Complement genes strongly predict recurrence and graft outcome in adult renal transplant recipients with atypical hemolytic and uremic syndrome

Recurrent complement-mediated Hemolytic uremic syndrome after kidney transplantation

Hereditary forms of hemolytic uremic syndrome (HUS), formerly known as atypical HUS, typically involve mutations in genes encoding for components of the alternative pathway of complement, therefore they are often referred to as complement-mediated HUS (cHUS). This condition has a high risk of recurrence in the transplanted kidney, leading to accelerated graft loss. The availability of anti-complement component C5 antibody eculizumab has enabled successful transplantation with a notably reduced recurrence rate and improved prognosis. Open questions are related to the potential for complement inhibitor discontinuation, ideal timing of treatment withdrawal, and patient selection based on genetic abnormalities. Our review delves into the pathophysiology, classification, genetic predispositions, and management strategies for cHUS in the native and transplant kidneys.

"Eculizumab First" in the Management of Posttransplant Thrombotic Microangiopathy

Introduction

Posttransplant thrombotic microangiopathy (PT-TMA) is an uncommon event that characterizes approximately 3% to 14% of kidney transplants (KTs), and that is associated with a higher risk of delayed graft function and graft loss. PT-TMA occurs more frequently within the first 3 months after transplant and can be a manifestation of de novo disease or the recurrence of previous atypical hemolytic uremic syndrome (aHUS). Abnormalities in complement regulation genes could explain the increased susceptibility of some patients to PT-TMA. Eculizumab is a humanized monoclonal antibody that inhibits the formation of the membrane attack complex C5b-9. The aim of this study is to evaluate the efficacy of eculizumab as treatment for PT-TMA.

Methods

We retrospectively analyzed clinical records of 45 KT patients who received eculizumab immediately after the clinical diagnosis of PT-TMA.

Results

Kidney biopsy was performed in 91.1% of patients, and complement genetic study was performed in 64.4%. Of the kidney biopsies, 85.4% showed signs of TMA; genetic analysis revealed 1 pathogenetic variant, 2 variants of uncertain significance, 1 likely benign variant, 8 risk polymorphisms, and 27 risk haplotypes. After 2 weeks from the treatment starting, hemoglobin and platelets significantly increased. A remarkable improvement in kidney function was also observed. After 6 months, 28.8% of patients had a complete renal recovery whereas 44.4% had a partial recovery.

Conclusion

This is, to our knowledge, the largest series of KT patients with PT-TMA treated with eculizumab. These data suggest that eculizumab is associated with a normalization of hemolysis indices and an important and progressive improvement of graft function.

Ex Vivo Test of Complement Dysregulation in Atypical Hemolytic Uremic Syndrome Kidney Transplant patients: A Pilot Study

Introduction

In 2014, a complement assay, which evaluates C5b-9 deposition on endothelial cells, was proposed as a biomarker for atypical hemolytic uremic syndrome (aHUS). Early diagnosis and/or prediction of aHUS (relapse) is pivotal in aHUS kidney transplant recipients who do not receive eculizumab prophylaxis.

Methods

In this pilot study, serum samples of transplanted patients with aHUS in remission without eculizumab and patients with other primary kidney diseases (controls) were blinded and evaluated in the complement assay.

Results

We included 13 patients with aHUS (4 males, 9 females) of median age of 54 years (range: 35-69) and median of 5.9 years (range: 0.25-14.1) after transplantation; and 13 controls (7 males, 6 females) of median age of 42 years (range: 27-60) and median of 5.8 years (range: 1.6-11.7) after transplantation. There were no significant differences in C5b-9 deposits between patients with aHUS and controls on resting cells (median of 136% [range: 93%-382%] and 121% [range: 75%-200%], respectively) and activated cells (median of 196% [range: 99%-388%] and 170% [range: 113%-260%], respectively). Three patients with aHUS and 4 controls showed elevated C5b-9 deposits on resting cells, which should correspond to active aHUS. None of these patients had laboratory signs of thrombotic microangiopathy (TMA). During follow-up (15.8 months, range: 6-21), estimated glomerular filtration rate remained stable in all. In 5 patients with aHUS with a genetic variant, no increase in C5b-9 deposits was found on activated endothelial cells, which contrasts with the literature suggesting that the test should identify carriers of a genetic variant.

Conclusion

Our data question the routine use of the ex vivo complement assay in kidney transplant patients. Future studies should evaluate the test characteristics of assay in kidney transplant patients.

Recommendations for the individualised management of atypical hemolytic uremic syndrome in adults

Background

Despite significant advances in therapeutic management of atypical hemolytic uremic syndrome (aHUS), guidelines are not timely updated and achieving a consensus on management recommendations remains a topic of ongoing discussion.

Methods

A Scientific Committee with five experts was set up. A literature review was conducted and publications addressing the classification of aHUS, patient profiles and therapeutic approach were selected. Recommendations were proposed at an initial meeting, evaluated through an online questionnaire and validated during a second meeting.

Results

Patients with confirmed or clear suspicion of aHUS should be treated with C5 inhibitors within 24 h of the diagnosis or suspicion of aHUS. Treatment monitoring and the decision to interrupt treatment should be individualised according to the risk of relapse and each patient's evolution. aHUS with a genetic variant or associated with pregnancy should be treated for at least 6-12 months; de novo aHUS associated with kidney transplant until renal function is recovered and genetic variants are ruled out; aHUS associated with malignant hypertension until genetic variants are ruled out; aHUS associated with non-kidney transplant, autoimmune diseases, infection-or drug-induced until the thrombotic microangiopathy is resolved. Patients with a high risk of relapse should be treated for longer than 6-12 months.

Conclusion

These recommendations provides physicians who are not familiar with the disease with recommendations for the management of aHUS in adults. The experts who participated advocate early treatment, maintenance for at least 6-12 months and treatment interruption guided by genetic background, trigger factors, risk of relapse and evolution.

The role of complement in kidney disease

The complement cascade comprises soluble and cell surface proteins and is an important arm of the innate immune system. Once activated, the complement system rapidly generates large quantities of protein fragments that are potent mediators of inflammatory, vasoactive and metabolic responses. Although complement is crucial to host defence and homeostasis, its inappropriate or uncontrolled activation can also drive tissue injury. For example, the complement system has been known for more than 50 years to be activated by glomerular immune complexes and to contribute to autoimmune kidney disease. Notably, the latest research shows that complement is also activated in kidney diseases that are not traditionally thought of as immune-mediated, including haemolytic-uraemic syndrome, diabetic kidney disease and focal segmental glomerulosclerosis. Several complement-targeted drugs have been approved for the treatment of kidney disease, and additional anti-complement agents are being investigated in clinical trials. These drugs are categorically different from other immunosuppressive agents and target pathological processes that are not effectively inhibited by other classes of immunosuppressants. The development of these new drugs might therefore have considerable benefits in the treatment of kidney disease.

Rare Variants in Complement Gene in C3 Glomerulopathy and Immunoglobulin-Mediated Membranoproliferative GN

BACKGROUND

C3 glomerulopathy and idiopathic immunoglobulin-mediated membranoproliferative GN (Ig-MPGN) are rare complement-mediated kidney diseases. Inherited forms of C3 glomerulopathy/Ig-MPGN are rarely described.

METHODS

Three hundred ninety-eight patients with C3 glomerulopathy ( n =296) or Ig-MPGN ( n =102) from a national registry were screened for three complement genes: factor H ( CFH ), factor I ( CFI ), and C3 . Patients with rare variant (minor allele frequency <0.1%) were included. Epidemiologic, clinical, and immunologic data at diagnosis and kidney outcomes of patients were retrospectively collected.

