Paroxysmal nocturnal haemoglobinuria

Hematopoietic Cell Transplantation for Paroxysmal Nocturnal Hemoglobinuria in the Age of Eculizumab

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare, acquired clonal hematopoietic cell disease characterized by the destruction of hematopoietic cells through activation of the complement system with manifestations that can be life-threatening including hemolysis, thrombosis, and marrow failure. Allogeneic hematopoietic cell transplantation (HCT) remains the sole cure for PNH, but eculizumab, a terminal complement inhibitor of C5, has been used to prevent complement-mediated hemolysis in patients with PNH since its approval by the Food and Drug Administration in 2007. We examined outcomes of HCT in patients with PNH to evaluate the effects of disease subtype, conditioning intensity, and eculizumab use either pre-HCT or post-HCT. Fifty-five patients with a diagnosis of PNH underwent at least 1 HCT, with 4 patients requiring a second HCT for graft failure. The median age at the time of first HCT was 30.0 years (range, 4.2 to 66.9 years). Seventeen patients (30.9%) had classical PNH, and the remaining 38 patients had PNH associated with another marrow disorder (aplastic anemia in 26 of the 38). Indications for HCT included pancytopenia in 47.3% of the patients, myeloid malignancy (myelodysplastic syndrome, myeloproliferative neoplasm, or acute myelogenous leukemia) in 21.8%, recurrent hemolysis in 20.0%, and thrombosis in 10.9%. Of the 55 first HCTs, 26 were performed with myeloablative conditioning, 27 were performed with reduced-intensity conditioning, and 2 sets of identical twins underwent HCT without any conditioning. Donor types included HLA-matched related in 38.2%, HLA-matched unrelated in 34.5%, single HLA-allele mismatched unrelated in 16.4%, umbilical cord blood in 5.5%, syngeneic in 3.6%, and HLA-haploidentical in 1.8%. The median duration of follow-up in surviving patients was 6.1 years (range, 2.1 to 46.1 years) after first HCT. The median time to neutrophil and platelet engraftment was 17 days and 19 days, respectively; all but 2 patients (96.3%) had sustained engraftment. Overall survival was 70% at 5 years. Neither the choice of conditioning intensity nor PNH subtype affected survival. Nineteen patients died during follow-up, including 12 patients before day +365. Six patients received treatment with eculizumab before HCT, and 2 were treated after HCT. All patients treated with eculizumab were alive at a median follow-up of 2.3 years (range, .2 to 6.9 years). Both patients treated with eculizumab after HCT had minimal to no acute GVHD (aGVHD), with grade I skin aGVHD in 1 patient and no aGVHD in the other patient, and no chronic GVHD at 2.1 and 4.1 years post-HCT, respectively. With the approval of eculizumab, the indications for HCT include persistent hemolysis, persistent thrombosis, and associated marrow failure. Administration of eculizumab before and after HCT warrants further study, particularly considering our observation of minimal to no GVHD in 2 patients who received eculizumab after HCT.

Ravulizumab (ALXN1210) vs eculizumab in C5-inhibitor-experienced adult patients with PNH: the 302 study

Ravulizumab, a new complement component C5 inhibitor administered every 8 weeks, was noninferior to eculizumab administered every 2 weeks in complement-inhibitor-naive patients with paroxysmal nocturnal hemoglobinuria (PNH). This study assessed noninferiority of ravulizumab to eculizumab in clinically stable PNH patients during previous eculizumab therapy. In this phase 3, open-label, multicenter study, 195 PNH patients on labeled-dose (900 mg every 2 weeks) eculizumab for >6 months were randomly assigned 1:1 to switch to ravulizumab (n = 97) or continue eculizumab (n = 98). Primary efficacy end point was percentage change in lactate dehydrogenase (LDH) from baseline to day 183. Key secondary end points included proportion of patients with breakthrough hemolysis, change in Functional Assessment of Chronic Illness Therapy (FACIT)-Fatigue score, transfusion avoidance, and stabilized hemoglobin. In 191 patients completing 183 days of treatment, ravulizumab was noninferior to eculizumab (P _inf < .0006 for all end points), including percentage change in LDH (difference, 9.21% [95% confidence interval (CI), -0.42 to 18.84], P = .058 for superiority), breakthrough hemolysis (difference, 5.1 [95% CI, -8.89 to 18.99]), change in FACIT-Fatigue score (difference, 1.47 [95% CI, -0.21 to 3.15]), transfusion avoidance (difference, 5.5 [95% CI, -4.27 to 15.68]), and stabilized hemoglobin (difference, 1.4 [95% CI, -10.41 to 13.31]). The most frequently reported adverse event was headache (26.8%, ravulizumab; 17.3%, eculizumab). No meningococcal infections or discontinuations due to adverse events occurred. Patients with PNH may be safely and effectively switched from labeled-dose eculizumab administered every 2 weeks to ravulizumab administered every 8 weeks. This trial was funded by Alexion Pharmaceuticals, Inc., and is registered at www.clinicaltrials.gov as #NCT03056040.

