Successful plasma therapy for atypical hemolytic uremic syndrome caused by factor H deficiency owing to a novel mutation in the complement cofactor protein domain 15

The 4 functional segments of Factor H: Role in physiological target recognition and contribution to disease

Factor H controls proximal complement activation, and its dysfunction leads to diseases that often manifest in the kidney. Structural and functional analyses have identified 4 distinct functional segments: an N-terminal regulatory unit, a cell binding unit, a segment with combined low-affinity C3b and heparin sites, and a C-terminal recognition or sensor unit with overlapping C3b/C3d and heparin sites. Three segments are linked to diseases. The regulatory segment is affected in C3 glomerulopathy and antineutrophil cytoplasmic antibody-associated vasculitis. The second segment includes the Y402H polymorphism of age-related macular degeneration, is associated with different types of cancer, and is targeted by pathogens. The C-terminal sensor segment is involved in atypical hemolytic uremic syndrome, in FHR1:FHR3 deficient and autoantibody-positive hemolytic uremic syndrome form and is exploited by pathogens. Factor H function is modulated by Factor H like protein 1 and FHR1, 2 plasma proteins that share segments with Factor H. This interplay is critical for fine-tuning local complement. Understanding Factor H's physiological role, as well as the impact of its absence, mutations, or autoantibody targeting, provides insights into disease mechanisms and provides opportunities for therapeutic intervention by using full-length Factor H, its fragments, or complement-modulatory compounds.

Successfully treated C3 glomerulopathy in which protein and genetic analyses were useful for diagnosis

C3 glomerulopathy is a rare disease that results in nephritis due to complement dysregulation and is characterized by C3 deposition in the glomerulus. Dysregulation of the alternative pathway underlies the pathogenesis, but activation of the terminal pathway is also common. The disease is often caused by acquired rather than genetic factors, i.e., autoantibodies against C3 or C5 converting enzyme (convertase) and other complement-related proteins. We report a case of C3 glomerulopathy diagnosed by renal biopsy that responded well to corticosteroids and went into complete remission within two months. Analysis of complements and complement-related proteins revealed a low level of C3 and a high level of soluble terminal pathway protein complex (sC5b-9). Under genetic analysis about complement-related genes, no pathogenic variant was observed. Based on these findings, we diagnosed this patient with C3 glomerulopathy with autoantibodies. Corticosteroids had a marked effect, which also supports this speculation. Analyses of complements and complement-related proteins, and genetic variants may be useful in understanding the pathogenesis of C3 glomerulopathy and in selecting treatment options.

C3 glomerulopathy: a kidney disease mediated by alternative pathway deregulation

C3 glomerulopathy (C3G) is an ultra-rare complement-mediated kidney disease caused by to the deregulation of the alternative pathway (AP) of proximal complement. Consequently, all effector loops of the complement are active and can lead to pathologies, such as C3a- and C5a-mediated inflammation, C3b opsonization, surface C3b-mediated AP C3 convertase assembly, C3 cleavage product deposition in the glomerulus, and lytic C5b-9/MAC cell damage. The most common pathologic mechanisms are defective chronic alternative pathway deregulation, mostly occurring in the plasma, often causing C3 consumption, and chronic complement-mediated glomerular damage. C3G develops over several years, and loss of renal function occurs in more than 50% of patients. C3G is triggered by both genetic and autoimmune alterations. Genetic causes include mutations in individual complement genes and chromosomal variations in the form of deletions and duplications affecting genes encoding complement modulators. Many genetic aberrations result in increased AP C3 convertase activity, either due to decreased activity of regulators, increased activity of modulators, or gain-of-function mutations in genes encoding components of the convertase. Autoimmune forms of C3G do also exist. Autoantibodies target individual complement components and regulators or bind to neoepitopes exposed in the central alternative pathway C3 convertase, thereby increasing enzyme activity. Overactive AP C3 convertase is common in C3G patients. Given that C3G is a complement disease mediated by defective alternative pathway action, complement blockade is an emerging concept for therapy. Here, we summarize both the causes of C3G and the rationale for complement inhibition and list the inhibitors that are being used in the most advanced clinical trials for C3G. With several inhibitors in phase II and III trials, it is expected that effectice treatment for C3G will become availabe in the near future.

Promotion of an Antitumor Immune Program by a Tumor-specific, Complement-activating Antibody

Tumor-targeting Abs can be used to initiate an antitumor immune program, which appears essential to achieve a long-term durable clinical response to cancer. We previously identified an anti-complement factor H (CFH) autoantibody associated with patients with early-stage non-small cell lung cancer. We cloned from their peripheral B cells an mAb, GT103, that specifically recognizes CFH on tumor cells. Although the underlying mechanisms are not well defined, GT103 targets a conformationally distinct CFH epitope that is created when CFH is associated with tumor cells, kills tumor cells in vitro, and has potent antitumor activity in vivo. In the effort to better understand how an Ab targeting a tumor epitope can promote an effective antitumor immune response, we used the syngeneic CMT167 lung tumor C57BL/6 mouse model, and we found that murinized GT103 (mGT103) activates complement and enhances antitumor immunity through multiple pathways. It creates a favorable tumor microenvironment by decreasing immunosuppressive regulatory T cells and myeloid-derived suppressor cells, enhances Ag-specific effector T cells, and has an additive antitumor effect with anti-PD-L1 mAb. Furthermore, the immune landscape of tumors from early-stage patients expressing the anti-CFH autoantibody is associated with an immunologically active tumor microenvironment. More broadly, our results using an mAb cloned from autoantibody-expressing B cells provides novel, to our knowledge, mechanistic insights into how a tumor-specific, complement-activating Ab can generate an immune program to kill tumor cells and inhibit tumor growth.

Anti-complement factor H (CFH) autoantibodies could delay pristane-induced lupus nephritis

PURPOSE

Anti-complement factor H (CFH) autoantibodies could be detected in lupus and its significance remained to be elucidated. Herein, we aimed to explore the roles of anti-CFH autoantibodies based on pristane-induced lupus mice.

METHODS

Twenty-four female Balb/c mice were randomly divided into four groups, with one group injected with pristane (pristane group), one group with pristane and then human CFH (hCFH) (pristane-CFH group) 3 times, and the other two as vertical controls, PBS group and PBS-CFH group. Histopathological analysis was performed six months after pristane administration. Levels of hCFH, anti-CFH autoantibodies and anti-dsDNA antibody were detected. Murine IgG (mIgG) were purified and cross-reactivity, epitopes, subclasses and functional analysis were further evaluated in vitro.

RESULTS

Immunization with hCFH and subsequent development of anti-CFH autoantibodies significantly attenuated nephritis of pristane-induced lupus, including lower levels of urinary protein and serum creatinine, decreased levels of serum anti-dsDNA antibody, greatly ameliorated renal histopathologic damage, decreased IgG, complements (C1q, C3) deposits and lower inflammatory factor (IL-6) expression in glomerulus. Furthermore, the purified mIgG (contained anti-CFH autoantibodies) could recognize both hCFH and murine CFH, and the epitopes were predominantly located in hCFH short consensus repeats (SCRs) 1-4, 7 and 11-14. The IgG subclasses were predominant IgG1. The autoantibodies could enhance the binding between hCFH and C3b, and increase factor I mediated-C3b lysis in vitro.