RESULTS

Fifty-three different rare variants, including 30 (57%), 13 (24%), and ten (19%) in CFH , CFI , and C3 variants, were identified in 66/398 (17%) patients. Thirty-eight (72%) variants were classified as pathogenic, including 20/30 (66%) and 11/13 (84%) variants in CFH and CFI , respectively, impairing synthesis of factor H or factor I regulators. Fifteen of 53 (27%) variants were of unknown significance. At diagnosis, 69% of patients were adult (median age of 31 years). With the exception of biologic stigma of thrombotic microangiopathy, which was more frequent in patients with CFI variants (5/14 [36%] versus 1/37 [3%] and 0% in the CFH group and C3 group, respectively, P < 0.001), the clinical and histologic features were similar among the three variants groups. The kidney outcome was poor regardless of the age at onset and treatment received. Sixty-five percent (43/66) of patients with rare variant reach kidney failure after a median delay of 41 (19-104) months, compared with 28% (55/195) after a median delay of 34 (12-143) months in the nonvariant group. Among 36 patients who received a kidney transplant, 2-year recurrence was frequent, occurring in 39% (12/31), without difference between variant groups, and led to graft failure in three cases.

CONCLUSIONS

In our cohort, 17% of C3 glomerulopathy/Ig-MPGN cases were associated with rare variants in the CFH , CFI , or C3 genes. In most cases, a quantitative deficiency in factor H or factor I was identified. The presence of a rare variant was associated with poor kidney survival.

PODCAST

This article contains a podcast at https://dts.podtrac.com/redirect.mp3/www.asn-online.org/media/podcast/CJASN/2023_11_08_CJN0000000000000252.mp3.

TMA in Kidney Transplantation

Thrombotic microangiopathy (TMA) is a rare and devastating complication of kidney transplantation, which often leads to graft failure. Posttransplant TMA (PT-TMA) may occur either de novo or as a recurrence of the disease. De novo TMA can be triggered by immunosuppressant drugs, antibody-mediated rejection, viral infections, and ischemia/reperfusion injury in patients with no evidence of the disease before transplantation. Recurrent TMA may occur in the kidney grafts of patients with a history of atypical hemolytic uremic syndrome (aHUS) in the native kidneys. Studies have shown that some patients with aHUS carry genetic abnormalities that affect genes that code for complement regulators (CFH, MCP, CFI) and components (C3 and CFB), whereas in 10% of patients (mostly children), anti-FH autoantibodies have been reported. The incidence of aHUS recurrence is determined by the underlying genetic or acquired complement abnormality. Although treatment of the causative agents is usually the first line of treatment for de novo PT-TMA, this approach might be insufficient. Plasma exchange typically resolves hematologic abnormalities but does not improve kidney function. Targeted complement inhibition is an effective treatment for recurrent TMA and may be effective in de novo PT-TMA as well, but it is necessary to establish which patients can benefit from different therapeutic options and when and how these can be applied.

Targeting the Complement Pathway in Kidney Transplantation

The complement system is paramount in the clearance of pathogens and cell debris, yet is increasingly recognized as a key component in several pathways leading to allograft injury. There is thus a growing interest in new biomarkers to assess complement activation and guide tailored therapies after kidney transplantation (KTx). C5 blockade has revolutionized post-transplant management of atypical hemolytic uremic syndrome, a paradigm of complement-driven disease. Similarly, new drugs targeting the complement amplification loop hold much promise in the treatment and prevention of recurrence of C3 glomerulopathy. Although unduly activation of the complement pathway has been described after brain death and ischemia reperfusion, any clinical attempts to mitigate the ensuing renal insults have so far provided mixed results. However, the intervention timing, strategy, and type of complement blocker need to be optimized in these settings. Furthermore, the fast-moving field of ex vivo organ perfusion technology opens new avenues to deliver complement-targeted drugs to kidney allografts with limited iatrogenic risks. Complement plays also a key role in the pathogenesis of donor-specific ABO- and HLA-targeted alloantibodies. However, C5 blockade failed overall to improve outcomes in highly sensitized patients and prevent the progression to chronic antibody-mediated rejection (ABMR). Similarly, well-conducted studies with C1 inhibitors in sensitized recipients yielded disappointing results so far, in part, because of subtherapeutic dosage used in clinical studies. The emergence of new complement blockers raises hope to significantly reduce the negative effect of ischemia reperfusion, ABMR, and nephropathy recurrence on outcomes after KTx.

ABO Incompatible Kidney Transplant in a Patient With Atypical Hemolytic Uremic Syndrome: Case Report

Kidney transplant (KT) or renal transplant is 1 of the preferred treatment options for patients with end-stage renal disease, but the presence of atypical hemolytic uremic syndrome (aHUS) further increases the risk of reoccurrence with graft rejection, and poor outcomes. ABO incompatibility further adds to the rejection risk. Here, we present a case of a young adult with a history of aHUS undergoing a successful ABO-incompatible (ABOi) renal transplant. ABO incompatibility desensitization was carried out, and the antibody titer was reduced to nullify the risk of rejection. Graft acceptance was facilitated by triple immunosuppression (steroid, tacrolimus, and mycophenolate mofetil), and 4-month serum creatinine follow-up indicated the absence of antibody-mediated rejection and recurrence of aHUS. This case demonstrates that in patients with aHUS, ABOi renal transplant can be performed successfully.

Isolated arterial mucoid intimal thickening lesion in early post-transplant kidney allograft biopsies

INTRODUCTION

Thrombotic microangiopathy (TMA) on kidney biopsy shows a variable combination of features: arterial mucoid intimal thickening, acellular closure of glomerular capillary loops, fragmented red blood cells, fibrin thrombi, and arterial fibrinoid necrosis. However, some early post-transplant kidney biopsies show only arterial mucoid intimal thickening. We aimed to elucidate the importance of this finding.

METHODS

We identified 19 biopsies showing isolated arterial mucoid intimal thickening and compared them with 22 bona fide TMA biopsies identified based on the pathological findings (excluding rejection) (2011-2020). Additionally, delayed graft function (DGF) (n = 237), and no DGF (control, n = 1314) groups were included for survival analysis.

RESULTS

Seven of 19 cases with isolated arterial mucoid intimal thickening showed peripheral blood schistocytes but no other systemic features of TMA. Eight patients underwent adjustments in maintenance immunosuppression (mainly calcineurin inhibitors). None of the cases progressed to full-blown TMA on consecutive biopsies. The overall and death-censored graft survival rates in this group were comparable to the DGF group, but significantly better than the TMA group (P = .005 and .04, respectively).

CONCLUSIONS

Isolated arterial mucoid intimal thickening in early post-transplant biopsies may be an early/mild form of TMA, probably requiring adjustment in immunosuppressive regimen. Careful exclusion of known causes of TMA, and donor-derived arterial injury are important.

Complement factor I: Regulatory nexus, driver of immunopathology, and therapeutic

Complement factor I (FI) is the nexus for classical, lectin and alternative pathway complement regulation. FI is an 88 kDa plasma protein that circulates in an inactive configuration until it forms a trimolecular complex with its cofactor and substrate whereupon a structural reorganization allows the catalytic triad to cleave its substrates, C3b and C4b. In keeping with its role as the master complement regulatory enzyme, deficiency has been linked to immunopathology. In the setting of complete FI deficiency, a consumptive C3 deficiency results in recurrent infections with encapsulated microorganisms. Aseptic cerebral inflammation and vasculitic presentations are also less commonly observed. Heterozygous mutations in the factor I gene (CFI) have been demonstrated to be enriched in atypical haemolytic uraemic syndrome, albeit with a very low penetrance. Haploinsufficiency of CFI has also been associated with decreased retinal thickness and is a strong risk factor for the development of age-related macular degeneration. Supplementation of FI using plasma purified or recombinant protein has long been postulated, however, technical difficulties prevented progression into clinical trials. It is only using gene therapy that CFI supplementation has reached the clinic with GT005 in phase I/II clinical trials for geographic atrophy.

