A new paradigm: Diagnosis and management of HSCT-associated thrombotic microangiopathy as multi-system endothelial injury

[Thrombotic microangiopathy and cancer]

Thrombotic microangiopathy (TMA) is a group of disorders characterized by mechanical hemolytic anemia with thrombocytopenia and an ischemic organic lesion of variable and potentially fatal importance affecting mostly the kidneys and the brain with histologically a disseminated and occlusive microvasculopathy. The incidence of TMA represents 15% of acute kidney failure in oncological setting, largely due to the introduction of anti-angiogenic agents over the past decade. It may be more rarely related to cancer itself. The iatrogenic TMA can be classified into 2 types: The type I, secondary to chemotherapy (mitomycinC, gemcitabine), exposes to a chronic dose-dependent renal injury as well as an increase in morbidity and mortality; iatrogenic type II, secondary to anti-angiogenic agents', results in a dose-independent renal involvement and renal functional recovery is usual when the drug is discontinued. There is no randomized controlled trial to establish EBM-type management in TMA support. However, complement activation pathways and regulatory factors analyses allowed us to understand the mechanisms of endothelial lesions. As a result, the current trend includes the use of immunosuppressive agents in recurrent or plasmapheresis-refractory MAT.

Clinical dissection of thrombotic microangiopathy

Differential treatment strategies are applied in thrombotic microangiopathy (TMA) according to the sub-classifications. Hence, it is worthwhile to overview clinical manifestations and outcomes of overall TMA patients according to sub-classifications. We analyzed TMA patients whose serum lactate dehydrogenase levels >250 IU/L, with the presence of schistocytes in their peripheral blood smear, or with typical vascular pathologic abnormalities in their renal biopsy. We compared clinical manifestations including overall survival (OS) and renal survival according to TMA causes. A total of 117 TMA patients (57 primary and 60 secondary TMA) were analyzed. Renal symptom was the most common manifestation in whole patients, while renal function at diagnosis was worst in pregnancy-related TMA group. Primary TMA patients had more frequent CNS symptom and hematologic manifestation compared to secondary TMAs. Among secondary TMAs, pregnancy- and HSCT-related TMA patients showed prevalent hemolytic features. During 150.2 months of follow-up, 5-year OS rate was 64.8%. Poor prognostic factors included older age, combined hematologic and solid organ malignancies, lower hemoglobin levels, and lower serum albumin levels. There was no significant difference in OS between primary and secondary TMAs. Seventy-eight percent of patients experienced AKI during TMA. Five-year death-censored renal survival rate was poor with only 69.2%. However, excellent renal outcome was observed in pregnancy-associated TMA. TMA showed various clinical manifestations according to their etiology. Notably, both OS and renal survival were poor regardless of their etiologies except pregnancy-associated TMA. Physicians should differentiate a variety of TMA categories and properly manage this complex disease entity.

Long-term systolic function in children and young adults after hematopoietic stem cell transplant

Congestive heart failure and subclinical left ventricular systolic dysfunction (LVSD) affect long-term survivors of hematopoietic stem cell transplant (HSCT). Echocardiographic measurements of global longitudinal and circumferential strain have shown promise in identifying subclinical LVSD in cancer survivors. We analyzed echocardiograms in 95 children and young adults with malignancies or bone marrow failure syndromes performed before HSCT and 1-6 years after HSCT. We additionally measured the biomarkers soluble suppression of tumorigenicity-2 (sST-2) and cardiac troponin-I (cTn-I) in the same children through 49 days post HSCT. Ejection fraction (EF) after HSCT was unchanged from baseline (baseline: z-score -0.73 vs long-term follow up: -0.44, P=0.11). Global longitudinal strain was unchanged from baseline (-20.66 vs -20.74%, P=0.90) as was global circumferential strain (-24.3 vs -23.5%, P=0.32). Levels of sST-2 were elevated at all time points compared with baseline samples and cTn-I was elevated at days 14 and 28. Cardiac biomarkers at any time point did not correlate with long-term follow-up EF. In children and young adult survivors of HSCT, EF was unchanged in the first years after HSCT. Elevation in cardiac biomarkers occurring after HSCT suggest subclinical cardiac injury occurs in many patients and long-term monitoring for LVSD should continue.

