Complement Activation and Inhibition in Autoimmune Hemolytic Anemia: Focus on Cold Agglutinin Disease

Safety, tolerability, and activity of the active C1s antibody riliprubart in cold agglutinin disease: a phase 1b study

ABSTRACT

Cold agglutinin disease is a rare autoimmune hemolytic anemia characterized by complement pathway-mediated hemolysis. Riliprubart (SAR445088, BIVV020), a second-generation classical complement inhibitor, is a humanized monoclonal antibody that selectively inhibits only the activated form of C1s. This Phase 1b study evaluated the safety, tolerability, and effect on hemolysis of riliprubart in adult patients with cold agglutinin disease. On day 1, 12 patients received a single IV dose of either 30 mg/kg (n = 6) or 15 mg/kg (n = 6) of riliprubart and were subsequently followed for 15 weeks. Riliprubart was generally well tolerated; there were no treatment-emergent serious adverse events, or treatment-emergent adverse events leading to death or permanent study discontinuation. There were no reports of serious infections, encapsulated bacterial infections including meningococcal infections, hypersensitivity, or thromboembolic events. Rapid improvements in hemoglobin (day 5) and bilirubin (day 1) were observed in both treatment cohorts. Mean hemoglobin levels were maintained at >11.0 g/dL from day 29 and mean levels of bilirubin were normalized by day 29; both responses were maintained throughout the study. Improvements in clinical markers closely correlated with a sustained reduction in the 50% hemolytic complement (CH50) throughout the study. Mean C4 levels, an in vivo marker of treatment activity, increased 1 week after treatment with either dose of riliprubart and were sustained throughout the study. In conclusion, a single IV dose of riliprubart was well tolerated, and led to rapid classical complement inhibition, control of hemolysis, and improvement in anemia, all of which were sustained over 15 weeks. This trial was registered at www.ClinicalTrials.gov as #NCT04269551.

Severe Acute Kidney Injury in Children as a Rare Complication of Paroxysmal Cold Hemoglobinuria

Paroxysmal cold hemoglobinuria (PCH) is a rare condition in childhood characterized by complement-mediated premature destruction of red blood cells. PCH is associated with intravascular hemolysis causing hemoglobinuria, which may result in acute kidney injury of various severity. We aimed to retrospectively analyze clinical and laboratory features of children with PCH-associated acute kidney injury received at tertiary Pediatric Hematology and Nephrology Center, University Motol Hospital, Prague, Czech Republic during the period 2016 to 2022. We present here 3 children with PCH-associated acute kidney failure requiring renal replacement therapy. We highlight the association of PCH with kidney disease. Renal parameters and urine examination should be regularly tested in all children with PCH.

Long-term sutimlimab improves quality of life for patients with cold agglutinin disease: CARDINAL 2-year follow-up

Cold agglutinin disease (CAD) is a rare form of autoimmune hemolytic anemia with a substantial burden on patient's quality of life. CARDINAL was a 2-part, open-label, single-arm, multicenter phase 3 study evaluating the C1s inhibitor, sutimlimab, for treatment of CAD. Part A consisted of the pivotal study phase, with the part B extension phase assessing long-term safety and durability of response including patient-reported outcomes, which is the focus of this report. Altogether, 22 patients continued from part A to part B, majority female (68.2%) with a median age of 71.5 years (range, 55-85). Throughout treatment, score improvement on the Functional Assessment of Chronic Illness Therapy (FACIT)-Fatigue scale exceeded a predefined, group-level clinically important change of ≥5 points vs baseline, with a mean (standard error [SE]) change of 11.7 (3.7) points at week 135. The 12-Item Short Form Health Survey physical and mental component scores remained above baseline, with week 123 mean change (SE) exceeding clinically important changes of 3.9 for physical and 2.8 for mental component scores at 4.7 (2.8) and 3.8 (5.7) points, respectively. EuroQol Visual Analogue Scale, scoring patients' self-rated health, also remained above baseline with a change of 17.1 (5.6) points at week 135. Patient Global Impression of (fatigue) Severity improved vs baseline, corroborating FACIT-Fatigue scores. Patient Global Impression of Change indicated a reduction in perceived disease burden. Data from CARDINAL part B support sustained alleviation of CAD disease burden after long-term treatment with sutimlimab over 2 years, returning toward baseline upon treatment cessation. This trial was registered at www.clinicaltrials.gov as #NCT03347396.

Sutimlimab: A Complement C1s Inhibitor for the Management of Cold Agglutinin Disease-Associated Hemolysis

OBJECTIVE

To review the pharmacology, pharmacokinetics, efficacy, safety, dosing and administration, and place in therapy of sutimlimab for the management of cold agglutinin disease (CAD)-associated hemolysis.

DATA SOURCES

A literature search of PubMed (1966-October 2022) was conducted using the keywords sutimlimab, BIVV009, and cold agglutinin. Data were also obtained from prescribing information, meeting abstracts, and clinicaltrials.gov.

STUDY SELECTION AND DATA EXTRACTION

All published prospective clinical trials, prescribing information, and meeting abstracts on sutimlimab for the treatment of CAD were reviewed.

DATA SYNTHESIS

Sutimlimab is a first-in-class complement C1s inhibitor indicated for the treatment of CAD-associated hemolysis. This approval was based on the phase III CARDINAL trial, which evaluated sutimlimab in patients with CAD-associated hemolysis. The primary endpoint of achieving a hemoglobin of ≥12 g/dL or increase of ≥2 above baseline was achieved by 54% of patients with sutimlimab in the 26-week trial. The phase III CADENZA trial was a placebo-controlled trial in which sutimlimab has demonstrated a significant improvement in the composite endpoint of hemoglobin increase of ≥1.5 g/dL, avoidance of transfusion, and avoidance of additional CAD therapies (73% sutimlimab vs 15% placebo).

RELEVANCE TO PATIENT CARE AND CLINICAL PRACTICE IN COMPARISON WITH EXISTING DRUGS

Sutimlimab rapidly halts hemolysis, improves hemoglobin, and improves quality-of-life in patients with CAD. Safety issues with sutimlimab include infusion-related reactions and risk of serious infections with encapsulated bacteria.

