatric patients with proteinuria and evidence of terminal complement activation (elevated sC5b-9) had a 1-year post-HSCT survival of <20% versus 100% in those with normal sC5b-9 levels and no proteinuria (Jodele S, et al. Blood. 2014;124:645-653). In the HSCT setting, toxic conditioning regimens, infection, and graft-versus-host disease (GVHD) can cause endothelial injury, which triggers activation of the lectin pathway of complement and in turn the coagulation cascade, together leading to TMA. Narsoplimab (OMS721) is a fully human IgG4 monoclonal antibody that inhibits mannan-binding lectin-associated serine protease-2 (MASP-2), the effector enzyme of the lectin pathway and an activator of the coagulation cascade. Narsoplimab was previously evaluated for safety and efficacy in adults with high-risk HSCT-TMA in an open-label pivotal trial (NCT02222545); narsoplimab treatment was well tolerated and resulted in clinical response and favorable overall survival (Khaled SK, et al. J Clin Oncol. 2022; JCO2102389). Currently, HSCT-TMA has no approved therapy, and therefore represents a significant unmet medical need. Here, we describe the design of the first clinical trial evaluating the efficacy and safety of narsoplimab in pediatric patients with HSCT-TMA. Study Design and Methods: This is an open-label, multi-center Phase 2 trial of narsoplimab in pediatric patients (Figure 1). Eligible patients are aged ≥28 days to <18 years, have received alloHSCT for the treatment of non-malignant or malignant disease, and have been diagnosed with high-risk HSCT-TMA. Exclusion criteria include prior treatment with eculizumab, ravulizumab, or defibrotide within 3 months prior to screening, having Shiga toxin-producing Escherichia coli hemolytic uremic syndrome (STEC-HUS), or ADAMTS13 activity <10%. Patients will receive narsoplimab 4 mg/kg via intravenous (IV) infusion twice weekly during the 8-week treatment period (Days 1-56). If a patient meets all clinical response criteria prior to 8 weeks of treatment, dosing may be decreased to 4 mg/kg IV once weekly until the end of the treatment period. Narsoplimab can be used in conjunction with standard-of-care treatments. At the end of the treatment period, patients will enter a 44-week follow-up period (Days 60-365). The planned recruitment is at least 18 pediatric patients, distributed across the age range. The primary endpoint is 100-day survival from date of HSCT-TMA diagnosis. Secondary endpoints include: safety, survival at 52 weeks, overall survival from date of HSCT-TMA diagnosis, anti-drug antibody response, clinical response rate, narsoplimab pharmacokinetics and measurement of lectin pathway activity. Conclusion: Following the favorable results obtained in a pivotal Phase 2 study in adults with HSCT-TMA, further evaluation of narsoplimab efficacy and safety in pediatric patients with high-risk HSCT-TMA is warranted. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Pulmonary Manifestations and Vascular Changes in Pediatric Transplantation-Associated Thrombotic Microangiopathy

Although transplant-associated thrombotic microangiopathy (TA-TMA) commonly complicates pediatric hematopoietic cellular therapy (HCT), pulmonary manifestations and histology of TA-TMA (pTA-TMA) are rarely reported, with scant data available on timing, risk factors, pathogenesis, and outcomes. Pulmonary hypertension (PH) and diffuse alveolar hemorrhage (DAH) are recognized manifestations of pTA-TMA. The objective of this study was to characterize the pathologic findings, outcomes, and coincident diagnoses preceding biopsy-proven pTA-TMA. In Institutional Review Board- approved retrospective studies, available lung tissue was reviewed at 2 institutions between January 2016 and August 2021 to include those with pulmonary vascular pathology. Histologic features of pTA-TMA were present in 10 children with prior respiratory decline after an allogeneic HCT (allo-HCT; n=9) or autologous HCT (n=1). Pathologic lesions included muscular medialization, microthrombi, and red cell fragments, in addition to perivasculitis and intimal arteritis. Parenchymal findings included diffuse alveolar damage, organizing pneumonia, and plasmocytic infiltrates. Six children were clinically diagnosed with TA-TMA, and all were treated with eculizumab, at a median of 2.5 days after clinical diagnosis (range, 0 to 11 days). Four were identified postmortem. Coincident pulmonary infection was confirmed in 8 of the 10 patients. Five allo-HCT recipients (56%) experienced graft-versus-host disease (GVHD; 4 acute, 1 chronic) prior to the onset of respiratory symptoms. Two patients (20%) had clinically recognized DAH, although 9 (90%) had evidence of DAH on histology. Although all 10 patients underwent echocardiography at the time of symptom onset and 9 had serial echocardiograms, only 2 patients had PH detected. Treatments varied and included sildenafil (n=3), steroids (n=1), and eculizumab (n=6). One patient was alive at the time of this report; the remaining 9 died, at a median of 52 days after onset of respiratory symptoms (range 4 to 440 days) and a median of 126 days post-HCT (range, 13 to 947 days). pTA-TMA is a heterogeneous histologic disease characterized by arteriolar inflammation, microthrombi, and often DAH. pTA-TMA presented with respiratory decline with systemic TA-TMA in all patients. Clinicians should maintain a high degree of suspicion for DAH in patients with TA-TMA and pulmonary symptoms. Coincident rates of GVHD and pulmonary infections were high, whereas the rate of PH identified by echocardiography was 20%. Outcomes were poor despite early use of eculizumab and other therapies. Our data merit consideration of pTA-TMA in patients with acute respiratory decline in the setting of systemic TA-TMA, GVHD, and infection. Investigation of additional therapies for pTA-TMA is needed as well. © 2022 American Society for Transplantation and Cellular Therapy. Published by Elsevier Inc.

