Paroxysmal nocturnal hemoglobinuria and other complement-mediated hematological disorders

Oral Iptacopan Monotherapy in Paroxysmal Nocturnal Hemoglobinuria

BACKGROUND

Persistent hemolytic anemia and a lack of oral treatments are challenges for patients with paroxysmal nocturnal hemoglobinuria who have received anti-C5 therapy or have not received complement inhibitors. Iptacopan, a first-in-class oral factor B inhibitor, has been shown to improve hemoglobin levels in these patients.

METHODS

In two phase 3 trials, we assessed iptacopan monotherapy over a 24-week period in patients with hemoglobin levels of less than 10 g per deciliter. In the first, anti-C5-treated patients were randomly assigned to switch to iptacopan or to continue anti-C5 therapy. In the second, single-group trial, patients who had not received complement inhibitors and who had lactate dehydrogenase (LDH) levels more than 1.5 times the upper limit of the normal range received iptacopan. The two primary end points in the first trial were an increase in the hemoglobin level of at least 2 g per deciliter from baseline and a hemoglobin level of at least 12 g per deciliter, each without red-cell transfusion; the primary end point for the second trial was an increase in hemoglobin level of at least 2 g per deciliter from baseline without red-cell transfusion.

RESULTS

In the first trial, 51 of the 60 patients who received iptacopan had an increase in the hemoglobin level of at least 2 g per deciliter from baseline, and 42 had a hemoglobin level of at least 12 g per deciliter, each without transfusion; none of the 35 anti-C5-treated patients attained the end-point levels. In the second trial, 31 of 33 patients had an increase in the hemoglobin level of at least 2 g per deciliter from baseline without red-cell transfusion. In the first trial, 59 of the 62 patients who received iptacopan and 14 of the 35 anti-C5-treated patients did not require or receive transfusion; in the second trial, no patients required or received transfusion. Treatment with iptacopan increased hemoglobin levels, reduced fatigue, reduced reticulocyte and bilirubin levels, and resulted in mean LDH levels that were less than 1.5 times the upper limit of the normal range. Headache was the most frequent adverse event with iptacopan.

CONCLUSIONS

Iptacopan treatment improved hematologic and clinical outcomes in anti-C5-treated patients with persistent anemia - in whom iptacopan showed superiority to anti-C5 therapy - and in patients who had not received complement inhibitors. (Funded by Novartis; APPLY-PNH ClinicalTrials.gov number, NCT04558918; APPOINT-PNH ClinicalTrials.gov number, NCT04820530.).

Paroxysmal nocturnal hemoglobinuria: Where we stand

For the last 20 years, therapy of paroxysmal nocturnal hemoglobinuria (PNH) relied-up until recently-on antibody based terminal complement inhibitionon. PNH pathophysiology-a mutational defect leading to partial or complete absence of complement-regulatory proteins on blood cells-leads to intravascular hemolysis and consequences such as thrombosis and other sequelae. A plethora of new drugs interfering with the proximal and terminal complement cascade are under recent development and the first "proof-of-pinciple" proximal complement inhibitor targeting C3 has been approved in 2021. "PNH: where we stand" will try to give a brief account on where we came from and where we stand focusing on approved therapeutic options. The associated improvements as well as potential consequences of actual and future treatments as well as their impact on the disease will continue to necessitate academic and scientific focus on improving treatment options as well as on side effects and outcomes relevant to individual patient lives and circumstances in order to develop effective, safe, and available treatment for all hemolytic PNH patients globally.

The complement alternative pathway in paroxysmal nocturnal hemoglobinuria: From a pathogenic mechanism to a therapeutic target

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare clonal, not malignant, hematological disease characterized by intravascular hemolysis, thrombophilia and bone marrow failure. While this latter presentation is due to a T-cell mediated auto-immune disorder resembling acquired aplastic anemia, the first two clinical presentations are largely driven by the complement pathway. Indeed, PNH is characterized by a broad impairment of complement regulation on affected cells, which is due to the lack of the complement regulators CD55 and CD59. The deficiency of these two proteins from PNH blood cells is due to the somatic mutation in the phosphatidylinositol N-acetylglucosaminyltransferase subunit A gene causing the disease, which impairs the surface expression of all proteins linked via the glycosylphosphatidylinositol anchor. The lack of the complement regulators CD55 and CD59 on PNH erythrocytes accounts for the hallmark of PNH, which is the chronic, complement-mediated intravascular hemolysis. This hemolysis results from the impaired regulation of the alternative pathway upstream in the complement cascade, as well as of the downstream terminal pathway. PNH represented the first indication for the development of anti-complement agents, and the therapeutic interception of the complement cascade at the level of C5 led to remarkable changes in the natural history of the disease. Nevertheless, the clinical use of an inhibitor of the terminal pathway highlighted the broader derangement of complement regulation in PNH, shedding light on the pivotal role of the complement alternative pathway. Here we review the current understanding of the role of the alternative pathway in PNH, including the emergence of C3-mediated extravascular hemolysis in PNH patients on anti-C5 therapies. These observations provide the rationale for the development of novel complement inhibitors for the treatment of PNH. Recent preclinical and clinical data on proximal complement inhibitors intercepting the alternative pathway with the aim of improving the treatment of PNH are discussed, together with their clinical implications which are animating a lively debate in the scientific community.

Aplastic anemia and paroxysmal nocturnal hemoglobinuria in children and adults in two centers of Northern Greece

Bone marrow failure (BMF) syndromes are a group of various hematological diseases with cytopenia as a main common characteristic. Given their rarity and continuous progress in the field, we aim to provide data considering the efficiency and safety of the therapeutic methods, focusing on the treatment of aplastic anemia(AA) and paroxysmal nocturnal hemoglobinuria (PNH). We enrolled consecutive patients diagnosed with BMF in two referral centers of Northern Greece from 2008 to 2020. We studied 43 patients with AA (37 adults and 6 children/adolescents) and 6 with classical PNH. Regarding classical PNH, 4 patients have received eculizumab treatment with 1/4 presenting extravascular hemolysis. Among 43 patients with aplastic anemia, PNH clones were detected in 11. Regarding patients that did not receive alloHCT (n=15), 14/15 were treated with ATG and cyclosporine as first line, with the addition of eltrombopag in patients treated after its approval (n=9). With a median follow-up of 16.7 (1.8-56.2) months from diagnosis, 12/14 (85.7%) are alive (4-year OS: 85.1%). AlloHCT was performed in 28 patients. Five patients developed TA-TMA which did not resolve in 3/5 (all with a pre-transplant PNH clone). With the follow-up among survivors reaching 86.3 (6.3-262.4) months, 10-year OS was 56.9%, independently associated with PNH clones after adjusting for age (p=0.024). In conclusion, our real-world experience confirms that novel treatments are changing the field of BMF syndromes. Nevertheless, there is still an unmet need to personalize algorithms in this field.

Pancytopenia in a Case of Aplastic Anaemia/Paroxysmal Nocturnal Haemoglobinuria Unmasked by SARS-CoV-2 Infection: A Case Report

During an acute SARS-CoV-2 infection, a diagnosis of Aplastic Anaemia associated with Paroxysmal Nocturnal Haemoglobinuria (AA/PNH) was made in a 78-year-old woman who had presented to the emergency department with severe pancytopenia. It is possible that she had subclinical AA/PNH that was unmasked during the acute COVID-19 infection, but we can also suspect a direct role of the virus in the pathogenesis of the disease, or we can hypothesize that COVID-19 infection changed the phosphatidylinositol glycan class A (PIGA) gene pathway.