CONCLUSIONS

Sutimlimab provides an additional therapeutic option in the treatment of CAD-associated hemolysis that can lead to rapid improvement in hemoglobin and anemia-related symptoms.

Monoclonal antibodies for treatment of cold agglutinin disease

INTRODUCTION

Cold agglutinin disease (CAD) is a difficult-to-treat autoimmune hemolytic anemia and B cell lymphoproliferative disorder associated with fatigue, acrocyanosis and a risk of thromboembolic events. Cold-induced binding of autoantibodies agglutinates red blood cells and triggers the classical complement pathway, leading to predominantly extravascular hemolysis.

AREAS COVERED

This review summarizes clinical and experimental antibody-based treatments for CAD and analyzes the risks and benefits of B cell and complement directed therapies, and discusses potential future treatments for CAD.

EXPERT OPINION

Conventional treatment of CAD includes a B cell targeted treatment approach with rituximab, yielding only limited treatment success. Addition of a cytotoxic agent (e.g. bendamustine) increases efficacy but this is accompanied by an increased risk of neutropenia and infection. Novel complement-directed therapies have emerged and were shown to have a good efficacy against hemolysis and safety profile but are expensive and unable to address circulatory symptoms. Complement inhibition with sutimlimab may be used as a bridging strategy until B cell directed therapy with rituximab takes effect or continued indefinitely if needed. Future antibody-based treatment approaches for CAD involve the further development of complement-directed antibodies, combination of rituximab and bortezomib, and daratumumab. Non-antibody based prospective treatments may include the use of Bruton tyrosine kinase inhibitors.

Sutimlimab for the Treatment of Cold Agglutinin Disease

Cold agglutinin disease (CAD) is a rare autoimmune hemolytic anemia and a bone marrow clonal lymphoproliferative disorder. Hemolysis in CAD is complement-dependent and mediated by the classical activation pathway. Patients also frequently suffer from fatigue and cold-induced circulatory symptoms. Although not all patients need treatment, the symptom burden has previously been underestimated. Effective therapies target the clonal lymphoproliferation or the complement activation. Sutimlimab, a humanized monoclonal IgG4 antibody that binds and inactivates complement protein C1s, is the most extensively investigated complement inhibitor for the treatment of CAD. This review addresses the preclinical studies of sutimlimab and the studies of pharmacokinetics and pharmacodynamics. We then describe and discuss the prospective clinical trials that established sutimlimab as a rapidly acting, highly efficacious, and low-toxic therapeutic agent. This complement inhibitor does not improve the cold-induced circulatory symptoms, which are not complement-mediated. Sutimlimab is approved for the treatment of CAD in the US, Japan, and the European Union. A tentative therapeutic algorithm is presented. The choice of therapy for CAD should be based on an individual assessment, and patients requiring therapy should be considered for inclusion in clinical trials.

Sutimlimab provides clinically meaningful improvements in patient-reported outcomes in patients with cold agglutinin disease: Results from the randomised, placebo-controlled, Phase 3 CADENZA study

Cold agglutinin disease (CAD) is a rare chronic autoimmune haemolytic anaemia, driven mainly by classical complement pathway activation, leading to profound fatigue and poor quality of life. In the Phase 3 CADENZA trial, sutimlimab-a C1s complement inhibitor-rapidly halted haemolysis, increased haemoglobin levels and improved fatigue versus placebo in patients with CAD without a recent history of transfusion. Patient-reported outcomes (PROs) included Functional Assessment of Chronic Illness Therapy-Fatigue (FACIT-Fatigue), 12-Item Short Form Health Survey (SF-12), EuroQol visual analogue scale (EQ-VAS), Patient Global Impression of Change (PGIC) and Patient Global Impression of (fatigue) Severity (PGIS). Sutimlimab resulted in significant rapid and meaningful improvements versus placebo in PROs. From Week 1, the FACIT-Fatigue mean score increased >5 points above baseline (considered a clinically important change [CIC]). Least-squares (LS) mean change in FACIT-Fatigue score from baseline to treatment assessment timepoint was 10.8 vs. 1.9 points (sutimlimab vs. placebo; p < 0.001). Improvements in physical (PCS) and mental (MCS) component scores of the SF-12 were also considered CICs (LS mean changes from baseline to Week 26: PCS 5.54 vs. 1.57 [p = 0.064]; MCS 5.65 vs. -0.48 [p = 0.065]). These findings demonstrate that in addition to improving haematologic parameters, sutimlimab treatment demonstrates significant patient-reported benefits. Study registered at www.clinicaltrials.gov: NCT03347422.

The choice of new treatments in autoimmune hemolytic anemia: how to pick from the basket?

Autoimmune hemolytic anemia (AIHA) is defined by increased erythrocyte turnover mediated by autoimmune mechanisms. While corticosteroids remain first-line therapy in most cases of warm-antibody AIHA, cold agglutinin disease is treated by targeting the underlying clonal B-cell proliferation or the classical complement activation pathway. Several new established or investigational drugs and treatment regimens have appeared during the last 1-2 decades, resulting in an improvement of therapy options but also raising challenges on how to select the best treatment in individual patients. In severe warm-antibody AIHA, there is evidence for the upfront addition of rituximab to prednisolone in the first line. Novel agents targeting B-cells, extravascular hemolysis, or removing IgG will offer further options in the acute and relapsed/refractory settings. In cold agglutinin disease, the development of complement inhibitors and B-cell targeting agents makes it possible to individualize therapy, based on the disease profile and patient characteristics. For most AIHAs, the optimal treatment remains to be found, and there is still a need for more evidence-based therapies. Therefore, prospective clinical trials should be encouraged.

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.