Basiliximab for early perioperative transplant-associated thrombotic microangiopathy after lung transplantation: a case report

BackgroundThrombotic microangiopathy is a syndrome characterized by microangiopathic hemolytic anemia and platelet aggregation, which is caused by endothelial injury, microcirculation thrombosis, and fibrin deposition. Transplant-associated thrombotic microangiopathy rarely occurs after lung transplantation and the onset is generally later than that after bone marrow or other solid organ transplantation. The treatment is to stop administration of the causal agent, which is often a calcineurin inhibitor, such as tacrolimus and cyclosporine. We herein report the case of a patient with early post-transplant thrombotic microangiopathy after lung transplantation treated by introducing basiliximab and temporarily stopping any calcineurin inhibitors until resuming treatment with an alternative calcineurin inhibitor.Case presentationA 58-year-old Asian woman underwent bilateral lung transplantation for hypersensitivity pneumonitis caused by an avian antigen, or bird fancier’s lung disease. Postoperatively, she was started on triple immunosuppressive therapy, which included tacrolimus, mycophenolate mofetil, and steroids. On postoperative day 6, she developed thrombocytopenia followed by fever, hemolytic anemia, renal dysfunction, and purpura on her limbs and abdomen. She was diagnosed with transplant-associated thrombotic microangiopathy, and tacrolimus was thought to be the causal agent. We stopped tacrolimus and administered basiliximab. Then, she developed oliguria and needed continuous hemodiafiltration. On postoperative day 14, the platelet count recovered and she was switched from basiliximab to cyclosporine. Using this protocol, worsening thrombotic microangiopathy and acute rejection were avoided.ConclusionsWe report the case of a patient with early post-transplant thrombotic microangiopathy after lung transplantation that was treated with basiliximab. Switching from calcineurin inhibitors using basiliximab may be an option for treating thrombotic microangiopathy without increasing the risk of acute rejection.

344.7: Early Post-operative Thrombotic Microangiopathy in Deceased Donor Kidney Transplant: Case Series