Emerging drugs for the treatment of paroxysmal nocturnal hemoglobinuria

INTRODUCTION

Eculizumab, the first anti-C5 monoclonal antibody approved for patients with paroxysmal nocturnal hemoglobinuria (PNH), has revolutionized the natural history of this disease, blocking intravascular hemolysis, reducing the risk of thrombo-embolic events, resulting in a significant improvement in survival and quality of life. However, the hematological response to eculizumab is extremely heterogeneous, with only one-third of PNH patients reaching normal hemoglobin levels.

AREAS COVERED

This article reviews the current new drugs being investigated in phase II and III trials for adult PNH patients. Literature search was performed using Medline and Clinicaltrials.org databases.

EXPERT OPINION

The new molecules have been classified according to the target of the complement system on which they act; we have novel terminal complement inhibitors, which target C5, and proximal complement inhibitors, which interfere with C3 or even further upstream (factor B and D). Ravulizumab is the first next-generation C5 inhibitor, approved by FDA and EMA, which reproduced the excellent results achieved with eculizumab, trying to improve the convenience of patients. However, unresolved issues remain, such as C3-mediated extravascular hemolysis, on which novel proximal complement inhibitors are showing their efficacy. Pegcetacoplan is the first C3-inihibitor approved by FDA. Long-term safety data for novel complement inhibitors are needed.

Discovering C3 targeting therapies for paroxysmal nocturnal hemoglobinuria: Achievements and pitfalls

The treatment of paroxysmal nocturnal hemoglobinuria (PNH) was revolutionized by the introduction of the anti-C5 agent eculizumab, which resulted in sustained control of intravascular hemolysis, leading to transfusion avoidance and hemoglobin stabilization in at least half of all patients. Nevertheless, extravascular hemolysis mediated by C3 has emerged as inescapable phenomenon in PNH patients on anti-C5 treatment, frequently limiting its hematological benefit. More than 10 years ago we postulated that therapeutic interception of the complement cascade at the level of C3 should improve the clinical response in PNH. Compstatin is a 13-residue disulfide-bridged peptide binding to both human C3 and C3b, eventually disabling the formation of C3 convertases and thereby preventing complement activation via all three of its activating pathways. Several generations of compstatin analogs have been tested in vitro, and their clinical evaluation has begun in PNH and other complement-mediated diseases. Pegcetacoplan, a pegylated form of the compstatin analog POT-4, has been investigated in two phase I/II and one phase III study in PNH patients. In the phase III study, PNH patients with residual anemia already on eculizumab were randomized to receive either pegcetacoplan or eculizumab in a head-to-head comparison. At week 16, pegcetacoplan was superior to eculizumab in terms of hemoglobin change from baseline (the primary endpoint), as well as in other secondary endpoints tracking intravascular and extravascular hemolysis. Pegcetacoplan showed a good safety profile, even though breakthrough hemolysis emerged as a possible risk requiring additional attention. Here we review all the available data regarding this innovative treatment that has recently been approved for the treatment of PNH.

Current Opinions on the Clinical Utility of Ravulizumab for the Treatment of Paroxysmal Nocturnal Hemoglobinuria

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare disorder of hematopoietic stem cells genetically defined by the acquisition of somatic mutations in the X-linked phosphatidylinositol glycan anchor biosynthesis, class A (PIGA) gene. PIGA is essential for the synthesis of glycosyl phosphatidylinositol (GPI) anchor proteins and its mutations result in a deficiency of such molecules on the membrane of blood cells derived from the mutant clone. In particular, the lack of the GPI-linked complement regulatory proteins CD55 and CD59 is responsible for the increased sensitivity of PNH erythrocytes to complement-mediated destruction. Indeed, the classical clinical picture of PNH includes signs and symptoms of intravascular hemolysis along with variable degrees of cytopenia and a strong tendency to thrombosis, hallmarks of the disease. Before the introduction of anti-complement inhibitors, PNH was characterized by a high mortality primarily due to thrombotic events. The approval of the terminal anti-complement inhibitor eculizumab in 2007 introduced a paradigm shift in the treatment of the disease with improvement of the chronic hemolytic process and dramatic reduction of the thrombotic rate. However, eculizumab has a relatively short half-life when considering a life-long treatment, with obvious consequences as to the quality of life of treated patients necessitating relatively frequent drug administrations. Moreover, up to 30% of PNH patients undergoing eculizumab therapy show a suboptimal response, continuing to require red cell transfusions because of extravascular hemolysis or breakthrough hemolytic episodes. In 2019, the FDA approved the second-generation C5 inhibitor ravulizumab, a long-lasting agent with a better control of disease manifestations. Herein, we discuss the use of ravulizumab in PNH, its differences with first-generation C5 inhibitors, the research evidence supporting the safety and efficacy of this drug and its impact on costs for health systems and quality of life of PNH patients.

Phase 2 study of danicopan in patients with paroxysmal nocturnal hemoglobinuria with an inadequate response to eculizumab

Paroxysmal nocturnal hemoglobinuria (PNH) is characterized by uncontrolled terminal complement activation and subsequent intravascular hemolysis (IVH). C5 inhibitors prevent membrane attack complex formation, but patients may experience extravascular hemolysis (EVH) and continue to require blood transfusions. Danicopan, an oral proximal complement inhibitor of alternative pathway factor D (FD), is designed to control IVH and EVH. In a phase 2 dose-finding trial, eculizumab-treated transfusion-dependent patients with PNH (n = 12) received danicopan, 100 to 200 mg thrice daily, in addition to their eculizumab regimen for 24 weeks. End points included hemoglobin (Hgb) change vs baseline at week 24 (primary), reduction in blood transfusions, and patient-reported outcomes. Safety, tolerability, and pharmacokinetics/pharmacodynamics were measured. Twelve patients received ≥1 danicopan dose; 1 patients discontinued from a serious adverse event deemed unlikely related to danicopan. Eleven patients completed the 24-week treatment period. Addition of danicopan resulted in a mean Hgb increase of 2.4 g/dL at week 24. In the 24 weeks prior to danicopan, 10 patients received 31 transfusions (50 units) compared with 1 transfusion (2 units) in 1 patient during the 24-week treatment period. Mean Functional Assessment of Chronic Illness Therapy (FACIT)-Fatigue score increased by 11 points from baseline to week 24. The most common adverse events were headache, cough, and nasopharyngitis. Addition of danicopan, a first-in-class FD inhibitor, led to a meaningful improvement in Hgb and reduced transfusion requirements in patients with PNH who were transfusion-dependent on eculizumab. These benefits were associated with improvement of FACIT-Fatigue. This trial was registered at www.clinicaltrials.gov as #NCT03472885.

