New perspectives on the approach to patients with atypical Hemolytic Uremic Syndrome candidates for renal transplantation

Atypical hemolytic uremic syndrome (aHUS) is one of the most challenging diseases for a nephrologist, with high rates of progression to end- -stage kidney disease (ESKD) and post-transplant recurrence. Complement dysregulation has been found in up to 70% of cases, which can be hereditary or acquired. Over the last few years, knowledge of the pathogenesis of aHUS has greatly increased, with the unravelling of the complement’s role, providing not only the chance for individualized post-transplant recurrence risk assessment, but also the possibility of a highly effective treatment through pharmacological C5-9 blockade with eculizumab. The overall outcome and prognosis of patients with aHUS has dramatically improved since the approval of this drug in 2011, allowing renal transplant to be a much safer option for these patients. Our aim was to present a proposal for the management of patients with aHUS, candidates for renal transplantation, in the light of the most recent studies.

Malignancy and Immune Disorders in Patients With Hereditary Angioedema

Background With the advent of new therapies, patients with hereditary angioedema (HAE) are living longer lives. Although complement dysregulation has been linked to various disease states, it is currently not known if HAE patients are at an increased risk of developing malignancy or autoimmune conditions. Case Presentation : We reviewed the charts of 49 HAE patients and identified 6 patients who had a co-existing malignancy diagnosis (two with breast cancer, one with melanoma, one with pancreatic cancer, one with renal cancer and one with cervical dysplasia) and 6 patients who had a diagnosis of a co-existing immune disorder (two with rheumatoid arthritis, two with ulcerative colitis, one with chronic urticaria with hypothyroidism and one with Sjogren’s syndrome). Nearly all malignancy cases occurred in older HAE patients (> 50 years) and malignancy was diagnosed before HAE in 3 of the patients. Conclusions Our case series has identified multiple hereditary angioedema (HAE) patients with co-existing malignancy and immune disorders. Based on these findings, we would advocate that physicians managing HAE patients should maintain a high index of suspicion for these conditions.

Complement dysregulation is associated with severe COVID-19 illness

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) may manifest as thrombosis, stroke, renal failure, myocardial infarction, and thrombocytopenia, reminiscent of other complement-mediated diseases. Multiple clinical and preclinical studies have implicated complement in the pathogenesis of COVID-19 illness. We previously found that the SARS-CoV-2 spike protein activates the alternative pathway of complement (APC) in vitro through interfering with the function of complement factor H, a key negative regulator of APC. Here, we demonstrated that serum from 58 COVID-19 patients (32 patients with minimal oxygen requirement, 7 on high flow oxygen, 17 requiring mechanical ventilation and 2 deaths) can induce complement-mediated cell death in a functional assay (the modified Ham test) and increase membrane attack complex (C5b-9) deposition on the cell surface. A positive mHam assay (>20% cellkilling) was present in 41.2% COVID-19 patients requiring intubation (n=7/17) and only 6.3% in COVID-19 patients requiring minimal oxygen support (n=2/32). C5 and factor D inhibition effectively mitigated the complement amplification induced by COVID-19 patient serum. Increased serum factor Bb level was associated with disease severity in COVID-19 patients, suggesting that APC dysregulation plays an important role. Moreover, SARS-CoV-2 spike proteins directly block complement factor H from binding to heparin, which may lead to complement dysregulation on the cell surface. Taken together, our data suggest that complement dysregulation contributes to the pathogenesis of COVID-19 and may be a marker of disease severity.

The Syndromes of Thrombotic Microangiopathy: A Critical Appraisal on Complement Dysregulation

Thrombotic microangiopathy (TMA) is a rare and potentially life-threatening condition that can be caused by a heterogeneous group of diseases, often affecting the brain and kidneys. TMAs should be classified according to etiology to indicate targets for treatment. Complement dysregulation is an important cause of TMA that defines cases not related to coexisting conditions, that is, primary atypical hemolytic uremic syndrome (HUS). Ever since the approval of therapeutic complement inhibition, the approach of TMA has focused on the recognition of primary atypical HUS. Recent advances, however, demonstrated the pivotal role of complement dysregulation in specific subtypes of patients considered to have secondary atypical HUS. This is particularly the case in patients presenting with coexisting hypertensive emergency, pregnancy, and kidney transplantation, shifting the paradigm of disease. In contrast, complement dysregulation is uncommon in patients with other coexisting conditions, such as bacterial infection, drug use, cancer, and autoimmunity, among other disorders. In this review, we performed a critical appraisal on complement dysregulation and the use of therapeutic complement inhibition in TMAs associated with coexisting conditions and outline a pragmatic approach to diagnosis and treatment. For future studies, we advocate the term complement-mediated TMA as opposed to the traditional atypical HUS-type classification.

Erythrocytes Identify Complement Activation in Patients with COVID-19

COVID-19, the disease caused by the SARS-CoV-2 virus, can progress to multi-system organ failure and viral sepsis characterized by respiratory failure, arrhythmias, thromboembolic complications, and shock with high mortality. Autopsy and pre-clinical evidence implicate aberrant complement activation in endothelial injury and organ failure. Erythrocytes express complement receptors and are capable of binding immune complexes; therefore, we investigated complement activation in COVID-19 patients using erythrocytes as a tool to diagnose complement activation. We discovered enhanced C3b and C4d deposition on erythrocytes in COVID-19 sepsis patients and non-COVID sepsis patients compared with healthy controls, supporting the role of complement in sepsis-associated organ injury. Our data suggest that erythrocytes may contribute to a precision medicine approach to sepsis and have diagnostic value in monitoring complement dysregulation in COVID-19-sepsis and non-COVID sepsis and identifying patients who may benefit from complement targeted therapies.