CONCLUSION

Our results suggested that anti-CFH autoantibodies could attenuate pristane-induced lupus nephritis by increasing bio-functions of CFH on regulating complement activation and controlling inflammation.

An Interdisciplinary Diagnostic Approach to Guide Therapy in C3 Glomerulopathy

Since the re-classification of membranoproliferative glomerulonephritis the new disease entity C3 glomerulopathy is diagnosed if C3 deposition is clearly dominant over immunoglobulins in immunohistochemistry or immunofluorescence. Although this new definition is more orientated at the pathophysiology as mediated by activity of the alternative complement pathway C3 glomerulopathy remains a heterogenous group of disorders. Genetic or autoimmune causes are associated in several but not in all patients with this disease. However, prognosis is poorly predictable, and clinicians cannot directly identify patients that might benefit from therapy. Moreover, therapy may range from supportive care alone, unspecific immune suppression, plasma treatment, or plasma exchange to complement inhibition. The current biopsy based diagnostic approaches sometimes combined with complement profiling are not sufficient to guide clinicians neither (i) whether to treat an individual patient, nor (ii) to choose the best therapy. With this perspective, we propose an interdisciplinary diagnostic approach, including detailed analysis of the kidney biopsy for morphological alterations and immunohistochemical staining, for genetic analyses of complement genes, complement activation patterning in plasma, and furthermore for applying novel approaches for convertase typing and complement profiling directly in renal tissue. Such a combined diagnostic approach was used here for a 42-year-old female patient with a novel mutation in the Factor H gene, C3 glomerulopathy and signs of chronic endothelial damage. We present here an approach that might in future help to guide therapy of renal diseases with relevant complement activation, especially since diverse new anti-complement agents are under clinical investigation.

Mathematical Modeling of Complement Pathway Dynamics for Target Validation and Selection of Drug Modalities for Complement Therapies

Motivation: The complement pathway plays a critical role in innate immune defense against infections. Dysregulation between activation and regulation of the complement pathway is widely known to contribute to several diseases. Nevertheless, very few drugs that target complement proteins have made it to the final regulatory approval because of factors such as high concentrations and dosing requirements for complement proteins and serious side effects from complement inhibition.

Methods: A quantitative systems pharmacology (QSP) model of the complement pathway has been developed to evaluate potential drug targets to inhibit complement activation in autoimmune diseases. The model describes complement activation via the alternative and terminal pathways as well as the dynamics of several regulatory proteins. The QSP model has been used to evaluate the effect of inhibiting complement targets on reducing pathway activation caused by deficiency in factor H and CD59. The model also informed the feasibility of developing small-molecule or large-molecule antibody drugs by predicting the drug dosing and affinity requirements for potential complement targets.

Results: Inhibition of several complement proteins was predicted to lead to a significant reduction in complement activation and cell lysis. The complement proteins that are present in very high concentrations or have high turnover rates (C3, factor B, factor D, and C6) were predicted to be challenging to engage with feasible doses of large-molecule antibody compounds (≤20 mg/kg). Alternatively, complement fragments that have a short half-life (C3b, C3bB, and C3bBb) were predicted to be challenging or infeasible to engage with small-molecule compounds because of high drug affinity requirements (>1 nM) for the inhibition of downstream processes. The drug affinity requirements for disease severity reduction were predicted to differ more than one to two orders of magnitude than affinities needed for the conventional 90% target engagement (TE) for several proteins. Thus, the QSP model analyses indicate the importance for accounting for TE requirements for achieving reduction in disease severity endpoints during the lead optimization stage.

Uncommon Presentation of Atypical Hemolytic Uremic Syndrome: A Case Report

Atypical hemolytic uremic syndrome (aHUS) is an ultra-rare disease characterized by microangiopathic hemolytic anemia, thrombocytopenia and renal damage. Its presentation as nephrotic syndrome (NS) during first year of life is uncommon; we describe a child with clinical and laboratory findings of NS whose renal biopsy revealed thrombotic microangiopathy (TMA). A previously healthy 4-month-old male was admitted with severe dehydration, diarrhea and anuria. Laboratory results showed electrolyte disturbances, increased serum creatinine, anemia without schistocytes, thrombocytosis, normal lactic dehydrogenase (LDH) levels, hypoalbuminemia hypercholesterolemia and decreased C3 levels. After rehydration hematuria and massive proteinuria were also documented and an initial diagnosis of NS of the first year was established. Studies seeking for infectious agents were negative. During hospitalization he continued to be oligo-anuric needing dialysis and a renal biopsy was performed, which showed TMA findings. We here considered the diagnosis of aHUS and started plasma infusions as a bridge until starting eculizumab. After two infusions urine output improved leading to discontinuation dialysis. The diagnoses of STEC infection and thrombocytopenic thrombotic purpura were ruled out. Factor B, H, I and properdin levels were normal. Antibodies against CFH negative were negative. Screening for genes causative of aHUS detected a heterozygous variant in CFHR3 of uncertain significance. On day 20, treatment was switched to eculizumab, which induced a progressive remission of the NS. This case outlines the need for a heightened diagnosis suspicion of this already rare disease since early initiation of eculizumab therapy improves its prognosis.

Murine Factor H Co-Produced in Yeast With Protein Disulfide Isomerase Ameliorated C3 Dysregulation in Factor H-Deficient Mice

Recombinant human factor H (hFH) has potential for treating diseases linked to aberrant complement regulation including C3 glomerulopathy (C3G) and dry age-related macular degeneration. Murine FH (mFH), produced in the same host, is useful for pre-clinical investigations in mouse models of disease. An abundance of FH in plasma suggests high doses, and hence microbial production, will be needed. Previously, Pichia pastoris produced useful but modest quantities of hFH. Herein, a similar strategy yielded miniscule quantities of mFH. Since FH has 40 disulfide bonds, we created a P. pastoris strain containing a methanol-inducible codon-modified gene for protein-disulfide isomerase (PDI) and transformed this with codon-modified DNA encoding mFH under the same promoter. What had been barely detectable yields of mFH became multiple 10s of mg/L. Our PDI-overexpressing strain also boosted hFH overproduction, by about tenfold. These enhancements exceeded PDI-related production gains reported for other proteins, all of which contain fewer disulfide-stabilized domains. We optimized fermentation conditions, purified recombinant mFH, enzymatically trimmed down its (non-human) N-glycans, characterised its functions in vitro and administered it to mice. In FH-knockout mice, our de-glycosylated recombinant mFH had a shorter half-life and induced more anti-mFH antibodies than mouse serum-derived, natively glycosylated, mFH. Even sequential daily injections of recombinant mFH failed to restore wild-type levels of FH and C3 in mouse plasma beyond 24 hours after the first injection. Nevertheless, mFH functionality appeared to persist in the glomerular basement membrane because C3-fragment deposition here, a hallmark of C3G, remained significantly reduced throughout and beyond the ten-day dosing regimen.