Advancing therapeutic complement inhibition in hematologic diseases: PNH and beyond

Complement is an elaborate system of the innate immunity. Genetic variants and autoantibodies leading to excessive complement activation are implicated in a variety of human diseases. Among them, the hematologic disease paroxysmal nocturnal hemoglobinuria (PNH) remains the prototype model of complement activation and inhibition. Eculizumab, the first-in-class complement inhibitor, was approved for PNH in 2007. Addressing some of the unmet needs, a long-acting C5 inhibitor, ravulizumab, and a C3 inhibitor, pegcetacoplan have been also now approved with PNH. Novel agents, such as factor B and factor D inhibitors, are under study with very promising results. In this era of several approved targeted complement therapeutics, selection of the proper drug needs to be based on a personalized approach. Beyond PNH, complement inhibition has also shown efficacy and safety in cold agglutinin disease (CAD), primarily with the C1s inhibitor of the classical complement pathway, sutimlimab, but also with pegcetacoplan. Furthermore, C5 inhibition with eculizumab and ravulizumab, as well as inhibition of the lectin pathway with narsoplimab, are investigated in transplant-associated thrombotic microangiopathy (TA-TMA). With this revolution of next-generation complement therapeutics, additional hematologic entities, such as delayed hemolytic transfusion reaction (DHTR) or immune thrombocytopenia (ITP), might also benefit from complement inhibitors. Therefore, this review aims to describe state-of-the-art knowledge of targeting complement in hematologic diseases focusing on: a) complement biology for the clinician, b) complement activation and therapeutic inhibition in prototypical complement-mediated hematologic diseases, c) hematologic entities under investigation for complement inhibition, and d) other complement-related disorders of potential interest to hematologists.

The complement cascade in the regulation of neuroinflammation, nociceptive sensitization, and pain

The complement cascade is a key component of the innate immune system that is rapidly recruited through a cascade of enzymatic reactions to enable the recognition and clearance of pathogens and promote tissue repair. Despite its well-understood role in immunology, recent studies have highlighted new and unexpected roles of the complement cascade in neuroimmune interaction and in the regulation of neuronal processes during development, aging, and in disease states. Complement signaling is particularly important in directing neuronal responses to tissue injury, neurotrauma, and nerve lesions. Under physiological conditions, complement-dependent changes in neuronal excitability, synaptic strength, and neurite remodeling promote nerve regeneration, tissue repair, and healing. However, in a variety of pathologies, dysregulation of the complement cascade leads to chronic inflammation, persistent pain, and neural dysfunction. This review describes recent advances in our understanding of the multifaceted cross-communication that takes place between the complement system and neurons. In particular, we focus on the molecular and cellular mechanisms through which complement signaling regulates neuronal excitability and synaptic plasticity in the nociceptive pathways involved in pain processing in both health and disease. Finally, we discuss the future of this rapidly growing field and what we believe to be the significant knowledge gaps that need to be addressed.

How we('ll) treat paroxysmal nocturnal haemoglobinuria: diving into the future

Paroxysmal nocturnal haemoglobinuria (PNH) is characterized by complement-mediated intravascular haemolysis, severe thrombophilia and bone marrow failure. While for patients with bone marrow failure the treatment follows that of immune-mediated aplastic anaemia, that of classic, haemolytic PNH is based on anti-complement medication. The anti-C5 monoclonal antibody eculizumab has revolutionized treatment, resulting in control of intravascular haemolysis and thromboembolic risk, with improved long-term survival. Novel strategies of complement inhibition are emerging. New anti-C5 agents reproduce the safety and efficacy of eculizumab, with improved patient convenience. Proximal complement inhibitors have been developed to address C3-mediated extra-vascular haemolysis and seem to improve haematological response.

The Complement System in Ovarian Cancer: An Underexplored Old Path

Ovarian cancer is one of the most lethal gynecological cancers. Current therapeutic strategies allow temporary control of the disease, but most patients develop resistance to treatment. Moreover, although successful in a range of solid tumors, immunotherapy has yielded only modest results in ovarian cancer. Emerging evidence underscores the relevance of the components of innate and adaptive immunity in ovarian cancer progression and response to treatment. Particularly, over the last decade, the complement system, a pillar of innate immunity, has emerged as a major regulator of the tumor microenvironment in cancer immunity. Tumor-associated complement activation may support chronic inflammation, promote an immunosuppressive microenvironment, induce angiogenesis, and activate cancer-related signaling pathways. Recent insights suggest an important role of complement effectors, such as C1q or anaphylatoxins C3a and C5a, and their receptors C3aR and C5aR1 in ovarian cancer progression. Nevertheless, the implication of these factors in different clinical contexts is still poorly understood. Detailed knowledge of the interplay between ovarian cancer cells and complement is required to develop new immunotherapy combinations and biomarkers. In this context, we discuss the possibility of targeting complement to overcome some of the hurdles encountered in the treatment of ovarian cancer.

Safety of current treatments for paroxysmal nocturnal hemoglobinuria

Introduction: Eculizumab, which is indicated to treat patients with paroxysmal nocturnal hemoglobinuria (PNH), is proven to decrease intravascular hemolysis and thrombosis and improve survival. Ravulizumab is a long-acting, second-generation complement component 5 (C5) inhibitor designed to alleviate the burden of the eculizumab treatment schedule and reduce the frequency of breakthrough hemolysis. As the clinical benefits of these treatments have been emphasized, their safety also should be considered. Areas covered: This article reviews safety data for the current approved PNH treatments from published articles about eculizumab and ravulizumab in patients with PNH. Special settings (pregnancy, pediatrics, long-term safety of continued eculizumab treatment, and extravascular hemolysis) are also discussed. Expert opinion: In phase 3 trials, eculizumab and ravulizumab were found to be safe and well tolerated. In addition, 10 years of experience with eculizumab provided evidence that mitigates initial concerns about infectious events. However, to minimize meningococcal infections, vaccination and close monitoring remain essential. Because extravascular hemolysis limits eculizumab efficacy in some patients, continued investigation of proximal complement inhibitors is warranted to obviate this mechanism. Long-term safety data for ravulizumab treatment are needed.

Modeling the activation of the alternative complement pathway and its effects on hemolysis in health and disease

The complement system is a powerful mechanism of innate immunity poised to eliminate foreign cells and pathogens. It is an intricate network of >35 proteins, which, once activated, leads to the tagging of the surface to be eliminated, produces potent chemoattractants to recruit immune cells, and inserts cytotoxic pores into nearby lipid surfaces. Although it can be triggered via different pathways, its net output is largely based on the direct or indirect activation of the alternative pathway. Complement dysregulation or deficiencies may cause severe pathologies, such as paroxysmal nocturnal hemoglobinuria (PNH), where a lack of complement control proteins leads to hemolysis and life-threatening anemia. The complexity of the system poses a challenge for the interpretation of experimental data and the design of effective pharmacological therapies. To address this issue, we developed a mathematical model of the alternative complement pathway building on previous modelling efforts. The model links complement activation to the hemolytic activity of the terminal alternative pathway, providing an accurate description of pathway activity as observed in vitro and in vivo, in health and disease. Through adjustment of the parameters describing experimental conditions, the model was capable of reproducing the results of an array of standard assays used in complement research. To demonstrate its clinical applicability, we compared model predictions with clinical observations of the recovery of hematological biomarkers in PNH patients treated with the complement inhibiting anti-C5 antibody eculizumab. In conclusion, the model can enhance the understanding of complement biology and its role in disease pathogenesis, help identifying promising targets for pharmacological intervention, and predict the outcome of complement-targeting pharmacological interventions.

Paroxysmal cold hemoglobinuria successfully treated with complement inhibition

This is the first-ever demonstration of successful treatment of paroxysmal cold hemoglobinuria using the complement inhibitor eculizumab.