Cold AIHA and the best treatment strategies

Cold-reactive autoimmune hemolytic anemia (AIHA) is rare among the hemolytic anemias. It results when 1 of a variety of processes causes the generation of immunoglobulin M (IgM) autoantibodies against endogenous erythrocytes, resulting in complement activation and predominantly intravascular hemolysis. Cold AIHA is typically a primary lymphoproliferative disorder with marrow B-cell clones producing pathogenic IgM. More rarely, secondary cold AIHA (cAIHA) can develop from malignancy, infection, or other autoimmune disorders. However, in children cAIHA is typically post infection, mild, and self-limited. Symptoms include a sequelae of anemia, fatigue, and acrocyanosis. The severity of disease is variable and highly dependent on the thermal binding range of the autoantibody. In adults, treatment has most commonly focused on reducing antibody production with rituximab-based regimens. The addition of cytotoxic agents to rituximab improves response rates, but at the expense of tolerability. Recent insights into the cause of cold agglutinin disease as a clonal disorder driven by complement form the basis of newer therapeutic options. While rituximab-based regimens are still the mainstay of therapy, options have now expanded to include complement-directed treatments and other B-cell-directed or plasma-cell-directed therapies.

Pitfalls in complement analysis: A systematic literature review of assessing complement activation

Background

The complement system is an essential component of our innate defense and plays a vital role in the pathogenesis of many diseases. Assessment of complement activation is critical in monitoring both disease progression and response to therapy. Complement analysis requires accurate and standardized sampling and assay procedures, which has proven to be challenging.

Objective

We performed a systematic analysis of the current methods used to assess complement components and reviewed whether the identified studies performed their complement measurements according to the recommended practice regarding pre-analytical sample handling and assay technique. Results are supplemented with own data regarding the assessment of key complement biomarkers to illustrate the importance of accurate sampling and measuring of complement components.

Methods

A literature search using the Pubmed/MEDLINE database was performed focusing on studies measuring the key complement components C3, C5 and/or their split products and/or the soluble variant of the terminal C5b-9 complement complex (sTCC) in human blood samples that were published between February 2017 and February 2022. The identified studies were reviewed whether they had used the correct sample type and techniques for their analyses.

Results

A total of 92 out of 376 studies were selected for full-text analysis. Forty-five studies (49%) were identified as using the correct sample type and techniques for their complement analyses, while 25 studies (27%) did not use the correct sample type or technique. For 22 studies (24%), it was not specified which sample type was used.

Conclusion

A substantial part of the reviewed studies did not use the appropriate sample type for assessing complement activation or did not mention which sample type was used. This deviation from the standardized procedure can lead to misinterpretation of complement biomarker levels and hampers proper comparison of complement measurements between studies. Therefore, this study underlines the necessity of general guidelines for accurate and standardized complement analysis

Complement C1s as a diagnostic marker and therapeutic target: Progress and propective

The molecules of the complement system connect the effectors of innate and adaptive immunity and play critical roles in maintaining homeostasis. Among them, the C1 complex, composed of C1q, C1r, and C1s (C1qr₂s₂), is the initiator of the classical complement activation pathway. While deficiency of C1s is associated with early-onset systemic lupus erythematosus and increased susceptibility to bacteria infections, the gain-of- function variants of C1r and C1s may lead to periodontal Ehlers Danlos syndrome. As C1s is activated under various pathological conditions and associated with inflammation, autoimmunity, and cancer development, it is becoming an informative biomarker for the diagnosis and treatment of a variety of diseases. Thus, more sensitive and convenient methods for assessing the level as well as activity of C1s in clinic samples are highly desirable. Meanwhile, a number of small molecules, peptides, and monoclonal antibodies targeting C1s have been developed. Some of them are being evaluated in clinical trials and one of the antibodies has been approved by US FDA for the treatment of cold agglutinin disease, an autoimmune hemolytic anemia. In this review, we will summarize the biological properties of C1s, its association with development and diagnosis of diseases, and recent progress in developing drugs targeting C1s. These progress illustrate that the C1s molecule is an effective biomarker and promising drug target.

Sutimlimab improves quality of life in patients with cold agglutinin disease: results of patient-reported outcomes from the CARDINAL study

Patients with cold agglutinin disease (CAD) experience fatigue and poor quality of life. However, previous CAD-related studies have not explored patient-reported outcomes such as the Functional Assessment of Chronic Illness Therapy (FACIT)-Fatigue. Sutimlimab, a C1s complement inhibitor, has been shown to halt haemolysis in CAD. Here, we present 26-weeks' patient-reported data from CARDINAL Part A (ClinicalTrials.gov, NCT03347396), which assessed efficacy and safety of sutimlimab in patients with CAD and recent history of transfusion. Aside from measuring changes in haemolytic markers, FACIT-Fatigue was measured at the treatment assessment timepoint (TAT; average of weeks 23, 25, and 26). Exploratory endpoints included the change in EuroQol 5-dimension 5-level questionnaire (EQ-5D-5L) and the 12-Item Short Form Health Survey (SF-12) at TAT, and Patient Global Impression of Change (PGIC), and Patient Global Impression of (fatigue) Severity (PGIS) at week 26. Mean (range) FACIT-Fatigue scores increased from 32.5 (14.0-47.0) at baseline (a score indicative of severe fatigue) to 44.3 (28.0-51.0) at TAT. Considerable improvements were reported for EQ-5D-5L at TAT, SF-12 scores at TAT, and PGIC and PGIS scores at week 26. Sutimlimab treatment resulted in sustained improvements in symptoms of fatigue and overall quality of life in patients with CAD. NCT03347396. Registered 20 November, 2017.

Overview on the role of complement-specific autoantibodies in diseases

The complement system is recognized as a major pathogenic or contributing factor in an ever-growing number of diseases. In addition to inherited factors, autoantibodies to complement proteins have been detected in various systemic and organ-specific disorders. These include antibodies directed against complement components, regulators and receptors, but also protein complexes such as autoantibodies against complement convertases. In some cases, the autoantibodies are relatively well characterized and a pathogenic role is incurred and their detection has diagnostic value. In other cases, the relevance of the autoantibodies is rather unclear. This review summarizes what we know of complement specific autoantibodies in diseases and identifies unresolved questions regarding their functional effect and relevance.