Background: Transplant associated thrombotic microangiopathy (TA-TMA) is well recognized as a serious complication of renal transplantation. TA-TMA is characterized by injury of arterioles and capillaries and encompasses syndromes of thrombocytopenia, microangiopathic hemolytic anemia(MAHA) and variable degrees of kidney graft dysfunction. TA-TMA can be classified into recurrent TMA (from underlying complement mutations) and de novo TMA. The incidence of de novo TMA ranges from 3-14%. Causes of de novo TMA include immunosuppressive drugs (tacrolimus, mTOR inhibitors, valgancyclovir), ischemia reperfusion injury, viral infections (CMV, Parvovirus B19, HIV, HHV-6) and antibody-mediated rejection. We have found that many of these cases also have very low levels of ADAMTS13 but do not meeting clinical criteria for TTP. If the latter is secondary to endothelial damage vs consumption process is still unknown. Objective: The purpose of this study was to identify if any specific risk factors or variables are associated with TA-TMA in the setting of deceased donor kidney transplantation (DDKT). Methods: We retrospectively collected data on 11 patients who were diagnosed with TA-TMA in the immediate post operative period (defined as less than 2 weeks from transplant date) since January, 2017. We analyzed donor characteristics including age, type of deceased donor, last known platelet count, biopsy features, pump parameters, cold ischemia time (CIT), warm ischemia time (WIT), reperfusion injury (RI) described at transplant surgery. Recipient variables included baseline platelet count on admission, the post-op day of diagnosis and at resolution (defined as platelet count > 100K and no need for additional transfusion), the use of thymoglobulin, ADAMS13 activity, changes in maintenance immunosuppression, evidence of post op bleeding, delayed graft function (DGF) and its recovery, and renal function at 1 and 3 months post transplant (Table). Results: 72% of the kidneys were from donation after cardiac death donors (DCD). The mean arterial pressure on the perfusion pump was 39 ± 7 mmHg and the flow was 148 ± 35 ml/sec. 81 % of the donor biopsies showed mild ATN, 72% had evidence of atherosclerosis and 54% of fibrosis and only one showed fibrin thrombi in the glomerulus. The mean CIT and WIT were 1913 ± 423 and 27 ± 32 min, respectively. The mean donor platelet count and baseline recipient’s platelet count were 209 ± 210 and 166 ± 71 x 10(3)/mcl, respectively. The TA-TMA event occurred on post op day 3± 1.3 with a mean platelet count of 45 ± 19 x 10(3)/mcl. ADAMTS 13 level was <10% in 54% of the cases and LDH level 2880 ± 55 U/L. 3 patients received FFP infusions, 5 received plasmapheresis and 3 received conservative treatment. The microangiopathic hemolytic anemia recovered in 10 ± 2.4 days to a platelet count of 130 ± 67 x 10(3)/mcl. There were 6 cases of post op bleeding (55%) with 4 requiring surgical intervention and 4 cases of RI (36%). Of the 8 patients that sustained DGF, 6 recovered at one month, one recovered at 3 months post transplant (having history of low C3 and late biopsy proven TMA) and one died. The mean SCr and eGFR at 1 and 3 months were 2± 1.1, 51 ± 34 and 1 ± 0.5 mg/dl and 66± 30 ml/min, respectively.There were no statistical differences on the above parameters when the patients were grouped by the presence of post operatory bleeding. However, when we added the reperfusion injury factor, we found a lower ADAMTS 13 levels of 17 ±7 UI/dl in the non bleeding group who sustained RI (60%) vs 21± 37 UI/dl in the bleeding group who had only one patient with RI (17%) (p=0.24). Conclusions: TA-TMA in the immediate postoperative period can be difficult to diagnose and treat. Our findings demonstrated that 55% of the cases were associated with post operatory bleeding leading to the reduction of ADAMTS 13 levels, most likely by platelet consumption. 36% were related to reperfusion injury where the consumption of ADAMTS 13 could be explained by direct endothelial damage. None of the patients needed other than conservative therapy. This data needs to be correlated in a larger cohort. In this context we are planning to prospectively study ADAMTS 13 activity in the immediate post kidney transplant period.

What complements complement in transplant-associated thrombotic microangiopathy?

Transplant-associated thrombotic microangiopathy remains a lethal complication of haematopoietic stem cell transplant and not all patients respond to terminal complement inhibitors. Qi et al. show that hypoxia-inducible factor-1α (HIF-1α) may be a previously unrecognized driver of this endothelial injury syndrome. Commentary on Qi et al. Upregulation of HIF-1α contributes to complement activation in transplantation-associated thrombotic microangiopathy. Br J Haematol. 2022 199:603-615.

N-Acetylcysteine as Prophylactic Therapy for Transplantation-Associated Thrombotic Microangiopathy: A Randomized, Placebo-Controlled Trial