C3(H2O) prevents rescue of complement-mediated C3 glomerulopathy in Cfh-/- Cfd-/- mice

Therapeutic complement inhibition is a major focus for novel drug development. Of upstream targets, factor D (FD) is appealing because it circulates in plasma at low concentrations and has a single function: to cleave factor B to generate C3 convertase of the alternative pathway (AP). Mice with a targeted deletion of factor H (FH; Cfh-/- mice) develop C3 glomerulopathy (C3G) due to uncontrolled AP activity. To assess the impact of FD inhibition, we studied Cfh-/- Cfd-/- mice. We show that C3G in Cfh-/- mice is not rescued by removing FD. We used serum from Cfh-/- Cfd-/- mice to demonstrate that residual AP function occurs even when both FD and FH are missing and that hemolytic activity is present due to the action of C3(H2O). We propose that uncontrolled tick-over leads to slow activation of the AP in Cfh-/- Cfd-/- mice and that a minimal threshold of FH is necessary if tissue deposition of C3 is to be prevented. The FD/FH ratio dictates serum C3 level and renal C3b deposition. In C3G patients with chronic renal disease, the FD/FH ratio correlates inversely with C3 and C5 serum levels, suggesting that continuous AP control may be difficult to achieve by targeting FD.

Glycated Plasma Proteins as More Sensitive Markers for Glycemic Control in Type 1 Diabetes

PURPOSE

Glycated hemoglobin (HbA1c) is used clinically for diagnosis and therapeutic management of diabetes. However, HbA1c reflects average blood glucose level over a long period. The aim of this study is to look for short period, more sensitive protein markers that correlate better with glycemic level.

EXPERIMENTAL DESIGN

The glycated proteome of human plasma from type 1 diabetic individuals with good and poor (n = 20 each) glycemic control are analyzed using an online two-dimensional proteomics approach. Selected glycated peptides are further validated for their potential as candidate biomarkers using parallel reaction monitoring.

RESULTS

305 glycated peptides are quantified and 290 are significantly increased in samples with poor glycemic control. 76 of the 88 selected glycated peptides have receiver operating characteristic area under curve (AUC) values greater than 0.8. Six validated glycated peptides with high AUC show high correlation with HbA1c and have higher fold changes between poor and good glycemic control than HbA1c. The parent proteins have half-lives shorter than HbA1c.

CONCLUSIONS AND CLINICAL RELEVANCE

Using an advanced proteomics platform for protein glycation analysis, glycated peptides and proteins are identified that are promising as more sensitive, shorter term indicators of glycemic control in diabetic patients than the commonly used HbA1c.

C3 glomerulopathy - understanding a rare complement-driven renal disease

The C3 glomerulopathies are a group of rare kidney diseases characterized by complement dysregulation occurring in the fluid phase and in the glomerular microenvironment, which results in prominent complement C3 deposition in kidney biopsy samples. The two major subgroups of C3 glomerulopathy - dense deposit disease (DDD) and C3 glomerulonephritis (C3GN) - have overlapping clinical and pathological features suggestive of a disease continuum. Dysregulation of the complement alternative pathway is fundamental to the manifestations of C3 glomerulopathy, although terminal pathway dysregulation is also common. Disease is driven by acquired factors in most patients - namely, autoantibodies that target the C3 or C5 convertases. These autoantibodies drive complement dysregulation by increasing the half-life of these vital but normally short-lived enzymes. Genetic variation in complement-related genes is a less frequent cause. No disease-specific treatments are available, although immunosuppressive agents and terminal complement pathway blockers are helpful in some patients. Unfortunately, no treatment is universally effective or curative. In aggregate, the limited data on renal transplantation point to a high risk of disease recurrence (both DDD and C3GN) in allograft recipients. Clinical trials are underway to test the efficacy of several first-generation drugs that target the alternative complement pathway.

Where are we with haemolytic uremic syndrome?

Haemolytic uremic syndrome (HUS) is characterised by microangiopathic haemolytic anaemia with acute kidney injury. It is currently classified into two main categories: Shiga-toxin producing E. coli-hemolytic uremic syndrome (STEC-HUS) and atypical haemolytic uremic syndrome (aHUS). Endothelial cell damage is the common pathway in HUS to developing thrombotic microangiopathy. Atypical HUS includes primary, secondary and aHUS due to metabolic diseases. In the majority of aHUS cases, hyperactivity of the alternative complement pathway plays a central role. Therefore, treatment is based on complement inhibitors like eculizumab, a drug that has revolutionised the natural history of the disease. Relapses are frequent after kidney transplant and thus confer a poor prognosis.

An Engineered Complement Factor H Construct for Treatment of C3 Glomerulopathy

Background C3 glomerulopathy (C3G) is associated with dysregulation of the alternative pathway of complement activation, and treatment options for C3G remain limited. Complement factor H (FH) is a potent regulator of the alternative pathway and might offer a solution, but the mass and complexity of FH makes generation of full-length FH far from trivial. We previously generated a mini-FH construct, with FH short consensus repeats 1-5 linked to repeats 18-20 (FH1-5^18-20), that was effective in experimental C3G. However, the serum t1/2 of FH1-5^18-20 was significantly shorter than that of serum-purified FH.Methods We introduced the oligomerization domain of human FH-related protein 1 (denoted by R1-2) at the carboxy or amino terminus of human FH1-5^18-20 to generate two homodimeric mini-FH constructs (FHR1-2^1-5^18-20 and FH1-5^18-20^R1-2, respectively) in Chinese hamster ovary cells and tested these constructs using binding, fluid-phase, and erythrocyte lysis assays, followed by experiments in FH-deficient Cfh-/- mice.Results FHR1-2^1-5^18-20 and FH1-5^18-20^R1-2 homodimerized in solution and displayed avid binding profiles on clustered C3b surfaces, particularly FHR1-2^1-5^18-20 Each construct was >10-fold more effective than FH at inhibiting cell surface complement activity in vitro and restricted glomerular basement membrane C3 deposition in vivo significantly better than FH or FH1-5^18-20 FH1-5^18-20^R1-2 had a C3 breakdown fragment binding profile similar to that of FH, a >5-fold increase in serum t1/2 compared with that of FH1-5^18-20, and significantly better retention in the kidney than FH or FH1-5^18-20Conclusions FH1-5^18-20^R1-2 may have utility as a treatment option for C3G or other complement-mediated diseases.

Maternal and Fetal Outcomes of Pregnancies in Women with Atypical Hemolytic Uremic Syndrome

Atypical HUS (aHUS) is a disorder most commonly caused by inherited defects of the alternative pathway of complement, or the proteins that regulate this pathway, and life-threatening episodes of aHUS can be provoked by pregnancy. We retrospectively and prospectively investigated 27 maternal and fetal pregnancy outcomes in 14 women with aHUS from the Vienna Thrombotic Microangiopathy Cohort. Seven pregnancies (26%) were complicated by pregnancy-associated aHUS (p-aHUS), of which three appeared to be provoked by infection, bleeding, and curettage, and three individuals were considered to have preeclampsia/HELLP syndrome before the definitive diagnosis of p-aHUS was made. Mutations in genes that encode the complement alternative pathway proteins or the molecules that regulate this pathway were detected in 71% of the women, with no relationship to pregnancy outcome. Twenty-one pregnancies (78%) resulted in a live birth, two preterm infants were stillborn, and four pregnancies resulted in early spontaneous abortions. Although short-term renal outcome was good in most women, long-term renal outcome was poor; among the 14 women, four had CKD stage 1-4, five had received a renal allograft, and three were dialysis-dependent at study end. We prospectively followed nine pregnancies of four women and treated six of these pregnancies with prophylactic plasma infusions (one pregnancy resulted in p-aHUS, one intrauterine fetal death occurred, and seven pregancies were uneventful). Our study emphasizes the frequency of successful pregnancies in women with aHUS. Close monitoring of such pregnancies for episodes of thrombotic microangiopathy is essential but, the best strategy to prevent these episodes remains unclear.

