Efficacy and Safety of Eculizumab in the Treatment of Transplant-Associated Thrombotic Microangiopathy: A Systematic Review and Meta-Analysis

Transplant-associated thrombotic microangiopathy in pediatrics: incidence, risk factors, therapeutic options, and outcome based on data from a single center

Background

Transplant-associated thrombotic microangiopathy (TA-TMA) is a critical complication of hematopoietic stem cell transplantation. Awareness about TA-TMA has increased in recent years, resulting in the implementation of TA-TMA screening in most centers.

Methods

Retrospective analysis of children who underwent autologous or allogeneic hematopoietic stem cell transplantation at our center between January 2018 and December 2022 was conducted to evaluate the incidence, clinical features, and outcomes of TA-TMA following the administration of different therapeutic options.

Results

A total of 45 patients comprised the study cohort, of whom 10 developed TA-TMA with a cumulative incidence of 22% by 100 days after transplantation. Patients with and without TA-TMA in our cohort displayed an overall survival of 80% and 88%, respectively (p = 0.48), and a non-relapse mortality of 0% and 5.7%, respectively (p = 0.12), at 1 year after transplantation. Risk factors for TA-TMA development included allogeneic transplantation and total body irradiation-based conditioning regime. Among the 10 patients with TA-TMA, 7 did not meet the high-risk criteria described by Jodele and colleagues. Of these seven patients, two responded to calcineurin-inhibitor withdrawal without further therapy and five developed multiorgan dysfunction syndrome and were treated with anti-inflammatory steroids (prednisone), and all responded to therapy. The three patients with high-risk TA-TMA were treated with complement blockade or prednisone, and all responded to therapy.

Conclusion

TA-TMA is a multifactorial complication with high morbidity rates. Patients with high-risk TA-TMA may benefit from complement blockade using eculizumab. No consensus has been reached regarding therapy for patients who do not meet high-risk criteria. Our analysis showed that these patients may respond to anti-inflammatory treatment with prednisone.

Genetic Susceptibility in Endothelial Injury Syndromes after Hematopoietic Cell Transplantation and Other Cellular Therapies: Climbing a Steep Hill

Hematopoietic stem cell transplantation (HSCT) remains a cornerstone in the management of patients with hematological malignancies. Endothelial injury syndromes, such as HSCT-associated thrombotic microangiopathy (HSCT-TMA), veno-occlusive disease/sinusoidal obstruction syndrome (SOS/VOD), and capillary leak syndrome (CLS), constitute complications after HSCT. Moreover, endothelial damage is prevalent after immunotherapy with chimeric antigen receptor-T (CAR-T) and can be manifested with cytokine release syndrome (CRS) or immune effector cell-associated neurotoxicity syndrome (ICANS). Our literature review aims to investigate the genetic susceptibility in endothelial injury syndromes after HSCT and CAR-T cell therapy. Variations in complement pathway- and endothelial function-related genes have been associated with the development of HSCT-TMA. In these genes, CFHR5, CFHR1, CFHR3, CFI, ADAMTS13, CFB, C3, C4, C5, and MASP1 are included. Thus, patients with these variations might have a predisposition to complement activation, which is also exaggerated by other factors (such as acute graft-versus-host disease, infections, and calcineurin inhibitors). Few studies have examined the genetic susceptibility to SOS/VOD syndrome, and the implicated genes include CFH, methylenetetrahydrofolate reductase, and heparinase. Finally, specific mutations have been associated with the onset of CRS (PFKFB4, CX3CR1) and ICANS (PPM1D, DNMT3A, TE2, ASXL1). More research is essential in this field to achieve better outcomes for our patients.