Transplantation-associated thrombotic microangiopathy (TA-TMA) is a life-threatening complication for patients undergoing hematopoietic stem cell transplantation (HSCT). N-acetylcysteine (NAC) has recently been considered as a potential treatment for patients with thrombotic thrombocytopenic purpura. To assess the value of NAC for the prevention of TA-TMA, we conducted a prospective study at the First Affiliated Hospital of Soochow University. This open-label, randomized placebo-controlled trial included 160 patients who were scheduled for allogeneic HSCT. Participants were assigned at random 1:1 to either oral NAC (50 mg/kg/day from 9 days before HSCT to 30 days after HSCT) or placebo treatment. The primary outcome was the incidence of TA-TMA. Overall survival (OS) and event-free survival (EFS) were assessed in the NAC and placebo control groups. The incidence of TA-TMA was 9.1% (95% confidence interval [CI], 2% to 16.2%) in the NAC group, compared with 23% (95% CI, 13.2% to 32.8%) in the control group, with a rate ratio of .34 (95% CI, .123 to .911; P=.039). The median time to the onset of TA-TMA was 60 days (interquartile range [IQR], 42 to 129 days) in the NAC group and 36 days (IQR, 30.5 to 51 days) in the control group (P=.063). The 2-year OS rate was 75.4% (95% CI, 28.65% to 73.53%) in the NAC group and 63.0% (95% CI, 50.8% to 73.5%) in the control group, with a hazard ratio (HR) of .622 (95% CI, .334-1.155; P=.132). The EFS rate was 25.8% in the NAC patients and 8.1% in controls (HR, .254; 95% CI, .094 to .692; P=.024). The median time of EFS was 60 days in the NAC group and 38 days in controls. Our findings suggest that NAC may be a potential treatment to reduce the incidence of TA-TMA.

Epidemiology and outcomes of pediatric transplant-associated thrombotic microangiopathy in Hong Kong.

Transplant-associated thrombotic microangiopathy (TA-TMA) is an under-recognized yet potentially devastating complication of hematopoietic stem cell transplantation (HSCT) which had increased awareness in recent years. This report summarizes the demographics and outcomes of pediatric TA-TMA in Hong Kong. All patients aged below 18 years who underwent HSCT in the Hong Kong Children's Hospital and were diagnosed to have TA-TMA during the 2-year period from April 1, 2019 to March 31, 2021 were included. A total of 73 transplants (51 allogeneic and 22 autologous) in 63 patients had been performed. Six patients (four males and two females) developed TA-TMA at a median duration of 2.5 months post-HSCT. The incidence rate was 9.52%. Of the six TA-TMA patients, five underwent allogenic one underwent autologous HSCT, respectively. Three of them were histologically proven. All four patients with cyclosporine had stopped the drug once TA-TMA was suspected. Median six doses of eculizumab were administered to five out of six patients. Three patients died (two due to fungal infection and one due to acute-on-chronic renal failure) within 3 months upon diagnosis of TA-TMA. Among three survivors, two stabilized with mild stage 2 chronic kidney disease (CKD) while the other suffered from stage 5 end-stage CKD requiring lifelong dialysis. In conclusion, recognition and diagnosis of TA-TMA are challenging. Early recognition and prompt administration of complement blockage with eculizumab may be beneficial in selected cases. Further prospective research studies are recommended to improve the management and outcomes of TA-TMA.

Upregulation of HIF-1α contributes to complement activation in transplantation-associated thrombotic microangiopathy.

Transplantation-associated thrombotic microangiopathy (TA-TMA) is a severe complication of haematopoietic stem cell transplantation (HSCT). Complement activation is involved in the development of TA-TMA. However, the underlying mechanism is unclear. Therefore, 21 samples of TA-TMA and 1:1 matched controls were measured for hypoxia-inducible factor-1α (HIF-1α) and complement protein. The mechanism was investigated both in vitro and in vivo. In this study, we found that levels of HIF-1α were significantly higher in TA-TMA patients than that in non-TA-TMA controls. Upregulation of HIF-1α induced an increase in membrane-bound complement C3 and dysfunction of human umbilical vein endothelial cells (HUVECs) in vitro. Increasing HIF-1α in vivo led to C3 and C5b-9 deposition in the glomerular endothelial capillary complex, thrombocytopenia, anaemia, and increased serum lactate dehydrogenase (LDH) levels in wild-type (WT) but not in C3-/- mice subjected to HSCT. High platelet aggregation in peripheral blood and CD41-positive microthrombi in the kidney were also found in dimethyloxallyl glycine (DMOG)-treated mice, recapitulating the TA-TMA phenotype seen in patients. Comprehensive analysis, including DNA array, luciferase reporter assay, chromatin immunoprecipitation (ChIP)-seq, and quantitative polymerase chain reaction (PCR), revealed that HIF-1α interacted with the promoter of complement factor H (CFH) to inhibit its transcription. Decreased CFH led to complement activation in endothelial cells.