Circulating dsDNA, endothelial injury, and complement activation in thrombotic microangiopathy and GVHD

Transplant-associated thrombotic microangiopathy (TA-TMA) is a common and poorly recognized complication of hematopoietic stem cell transplantation (HSCT) associated with excessive complement activation, likely triggered by endothelial injury. An important missing piece is the link between endothelial injury and complement activation. We hypothesized that neutrophil extracellular traps (NETs) mechanistically link endothelial damage with complement activation and subsequent TA-TMA. Neutrophil activation releases granule proteins together with double-stranded DNA (dsDNA) to form extracellular fibers known as NETs. NETs have been shown to activate complement and can be assessed in humans by quantification of dsDNA in serum. We measured levels of dsDNA, as a surrogate for NETs in 103 consecutive pediatric allogeneic transplant recipients at day 0, +14, +30, +60, and +100. A spike in dsDNA production around day +14 during engraftment was associated with subsequent TA-TMA development. Peak dsDNA production around day +14 was associated with interleukin-8-driven neutrophil recovery. Increased dsDNA levels at days +30, +60, and +100 were also associated with increased mortality and gastrointestinal graft-versus-host disease (GVHD). NETs may serve as a mechanistic link between endothelial injury and complement activation. NET formation may be one mechanism contributing to the clinical overlap between GVHD and TA-TMA.

Transplant-associated thrombotic microangiopathy is an endothelial complication associated with refractoriness of acute GvHD

There is increasing evidence that endothelial dysfunction is involved in refractoriness of acute GvHD (aGvHD). Here we investigated the hypothesis that another endothelial complication, transplant-associated thrombotic microangiopathy (TMA), contributes to the pathogenesis of aGvHD refractoriness. TMA was retrospectively assessed in 771 patients after allogeneic stem cell transplantation (alloSCT). Incidences of TMA and refractory aGvHD were correlated with biomarkers of endothelial damage obtained before alloSCT for patients receiving or not receiving statin-based endothelial prophylaxis (SEP). Diagnostic criteria for TMA and refractory aGvHD were met by 41 (5.3%) and 76 (10%) patients, respectively. TMA was overrepresented in patients with refractory aGvHD (45.0 vs 2.3% in all other patients, P<0.001). TMA independently increased mortality. Elevated pretransplant suppressor of tumorigenicity-2 and nitrates along with high-risk variants of the thrombomodulin gene were associated with increased risk of TMA. In contrast, SEP abolished the unfavorable outcome predicted by pretransplant biomarkers on TMA risk. Patients on SEP had a significantly lower risk of TMA (P=0.001) and refractory aGvHD (P=0.055) in a multivariate multistate model. Our data provide evidence that TMA contributes to the pathogenesis of aGvHD refractoriness. Patients with an increased TMA risk can be identified pretransplant and may benefit from pharmacological endothelium protection.

None of the above: thrombotic microangiopathy beyond TTP and HUS

Acquired thrombotic thrombocytopenic purpura (TTP) and hemolytic uremic syndrome (HUS) are appropriately at the top of a clinician's differential when a patient presents with a clinical picture consistent with an acute thrombotic microangiopathy (TMA). However, there are several additional diagnoses that should be considered in patients presenting with an acute TMA, especially in patients with nondeficient ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13) activity (>10%). An increased awareness of drug-induced TMA is also essential because the key to their diagnosis more often is an appropriately detailed medical history to inquire about potential exposures. Widespread inflammation and endothelial damage are central in the pathogenesis of the TMA, with the treatment directed at the underlying disease if possible. TMA presentations in the critically ill, drug-induced TMA, cancer-associated TMA, and hematopoietic transplant-associated TMA (TA-TMA) and their specific treatment, where applicable, will be discussed in this manuscript. A complete assessment of all the potential etiologies for the TMA findings including acquired TTP will allow for a more accurate diagnosis and prevent prolonged or inappropriate treatment with plasma exchange therapy when it is less likely to be successful.

The injured heart: early cardiac effects of hematopoietic stem cell transplantation in children and young adults

We hypothesized that subclinical cardiac injury in the peri-transplant period is more frequent than currently appreciated in children and young adults. We performed echocardiographic screening on 227 consecutive patients prior to hematopoietic stem cell transplantation (HSCT), and 7, 30 and 100 days after transplant. We measured cardiac biomarkers cardiac troponin-I (cTn-I), and soluble suppressor of tumorigenicity 2 (sST2) prior to transplant, during conditioning, and days +7, +14, +28 and +49 in 26 patients. We subsequently analyzed levels of cTn-I every 48-72 h in 15 consecutive children during conditioning. Thirty-two percent (73/227) of patients had a new abnormality on echocardiogram. New left ventricular systolic dysfunction (LVSD) occurred in 6.2% of subjects and new pericardial effusion in 27.3%. Eight of 227 (3.5%) patients underwent pericardial drain placement, and 5 (2.2%) received medical therapy for clinically occult LVSD. cTn-I was elevated in 53.0% of all samples and sST2 in 38.2%. At least one sample had a detectable cTn-I in 84.6% of patients and an elevated sST2 in 76.9%. Thirteen of fifteen patients monitored frequently during condition had elevation of cTn-I. Echocardiographic and biochemical abnormalities are frequent in the peri-HSCT period. Echocardiogram does not detect all subclinical cardiac injuries that may become clinically relevant over longer periods.

