Alternative Complement Pathway Inhibition Does Not Abrogate Meningococcal Killing by Serum of Vaccinated Individuals

Complement inhibitors in pediatric kidney diseases: new therapeutic opportunities

Historically, the complement system (classical, lectin, alternative, and terminal pathways) is known to play a crucial role in the etiopathogenesis of many kidney diseases. Direct or indirect activation in these settings is revealed by consumption of complement proteins at the serum level and kidney tissue deposition seen by immunofluorescence and electron microscopy. The advent of eculizumab has shown that complement inhibitors may improve the natural history of certain kidney diseases. Since then, the number of available therapeutic molecules and experimental studies on complement inhibition has increased exponentially. In our narrative review, we give a summary of the main complement inhibitors that have completed phase II and phase III studies or are currently used in adult and pediatric nephrology. The relevant full-text works, abstracts, and ongoing trials (clinicaltrials.gov site) are discussed. Data and key clinical features are reported for eculizumab, ravulizumab, crovalimab, avacopan, danicopan, iptacopan, pegcetacoplan, and narsoplimab. Many of these molecules have been shown to be effective in reducing proteinuria and stabilizing kidney function in different complement-mediated kidney diseases. Thanks to their efficacy and target specificity, these novel drugs may radically improve the outcome of complement-mediated kidney diseases, contributing to an improvement in our understanding of their underlying pathophysiology.

Triple-fusion protein (TriFu): A potent, targeted, enzyme-like inhibitor of all three complement activation pathways

The introduction of a therapeutic anti-C5 antibody into clinical practice in 2007 inspired a surge into the development of complement-targeted therapies. This has led to the recent approval of a C3 inhibitory peptide, an antibody directed against C1s and a full pipeline of several complement inhibitors in preclinical and clinical development. However, no inhibitor is available that efficiently inhibits all three complement initiation pathways and targets host cell surface markers as well as complement opsonins. To overcome this, we engineered a novel fusion protein combining selected domains of the three natural complement regulatory proteins decay accelerating factor, factor H and complement receptor 1. Such a triple fusion complement inhibitor (TriFu) was recombinantly expressed and purified alongside multiple variants and its building blocks. We analyzed these proteins for ligand binding affinity and decay acceleration activity by surface plasmon resonance. Additionally, we tested complement inhibition in several in vitro/ex vivo assays using standard classical and alternative pathway restricted hemolysis assays next to hemolysis assays with paroxysmal nocturnal hemoglobinuria erythrocytes. A novel in vitro model of the alternative pathway disease C3 glomerulopathy was established to evaluate the potential of the inhibitors to stop C3 deposition on endothelial cells. Next to the novel engineered triple fusion variants which inactivate complement convertases in an enzyme-like fashion, stoichiometric complement inhibitors targeting C3, C5, factor B, and factor D were tested as comparators. The triple fusion approach yielded a potent complement inhibitor that efficiently inhibits all three complement initiation pathways while targeting to surface markers.

Results of a randomized double-blind placebo-controlled Phase 2 study propose iptacopan as an alternative complement pathway inhibitor for IgA nephropathy