Change in Neurocognitive Function in Patients Who Receive CAR-T Cell Therapies: A Steep Hill to Climb

Immunotherapy with chimeric antigen receptor T (CAR-T) cell therapies has brought substantial improvement in clinical outcomes in patients with relapsed/refractory B cell neoplasms. However, complications such as cytokine release syndrome (CRS) and immune effector cell-associated neurotoxicity syndrome (ICANS) limit the therapeutic efficacy of this treatment approach. ICANS can have a broad range of clinical manifestations, while various scoring systems have been developed for its grading. Cognitive decline is prevalent in CAR-T therapy recipients including impaired attention, difficulty in item naming, and writing, agraphia, and executive dysfunction. In this review, we aim to present the diagnostic methods and tests that have been used for the recognition of cognitive impairment in these patients. Moreover, up-to-date data about the duration of cognitive impairment symptoms after the infusion are presented. More research on the risk factors, pathogenesis, preventive measures, and therapy of neurocognitive impairment is crucial for better outcomes for our patients.

Successful haploidentical hematopoietic stem cell transplantation for paroxysmal nocturnal hemoglobinuria with severe pancytopenia developed after long-term aplastic anemia treatment

Haploidentical hematopoietic stem cell transplantation (HSCT) with posttransplant cyclophosphamide is an alternative treatment for aplastic anemia-paroxysmal nocturnal hemoglobinuria (PNH) syndrome with poor prognostic factors. Ravulizumab treatment for PNH before HSCT might have a beneficial effect.

Thrombotic Microangiopathy After Hematopoietic Stem Cell and Solid Organ Transplantation: A Review for Intensive Care Physicians

Intensive care physicians may assume the primary care of patients with transplant-associated thrombotic microangiopathy (TA-TMA), an uncommon but potentially critical complication of hematopoietic stem cell transplants (HSCTs) and solid organ transplants. TA-TMA can have a dramatic presentation with multiple organ dysfunction syndrome (MODS) associated with high morbidity and mortality. The typical presenting clinical features are hemolytic anemia, thrombocytopenia, refractory hypertension, proteinuria and worsening renal failure. Intestinal involvement, with abdominal pain, nausea and vomiting, gastrointestinal bleeding, and ascites are also common. Cardiopulmonary involvement may develop from various causes including pulmonary arteriolar hypertension, pleural and pericardial effusions, and diffuse alveolar hemorrhage. Due to other often concurrent complications after HSCT, early diagnosis and effective management of TA-TMA may be challenging. Close collaboration between ICU and transplant physicians, along with other relevant specialists, is needed to best manage these patients. There are currently no approved therapies for the treatment of TA-TMA. Plasma exchange and rituximab are not recommended unless circulating factor H (CFH) antibodies or thrombotic thrombocytopenic purpura (TTP; ADAMTS activity < 10%) are diagnosed or highly suspected. The role of the complement pathway activation in the pathophysiology of TA-TMA has led to the successful use of targeted complement inhibitors, such as eculizumab. However, the relatively larger studies using eculizumab have been mostly conducted in the pediatric population with limited data on the adult population. This review is focused on the role of intensive care physicians to emphasize the clinical approach to patients with suspected TA-TMA and to discuss diagnosis and treatment strategies.

Eculizumab treatment in paediatric patients diagnosed with aHUS after haematopoietic stem cell transplantation: a HSCT-TMA case series from Japanese aHUS post-marketing surveillance

Haematopoietic stem-cell transplantation (HSCT)-associated thrombotic microangiopathy (HSCT-TMA) is a serious complication with high mortality. Accumulating evidence suggests that complement dysregulation is potentially involved in the development of HSCT-TMA. We retrospectively analysed the clinical characteristics and outcomes of thirteen paediatric patients who were diagnosed with atypical haemolytic uremic syndrome and treated with eculizumab to manage HSCT-TMA during post-marketing surveillance in Japan. The median time from HSCT to TMA was 31 days (Interquartile range, IQR;21-58) and the median doses of eculizumab was three (IQR;2-5). Seven patients (54%) were alive at the last follow-up while six died due to complications related to HSCT. Six of seven survivors initiated eculizumab after insufficient response to plasma therapy. Following eculizumab treatment, median platelet counts and LDH levels in all survivors significantly improved and renal function improved in 4/7 patients. All survivors possessed potential risk factors of complement overactivation. During the follow-up period after eculizumab discontinuation (median;111.5 days, IQR;95-555), no TMA recurrence was observed. In this analysis, eculizumab showed benefit in over half of this paediatric patient population. Ongoing clinical studies are expected to optimize the treatment regimen of terminal complement pathway inhibitor, and it may become a therapeutic option for paediatric HSCT-TMA in the future.