Complement System as a New Target for Hematopoietic Stem Cell Transplantation-Related Thrombotic Microangiopathy.

Thrombotic microangiopathy (TMA) is a complication that may occur after autologous or allogeneic hematopoietic stem cell transplantation (HSCT) and is conventionally called transplant-associated thrombotic microangiopathy (TA-TMA). Despite the many efforts made to understand the mechanisms of TA-TMA, its pathogenesis is largely unknown, its diagnosis is challenging and the case-fatality rate remains high. The hallmarks of TA-TMA, as for any TMA, are platelet consumption, hemolysis, and organ dysfunction, particularly the kidney, leading also to hypertension. However, coexisting complications, such as infections and/or immune-mediated injury and/or drug toxicity, together with the heterogeneity of diagnostic criteria, render the diagnosis difficult. During the last 10 years, evidence has been provided on the involvement of the complement system in the pathophysiology of TA-TMA, supported by functional, genetic, and therapeutic data. Complement dysregulation is believed to collaborate with other proinflammatory and procoagulant factors to cause endothelial injury and consequent microvascular thrombosis and tissue damage. However, data on complement activation in TA-TMA are not sufficient to support a systematic use of complement inhibition therapy in all patients. Thus, it seems reasonable to propose complement inhibition therapy only to those patients exhibiting a clear complement activation according to the available biomarkers. Several agents are now available to inhibit complement activity: two drugs have been successfully used in TA-TMA, particularly in pediatric cases (eculizumab and narsoplimab) and others are at different stages of development (ravulizumab, coversin, pegcetacoplan, crovalimab, avacopan, iptacopan, danicopan, BCX9930, and AMY-101).

The Role of Complement in HSCT-TMA: Basic Science to Clinical Practice.

Hematopoietic stem cell transplantation-associated thrombotic microangiopathy (HSCT-TMA) is a common complication occurring post-HSCT and is associated with substantial morbidity and mortality if not promptly identified and treated. Emerging evidence suggests a central role for the complement system in the pathogenesis of HSCT-TMA. The complement system has also been shown to interact with other pathways and processes including coagulation and inflammation, all of which are activated following HSCT. Three endothelial cell-damaging “hits” are required for HSCT-TMA genesis: a genetic predisposition or existing damage, an endothelial cell-damaging conditioning regimen, and additional damaging insults. Numerous risk factors for the development of HSCT-TMA have been identified (including primary diagnosis, graft type, and conditioning regimen) and validated lists of relatively simple diagnostic signs and symptoms exist, many utilizing routine clinical and laboratory assessments. Despite the relative ease with which HSCT-TMA can be screened for, it is often overlooked or masked by other common post-transplant conditions. Recent evidence that patients with HSCT-TMA may also concurrently present with these differential diagnoses only serve to further confound its identification and treatment. HSCT-TMA may be treated, or even prevented, by removing or ameliorating triggering “hits”, and recent studies have also shown substantial utility of complement-targeted therapies in this patient population. Further investigation into optimal management and treatment strategies is needed. Greater awareness of TMA post-HSCT is urgently needed to improve patient outcomes; the objective of this article is to clarify current understanding, explain underlying complement biology and provide simple tools to aid the early recognition, management, and monitoring of HSCT-TMA.Supplementary InformationThe online version contains supplementary material available at 10.1007/s12325-022-02184-4.

Novel Insights into Factor D Inhibition.

Complement-mediated diseases or complementopathies, such as Paroxysmal nocturnal hemoglobinuria (PNH), cold agglutinin disease (CAD), and transplant-associated thrombotic microangiopathy (TA-TMA), demand advanced complement diagnostics and therapeutics be adopted in a vast field of medical specialties, such as hematology, transplantation, rheumatology, and nephrology. The miracle of complement inhibitors as “orphan drugs” has dramatically improved morbidity and mortality in patients with otherwise life-threatening complementopathies. Efficacy has been significantly improved by upstream inhibition in patients with PNH. Different molecules may exert diverse characteristics in vitro and in vivo. Further studies remain to show safety and efficacy of upstream inhibition in other complementopathies. In addition, cost and availability issues are major drawbacks of current treatments. Therefore, further developments are warranted to address the unmet clinical needs in the field of complementopathies. This state-of-the-art narrative review aims to delineate novel insights into factor D inhibition as a promising target for complementopathies.

Transplant-associated thrombotic microangiopathy: a rare but deadly complication post orthotopic heart transplantation.