The MFHR1 Fusion Protein Is a Novel Synthetic Multitarget Complement Inhibitor with Therapeutic Potential

The complement system is essential for host defense, but uncontrolled complement system activation leads to severe, mostly renal pathologies, such as atypical hemolytic uremic syndrome or C3 glomerulopathy. Here, we investigated a novel combinational approach to modulate complement activation by targeting C3 and the terminal pathway simultaneously. The synthetic fusion protein MFHR1 links the regulatory domains of complement factor H (FH) with the C5 convertase/C5b-9 inhibitory fragment of the FH-related protein 1. In vitro, MFHR1 showed cofactor and decay acceleration activity and inhibited C5 convertase activation and C5b-9 assembly, which prevented C3b deposition and reduced C3a/C5a and C5b-9 generation. Furthermore, this fusion protein showed the ability to escape deregulation by FH-related proteins and form multimeric complexes with increased inhibitory activity. In addition to substantially inhibiting alternative and classic pathway activation, MFHR1 blocked hemolysis mediated by serum from a patient with aHUS expressing truncated FH. In FH-/- mice, MFHR1 administration augmented serum C3 levels, reduced abnormal glomerular C3 deposition, and ameliorated C3 glomerulopathy. Taking the unique design of MFHR1 into account, we suggest that the combination of proximal and terminal cascade inhibition together with the ability to form multimeric complexes explain the strong inhibitory capacity of MFHR1, which offers a novel basis for complement therapeutics.

Syndromes of Thrombotic Microangiopathy

Thrombotic thrombocytopenia purpura (TTP) and the hemolytic uremic syndrome (HUS) are rare thrombotic microangiopathies that can be rapidly fatal. Although the acquired versions of TTP and HUS are generally highest on this broad differential, multiple rarer entities can produce a clinical picture similar to TTP/HUS, including microangiopathic hemolysis, renal failure, and neurologic compromise. More recent analysis has discovered a host of genetic factors that can produce microangiopathic hemolytic syndromes. This article discusses the current understanding of thrombotic microangiopathy and outlines the pathophysiology and causative agents associated with each distinct syndrome as well as the most accepted treatments.

Local complement activation in aqueous humor in patients with age-related macular degeneration

PurposeTo investigate complement activation in aqueous humor and in plasma of patients with neovascular age-related macular degeneration (nAMD).Patients and methodsAqueous humor and EDTA-plasma of 31 nAMD patients and 30 age-matched controls was collected. The levels of the complement factor 3 (C3), the regulators factor H (FH), and factor I (FI), and of the complement activation products Ba, C3a, and the terminal complement complex (sC5b-9) were measured. Associations between complement levels and phenotype were determined using Mann-Whitney U-test.ResultsIn plasma, no significant differences were found between the nAMD group and the control group. In aqueous humor, significantly increased levels of Ba (P=0.002), and C3a (P=0.002) indicate local complement activation in nAMD patients and a trend for a concomitant upregulation of the complement regulators FH (P=0.02) and FI (P=0.04).ConclusionsOur findings provide strong evidence for a local complement dysregulation in nAMD patients.

Moss-Produced, Glycosylation-Optimized Human Factor H for Therapeutic Application in Complement Disorders

Genetic defects in complement regulatory proteins can lead to severe renal diseases, including atypical hemolytic uremic syndrome and C3 glomerulopathies, and age-related macular degeneration. The majority of the mutations found in patients with these diseases affect the glycoprotein complement factor H, the main regulator of the alternative pathway of complement activation. Therapeutic options are limited, and novel treatments, specifically those targeting alternative pathway activation, are highly desirable. Substitution with biologically active factor H could potentially treat a variety of diseases that involve increased alternative pathway activation, but no therapeutic factor H is commercially available. We recently reported the expression of full-length recombinant factor H in moss (Physcomitrella patens). Here, we present the production of an improved moss-derived recombinant human factor H devoid of potentially immunogenic plant-specific sugar residues on protein N-glycans, yielding approximately 1 mg purified moss-derived human factor H per liter of initial P. patens culture after a multistep purification process. This glycosylation-optimized factor H showed full in vitro complement regulatory activity similar to that of plasma-derived factor H and efficiently blocked LPS-induced alternative pathway activation and hemolysis induced by sera from patients with atypical hemolytic uremic syndrome. Furthermore, injection of moss-derived factor H reduced C3 deposition and increased serum C3 levels in a murine model of C3 glomerulopathy. Thus, we consider moss-produced recombinant human factor H a promising pharmaceutical product for therapeutic intervention in patients suffering from complement dysregulation.

Exchange transfusion for neonate with haemolytic uremic syndrome

Introduction

Haemolytic uremic syndrome (HUS) is one of the most common causes of acute renal failure in children but it is uncommon in newborns. To our knowledge only five cases have been reported so far (probably underreported). The known modalities of treatment include transfusion of plasma and plasmapheresis. We report a case of neonatal HUS for whom we performed an exchange transfusion to good effect.

Case description

A term vaginally born baby, meconium stained and floppy at birth presented with severe anaemia in the first few hours of life. The baby later on developed renal failure and blood picture was suggestive of severe thrombocytopenia and microangiopathic haemolytic anaemia. No extra renal manifestations of birth asphyxia were noted. A double volume exchange transfusion was performed relatively early and subsequently platelet and haemoglobin stabilised and renal failure improved.

Discussion and evaluation

The clinical impression in this case was convincing of neonatal HUS, likely attributable to birth asphyxia but needs to be differentiated from disseminated intravascular coagulation (DIC) and thrombotic thrombocytopenic purpura (TTP). The coagulation profile is usually normal in HUS but it is abnormal in DIC, whereas in TTP one would find hyperbilirubinemia, increased creatinine, haemolysis etc. TTP is rare but not very uncommon in infancy. Congenital TTP is attributed to an inherent deficiency of ADAMTS-13, which is a vWF-cleaving metalloprotease. Irrespective of the etiology of HUS in our case, a dramatic response was observed with exchange transfusion. Transfusion of fresh frozen plasma (FFP) and plasmapheresis are known treatment modalities. FFP replaces the missing or altered complement factors and plasmapheresis removes antibodies, immune complexes and toxins. An exchange transfusion combines both these functions.

Conclusions

In the absence of facilities for plasmapheresis, exchange transfusion is a good alternative.

Overview of C3 Glomerulopathy

C3 glomerulopathy is an umbrella term, which includes several rare forms of glomerulonephritis (GN) with underlying defects in the alternate complement cascade. A common histological feature noted in all these GN is dominant C3 deposition in the glomerulus. In this review, we will provide an overview of the complement system as well as mediators, with an introduction to pharmaceutical agents that can alter the pathway.

