Validation of Early Increase in Complement Activation Marker sC5b-9 as a Predictive Biomarker for the Development of Thrombotic Microangiopathy After Stem Cell Transplantation

Hemostasis and complement in allogeneic hematopoietic stem cell transplantation: clinical significance of two interactive systems

Hematopoietic stem cell transplantation (HCT) represents a curative treatment option for certain malignant and nonmalignant hematological diseases. Conditioning regimens before HCT, the development of graft-versus-host disease (GVHD) in the allogeneic setting, and delayed immune reconstitution contribute to early and late complications by inducing tissue damage or humoral alterations. Hemostasis and/or the complement system are biological regulatory defense systems involving humoral and cellular reactions and are variably involved in these complications after allogeneic HCT. The hemostasis and complement systems have multiple interactions, which have been described both under physiological and pathological conditions. They share common tissue targets, such as the endothelium, which suggests interactions in the pathogenesis of several serious complications in the early or late phase after HCT. Complications in which both systems interfere with each other and thus contribute to disease pathogenesis include transplant-associated thrombotic microangiopathy (HSCT-TMA), sinusoidal obstruction syndrome/veno-occlusive disease (SOS/VOD), and GVHD. Here, we review the current knowledge on changes in hemostasis and complement after allogeneic HCT and how these changes may define clinical impact.

The function of the complement system remains fully intact throughout the course of allogeneic stem cell transplantation

Introduction

Hematopoietic stem cell transplantation (HSCT) is associated with immune complications and endothelial dysfunction due to intricate donor-recipient interactions, conditioning regimens, and inflammatory responses.

Methods

This study investigated the role of the complement system during HSCT and its interaction with the cytokine network. Seventeen acute myeloid leukemia patients undergoing HSCT were monitored, including blood sampling from the start of the conditioning regimen until four weeks post-transplant. Clinical follow-up was 200 days.

Results

Total complement functional activity was measured by WIELISA and the degree of complement activation by ELISA measurement of sC5b-9. Cytokine release was measured using a 27-multiplex immuno-assay. At all time-points during HSCT complement functional activity remained comparable to healthy controls. Complement activation was continuously stable except for two patients demonstrating increased activation, consistent with severe endotheliopathy and infections. In vitro experiments with post-HSCT whole blood challenged with Escherichia coli, revealed a hyperinflammatory cytokine response with increased TNF, IL-1β, IL-6 and IL-8 formation. Complement C3 inhibition markedly reduced the cytokine response induced by Staphylococcus aureus, Aspergillus fumigatus, and cholesterol crystals.

Discussion

In conclusion, HSCT patients generally retained a fully functional complement system, whereas activation occurred in patients with severe complications. The complement-cytokine interaction indicates the potential for new complement-targeting therapeutic strategies in HSCT.

Prospective Clinical and Biomarker Validation of the American Society for Transplantation and Cellular Therapy Consensus Definition for Transplantation-Associated Thrombotic Microangiopathy

Transplantation-associated thrombotic microangiography (TA-TMA) is a disorder that causes severe complications after allogeneic hematopoietic cell transplantation (allo-HCT). Diagnosing TA-TMA is challenging because of the lack of standardized criteria. In this study, we aimed to evaluate the new TA-TMA consensus definition from the American Society for Transplantation and Cellular Therapy (ASTCT) panel as part of an ongoing prospective pediatric cohort study, and also to compare the impact and outcomes of using the current definition of clinical TMA (cTMA) versus the new consensus definition. We included patients age 0 to 18 years who underwent their first allo-HCT between May 2021 and January 2023 at Texas Children's Hospital. We compared the incidence, biomarkers, and outcomes of TA-TMA applying the previous and recently proposed screening algorithms and definitions. Whereas use of the classic microangiopathic hemolytic anemia (MAHA)-based cTMA definition led to an incidence of 12.7% by day 100 post-transplantation, the ASTCT-HR definition doubled the incidence to 28.5% by day 100. In contrast to patients with a concordant diagnosis (+/+), who had significantly worse post-transplantation survival, those reclassified as TA-TMA only by the new definition (-/+) had a significantly different prognosis (100% survival at day 100) despite the lack of TMA-directed therapy. Furthermore, biomarkers of the terminal and alternative complement pathways (sC5b9 and Ba, respectively) were significantly elevated compared with non-TMA patients around day 15 in the concordant group (+/+) but not in the discordant group (-/+). The recently proposed ASTCT consensus TA-TMA diagnosis is more sensitive and allows earlier recognition of manifestation that requires closer clinical monitoring but risks overdiagnosis and overtreatment. We recommend additional prospective validation.