Pericardial Effusion Following Hematopoietic Cell Transplantation in Children and Young Adults Is Associated with Increased Risk of Mortality

Hematopoietic cell transplantation (HCT) is curative for many pediatric malignant and nonmalignant disorders but is associated with significant morbidity and mortality, including the development of pericardial effusion (PEF). We report the results of a retrospective chart review performed to assess the incidence, risk factors, and prognostic significance of PEF in pediatric HCT recipient at Lucile Packard Children's Hospital of Stanford University. A total of 119 patients undergoing HCT between January 2010 and December 2013 were selected through the hospital's Pediatric Stem Cell Transplant Program database. A retrospective chart review, including review of documentation, correspondence, imaging reports, laboratory values, and death records, was performed to collect data. The overall incidence of PEF in our population was 21%. Risk factors for the development of PEF included unrelated donor transplants and cord blood as the stem cell source (P = .005), whereas HLA mismatch approached significance (P = .05). The risk for development of PEF was found to not be significantly associated with acute or chronic graft-versus-host disease (GVHD), age at transplantation, sex, conditioning regimen, or viral reactivation status. Of interest, 6 of the 119 patients were found to have transplant-associated thrombotic microangiopathy (TA-TMA). Four of those 6 patients developed PEF, suggesting TA-TMA as a risk factor for PEF. Eight of the 25 patients who developed PEF (32%) required pericardiocentesis. Five out of the 8 patients requiring pericardiocentesis died owing to causes unrelated to the procedure or to PEF itself. Pericardial fluid testing in 4 of these patients (50%) was positive for human herpesvirus 6, Epstein-Barr virus, cytomegalovirus, and/or adenovirus. Finally, of significant interest, patients with PEF had a statistically significant higher likelihood of mortality compared with those without PEF (44% versus 17%; P = .007).

Pathophysiology of GvHD and Other HSCT-Related Major Complications

For over 60 years, hematopoietic stem cell transplantation has been the major curative therapy for several hematological and genetic disorders, but its efficacy is limited by the secondary disease called graft versus host disease (GvHD). Huge advances have been made in successful transplantation in order to improve patient quality of life, and yet, complete success is hard to achieve. This review assimilates recent updates on pathophysiology of GvHD, prophylaxis and treatment of GvHD-related complications, and advances in the potential treatment of GvHD.

Specific Etiologies Associated With the Multiple Organ Dysfunction Syndrome in Children: Part 1

OBJECTIVE

To describe a number of the conditions associated with multiple organ dysfunction syndrome presented as part of the Eunice Kennedy Shriver National Institute of Child Health and Human Development multiple organ dysfunction syndrome workshop (March 26-27, 2015).

DATA SOURCES

Literature review, research data, and expert opinion.

STUDY SELECTION

Not applicable.

DATA EXTRACTION

Moderated by an expert from the field, issues relevant to the association of multiple organ dysfunction syndrome with a variety of conditions were presented, discussed, and debated with a focus on identifying knowledge gaps and research priorities.

DATA SYNTHESIS

Summary of presentations and discussion supported and supplemented by the relevant literature.

CONCLUSIONS

There is a wide range of medical conditions associated with multiple organ dysfunction syndrome in children. Traditionally, sepsis and trauma are the two conditions most commonly associated with multiple organ dysfunction syndrome both in children and adults. However, there are a number of other pathophysiologic processes that may result in multiple organ dysfunction syndrome. In this article, we discuss conditions such as cancer, congenital heart disease, and acute respiratory distress syndrome. In addition, the relationship between multiple organ dysfunction syndrome and clinical therapies such as hematopoietic stem cell transplantation and cardiopulmonary bypass is also considered. The purpose of this article is to describe the association of multiple organ dysfunction syndrome with a variety of conditions in an attempt to identify similarities, differences, and opportunities for therapeutic intervention.