Sutimlimab in patients with cold agglutinin disease: results of the randomized placebo-controlled phase 3 CADENZA trial

Sutimlimab, a first-in-class humanized immunoglobulin G4 (IgG4) monoclonal antibody that selectively inhibits the classical complement pathway at C1s, rapidly halted hemolysis in the single-arm CARDINAL study in recently transfused patients with cold agglutinin disease (CAD). CADENZA was a 26-week randomized, placebo-controlled phase 3 study to assess safety and efficacy of sutimlimab in patients with CAD without recent (within 6 months prior to enrollment) transfusion history. Forty-two patients with screening hemoglobin ≤10 g/dL, elevated bilirubin, and ≥1 CAD symptom received sutimlimab (n = 22) or placebo (n = 20) on days 0 and 7 and then biweekly. Composite primary endpoint criteria (hemoglobin increase ≥1.5 g/dL at treatment assessment timepoint [mean of weeks 23, 25, 26], avoidance of transfusion, and study-prohibited CAD therapy [weeks 5-26]) were met by 16 patients (73%) on sutimlimab, and 3 patients (15%) on placebo (odds ratio, 15.9 [95% confidence interval, 2.9, 88.0; P < .001]). Sutimlimab, but not placebo, significantly increased mean hemoglobin and FACIT-Fatigue scores at treatment assessment timepoint. Sutimlimab normalized mean bilirubin by week 1. Improvements correlated with near-complete inhibition of the classical complement pathway (2.3% mean activity at week 1) and C4 normalization. Twenty-one (96%) sutimlimab patients and 20 (100%) placebo patients experienced ≥1 treatment-emergent adverse event. Headache, hypertension, rhinitis, Raynaud phenomenon, and acrocyanosis were more frequent with sutimlimab vs placebo, with a difference of ≥3 patients between groups. Three sutimlimab patients discontinued owing to adverse events; no placebo patients discontinued. These data demonstrate that sutimlimab has potential to be an important advancement in the treatment of CAD. This trial was registered at www.clinicaltrials.gov as #NCT03347422.

Sutimlimab for treatment of cold agglutinin disease: why, how and for whom?

Therapies for cold agglutinin disease have been directed at the pathogenic B-cell clone. Sutimlimab, a monoclonal antibody that targets C1s, is the first complement inhibitor to be extensively studied in cold agglutinin disease. Sutimlimab selectively blocks the classical activation pathway and leaves the alternative and lectin pathways intact. Trials have documented high response rates with rapid improvement in hemolysis, hemoglobin levels and fatigue scores and low toxicity. Sutimlimab was recently approved in the USA. This drug appears to be particularly useful in severely anemic patients who require a rapid response, in acute exacerbations that do not resolve spontaneously and in patients in whom chemoimmunotherapy is contraindicated or has failed. The choice of therapy in cold agglutinin disease should be individualized.

Complement-mediated hemolysis persists year round in patients with cold agglutinin disease

BACKGROUND

Cold agglutinin disease (CAD) is a rare autoimmune hemolytic anemia mediated by immunoglobulin M autoantibodies that bind to the "I" antigen on erythrocytes. IgM binding results in either agglutination at ≤37°C, activation of the classical complement pathway, or both. Patients with CAD can have transient agglutination-mediated circulatory symptoms triggered by exposure to cold conditions. Separately, patients with CAD can experience complement-mediated symptoms such as anemia, hemolysis, and fatigue, but the effect of the season on these complement-mediated manifestations of CAD and clinical outcomes is not well understood.

METHODS

Using data from the Optum® de-identified Electronic Health Record dataset, we compared hemoglobin, markers of hemolysis (bilirubin and lactate dehydrogenase [LDH]), and healthcare resource utilization (HRU) between seasons for 594 patients (62% female; 66% aged ≥65 years) with CAD (defined as having CAD-related terms in their clinical notes on ≥3 separate occasions between December 2008 and May 2016). Laboratory parameters and HRU were compared between seasons using multivariate regression models.

RESULTS

Estimated median hemoglobin (9.87 g/dL in summer and 9.86 g/dL in winter; P = 0.944) and bilirubin (1.04 mg/dL in summer and 1.09 mg/dL in winter; P = 0.257) were similar in winter versus summer. While LDH was statistically significantly higher in winter compared with summer (P < 0.001), the estimated median value was above normal for both seasons (309 U/L in summer and 367 U/L in winter). HRU measures and transfusion and thromboembolism rates were similar across seasons.

CONCLUSIONS

Patients with CAD had evidence of persistent chronic hemolysis, HRU, and thromboembolism risk year round.

Healthcare resource utilization among patients with cold agglutinin disease in Denmark

OBJECTIVES

Cold agglutinin disease (CAD) is a rare form of autoimmune hemolytic anemia that may manifest in complement-mediated chronic hemolytic anemia, profound fatigue, and transient agglutination-mediated circulatory symptoms. This study compared the healthcare resource utilization (HRU) of patients with CAD with a matched non-CAD comparison cohort using national Danish health registry data.

METHODS

All cases of CAD were identified from 1 January 1999 to 30 June 2016, in the Danish National Patient Registry using the International Classification of Diseases, Tenth Revision, discharge diagnosis codes. A subcohort of patients with primary CAD was identified based on the absence of secondary predisposing concomitant diseases. CAD cases were matched to individuals without CAD from the general population based on birth year, sex, and 19 disease categories of the Charlson Comorbidity Index. Comparative analyses assessed inpatient hospitalizations, outpatient clinic visits, emergency room visits, transfusion use, and expensive drug use between cohorts 6 months before and 12 months after the admission date of the first hospital visit with CAD diagnosis (index date).

RESULTS

A total of 104 patients with CAD were matched to 1003 comparison cohort members. Throughout the 12 months after the index date, patients with CAD were more likely to have at least one inpatient hospitalization (odds ratio [OR], 3.9; 95% confidence interval [CI], 2.5-6.0), outpatient clinic visit (OR, 17.2; 95% CI, 6.8-43.1), and blood transfusion (OR, 93.0; 95% CI, 33.3-259.8) than matched comparisons. HRU was similarly higher among patients with CAD than matched comparisons during the 6 months before the index date. Findings were similar among patients with primary CAD.