Targeting the alternative complement pathway is an attractive therapeutic strategy given its role in the pathogenesis of immunoglobulin A nephropathy (IgAN). Iptacopan (LNP023) is an oral, proximal alternative complement inhibitor that specifically binds to Factor B. Our randomized, double-blind, parallel-group adaptive Phase 2 study (NCT03373461) enrolled patients with biopsy-confirmed IgAN (within previous three years) with estimated glomerular filtration rates of 30 mL/min/1.73 m2 and over and urine protein 0.75 g/24 hours and over on stable doses of renin angiotensin system inhibitors. Patients were randomized to four iptacopan doses (10, 50, 100, or 200 mg bid) or placebo for either a three-month (Part 1; 46 patients) or a six-month (Part 2; 66 patients) treatment period. The primary analysis evaluated the dose-response relationship of iptacopan versus placebo on 24-hour urine protein-to-creatinine ratio (UPCR) at three months. Other efficacy, safety and biomarker parameters were assessed. Baseline characteristics were generally well-balanced across treatment arms. There was a statistically significant dose-response effect, with 23% reduction in UPCR achieved with iptacopan 200 mg bid (80% confidence interval 8-34%) at three months. UPCR decreased further through six months in iptacopan 100 and 200 mg arms (from a mean of 1.3 g/g at baseline to 0.8 g/g at six months in the 200 mg arm). A sustained reduction in complement biomarker levels including plasma Bb, serum Wieslab, and urinary C5b-9 was observed. Iptacopan was well-tolerated, with no reports of deaths, treatment-related serious adverse events or bacterial infections, and led to strong inhibition of alternative complement pathway activity and persistent proteinuria reduction in patients with IgAN. Thus, our findings support further evaluation of iptacopan in the ongoing Phase 3 trial (APPLAUSE-IgAN; NCT04578834).

Activation of the complement system by nanoparticles and strategies for complement inhibition

The complement system is a multicomponent and multifunctional arm of the innate immune system. Complement contributes to non-specific host defence and maintains homeostasis through multifaceted processes and pathways, including crosstalk with the adaptive immune system, the contact (coagulation) and the kinin systems, and alarmin high-mobility group box 1. Complement is also present intracellularly, orchestrating a wide range of housekeeping and physiological processes in both immune and nonimmune cells, thus showing its more sophisticated roles beyond innate immunity, but its roles are still controversial. Particulate drug carriers and nanopharmaceuticals typically present architectures and surface patterns that trigger complement system in different ways, resulting in both beneficial and adverse responses depending on the extent of complement activation and regulation as well as pathophysiological circumstances. Here we consider the role of complement system and complement regulations in host defence and evaluate the mechanisms by which nanoparticles trigger and modulate complement responses. Effective strategies for the prevention of nanoparticle-mediated complement activation are introduced and discussed.

Cold exposure induces vaso-occlusion and pain in sickle mice that depend on complement activation

Vaso-occlusive pain episodes (VOE) cause severe pain in patients with sickle cell disease (SCD). Vaso-occlusive events promote ischemia/reperfusion pathobiology that activates complement. We hypothesized that complement activation is linked to VOE. We used cold to induce VOE in the Townes sickle homozygous for hemoglobin S (HbSS) mouse model and complement inhibitors to determine whether anaphylatoxin C5a mediates VOE. We used a dorsal skinfold chamber to measure microvascular stasis (vaso-occlusion) and von Frey filaments applied to the plantar surface of the hind paw to assess mechanical hyperalgesia in HbSS and control Townes mice homozygous for hemoglobin A (HbAA) mice after cold exposure at 10°C/50°F for 1 hour. Cold exposure induced more vaso-occlusion in nonhyperalgesic HbSS mice (33%) than in HbAA mice (11%) or HbSS mice left at room temperature (1%). Cold exposure also produced mechanical hyperalgesia as measured by paw withdrawal threshold in HbSS mice compared with that in HbAA mice or HbSS mice left at room temperature. Vaso-occlusion and hyperalgesia were associated with an increase in complement activation fragments Bb and C5a in plasma of HbSS mice after cold exposure. This was accompanied by an increase in proinflammatory NF-κB activation and VCAM-1 and ICAM-1 expression in the liver. Pretreatment of nonhyperalgesic HbSS mice before cold exposure with anti-C5 or anti-C5aR monoclonal antibodies (mAbs) decreased vaso-occlusion, mechanical hyperalgesia, complement activation, and liver inflammatory markers compared with pretreatment with control mAb. Anti-C5 or -C5aR mAb infusion also abrogated mechanical hyperalgesia in HbSS mice with ongoing hyperalgesia at baseline. These findings suggest that C5a promotes vaso-occlusion, pain, and inflammation during VOE and may play a role in chronic pain.