Specific Etiologies Associated With the Multiple Organ Dysfunction Syndrome in Children: Part 2

OBJECTIVE

To describe a number of conditions and therapies associated with multiple organ dysfunction syndrome presented as part of the Eunice Kennedy Shriver National Institute of Child Health and Human Development Multiple Organ Dysfunction Workshop (March 26-27, 2015). In addition, the relationship between burn injuries and multiple organ dysfunction syndrome is also included although it was not discussed at the workshop.

DATA SOURCES

Literature review, research data, and expert opinion.

STUDY SELECTION

Not applicable.

DATA EXTRACTION

Moderated by an expert from the field, issues relevant to the association of multiple organ dysfunction syndrome with a variety of conditions and therapies were presented, discussed, and debated with a focus on identifying knowledge gaps and the research priorities.

DATA SYNTHESIS

Summary of presentations and discussion supported and supplemented by relevant literature.

CONCLUSIONS

Sepsis and trauma are the two conditions most commonly associated with multiple organ dysfunction syndrome both in children and adults. However, many other pathophysiologic processes may result in multiple organ dysfunction syndrome. In this article, we discuss conditions such as liver failure and pancreatitis, pathophysiologic processes such as ischemia and hypoxia, and injuries such as trauma and burns. Additionally, therapeutic interventions such as medications, blood transfusions, transplantation may also precipitate and contribute to multiple organ dysfunction syndrome. The purpose of this article is to describe the association of multiple organ dysfunction syndrome with a variety of conditions and therapies in an attempt to identify similarities, differences, and opportunities for therapeutic intervention.

The Biology of Chronic Graft-versus-Host Disease: A Task Force Report from the National Institutes of Health Consensus Development Project on Criteria for Clinical Trials in Chronic Graft-versus-Host Disease

Chronic graft-versus-host disease (GVHD) is the leading cause of late, nonrelapse mortality and disability in allogeneic hematopoietic cell transplantation recipients and a major obstacle to improving outcomes. The biology of chronic GVHD remains enigmatic, but understanding the underpinnings of the immunologic mechanisms responsible for the initiation and progression of disease is fundamental to developing effective prevention and treatment strategies. The goals of this task force review are as follows: This document is intended as a review of our understanding of chronic GVHD biology and therapies resulting from preclinical studies, and as a platform for developing innovative clinical strategies to prevent and treat chronic GVHD.

Transplantation-associated thrombotic microangiopathy isolated to a congenital anomaly of the lung

TA-TMA is a post-hematopoietic stem cell transplant complication with clinical features of hemolytic anemia and thrombocytopenia. A 26-month-old child who had had an allogeneic transplant for treatment of DBA developed severe TA-TMA with heavy red blood cell and platelet transfusion dependence. Incidentally, he was found to have a lung sequestration. TA-TMA resolved and transfusion dependence resolved after resection of the sequestration. The finding suggests the malformation vasculature was selectively vulnerable to the trigger of TA-TMA-raising perhaps a clue to basic pathophysiology of TA-TMA and/or vascular malformations.

Neurologic Complications after Allogeneic Hematopoietic Stem Cell Transplantation

Neurologic complications after hematopoietic stem cell transplantation are frequently life-threatening, and their clinical management can be highly challenging. A wide spectrum of causative factors-including drug-related toxicities; infections sustained by virus, bacteria, or invasive molds; metabolic encephalopathy; cerebrovascular disorders; immune-mediated disorders; and disease recurrence-may lead to potentially lethal complications. Moreover, given that some neurologic complications are not uncommonly diagnosed post mortem, their overall incidence is likely to be underestimated. Their prompt recognition and timely treatment are of paramount importance to reduce the risk for transplantation-related death.

Is complement blockade an acceptable therapeutic strategy for hematopoietic cell transplant-associated thrombotic microangiopathy?

Diagnosis and management of hematopoietic cell transplant-associated thrombotic microangiopathy (TA-TMA) are very complex and controversial, given multiple ongoing issues and comorbidities in sick transplant recipients. Complement activation via classic and alternative pathways is emerging as a potential pathogenetic mechanism in the development of TA-TMA. Complement-centric diagnostic strategy using functional and genetic tests may possibly support diagnosis, enhance molecular understanding and direct drug development. Complement blockade using eculizumab has shown some promising rates of hematologic responses, however, survival may still be poor. Early discontinuation of calcineurin inhibitor where feasible, use of eculizumab, aggressive infection prophylaxis, close monitoring and early treatment of potential complications including GvHD and organ failure may improve outcomes. A number of complement inhibitors are in the development and may change treatment paradigm. Future studies are important to better understand TA-TMA as a disease process and may aim to confirm the role of complement activation in TA-TMA, enhance diagnostic strategy, determine therapeutic approaches and strategies to reduce the risk of other complications particularly infection and GvHD.