Transplant-associated thrombotic microangiopathy: a rare but deadly complication post orthotopic heart transplantation.

P1344: METHODOLOGY OF AN INTERNATIONAL MULTI-CENTER RETROSPECTIVE REVIEW OF TRANSPLANT-ASSOCIATED THROMBOTIC MICROANGIOPATHY (TA-TMA) BY THE TA-TMA WORKING GROUP

Background: Transplant-associated thrombotic microangiopathy (TA-TMA) is a serious and potentially life-threatening complication after allogeneic hematopoietic cell transplantation (alloHCT). Multiple sets of clinical diagnostic criteria for TA-TMA have been developed in adult and pediatric settings based on single-institution chart review or expert panels, but none have been rigorously evaluated across multiple centers to assess validity or reproducibility. The TA-TMA Working Group is conducting a multi-national, multi-center, retrospective study to identify and confirm potential adult and pediatric cases of TA-TMA. The aim of creating a large cohort of adjudicated TA-TMA cases is to better understand the incidence, risk factors, clinical outcomes, and healthcare resource utilization (HRU) associated with this condition. Aims: To describe the multiple-adjudication methodology employed to confirm diagnosis of TA-TMA across adult and pediatric transplant centers. Methods: Twelve US and EU centers retrospectively screened medical records of patients who received alloHCT between 2015 and 2017 using 5 criteria: schistocytosis (>2 per high-power field); LDH level above ULN; doubling of baseline creatinine; platelet refractoriness (50% decrease in platelet count and/or platelet count less than individual center’s transfusion threshold x 4 days despite transfusions); and decreased haptoglobin. Cases meeting ≥3 criteria within a 10-day period during the first 12 months after alloHCT were considered potential TA-TMA and were further evaluated by 2 clinicians from each transplant center. Patients who had a positive biopsy, were diagnosed with TA-TMA or aHUS, or had received eculizumab following alloHCT were considered to have definite TA-TMA. Of all positive cases determined by local adjudications, 30% will be randomly selected for central adjudication by independent adult and pediatric adjudication committees. Central adjudicators have access to relevant laboratory and radiologic data. In cases with 2 discordant decisions, a third central adjudicator will be assigned to break the tie. In cases of 3 discordant decisions regarding the diagnosis of TA-TMA, the case will be forwarded for discussion led by the central adjudication chair. All cases determined as positive TA-TMA after local and central adjudication will be aggregated and analyzed to evaluate clinical outcomes, risk factors for TA-TMA, disease course, survival and non-relapse mortality, and HRU. Results: As of March 1, 2022, 3,732 cases have been screened at 11 transplant centers and 836 were considered potential TA-TMA that met ≥3 criteria. To date, local adjudication at 8 centers determined 179 cases were positive TA-TMA. Due to variations in laboratory standards at different centers, a challenge encountered in this study was harmonization of screening criteria. For example, labs at several centers did not quantify number of schistocytes as part of their CBC, which restricted screening of potential TA-TMA cases to 4 criteria, leading to some cases being categorized as “unknown.” These outcomes highlight the differences in assessing TA-TMA at multiple centers. Summary/Conclusion: This is the first multi-center comprehensive retrospective study to evaluate TA-TMA with a formalized process for independent local and central adjudication to verify TA-TMA diagnosis. The large cohort of TA-TMA cases identified in this study should enable validation of current and future diagnostic criteria, improve our understanding of prognostic/risk factors, and enhance awareness of this disease.

Successful desensitization of high level donor-specific anti-HLA antibody in patients with hematological diseases receiving haploidentical allografts.

Donor-specific anti-human leukocyte antigen (HLA) antibody (DSA) is associated with a higher incidence of graft failure and mortality in HLA-mismatched allograft settings. However, the optimal protocol of desensitization for patients with positive DSA remains uncertain. We investigated the effectiveness of a desensitization protocol, including rituximab, high-dose intravenous immunoglobulin (IVIG), and a single session of plasma exchange (PE), for haploidentical allograft recipients with a high mean fluorescence intensity (MFI) level of DSA (≥ 5,000). Eleven patients with hematological disease who had positive DSA (median, 11,676, range 5387-20,435) were desensitized by the protocol. All of the patients achieved hematopoietic recovery. The median times for neutrophil and platelet engraftment were 13 (range, 11-26) days and 19 (range, 11-90) days, respectively. Grade II-IV acute graft-versus-host disease (GVHD) was seen in one patient and was controlled completely. Chronic cutaneous GVHD was seen in eight patients. Nine patients are alive with good performance so far. One patient suffered extramedullary relapse, and one patient died of transplantation-associated thrombotic microangiopathy. The 1-year probability of overall survival was 81.8%. These results suggest that successful desensitization could be obtained by a combination of rituximab, high-dose IVIG, and PE for haploidentical allograft recipients with high MFI levels of DSA.