Current Status of Adverse Event Profile of Cyclosporine in Kidney, Stem Cell, and Heart Transplantations Using the Japanese Pharmacovigilance Database

Background: Cyclosporine is widely used to prevent allograft rejection after transplantation. The purpose of this study was to clarify the adverse events profiles associated with cyclosporine in transplant patients using a spontaneous reporting system database.

Methods: Retrospective pharmacovigilance disproportionality analysis was conducted using the Japanese Adverse Drug Event Report (JADER) database, with the reporting odds ratio (ROR) and 95% confidence interval (CI) for each adverse event.

Results: The database comprised 3,327, 958, and 956 reports associated with cyclosporine in the kidney, stem cell, and heart transplant patients, respectively. Infectious and renal disorders were commonly detected in these transplant patients. The signal scores of cyclosporine for toxic nephropathy were noteworthy in the kidney (ROR: 15.1, 95% CI: 11-20.8) and stem cell (ROR, 216; 95% CI, 29.3-1593) transplantation. Cyclosporine in heart transplantation was strongly associated with gastric cancer (ROR, 39.4; 95% CI, 16.7-93.2), but not kidney or stem cell transplantation.

Conclusion: It was suggested that there is a diversity in the strength of the association between cyclosporine and adverse events in the kidney, stem cell, and heart transplantation. Our results may provide useful information for treatment with cyclosporine, although further research with more data is needed.

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).

Decreased complement 4d increases poor prognosis in patients with non‑small cell lung cancer combined with gastrointestinal lymph node metastasis

Lung cancer is a common malignancy that is difficult to treat and has a high risk of mortality. Although gastrointestinal lymph node metastasis has long been known to exert major impact on the prognosis of lung cancer, the mechanism of its occurrence and potential biological markers remain elusive. Therefore, the present study retrospectively analyzed data from 132 patients with non-small cell lung cancer (NSCLC) combined with lymph node metastasis between February 2010 and April 2019 from the First Affiliated Hospital of Soochow University (Suzhou, China) and Sichuan Cancer Hospital (Chengdu, China). Overall survival was assessed using Kaplan-Meier analysis and Cox logistic regression model. In addition, a prediction model was constructed based on immune indicators such as complement C3b and C4d (measured by ELISA), before the accuracy of this model was validated using calibration curves for 5-year OS. Among the 132 included patients, a total of 92 (70.0%) succumbed to the disease within 5 years. Multifactorial analysis revealed that complement C3b deficiency increased the risk of mortality by nearly two-fold [hazard ratio (HR)=2.23; 95% CI=1.20-4.14; P=0.017], whilst complement C4d deficiency similarly increased the risk of mortality by two-fold (HR=2.14; 95% CI=1.14-4.00; P=0.012). The variables were subsequently screened using Cox model to construct a prediction model based on complement C3b and C4d levels before a Nomogram plotted. By internal validation for the 132 patients, the Nomogram accurately estimated the risk of mortality, with a corrected C-index of 0.810. External validation of the model in another 50 patients from Sichuan Cancer Hospital revealed an accuracy of 77.0%. Overall, this mortality risk prediction model constructed based on complement levels showed accuracy in assessing the prognosis of patients with metastatic NSCLC. Therefore, complement C3b and C4d have potential for use as biomarkers to predict the risk of mortality in such patients.

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.

A systematic review of diagnostic, prognostic, and risk blood and urine biomarkers of transplant-associated thrombotic microangiopathy