Antineoplastic Treatment and Renal Injury: An Update on Renal Pathology Due to Cytotoxic and Targeted Therapies

Cancer patients experience kidney injury from multiple sources, including the tumor itself, diagnostic procedures, hypovolemia, infection, and drug exposure, superimposed upon baseline chronic damage. This review will focus on cytotoxic or targeted chemotherapy-associated renal injury. In this setting, tubulointerstitial injury and thrombotic microangiopathy (vascular injury) are more common than other forms of kidney injury including glomerular. Cisplatin, pemetrexed, and ifosfamide are well-known causes of acute tubular injury/necrosis. Acute interstitial nephritis seems underrecognized in this clinical setting. Interstitial nephritis is emerging as an "immune-related adverse effect" (irAE's) with immune checkpoint inhibitors in small numbers of patients. Acute kidney injury is rarely reported with targeted therapies such as BRAF inhibitors (vemurafinib, dabrafenib), ALK inhibitors (crizotinib), and mTOR inhibitors (everolimus, temsirolimus), but additional biopsy data are needed. Tyrosine kinase inhibitors and monoclonal antibodies that block the vascular endothelial growth factor pathway are most commonly associated with thrombotic microangiopathy. Other causes of thrombotic microangiopathy in the cancer patients include cytotoxic chemotherapies such as gemcitabine and mitomycin C, hematopoietic stem cell transplant, and cancer itself (usually high-stage adenocarcinoma with marrow and vascular invasion). Cancer patients are historically underbiopsied, but biopsy can reveal type, acuity, and chronicity of renal injury, and facilitate decisions concerning continuation of chemotherapy and/or initiation of renoprotective therapy. Biopsy may also reveal unrelated and unanticipated findings in need of treatment.

Therapeutic complement inhibition in complement-mediated hemolytic anemias: Past, present and future

The introduction in the clinic of anti-complement agents represented a major achievement which gave to physicians a novel etiologic treatment for different human diseases. Indeed, the first anti-complement agent eculizumab has changed the treatment paradigm of paroxysmal nocturnal hemoglobinuria (PNH), dramatically impacting its severe clinical course. In addition, eculizumab is the first agent approved for atypical Hemolytic Uremic Syndrome (aHUS), a life-threatening inherited thrombotic microangiopathy. Nevertheless, such remarkable milestone in medicine has brought to the fore additional challenges for the scientific community. Indeed, the list of complement-mediated anemias is not limited to PNH and aHUS, and other human diseases can be considered for anti-complement treatment. They include other thrombotic microangiopathies, as well as some antibody-mediated hemolytic anemias. Furthermore, more than ten years of experience with eculizumab led to a better understanding of the individual steps of the complement cascade involved in the pathophysiology of different human diseases. Based on this, new unmet clinical needs are emerging; a number of different strategies are currently under development to improve current anti-complement treatment, trying to address these specific clinical needs. They include: (i) alternative anti-C5 agents, which may improve the heaviness of eculizumab treatment; (ii) broad-spectrum anti-C3 agents, which may improve the efficacy of anti-C5 treatment by intercepting the complement cascade upstream (i.e., preventing C3-mediated extravascular hemolysis in PNH); (iii) targeted inhibitors of selective complement activating pathways, which may prevent early pathogenic events of specific human diseases (e.g., anti-classical pathway for antibody-mediated anemias, or anti-alternative pathway for PNH and aHUS). Here we briefly summarize the status of art of current and future complement inhibition for different complement-mediated anemias, trying to identify the most promising approaches for each individual disease.

Healthcare Burden, Risk Factors, and Outcomes of Mucosal Barrier Injury Laboratory-Confirmed Bloodstream Infections after Stem Cell Transplantation