D-dimer and sinusoidal obstructive syndrome-novel poor prognostic features of thrombotic microangiopathy in children after hematopoietic cellular therapy in a single institution prospective cohort study

Transplant-associated thrombotic microangiopathy (TA-TMA) is a common, severe complication of allogeneic hematopoietic cellular therapy (HCT). Even when treated in many studies, morbidity and mortality rates are high. This prospective single-institution cohort study serially enrolled all allogeneic HCT recipients from August 2019-August 2022. Patients were universally screened for TA-TMA and intermediate and high-risk patients were immediately treated with eculizumab. Sub-distribution cox-proportional hazards models were used to identify sub-distribution hazard ratios (sHR)  for multi-organ dysfunction (MOD) and non-relapse-related mortality (NRM). Of 136 patients, 36 (26%) were diagnosed with TA-TMA and 21/36 (58%) developed MOD, significantly more than those without TA-TMA, (p < .0001). Of those with TA-TMA, 18 (50%) had high-risk TA-TMA (HR-TA-TMA), 11 (31%) had intermediate-risk TA-TMA (IR-TA-TMA), and 8 (22%) had standard risk (SR-TA-TMA). Twenty-six were treated with eculizumab (1/8 SR, 7/11 IR, and 18/18 HR). Elevated D-dimer predicted the development of MOD (sHR 7.6, 95% confidence interval [CI] 1.8-32.3). Children with concurrent sinusoidal obstructive syndrome (SOS) and TA-TMA had an excess risk of MOD of 34% and data supported a biologic interaction. The adjusted NRM risk was significantly higher in the TA-TMA patients (sHR 10.54, 95% CI 3.8-29.2, p < .0001), despite prompt treatment with eculizumab. Significant RF for NRM in TA-TMA patients included SOS (HR 2.89, 95% 1.07-7.80) and elevated D-dimer (HR 3.82, 95% CI 1.14-12.84). An unrelated donor source and random urine protein to creatine ratio ≥2 mg/mg were significantly associated with no response to eculizumab (odds ratio 15, 95% CI 2.0-113.6 and OR 6.5, 95% CI 1.1-38.6 respectively). TA-TMA was independently associated with NRM despite early diagnosis and treatment with eculizumab in this large pediatric transplant cohort. Prognostic implications of D-dimer in TA-TMA merit further investigation as this is a readily accessible biomarker. Concurrent SOS is an exclusion criterion of many ongoing clinical trials, but these data highlight these patients could benefit from novel therapeutic approaches. Multi-institutional clinical trials are needed to understand the impact of TA-TMA-targeted therapies.

Soluble Urokinase-Type Plasminogen Activator Receptor (suPAR) and Growth Differentiation Factor-15 (GDF-15) Levels Are Significantly Associated with Endothelial Injury Indices in Adult Allogeneic Hematopoietic Cell Transplantation Recipients