Transplant-associated thrombotic microangiopathy (TA-TMA) is an increasingly recognized complication of allogeneic and autologous hematopoietic cellular therapy (HCT), associated with significant morbidity and mortality. Although the central drivers of the disease are thought to be endothelial damage and complement activation, no specific diagnostic biomarkers have been identified. TA-TMA is typically diagnosed using criteria comprised of non-specific clinical and laboratory features. Some patients will have a self-remitting course, but more than half develop multi-organ dysfunction or die, making prognostic biomarkers critical. Prevention of TA-TMA, an approach central to other HCT complications such as graft-versus-host disease, is largely untested in part due to a lack of identified early high-risk biomarkers. We conducted a systematic review to summarize the diagnostic, early risk, and prognostic biomarkers of TA-TMA. We screened the titles and abstracts of 1524 citations. After screening out duplications, we read the abstracts of 979 papers and fully reviewed 132 full-text publications. Thirty-one publications fulfilled the inclusion criteria of more than five patients with TA-TMA and a reported measure of association with diagnosis, prognosis, or risk of later development of the disease. Fourteen studies (45%) were with adults, 12 (39%) were with children <18 years old, three included both children and adults, and two did not report age. There were 53 biomarker or biomarker signature entries, and a total of 27 unique biomarkers. Only four biomarkers reported sensitivity and specificity. The single biomarker with the most robust data was sC5b-9, which conferred diagnostic, prognostic, and risk implications. Studies of combinations of biomarkers were rare. No meta-analyses were performed because of significant heterogeneity between studies. The limitations of studies included small sample size, study designs with a high risk of bias (i.e., case-control), the timing of sample collection, and the selection of controls. Furthermore, only two (6%) studies included a training and validation cohort. Cut-off points are needed to stratify groups, as most biomarkers do not have normal values, or normal values cannot be assumed in the HCT setting. In the future, multi-institutional, collaborative efforts are needed to perform rigorously designed, prospective studies with serially enrolled patients, with samples collected at the time of TA-TMA diagnosis, careful selection of controls, and validation of selected biomarkers and cut-off points in a separate cohort.

Emerging therapeutic and preventive approaches to transplant-associated thrombotic microangiopathy

PURPOSE OF REVIEW

Transplant-associated thrombotic microangiopathy (TA-TMA) is a complication that can occur in both allogeneic and autologous haematopoietic cellular therapy (HCT) recipients and is associated with significant morbidity and mortality. Although TA-TMA is a complex disease, there is emerging evidence that complement activation and endothelial dysfunction play a key role in the pathophysiology of the disease. The use of eculizumab has improved survival in patients with high risk and severe disease, but mortality rates in treated patients still exceed 30%, highlighting the need for novel approaches.

RECENT FINDINGS

There are multiple ongoing and planned clinical trials investigating novel complement agents in TA-TMA and other TMAs. Drugs vary by targets of the complement system, mechanism, and form of administration. Clinical trial designs include single arm studies that span across multiple age groups including children, and double-blind, randomized, placebo-controlled studies. These studies will provide robust data to inform the care of patients with TA-TMA in the future. In addition to multiple promising therapeutic agents, preventing TA-TMA is an emerging strategy. Agents known to protect the endothelium from damage and augment endothelial function by promoting anti-inflammatory and antithrombotic effects may have a role in preventing TA-TMA or ameliorating the severity, though additional studies are needed.

SUMMARY

Novel therapeutic agents for TA-TMA inhibition of the complement system are under investigation and prophylactic strategies of endothelial protection are emerging. Further understanding of the pathophysiology of the disease may identify additional therapeutic targets. Multiinstitutional, collaborative clinical trials are needed to determine the safety and efficacy of these agents going forward.

Structural basis of soluble membrane attack complex packaging for clearance

Unregulated complement activation causes inflammatory and immunological pathologies with consequences for human disease. To prevent bystander damage during an immune response, extracellular chaperones (clusterin and vitronectin) capture and clear soluble precursors to the membrane attack complex (sMAC). However, how these chaperones block further polymerization of MAC and prevent the complex from binding target membranes remains unclear. Here, we address that question by combining cryo electron microscopy (cryoEM) and cross-linking mass spectrometry (XL-MS) to solve the structure of sMAC. Together our data reveal how clusterin recognizes and inhibits polymerizing complement proteins by binding a negatively charged surface of sMAC. Furthermore, we show that the pore-forming C9 protein is trapped in an intermediate conformation whereby only one of its two transmembrane β-hairpins has unfurled. This structure provides molecular details for immune pore formation and helps explain a complement control mechanism that has potential implications for how cell clearance pathways mediate immune homeostasis.

To prevent unregulated complement activation, extracellular chaperones capture soluble precursors to the membrane attack complex (sMAC). Here, structural analysis of sMAC reveals how clusterin recognizes heterogeneous sMAC complexes and inhibits polymerization of complement protein C9.