Mucosal barrier injury laboratory-confirmed bloodstream infections (MBI-LCBIs) lead to significant morbidity, mortality, and healthcare resource utilization in hematopoietic stem cell transplant (HSCT) patients. Determination of the healthcare burden of MBI-LCBIs and identification of patients at risk of MBI-LCBIs will allow researchers to identify strategies to reduce MBI-LCBI rates. The objective of our study was to describe the incidence, risk factors, timing, and outcomes of MBI-LCBIs in hematopoietic stem cell transplant patients. We performed a retrospective analysis of 374 patients who underwent HSCT at a large free-standing academic children's hospital to determine the incidence, risk factors, and outcomes of patients that developed a bloodstream infection (BSI) including MBI-LCBI, central line-associated BSI (CLABSI), or secondary BSI in the first year after HSCT. Outcome measures included nonrelapse mortality (NRM), central venous catheter removal within 7 days of positive culture, shock, admission to the pediatric intensive care unit (PICU) within 48 hours of positive culture, and death within 10 days of positive culture. One hundred seventy BSIs were diagnosed in 100 patients (27%): 80 (47%) MBI-LCBIs, 68 (40%) CLABSIs, and 22 (13%) secondary infections. MBI-LCBIs were diagnosed at a significantly higher rate in allogeneic HSCT patients (18% versus 7%, P = .007). Reduced-intensity conditioning (OR, 1.96; P = .015) and transplant-associated thrombotic microangiopathy (OR, 2.94; P = .0004) were associated with MBI-LCBI. Nearly 50% of all patients with a BSI developed septic shock, 10% died within 10 days of positive culture, and nearly 25% were transferred to the PICU. One-year NRM was significantly increased in patients with 1 (34%) and more than 1 (56%) BSIs in the first year post-HSCT compared with those who did not develop BSIs (14%) (P ≤ .0001). There was increased 1-year NRM in patients with at least 1 MBI-LCBI (OR, 1.94; P = .018) and at least 1 secondary BSI (OR, 2.87; P = .0023) but not CLABSIs (OR, 1.17; P = .68). Our data demonstrate that MBI-LCBIs lead to substantial use of healthcare resources and are associated with significant morbidity and mortality. Reduction in frequency of MBI-LCBI should be a major public health and scientific priority.

The alternative pathway of complement and the thrombotic microangiopathies

Thrombotic microangiopathies (TMA) are disorders defined by microangiopathic hemolytic anemia, non-immune thrombocytopenia and have multi-organ involvement including the kidneys, brain, gastrointestinal, respiratory tract and skin. Emerging evidence points to the central role of complement dysregulation in leading to microvascular endothelial injury which is crucial for the development of TMAs. This key insight has led to the development of complement-targeted therapy. Eculizumab is an anti-C5 monoclonal antibody, which has revolutionized the treatment of atypical hemolytic uremic syndrome. Several other anti-complement therapeutic agents are currently in development, offering a potential armamentarium of therapies available to treat complement-mediated TMAs. The development of sensitive, reliable and easy to perform assays to monitor complement activity and therapeutic efficacy will be key to devising an individualized treatment regime with the potential of safely weaning or discontinuing treatment in the appropriate clinical setting.

New approaches in the diagnosis, pathophysiology, and treatment of pediatric hematopoietic stem cell transplantation-associated thrombotic microangiopathy

Hematopoietic stem cell transplantation (HSCT)-associated thrombotic microangiopathy (TA-TMA) is an understudied complication of HSCT that significantly affects transplant-related morbidity and mortality. Over the past several decades, the cause of TA-TMA has remained unknown, limiting treatment options to non-specific therapies adapted from other diseases. Recent prospective studies dedicated to the study of TA-TMA have provided new insights into the pathogenesis of, and genetic susceptibility to TA-TMA, raising awareness of this important transplant complication and allowing for the identification of potentially novel therapeutic targets. Specifically, many patients with TA-TMA develop multi-organ tissue injury through endothelial damage mediated by the activation of the complement pathway, leading to rational therapeutic strategies including complement blockade. This new knowledge has the potential to favorably influence clinical practice and change the standard of care for how patients with TA-TMA are managed. In this review, we summarize novel approaches to the recognition and management of TA-TMA, using case examples to illustrate key clinical points that hopefully lead to improved short and long-term outcomes for these complex HSCT patients, who remain at significant risk for treatment-related morbidity and mortality.

The endothelium as the common denominator in malignant hypertension and thrombotic microangiopathy

The endothelium plays a pivotal role in vascular biology. The endothelium is the primary site of injury in thrombotic microangiopathies including malignant hypertension. Endothelial injury in thrombotic microangiopathies is the result of increased shear stress, toxins, and/or dysregulated complement activation. Endothelial injury can lead to microvascular thrombosis resulting in ischemia and organ dysfunction, the clinical hallmarks of thrombotic microangiopathies. Currently, available therapies target the underlying mechanisms that lead to endothelial injury in these conditions. Ongoing investigations aim at identifying drugs that protect the endothelium.