Ravulizumab (ALXN1210) vs eculizumab in adult patients with PNH naive to complement inhibitors: the 301 study

Ravulizumab (ALXN1210), a new complement C5 inhibitor, provides immediate, complete, and sustained C5 inhibition. This phase 3, open-label study assessed the noninferiority of ravulizumab to eculizumab in complement inhibitor-naive adults with paroxysmal nocturnal hemoglobinuria (PNH). Patients with lactate dehydrogenase (LDH) ≥1.5 times the upper limit of normal and at least 1 PNH symptom were randomized 1:1 to receive ravulizumab or eculizumab for 183 days (N = 246). Coprimary efficacy end points were proportion of patients remaining transfusion-free and LDH normalization. Secondary end points were percent change from baseline in LDH, change from baseline in Functional Assessment of Chronic Illness Therapy (FACIT)-Fatigue score, proportion of patients with breakthrough hemolysis, stabilized hemoglobin, and change in serum free C5. Ravulizumab was noninferior to eculizumab for both coprimary and all key secondary end points (P_inf < .0001): transfusion avoidance (73.6% vs 66.1%; difference of 6.8% [95% confidence interval (CI), -4.66, 18.14]), LDH normalization (53.6% vs 49.4%; odds ratio, 1.19 [0.80, 1.77]), percent reduction in LDH (-76.8% vs -76.0%; difference [95% CI], -0.83% [-5.21, 3.56]), change in FACIT-Fatigue score (7.07 vs 6.40; difference [95% CI], 0.67 [-1.21, 2.55]), breakthrough hemolysis (4.0% vs 10.7%; difference [95% CI], -6.7% [-14.21, 0.18]), and stabilized hemoglobin (68.0% vs 64.5%; difference [95% CI], 2.9 [-8.80, 14.64]). The safety and tolerability of ravulizumab and eculizumab were similar; no meningococcal infections occurred. In conclusion, ravulizumab given every 8 weeks achieved noninferiority compared with eculizumab given every 2 weeks for all efficacy end points, with a similar safety profile. This trial was registered at www.clinicaltrials.gov as #NCT02946463.

Complement-driven anemia: more than just paroxysmal nocturnal hemoglobinuria

Atypical hemolytic uremic syndrome (aHUS); hemolysis, elevated liver function tests, and low platelets syndrome; and transplant-associated thrombotic microangiopathy are related conditions, in that many patients harbor germline heterozygous mutations in genes that regulate the alternative pathway of complement (APC). Penetrance is variable because development of clinically significant disease appears to require supervention of a process such as inflammation. Complement activation on the endothelial surfaces leads to endothelial damage, platelet consumption, microthrombi, and a mechanical hemolytic anemia with schistocytes. Paroxysmal nocturnal hemoglobinuria (PNH) is a clonal hematopoietic disease caused by expansion of a stem cell that harbors a somatic mutation in PIGA PIGA mutant blood cells are deficient in the complement regulator proteins CD55 and CD59, making them susceptible to intravascular hemolysis due to a failure to regulate the APC on erythrocytes. Eculizumab is a monoclonal antibody that binds to C5 and inhibits terminal complement by interfering with the cleavage of C5 by the C5 convertases. The drug is approved by the US Food and Drug Administration for the treatment of aHUS and PNH; however, a new generation of complement inhibitors that block C5 and other components of the complement cascade is showing promise in preclinical and clinical trials.