Reduced red blood cell surface level of Factor H as a mechanism underlying paroxysmal nocturnal hemoglobinuria

The absence of the cell-surface complement inhibitors CD55 and CD59 is considered the mechanism underlying the complement-mediated destruction of affected red blood cells (RBCs) in paroxysmal nocturnal hemoglobinuria (PNH) patients, but Factor H (FH), a fluid-phase complement inhibitor, has also been proposed to be involved. However, the status of FH on the PNH patient RBC surface is unclear and its precise role in PNH pathogenesis remains to be further defined. In this study, we identified significantly lower levels of surface-bound FH on the affected CD59^- RBCs than on the unaffected CD59⁺ RBCs. Although this reduction in surface-bound FH on PNH RBCs was accompanied by decreased surface sialic acid levels, the enzymatic removal of sialic acids from these RBCs did not significantly affect the levels of surface-bound FH. We further observed higher surface levels of FH on the C3b/iC3b/C3d^high RBCs than on C3b/iC3b/C3d^low RBCs within the affected PNH RBCs of patients treated with eculizumab. Finally, we determined that enhanced surface levels of FH on CD55/CD59-deficient RBCs from mice and PNH patients protected against complement-mediated hemolysis. Taken together, our results suggest that a reduced surface level of FH is another important mechanism underlying the pathogenesis of PNH.

Complement in Hemolysis- and Thrombosis- Related Diseases

The complement system, originally classified as part of innate immunity, is a tightly self-regulated system consisting of liquid phase, cell surface, and intracellular proteins. In the blood circulation, the complement system, platelets, coagulation system, and fibrinolysis system form a close and complex network. They activate and regulate each other and jointly mediate immune monitoring and tissue homeostasis. The dysregulation of each cascade system results in clinical manifestations and the progression of different diseases, such as sepsis, atypical hemolytic uremic syndrome, C3 glomerulonephritis, systemic lupus erythematosus, or ischemia–reperfusion injury. In this review, we summarize the crosstalk between the complement system, platelets, and coagulation, provide integrative insights into how complement dysfunction leads to hemopathic progression, and further discuss the therapeutic relevance of complement in hemolytic and thrombotic diseases.

Deep vein thrombosis: a less noticed complication in hematologic malignancies and immunologic disorders

Deep vein thrombosis (DVT) is a common complication in hematologic malignancies and immunologic disorders that coagulation and inflammatory factors play a crucial role in its occurrence. The content used in this article has been obtained by PubMed database and Google Scholar search engine of English-language articles (1980-2019) using the "Deep vein thrombosis," "Hematologic malignancies," "Immunologic disorders" and "Treatment." Increased levels of coagulation factors, the presence of genetic disorders, or the use of thrombotic drugs that stimulate coagulation processes are risk factors for the development of DVT in patients with hematologic malignancies. Inflammatory and auto-anti-inflammatory factors, along with coagulant factors, play an essential role in the formation of venous thrombosis in patients with immunological disorders by increasing the recruitment of inflammatory cells and adhesion molecules. Therefore, anti-coagulants in hematologic malignancies and immunosuppressants in immune disorders can reduce the risk of developing DVT by reducing thrombotic and inflammatory activity. Considering the increased risk of DVT due to impaired coagulation and inflammation processes, analysis of coagulation and inflammatory factors have prognostic values in patients with immunologic deficiencies and hematologic malignancies. Evaluation of these factors as diagnostic and prognostic biomarkers in the prediction of thrombotic events could be beneficial in implementing effective treatment strategies for DVT.

Anti-complement Treatment for Paroxysmal Nocturnal Hemoglobinuria: Time for Proximal Complement Inhibition? A Position Paper From the SAAWP of the EBMT

The treatment of paroxysmal nocturnal hemoglobinuria has been revolutionized by the introduction of the anti-C5 agent eculizumab; however, eculizumab is not the cure for Paroxysmal nocturnal hemoglobinuria (PNH), and room for improvement remains. Indeed, the hematological benefit during eculizumab treatment for PNH is very heterogeneous among patients, and different response categories can be identified. Complete normalization of hemoglobin (complete and major hematological response), is seen in no more than one third of patients, while the remaining continue to experience some degree of anemia (good and partial hematological responses), in some cases requiring regular red blood cell transfusions (minor hematological response). Different factors contribute to residual anemia during eculizumab treatment: underlying bone marrow dysfunction, residual intravascular hemolysis and the emergence of C3-mediated extravascular hemolysis. These two latter pathogenic mechanisms are the target of novel strategies of anti-complement treatments, which can be split into terminal and proximal complement inhibitors. Many novel terminal complement inhibitors are now in clinical development: they all target C5 (as eculizumab), potentially paralleling the efficacy and safety profile of eculizumab. Possible advantages over eculizumab are long-lasting activity and subcutaneous self-administration. However, novel anti-C5 agents do not improve hematological response to eculizumab, even if some seem associated with a lower risk of breakthrough hemolysis caused by pharmacokinetic reasons (it remains unclear whether more effective inhibition of C5 is possible and clinically beneficial). Indeed, proximal inhibitors are designed to interfere with early phases of complement activation, eventually preventing C3-mediated extravascular hemolysis in addition to intravascular hemolysis. At the moment there are three strategies of proximal complement inhibition: anti-C3 agents, anti-factor D agents and anti-factor B agents. These agents are available either subcutaneously or orally, and have been investigated in monotherapy or in association with eculizumab in PNH patients. Preliminary data clearly demonstrate that proximal complement inhibition is pharmacologically feasible and apparently safe, and may drastically improve the hematological response to complement inhibition in PNH. Indeed, we envision a new scenario of therapeutic complement inhibition, where proximal inhibitors (either anti-C3, anti-FD or anti-FB) may prove effective for the treatment of PNH, either in monotherapy or in combination with anti-C5 agents, eventually leading to drastic improvement of hematological response.

Red Blood Cell Homeostasis and Altered Vesicle Formation in Patients With Paroxysmal Nocturnal Hemoglobinuria

A subset of the red blood cells (RBCs) of patients with paroxysmal nocturnal hemoglobinuria (PNH) lacks GPI-anchored proteins. Some of these proteins, such as CD59, inhibit complement activation and protect against complement-mediated lysis. This pathology thus provides the possibility to explore the involvement of complement in red blood cell homeostasis and the role of GPI-anchored proteins in the generation of microvesicles (MVs) in vivo. Detailed analysis of morphology, volume, and density of red blood cells with various CD59 expression levels from patients with PNH did not provide indications for a major aberration of the red blood cell aging process in patients with PNH. However, our data indicate that the absence of GPI-anchored membrane proteins affects the composition of red blood cell-derived microvesicles, as well as the composition and concentration of platelet-derived vesicles. These data open the way toward a better understanding on the pathophysiological mechanism of PNH and thereby to the development of new treatment strategies.

An LC–MS/MS approach to assess total and free protein target in the serum of cynomolgus monkey

Aim: Develop LC–MS/MS-based assays to measure total and free complement C5 in cynomolgus monkey serum as a target engagement biomarker for pharmacokinetic/pharmacodynamic correlation study. Materials & methods/results: The C5-specific signature peptide derived from pellet digestion of serum proteins with and without prior immunodepletion of the drug-bound C5 by protein A beads was quantified to assess free and total C5 levels, respectively. Conditions for immunodepletion by protein A were optimized to ensure complete depletion of IgGs (and drug-bound C5). The effect of sample dilution on drug-target dissociation and thus free C5 measurement was evaluated by applying a mathematical simulation. Conclusion: The procedure described here allows for the assessment of protein target engagement, aiding in pharmacokinetic/pharmacodynamic correlation analysis and human dose projection.