Hematopoietic stem cell transplantation-associated thrombotic microangiopathy (HSCT-TMA) and graft-versus-host disease (GvHD) represent life-threatening syndromes after allogeneic hematopoietic stem cell transplantation (allo-HSCT). In both conditions, endothelial dysfunction is a common denominator, and development of relevant biomarkers is of high importance for both diagnosis and prognosis. Despite the fact that soluble urokinase plasminogen activator receptor (suPAR) and growth differentiation factor-15 (GDF-15) have been determined as endothelial injury indices in various clinical settings, their role in HSCT-related complications remains unexplored. In this context, we used immunoenzymatic methods to measure suPAR and GDF-15 levels in HSCT-TMA, acute and/or chronic GVHD, control HSCT recipients, and apparently healthy individuals of similar age and gender. We found considerably greater SuPAR and GDF-15 levels in HSCT-TMA and GVHD patients compared to allo-HSCT and healthy patients. Both GDF-15 and suPAR concentrations were linked to EASIX at day 100 and last follow-up. SuPAR was associated with creatinine and platelets at day 100 and last follow-up, while GDF-15 was associated only with platelets, suggesting that laboratory values do not drive EASIX. SuPAR, but not GDF-15, was related to soluble C5b-9 levels, a sign of increased HSCT-TMA risk. Our study shows for the first time that suPAR and GDF-15 indicate endothelial damage in allo-HSCT recipients. Rigorous validation of these biomarkers in many cohorts may provide utility for their usefulness in identifying and stratifying allo-HSCT recipients with endothelial cell impairment.

Diagnosis and management of endothelial disorders following haematopoietic stem cell transplantation

Haematopoietic stem cell transplantation is a mainstay of therapy for numerous malignant and nonmalignant diseases. Endothelial activation and dysfunction occur after stem cell transplantation, driven by various patient- and transplant-specific factors. This can manifest as one of the relatively uncommon endothelial injury syndromes, such as sinusoidal obstruction syndrome, transplant-associated thrombotic microangiopathy, idiopathic pneumonia syndrome, capillary leak syndrome, engraftment syndrome or posterior reversible encephalopathy syndrome. This review focuses on the pathogenesis, classification and diagnosis of these disorders, as well as provides guidance on risk mitigation and treatment.

MASP2 inhibition by narsoplimab suppresses endotheliopathies characteristic of transplant-associated thrombotic microangiopathy: in vitro and ex vivo evidence

Transplant-associated thrombotic microangiopathy (TA-TMA) is an endotheliopathy complicating up to 30% of allogeneic hematopoietic stem cell transplants (alloHSCT). Positive feedback loops among complement, pro-inflammatory, pro-apoptotic, and coagulation cascade likely assume dominant roles at different disease stages. We hypothesized that mannose-binding lectin-associated serine protease 2 (MASP2), principal activator of the lectin complement system, is involved in the microvascular endothelial cell (MVEC) injury characteristic of TA-TMA through pathways that are susceptible to suppression by anti-MASP2 monoclonal antibody narsoplimab. Pre-treatment plasmas from 8 of 9 TA-TMA patients achieving a complete TMA response in a narsoplimab clinical trial activated caspase 8, the initial step in apoptotic injury, in human MVEC. This was reduced to control levels following narsoplimab treatment in 7 of the 8 subjects. Plasmas from 8 individuals in an observational TA-TMA study, but not 8 alloHSCT subjects without TMA, similarly activated caspase 8, which was blocked in vitro by narsoplimab. mRNA sequencing of MVEC exposed to TA-TMA or control plasmas with and without narsoplimab suggested potential mechanisms of action. The top 40 narsoplimab-affected transcripts included upregulation of SerpinB2, which blocks apoptosis by inactivating procaspase 3; CHAC1, which inhibits apoptosis in association with mitigation of oxidative stress responses; and pro-angiogenesis proteins TM4SF18, ASPM, and ESM1. Narsoplimab also suppressed transcripts encoding pro-apoptotic and pro-inflammatory proteins ZNF521, IL1R1, Fibulin-5, aggrecan, SLC14A1, and LOX1, and TMEM204, which disrupts vascular integrity. Our data suggest benefits to narsoplimab use in high-risk TA-TMA and provide a potential mechanistic basis for the clinical efficacy of narsoplimab in this disorder.