How we treat paroxysmal nocturnal hemoglobinuria: A consensus statement of the Canadian PNH Network and review of the national registry

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare hematologic disease characterized by intravascular hemolysis, thrombophilia, and marrow failure. Its phenotype is due to absent or reduced expression of GPI-linked complement regulators and subsequent sensitivity of hematopoietic cells to complement-mediated damage and lysis. Introduction of the terminal complement inhibitor eculizumab drastically improved outcomes in PNH patients; however, despite this improvement, there remain several challenges faced by PNH patients and physicians who care for them. One of the most important is increasing awareness of the heterogeneity with which patients can present, which can lead to significant delays in recognition. Data from the Canadian PNH Registry are presented to demonstrate the variety of presenting symptoms. In Canada, geography precludes consolidation of care to just a few centers, so management is distributed across academic hospitals, linked together as the Canadian PNH Network. The Network over the last several years has developed educational programs and clinical checklists and has worked to standardize access to diagnostics across the country. Herein, we address some of the common diagnostic and therapeutic challenges faced by PNH physicians and give our recommendations. Gaps in knowledge are also addressed, and where appropriate, consensus opinion is provided.

Developments in anti-complement therapy; from disease to clinical trial

The complement system is well known for its role in innate immunity and in maintenance of tissue homeostasis, providing a first line of defence against infection and playing a key role in flagging apoptotic cells and debris for disposal. Unfortunately complement also contributes to pathogenesis of a number of diseases; in some cases driving pathology, and in others amplifying or exacerbating the inflammatory and damaging impact of non-complement disease triggers. The role of complement in pathogenesis of an expanding number of diseases has driven industry and academia alike to develop an impressive arsenal of anti-complement drugs which target different proteins and functions of the complement cascade. Evidence from genetic and biochemical analyses, combined with improved identification of complement biomarkers and supportive data from sophisticated animal models of disease, has driven a drug development landscape in which the indications selected for clinical trial cluster in three 'target' tissues: the kidney, eye and vasculature. While the disease triggers may differ, complement activation and amplification is a common feature in many diseases which affect these three tissues. An abundance of drugs are in clinical development, some show favourable progression whereas others experience significant challenges. However, these hurdles in themselves drive an ever-evolving portfolio of 'next-generation' drugs with improved pharmacokinetic and pharmacodynamics properties. In this review we discuss the indications which are in the drug development 'spotlight' and review the relevant indication validation criteria. We present current progress in clinical trials, highlighting successes and difficulties, and look forward to approval of a wide selection of drugs for use in man which give clinicians choice in mechanistic target, modality and route of delivery.

Impairment of Nitric Oxide Pathway by Intravascular Hemolysis Plays a Major Role in Mice Esophageal Hypercontractility: Reversion by Soluble Guanylyl Cyclase Stimulator

Paroxysmal nocturnal hemoglobinuria (PNH) patients display exaggerated intravascular hemolysis and esophageal disorders. Since excess hemoglobin in the plasma causes reduced nitric oxide (NO) bioavailability and oxidative stress, we hypothesized that esophageal contraction may be impaired by intravascular hemolysis. This study aimed to analyze the alterations of the esophagus contractile mechanisms in a murine model of exaggerated intravascular hemolysis induced by phenylhydrazine (PHZ). For comparative purposes, sickle cell disease (SCD) mice were also studied, a less severe intravascular hemolysis model. Esophagus rings were dissected free and placed in organ baths. Plasma hemoglobin was higher in PHZ compared with SCD mice, as expected. The contractile responses produced by carbachol (CCh), KCl, and electrical-field stimulation (EFS) were superior in PHZ esophagi compared with control but remained unchanged in SCD mice. Preincubation with the NO-independent soluble guanylate cyclase stimulator 3-(4-amino-5-cyclopropylpyrimidin-2-yl)-1-(2-fluorobenzyl)-1H-pyrazolo[3,4-b]pyridine (BAY 41-2272; 1 μM) completely reversed the increased contractile responses to CCh, KCl, and EFS in PHZ mice, but responses remained unchanged with prior treatment with NO donor sodium nitroprusside (300 μM). Protein expression of 3-nitrotyrosine and 4-hydroxynonenal increased in esophagi from PHZ mice, suggesting a state of oxidative stress. In endothelial nitric oxide synthase gene-deficient mice, the contractile responses elicited by KCl and CCh were increased in the esophagus but remained unchanged with the intravascular hemolysis induced by PHZ. In conclusion, our results show that esophagus hypercontractile state occurs in association with lower NO bioavailability due to exaggerated hemolysis intravascular and oxidative stress. Moreover, our study supports the hypothesis that esophageal disorders in PNH patients are secondary to intravascular hemolysis affecting the NO-cGMP pathway.