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.

Assessing the Impact of Prophylactic Eculizumab on Renal Graft Survival in Atypical Hemolytic Uremic Syndrome

BACKGROUND

Atypical hemolytic uremic syndrome (aHUS) is a rare cause of end-stage kidney disease and associated with poor outcomes after kidney transplantation from early disease recurrence. Prophylactic eculizumab treatment at the time of transplantation is used in selected patients with aHUS. We report a retrospective case note review describing transplant outcomes in patients with aHUS transplanted between 1978 and 2017, including those patients treated with eculizumab.

METHODS

The National Renal Complement Therapeutics Centre database identified 118 kidney transplants in 86 recipients who had a confirmed diagnosis of aHUS. Thirty-eight kidney transplants were performed in 38 recipients who received prophylactic eculizumab. The cohort not treated with eculizumab comprised 80 transplants in 60 recipients and was refined to produce a comparable cohort of 33 transplants in 32 medium and high-risk recipients implanted since 2002. Complement pathway genetic screening was performed. Graft survival was censored for graft function at last follow-up or patient death. Graft survival without eculizumab treatment is described by complement defect status and by Kidney Disease: Improving Global Outcomes risk stratification.

RESULTS

Prophylactic eculizumab treatment improved renal allograft survival ( P = 0.006) in medium and high-risk recipients with 1-y survival of 97% versus 64% in untreated patients. Our data supports the risk stratification advised by Kidney Disease: Improving Global Outcomes.

CONCLUSIONS

Prophylactic eculizumab treatment dramatically improves graft survival making transplantation a viable therapeutic option in aHUS.

How I diagnose and treat atypical hemolytic uremic syndrome

Our understanding and management of atypical hemolytic uremic syndrome (aHUS) have dramatically improved in the last decade. aHUS has been established as a prototypic disease resulting from a dysregulation of the complement alternative C3 convertase. Subsequently, prospective nonrandomized studies and retrospective series have shown the efficacy of C5 blockade in the treatment of this devastating disease. C5 blockade has become the cornerstone of the treatment of aHUS. This therapeutic breakthrough has been dulled by persistent difficulties in the positive diagnosis of aHUS, and the latter remains, to date, a diagnosis by exclusion. Furthermore, the precise spectrum of complement-mediated renal thrombotic microangiopathy is still a matter of debate. Nevertheless, long-term management of aHUS is increasingly individualized and lifelong C5 blockade is no longer a paradigm that applies to all patients with this disease. The potential benefit of complement blockade in other forms of HUS, notably secondary HUS, remains uncertain.

Pharmacological Management of Atypical Hemolytic Uremic Syndrome in Pediatric Patients: Current and Future

Atypical hemolytic uremic syndrome is a thrombotic microangiopathy characterized by hemolysis, thrombocytopenia, and acute kidney injury, usually caused by alternative complement system overactivation due to pathogenic genetic variants or antibodies to components or regulatory factors in this pathway. Previously, a lack of effective treatment for this condition was associated with mortality, end-stage kidney disease, and the risk of disease recurrence after kidney transplantation. Plasma therapy has been used for atypical hemolytic uremic syndrome treatment with inconsistent results. Complement-blocking treatment changed the outcome and prognosis of patients with atypical hemolytic uremic syndrome. Early administration of eculizumab, a monoclonal C5 antibody, leads to improvements in hematologic, kidney, and systemic manifestations in patients with atypical hemolytic uremic syndrome, even with apparent dialysis dependency. Pre- and post-transplant use of eculizumab is effective in the prevention of atypical hemolytic uremic syndrome recurrence. Evidence on eculizumab use in secondary hemolytic uremic syndrome cases is controversial. Recent data favor the restrictive use of eculizumab in carefully selected atypical hemolytic uremic syndrome cases, but close monitoring for relapse after drug discontinuation is emphasized. Prophylaxis for meningococcal infection is important. The long-acting C5 monoclonal antibody ravulizumab is now approved for atypical hemolytic uremic syndrome treatment, enabling a reduction in the dosing frequency and improving the quality of life in patients with atypical hemolytic uremic syndrome. New strategies for additional and novel complement blockage medications in atypical hemolytic uremic syndrome are under investigation.

Alternative pathway diagnostics

Uncontrolled alternative pathway activation is the primary driver of several diseases, and it contributes to the pathogenesis of many others. Consequently, diagnostic tests to monitor this arm of the complement system are increasingly important. Defects in alternative pathway regulation are strong risk factors for disease, and drugs that specifically block the alternative pathway are entering clinical use. A range of diagnostic tests have been developed to evaluate and monitor the alternative pathway, including assays to measure its function, expression of alternative pathway constituents, and activation fragments. Genetic studies have also revealed many disease-associated variants in alternative pathway genes that predict the risk of disease and prognosis. Newer imaging modalities offer the promise of non-invasively detecting and localizing pathologic complement activation. Together, these various tests help in the diagnosis of disease, provide important prognostic information, and can help guide therapy with complement inhibitory drugs.

Eculizumab Rescue Therapy in Patients with Recurrent Atypical Hemolytic Uremic Syndrome After Kidney Transplantation

Introduction

Since 2016, kidney transplantation in patients with atypical hemolytic uremic syndrome (aHUS) in the Netherlands is performed without eculizumab prophylaxis. Eculizumab is given in case of posttransplant aHUS recurrence. Eculizumab therapy is monitored in the CUREiHUS study.

Methods

All participating kidney transplant patients who received eculizumab therapy for a suspected posttransplant aHUS recurrence were evaluated. Overall recurrence rate was monitored prospectively at Radboud University Medical Center.

Results

In the period from January 2016 until October 2020, we included 15 (12 females, 3 males; median age 42 years, range 24-66 years) patients with suspected aHUS recurrence after kidney transplantation in this study. The time interval to recurrence showed a bimodal distribution. Seven patients presented early after transplantation (median 3 months, range 0.3-8.8 months), with typical aHUS features: rapid loss of estimated glomerular filtration rate (eGFR) and laboratory signs of thrombotic microangiopathy (TMA). Eight patients presented late (median 46 months, range 18-69 months) after transplantation. Of these, only 3 patients had systemic TMA, whereas 5 patients presented with slowly deteriorating eGFR without systemic TMA. Treatment with eculizumab resulted in improvement or stabilization of eGFR in 14 patients. Eculizumab discontinuation was tried in 7 patients; however, it was successful only in 3. At the end of the follow-up (median 29 months, range 3-54 months after start of eculizumab), 6 patients had eGFR <30 ml/min per 1.73 m². Graft loss had occurred in 3 of them. Overall, aHUS recurrence rate without eculizumab prophylaxis was 23%.

Conclusions

Rescue treatment of posttransplant aHUS recurrence is effective; however, some patients suffer from irreversible loss of kidney function, likely caused by delayed diagnosis and treatment and/or too aggressive discontinuation of eculizumab. Physicians should be aware that recurrence of aHUS can present without evidence of systemic TMA.

The current therapeutic approach for anaemia after kidney transplant

PURPOSE OF REVIEW

Anaemia after kidney transplantation is a common finding with no uniform management guideline. Most approaches are derived from the chronic kidney disease (CKD) population. Recent advances for the treatment of anaemia in patients with CKD/End stage renal disease include hypoxia-inducible factor-prolyl hydroxylase inhibitor (HIF-PHi), a novel class of oral erythropoietin-stimulating agents (ESAs). We present relevant studies of HIF-PHi in the transplant population and its implications on the management of posttransplant anaemia.