CONCLUSIONS

Characterization of HRU among European patients with CAD has not previously been conducted. This study shows that patients with CAD utilize significant resources in Denmark. Increased HRU uses among patients with CAD before diagnosis presents opportunities for earlier diagnosis and management.

Thrombosis associated with mycoplasma pneumoniae infection (Review)

Mycoplasma pneumoniae is a common pathogen causing respiratory infections in children and adults. In addition to respiratory diseases, Mycoplasma pneumoniae is also involved in numerous extrapulmonary diseases. Thrombosis is an extrapulmonary manifestation associated with Mycoplasma pneumoniae infection. In recent years, an increasing number of case reports have been published identifying thrombosis secondary to Mycoplasma pneumoniae infection. In the present study, the available relevant literature in English available on PubMed, Medline and Web of Science was consulted. The results of the present study demonstrated that in patients with thrombosis caused by Mycoplasma pneumoniae infection, some of the factors causing thrombosis are transient and some are due to hereditary thrombophilia. Following timely treatment, the majority of patients recovered completely but some patients had a poor prognosis. The present review focuses on the pathogenesis, clinical features, treatment and prognosis of this crucial issue, which contributes toward the understanding of the disease.

Halting targeted and collateral damage to red blood cells by the complement system

The complement system is an important defense mechanism against pathogens; however, in certain pathologies, the system also attacks human cells, such as red blood cells (RBCs). In paroxysmal nocturnal hemoglobinuria (PNH), RBCs lack certain complement regulators which sensitize them to complement-mediated lysis, while in autoimmune hemolytic anemia (AIHA), antibodies against RBCs may initiate complement-mediated hemolysis. In recent years, complement inhibition has improved treatment prospects for these patients, with eculizumab now the standard of care for PNH patients. Current complement inhibitors are however not sufficient for all patients, and they come with high costs, patient burden, and increased infection risk. This review gives an overview of the underlying pathophysiology of complement-mediated hemolysis in PNH and AIHA, the role of therapeutic complement inhibition nowadays, and the high number of complement inhibitors currently under investigation, as for almost every complement protein, an inhibitor is being developed. The focus lies with novel therapeutics that inhibit complement activity specifically in the pathway that causes pathology or those that reduce costs or patient burden through novel administration routes.

Cold Agglutinins and Cryoglobulins Associate With Clinical and Laboratory Parameters of Cold Urticaria

Mast cell-activating signals in cold urticaria are not yet well defined and are likely to be heterogeneous. Cold agglutinins and cryoglobulins have been described as factors possibly associated with cold urticaria, but their relevance has not been explained. We performed a single-center prospective cohort study of 35 cold urticaria patients. Cold agglutinin and cryoglobulin test results, demographics, detailed history data, cold stimulation test results, complete blood count values, C-reactive protein, total immunoglobulin E levels, and basal serum tryptase levels were analyzed. Forty six percent (n = 16) of 35 tested patients had a positive cold agglutinin test and 27% (n = 9) of 33 tested patients had a positive cryoglobulin test. Cold agglutinin positive patients, when compared to cold agglutinin negative ones, were mainly female (P = 0.030). No gender-association was found for cryoglobulins. A positive cold agglutinin test, but not a positive cryoglobulin test, was associated with a higher rate of reactions triggered by cold ambient air (P = 0.009) or immersion in cold water (P = 0.041), and aggravated by increased summer humidity (P = 0.007). Additionally, patients with a positive cold agglutinin test had a higher frequency of angioedema triggered by ingestion of cold foods or drinks (P = 0.043), and lower disease control based on Urticaria Control Test (P = 0.023). Cold agglutinin levels correlated with erythrocyte counts (r = −0.372, P = 0.028) and monocyte counts (r = −0.425, P = 0.011). Cryoglobulin concentrations correlated with basal serum tryptase levels (r = 0.733, P = 0.025) and cold urticaria duration (r = 0.683, P = 0.042). Results of our study suggest that cold agglutinins and cryoglobulins, in a subpopulation of cold urticaria patients, are linked to the course and possibly the pathogenesis of their disease.

Thrombotic Complications in Patients with Immune-Mediated Hemolysis

Autoimmune hemolytic anemias are rare and heterogeneous disorders characterized by hemolysis, which is a well-recognized risk factor for thrombosis. The most common immune-mediated anemias are represented by autoimmune hemolytic anemia and paroxysmal nocturnal hemoglobinuria, both associated with a high rate of thrombosis. Multiple pathophysiological mechanisms for thrombosis have been proposed, involving hemolysis itself and additional effects of the immune system. Despite the increasing awareness of the thrombotic risk in these conditions, evidence-based guidance on prevention and management of thrombotic events is lacking. We herein report available evidence on epidemiological data on thrombosis and thrombophilia in immune-mediated hemolysis, together with possible underlying pathophysiological mechanisms. In addition, we summarize current recommendations for treatment of thrombosis in immune-mediated hemolysis. In particular, we address the issue of thrombotic complications treatment and prophylaxis by proposing a therapeutic algorithm, focusing on specific situations such as splenectomy and pregnancy.

Sutimlimab in Cold Agglutinin Disease

BACKGROUND

Cold agglutinin disease is a rare autoimmune hemolytic anemia characterized by hemolysis that is caused by activation of the classic complement pathway. Sutimlimab, a humanized monoclonal antibody, selectively targets the C1s protein, a C1 complex serine protease responsible for activating this pathway.

METHODS

We conducted a 26-week multicenter, open-label, single-group study to assess the efficacy and safety of intravenous sutimlimab in patients with cold agglutinin disease and a recent history of transfusion. The composite primary end point was a normalization of the hemoglobin level to 12 g or more per deciliter or an increase in the hemoglobin level of 2 g or more per deciliter from baseline, without red-cell transfusion or medications prohibited by the protocol.