Be on Target: Strategies of Targeting Alternative and Lectin Pathway Components in Complement-Mediated Diseases

The complement system has moved into the focus of drug development efforts in the last decade, since its inappropriate or uncontrolled activation has been recognized in many diseases. Some of them are primarily complement-mediated rare diseases, such as paroxysmal nocturnal hemoglobinuria, C3 glomerulonephritis, and atypical hemolytic uremic syndrome. Complement also plays a role in various multifactorial diseases that affect millions of people worldwide, such as ischemia reperfusion injury (myocardial infarction, stroke), age-related macular degeneration, and several neurodegenerative disorders. In this review, we summarize the potential advantages of targeting various complement proteins with special emphasis on the components of the lectin (LP) and the alternative pathways (AP). The serine proteases (MASP-1/2/3, factor D, factor B), which are responsible for the activation of the cascade, are straightforward targets of inhibition, but the pattern recognition molecules (mannose-binding lectin, other collectins, and ficolins), the regulatory components (factor H, factor I, properdin), and C3 are also subjects of drug development. Recent discoveries about cross-talks between the LP and AP offer new approaches for clinical intervention. Mannan-binding lectin-associated serine proteases (MASPs) are not just responsible for LP activation, but they are also indispensable for efficient AP activation. Activated MASP-3 has recently been shown to be the enzyme that continuously supplies factor D (FD) for the AP by cleaving pro-factor D (pro-FD). In this aspect, MASP-3 emerges as a novel feasible target for the regulation of AP activity. MASP-1 was shown to be required for AP activity on various surfaces, first of all on LPS of Gram-negative bacteria.

The effect on the immunology laboratory of the expansion in complement therapeutics

The approval in the US and Europe of Eculizumab in 2007 marked a change in complement therapeutics, and with it the landscape for complement testing in the clinical immunology laboratory changed. The change had begun even before that when C1-Inhibitor preparations were approved in the 1980s in Europe. There are now two classes of approved drugs that may impact the immunology laboratory, with two dozen more with novel modalities and potential indications that are in various stages of development. Every pathway and about every component of complement has been targeted by these drug development programs, and the modalities of the drugs in development are diverse. These developments will likely result in more laboratories offering more complement testing, so this review looks forward to some of those possible changes in testing.

Therapeutic potential of staphylococcal superantigen-like protein 7 for complement-mediated hemolysis

Previous studies have demonstrated that staphylococcal superantigen-like protein 7 (SSL7), a protein produced by Staphylococcus aureus, potently inhibits the formation of the complement membrane attack complex by binding to complement component 5 (C5). However, because of the predicted immunogenicity of SSL7 as a foreign protein in humans, its potential as a new complement inhibitor for treating complement-mediated diseases is uncertain. In this study, we found that administration of SSL7 significantly prevented complement-mediated hemolysis and reduced hemoglobinuria in a mouse model of complement-mediated intravascular hemolysis. Interestingly, although repetitive administrations of SSL7 elicited anti-SSL7 antibody production, administration of SSL7 at a dose of 2 μg/mouse was still able to significantly attenuate complement-mediated intravascular hemolysis in vivo in the presence of the antibodies. In addition, even though anti-SSL7 antibodies were detectable in normal human donors, these antibodies did not significantly reduce the complement inhibitory activity of SSL7 in in vitro assays. Finally, inoculation of SSL7 in the anterior chamber of the eye suppressed the production of SSL7-reactive antibodies after repetitive SSL7 administration. These results suggest that SSL7 could be developed as an economical alternative to the existing C5-targeted drug, eculizumab, especially for controlling acute complement activation in catastrophic conditions such as drug-induced immune hemolytic anemia and ABO-incompatible erythrocyte transfusions. These data also suggest that approaches such as anterior chamber-associated immune deviation could be employed to establish an antigen-specific immune tolerance for long-term SSL7 administration.

KEY MESSAGES

• SSL7 functions in the presence of anti-SSL7 antibodies both in vitro and in vivo. • SSL7 has the potential to be developed as a new and economical complement inhibitor for treating complement-mediated hemolysis.