Development and characterization of narsoplimab, a selective MASP-2 inhibitor, for the treatment of lectin-pathway-mediated disorders

Introduction

Overactivation of the lectin pathway of complement plays a pathogenic role in a broad range of immune-mediated and inflammatory disorders; mannan-binding lectin-associated serine protease-2 (MASP-2) is the key effector enzyme of the lectin pathway. We developed a fully human monoclonal antibody, narsoplimab, to bind to MASP-2 and specifically inhibit lectin pathway activation. Herein, we describe the preclinical characterization of narsoplimab that supports its evaluation in clinical trials.

Methods and results

ELISA binding studies demonstrated that narsoplimab interacted with both zymogen and enzymatically active forms of human MASP-2 with high affinity (KD 0.062 and 0.089 nM, respectively) and a selectivity ratio of >5,000-fold relative to closely related serine proteases C1r, C1s, MASP-1, and MASP-3. Interaction studies using surface plasmon resonance and ELISA demonstrated approximately 100-fold greater binding affinity for intact narsoplimab compared to a monovalent antigen binding fragment, suggesting an important contribution of functional bivalency to high-affinity binding. In functional assays conducted in dilute serum under pathway-specific assay conditions, narsoplimab selectively inhibited lectin pathway-dependent activation of C5b-9 with high potency (IC50 ~ 1 nM) but had no observable effect on classical pathway or alternative pathway activity at concentrations up to 500 nM. In functional assays conducted in 90% serum, narsoplimab inhibited lectin pathway activation in human serum with high potency (IC50 ~ 3.4 nM) whereas its potency in cynomolgus monkey serum was approximately 10-fold lower (IC50 ~ 33 nM). Following single dose intravenous administration to cynomolgus monkeys, narsoplimab exposure increased in an approximately dose-proportional manner. Clear dose-dependent pharmacodynamic responses were observed at doses >1.5 mg/kg, as evidenced by a reduction in lectin pathway activity assessed ex vivo that increased in magnitude and duration with increasing dose. Analysis of pharmacokinetic and pharmacodynamic data revealed a well-defined concentration-effect relationship with an ex vivo EC50 value of approximately 6.1 μg/mL, which was comparable to the in vitro functional potency (IC50 33 nM; ~ 5 μg/mL).

Discussion

Based on these results, narsoplimab has been evaluated in clinical trials for the treatment of conditions associated with inappropriate lectin pathway activation, such as hematopoietic stem cell transplantation-associated thrombotic microangiopathy.

Current Understanding of Complement Proteins as Therapeutic Targets for the Treatment of Immunoglobulin A Nephropathy

Immunoglobulin A nephropathy (IgAN) is the most common primary glomerulonephritis worldwide and a frequent cause of kidney failure. Currently, the diagnosis necessitates a kidney biopsy, with routine immunofluorescence microscopy revealing IgA as the dominant or co-dominant immunoglobulin in the glomerular immuno-deposits, often with IgG and sometimes IgM or both. Complement protein C3 is observed in most cases. IgAN leads to kidney failure in 20-40% of patients within 20 years of diagnosis and reduces average life expectancy by about 10 years. There is increasing clinical, biochemical, and genetic evidence that the complement system plays a paramount role in the pathogenesis of IgAN. The presence of C3 in the kidney immuno-deposits differentiates the diagnosis of IgAN from subclinical glomerular mesangial IgA deposition. Markers of complement activation via the lectin and alternative pathways in kidney-biopsy specimens are associated with disease activity and are predictive of poor outcome. Levels of select complement proteins in the circulation have also been assessed in patients with IgAN and found to be of prognostic value. Ongoing genetic studies have identified at least 30 loci associated with IgAN. Genes within some of these loci encode complement-system regulating proteins that can interact with immune complexes. The growing appreciation for the central role of complement components in IgAN pathogenesis highlighted these pathways as potential treatment targets and sparked great interest in pharmacological agents targeting the complement cascade for the treatment of IgAN, as evidenced by the plethora of ongoing clinical trials.