RESULTS

A total of 24 patients were enrolled and received at least one dose of sutimlimab; 13 patients (54%) met the criteria for the composite primary end point. The least-squares mean increase in hemoglobin level was 2.6 g per deciliter at the time of treatment assessment (weeks 23, 25, and 26). A mean hemoglobin level of more than 11 g per deciliter was maintained in patients from week 3 through the end of the study period. The mean bilirubin levels normalized by week 3. A total of 17 patients (71%) did not receive a transfusion from week 5 through week 26. Clinically meaningful reductions in fatigue were observed by week 1 and were maintained throughout the study. Activity in the classic complement pathway was rapidly inhibited, as assessed by a functional assay. Increased hemoglobin levels, reduced bilirubin levels, and reduced fatigue coincided with inhibition of the classic complement pathway. At least one adverse event occurred during the treatment period in 22 patients (92%). Seven patients (29%) had at least one serious adverse event, none of which were determined by the investigators to be related to sutimlimab. No meningococcal infections occurred.

CONCLUSIONS

In patients with cold agglutinin disease who received sutimlimab, selective upstream inhibition of activity in the classic complement pathway rapidly halted hemolysis, increased hemoglobin levels, and reduced fatigue. (Funded by Sanofi; CARDINAL ClinicalTrials.gov number, NCT03347396.).

Therapeutic Targeting of the Complement System: From Rare Diseases to Pandemics

The complement system was discovered at the end of the 19th century as a heat-labile plasma component that "complemented" the antibodies in killing microbes, hence the name "complement." Complement is also part of the innate immune system, protecting the host by recognition of pathogen-associated molecular patterns. However, complement is multifunctional far beyond infectious defense. It contributes to organ development, such as sculpting neuron synapses, promoting tissue regeneration and repair, and rapidly engaging and synergizing with a number of processes, including hemostasis leading to thromboinflammation. Complement is a double-edged sword. Although it usually protects the host, it may cause tissue damage when dysregulated or overactivated, such as in the systemic inflammatory reaction seen in trauma and sepsis and severe coronavirus disease 2019 (COVID-19). Damage-associated molecular patterns generated during ischemia-reperfusion injuries (myocardial infarction, stroke, and transplant dysfunction) and in chronic neurologic and rheumatic disease activate complement, thereby increasing damaging inflammation. Despite the long list of diseases with potential for ameliorating complement modulation, only a few rare diseases are approved for clinical treatment targeting complement. Those currently being efficiently treated include paroxysmal nocturnal hemoglobinuria, atypical hemolytic-uremic syndrome, myasthenia gravis, and neuromyelitis optica spectrum disorders. Rare diseases, unfortunately, preclude robust clinical trials. The increasing evidence for complement as a pathogenetic driver in many more common diseases suggests an opportunity for future complement therapy, which, however, requires robust clinical trials; one ongoing example is COVID-19 disease. The current review aims to discuss complement in disease pathogenesis and discuss future pharmacological strategies to treat these diseases with complement-targeted therapies. SIGNIFICANCE STATEMENT: The complement system is the host's defense friend by protecting it from invading pathogens, promoting tissue repair, and maintaining homeostasis. Complement is a double-edged sword, since when dysregulated or overactivated it becomes the host's enemy, leading to tissue damage, organ failure, and, in worst case, death. A number of acute and chronic diseases are candidates for pharmacological treatment to avoid complement-dependent damage, ranging from the well established treatment for rare diseases to possible future treatment of large patient groups like the pandemic coronavirus disease 2019.

Features of serum complement C3 and C4 levels in autoimmune hemolytic anemia patients

INTRODUCTION

Abnormally activated complement system induces erythrolysis in a part of autoimmune hemolytic anemia (AIHA) patients. However, the alterations in serum complement levels in these patients are seldom reported. In this study, we aimed to evaluate the serum complement features of AIHA patients according to different clinical and laboratory characteristics and to find relationships between complement levels and hemolysis-associated laboratory indexes.

METHODS

A retrospective analysis of 146 AIHA patients was performed, and serum complement C3 and C4 levels were compared between control subjects and AIHA patients with different subtypes. Correlations of serum C3/C4 levels with titers of cold agglutinin test (CAT), direct antiglobulin test (DAT), and serological indexes were assessed. Spearman correlation analysis was performed to analyze the relationship between serum complement levels and other laboratory indexes.

RESULTS

Autoimmune hemolytic anemia patients showed reduced serum C3 levels, while serum C4 levels tended to be lower in DAT-positive AIHA patients but not in DAT-negative AIHA patients. Patients with warm AIHA secondary to connective tissue diseases and cold agglutinin disease/cold agglutinin syndrome had the lowest serum C3/C4 levels. Serum C4 levels were negatively correlated with CAT (P = .004) and DAT (anti-C3d) (P = .007) titers. In patients with positive CAT and/or DAT (anti-C3d) but negative DAT (anti-IgG), serum C3/C4 levels were negatively correlated with indirect bilirubin (P = .017 and =.026, respectively).

CONCLUSION

The study findings may be helpful in not only unraveling the mechanism underlying hemolysis in AIHA but also diagnosing AIHA and selecting targeted treatment strategies.

RNA sequencing of whole blood in dogs with primary immune-mediated hemolytic anemia (IMHA) reveals novel insights into disease pathogenesis

Immune-mediated hemolytic anemia (IMHA) is a life-threatening autoimmune disorder characterized by a self-mediated attack on circulating red blood cells. The disease occurs naturally in both dogs and humans, but is significantly more prevalent in dogs. Because of its shared features across species, dogs offer a naturally occurring model for studying IMHA in people. In this study, we used RNA sequencing of whole blood from treatment-naïve dogs to study transcriptome-wide changes in gene expression in newly diagnosed animals compared to healthy controls. We found many overexpressed genes in pathways related to neutrophil function, coagulation, and hematopoiesis. In particular, the most highly overexpressed gene in cases was a phospholipase scramblase, which mediates the externalization of phosphatidylserine from the inner to the outer leaflet of cell membranes. This family of genes has been shown to be critically important for programmed cell death of erythrocytes as well as the initiation of the clotting cascade. Unexpectedly, we found marked underexpression of many genes related to lymphocyte function. We also identified groups of genes that are highly associated with the inflammatory response and red blood cell regeneration in affected dogs. We did not find any genes that distinguished dogs that lived vs. those that died at 30 days following diagnosis, nor did we find any relevant genomic signatures of microbial organisms in the blood of affected animals. Future studies are warranted to validate these findings and assess their implication in developing novel therapeutic approaches for dogs and humans with IMHA.