Eculizumab Bridging before Bone Marrow Transplant for Marrow Failure Disorders Is Safe and Does Not Limit Engraftment

Paroxysmal nocturnal hemoglobinuria (PNH) often develops secondary to other bone marrow failure (BMF) disorders, especially aplastic anemia (AA). Patients with the AA/PNH syndrome may require treatment with both eculizumab to reduce intravascular hemolysis and the risk of thrombosis and allogeneic stem cell transplant for the severe BMF. There has been concern that eculizumab could adversely affect the outcomes for transplant in these patients. This is a retrospective, single-center study of severe AA (SAA)/PNH patients treated with eculizumab immediately before the start of conditioning for transplant. Metrics of engraftment and infectious outcomes are described. Eight patients with SAA/PNH and PNH-related symptoms were treated with eculizumab and then proceeded to transplant. All were successfully transplanted without adverse events related to C5 blockage before conditioning. All were also cured of their both PNH and SAA. Eculizumab is safe and efficacious in patients with PNH clones who require transplant. This is sometimes required to "bridge" patients before bone marrow transplantation and does not appear to adversely impact outcomes even when using HLA matched unrelated or haploidentical donors.

Clonal Hematopoiesis in Aging

Purpose of Review

Clonal hematopoiesis of indeterminate potential (CHIP) is a common, age-associated condition characterized by the acquisition of somatic mutations. This concise review explores our current understanding of the mechanisms that influence the development of clonality with aging and its potential malignant and non-malignant clinical implications.

Recent Findings

Aging of the hematopoietic system results in phenotypic changes that favor clonal dominance. Cell-extrinsic factors provide additional selective pressures that further shape clonal architecture. Even so, small clones with candidate driver mutations appear to be ubiquitous with age and largely benign in the absence of strong selective pressures. Benign clonal expansion may compensate for the loss of regenerative HSC capacity as we age.

Summary

CHIP is a marker of aging that reflects the biologic interplay between HSC aging and cell-extrinsic factors. The clinical significance of CHIP is highly variable and dependent on clinical context. Distinguishing the causal relationships and confounding factors that regulate clonal behavior will be essential to define the mechanistic role of CHIP in aging and potentially mitigate its clinical consequences.

Venom from Bothrops lanceolatus, a Snake Species Native to Martinique, Potently Activates the Complement System

Bothrops lanceolatus snake venom causes systemic thrombotic syndrome but also local inflammation involving extensive oedema, pain, and haemorrhage. Systemic thrombotic syndrome may lead to fatal pulmonary embolism and myocardial and cerebral infarction. Here, we investigated the ability of B. lanceolatus venom to activate the Complement system (C) in order to improve the understanding of venom-induced local inflammation. Data presented show that B. lanceolatus venom is able to activate all C-pathways. In human serum, the venom strongly induced the generation of anaphylatoxins, such as C5a and C4a, and the Terminal Complement complex. The venom also induced cleavage of purified human components C3, C4, and C5, with the production of biologically active C5a. Furthermore, the venom enzymatically inactivated the soluble C-regulator and the C1-inhibitor (C1-INH), and significantly increased the expression of bound C-regulators, such as MCP and CD59, on the endothelial cell membrane. Our observations that B. lanceolatus venom activates the three Complement activation pathways, resulting in anaphylatoxins generation, may suggest that this could play an important role in local inflammatory reaction and systemic thrombosis caused by the venom. Inactivation of C1-INH, which is also an important inhibitor of several coagulation proteins, may also contribute to inflammation and thrombosis. Thus, further in vivo studies may support the idea that therapeutic management of systemic B. lanceolatus envenomation could include the use of Complement inhibitors as adjunct therapy.

Common and rare genetic variants of complement components in human disease

Genetic variability in the complement system and its association with disease has been known for more than 50 years, but only during the last decade have we begun to understand how this complement genetic variability contributes to the development of diseases. A number of reports have described important genotype-phenotype correlations that associate particular diseases with genetic variants altering specific aspects of the activation and regulation of the complement system. The detailed functional characterization of some of these genetic variants provided key insights into the pathogenic mechanisms underlying these pathologies, which is facilitating the design of specific anti-complement therapies. Importantly, these analyses have sometimes revealed unknown features of the complement proteins. As a whole, these advances have delineated the functional implications of genetic variability in the complement system, which supports the implementation of a precision medicine approach based on the complement genetic makeup of the patients. Here we provide an overview of rare complement variants and common polymorphisms associated with disease and discuss what we have learned from them.