Cerebral vascular injury in transplant-associated thrombotic microangiopathy

AbstractTransplant-associated thrombotic microangiopathy (TA-TMA) and atypical hemolytic uremic syndrome (aHUS) are complement-mediated TMAs. The central nervous system (CNS) is the most common extrarenal organ affected by aHUS, and, despite mechanistic overlap between aHUS and TA-TMA, CNS involvement is rarely reported in TA-TMA, suggesting that CNS involvement in TA-TMA may be underdiagnosed and that these patients may benefit from complement blockers. In addition, there are no widely used histologic or radiologic criteria for the diagnosis of TMA in the brain. Thirteen recipients of pediatric hematopoietic cell transplants (HCTs) who had TA-TMA and who underwent autopsy were studied. Seven of 13 brains had vascular injury, and 2 had severe vascular injury. Neurologic symptoms correlated with severe vascular injury. Classic TMA histology was present and most often observed in the cerebellum, brainstem, and cerebral white matter. Abnormalities in similar anatomic regions were seen on imaging. Brain imaging findings related to TMA included hemorrhages, siderosis, and posterior reversible encephalopathy syndrome. We then studied 100 consecutive HCT recipients to identify differences in neurologic complications between patients with and those without TA-TMA. Patients with TA-TMA were significantly more likely to have a clinical concern for seizure, have an electroencephalogram performed, and develop altered mental status. In summary, our study confirms that TA-TMA involves the brains of recipients of HCT and is associated with an increased incidence of neurologic symptoms. Based on these findings, we propose that patients with low- or moderate-risk TA-TMA who develop neurologic complications should be considered for TA-TMA–directed therapy.

Transplantation-Associated Thrombotic Microangiopathy Risk Stratification: Is There a Window of Opportunity to Improve Outcomes?

Transplantation-associated thrombotic microangiopathy (TA-TMA) can range from a self-limiting condition to a lethal transplantation complication. It is important to identify TA-TMA patients at risk for severe multiorgan endothelial injury to implement targeted therapies in a timely manner. Current therapeutic approaches with complement blockade have improved survival markedly in high-risk TA-TMA patients, yet one-third of these patients respond inadequately to eculizumab therapy. Poor response may indicate that substantial endothelial injury has already occurred and raises the possibility that earlier intervention may improve outcomes. The goal of this study was to identify additional TA-TMA patients who would benefit from early targeted intervention and update TA-TMA risk stratification methods to reflect these findings. We studied 130 HSCT recipients with a diagnosis of TA-TMA who were screened prospectively and stratified into 3 TA-TMA risk groups (high-risk, n=64; moderate-risk, n=48; 18 low-risk, n=18). We specifically examined TA-TMA biomarkers and clinical outcomes in subjects who were not offered complement blocking therapy (moderate-risk and low-risk TA-TMA subjects) and compared them with those who received TA-TMA-targeted therapy (high-risk TA-TMA subjects). One-year post-HSCT survival for subjects with untreated moderate-risk TA-TMA was similar to those with high-risk TA-TMA receiving eculizumab therapy (71% versus 66%; P=.40), indicating that a subset of moderate-risk patients may benefit from therapy. A detailed analysis of moderate-risk subjects highlighted the importance of relative as well as absolute complement pathway activation in determining organ injury. We demonstrated that activated terminal complement (measured by elevated blood sC5b-9) alone is a valuable indicator of reduced survival. Moderate-risk TA-TMA subjects with elevated sC5b-9 levels had a nearly 3-fold higher risk of mortality that was statistically significant in multivariant analyses (P=.01). A "dose effect" also was observed, and higher sC5b-9 levels were associated with worse outcomes. Furthermore, all moderate-risk patients with sustained sC5b-9 elevation for >2 weeks ultimately developed multiorgan dysfunction syndrome (MODS). This indicates that scheduled sC5b-9 measurements could promptly identify patients at risk for poor outcomes and would facilitate early TA-TMA-directed therapy to prevent organ injury. Untreated low-risk TA-TMA patients had a 1-year post-HSCT survival of 94% and should be observed without targeted interventions. Routine TA-TMA screening and complement-blocking therapies have markedly improved the outcomes for high-risk TA-TMA patients, and our study suggests that additional patients may benefit from TA-TMA treatment. This study provides further support for prospective TA-TMA screening as an integral tool for identifying patients at greatest risk for organ injury and death from TA-TMA. An updated TA-TMA risk algorithm that incorporates relevant laboratory biomarkers, clinical findings, and comorbid conditions was generated using this study's findings, and we propose clinical implementation of this algorithm for the management of TA-TMA.