RECENT FINDINGS

Data on HIF-PHi use in the kidney transplant population are promising. Limited data demonstrate a significant increase in haemoglobin, with a comparable safety profile to epoetin. Reported adverse effects include overcorrection and low iron stores.

SUMMARY

Current therapeutic approaches to anaemia in the kidney transplant population is mostly derived from the CKD population. More studies are needed on HIF-Phi, a novel class of ESAs that has thus far demonstrated promise in the kidney transplant population.

Safety and impact of eculizumab withdrawal in patients with atypical haemolytic uraemic syndrome: protocol for a multicentre, open-label, prospective, single-arm study

INTRODUCTION

Atypical haemolytic uraemic syndrome (aHUS) is a rare, life-threatening disease caused by excessive activation of part of the immune system called complement. Eculizumab is an effective treatment, controlling aHUS in 90% of patients. Due to the risk of relapse, lifelong treatment is currently recommended. Eculizumab treatment is not without problems, foremost being the risk of severe meningococcal infection, the burden of biweekly intravenous injections and the high cost.This paper describes the design of the Stopping Eculizumab Treatment Safely in aHUS trial that aims to establish whether a safety monitoring protocol, including the reintroduction of eculizumab for those who relapse, could be a safe, alternative treatment strategy for patients with aHUS.

METHODS AND ANALYSIS

This is a multicentre, non-randomised, open-label study of eculizumab withdrawal with continuous monitoring of thrombotic microangiopathy-related serious adverse events using the Bayes factor single-arm design. 30 patients will be recruited to withdraw from eculizumab and have regular blood and urine tests for 24 months, to monitor for disease activity. If relapse occurs, treatment will be restarted within 24 hours of presentation. 20 patients will remain on treatment and complete health economic questionnaires only. An embedded qualitative study will explore the views of participants.

ETHICS AND DISSEMINATION

A favourable ethical opinion and approval was obtained from the North East-Tyne & Wear South Research Ethics Committee. Outcomes will be disseminated via peer-reviewed articles and conference presentations.

TRIAL REGISTRATION NUMBER

EudraCT number: 2017-003916-37 and ISRCTN number: ISRCTN17503205.

Diagnosis and treatment of thrombotic microangiopathy

Thrombotic microangiopathy (TMA) is characterized by thrombocytopenia, microangiopathic haemolytic anaemia and end organ damage. TMAs have varying underlying pathophysiology and can therefore present with an array of clinical presentations. Renal involvement is common as the kidney is particularly susceptible to the endothelial damage and microvascular occlusion. TMAs require rapid assessment, diagnosis, and commencement of appropriate treatment due to the high morbidity and mortality associated with them. Ground-breaking research into the pathogenesis of TMAs over the past 20 years has driven the successful development of targeted therapeutics revolutionizing patient outcomes. This review outlines the clinical presentations, pathogenesis, diagnostic tests and treatments for TMAs.

Early graft loss due to acute thrombotic microangiopathy accompanied by complement gene variants in living-related kidney transplantation: case series report

Background

Recently, early graft loss has become very rare in living-related kidney transplantation (LKT) as a result of decreased risk of hyperacute rejection and improvements in immunosuppressive regimens. Post-transplant acute thrombotic microangiopathy (TMA) is a rare, multi-factorial disease that often occurs shortly after kidney transplantation and is usually resistant to treatment with dismal renal outcomes. The complement genetic variants may accelerate the development of TMA. However, the complement genetic test was seldom performed in unknown native kidney disease recipients scheduled for LKT.

Case presentation

We reported three cases of unknown native kidney diseases who had fulminant TMA in the allograft shortly after LKT. Both the donors and the recipients were noted to carry complement genetic variants, which were identified by genetic testing after transplantation. However, all recipients were refractory to treatment and had allograft loss within 3 months after LKT.

Conclusion

This case series highlights the suggestion to screen complement gene variants in both the donors and the recipients with unknown native kidney diseases scheduled for LKT.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12882-022-02868-7.

Pharmacotherapeutic options for the prevention of kidney transplant rejection: the evidence to date

INTRODUCTION

Although early rejection episodes are successfully controlled, the problem of unrecognized production of de novo anti HLA antibodies and associated chronic rejection still persists.

AREAS COVERED

In addition to the standard induction and maintenance therapy, we present a couple of new drugs as induction (Alemtuzumab), CNI free protocol (Belatacept, Sirolimus, Everolimus), maintenance treatment in transplant patients with various type of malignancies (T cell targeted immunomodulators blocking the immune checkpoints CTLA-4, PD1/PDL1) and TMA (aHUS) -eculizimab, and IL6 receptor antagonists in antibody mediated rejection (AMR).

EXPERT OPINION

There are couple of issues still preventing improvement in kidney transplant long-term outcomes with current and anticipated future immunosuppression: patient more susceptible to infection and CNI nephrotoxicity in kidneys obtained from elderly donors, highly sensitized patients with limited chances to get appropriate kidney and a higher risk for late AMR. A lower rate of CMV/BK virus infections has been observed in everolimus treated patients. Belatacept use has been justified only in EBV seropositive kidney transplants due to the increased risk of PTLD. Eculizumab upon recurrence of aHUS is a sole cost-effective option. A new IL-6 blocking drug (clazakizumab/tocilizumab) is promising option for prevention/treatment of AMR. Clinical experience in tailoring immunosuppression for as long as possible graft and patient survival is inevitable.

A Guide for Adult Nephrologists and Hematologists to Managing Atypical Hemolytic Uremic Syndrome and C3 Glomerulopathy in Teens Transitioning to Young Adults

Atypical hemolytic uremic syndrome and C3 glomerulopathy/immune complex membranoproliferative glomerulonephritis are ultra-rare chronic, complement-mediated diseases with childhood manifestation in a majority of cases. Transition of clinical care of patients from pediatric to adult nephrologists-typically with controlled disease in native or transplant kidneys in case of atypical hemolytic uremic syndrome and often with chronic progressive disease despite treatment efforts in case of C3 glomerulopathy/immune complex membranoproliferative glomerulonephritis-identifies a challenging juncture in the journey of these patients. Raising awareness for the vulnerability of this patient cohort; providing education on disease pathophysiology and management including the use of new, high-precision complement antagonists; and establishing an ongoing dialog of patients, families, and all members of the health care team involved on either side of the age divide will be inevitable to ensure optimal patient outcomes and a safe transition of these patients to adulthood.

Evaluation of Genetic Kidney Diseases in Living Donor Kidney Transplantation: Towards Precision Genomic Medicine in Donor Risk Assessment

Purpose of Review

To provide a comprehensive update on the role of genetic testing for the evaluation of kidney transplant recipient and living donor candidates.

Recent Findings

The evaluation of candidates for living donor transplantation and their potential donors occurs within an ever-changing landscape impacted by new evidence and risk assessment techniques. Criteria that were once considered contraindications to living kidney donation are now viewed as standard of care, while new tools identify novel risk markers that were unrecognized in past decades. Recent work suggests that nearly 10% of a cohort of patients with chronic/end-stage kidney disease had an identifiable genetic etiology, many whose original cause of renal disease was either unknown or misdiagnosed. Some also had an incidentally found genetic variant, unrelated to their nephropathy, but medically actionable. These patterns illustrate the substantial potential for genetic testing to better guide the selection of living donors and recipients, but guidance on the proper application and interpretation of novel technologies is in its infancy. In this review, we examine the utility of genetic testing in various kidney conditions, and discuss risks and unresolved challenges. Suggested algorithms in the context of related and unrelated donation are offered.