Design and Rationale of the APPELHUS Phase 3 Open-Label Study of Factor B Inhibitor Iptacopan for Atypical Hemolytic Uremic Syndrome

Introduction

Atypical hemolytic uremic syndrome (aHUS) is a rare, progressive, and life-threatening form of thrombotic microangiopathy (TMA) which is caused by dysregulation of the alternative complement pathway (AP). Complement inhibition is an effective therapeutic strategy in aHUS, though current therapies require intravenous administration and increase the risk of infection by encapsulated organisms, including meningococcal infection. Further studies are required to define the optimal duration of existing therapies, and to identify new agents that are convenient for long-term administration. Iptacopan (LNP023) is an oral, first-in-class, highly potent, proximal AP inhibitor that specifically binds factor B (FB). In phase 2 studies of IgA nephropathy, paroxysmal nocturnal hemoglobinuria, and C3 glomerulopathy, iptacopan inhibited the AP, showed clinically relevant benefits, and was well tolerated. Iptacopan thus has the potential to become an effective and safe treatment for aHUS, with the convenience of oral administration.

Methods

Alternative Pathway Phase III to Evaluate LNP023 in aHUS (APPELHUS; NCT04889430) is a multicenter, single-arm, open-label, phase 3 study to evaluate the efficacy and safety of iptacopan in patients (N = 50) with primary complement-mediated aHUS naïve to complement inhibitor therapy (including anti-C5). Eligible patients must have evidence of TMA (platelet count <150 × 10⁹/l, lactate dehydrogenase ≥1.5 × upper limit of normal, hemoglobin ≤ lower limit of normal, serum creatinine ≥ upper limit of normal) and will receive iptacopan 200 mg twice daily. The primary objective is to assess the proportion of patients achieving complete TMA response without the use of plasma exchange or infusion or anti-C5 antibody during 26 weeks of iptacopan treatment.

Conclusion

APPELHUS will determine if iptacopan is safe and efficacious in patients with aHUS.

In vaccinated individuals serum bactericidal activity against B meningococci is abrogated by C5 inhibition but not by inhibition of the alternative complement pathway

Introduction

Several diseases caused by the dysregulation of complement activation can be treated with inhibitors of the complement components C5 and/or C3. However, complement is required for serum bactericidal activity (SBA) against encapsulated Gram-negative bacteria. Therefore, C3 and C5 inhibition increases the risk of invasive disease, in particular by Neisseria meningitidis. As inhibitors against complement components other than C3 and C5 may carry a reduced risk of infection, we compared the effect of inhibitors targeting the terminal pathway (C5), the central complement component C3, the alternative pathway (FB and FD), and the lectin pathway (MASP-2) on SBA against serogroup B meningococci.

Methods

Serum from adults was collected before and after vaccination with the meningococcal serogroup B vaccine 4CMenB and tested for meningococcal killing. Since the B capsular polysaccharide is structurally similar to certain human polysaccharides, 4CMenB was designed to elicit antibodies against meningococcal outer membrane proteins.

Results

While only a few pre-vaccination sera showed SBA against the tested B meningococcal isolates, 4CMenB vaccination induced potent complement-activating IgG titers against isolates expressing a matching allele of the bacterial cell surface-exposed factor H-binding protein (fHbp). SBA triggered by these cell surface protein-specific antibodies was blocked by C5 and reduced by C3 inhibition, whereas alternative (factor B and D) and lectin (MASP-2) pathway inhibitors had no effect on the SBA of post-4CMenB vaccination sera.

Discussion

Compared to the SBA triggered by A,C,W,Y capsule polysaccharide conjugate vaccination, SBA against B meningococci expressing a matching fHbp allele was remarkably resilient against the alternative pathway inhibition.