The genetic fingerprint of susceptibility for transplant-associated thrombotic microangiopathy

Transplant-associated thrombotic microangiopathy (TA-TMA) occurs frequently after hematopoietic stem cell transplantation (HSCT) and can lead to significant morbidity and mortality. There are no data addressing individual susceptibility to TA-TMA. We performed a hypothesis-driven analysis of 17 candidate genes known to play a role in complement activation as part of a prospective study of TMA in HSCT recipients. We examined the functional significance of gene variants by using gene expression profiling. Among 77 patients undergoing genetic testing, 34 had TMA. Sixty-five percent of patients with TMA had genetic variants in at least one gene compared with 9% of patients without TMA (P < .0001). Gene variants were increased in patients of all races with TMA, but nonwhites had more variants than whites (2.5 [range, 0-7] vs 0 [range, 0-2]; P < .0001). Variants in ≥3 genes were identified only in nonwhites with TMA and were associated with high mortality (71%). RNA sequencing analysis of pretransplantation samples showed upregulation of multiple complement pathways in patients with TMA who had gene variants, including variants predicted as possibly benign by computer algorithm, compared with those without TMA and without gene variants. Our data reveal important differences in genetic susceptibility to HSCT-associated TMA based on recipient genotype. These data will allow prospective risk assessment and intervention to prevent TMA in highly susceptible transplant recipients. Our findings may explain, at least in part, racial disparities previously reported in transplant recipients and may guide treatment strategies to improve outcomes.

Histologic Features of Intestinal Thrombotic Microangiopathy in Pediatric and Young Adult Patients after Hematopoietic Stem Cell Transplantation

High-risk transplantation-associated thrombotic microangiopathy (TMA) can present with multisystem involvement and is associated with a poor outcome after hematopoietic stem cell transplantation (HSCT), with < 20% 1-year survival. TMA may involve the intestinal vasculature and can present with bleeding and ischemic colitis. There are no established pathologic criteria for the diagnosis of intestinal TMA (iTMA). The goal of our study was to identify histologic features of iTMA and describe associated clinical features. We evaluated endoscopic samples from 50 consecutive HSCT patients for 8 histopathologic signs of iTMA and compared findings in 3 clinical groups based on the presence or absence of systemic high-risk TMA (hrTMA) and the presence or absence of clinically staged intestinal graft-versus-host disease (iGVHD): TMA/iGVHD, no TMA/iGVHD, and no TMA/no iGVHD. Thirty percent of the study subjects had a clinical diagnosis of systemic hrTMA. On histology, loss of glands, intraluminal schistocytes, intraluminal fibrin, intraluminal microthrombi, endothelial cell separation, and total denudation of mucosa were significantly more common in the hrTMA group (P < .05). Intravascular thrombi were seen exclusively in patients with hrTMA. Mucosal hemorrhages and endothelial cell swelling were more common in hrTMA patients but this difference did not reach statistical significance. Patients with hrTMA were more likely to experience significant abdominal pain and gastrointestinal bleeding requiring multiple blood transfusions (P < .05). Our study shows that HSCT patients with systemic hrTMA can have significant bowel vascular injury that can be identified using defined histologic criteria. Recognition of these histologic signs in post-transplantation patients with significant gastrointestinal symptoms may guide clinical decisions.

Variable Eculizumab Clearance Requires Pharmacodynamic Monitoring to Optimize Therapy for Thrombotic Microangiopathy after Hematopoietic Stem Cell Transplantation

Thrombotic microangiopathy (TMA) after hematopoietic stem cell transplantation (HSCT) associated with terminal complement activation, as measured by elevated plasma terminal complement (sC5b-9) concentrations, has a very high mortality. The complement inhibitor eculizumab may be a therapeutic option for HSCT-associated TMA. We examined the pharmacokinetics and pharmacodynamics (PK/PD) of eculizumab in children and young adult HSCT recipients with TMA and activated complement to determine drug dosing requirements for future efficacy trials. We analyzed prospectively collected laboratory samples and clinical data from 18 HSCT recipients with high-risk TMA presenting with complement activation who were treated with eculizumab. We measured eculizumab serum concentrations, total hemolytic complement activity, and plasma sC5b-9 concentrations. Population PK/PD analyses correlated eculizumab concentrations with complement blockade and clinical response and determined interindividual differences in PK parameters. We also compared transplant survival in patients treated with eculizumab (n = 18) with patients with the same high-risk TMA features who did not receive any targeted therapy during a separate prospective observational study (n = 11). In the PK analysis, we found significant interpatient variability in eculizumab clearance, ranging from 16 to 237 mL/hr/70 kg in the induction phase. The degree of complement activation measured by sC5b-9 concentrations at the start of therapy, in addition to actual body weight, was a significant determinant of eculizumab clearance and disease response. Sixty-one percent of treated patients had complete resolution of TMA and were able to safely discontinue eculizumab without disease recurrence. Overall survival was significantly higher in treated subjects compared with untreated patients (56% versus 9%, P = .003). Complement blocking therapy is associated with improved survival in HSCT patients with high-risk TMA who historically have dismal outcomes, but eculizumab pharmacokinetics in HSCT recipients differ significantly from reports in other diseases like atypical hemolytic uremic syndrome and paroxysmal nocturnal hemoglobinuria. Our eculizumab dosing algorithm, including pr-treatment plasma sC5b-9 concentrations, patient's actual body weight, and the first eculizumab dose (mg), accurately determined eculizumab concentration-time profiles for HSCT recipients with high-risk TMA. This algorithm may guide eculizumab treatment and ensure that future efficacy studies use the most clinically appropriate and cost-efficient dosing schedules.