Expanding Horizons in Complement Analysis and Quality Control

Complement not only plays a key role in host microbial defense but also modulates the adaptive immune response through modification of T- and B-cell reactivity. Moreover, a normally functioning complement system participates in hematopoiesis, reproduction, lipid metabolism, and tissue regeneration. Because of its powerful inflammatory potential, multiple regulatory proteins are needed to prevent potential tissue damage. In clinical practice, dysregulation and overactivation of the complement system are major causes of a variety of inflammatory and autoimmune diseases ranging from nephropathies, age-related macular degeneration (AMD), and systemic lupus erythematosus (SLE) to graft rejection, sepsis, and multi-organ failure. The clinical importance is reflected by the recent development of multiple drugs targeting complement with a broad spectrum of indications. The recognition of the role of complement in diverse diseases and the advent of complement therapeutics has increased the number of laboratories and suppliers entering the field. This has highlighted the need for reliable complement testing. The relatively rapid expansion in complement testing has presented challenges for a previously niche field. This is exemplified by the issue of cross-reactivity of complement-directed antibodies and by the challenges of the poor stability of many of the complement analytes. The complex nature of complement testing and increasing clinical demand has been met in the last decade by efforts to improve the standardization among laboratories. Initiated by the IUIS/ICS Committee for the Standardization and Quality Assessment in Complement Measurements 14 rounds of external quality assessment since 2010 resulted in improvements in the consistency of testing across participating institutions, while extending the global reach of the efforts to more than 200 laboratories in 30 countries. Worldwide trends of assay availability, usage, and analytical performance are summarized based on the past years’ experiences. Progress in complement analysis has been facilitated by the quality assessment and standardization efforts that now allow complement testing to provide a comprehensive insight into deficiencies and the activation state of the system. This in turn enables clinicians to better define disease severity, evolution, and response to therapy.

Transplant-associated thrombotic microangiopathy: elucidating prevention strategies and identifying high-risk patients

INTRODUCTION

Hematopoietic stem cell transplantation-associated thrombotic microangiopathy (TA-TMA) is a severe complication of transplant. TA-TMA is a multifactorial disease where generalized endothelial dysfunction leads to microangiopathic hemolytic anemia, intravascular platelet activation, and formation of microthrombi leading to end-organ injury. It is essential to identify patients at risk for this complication and to implement early interventions to improve TA-TMA associated transplant outcomes.

AREAS COVERED

Recognition of TA-TMA and associated multi-organ injury, risk predictors, contributing factors, differential diagnosis and targeting complement pathway in TA-TMA by summarizing peer reviewed manuscripts.

EXPERT OPINION

TA-TMA is an important transplant complication. Diagnostic and risk criteria are established in children and young adults and risk-based targeted therapies have been proposed using complement blockers. The immediate goal is to extend this work into adult stem cell transplant recipients by implementing universal TA-TMA screening practices. This will facilitate early TA-TMA diagnosis and targeted interventions, which will further improve survival. While complement blocking therapy is effective, about one third of patients are refractory to treatment and those patients commonly die. The next hurdle for the field is identifying reasons for failure, optimizing strategies for complement modifying therapy and searching for additional targetable pathways of endothelial injury.

Presumed complement-mediated, checkpoint inhibitor-induced, thrombotic microangiopathy in a patient with metastatic melanoma

Immune checkpoint inhibitors (ICIs) are associated with a variety of immune-related adverse events (irAEs), but haematological irAEs are rare. We report a case of presumed complement-mediated thrombotic microangiopathy (CM-TMA) in a 78-year-old man with metastatic melanoma following treatment with ICIs. Following two doses of combination nivolumab and ipilimumab therapy, he developed microangiopathic haemolytic anaemia, thrombocytopenia and increased creatinine. ADAMTS13 activity was preserved, CH50 was high, haptoglobin was depleted and a blood film demonstrated fragments. Given this constellation of findings, a diagnosis of CM-TMA was made. Immunotherapy was held and the patient received steroids and supportive care. Six months after his last dose of immunotherapy, he has no evidence of melanoma or CM-TMA. CM-TMA should be suspected in patients on ICI with unexplained anaemia and thrombocytopenia with preserved ADAMTS13 activity. Suspicion of complement dysregulation may have therapeutic implications, such as the necessity of complement pathway inhibition.