Efficacy of Targeted Complement Inhibition in Experimental C3 Glomerulopathy

C3 glomerulopathy refers to renal disorders characterized by abnormal accumulation of C3 within the kidney, commonly along the glomerular basement membrane (GBM). C3 glomerulopathy is associated with complement alternative pathway dysregulation, which includes functional defects in complement regulator factor H (FH). There is no effective treatment for C3 glomerulopathy. We investigated the efficacy of a recombinant mouse protein composed of domains from complement receptor 2 (CR2) and FH (CR2-FH) in two models of C3 glomerulopathy with either preexisting or triggered C3 deposition along the GBM. FH-deficient mice spontaneously develop renal pathology associated with abnormal C3 accumulation along the GBM and secondary plasma C3 deficiency. CR2-FH partially restored plasma C3 levels in FH-deficient mice 2 hours after intravenous injection. CR2-FH specifically targeted glomerular C3 deposits, reduced the linear C3 reactivity assessed with anti-C3 and anti-C3b/iC3b/C3c antibodies, and prevented further spontaneous accumulation of C3 fragments along the GBM. Reduction in glomerular C3d and C9/C5b-9 reactivity was observed after daily administration of CR2-FH for 1 week. In a second mouse model with combined deficiency of FH and complement factor I, CR2-FH prevented de novo C3 deposition along the GBM. These data show that CR2-FH protects the GBM from both spontaneous and triggered C3 deposition in vivo and indicate that this approach should be tested in C3 glomerulopathy.

A new paradigm: Diagnosis and management of HSCT-associated thrombotic microangiopathy as multi-system endothelial injury

Hematopoietic stem cell transplantation (HSCT)-associated thrombotic microangiopathy (TA-TMA) is now a well-recognized and potentially severe complication of HSCT that carries a high risk of death. In those who survive, TA-TMA may be associated with long-term morbidity and chronic organ injury. Recently, there have been new insights into the incidence, pathophysiology, and management of TA-TMA. Specifically, TA-TMA can manifest as a multi-system disease occurring after various triggers of small vessel endothelial injury, leading to subsequent tissue damage in different organs. While the kidney is most commonly affected, TA-TMA involving organs such as the lung, bowel, heart, and brain is now known to have specific clinical presentations. We now review the most up-to-date research on TA-TMA, focusing on the pathogenesis of endothelial injury, the diagnosis of TA-TMA affecting the kidney and other organs, and new clinical approaches to the management of this complication after HSCT.

Plasma exchange for kidney disease: what is the best evidence?

Therapeutic plasma exchange (TPE) has been used as adjunctive therapy for various kidney diseases dating back to the 1970s. In many cases, support for TPE was on mechanistic grounds given the potential to remove unwanted large molecular-weight substances such as autoantibodies, immune complexes, myeloma light chains, and cryoglobulins. More recently, growing evidence from randomized controlled trials, meta-analyses, and prospective studies has provided insights into more rational use of this therapy. This report describes the role of TPE for the 6 most common kidney indications in the 2013 Canadian Apheresis Group (CAG) registry and the evidence that underpins current recommendations and practice. These kidney indications include thrombotic microangiopathy, antiglomerular basement membrane disease, anti-neutrophil cytoplasmic antibody-associated vasculitis, cryoglobulinemia, recurrence of focal and segmental glomerulosclerosis in the kidney allograft, and kidney transplantation.

C3 glomerulopathy: clinicopathologic features and predictors of outcome

BACKGROUND AND OBJECTIVES

The term C3 glomerulopathy describes renal disorders characterized by the presence of glomerular deposits composed of C3 in the absence of significant amounts of Ig. On the basis of electron microscopy appearance, subsets of C3 glomerulopathy include dense deposit disease (DDD) and C3 glomerulonephritis (C3GN). The full spectrum of histologic change observed in C3 glomerulopathy has yet to be defined and pathologic predictors of renal outcome within this patient population remain largely unknown. This study thus characterized a large C3 glomerulopathy cohort and identified clinicopathologic predictors of renal outcome.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

All patients with kidney biopsies fulfilling criteria for C3 glomerulopathy from two quaternary renal centers within the United Kingdom and Ireland between 1992 and 2012 were retrospectively reviewed. We recorded histologic, demographic, and clinical data and determined predictors of ESRD using the Cox proportional hazards model.

RESULTS

Eighty patients with C3 glomerulopathy were identified: 21 with DDD and 59 with C3GN. Patients with DDD were younger, more likely to have low serum C3 levels, and more likely to have crescentic GN than patients with C3GN. Patients with C3GN were older and had more severe arteriolar sclerosis, glomerular sclerosis, and interstitial scarring than patients with DDD. Of 70 patients with available follow-up data, 20 (29%) progressed to ESRD after a median of 28 months. Age >16 years, DDD subtype, and crescentic GN were independent predictors of ESRD within the entire cohort. Renal impairment at presentation predicted ESRD only among patients with DDD.

CONCLUSIONS

Although detailed serologic and genetic data are lacking, this study nevertheless identifies important clinicopathologic distinctions between patients with DDD and C3GN. These include independent predictors of renal outcome. If replicated in other cohorts, these predictors could be used to stratify patients, enabling application of emerging mechanism-based therapies to patients at high risk for poor renal outcome.

C3 glomerulopathy: consensus report

C3 glomerulopathy is a recently introduced pathological entity whose original definition was glomerular pathology characterized by C3 accumulation with absent or scanty immunoglobulin deposition. In August 2012, an invited group of experts (comprising the authors of this document) in renal pathology, nephrology, complement biology, and complement therapeutics met to discuss C3 glomerulopathy in the first C3 Glomerulopathy Meeting. The objectives were to reach a consensus on: the definition of C3 glomerulopathy, appropriate complement investigations that should be performed in these patients, and how complement therapeutics should be explored in the condition. This meeting report represents the current consensus view of the group.

Treatment options for C3 glomerulopathy

PURPOSE OF REVIEW

The purpose of this review is to discuss emerging nomenclature, review the salient clinicopathological features and describe the therapeutic options available for the treatment of C3 glomerulopathy (C3G).

RECENT FINDINGS

C3G is minimally responsive to traditional immune suppression and randomized controlled trials to support therapy are absent. The burgeoning understanding of the role of the alternative complement pathway in C3G combined with animal data supporting the use of terminal complement blockade and a few reports suggesting that the anticomplement drug eculizumab may offer a therapeutic advantage have triggered great interest in the field of complement-mediated renal disease.

SUMMARY

Anticellular immune suppression and plasma therapy have limited efficacy in C3G. Data suggest that eculizumab may ameliorate disease in some C3G patients. The limited, recently published cohort data highlight crucial aspects of this group of diseases and support the need for extensive genetic and biomarker research to validate the pathologic mechanisms, delineate the spectrum of disease and guide the design of the rigorous trials to identify effective therapies for the treatment of C3G.