Bone Marrow as a Source of Cells for Paroxysmal Nocturnal Hemoglobinuria Detection

Objectives

To determine fluorescently labeled aerolysin (FLAER) binding and glycophosphatidylinositol–anchored protein expression in bone marrow (BM) cells of healthy volunteers and patients with paroxysmal nocturnal hemoglobinuria (PNH) detected in peripheral blood (PB); compare PNH clone size in BM and PB; and detect PNH in BM by commonly used antibodies.

Methods

Flow cytometry analysis of FLAER binding to leukocytes and expression of CD55/CD59 in erythrocytes. Analysis of CD16 in neutrophils and CD14 in monocytes in BM.

Results

FLAER binds to all normal BM leukocytes, and binding increases with cell maturation. In PNH, lymphocytic clones are consistently smaller than clones of other BM cells. PNH clones are detectable in mature BM leukocytes with high specificity and sensitivity using common antibodies.

Conclusions

PNH clone sizes measured in mature BM leukocytes and in PB are comparable, making BM suitable for PNH assessment. We further demonstrate that commonly used reagents (not FLAER or CD55/CD59) can reliably identify abnormalities of BM neutrophils and monocytes consistent with PNH cells.

Display of the Albumin-Binding Domain in the Envelope Improves Lentiviral Vector Bioavailability

Vesicular stomatitis virus G glycoprotein (VSVg) is extensively used for retroviral and lentiviral vector (LV) pseudotyping. However, VSVg pseudotyped vectors are serum inactivated, blocking the in vivo gene delivery. Several strategies have been employed to prevent complement inactivation, including chemical and genetic envelope modifications. This study employed the streptococcal albumin-binding domain (ABD) to generate a construct to express ABD as a glycosylphosphatidylinositol-anchored protein. LV particles bearing ABD are able to bind bovine and human serum albumin in vitro. Neither the lentiviral vector production titer nor the in vitro transduction was affected by the ABD display. The study demonstrated that ABD-bearing LVs are protected from human complement inactivation. More importantly, intravenous administration demonstrated that the presence of ABD significantly reduces lentivector sequestration in liver and bone-marrow cells. Therefore, the use of ABD represents an improvement for in vivo gene therapy applications. The results strongly point to ABD display as a universal strategy to increase the in vivo efficacy of different viral vectors.

Expanding Complement Therapeutics for the Treatment of Paroxysmal Nocturnal Hemoglobinuria

Paroxysmal nocturnal hemoglobinuria (PNH) is widely regarded as an archetypal complement-mediated disorder that has propelled complement drug discovery in recent decades. Its pathology is driven by chronic complement dysregulation resulting from the lack of the glycosyl phosphatidyl inositol-linked regulators DAF and CD59 on susceptible erythrocytes. This complement imbalance fuels persistent C3 activation on affected erythrocytes, which culminates in chronic complement-mediated intravascular hemolysis. The clinical application of eculizumab, a humanized anti-C5 antibody that blocks terminal pathway activation, has led to drastic improvement of therapeutic outcomes but has also unveiled hitherto elusive pathogenic mechanisms that are now known to contribute to the clinical burden of a significant proportion of patients with PNH. These emerging clinical needs have sparked a true resurgence of complement therapeutics that offer the promise of even more effective, disease-tailored therapies for PNH. Here, we review the current state of complement therapeutics with a focus on the clinical development of C3-targeted and alternative pathway-directed drug candidates for the treatment of PNH. We also discuss the relative advantages and benefits offered by each complement-targeting approach, including translational considerations that might leverage a more comprehensive clinical intervention for PNH.

Complement system's role in cancer and its therapeutic potential in ovarian cancer

Cancer immunotherapy is a strong candidate for the long-awaited new edition to standard cancer therapies. For an effective immunotherapy, it is imperative to delineate the players of antitumour immune response. As an important innate immune system effector mechanism, complement is highly likely to play a substantial role in cancer immunity. Studies suggest that there may be two different "states of complement" that show opposing effects on cancer cells; a complement profile that has antitumour effects with low expression of membrane-bound complement regulator proteins (mCRPs), lytic membrane attack complex (MAC) concentration and moderate C5a concentration, and a complement profile that has protumour effects with high expression of mCRPs, sublytic MAC and high concentrations of C5a. One of the cancers that urgently require innovative therapeutic approaches is ovarian cancer, and complement has a potential to be a good target for this purpose. A combinatorial approach where the complement cascade is fine-tuned by inhibiting some of its activities while promoting the others can prove to be a fruitful approach. Herein, we will briefly discuss the cancer-immune system interaction and then present a discussion of complement system's role in tumour immunity and its therapeutic potential for ovarian cancer immunotherapy.

Crosstalk between platelets and the complement system in immune protection and disease

Platelets have a central function in repairing vascular damage and stopping acute blood loss. They are equally central to thrombus formation in cardiovascular diseases such as myocardial infarction and ischaemic stroke. Beyond these classical prothrombotic diseases, immune mediated pathologies such as haemolytic uraemic syndrome (HUS) or paroxysmal nocturnal haemoglobinuria (PNH) also feature an increased tendency to form thrombi in various tissues. It has become increasingly clear that the complement system, part of the innate immune system, has an important role in the pathophysiology of these diseases. Not only does complement influence prothrombotic disease, it is equally involved in idiopathic thrombocytopenic purpura (ITP), an autoimmune disease characterised by thrombocytopenia. Thus, there are complex interrelationships between the haemostatic and immune systems, and platelets and complement in particular. Not only does complement influence platelet diseases such as ITP, HUS and PNH, it also mediates interaction between microbes and platelets during systemic infection, influencing the course of infection and development of protective immunity. This review aims to provide an integrative overview of the mechanisms underlying the interactions between complement and platelets in health and disease.

Complement depletion with humanised cobra venom factor: Efficacy in preclinical models of vascular diseases

The complement system is an intrinsic part of the immune system and has important functions in both innate and adaptive immunity. On the other hand, inadvertent or misdirected complement activation is also involved in the pathogenesis of many diseases, contributing solely or significantly to tissue injury and disease development. Multiple approaches to develop pharmacological agents to inhibit complement are currently being pursued. We have developed a conceptually different approach of not inhibiting but depleting complement, based on the complement-depleting activities of cobra venom factor (CVF), a non-toxic cobra venom component with structural and functional homology to complement component C3. We developed a humanised version of CVF by creating human complement component C3 derivatives with complement-depleting activities of CVF (humanised CVF) as a promising therapeutic agent for diseases with complement pathogenesis. Here we review the beneficial therapeutic effect of humanised CVF in several murine models of vascular diseases such as reperfusion injury.

The Evolving Landscape for Complement Therapeutics in Rheumatic and Autoimmune Diseases

The complement system is increasingly understood to play major roles in the pathogenesis of human inflammatory and autoimmune diseases. Because of this situation, there are rapidly expanding commercial efforts to develop novel complement inhibitors and effector pathway-modulating drugs. This review provides insights into the evolving understanding of the complement system components, mechanisms of activation within and across the 3 pathways (classical, alternative, and lectin), how the pathways are normally controlled and then dysregulated in target tissues, and what diseases are known to be, in large part, complement-dependent through the successful development and approval of complement therapeutics in patients. Mechanisms of complement activation in rheumatoid arthritis, lupus, and thrombotic microangiopathies are also illustrated. In addition, the specific therapeutic drugs that are both approved and under development are discussed in the context of both nonrheumatic and rheumatic diseases. Finally, the methods by which the complement system can be assessed in humans through biomarker studies are outlined, with the goal of understanding, in specific patients, how the system is functioning.