Targeting the Alternative Complement Pathway With Iptacopan to Treat IgA Nephropathy: Design and Rationale of the APPLAUSE-IgAN Study

Introduction

Targeting the alternative complement pathway (AP) is an attractive therapeutic strategy because of its role in immunoglobulin A nephropathy (IgAN) pathophysiology. Iptacopan (LNP023), a proximal complement inhibitor that specifically binds to factor B and inhibits the AP, reduced proteinuria and attenuated AP activation in a Phase 2 study of patients with IgAN, thereby supporting the rationale for its evaluation in a Phase 3 study.

Methods

APPLAUSE-IgAN (NCT04578834) is a multicenter, randomized, double-blind, placebo-controlled, parallel-group, Phase 3 study enrolling approximately 450 adult patients (aged ≥18 years) with biopsy-confirmed primary IgAN at high risk of progression to kidney failure despite optimal supportive treatment. Eligible patients receiving stable and maximally tolerated doses of angiotensin-converting enzyme inhibitors (ACEis) or angiotensin receptor blockers (ARBs) will be randomized 1:1 to either iptacopan 200 mg or placebo twice daily for a 24-month treatment period. A prespecified interim analysis (IA) will be performed when approximately 250 patients from the main study population complete the 9-month visit. The primary objective is to demonstrate superiority of iptacopan over placebo in reducing 24-hour urine protein-to-creatinine ratio (UPCR) at the IA and demonstrate the superiority of iptacopan over placebo in slowing the rate of estimated glomerular filtration rate (eGFR) decline (total eGFR slope) estimated over 24 months at study completion. The effect of iptacopan on patient-reported outcomes, safety, and tolerability will be evaluated as secondary outcomes.

Conclusions

APPLAUSE-IgAN will evaluate the benefits and safety of iptacopan, a novel targeted therapy for IgAN, in reducing complement-mediated kidney damage and thus slowing or preventing disease progression.

The case for complement component 5 as a target in neurodegenerative disease

INTRODUCTION

Complement-based drug discovery is undergoing a renaissance, empowered by new advances in structural biology, complement biology and drug development. Certain components of the complement pathway, particularly C1q and C3, have been extensively studied in the context of neurodegenerative disease, and established as key therapeutic targets. C5 also has huge therapeutic potential in this arena, with its druggability clearly demonstrated by the success of C5-inhibitor eculizumab.

AREAS COVERED

We will discuss the evidence supporting C5 as a target in neurodegenerative disease, along with the current progress in developing different classes of C5 inhibitors and the gaps in knowledge that will help progress in the field.

EXPERT OPINION

Validation of C5 as a therapeutic target for neurodegenerative disease would represent a major step forward for complement therapeutics research and has the potential to furnish disease-modifying drugs for millions of patients suffering worldwide. Key hurdles that need to be overcome for this to be achieved are understanding how C5a and C5b should be targeted to bring therapeutic benefit and demonstrating the ability to target C5 without creating vulnerability to infection in patients. This requires greater biological elucidation of its precise role in disease pathogenesis, supported by better chemical/biological tools.

The contribution of the alternative pathway in complement activation on cell surfaces depends on the strength of classical pathway initiation

Objectives

The complement system is an important component of innate immunity. The alternative pathway (AP) amplification loop is considered an essential feed forward mechanism for complement activation. However, the role of the AP in classical pathway (CP) activation has only been studied in ELISA settings. Here, we investigated its contribution on physiologically relevant surfaces of human cells and bacterial pathogens and in antibody-mediated complement activation, including in autoimmune haemolytic anaemia (AIHA) setting with autoantibodies against red blood cells (RBCs).