Antibody Inhibition of Properdin Prevents Complement-Mediated Intravascular and Extravascular Hemolysis

Paroxysmal nocturnal hemoglobinuria (PNH) is a serious blood disorder characterized by dysregulated complement activation on blood cells. Eculizumab, the current standard therapy and a humanized anti-C5 mAb, relieves anemia and thrombosis symptoms of PNH patients by preventing complement-dependent intravascular hemolysis (IVH). However, up to 20% of PNH patients on long-term eculizumab treatment still suffer from significant anemia and are transfusion dependent because of extravascular hemolysis (EVH) of C3-opsonized PNH erythrocytes. In this study, we show that function-blocking anti-properdin (P) mAbs dose-dependently inhibited autologous, complement-mediated hemolysis induced by factor H dysfunction. Furthermore, anti-human P (hP) mAbs potently and dose-dependently inhibited acidified serum-induced hemolysis of PNH erythrocytes (Ham test). In contrast to erythrocytes rescued by anti-C5 mAb, nonlysed PNH erythrocytes rescued by anti-P mAb incurred no activated C3 fragment deposition on their surface. These results suggested that anti-P mAbs may prevent EVH as well as IVH of PNH erythrocytes. To test the in vivo efficacy of anti-hP mAbs in preventing EVH, we generated a P humanized mouse by transgenic expression of hP in P knockout mice (hP-Tg/P^-/-). In a murine EVH model, complement-susceptible erythrocytes were completely eliminated within 3 d in control mAb-treated hP-Tg/P^-/- mice, whereas such cells were protected and persisted in hP-Tg/P^-/- mice treated with an anti-hP mAb. Collectively, these data suggest that anti-P mAbs can inhibit both IVH and EVH mediated by complement and may offer improved efficacy over eculizumab, the current standard therapy for PNH.

A potent complement factor C3-specific nanobody inhibiting multiple functions in the alternative pathway of human and murine complement

The complement system is a complex, carefully regulated proteolytic cascade for which suppression of aberrant activation is of increasing clinical relevance, and inhibition of the complement alternative pathway is a subject of intense research. Here, we describe the nanobody hC3Nb1 that binds to multiple functional states of C3 with subnanomolar affinity. The nanobody causes a complete shutdown of alternative pathway activity in human and murine serum when present in concentrations comparable with that of C3, and hC3Nb1 is shown to prevent proconvertase assembly, as well as binding of the C3 substrate to C3 convertases. Our crystal structure of the C3b-hC3Nb1 complex and functional experiments demonstrate that proconvertase formation is blocked by steric hindrance between the nanobody and an Asn-linked glycan on complement factor B. In addition, hC3Nb1 is shown to prevent factor H binding to C3b, rationalizing its inhibition of factor I activity. Our results identify hC3Nb1 as a versatile, inexpensive, and powerful inhibitor of the alternative pathway in both human and murine in vitro model systems of complement activation.

High sensitivity 8-color flow cytometry assay for paroxysmal nocturnal hemoglobinuria granulocyte and monocyte detections

Flow cytometry is the gold standard in diagnosis of paroxysmal nocturnal hemoglobinuria (PNH) by detecting the absence of glycol-phosphatidyl inositol (GPI)-linked protein expression on granulocyte and monocyte surfaces. However, the current assays are not optimized and require improvement, particularly in reducing background fluorescence and optimizing sensitivity and specificity. With more fluorochromes available and with advances in instrument engineering, rare populations may be identified with high sensitivity. The present study assessed an 8-color combination of comprehensive GPI-linked markers, namely fluorescein-labeled proaerolysin (FLAER), cluster of differentiation 157 (CD157), CD24 and CD14, and the lineage markers for granulocyte (CD15) and monocyte (CD64) cells to detect PNH clones. Additionally, to optimize the PNH flow assay, a 'dump' channel was used, comprised of CD5 and CD19, to exclude non-specific binding in order to reduce background. This method aimed to improve sensitivity and reduce the background to create an optimized PNH flow cocktail. The results demonstrated that the current 4-color PNH combination identifies a CD55^- and FLAER⁺ population that is not PNH clones. By contrast, the 8-color panel delineated PNH clones from both monocyte and granulocytes by using granulocyte antigen (CD15) and monocyte antigen (CD64) as a gating strategy. The sensitivity was 0.01% for granulocytes and 0.05% for monocytes with an acquisition of 100,000 monocyte and granulocyte events. The background on a normal whole blood sample was 0.00076% on monocytes and 0.00277% on granulocytes. Thus, overall, the 8-color PNH assay exhibited high levels of specificity and sensitivity. The 8-color combination facilitated the improvement and enhancement of sensitivity in PNH clone identification, and may provide a useful tool for pathologists in PNH diagnosis and for monitoring patients at risk of developing classical/hemolytic PNH, to enable treatment to be delivered promptly.