Functional and structural characterization of four mouse monoclonal antibodies to complement C3 with potential therapeutic and diagnostic applications

C3 is the central component of the complement system. Upon activation, C3 sequentially generates various proteolytic fragments, C3a, C3b, iC3b, C3dg, each of them exposing novel surfaces, which are sites of interaction with other proteins. C3 and its fragments are therapeutic targets and markers of complement activation. We report the structural and functional characterization of four monoclonal antibodies (mAbs) generated by immunizing C3-deficient mice with a mixture of human C3b, iC3b and C3dg fragments, and discuss their potential applications. This collection includes three mAbs interacting with native C3 and inhibiting AP complement activation; two of them by blocking the cleavage of C3 by the AP C3-converase and one by impeding formation of the AP C3-convertase. The interaction sites of these mAbs in the target molecules were determined by resolving the structures of Fab fragments bound to C3b and/or iC3b using electron microscopy. A fourth mAb specifically recognizes the iC3b, C3dg, and C3d fragments. It binds to an evolutionary-conserved neoepitope generated after C3b cleavage by FI, detecting iC3b/C3dg deposition over opsonized surfaces by flow cytometry and immunohistochemistry in human and other species. Because well-characterized anti-complement mAbs are uncommon, the mAbs reported here may offer interesting therapeutic and diagnostic opportunities.

Vasculitides and the Complement System: a Comprehensive Review

Systemic vasculitides are a group of rare diseases characterized by inflammation of the arterial or venous vessel wall, causing stenosis or thrombosis. Clinical symptoms may be limited to skin or to other organs or may include multiple manifestations as systemic conditions. The pathogenesis is related to the presence of leukocytes in the vessels and to the IC deposition, which implies the activation of the complement system (CS) and then the swelling and damage of vessel mural structures. The complement system (CS) is involved in the pathogenesis of several autoimmune diseases, including systemic vasculitides. This enzymatic system is a part of the innate immune system, and its function is linked to the modulation of the adaptive immunity and in bridging innate and adaptive responses. Its activation is also critical for the development of natural antibodies and T cell response and for the regulation of autoreactive B cells. Complement triggering contributes to inflammation-driven tissue injury, which occurs during the ischemia/reperfusion processes, vasculitides, nephritis, arthritis, and many others diseases. In systemic vasculitides, a group of uncommon diseases characterized by blood vessel inflammation, the contribution of CS in the development of inflammatory damage has been demonstrated. Treatment is mainly based on clinical manifestations and severity of organ involvement. Evidences on the efficacy of traditional immunosuppressive therapies have been collected as well as data from clinical trials that involve the modulation of the CS. In particular in small-medium-vessel vasculitides, the CS represents an attractive target. Herein, we reviewed the pathogenetic role of CS in these systemic vasculitides as urticarial vasculitis, ANCA-associated vasculitides, anti-glomerular basement membrane disease, cryoglobulinaemic vasculitides, Henoch-Schönlein purpura/IgA nephropathy, and Kawasaki disease and therefore its potential therapeutic use in this context.

From orphan drugs to adopted therapies: Advancing C3-targeted intervention to the clinical stage

Complement dysregulation is increasingly recognized as an important pathogenic driver in a number of clinical disorders. Complement-triggered pathways intertwine with key inflammatory and tissue destructive processes that can either increase the risk of disease or exacerbate pathology in acute or chronic conditions. The launch of the first complement-targeted drugs in the clinic has undeniably stirred the field of complement therapeutic design, providing new insights into complement's contribution to disease pathogenesis and also helping to leverage a more personalized, comprehensive approach to patient management. In this regard, a rapidly expanding toolbox of complement therapeutics is being developed to address unmet clinical needs in several immune-mediated and inflammatory diseases. Elegant approaches employing both surface-directed and fluid-phase inhibitors have exploited diverse components of the complement cascade as putative points of therapeutic intervention. Targeting C3, the central hub of the system, has proven to be a promising strategy for developing biologics as well as small-molecule inhibitors with clinical potential. Complement modulation at the level of C3 has recently shown promise in preclinical primate models, opening up new avenues for therapeutic intervention in both acute and chronic indications fueled by uncontrolled C3 turnover. This review highlights recent developments in the field of complement therapeutics, focusing on C3-directed inhibitors and alternative pathway (AP) regulator-based approaches. Translational perspectives and considerations are discussed, particularly with regard to the structure-guided drug optimization and clinical advancement of a new generation of C3-targeted peptidic inhibitors.

Complement in disease: a defence system turning offensive

Although the complement system is primarily perceived as a host defence system, a more versatile, yet potentially more harmful side of this innate immune pathway as an inflammatory mediator also exists. The activities that define the ability of the complement system to control microbial threats and eliminate cellular debris - such as sensing molecular danger patterns, generating immediate effectors, and extensively coordinating with other defence pathways - can quickly turn complement from a defence system to an aggressor that drives immune and inflammatory diseases. These host-offensive actions become more pronounced with age and are exacerbated by a variety of genetic factors and autoimmune responses. Complement can also be activated inappropriately, for example in response to biomaterials or transplants. A wealth of research over the past two decades has led to an increasingly finely tuned understanding of complement activation, identified tipping points between physiological and pathological behaviour, and revealed avenues for therapeutic intervention. This Review summarizes our current view of the key activating, regulatory, and effector mechanisms of the complement system, highlighting important crosstalk connections, and, with an emphasis on kidney disease and transplantation, discusses the involvement of complement in clinical conditions and promising therapeutic approaches.

Complement-Mediated Death of Ciliate Tetrahymena pyriformis Caused by Human Blood Serum

Toxicity of human blood serum for ciliate Tetrahymena pyriformis is determined by the complement system. When ciliate are dying after being exposed to blood serum, cell membrane permeability for low-molecular-weight compounds significantly increases, probably due to pore formation. Serine protease inhibitors or exposure to physical factors inducing complement inactivation (e.g., heating up to 56°C) completely prevented ciliate death under the effect of human serum. Activation of serum complement upon interaction with Tetrahymena cells occurred by the classical or lectin pathway, while the contribution of the alternative activation pathway was negligible.

Complement Activation in Placental Malaria

Sixty percent of all pregnancies worldwide occur in malaria endemic regions. Pregnant women are at greater risk of malaria infection than their non-pregnant counterparts and have a higher risk of adverse birth outcomes including low birth weight resulting from intrauterine growth restriction and/or preterm birth. The complement system plays an essential role in placental and fetal development as well as the host innate immune response to malaria infection. Excessive or dysregulated complement activation has been associated with the pathobiology of severe malaria and with poor pregnancy outcomes, dependent and independent of infection. Here we review the role of complement in malaria and pregnancy and discuss its part in mediating altered placental angiogenesis, malaria-induced adverse birth outcomes, and disruptions to the in utero environment with possible consequences on fetal neurodevelopment. A detailed understanding of the mechanisms underlying adverse birth outcomes, and the impact of maternal malaria infection on fetal neurodevelopment, may lead to biomarkers to identify at-risk pregnancies and novel therapeutic interventions to prevent these complications.