Genetic influences on plasma CFH and CFHR1 concentrations and their role in susceptibility to age-related macular degeneration

It is a longstanding puzzle why non-coding variants in the complement factor H (CFH) gene are more strongly associated with age-related macular degeneration (AMD) than functional coding variants that directly influence the alternative complement pathway. The situation is complicated by tight genetic associations across the region, including the adjacent CFH-related genes CFHR3 and CFHR1, which may themselves influence the alternative complement pathway and are contained within a common deletion (CNP147) which is associated with protection against AMD. It is unclear whether this association is mediated through a protective effect of low plasma CFHR1 concentrations, high plasma CFH or both. We examined the triangular relationships of CFH/CFHR3/CFHR1 genotype, plasma CFH or CFHR1 concentrations and AMD susceptibility in combined case–control (1256 cases, 1020 controls) and cross-sectional population (n = 1004) studies and carried out genome-wide association studies of plasma CFH and CFHR1 concentrations. A non-coding CFH SNP (rs6677604) and the CNP147 deletion were strongly correlated both with each other and with plasma CFH and CFHR1 concentrations. The plasma CFH-raising rs6677604 allele and raised plasma CFH concentration were each associated with AMD protection. In contrast, the protective association of the CNP147 deletion with AMD was not mediated by low plasma CFHR1, since AMD-free controls showed increased plasma CFHR1 compared with cases, but it may be mediated by the association of CNP147 with raised plasma CFH concentration. The results are most consistent with a regulatory locus within a 32 kb region of the CFH gene, with a major effect on plasma CFH concentration and AMD susceptibility.

Functional anatomy of complement factor H

Factor H (FH) is a soluble regulator of the proteolytic cascade at the core of the evolutionarily ancient vertebrate complement system. Although FH consists of a single chain of similar protein modules, it has a demanding job description. Its chief role is to prevent complement-mediated injury to healthy host cells and tissues. This entails recognition of molecular patterns on host surfaces combined with control of one of nature's most dangerous examples of a positive-feedback loop. In this way, FH modulates, where and when needed, an amplification process that otherwise exponentially escalates the production of the pro-inflammatory, pro-phagocytic, and pro-cytolytic cleavage products of complement proteins C3 and C5. Mutations and single-nucleotide polymorphisms in the FH gene and autoantibodies against FH predispose individuals to diseases, including age-related macular degeneration, dense-deposit disease, and atypical hemolytic uremic syndrome. Moreover, deletions or variations of genes for FH-related proteins also influence the risk of disease. Numerous pathogens hijack FH and use it for self-defense. As reviewed herein, a molecular understanding of FH function is emerging. While its functional oligomeric status remains uncertain, progress has been achieved in characterizing its three-dimensional architecture and, to a lesser extent, its intermodular flexibility. Models are proposed, based on the reconciliation of older data with a wealth of recent evidence, in which a latent circulating form of FH is activated by its principal target, C3b tethered to a self-surface. Such models suggest hypotheses linking sequence variations to pathophysiology, but improved, more quantitative, functional assays and rigorous data analysis are required to test these ideas.

Tailored eculizumab therapy in the management of complement factor H-mediated atypical hemolytic uremic syndrome in an adult kidney transplant recipient: a case report

Atypical hemolytic uremic syndrome (aHUS) is characterized by thrombocytopenia, microangiopathic hemolytic anemia, and acute kidney injury (AKI) which frequently progresses to end-stage renal disease (ESRD). In 50% of affected patients, mutations in complement regulatory proteins cause inappropriate complement activation with endothelial injury. Complement factor H (CFH) mutations cause 25% of aHUS cases; these patients have an 80% recurrence risk after kidney transplantation. Eculizumab, an anti-C5 antibody, is effective in limiting hemolysis episodes in patients with aHUS, but less is known about preventing recurrence after kidney transplantation. Herein we report the use of prophylactic eculizumab in an adult with aHUS who underwent kidney transplantation. A 31-year-old female presented with aHUS and progressive AKI associated with low complement 3 level leading to ESRD despite plasmapheresis and corticosteroids. She had a heterozygous nonsense mutation in CFH and reduced plasma CFH levels. She was given preoperative plasmapheresis and eculizumab and underwent living unrelated renal transplantation. Postoperatively, eculizumab was dosed to achieve low functional complement 5 levels and low soluble membrane attack complex levels and she has maintained excellent graft function without aHUS recurrence. We propose that eculizumab with titrated dosing should be used in CFH-mediated aHUS patients who are at a high risk of recurrence.

Manipulating the mediator: modulation of the alternative complement pathway C3 convertase in health, disease and therapy

The complement network is increasingly recognized as an important triage system that is able to differentiate between healthy host cells, microbial intruders, cellular debris and immune complexes, and tailor its actions accordingly. At the center of this triage mechanism is the alternative pathway C3 convertase (C3bBb), a potent enzymatic protein complex capable of rapidly converting the inert yet abundant component C3 into powerful effector fragments (C3a and C3b), thereby amplifying the initial response on unprotected surfaces and inducing a variety of effector functions. A fascinating molecular mechanism of convertase assembly and intrinsic regulation, as well as the interplay with a panel of cell surface-bound and soluble inhibitors are essential for directing complement attack to intruders and protecting healthy host cells. While efficiently keeping immune surveillance and homeostasis on track, the reliance on an intricate cascade of interaction and conversion steps also renders the C3 convertase vulnerable to derail. On the one hand, tissue damage, accumulation of debris, or polymorphisms in complement genes may unfavorably shift the balance between activation and regulation, thereby contributing to a variety of clinical conditions. On the other hand, pathogens developed powerful evasion strategies to avoid complement attack by targeting the convertase. Finally, we increasingly challenge our bodies with foreign materials such as biomaterial implants or drug delivery vehicles that may induce adverse effects that are at least partially caused by complement activation and amplification via the alternative pathway. The involvement of the C3 convertase in a range of pathological conditions put this complex into the spotlight of complement-targeted drug discovery efforts. Fortunately, the physiological regulation and microbial evasion approaches provide a rich source of inspiration for the development of powerful treatment options. This review provides insight into the current knowledge about the molecular mechanisms that drive C3 convertase activity, reveals common and divergent strategies of convertase inhibition employed by host and pathogens, and how this inhibitory arsenal can be tapped for developing therapeutic options to treat complement-related diseases.

Progress and Trends in Complement Therapeutics

The past few years have proven to be a highly successful and exciting period for the field of complement-directed drug discovery and development. Driven by promising experiences with the first marketed complement drugs, increased knowledge about the involvement of complement in health and disease, and improvements in structural and analytical techniques as well as animal models of disease, the field has seen a surge in creative approaches to therapeutically intervene at various stages of the cascade. An impressive panel of compounds that show promise in clinical trials is meanwhile being lined up in the pipelines of both small biotechnology and big pharmaceutical companies. Yet with this new focus on complement-targeted therapeutics, important questions concerning target selection, point and length of intervention, safety, and drug delivery emerge. In view of the diversity of the clinical disorders involving abnormal complement activity or regulation, which include both acute and chronic diseases and affect a wide range of organs, diverse yet specifically tailored therapeutic approaches may be needed to shift complement back into balance. This chapter highlights the key changes in the field that shape our current perception of complement-targeted drugs and provides a brief overview of recent strategies and emerging trends. Selected examples of complement-related diseases and inhibitor classes are highlighted to illustrate the diversity and creativity in field.