Summary

Genetic testing is a rapidly evolving strategy for the evaluation of candidates for living donor transplantation and their potential donors that has potential to improve risk assessment and optimize the safety of donation.

The role of properdin and Factor H in disease

The complement system consists of three pathways (alternative, classical, and lectin) that play a fundamental role in immunity and homeostasis. The multifunctional role of the complement system includes direct lysis of pathogens, tagging pathogens for phagocytosis, promotion of inflammatory responses to control infection, regulation of adaptive cellular immune responses, and removal of apoptotic/dead cells and immune complexes from circulation. A tight regulation of the complement system is essential to avoid unwanted complement-mediated damage to the host. This regulation is ensured by a set of proteins called complement regulatory proteins. Deficiencies or malfunction of these regulatory proteins may lead to pro-thrombotic hematological diseases, renal and ocular diseases, and autoimmune diseases, among others. This review focuses on the importance of two complement regulatory proteins of the alternative pathway, Factor H and properdin, and their role in human diseases with an emphasis on: (a) characterizing the main mechanism of action of Factor H and properdin in regulating the complement system and protecting the host from complement-mediated attack, (b) describing the dysregulation of the alternative pathway as a result of deficiencies, or mutations, in Factor H and properdin, (c) outlining the clinical findings, management and treatment of diseases associated with mutations and deficiencies in Factor H, and (d) defining the unwanted and inadequate functioning of properdin in disease, through a discussion of various experimental research findings utilizing in vitro, mouse and human models.

Complement Blockade Is a Promising Therapeutic Approach in a Subset of Critically Ill Adult Patients with Complement-Mediated Hemolytic Uremic Syndromes

Thrombotic microangiopathy (TMA) gathers consumptive thrombocytopenia, mechanical haemolytic anemia, and organ damage. Hemolytic uremic syndromes (HUS) are historically classified as primary or secondary to another disease once thrombotic thrombocytopenic purpura (TTP), Shiga-toxin HUS, and cobalamin C-related HUS have been ruled out. Complement genetics studies reinforced the link between complement dysregulation and primary HUS, contributing to reclassifying some pregnancy- and/or post-partum-associated HUS and to revealing complement involvement in severe and/or refractory hypertensive emergencies. By contrast, no firm evidence allows a plausible association to be drawn between complement dysregulation and Shiga-toxin HUS or other secondary HUS. Nevertheless, rare complement gene variants are prevalent in healthy individuals, thus providing an indication that an investigation into complement dysregulation should be carefully balanced and that the results should be cautiously interpreted with the help of a trained geneticist. Several authors have suggested reclassifying HUS in two entities, regardless of they are complement-mediated or not, since the use of eculizumab, an anti-C5 antibody, dramatically lowers the proportion of patients who die or suffer from end-stage renal disease within the year following diagnosis. Safety and the ideal timing of eculizumab discontinuation is currently under investigation, and the long-term consequences of HUS should be closely monitored over time once patients exit emergency departments.

Thrombotic microangiopathy in children

The syndrome of thrombotic microangiopathy (TMA) is a clinical-pathological entity characterized by microangiopathic hemolytic anemia, thrombocytopenia, and end organ involvement. It comprises a spectrum of underlying etiologies that may differ in children and adults. In children, apart from ruling out shigatoxin-associated hemolytic uremic syndrome (HUS) and other infection-associated TMA like Streptococcus pneumoniae-HUS, rare inherited causes including complement-associated HUS, cobalamin defects, and mutations in diacylglycerol kinase epsilon gene must be investigated. TMA should also be considered in the setting of solid organ or hematopoietic stem cell transplantation. In this review, acquired and inherited causes of TMA are described with a focus on particularities of the main causes of TMA in children. A pragmatic approach that may help the clinician tailor evaluation and management is provided. The described approach will allow for early initiation of treatment while waiting for the definitive diagnosis of the underlying TMA.

Recurrent Glomerular Disease after Kidney Transplantation: Diagnostic and Management Dilemmas

Recurrent glomerular disease after kidney transplant remains an important cause of allograft failure. Many of the different entities post-transplant still suffer from incomplete knowledge on pathophysiology, and therefore lack targeted and effective therapies. In this review, we focus on specific clinical dilemmas encountered by physicians in managing recurrent glomerular disease by highlighting new insights into the understanding and treatment of post-transplant focal segmental glomerulosclerosis, membranous nephropathy, atypical hemolytic uremic syndrome, C3 glomerulopathy, amyloid light-chain (AL) amyloidosis, and IgA nephropathy.

De Novo and Recurrent Thrombotic Microangiopathy After Renal Transplantation: Current Concepts in Management

Thrombotic microangiopathy is a well-recognized complication of kidney transplantation that leads frequently to allograft failure. This serious outcome can greatly depend on the underlying etiology and on the timing of therapeutic interventions. Thrombotic microangiopathy syndrome may occur with no previous history of thrombotic microangiopathy (that is, de novo thrombotic microangiopathy), mostly due to medica tions or infections. More frequently, it may recur after kidney transplant in patients with endstage renal failure due to atypical hemolytic uremic syndrome. However, for patients with Shiga-toxininduced hemolytic uremic syndrome, particularly pediatric patients, there is a favorable prognosis. A fundamental tool for management of this disease is genetic screening for abnormal mutations; this can recognize the suggested approach of therapy and may determine the outcome of the disease to a large extent. Although patients with complement factor H and I mutations have worse prognosis, other patients with membrane cofactor protein mutations, for example, have a more favorable prognosis. Accordingly, the plan of therapy can be tailored with a better chance of cure. Unfortunately, the successful use of the biological agent eculizumab, an anti-C5 agent, in some of these syndromes is largely impeded by its high cost, which is linked to its use as a life-long therapy. However, newly suggested therapeutic options may ameliorate this drawback.

Recurrent Glomerular Diseases in Renal Transplantation with Focus on Role of Electron Microscopy

Background

The common causes of renal transplant complications include active or chronic rejection process, infections, and toxicity but also recurrent or de novo diseases, which play an important role in affecting long-term graft function or graft loss.

Summary

Recurrent disease in renal transplantation is defined as recurrence of the original kidney disease leading to end-stage kidney disease. They comprise a heterogeneous group of predominantly glomerular and some tubulointerstitial and vascular lesions, which include primary kidney diseases (e.g., focal segmental glomerulosclerosis, membranous glomerulonephritis, and IgA nephropathy) or those secondary to systemic autoimmune, metabolic, and infectious processes that can range from subclinical to clinically overt acute, subacute, or chronic clinical presentations. In addition to the knowledge of prior renal disease and routine/periodic serum and urine testing for kidney function, a complete transplant renal biopsy examination is essential in the identification and differentiation of these diseases. The time of onset and severity of these diseases depend on the underlying etiopathogenetic mechanisms and the varied rates of recurrence in the early or late posttransplant period, often being modified by the current immunosuppressive protocols and other donor and recipient predisposing characteristics.

Key Messages

Transplant kidney biopsy findings provide diagnostic accuracy and prognostic information regarding the potential for reversibility along with detection of unsuspected or clinically symptomatic recurrent diseases, with any concomitant rejection process or toxicity, for appropriate therapeutic decision-making. Routine electron microscopy in transplant kidney biopsies is a valuable tool in recognizing fully developed or early/subtle features of evolving recurrent diseases, often during the subclinical phases, in for cause or surveillance allograft biopsies.

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.