Clinical characteristics and risk factors of pericardial effusion after hematopoietic stem cell transplantation in children with thalassemia major

Objective: To investigate the characteristics, risk factors and outcomes of thalassemia major (TM) children with pericardial effusion (PE) after allo-geneic hematopoietic stem cell transplantation (allo-HSCT). Methods: Clinical data of 446 TM children received allo-HSCT at Shenzhen Children's Hospital between January 2012 and December 2020 were analyzed retrospectively. Patients were divided into PE and non-PE group according to the occurrence of PE. Chi-square tests were used to investigate the risk factors that were associated with the development of PE. Kaplan-Meier method was used for survival analysis of the 2 groups. Results: Twenty-five out of 446 patients (5.6%) developed PE at a time of 75.0 (66.5, 112.5) days after allo-HSCT. Among these patients, 22 cases (88.0%) had PE within 6 months after allo-HSCT and 19 patients (76.0%) had PE within 100 days after allo-HSCT. The diagnoses of PE were confirmed using echocardiography. Pericardial tamponade was observed in only 1 patient, who later undergone emergency pericardiocentesis. The rest of patients received conservative managements alone. PE disappeared in all patients after treatment. Risk factors that were associated with the development of PE after allo-HSCT included the gender of patients, the type of transplantation, the number of mononuclear cells (MNC) infuse, pulmonary infection after HSCT and transplantation associated thrombotic microangiopathy (TA-TMA) (χ²=3.99, 10.20, 14.18, 36.24, 15.03, all P<0.05). In 239 patients that received haploidentical HSCT, the development of PE was associated with the gender of patients, pulmonary infection after HSCT and TA-TMA (χ²=4.48, 20.89, 12.70, all P<0.05). The overall survival rates of PE and non-PE groups were 96.0% (24/25) and 98.6% (415/421). The development of PE was not associated with the overall survival of TM children after allo-HSCT (χ²=1.73, P=0.188). Conclusions: PE mainly develop within 100 days after allo-HSCT in pediatric TM recipients. Haploidentical grafts, female gender, pulmonary infection after HSCT and TA-TMA are the main risk factors associated with PE development after transplant. However, the presence of PE don't have a significant impact on the outcomes of pediatric TM patients after allo-HSCT.

Acute graft-versus-host disease increase risk and accuracy in prediction model of transplantation-associated thrombotic microangiopathy in patients with myelodysplastic syndrome.

Allogeneic hematopoietic stem cell transplantation is the only curative therapy for patients with myelodysplastic syndrome. Transplantation-associated thrombotic microangiopathy (TA-TMA) remains a cause of death after transplantation. This study assessed the risk factors of TA-TMA and established a prediction model for this complication. We launched a real-world study from 303 MDS patients after allo-HSCT from Dec 1, 2007, to Jun 1, 2018. Logistic regression was used to analyze risk factors and to establish a nomogram. The accuracy of the model was assessed by C-index and calibration curve. TA-TMA class was associated with an over twofold increase in the risk of death (HR 2.66, 95% CI 1.39-5.09, p = 0.003). Stage III or IV acute graft-versus-host disease (aGVHD) (OR: 6.17, 95% CI: 2.19-17.18, p < 0.001) and occurrence time of aGVHD were the risk factors for TA-TMA. Next, we put these two variants and the other three variants into the prediction model via multivariate Lasso regression. In order to quantify the contribution of each factor, a nomogram was generated and displayed (C index of 0.783). TA-TMA predicts worsened outcomes of overall survival. A cross-validated multivariate score including aGVHD occurrence showed excellent concordance and efficacy of predicting TA-TMA in HSCT patients.