Monitoring and modeling treatment of atypical hemolytic uremic syndrome

Atypical hemolytic uremic syndrome (aHUS), is mainly present in children, who have high risks of end-stage kidney disease (ESKD), post-transplant recurrence and death. aHUS is linked to defective regulation of the complement alternative pathway (AP), with a prominent cause being mutation/inhibition of the negative regulator complement factor H (CFH). CFH function can be restored via infusion of fresh frozen plasma (FFP), a treatment that was effective for several years in a patient heterozygous for a cfh mutation, before the patient progressed to ESKD. While on dialysis, FFP was replaced with eculizumab, which blocks C5 cleavage and thus halts progression of the terminal complement pathway. Patient plasma samples collected during FFP and eculizumab treatment phases were assessed for AP activity (via erythrocyte lysis assays) and for overall complement activity (via ELISA-based screen). Assay results indicated that FFP partially restored AP regulation, an observation supported by in vitro modeling of FFP treatment using purified CFH, while eculizumab completely blocked complement activity. The same approach was used to model in vitro a potential aHUS treatment approach based on blocking the AP effector properdin (complement factor P; CFP) with an anti-properdin antibody. These results provide insights into the efficacy of aHUS treatment and highlight the usefulness of in vitro assays in monitoring and predicting therapeutic responses and testing new treatment possibilities.

Kidney diseases caused by complement dysregulation: acquired, inherited, and still more to come

Inherited and acquired dysregulation of the complement alternative pathway plays an important role in multiple renal diseases. In recent years, the identification of disease-causing mutations and genetic variants in complement regulatory proteins has contributed significantly to our knowledge of the pathogenesis of complement associated glomerulopathies. In these diseases defective complement control leading to the deposition of activated complement products plays a key role. Consequently, complement-related glomerulopathies characterized by glomerular complement component 3 (C3) deposition in the absence of local immunoglobulin deposits are now collectively described by the term “C3 glomerulopathies.” Therapeutic strategies for reestablishing complement regulation by either complement blockade with the anti-C5 monoclonal antibody eculizumab or plasma substitution have been successful in several cases of C3 glomerulopathies. However, further elucidation of the underlying defects in the alternative complement pathway is awaited to develop pathogenesis-specific therapies.

Membrano-proliferative glomerulonephritis, atypical hemolytic uremic syndrome, and a new complement factor H mutation: report of a case

BACKGROUND

Complement protein factor H (CFH) is a regulatory protein of the alternative complement pathway (AP); CFH mutations lead to a spectrum of different phenotypical manifestations of renal disease.

CASE-DIAGNOSIS/TREATMENT

We report the case of a boy with a novel CFH gene mutation who presented with a membranoproliferative (MPGN) pattern of glomerular injury and developed 2 years later atypical hemolytic uremic syndrome (aHUS); this description shows that CFH alteration leads to two different renal diseases in the same patient.

CONCLUSIONS

Our case suggests the possibility that complement dysregulation could determine different renal conditions, which may be part of the same disease spectrum. Early recognition of an evolution of glomerulopathies into aHUS may allow appropriate management and prevention of life-threatening consequences.

Management of hemolytic uremic syndrome

2011 has been a special year for hemolytic uremic syndrome (HUS): on the one hand, the dramatic epidemic of Shiga toxin producing E. coli -associated HUS in Germany brought the disease to the attention of the general population, on the other hand it has been the year when eculizumab, the first complement blocker available for clinical practice, was demonstrated as the potential new standard of care for atypical HUS. Here we review the therapeutic options presently available for the various forms of hemolytic uremic syndrome and show how recent knowledge has changed the therapeutic approach and prognosis of atypical HUS.

Plasma therapy for atypical haemolytic uraemic syndrome associated with heterozygous factor H mutations

Atypical haemolytic uraemic syndrome (aHUS) is frequently associated with mutations in the gene encoding complement factor H (CFH). The clinical response to plasma therapy in aHUS is variable. We present here our experience of plasma therapy in three aHUS patients with CFH mutations. Three children presented aged 4, 22 and 6 months (patients 1-3 respectively) in acute kidney injury requiring dialysis. Plasma therapy consisting of plasma filtration (patient 1) or plasma exchange (PEX; patients 2 and 3) was commenced early following presentation. This resulted in aHUS remission and cessation of dialysis after 2 weeks, 9 days and 2 weeks respectively. Relapses were common and associated with increasing the interval between PEX, but all responded to intensification of PEX therapy. Patient 1 recovered 50% of renal function after first presentation. She had four relapses and started peritoneal dialysis 41 months after presentation. Mutation screening of CFH showed a missense mutation (c.3546 G > T, p.Arg1182Ser) in exon 23. PEX in patient 2 was slowly tapered over 4 months to fortnightly sessions, but she relapsed when PEX was extended to every 4 weeks. Renal function remained normal 12 months post-presentation. Mutation screening of CFH showed a mutation in exon 23 (c.3590 T > C, p.Val1197Ala) and two additional sequence variants in exons 3 and 4. Patient 3 had two relapses associated with intercurrent illnesses concurrent with reducing PEX to weekly doses. Renal function was normal 5 months post-presentation. All three patients showed a good response to PEX with improved renal function both initially and following a relapse. Further research is necessary to determine the best maintenance strategy to delay or prevent end-stage kidney disease.

Atypical hemolytic uremic syndrome

Hemolytic uremic syndrome (HUS) is defined by the triad of mechanical hemolytic anemia, thrombocytopenia and renal impairment. Atypical HUS (aHUS) defines non Shiga-toxin-HUS and even if some authors include secondary aHUS due to Streptococcus pneumoniae or other causes, aHUS designates a primary disease due to a disorder in complement alternative pathway regulation. Atypical HUS represents 5 -10% of HUS in children, but the majority of HUS in adults. The incidence of complement-aHUS is not known precisely. However, more than 1000 aHUS patients investigated for complement abnormalities have been reported. Onset is from the neonatal period to the adult age. Most patients present with hemolytic anemia, thrombocytopenia and renal failure and 20% have extra renal manifestations. Two to 10% die and one third progress to end-stage renal failure at first episode. Half of patients have relapses. Mutations in the genes encoding complement regulatory proteins factor H, membrane cofactor protein (MCP), factor I or thrombomodulin have been demonstrated in 20-30%, 5-15%, 4-10% and 3-5% of patients respectively, and mutations in the genes of C3 convertase proteins, C3 and factor B, in 2-10% and 1-4%. In addition, 6-10% of patients have anti-factor H antibodies. Diagnosis of aHUS relies on 1) No associated disease 2) No criteria for Shigatoxin-HUS (stool culture and PCR for Shiga-toxins; serology for anti-lipopolysaccharides antibodies) 3) No criteria for thrombotic thrombocytopenic purpura (serum ADAMTS 13 activity > 10%). Investigation of the complement system is required (C3, C4, factor H and factor I plasma concentration, MCP expression on leukocytes and anti-factor H antibodies; genetic screening to identify risk factors). The disease is familial in approximately 20% of pedigrees, with an autosomal recessive or dominant mode of transmission. As penetrance of the disease is 50%, genetic counseling is difficult. Plasmatherapy has been first line treatment until presently, without unquestionable demonstration of efficiency. There is a high risk of post-transplant recurrence, except in MCP-HUS. Case reports and two phase II trials show an impressive efficacy of the complement C5 blocker eculizumab, suggesting it will be the next standard of care. Except for patients treated by intensive plasmatherapy or eculizumab, the worst prognosis is in factor H-HUS, as mortality can reach 20% and 50% of survivors do not recover renal function. Half of factor I-HUS progress to end-stage renal failure. Conversely, most patients with MCP-HUS have preserved renal function. Anti-factor H antibodies-HUS has favourable outcome if treated early.