Identifying Biomarkers from Transcriptomic Signatures in Renal Allograft Biopsies Using Deceased and Living Donors

The survival of transplant kidneys using deceased donors (DD) is inferior to living donors (LD). In this study, we conducted a whole-transcriptome expression analysis of 24 human kidney biopsies paired at 30 minutes and 3 months post-transplantation using DD and LD. The transcriptome profile was found significantly different between two time points regardless of donor types. There were 446 differentially expressed genes (DEGs) between DD and LD at 30 minutes and 146 DEGs at 3 months, with 25 genes common to both time points. These DEGs reflected donor injury and acute immune responses associated with inflammation and cell death as early as at 30 minutes, which could be a precious window of potential intervention. DEGs at 3 months mainly represented the changes of adaptive immunity, immunosuppressive treatment, remodeling or fibrosis via different networks and signaling pathways. The expression levels of 20 highly DEGs involved in kidney diseases and 10 genes dysregulated at 30 minutes were found correlated with renal function and histology at 12 months, suggesting they could be potential biomarkers. These genes were further validated by quantitative polymerase chain reaction (qPCR) in 24 samples analysed by microarray, as well as in a validation cohort of 33 time point unpaired allograft biopsies. This analysis revealed that SERPINA3, SLPI and CBF were up-regulated at 30 minutes in DD compared to LD, while FTCD and TASPN7 were up-regulated at both time points. At 3 months, SERPINA3 was up-regulated in LD, but down-regulated in DD, with increased VCAN and TIMP1, and decreased FOS, in both donors. Taken together, divergent transcriptomic signatures between DD and LD, and changed by the time post-transplantation, might contribute to different allograft survival of two type kidney donors. Some DEGs including FTCD and TASPN7 could be novel biomarkers not only for timely diagnosis, but also for early precise genetic intervention at donor preservation, implantation and post-transplantation, in particular to effectively improve the quality and survival of DD.

The Benefits of Complement Measurements for the Clinical Practice

The complement cascade is an evolutionary ancient innate immune defense system, playing a major role in the defense against infections. Its function in maintaining host homeostasis on activated cells has been emphasized by the crucial role of its overactivation in ever growing number of diseases, such as atypical hemolytic uremic syndrome (aHUS), autoimmune diseases as systemic lupus erythematosus (SLE), C3 glomerulopathies (C3GN), age-related macular degeneration (AMD), graft rejection, Alzheimer disease, and cancer, to name just a few. The last decade of research on complement has extended its implication in many pathological processes, offering new insights to potential therapeutic targets and asserting the necessity of reliable, sensitive, specific, accurate, and reproducible biomarkers to decipher complement role in pathology. We need to evaluate accurately which pathway or role should be targeted pharmacologically, and optimize treatment efficacy versus toxicity. This chapter is an introduction to the role of complement in human diseases and the use of complement-related biomarkers in the clinical practice. It is a part of a book intending to give reliable and standardized methods to evaluate complement according to nowadays needs and knowledge.

Inherited Kidney Complement Diseases

In the past 20 years, we have witnessed tremendous advances in our ability to diagnose and treat genetic diseases of the kidney caused by complement dysregulation. Staggering progress was realized toward a better understanding of the genetic underpinnings and pathophysiology of many forms of atypical hemolytic uremic syndrome (aHUS) and C3-dominant glomerulopathies that are driven by complement system abnormalities. Many of these seminal discoveries paved the way for the design and characterization of several innovative therapies, some of which have already radically improved patients' outcomes. This review offers a broad overview of the exciting developments that have occurred in the recent past, with a particular focus on single-gene (or Mendelian), complement-driven aHUS and C3-dominant glomerulopathies that should be of interest to both nephrologists and kidney researchers. The discussion is restricted to genes with robust associations with both aHUS and C3-dominant glomerulopathies (complement factor H, complement component 3, complement factor H-related proteins) or only aHUS (complement factor B, complement factor I, and membrane cofactor protein). Key questions and challenges are highlighted, along with potential avenues for future directions.

Hemolytic uremic syndrome and kidney transplantation in uncontrolled donation after circulatory death (DCD): A two-case report

Background: Hemolytic uremic syndrome (HUS) is a rare disease characterized by microangiopathic hemolysis, thrombocytopenia, and renal involvement. Complement-mediated atypical HUS (aHUS) is a result of genetic defects in the alternative complement pathway components or regulators. The introduction of eculizumab has improved renal and overall survival of aHUS patients. Nowadays, given organ shortage, it is necessary to consider kidney transplantation (KT) even in protocols with a high risk of HUS recurrence, such as from donation after circulatory death (DCD) donors. Here, we describe two patients with HUS who underwent a KT from an uncontrolled DCD (uDCD). Case summary: The first patient, affected by aHUS due to a heterozygous deletion in CFHR3-CFHR1 and a novel heterozygous variant in CFHR5 gene, underwent a KT with eculizumab prophylaxis. The patient did not experience a post-transplant aHUS recurrence. The second patient, who experienced an HUS episode characterized by a hypertensive crisis and with no underlying mutations in complement system genes, underwent a KT without eculizumab prophylaxis. At day 5, anti-complement treatment commenced due to hematological signs of thrombotic microangiopathy (TMA). After the introduction of eculizumab, we observed a stabilization of kidney function and hematological remission. Conclusion: We present herein two different patients with HUS who both underwent successful KT from uDCD donation under the umbrella of eculizumab therapy. Taking into account the importance of increasing the number of organs available for transplantation, uDCD could represent an additional resource in this subset of HUS patients.

Exploring the role of the complement system, endothelial injury, and microRNAs in thrombotic microangiopathy after kidney transplantation

Objective

We investigated whether the recipient’s complement system function, kidney graft endothelial ultrastructural injury, and microRNA (miRNA) expression before transplantation may be associated with the risk of posttransplant de novo thrombotic microangiopathy (TMA).

Methods

Complement system function assessment, histological and ultrastructural examination of preimplantation and kidney graft biopsies, and microRNA assessment were performed on kidney transplant recipients (KTRs) with de novo TMA.

Results

On the basis of the clinical course, histological findings, and miRNA patterns, the following two de novo TMA phenotypes were observed: a self-limiting disease that was localized to the kidney graft and a systemic disease that progressed to graft failure without timely treatment. Decreased alternative complement pathway activity and ultrastructural endothelial injury before transplantation were confirmed in all five KTRs and four of five KTRs, respectively, but they did not correlate with de novo TMA severity.

Conclusions

Alternative complement pathway abnormalities in KTRs and endothelial ultrastructural injury on preimplantation biopsy might be associated with de novo posttransplant TMA, although they did not predict posttransplant TMA severity (localized vs. systemic). The specific miRNA expression patterns in preimplantation kidney graft biopsies demonstrated a borderline statistically significant difference and might provide more accurate information on posttransplant TMA severity.

Complement testing in the clinical laboratory

The complement system is the human's first line of defense against microbial pathogens because of its important housekeeping and infection/inflammation roles. It is composed of a series of soluble and cell-bound proteins that are activated in a cascade effect, similar to the coagulation pathways. There are different pattern recognizing molecules that activate the complement system in response to stimuli or threats, acting through three initiation pathways: classical, lectin, and alternative. All three activation pathways converge at the C3 component and share the terminal pathway. The main outputs of the complement system action are lytic killing of microbes, the release of pro-inflammatory anaphylatoxins, and opsonization of targets. Laboratory testing is relevant in the setting of suspected complement deficiencies, as well as in the emerging number of diseases related to dysregulation (over-activation) of complement. Most common assays measure complement lytic activity and the different complement component concentrations. Specialized testing includes the evaluation of autoantibodies against complement components, activation fragments, and genetic studies. In this review, we cover laboratory testing for complement and the conditions with complement involvement, as well as current challenges in the field.