Methods

We evaluated the contribution of the AP to complement responses initiated through the CP on human RBCs by serum of AIHA patients and recombinant antibodies. Moreover, we studied complement activation on Neisseria meningitidis and Escherichia coli. The effect of the AP was examined using either AP-depleted sera or antibodies against factor B and factor D.

Results

We show that the amplification loop is redundant when efficient CP activation takes place. This is independent of the presence of membrane-bound complement regulators. The role of the AP may become significant when insufficient CP complement activation occurs, but this depends on antibody levels and (sub)class. Our data indicate that therapeutic intervention in the amplification loop will most likely not be effective to treat antibody-mediated diseases.

Conclusion

The AP can be bypassed through efficient CP activation. The AP amplification loop has a role in complement activation during conditions of modest activation via the CP, when it can allow for efficient complement-mediated killing.

Low-molecular weight inhibitors of the alternative complement pathway

Dysregulation of the alternative complement pathway predisposes individuals to a number of diseases. It can either be evoked by genetic alterations in or by stabilizing antibodies to important pathway components and typically leads to severe diseases such as paroxysmal nocturnal hemoglobinuria, atypical hemolytic uremic syndrome, C3 glomerulopathy, and age-related macular degeneration. In addition, the alternative pathway may also be involved in many other diseases where its amplifying function for all complement pathways might play a role. To identify specific alternative pathway inhibitors that qualify as therapeutics for these diseases, drug discovery efforts have focused on the two central proteases of the pathway, factor B and factor D. Although drug discovery has been challenging for a number of reasons, potent and selective low-molecular weight (LMW) oral inhibitors have now been discovered for both proteases and several molecules are in clinical development for multiple complement-mediated diseases. While the clinical development of these inhibitors initially focuses on diseases with systemic and/or peripheral tissue complement activation, the availability of LMW inhibitors may also open up the prospect of inhibiting complement in the central nervous system where its activation may also play an important role in several neurodegenerative diseases.

Inhibition of the different complement pathways has varying impacts on the serum bactericidal activity and opsonophagocytosis against Haemophilus influenzae type b

Defense against Haemophilus influenzae type b (Hib) is dependent on antibodies and complement, which mediate both serum bactericidal activity (SBA) and opsonophagocytosis. Here we evaluated the influence of capsule-specific antibodies and complement inhibitors targeting the central component C3, the alternative pathway (AP; fB, fD), the lectin pathway (LP; MASP-2) and the terminal pathway (C5) on both effector functions. Findings may be relevant for the treatment of certain diseases caused by dysregulation of the complement system, where inhibitors of complement factors C3 or C5 are used. Inhibitors against other complement components are being evaluated as potential alternative treatment options that may carry a reduced risk of infection by encapsulated bacteria. Serum and reconstituted blood of healthy adults were tested for bactericidal activity before and after vaccination with the Hib capsule-conjugate vaccine ActHIB. Most sera had bactericidal activity prior to vaccination, but vaccination significantly enhanced SBA titers. Independently of the vaccination status, both C3 and C5 inhibition abrogated SBA, whereas inhibition of the LP had no effect. AP inhibition had a major inhibitory effect on SBA of pre- vaccination serum, but vaccination mitigated this inhibition for all disease isolates tested. Despite this, SBA-mediated killing of some Hib isolates remained retarded. Even for the most serum-resistant isolate, SBA was the dominating defense mechanism in reconstituted whole blood, as addition of blood cells to the serum did not enhance bacterial killing. Limited Fc receptor-mediated opsonophagocytosis was unmasked when bacterial killing by the membrane attack complex was blocked. In the presence of C3 or C5 inhibitors, addition of post-vaccination, but not of pre-vaccination serum to the blood cells triggered opsonophagocytosis, leading to suppression of bacterial multiplication. Taken together, our data indicate that for host defense against Hib, killing by SBA is more efficient than by blood cell opsonophagocytosis. However, additional defense mechanisms, such as bacterial clearance by spleen and liver, may play an important role in preventing Hib-mediated sepsis, in particular for Hib isolates with increased serum-resistance. Results indicate potentially improved safety profile of AP inhibitors over C3 and C5 inhibitors as alternative therapeutic agents in patients with increased susceptibility to Hib infection.