The Multifaceted Immunology of Cytokine Storm Syndrome

Cytokine storm syndromes (CSSs) are potentially fatal hyperinflammatory states that share the underpinnings of persistent immune cell activation and uninhibited cytokine production. CSSs can be genetically determined by inborn errors of immunity (i.e., familial hemophagocytic lymphohistiocytosis) or develop as a complication of infections, chronic inflammatory diseases (e.g., Still disease), or malignancies (e.g., T cell lymphoma). Therapeutic interventions that activate the immune system such as chimeric Ag receptor T cell therapy and immune checkpoint inhibition can also trigger CSSs in the setting of cancer treatment. In this review, the biology of different types of CSSs is explored, and the current knowledge on the involvement of immune pathways and the contribution of host genetics is discussed. The use of animal models to study CSSs is reviewed, and their relevance for human diseases is discussed. Lastly, treatment approaches for CSSs are discussed with a focus on interventions that target immune cells and cytokines.

Narsoplimab for severe transplant-associated thrombotic microangiopathy

BACKGROUND

Transplantation-associated thrombotic microangiopathy (TA-TMA) is an endothelial injury syndrome linked to the overactivation of complement pathways. It manifests with microangiopathic hemolytic anemia, consumptive thrombocytopenia, and microvascular thrombosis leading to ischemic tissue injury. Mannose residues on fungi and viruses activate the mannose-binding lectin complement pathway, and hence activation of the lectin pathway could be one of the reasons for triggering TA-TMA. Narsoplimab, a human monoclonal antibody targeting MASP-2 is a potent inhibitor of the lectin pathway. We describe the transplant course of a pediatric patient who developed TA-TMA following Candida-triggered macrophage activation syndrome and was treated with Narsoplimab. The data collection was performed prospectively.

CASE PRESENTATION

The six-year-old girl underwent a human leucocyte antigen (HLA) haploidentical hematopoietic stem cell transplant using post-transplant Cyclophosphamide for severe aplastic anemia. In the second week of the transplant, the patient developed macrophage activation syndrome necessitating treatment with steroids and intravenous immunoglobulin. Subsequently, USG abdomen and blood fungal PCR revealed the diagnosis of hepatosplenic candidiasis. Candida-triggered macrophage activation syndrome responded to antifungals, steroids, intravenous immunoglobulin, and alemtuzumab. However, the subsequent clinical course was complicated by thrombotic microangiopathy. The patient developed hypertension in the 2nd week, followed by high lactate dehydrogenase (1010 U/L), schistocytes (5 per hpf), low haptoglobin (< 5 mg/dl), thrombocytopenia, and anemia in the 3rd week. Ciclosporin was stopped, and the patient was treated with 10 days of defibrotide without response. The course was further complicated by the involvement of the gastrointestinal tract and kidneys. She had per rectal bleeding with frequent but low-volume stools, severe abdominal pain, and hypoalbuminemia with a rising urine protein:creatinine ratio. Narsoplimab was started in the 5th week of the transplant. A fall in lactate dehydrogenase was observed after starting Narsoplimab. This was followed by the resolution of gastrointestinal symptoms, proteinuria, and recovery of cytopenia. The second episode of TA-TMA occurred with parvoviraemia and was also successfully treated with Narsoplimab.

CONCLUSION

Lectin pathway inhibition could be useful in treating the fatal complication of transplant-associated thrombotic microangiopathy.

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.

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.

Thrombotic microangiopathies: An illustrated review

The thrombotic microangiopathies (TMAs) are a heterogenous group of disorders with distinct pathophysiologies that cause occlusive microvascular or macrovascular thrombosis, and are characterized by microangiopathic hemolytic anemia, thrombocytopenia, and/or end-organ ischemia. TMAs are associated with significant morbidity and mortality, and data on the management of certain TMAs are often lacking. The nomenclature, classification, and management of various TMAs is constantly evolving as we learn more about these rare syndromes. Thorough clinical and laboratory evaluation is essential to distinguish various TMAs and arrive at an accurate diagnosis, which is key for appropriate management. In this illustrated review, we focus on thrombotic thrombocytopenic purpura (TTP), Shiga toxin-associated hemolytic uremic syndrome, complement-mediated hemolytic uremic syndrome, hematopoietic cell transplant-associated TMA, and drug-induced TMA, and describe their incidence, pathophysiology, diagnosis, and management. We also highlight emerging complement-directed therapies under investigation for the management of complement-mediated TMAs.