Transplantation in pediatric aHUS within the era of eculizumab therapy

aHUS is caused by the over-activation and dysregulation of the alternative complement pathway. Data regarding outcomes of pediatric aHUS patients after kidney transplantation are still very scarce. Accordingly, the aim of this study was to describe the clinical findings and outcomes of pediatric aHUS patients after renal transplantation. This is a retrospective, multicenter study including 12 patients from the national registry system. Among the 12 patients, eight had received prophylactic eculizumab and none of those patients (except one) had experienced aHUS recurrence during a median follow-up period of 58.5 (min-max, 4-94) months. Although eculizumab had been started on the day before transplantation in one of them, aHUS recurrence occurred during the transplantation procedure. Eculizumab had been stopped in only one patient who had no complement gene mutation after 35 months of therapy, and recurrence had not been observed during the 19 months of follow-up. In three patients, maintenance doses had been spaced out without any recurrence. One additional patient with anti-CFH antibody received only two doses of eculizumab for transplantation and had been followed for 46 months without aHUS recurrence. The remaining three patients had not received anti-C5 therapy and none of those patients experienced aHUS recurrence during a median follow-up period of 21 (min-max, 9-42) months. Prophylactic eculizumab is a safe and effective treatment for the prevention of aHUS recurrence. Eculizumab interval prolongation, discontinuation, and transplantation without eculizumab prophylaxis can be tried in selected patients with close follow-up.

Is the atypical hemolytic uremic syndrome risk polymorphism in Membrane Cofactor Protein MCPggaac relevant in kidney transplantation? A case report

aHUS is a rare disease characterized by episodes of TMA that frequently progresses to CKD and often recurs after KT. The most frequent cause of aHUS is defective regulation of complement activation because of genetic anomalies. Eculizumab interrupts the process of TMA and improves renal function. We describe one female patient with aHUS who debuted in 2005 at 3-mo-old with extrarenal manifestations and progressed to end-stage kidney disease (ESKD) within a year. Her family history included several affected members with similar bad outcomes. Our patient carries a strong aHUS genetic predisposition consisting in a pathogenic gain-of-function mutation in complement factor B concurrent with the MCP aHUS risk haplotype MCPggaac. She received a kidney transplant in 2011 without eculizumab prophylaxis. The graft, which was negative for the MCPggaac risk haplotype, had an unexpected excellent evolution without aHUS recurrence. Different retrospective studies have shown that the risk of aHUS recurrence after KT correlates well with the genetic load of aHUS risk factors. Knowing important contribution of the MCPggaac risk haplotype to the risk of developing aHUS in Factor B mutations carriers, we speculate whether the absence of this polymorphism in the graft that our patient received may have decreased the risk of aHUS recurrence after KT.

Clinical and Genetic Characteristics of Atypical Hemolytic Uremic Syndrome in Children: A Chinese Cohort Study

BACKGROUND

Atypical hemolytic uremic syndrome (aHUS) is a rare but critical illness. To this date, few studies have reported on the disease in Chinese children.

METHODS

We studied a Chinese pediatric cohort to delineate the clinical characteristics, genotypes, and prognosis. Ninety-one patients with aHUS were enrolled in this study.

RESULTS

Fifty-nine children (64.8%) had anti-complement-factor-H autoantibody-associated aHUS (anti-CFH aHUS). Of these children, 21 (46.7%) had complement factor-H-related protein 1 (CFHR1) homozygous deletion, and most patients with CFHR1 homozygous deletion also had complement factor-H-related protein 3 (CFHR3) homozygous deletions (76.2%). Using gene sequencing of 15 candidate genes, we identified 14 genetic variants in 46 aHUS patients, including 5 pathogenic or like pathogenic variants and 9 variants of uncertain significance. The average follow-up time was 46.1 ± 28 months. Among patients with anti-CFH aHUS, there was a correlation between CFHR1 homozygous deletion and patients with persistent proteinuria (odds ratio [OR] 6.954, 95% confidence interval [CI] 1.033-46.821, p = 0.046). As of the last follow-up, ESRD or deaths occurred in 3.6% of the children with anti-CFH aHUS and 26.7% of children with aHUS who were negative for anti-CFH.

CONCLUSIONS

Anti-complement-factor-H antibody positivity is the main cause of morbidity in Chinese children with aHUS. There may be a correlation between CFHR1 homozygous deletion and persistent proteinuria. Comprehensive assessment of anti-CFH antibodies and genetic variants is essential for the management of aHUS children.

Thrombotic Microangiopathy After Kidney Transplantation: An Underdiagnosed and Potentially Reversible Entity

Thrombotic microangiopathy is a rare but serious complication that affects kidney transplant recipients. It appears in 0.8–14% of transplanted patients and negatively affects graft and patient survival. It can appear in a systemic form, with hemolytic microangiopathic anemia, thrombocytopenia, and renal failure, or in a localized form, with progressive renal failure, proteinuria, or arterial hypertension. Post-transplant thrombotic microangiopathy is classified as recurrent atypical hemolytic uremic syndrome or de novo thrombotic microangiopathy. De novo thrombotic microangiopathy accounts for the majority of cases. Distinguishing between the 2 conditions can be difficult, given there is an overlap between them. Complement overactivation is the cornerstone of all post-transplant thrombotic microangiopathies, and has been demonstrated in the context of organ procurement, ischemia-reperfusion phenomena, immunosuppressive drugs, antibody-mediated rejection, viral infections, and post-transplant relapse of antiphospholipid antibody syndrome. Although treatment of the causative agents is usually the first line of treatment, this approach might not be sufficient. Plasma exchange typically resolves hematologic abnormalities but does not improve renal function. Complement blockade with eculizumab has been shown to be an effective therapy in post-transplant thrombotic microangiopathy, but it is necessary to define which patients can benefit from this therapy and when and how eculizumab should be used.

Prophylactic or Early Use of Eculizumab and Graft Survival in Kidney Transplant Recipients With Atypical Hemolytic Uremic Syndrome in the United States: Research Letter

Introduction:

Among kidney transplant recipients (KTRs) with end-stage kidney disease (ESKD) due to atypical hemolytic uremic syndrome (aHUS), recurrence is associated with poor allograft outcomes. We compared graft and patient survival of aHUS KTRs with and without prophylactic/early use of eculizumab, a monoclonal antibody that binds complement protein C5, at the time of transplantation.

Methods:

We conducted a retrospective cohort study using the United States Renal Data System. Out of 123 624 ESKD patients transplanted between January 1, 2008, and June 1, 2016, we identified 348 (0.28%) patients who had “hemolytic uremic syndrome” as the primary cause of ESKD. We then linked these patients to datasets containing the Healthcare Common Procedure Coding System (HCPCS) code for eculizumab infusion. Patients who received eculizumab prior to or within 30 days of transplant represented the exposure group. We calculated crude incidence rates and conducted exact logistic regression, adjusted for recipient age and sex, for the study outcomes of graft loss, death-censored graft loss, and mortality. We also estimated the average treatment effect (ATE) by propensity-score matching, to reduce the bias in the estimated treatment effect on graft loss.

Results:

Our final study cohort included 335 aHUS KTRs (23 received eculizumab, 312 did not), with a mean duration of follow-up of 5.8 ± 2.7 years. There were no significant differences in baseline demographic and clinical characteristics between the eculizumab versus non-eculizumab group. Patients who received prophylactic/early eculizumab were less likely to experience graft loss compared with those who did not receive eculizumab (0% vs 20%, P = .02), with an adjusted odds ratio of 0.13 (P = .02). In the propensity-score-matched sample, the ATE (eculizumab vs non-eculizumab) was −0.20 (95% confidence interval [CI] = −0.25 to −0.15, P < .001); thus, treatment was associated with an average of 20% reduction in graft loss. There was no significant difference in the risk of death between the 2 groups.

Conclusions:

Although there was no significant difference in the risk of death, prophylactic/early use of eculizumab was significantly associated with improved graft survival among aHUS KTRs. Given the high cost of eculizumab, randomized controlled trials are much needed to guide prophylactic strategies to prevent graft loss.