Germline mutations in the alternative pathway of complement predispose to HELLP syndrome

BACKGROUND

HELLP (hemolysis, elevated liver enzymes, and low platelets) syndrome is a severe variant of hypertensive disorders of pregnancy affecting approximately 1% of all pregnancies, and has significant maternal and fetal morbidity. Previously, we showed that upregulation of the alternative pathway of complement (APC) plays a role in HELLP syndrome. We hypothesize that HELLP syndrome follows a 2-hit disease model similar to atypical hemolytic uremic syndrome (aHUS), requiring both genetic susceptibility and an environmental risk factor. Our objective was to perform a comparative analysis of the frequency of APC activation and germline mutations in affected women and to create a predictive model for identifying HELLP syndrome.

METHODS

Pregnant women with HELLP syndrome, and healthy controls after 23 weeks of gestation were recruited, along with aHUS and thrombotic thrombocytopenic purpura participants. We performed a functional assay, the mHam, and targeted genetic sequencing in all groups.

RESULTS

Significantly more participants with rare germline mutations in APC genes were present in the HELLP cohort compared with controls (46% versus 8%, P = 0.01). In addition, significantly more HELLP participants were positive for the mHam when compared with controls (62% versus 16%, P = 0.009). Testing positive for both a germline mutation and the mHam was highly predictive for the diagnosis of HELLP syndrome.

CONCLUSION

HELLP syndrome is characterized by both activation of the APC and frequent germline mutations in APC genes. Similar to aHUS, treatment via complement inhibition to mitigate maternal and fetal morbidity and mortality may be possible.

FUNDING

National Heart Lung and Blood Institute grants T32HL007525 and R01HL133113.

Renal involvement in paroxysmal nocturnal hemoglobinuria: an update on clinical features, pathophysiology and treatment

OBJECTIVES

The present review summarizes the available knowledge regarding acute and chronic kidney dysfunction in patients with paroxysmal nocturnal hemoglobinuria (PNH) focusing on its clinical features, pathophysiology and treatment.

METHODS

A thorough PubMed search was performed using as main keywords: 'paroxysmal nocturnal hemoglobinuria', 'acute kidney injury', 'chronic kidney disease' and 'eculizumab'.

RESULTS

PNH's etiopathogenesis is based on acquired mutations that lead to the reduction or absence of CD55 and CD59 complement regulators, which are responsible for some of the disease's major clinical features, like intravascular hemolysis, cytopenias and thrombosis. PNH is often underdiagnosed, mainly due to its occasional mild manifestations and to its ability to mimic other severe clinical conditions. Various mechanisms have been proposed for the kidney damage attributed to the release of cell-free heme and free iron, including inflammatory response, oxidative stress, nitric oxide depletion, renal ischemia, membrane damage and apoptosis. Eculizumab, a terminal complement inhibitor, provides a safe and effective treatment option, especially when it is initiated early in the presence of kidney damage.

DISCUSSION

Kidney injury is a poorly investigated clinical feature of PNH that affects a significant portion of patients. Increased awareness is needed by physicians to recognize the early signs and symptoms of acute and chronic renal insufficiency, so as to initiate the necessary therapy. It is also important to re-evaluation of PNH-specific treatments during the course of the disease.

CONCLUSION

Understanding the difficult but at the same time impressive mechanisms behind PNH remains a challenge for treating physicians.

Novel mutations and phenotypes of epilepsy-associated genes in epileptic encephalopathies

Epileptic encephalopathies are severe epilepsy disorders with strong genetic bases. We performed targeted next-generation sequencing (NGS) in 70 patients with epileptic encephalopathies. The likely pathogenicity of variants in candidate genes was evaluated by American College of Medical Genetics and Genomics (ACMG) scoring taken together with the accepted clinical presentation. Thirty-three candidate variants were detected after population filtration and computational prediction. According to ACMG, 21 candidate variants, including 18 de novo variants, were assessed to be pathogenic/likely pathogenic with clinical concordance. Twelve variants were initially assessed as uncertain significance by ACMG, among which 3 were considered causative and 3 others were considered possibly causative after analysis of clinical concordance. In total, 24 variants were identified as putatively causative, among which 19 were novel findings. SCN1A mutations were identified in 50% of patients with Dravet syndrome. TSC1/TSC2 mutations were detected in 66.7% of patients with tuberous sclerosis. STXBP1 mutations were the main findings in patients with West syndrome. Mutations in SCN2A, KCNT1, KCNQ2 and CLCN4 were identified in patients with epileptic infantile with migrating focal seizures; among them, KCNQ2 and CLCN4 were first identified as potential causative genes. Only one CHD2 mutation was detected in patients with Lennox-Gastaut syndrome. This study highlighted the utility of targeted NGS in genetic diagnoses of epileptic encephalopathies and a comprehensive evaluation of the pathogenicity of variants based on ACMG scoring and assessment of clinical concordance. Epileptic encephalopathies differ in genetic causes, and the genotype-phenotype correlations would provide insights into the underlying pathogenic mechanisms.