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.

Targeting the Initiator Protease of the Classical Pathway of Complement Using Fragment-Based Drug Discovery

The initiating protease of the complement classical pathway, C1r, represents an upstream and pathway-specific intervention point for complement-related autoimmune and inflammatory diseases. Yet, C1r-targeted therapeutic development is currently underrepresented relative to other complement targets. In this study, we developed a fragment-based drug discovery approach using surface plasmon resonance (SPR) and molecular modeling to identify and characterize novel C1r-binding small-molecule fragments. SPR was used to screen a 2000-compound fragment library for binding to human C1r. This led to the identification of 24 compounds that bound C1r with equilibrium dissociation constants ranging between 160–1700 µM. Two fragments, termed CMP-1611 and CMP-1696, directly inhibited classical pathway-specific complement activation in a dose-dependent manner. CMP-1611 was selective for classical pathway inhibition, while CMP-1696 also blocked the lectin pathway but not the alternative pathway. Direct binding experiments mapped the CMP-1696 binding site to the serine protease domain of C1r and molecular docking and molecular dynamics studies, combined with C1r autoactivation assays, suggest that CMP-1696 binds within the C1r active site. The group of structurally distinct fragments identified here, along with the structure–activity relationship profiling of two lead fragments, form the basis for future development of novel high-affinity C1r-binding, classical pathway-specific, small-molecule complement inhibitors.

Healthcare resource utilization among commercially insured patients with cold agglutinin disease in the United States

Aims: Cold agglutinin disease (CAD) is a rare subtype of autoimmune hemolytic anemia associated with increased thromboembolism risk and early mortality. Healthcare resource utilization (HRU) in CAD has not been reported. We aimed to compare HRU of patients with CAD with a matched non-CAD cohort in the United States.Materials and methods: Patients with CAD were identified from 2006 to 2016 in the Optum-Humedica database using CAD terms in clinical notes and hematologist review. Patients were required to have Integrated Delivery Network records and ≥6 months' follow-up before and after the first CAD mention date (index date). Patients with CAD were matched to a non-CAD cohort based on demographics. Multivariate analyses assessed inpatient hospitalizations, outpatient visits, emergency room visits, and transfusion use between cohorts 6 months before and 12 months after the index date.Results: Of 814 patients with CAD, 410 met inclusion criteria and were matched to 3,390 patients without CAD. Mean age of patients with CAD was 68.0 years; approximately 62% were female. In the 12 months after the index date, mean inpatient hospitalizations (0.83 vs. 0.25), outpatient visits (17.26 vs. 6.77), emergency room visits (0.55 vs. 0.32), and transfusion days (1.05 vs. 0.05) were higher for patients with CAD than the matched non-CAD cohort (all p < .0001). Similarly, in the 6 months before the index date, patients with CAD had higher HRU than matched patients without CAD for all measures evaluated.Limitations: Results of this study are based on patient information from the Optum-Humedica database, which is limited to commercially insured patients and may not represent the overall CAD population.Conclusions: CAD places a substantial burden on patients and healthcare systems. In addition, the high HRU for patients with CAD observed in the 6 months before diagnosis indicates that disease awareness and better diagnostic practices may be needed.

Increased risk of thrombotic events in cold agglutinin disease: A 10-year retrospective analysis

BACKGROUND

Cold agglutinin disease (CAD) is a rare autoimmune hemolytic anemia mediated by IgM autoantibodies that trigger hemolysis via classical complement pathway. Increased incidence of thrombotic events (TEs) has been reported in patients with other forms of hemolysis. The incidence of TEs in patients with CAD is unknown.

OBJECTIVE

Evaluate TE risk in patients with CAD.

PATIENTS/METHODS

This is a matched cohort comparison study evaluating the risk of TEs in patients with CAD and without CAD over a 10-year period. A total of 608 patients with CAD were identified in the Optum Claims-Clinical data set by reviewing clinical notes for CAD terms and matched with up to 10 patients without CAD (N = 5873). TEs were defined as the first medical claim for a TE using International Classification of Diseases, Ninth and Tenth Revision codes. Cox regression models were used to estimate time to first TE. Sensitivity analyses were conducted to estimate TE risk among patients with primary CAD.

RESULTS

At least 1 TE occurred in 29.6% of patients with CAD and 17.6% of patients without CAD. The proportion of patients experiencing venous, arterial, and cerebral TEs were each higher among CAD patients. The overall risk of having TEs was higher in patients with CAD (adjusted hazard ratio [aHR], 1.94; 95% confidence interval [CI], 1.64-2.30). Patients with presumed primary CAD also demonstrated an increased risk of TEs (aHR, 1.80; 95% CI, 1.46-2.22). Patients with CAD with the fewest comorbidities had 2.44-fold higher risk of having a TE (95% CI, 1.70-3.52).

CONCLUSIONS

Patients with CAD have an increased risk of TEs when compared with a matched non-CAD population.

New Insights in the Pathogenesis and Therapy of Cold Agglutinin-Mediated Autoimmune Hemolytic Anemia

Autoimmune hemolytic anemias mediated by cold agglutinins can be divided into cold agglutinin disease (CAD), which is a well-defined clinicopathologic entity and a clonal lymphoproliferative disorder, and secondary cold agglutinin syndrome (CAS), in which a similar picture of cold-hemolytic anemia occurs secondary to another distinct clinical disease. Thus, the pathogenesis in CAD is quite different from that of polyclonal autoimmune diseases such as warm-antibody AIHA. In both CAD and CAS, hemolysis is mediated by the classical complement pathway and therefore can result in generation of anaphylotoxins, such as complement split product 3a (C3a) and, to some extent, C5a. On the other hand, infection and inflammation can act as triggers and drivers of hemolysis, exemplified by exacerbation of CAD in situations with acute phase reaction and the role of specific infections (particularly Mycoplasma pneumoniae and Epstein-Barr virus) as causes of CAS. In this review, the putative mechanisms behind these phenomena will be explained along with other recent achievements in the understanding of pathogenesis in these disorders. Therapeutic approaches have been directed against the clonal lymphoproliferation in CAD or the underlying disease in CAS. Currently, novel targeted treatments, in particular complement-directed therapies, are also being rapidly developed and will be reviewed.