Low efficacy of vaccination against serogroup B meningococci in patients with atypical hemolytic uremic syndrome

Background: The C5 complement inhibitor eculizumab is first-line treatment in atypical hemolytic uremic syndrome (aHUS) going along with a highly increased risk of meningococcal infections. Serogroup B meningococci (MenB) are the most frequently encountered cause for meningococcal infections in Europe. Efficacy of the protein-based MenB-vaccine Bexsero in aHUS has not been determined and testing is only possible in patients off-treatment with eculizumab as a human complement source is required.

Methods: Patients with aHUS were vaccinated with two doses of the protein-based MenB-vaccine Bexsero. Serum bactericidal antibody (SBA) titers against factor H binding protein (fHbp) of MenB were determined in 14 patients with aHUS off-treatment with eculizumab.

Results: Only 50% of patients showed protective human serum bactericidal antibody (hSBA) titers (≥1:4) against MenB following two vaccinations. Bactericidal antibody titers were relatively low (≤1:8) in three of seven patients with protective titers. While 71% of patients were on immunosuppressive treatment for either thrombotic microangiopathy or renal transplantation at either first or second vaccination, all four patients not receiving any immunosuppressive treatment showed protective bactericidal antibody response. Time between second vaccination and titer measurement was not significantly different between patients with protective titers compared with those with non-protective titers, while time between first and second vaccination was significantly longer in patients with protective titers going along with a tendency for reduction in immunosuppressive treatment.

Conclusions: Efficacy of vaccination against MenB is insufficient in patients with aHUS. Response to vaccination seems to be hampered by immunosuppression. Therefore, implementation of adequate antibiotic prophylaxis seems pivotal.

KDIGO Clinical Practice Guideline on the Evaluation and Management of Candidates for Kidney Transplantation

The 2020 Kidney Disease: Improving Global Outcomes (KDIGO) Clinical Practice Guideline on the Evaluation and Management of Candidates for Kidney Transplantation is intended to assist health care professionals worldwide who evaluate and manage potential candidates for deceased or living donor kidney transplantation. This guideline addresses general candidacy issues such as access to transplantation, patient demographic and health status factors, and immunological and psychosocial assessment. The roles of various risk factors and comorbid conditions governing an individual's suitability for transplantation such as adherence, tobacco use, diabetes, obesity, perioperative issues, causes of kidney failure, infections, malignancy, pulmonary disease, cardiac and peripheral arterial disease, neurologic disease, gastrointestinal and liver disease, hematologic disease, and bone and mineral disorder are also addressed. This guideline provides recommendations for evaluation of individual aspects of a candidate's profile such that each risk factor and comorbidity are considered separately. The goal is to assist the clinical team to assimilate all data relevant to an individual, consider this within their local health context, and make an overall judgment on candidacy for transplantation. The guideline development process followed the Grades of Recommendation Assessment, Development, and Evaluation (GRADE) approach. Guideline recommendations are primarily based on systematic reviews of relevant studies and our assessment of the quality of that evidence, and the strengths of recommendations are provided. Limitations of the evidence are discussed with differences from previous guidelines noted and suggestions for future research are also provided.

Functional and Genetic Landscape of Complement Dysregulation Along the Spectrum of Thrombotic Microangiopathy and its Potential Implications on Clinical Outcomes

Introduction

The syndromes of thrombotic microangiopathy (TMA) are diverse and represent severe endothelial damage caused by various mechanisms. The complement system plays a major role in a subset of patients with TMA, and its recognition is of clinical importance because it guides choice and duration of treatment.

Methods

We studied a well-defined cohort of patients with TMA and hypothesized that assessment of serum-induced ex vivo C5b9 formation on the endothelium and screening for rare variants in complement genes can better categorize TMA.

Results

Massive ex vivo C5b9 formation was found in all patients with primary atypical hemolytic uremic syndrome (n/N = 11/11) and in 59% of patients with TMA and coexisting conditions (n/N = 30/51). Massive ex vivo C5b9 formation was associated with rare genetic variants (45% [n/N = 20/44] vs. 0% [n/N = 0/21] patients with normal ex vivo C5b9 formation; P < 0.001). Massive ex vivo C5b9 formation was associated with favorable renal response to therapeutic complement inhibition in patients with TMA and coexisting conditions (86% [n/N = 12/14] vs. 31% [n/N = 5/16] of untreated patients; P < 0.001), indicating complement-mediated TMA rather than secondary disease. Among treated patients, the odds ratio for 1-year kidney survival was 12.0 (95% confidence interval 1.2-115.4). TMA recurrence was linked to rare genetic variants in all cases. Patients with normal ex vivo C5b9 formation had an acute, nonrelapsing form of TMA.

Conclusions

Ex vivo C5b9 formation and genetic testing appears to categorize TMAs into different groups because it identifies complement as a driving factor of disease, with potential therapeutic and prognostic implications.

Atypical hemolytic and uremic syndrome due to C3 mutation in pancreatic islet transplantation: a case report

Background

We here report on the first observation of a C3 mutation that is related to atypical hemolytic and uremic syndrome (aHUS), which occurred in a pancreatic islet transplant patient. Immunosuppressive treatments, such as calcineurin inhibitors, have been linked to undesirable effects like nephrotoxicity.

Case presentation

A 40-year-old man with brittle diabetes, who was included in the TRIMECO trial, became insulin-independent 2 months after pancreatic islet transplantation. About 15 months after islet transplantation, the patient exhibited acute kidney injury due to aHUS. Despite plasma exchange and eculizumab treatment, the patient developed end-stage renal disease.

A genetic workup identified a missense variant (p.R592Q) in the C3 gene. In vitro, this C3 variant had defective Factor I proteolytic activity with membrane proteins as cofactor proteins, which was thus classified as pathogenic. About 1 year after the aHUS episode, kidney transplantation was carried out under the protection of the specific anti-C5 monoclonal antibody eculizumab. The patient had normal kidney function, with preserved pancreatic islet function 4 years later.

Conclusions

Pancreatic islet transplantation could have triggered this aHUS episode, but this link needs to be clarified. Although prophylactic eculizumab maintains kidney allograft function, its efficacy still needs to be studied in larger populations.

Atypical Hemolytic Uremic Syndrome: New Challenges in the Complement Blockage Era

Atypical hemolytic uremic syndrome (aHUS) is a rare cause of thrombotic microangiopathy (TMA), characterized by microangiopathic hemolytic anemia, consumptive thrombocytopenia, and multisystem end organ involvement, most commonly affecting the kidney. Diagnosis is clinical, after exclusion of other TMA causes. Primary aHUS arises from genetic abnormalities, resulting in uncontrolled complement activity, while a variety of clinical scenarios cause secondary aHUS, including infection, pregnancy, malignancy, autoimmune disease, and medications. They can also induce a temporary complement deregulation with an overlap between both scenarios, which can make differential diagnosis difficult. Primary aHUS can be sporadic or familial and is associated with a high rate of progression to ESRD. Many aHUS patients relapse in the native or transplanted kidneys, leading to kidney failure. The introduction of eculizumab has changed the prognosis of aHUS, by inducing hematologic remission, improving or stabilizing kidney functions, and preventing graft failure. The early institution of appropriate therapy can prevent multiorgan damage, so is essential to recognize and differentiate the TMA syndromes. Eculizumab is considered now the first-line treatment, and it is recommended lifelong therapy. However, the high cost of therapy has led to make efforts to develop precise complement functional and genetic studies that help physicians to determine the appropriate duration of eculizumab therapy. Nowadays, more studies are needed to select candidates to adjustment of therapy.