Hematopoietic Stem Cell Transplant-Associated Thrombotic Microangiopathy

Hematopoietic stem cell transplant-associated thrombotic microangiopathy (TA-TMA) is a fatal, multifactorial disorder, which may present with thrombocytopenia, hemolysis, acute renal failure, mental status changes and involvement of other organs. The pathogenesis of TA-TMA is complex and includes multiple risk factors such as certain conditioning regimens, calcineurin inhibitors (CNIs), graft-versus-host disease (GVHD), human leukocyte antigen mismatch, and opportunistic infections. The end result of these insults is endothelial injury in the kidney and other organs. Recent studies also indicate a role of complement activation in tissue damage. The lack of sensitive and specific diagnostic tests for TA-TMA often results in delayed diagnosis. Biopsy is not always possible for diagnosis because of the risk of complications such as bleeding. Recently, an emerging role of renal-centered screening approach has been demonstrated, which utilize the monitoring of blood pressure, urine protein, serum lactate dehydrogenase and hemogram for early detection. Therapeutic options are limited, and plasma exchange plays a minor role. Withdrawal of offending agent such as CNIs and the use of rituximab can be effective in some patients. However, the current treatment strategy is suboptimal and associated with high mortality rate. Recently, eculizumab has been utilized in a few patients with good outcomes. Patients, who develop TA-TMA, are also at an increased risk of GVHD, infection, renal, cardiovascular, and other complications, which can contribute to high mortality. Better understanding of molecular pathogenesis, improvement in posttransplant management, leading to early diagnosis, and management of TA-TMA are required to improve outcomes of this fatal entity.

National Institutes of Health Consensus Development Project on Criteria for Clinical Trials in Chronic Graft-versus-Host Disease: V. The 2014 Ancillary Therapy and Supportive Care Working Group Report

The 2006 National Institutes of Health (NIH) Consensus paper presented recommendations by the Ancillary Therapy and Supportive Care Working Group to support clinical research trials in chronic graft-versus-host disease (GVHD). Topics covered in that inaugural effort included the prevention and management of infections and common complications of chronic GVHD, as well as recommendations for patient education and appropriate follow-up. Given the new literature that has emerged during the past 8 years, we made further organ-specific refinements to these guidelines. Minimum frequencies are suggested for monitoring key parameters relevant to chronic GVHD during systemic immunosuppressive therapy and, thereafter, referral to existing late effects consensus guidelines is advised. Using the framework of the prior consensus, the 2014 NIH recommendations are organized by organ or other relevant systems and graded according to the strength and quality of supporting evidence.

Management of hemolytic anemia following allogeneic stem cell transplantation

Hemolytic anemia (HA) is a frequent condition with variable pathophysiology. Hematopoietic stem cell transplantation (HSCT) is unique because it is performed across the ABO blood group barrier. Thereby, there is a transfer of plasma, red blood cells, and immunocompetent cells from the donor to the recipient, possibly leading to HA, due to red blood cell incompatibility. The underlying disease, drugs (particularly those used for conditioning and immunosuppressants), infections, graft-versus-host disease, and autoimmune diseases may all contribute to the clinical and laboratory picture of HA. Additionally, transplantation-associated thrombotic microangiopathy (TA-TMA) may occur and is associated with significant morbidity and mortality. This review highlights the current knowledge on HA after allogeneic HSCT, particularly due to ABO incompatibility. We follow the timeline of the transplantation process and discuss investigations, differential diagnosis, and prophylactic measures including graft processing to avoid hemolysis in case of ABO incompatibility. Finally, current therapeutic approaches for both TA-TMA and post-HSCT autoimmune HA, which are associated with high morbidity and mortality, are discussed.