Eculizumab and Beyond: The Past, Present, and Future of Complement Therapeutics

Dysregulation of the complement system underlies the pathophysiology of many diseases. Renewed interest in complement occurred with the recognition that its therapeutic inhibition was possible. Terminal complement blockade with the anti-C5 monoclonal antibody eculizumab significantly changed management and clinical outcomes of patients with paroxysmal nocturnal hemoglobinuria, and served as a proof of concept for other complement-mediated diseases. Eculizumab is also approved for atypical hemolytic uremic syndrome and myasthenia gravis. Multiple new disease indications have been identified, and novel complement inhibitors are in various stages of development, with several currently in human trials. Beyond C5, these new drugs block proximal complement, pathway-specific targets, convertase activity, and anaphylatoxin function. Though monoclonal antibodies are still common, peptides, RNAi, and small molecule inhibitors provide the opportunity for different administration routes and schedules. Several challenges still exist or will soon present themselves, including mitigation of infection risk, effective monitoring strategies, and how to choose between therapeutics when more than one is available. In this review, we will describe the lessons learned from the "eculizumab era," present many of the novel therapeutics currently or soon to be in trials, and highlight some of the challenges that will require attention as the field progresses.

Clinical Complement Analysis-An Overview

The complement system plays an important role in varying types of disease, ranging from inflammatory and autoimmune disorders to immune deficiency states. In addition, new settings have emerged where complement analysis is of interest to monitor complement-directed therapy and aid identification of transplant complications. Therefore, it is critical that clinical laboratories offer optimized and timely complement analysis. This review presents a comprehensive overview of the most important complement analysis methods that are currently used. It also points to some areas within complement diagnostics where development is needed, for example, regarding certain analytes for which practical methods suitable for the routine laboratory are lacking. Furthermore, it contains a more detailed discussion on complement autoantibody assessment. The list of analyses providing clinically valuable information includes analysis of complement function, quantification of individual complement components and complement activation fragments, identification of autoantibodies to complement, as well as genetic complement analyses. There is still a shortage of commercially available methods suitable for high-throughput screening of complement deficiency and for assessment of complement activation, but development is under way. There is also ongoing work within the complement community to improve standardization of measurements, and recently, an extensive quality assurance program has been initiated.

Novel insights into the treatment of complement-mediated hemolytic anemias

Complement-mediated hemolytic anemias can either be caused by deficiencies in regulatory complement components or by autoimmune pathogenesis that triggers inappropriate complement activation. In paroxysmal nocturnal hemoglobinuria (PNH) hemolysis is entirely complement-driven. Hemolysis is also thought to be complement-dependent in cold agglutinin disease (CAD) and in paroxysmal cold hemoglobinuria (PCH), whereas warm antibody autoimmune hemolytic anemia (wAIHA) is a partially complement-mediated disorder, depending on the subtype of wAIHA and the extent of complement activation. The pathophysiology, clinical presentation, and current therapies for these diseases are reviewed in this article. Novel, complement-directed therapies are being rapidly developed. Therapeutic terminal complement inhibition using eculizumab has revolutionized the therapy and prognosis in PNH but has proved less efficacious in CAD. Upstream complement modulation is currently being investigated and appears to be a highly promising therapy, and two such agents have entered phase II and III trials. Of these, the anti-C1s monoclonal antibody sutimlimab has shown favorable activity in CAD, while the anti-C3 cyclic peptide pegcetacoplan appears to be promising in PNH as well as CAD, and may also have a therapeutic potential in wAIHA.

Cold agglutinin disease: current challenges and future prospects

Cold agglutinin disease (CAD) is a complement-dependent, classical pathway-mediated immune hemolytic disease, accounting for 15–25% of autoimmune hemolytic anemia, and at the same time, a distinct clonal B-cell lymphoproliferative disorder of the bone marrow. The disease burden is often high, but not all patients require pharmacological treatment. Several therapies directed at the pathogenic B-cells are now available. Rituximab plus bendamustine or rituximab monotherapy should be considered first-line treatment, depending on individual patient characteristics. Novel treatment options that target the classical complement pathway are under development and appear very promising, and the C1s inhibitor sutimlimab is currently being investigated in two clinical Phase II and III trials. These achievements have raised new challenges and further prospects, which are discussed. Patients with CAD requiring therapy should be considered for clinical trials.

Development of Multiple Myeloma of the IgA Type in a Patient with Cold Agglutinin Disease: Transformation or Coincidence?

Cold agglutinin disease (CAD) is an autoimmune hemolytic anemia and a distinct, clonal bone marrow lymphoproliferative disorder, characterized in most cases by a monoclonal IgMκ serum protein. We describe a CAD patient presenting with a monoclonal immunoglobulin of the IgAλ class. For years, she remained asymptomatic apart from the hemolytic anemia until eventually she developed multiple myeloma (MM) of the IgAλ phenotype. Prior to the development of MM, her hemolytic anemia responded to rituximab monotherapy. After she was diagnosed with MM, both conditions responded well to bortezomib-based therapy. We performed further investigations to determine whether her MM represented a progression/transformation of CAD or an independent disease. Flow cytometry and biopsy findings convincingly confirmed two unrelated clonal B-cell disorders. On this background, we also discuss previously published reports on cold agglutinin activity in patients with IgA gammopathy. In conclusion, cold agglutinins of the IgA class do probably not result in CAD. If a monoclonal immunoglobulin other than IgMκ is found in a patient with CAD, the coexistence of two unrelated B-cell clones should be suspected.