Paroxysmal Nocturnal Hemoglobinuria (Pnh): Brain Mri Ischemic Lesions In Neurologically Asymtomatic Patients

This study investigated for the first time brain ischemic involvement in 19 consecutive neurologically asymptomatic PNH patients by non-enhanced cerebral MRI, and by intracranial arterial and venous angio-MRI. Eleven cases (58%, 7 aged <65) showed pathological findings: 9 white matter (WM) abnormalities related to chronic ischemic small vessel disease, 2 a focal abnormality >5 mm, and 5 cases a score >4 by the age-related white matter changes (ARWMC) scale. Compared with age and sex-matched controls (1:2 ratio), patients showed an increased frequency of periventricular WM vascular degeneration (32% versus 5.2%, p = 0.04) and of severe lesions (ARWMC scale score >4) (26% versus 2.6%, p = 0.05), and a higher overall ARWMC scale score (3.5 ± 1.07 versus 2.0 ± 0.8, mean ± SD, p < 0.0001). Notably, vascular abnormalities suspected for prior partial venous thrombosis, were observed in PNH cases only. MRI lesions were not related to blood counts, hemolytic markers, clone size, disease duration, and therapy with eculizumab. Neurological examination was unremarkable in all patients but one (Parkinson disease). Psychiatric assessment revealed a case of generalized anxiety disorder, 1 bipolar disorder type 2, and 1 adjustment disorder. In conclusion, brain MRI may be useful at diagnosis and during the course of the disease to explore subclinical neurological involvement.

Diseases of complement dysregulation-an overview

Atypical hemolytic uremic syndrome (aHUS), C3 glomerulopathy (C3G), and paroxysmal nocturnal hemoglobinuria (PNH) are prototypical disorders of complement dysregulation. Although complement overactivation is common to all, cell surface alternative pathway dysregulation (aHUS), fluid phase alternative pathway dysregulation (C3G), or terminal pathway dysregulation (PNH) predominates resulting in the very different phenotypes seen in these diseases. The mechanism underlying the dysregulation also varies with predominant acquired autoimmune (C3G), somatic mutations (PNH), or inherited germline mutations (aHUS) predisposing to disease. Eculizumab has revolutionized the treatment of PNH and aHUS although has been less successful in C3G. With the next generation of complement therapeutic in late stage development, these archetypal complement diseases will provide the initial targets.

Acute myeloid leukemia and fatal Scedosporium prolificans sepsis after eculizumab treatment for paroxysmal nocturnal hemoglobinuria: a case report

Eculizumab has become the standard of care for patients with paroxysmal nocturnal hemoglobinuria (PNH). As more patients are treated, the long-term outcomes of these patients will become apparent. We recently treated a patient who developed PNH in the setting of aplastic anemia. The patient developed acute myeloid leukemia less than three years after initiating eculizumab. The patient also died suddenly from Scedosporium sepsis during induction therapy. This patient's course seemed more aggressive than would be expected. The possible effect of complement blockade is discussed.

Haemostasis and innate immunity - a complementary relationship: A review of the intricate relationship between coagulation and complement pathways

Coagulation and innate immunity are linked evolutionary processes that orchestrate the host defence against invading pathogens and injury. The complement system is integral to innate immunity and shares numerous interactions with components of the haemostatic pathway, helping to maintain physiological equilibrium. The term 'immunothrombosis' was introduced in 2013 to embrace this process, and has become an area of much recent interest. What is less apparent in the literature however is an appreciation of the clinical manifestations of the coagulation-complement interaction and the consequences of dysregulation of either system, as seen in many inflammatory and thrombotic disease states, such as sepsis, trauma, atherosclerosis, antiphospholipid syndrome (APS), paroxysmal nocturnal haemoglobinuria (PNH) and some thrombotic microangiopathies to name a few. The growing appreciation of this immunothrombotic phenomenon will foster the drive for novel therapies in these disease states, including anticoagulants as immunomodulators and targeted molecular therapies.