Endothelial Dysfunction after Hematopoietic Stem Cell Transplantation: A Review Based on Physiopathology

Endothelial dysfunction (ED) is frequently encountered in transplant medicine. ED is an argument of high complexity, and its understanding requires a wide spectrum of knowledge based on many fields of basic sciences such as molecular biology, immunology, and pathology. After hematopoietic stem cell transplantation (HSCT), ED participates in the pathogenesis of various complications such as sinusoidal obstruction syndrome/veno-occlusive disease (SOS/VOD), graft-versus-host disease (GVHD), transplant-associated thrombotic microangiopathy (TA-TMA), idiopathic pneumonia syndrome (IPS), capillary leak syndrome (CLS), and engraftment syndrome (ES). In the first part of the present manuscript, we briefly review some biological aspects of factors involved in ED: adhesion molecules, cytokines, Toll-like receptors, complement, angiopoietin-1, angiopoietin-2, thrombomodulin, high-mobility group B-1 protein, nitric oxide, glycocalyx, coagulation cascade. In the second part, we review the abnormalities of these factors found in the ED complications associated with HSCT. In the third part, a review of agents used in the treatment of ED after HSCT is presented.

Eculizumab precision dosing algorithm for thrombotic microangiopathy in children and young adults undergoing HSCT

This large study examined eculizumab PK/PD in bleeding and nonbleeding patients with TA-TMA.

PK/PD model-based eculizumab dosing is needed for bleeding in TA-TMA, whereas fixed-dose regimens are effective in nonbleeding patients.

Transplant-associated thrombotic microangiopathy (TA-TMA) is a fatal posttransplant complication of hematopoietic stem cell transplantation. We recently reported that survival for TA-TMA has been improved by early intervention with eculizumab, a complement C5 inhibitor, guided by pharmacokinetic/pharmacodynamic (PK/PD) model-informed precision dosing. However, patients with gastrointestinal bleeding showed poor survival, even when treated with more frequent doses. Our objective was to develop separate models in bleeding and nonbleeding patients with TA-TMA and to propose precision dosing algorithms. Eculizumab PK/PD was analyzed in 19 bleeding and 38 nonbleeding patients (0.5-29.9 years of age). A complement activation biomarker (sC5b-9) and body weight were identified as significant determinants of eculizumab clearance regardless of bleeding. Eculizumab clearance after the first dose was higher in bleeding than in nonbleeding patients (83.8 vs 61.3 mL/h per 70 kg; P = .07). The high clearance was maintained over treatment doses in bleeding patients, whereas nonbleeding patients showed a time-dependent decrease in clearance. sC5b-9 levels were highest before the first dose and decreased over time, regardless of bleeding complications. A Monte Carlo Simulation analysis showed that the current dosing protocols recommended for atypical hemolytic uremic syndrome had <15% probability of attaining the target concentration of >100 μg/mL eculizumab in nonbleeding patients. We identified an intensified loading protocol to reach 80% target attainment. Our data clearly showed the need for individualized dosing for patients with significant bleeding and for ongoing dose adjustments to optimize outcomes. The developed models will be incorporated into a clinical decision guideline for precision dosing to improve outcomes in children and young adults with TA-TMA.

Management of thrombotic microangiopathy after hematopoietic cell transplantation: A position statement of ThREG (Turkish Hematology Research and Education Group)

Hematopoietic stem cell transplantation associated-thrombotic microangiopathy (TA-HCT) is one of the early complications of endothelial origin in the course of HCT. Endothelial damage to the microvascular structure and the platelet-rich microthrombi, which are formed as a result of accompanying complement activation, constitute the main pathological conditions resulting TA-TMA. Early diagnosis and management are of utmost importance to prevent multi-organ failure and death. This review summarizes the current understanding of TA-TMA regarding pathogenesis, definition, differential diagnosis, risk factors, surveillance for early diagnosis and management.