Alternative Complement Pathway Inhibition With Iptacopan for the Treatment of C3 Glomerulopathy-Study Design of the APPEAR-C3G Trial

Introduction

Complement 3 glomerulopathy (C3G) is a rare kidney disease characterized by dysregulation of the alternative pathway (AP) of the complement system. About 50% of patients with C3G progress to kidney failure within 10 years of diagnosis. Currently, there are no approved therapeutic agents for C3G. Iptacopan is an oral, first-in-class, potent, and selective inhibitor of factor B, a key component of the AP. In a Phase II study, treatment with iptacopan was associated with a reduction in proteinuria and C3 deposit scores in C3G patients with native and transplanted kidneys, respectively.

Methods

APPEAR-C3G (NCT04817618) is a randomized, double-blind, and placebo-controlled Phase III study to evaluate the efficacy and safety of iptacopan in C3G patients, enrolling 68 adults with biopsy-confirmed C3G, reduced C3 (<77 mg/dl), proteinuria ≥1.0 g/g, and estimated glomerular filtration rate (eGFR) ≥30 ml/min per 1.73 m². All patients will receive maximally tolerated angiotensin-converting enzyme inhibitor/angiotensin receptor blocker and vaccination against encapsulated bacteria. Patients with any organ transplantation, progressive crescentic glomerulonephritis (GN), monoclonal gammopathy of undetermined significance, or kidney biopsy with >50% interstitial fibrosis/tubular atrophy, will be excluded. Patients will be randomized 1:1 to receive either iptacopan 200 mg twice daily or placebo for 6 months, followed by open-label treatment with iptacopan 200 mg twice daily for all patients for 6 months. The primary objective is to evaluate the efficacy of iptacopan versus placebo on proteinuria reduction urine protein:creatinine ratio (UPCR) (24 h urine). Key secondary endpoints will assess kidney function measured by eGFR, histological disease total activity score, and fatigue.

Conclusion

This study aims to demonstrate the clinical benefits of AP inhibition with iptacopan in C3G.

Iptacopan monotherapy in patients with paroxysmal nocturnal hemoglobinuria: a 2-cohort open-label proof-of-concept study

Iptacopan (LNP023) is a novel, oral selective inhibitor of complement factor B under clinical development for paroxysmal nocturnal hemoglobinuria (PNH). In this ongoing open-label phase 2 study, PNH patients with active hemolysis were randomized to receive single-agent iptacopan twice-daily, at a dose of either 25 mg for 4 weeks followed by 100 mg for up to 2 years (cohort 1) or 50 mg for 4 weeks followed by 200 mg for up to 2 years (cohort 2). At the time of interim analysis, of 13 PNH patients enrolled, all 12 evaluable for efficacy achieved the primary endpoint of reduction in serum lactate dehydrogenase (LDH) levels by at least 60% by week 12 as compared to baseline; mean LDH levels dropped rapidly and durably, namely by 77% and 85% at week 2 and by 86% and 86% at week 12 in cohorts 1 and 2, respectively. Most patients achieved a clinically meaningful improvement in hemoglobin levels and all but one patient remained transfusion-free up to week 12. Other markers of hemolysis, including bilirubin, reticulocytes and haptoglobin, showed consistent improvements. No thromboembolic events were reported, and iptacopan was well tolerated, with no severe or serious adverse events reported up until the data cutoff. In addition to the previously reported beneficial effect of iptacopan add-on therapy to eculizumab, this study showed that iptacopan monotherapy in treatment-naïve PNH patients resulted in normalization of hemolytic markers and rapid transfusion-free improvement of hemoglobin levels in most patients. Registered at www.clinicaltrials.gov as NCT03896152.