Atypical hemolytic uremic syndrome

Hemolytic uremic syndrome (HUS) is defined by the triad of mechanical hemolytic anemia, thrombocytopenia and renal impairment. Atypical HUS (aHUS) defines non Shiga-toxin-HUS and even if some authors include secondary aHUS due to Streptococcus pneumoniae or other causes, aHUS designates a primary disease due to a disorder in complement alternative pathway regulation. Atypical HUS represents 5 -10% of HUS in children, but the majority of HUS in adults. The incidence of complement-aHUS is not known precisely. However, more than 1000 aHUS patients investigated for complement abnormalities have been reported. Onset is from the neonatal period to the adult age. Most patients present with hemolytic anemia, thrombocytopenia and renal failure and 20% have extra renal manifestations. Two to 10% die and one third progress to end-stage renal failure at first episode. Half of patients have relapses. Mutations in the genes encoding complement regulatory proteins factor H, membrane cofactor protein (MCP), factor I or thrombomodulin have been demonstrated in 20-30%, 5-15%, 4-10% and 3-5% of patients respectively, and mutations in the genes of C3 convertase proteins, C3 and factor B, in 2-10% and 1-4%. In addition, 6-10% of patients have anti-factor H antibodies. Diagnosis of aHUS relies on 1) No associated disease 2) No criteria for Shigatoxin-HUS (stool culture and PCR for Shiga-toxins; serology for anti-lipopolysaccharides antibodies) 3) No criteria for thrombotic thrombocytopenic purpura (serum ADAMTS 13 activity > 10%). Investigation of the complement system is required (C3, C4, factor H and factor I plasma concentration, MCP expression on leukocytes and anti-factor H antibodies; genetic screening to identify risk factors). The disease is familial in approximately 20% of pedigrees, with an autosomal recessive or dominant mode of transmission. As penetrance of the disease is 50%, genetic counseling is difficult. Plasmatherapy has been first line treatment until presently, without unquestionable demonstration of efficiency. There is a high risk of post-transplant recurrence, except in MCP-HUS. Case reports and two phase II trials show an impressive efficacy of the complement C5 blocker eculizumab, suggesting it will be the next standard of care. Except for patients treated by intensive plasmatherapy or eculizumab, the worst prognosis is in factor H-HUS, as mortality can reach 20% and 50% of survivors do not recover renal function. Half of factor I-HUS progress to end-stage renal failure. Conversely, most patients with MCP-HUS have preserved renal function. Anti-factor H antibodies-HUS has favourable outcome if treated early.

Small vessels, big trouble in the kidneys and beyond: hematopoietic stem cell transplantation–associated thrombotic microangiopathy

Transplantation-associated thrombotic microangiopathy (TA-TMA) is a challenging diagnosis after hematopoietic stem cell transplantation. Although endothelial injury represents the final common pathway of disease, the exact pathophysiology of TA-TMA remains unclear. Potential causes include infections, chemotherapy, radiation, and calcineurin inhibitors. Recent literature addresses the roles of cytokines, graft-versus-host disease, the coagulation cascade, and complement in the pathogenesis of TA-TMA. Current diagnostic criteria are unsatisfactory, because patients who have received a transplant can have multiple other reasons for the laboratory abnormalities currently used to diagnose TA-TMA. Moreover, our lack of understanding of the exact mechanism of disease limits the development and evaluation of potential treatments. Short- and long-term renal complications contribute to TA-TMA's overall poor prognosis. In light of these challenges, future research must validate novel markers of disease to aid in early diagnosis, guide current and future treatments, prevent long-term morbidity, and improve outcomes. We focus on TA-TMA as a distinct complication of hematopoietic stem cell transplantation, emphasizing the central role of the kidney in this disease.

Complement deficiency states and associated infections

A major function of the immune system is to protect the host from microbial infections. The complement system plays important roles in both the innate and the adaptive immune defense and also acts as a bridge between these arms of immunity. This is obvious from complement deficiencies which in varying degree, depending on which factor is missing, are associated with increased infection susceptibility and also increased risk for other, mainly autoimmune diseases. Genetically determined deficiencies are described for almost all complement proteins but the consequences show a wide variation. Here the genetic defects and molecular abnormalities in complement deficient persons, related clinically relevant infections and the options for prevention and therapy are reviewed. The roles of complement in host defense against common infections are also discussed.

Eculizumab induces long-term remission in recurrent post-transplant HUS associated with C3 gene mutation

A 15-year-old male patient developed atypical hemolytic uremic syndrome (aHUS) at 16 months of age leading to end-stage renal disease. The family history was suggestive of autosomal dominant aHUS, and he was more recently found to have a C3 heterozygous gene mutation (1835C>T mutation in exon 14, which determines the amino-acidic substitution R570W) with no other complement abnormalities. He had two renal transplants, the first at 2.5 years, and the second at 8 years of age, but allograft dysfunction developed in both transplants leading to graft failure due to recurrent HUS at 5 years and 18 months post-transplantation respectively. At 15 years of age he received a third transplant from a deceased donor with pre-emptive plasmapheresis. He had immediate graft function and nadir serum creatinine was 1.3-1.4 mg/dl. Severe allograft dysfunction and hypertension developed 2 months after transplantation following influenza infection. Renal allograft biopsy showed thrombotic microangiopathy. He received plasmapheresis followed by eculizumab therapy. Allograft function returned to baseline 3 weeks after starting therapy, and post-treatment allograft biopsies showed improvement in thrombotic microangiopathy. He continues to receive eculizumab every 2 weeks with stable graft function 13 months after transplantation.

aHUS caused by complement dysregulation: new therapies on the horizon

Atypical hemolytic uremic syndrome (aHUS) is a heterogeneous disease that is caused by defective complement regulation in over 50% of cases. Mutations have been identified in genes encoding both complement regulators [complement factor H (CFH), complement factor I (CFI), complement factor H-related proteins (CFHR), and membrane cofactor protein (MCP)], as well as complement activators [complement factor B (CFB) and C3]. More recently, mutations have also been identified in thrombomodulin (THBD), an anticoagulant glycoprotein that plays a role in the inactivation of C3a and C5a. Inhibitory autoantibodies to CFH account for an additional 5-10% of cases and can occur in isolation or in association with mutations in CFH, CFI, CFHR 1, 3, 4, and MCP. Plasma therapies are considered the mainstay of therapy in aHUS secondary to defective complement regulation and may be administered as plasma infusions or plasma exchange. However, in certain cases, despite initiation of plasma therapy, renal function continues to deteriorate with progression to end-stage renal disease and renal transplantation. Recently, eculizumab, a humanized monoclonal antibody against C5, has been described as an effective therapeutic strategy in the management of refractory aHUS that has failed to respond to plasma therapy. Clinical trials are now underway to further evaluate the efficacy of eculizumab in the management of both plasma-sensitive and plasma-resistant aHUS.