Complement, a target for therapy in inflammatory and degenerative diseases

Complement is a key component of immunity with crucial inflammatory and opsonic properties; inappropriate activation of complement triggers or exacerbates inflammatory disease.

Complement dysregulation is a core feature of some diseases and contributes to pathology in many others.

Approved agents have been developed for and are highly effective in some orphan applications, but their progress to use in more common diseases has been slow.

Numerous challenges, such as target concentration or high turnover, limit the efficacy of these agents in humans.

Numerous novel agents targeting different parts of the complement system in different ways are now emerging from pre-clinical studies and are entering Phase I/II trials; these agents bring the potential for more-effective and more-specific anti-complement therapies in disease.

Other agents, both biologic and small molecule, are in Phase II or III trials for both rare and common diseases — administration routes include localized (for example, intravitreal) and systemic routes.

There is an urgent need to develop biomarkers and imaging methods that enable monitoring of the effects and efficacy of anti-complement agents.

The complement cascade, a key regulator of innate immunity, is a rich source of potential therapeutic targets for diseases including autoimmune, inflammatory and degenerative disorders. Morgan and Harris discuss the progress made in modulating the complement system and the existing challenges, including dosing, localization of the drug to the target and how to interfere with protein–protein interactions.

The complement system is a key innate immune defence against infection and an important driver of inflammation; however, these very properties can also cause harm. Inappropriate or uncontrolled activation of complement can cause local and/or systemic inflammation, tissue damage and disease. Complement provides numerous options for drug development as it is a proteolytic cascade that involves nine specific proteases, unique multimolecular activation and lytic complexes, an arsenal of natural inhibitors, and numerous receptors that bind to activation fragments. Drug design is facilitated by the increasingly detailed structural understanding of the molecules involved in the complement system. Only two anti-complement drugs are currently on the market, but many more are being developed for diseases that include infectious, inflammatory, degenerative, traumatic and neoplastic disorders. In this Review, we describe the history, current landscape and future directions for anti-complement therapies.

Complement therapeutics in inflammatory diseases: promising drug candidates for C3-targeted intervention

There is increasing appreciation that complement dysregulation lies at the heart of numerous immune-mediated and inflammatory disorders. Complement inhibitors are therefore being evaluated as new therapeutic options in various clinical translation programs and the first clinically approved complement-targeted drugs have profoundly impacted the management of certain complement-mediated diseases. Among the many members of the intricate protein network of complement, the central component C3 represents a 'hot-spot' for complement-targeted therapeutic intervention. C3 modulates both innate and adaptive immune responses and is linked to diverse immunomodulatory systems and biological processes that affect human pathophysiology. Compelling evidence from preclinical disease models has shown that C3 interception may offer multiple benefits over existing therapies or even reveal novel therapeutic avenues in disorders that are not commonly regarded as complement-driven, such as periodontal disease. Using the clinically developed compstatin family of C3 inhibitors and periodontitis as illustrative examples, this review highlights emerging therapeutic concepts and developments in the design of C3-targeted drug candidates as novel immunotherapeutics for oral and systemic inflammatory diseases.

Role of complement and complement regulatory proteins in the complications of diabetes

It is well established that the organ damage that complicates human diabetes is caused by prolonged hyperglycemia, but the cellular and molecular mechanisms by which high levels of glucose cause tissue damage in humans are still not fully understood. The prevalent hypothesis explaining the mechanisms that may underlie the pathogenesis of diabetes complications includes overproduction of reactive oxygen species, increased flux through the polyol pathway, overactivity of the hexosamine pathway causing intracellular formation of advanced glycation end products, and activation of protein kinase C isoforms. In addition, experimental and clinical evidence reported in past decades supports a strong link between the complement system, complement regulatory proteins, and the pathogenesis of diabetes complications. In this article, we summarize the body of evidence that supports a role for the complement system and complement regulatory proteins in the pathogenesis of diabetic vascular complications, with specific emphasis on the role of the membrane attack complex (MAC) and of CD59, an extracellular cell membrane-anchored inhibitor of MAC formation that is inactivated by nonenzymatic glycation. We discuss a pathogenic model of human diabetic complications in which a combination of CD59 inactivation by glycation and hyperglycemia-induced complement activation increases MAC deposition, activates pathways of intracellular signaling, and induces the release of proinflammatory, prothrombotic cytokines and growth factors. Combined, complement-dependent and complement-independent mechanisms induced by high glucose promote inflammation, proliferation, and thrombosis as characteristically seen in the target organs of diabetes complications.

Compstatin: a C3-targeted complement inhibitor reaching its prime for bedside intervention

There is a growing awareness that complement plays an integral role in human physiology and disease, transcending its traditional perception as an accessory system for pathogen clearance and opsonic cell killing. As the list of pathologies linked to dysregulated complement activation grows longer, it has become clear that targeted modulation of this innate immune system opens new windows of therapeutic opportunity for anti-inflammatory drug design. Indeed, the introduction of the first complement-targeting drugs has reignited a vibrant interest in the clinical translation of complement-based inhibitors. Compstatin was discovered as a cyclic peptide that inhibits complement activation by binding C3 and interfering with convertase formation and C3 cleavage. As the convergence point of all activation pathways and a molecular hub for crosstalk with multiple pathogenic pathways, C3 represents an attractive target for therapeutic modulation of the complement cascade. A multidisciplinary drug optimization effort encompassing rational 'wet' and in silico synthetic approaches and an array of biophysical, structural and analytical tools has culminated in an impressive structure-function refinement of compstatin, yielding a series of analogues that show promise for a wide spectrum of clinical applications. These new derivatives have improved inhibitory potency and pharmacokinetic profiles and show efficacy in clinically relevant primate models of disease. This review provides an up-to-date survey of the drug design effort placed on the compstatin family of C3 inhibitors, highlighting the most promising drug candidates. It also discusses translational challenges in complement drug discovery and peptide drug development and reviews concerns related to systemic C3 interception.

Eculizumab for treating patients with paroxysmal nocturnal hemoglobinuria

BACKGROUND

Paroxysmal nocturnal hemoglobinuria (PNH) is a chronic, not malignant, disease of the hematopoietic stem cells, associated with significant morbidity and mortality. It is a rare disease with an estimated incidence of 1.3 new cases per one million individuals per year. The treatment of PNH has been largely empirical and symptomatic, with blood transfusions, anticoagulation, and supplementation with folic acid or iron. Eculizumab, a biological agent that inhibits complement cascade, was developed for preventing hemolytic anemia and severe thrombotic episodes.

OBJECTIVES

To assess the clinical benefits and harms of eculizumab for treating patients with paroxysmal nocturnal hemoglobinuria (PNH).

SEARCH METHODS

We conducted a comprehensive search strategy. We searched the Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library 2014, Issue 5), Ovid MEDLINE (from 1946 to 15 May 2014), EMBASE (from 1980 to 25 June 2014), and LILACS (from 1982 to 25 June 2014). We did not apply any language restrictions.

SELECTION CRITERIA

We included randomized controlled trials (RCTs) irrespective of their publication status or language. No limits were applied with respect to period of follow-up. We excluded quasi-RCTs. We included trials comparing eculizumab with placebo or best available therapy. We included any patient with a confirmed diagnosis of PNH. Primary outcome was overall survival.