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

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

Complement C5 is not critical for the formation of sub-RPE deposits in Efemp1 mutant mice

The complement system plays a role in the formation of sub-retinal pigment epithelial (RPE) deposits in early stages of age-related macular degeneration (AMD). But the specific mechanisms that connect complement activation and deposit formation in AMD patients are unknown, which limits the development of efficient therapies to reduce or stop disease progression. We have previously demonstrated that C3 blockage prevents the formation of sub-RPE deposits in a mouse model of EFEMP1-associated macular degeneration. In this study, we have used double mutant Efemp1R345W/R345W:C5-/- mice to investigate the role of C5 in the formation of sub-RPE deposits in vivo and in vitro. The data revealed that the genetic ablation of C5 does not eliminate the formation of sub-RPE deposits. Contrarily, the absence of C5 in RPE cultures promotes complement dysregulation that results in increased activation of C3, which likely contributes to deposit formation even in the absence of EFEMP1-R345W mutant protein. The results also suggest that genetic ablation of C5 alters the extracellular matrix turnover through an effect on matrix metalloproteinases in RPE cell cultures. These results confirm that C3 rather than C5 could be an effective therapeutic target to treat early AMD.

MO126CLINICAL AND BIOMARKER CHARACTERISTICS OF PATIENTS WITH C3G OR IC-MPGN ENROLLED IN TWO PHASE II STUDIES INVESTIGATING THE FACTOR D INHIBITOR DANICOPAN*

Background and Aims C3 glomerulopathy (C3G) and immune complex membranoproliferative glomerulonephritis (IC-MPGN) are rare, progressive kidney diseases requiring a biopsy for definite diagnosis. Both C3G and IC-MPGN are attributed to complement dysregulation, with dysregulation of the alternative pathway established in C3G and implicated in IC-MPGN (alongside classical pathway activation by immune complexes). We describe the baseline biomarker and clinical characteristics of patients participating in two C3G/IC-MPGN phase II studies of the investigational, oral complement factor D (FD) inhibitor, danicopan (ALXN2040/ACH-4471). Method The first study (NCT03369236) was a double-blind, placebo-controlled, randomised, 6-month (+open label extension) trial of patients with biopsy-confirmed C3G of the native kidney treated with danicopan or placebo. The second study (NCT03459443) was a single-arm, open-label, 12-month (+extension) trial of patients with biopsy-confirmed C3G or IC-MPGN treated with danicopan. In both studies, all patients were to have proteinuria ≥500 mg/day and estimated glomerular filtration rate (eGFR) ≥30 mL/min/1.73 m2 (calculated by the Modification of Diet in Renal Disease equation for patients ≥18 years and the Schwartz equation for patients <18 years). Complement biomarkers including, but not limited to, C3, C4, AP activity, classical pathway activity, FD, Ba, Bb, sC5b-9, and C5 were measured in serum or plasma prior to dosing. Spearman correlation coefficients (rs) were determined between biomarkers of complement, eGFR, and/or proteinuria. Results A total of 35 patients were included in this analysis (13 from study 1 and 22 from study 2). The majority of patients were male (9 [69%] in study 1, 12 [55%] in study 2), with mean (SD) ages at baseline of 25.2 (7.63) years in study 1 and 24.3 (9.90) years in study 2. Most patients had received prior angiotensin converting enzyme inhibitors/receptor blockers (12 [92%] in study 1, 19 [86%] in study 2), and/or immunosuppressants (10 [77%] in study 1, 12 [55%] in study 2). Baseline clinical and biomarker data are shown in Table 1. Baseline eGFR was moderately correlated with proteinuria (uPCR24, rs=-0.40 [p=0.022]); baseline uPCR24 was also moderately correlated with Ba (rs=0.42 [p=0.016]) and FD (rs=0.53 [p=0.002]). Ba and FD elevations showed strong correlations with lower eGFR (rs=-0.79 and -0.88, respectively [p<0.0001]), as seen in Figure 1A and B. Reduced circulating C3 strongly correlated with increased sC5b-9 (rs=-0.70 [p<0.0001]) and reduced C5 level (rs=0.80 [p<0.0001]), as seen in Figure 1C and D. Conclusion Data from two danicopan clinical studies in C3G patients show correlations with renal impairment and proteinuria were observed for some, but not all, complement biomarkers. Factor Ba and FD are strongly associated with eGFR, suggesting that these biomarkers cannot easily be used as markers of complement dysregulation or activity. Interpretation of changes in these complement proteins needs to include not only the nature of the complement dysregulation and influence of the complement therapeutic being tested, but also eGFR. Additional urinary biomarkers, biopsy findings, autoantibodies, and genetic variants are currently being analysed and findings from this study will contribute to a better understanding of C3G and IC-MPGN.

Complement in structure and immune homeostasis in placenta

Aberrant complement activation can induce “thrombo-inflammation” attacks to host tissue. Beside kidney and blood vessel, the placenta is also susceptible to these attacks. Complement dysregulation is recently classified as one of the new mechanisms leading to pregnancy disorders. Studies have indicated that dampening complement activation can ameliorate pregnancy outcomes. During pregnancy, the mother’s immune system is finely domesticated to accept the semi-allogeneic fetal antigens. As an important part of the innate immune system, some interesting changes have also taken place in complement system during pregnancy. The complement proteins are highly expressed in placenta, and their split products are increased. They are tuned in maintain placental immunity and structural homeostasis. An abundance of evidence shew that complement protein deficiency lead to autoimmunity disease and pathological pregnancy marked by excessive inflammation. Although complement suppressing strategies have been proven effective in treating some pathological pregnancy in individual case studies. we should take the dual role of the complement into consideration that fully and completely inhibit of complement may not be a wise choice.