DATA COLLECTION AND ANALYSIS

We independently performed a duplicate selection of eligible trials, risk of bias assessment, and data extraction. We estimated risk ratios (RRs) and 95% confidence interval (CIs) for dichotomous outcomes, and mean differences (MDs) and 95% CIs for continuous outcomes. We used a random-effects model for analysis.

MAIN RESULTS

We identified one multicenter (34 sites) phase III RCT involving 87 participants. The trial compared eculizumab versus placebo, and was conducted in the US, Canada, Europe, and Australia with 26 weeks of follow-up. This small trial had high risk of bias in many domains (attrition and selective reporting). It was sponsored by a pharmaceutical company. No patients died during the study. By using the European Organization for Research and Treatment of Cancer Quality of Life Questionnaire (scores can range from 0 to 100, with higher scores on the global health status and functioning scales indicating improvement), the trial showed improvement in health-related quality of life in patients treated with eculizumab (mean difference (MD) 19.4, 95% CI 8.25 to 30.55; P = 0.0007; low quality of evidence). By using the Functional Assessment of Chronic Illness Therapy Fatigue instrument (scores can range from 0 to 52, with higher scores indicating improvement in fatigue), the trial showed a reduction in fatigue (MD 10.4, 95% CI 9.97 to 10.83; P = 0.00001; moderate quality of evidence) in the eculizumab group compared with placebo. Eculizumab compared with placebo showed a greater proportion of patients with transfusion independence: 51% (22/43) versus 0% (0/44); risk ratio (RR) 46.02, 95% CI 2.88 to 735.53; P = 0.007; moderate quality of evidence; and withdrawal for any reason: 4.7% (2/43) versus 22.72% (10/44); RR 0.20, 95% CI 0.05 to 0.88; P = 0.03; moderate quality of evidence. Due to the low rate of events observed, the included trial did not show any difference between eculizumab and placebo in terms of serious adverse events: 9.3% (4/43) versus 20.4% (9/44); RR 0.15, 95% CI 0.15 to 1.37; P = 0.16; low quality of evidence. We did not observe any difference between intervention and placebo for the most frequent adverse events. One participant receiving placebo showed an episode of thrombosis. The trial did not assess overall survival, transformation to myelodysplastic syndrome and acute myelogenous leukemia, or development or recurrence of aplastic anemia on treatment.

AUTHORS' CONCLUSIONS

This review has detected an absence of evidence for eculizumab compared with placebo for treating paroxysmal nocturnal hemoglobinuria (PNH), in terms of overall survival, nonfatal thrombotic events, transformation to myelodysplastic syndrome and acute myelogenous leukemia, and development and recurrence of aplastic anemia on treatment. Current evidence indicates that compared with placebo, eculizumab increases health-related quality of life and increases transfusion independence. During the execution of the included trial, no patients died. Furthermore, the intervention seems to reduce fatigue and withdrawals for any reason. The safety profile of eculizumab is unclear. These conclusions are based on one small trial with risk of attrition and selective reporting bias.Therefore, prescription of eculizumab for treating patients with PNH can neither be supported nor rejected, unless new evidence from a large high quality trial alters this conclusion. Therefore, we urge the reader to interpret the trial results with much caution. Future trials on this issue should be conducted according to the SPIRIT statement and reported according to the CONSORT statement by independent investigators, and using the Foundation of Patient-Centered Outcomes Research recommendations.

A novel antibody against human factor B that blocks formation of the C3bB proconvertase and inhibits complement activation in disease models

The alternative pathway (AP) is critical for the efficient activation of complement regardless of the trigger. It is also a major player in pathogenesis, as illustrated by the long list of diseases in which AP activation contributes to pathology. Its relevance to human disease is further emphasized by the high prevalence of pathogenic inherited defects and acquired autoantibodies disrupting components and regulators of the AP C3-convertase. Because pharmacological downmodulation of the AP emerges as a broad-spectrum treatment alternative, there is a powerful interest in developing new molecules to block formation and/or activity of the AP C3-convertase. In this paper, we describe the generation of a novel mAb targeting human factor B (FB). mAb FB48.4.2, recognizing with high affinity an evolutionary-conserved epitope in the Ba fragment of FB, very efficiently inhibited formation of the AP C3-proconvertase by blocking the interaction between FB and C3b. In vitro assays using rabbit and sheep erythrocytes demonstrated that FB28.4.2 was a potent AP inhibitor that blocked complement-mediated hemolysis in several species. Using ex vivo models of disease we demonstrated that FB28.4.2 protected paroxysmal nocturnal hemoglobinuria erythrocytes from complement-mediated hemolysis and inhibited both C3 fragment and C5b-9 deposition on ADP-activated HMEC-1 cells, an experimental model for atypical hemolytic uremic syndrome. Moreover, i.v. injection of FB28.4.2 in rats blocked complement activation in rat serum and prevented the passive induction of experimental autoimmune Myasthenia gravis. As a whole, these data demonstrate the potential value of FB28.4.2 for the treatment of disorders associated with AP complement dysregulation in man and animal models.

Complement in paroxysmal nocturnal hemoglobinuria: exploiting our current knowledge to improve the treatment landscape

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare hematological disorder associated with an acquired deficiency in glycophosphatidylinositol-anchor biosynthesis that renders erythrocytes susceptible to complement attack. Intravascular hemolysis via the membrane attack complex is a clinical hallmark of the disease, and C5 blockade is currently the only approved treatment for PNH. However, residual anemia is an emerging observation for many PNH patients receiving anti-C5 treatment. A range of complement-targeted therapeutic approaches, encompassing surface-directed inhibition of C3 convertases, blockade of membrane attack complex assembly or C3 interception using peptidic inhibitors, has yielded promising results and offers leverage for even more effective treatment of PNH. This article discusses recent advances in this rapidly evolving field, integrating critical perspectives from preclinical PNH models and diverse complement modulation strategies with genetic insights and therapy response profiles. It also evaluates the relative efficacy, limitations and benefits afforded by C3 or C5 inhibition in the context of PNH therapeutics.

Biomechanical properties of red blood cells in health and disease towards microfluidics

Red blood cells (RBCs) possess a unique capacity for undergoing cellular deformation to navigate across various human microcirculation vessels, enabling them to pass through capillaries that are smaller than their diameter and to carry out their role as gas carriers between blood and tissues. Since there is growing evidence that red blood cell deformability is impaired in some pathological conditions, measurement of RBC deformability has been the focus of numerous studies over the past decades. Nevertheless, reports on healthy and pathological RBCs are currently limited and, in many cases, are not expressed in terms of well-defined cell membrane parameters such as elasticity and viscosity. Hence, it is often difficult to integrate these results into the basic understanding of RBC behaviour, as well as into clinical applications. The aim of this review is to summarize currently available reports on RBC deformability and to highlight its association with various human diseases such as hereditary disorders (e.g., spherocytosis, elliptocytosis, ovalocytosis, and stomatocytosis), metabolic disorders (e.g., diabetes, hypercholesterolemia, obesity), adenosine triphosphate-induced membrane changes, oxidative stress, and paroxysmal nocturnal hemoglobinuria. Microfluidic techniques have been identified as the key to develop state-of-the-art dynamic experimental models for elucidating the significance of RBC membrane alterations in pathological conditions and the role that such alterations play in the microvasculature flow dynamics.