Recombinant to modified factor VIII and factor IX - chromogenic and one-stage assays issues

Variability in combinations of APTT reagent and substrate plasma for a one-stage clotting assay to measure factor VIII products

INTRODUCTION

An investigation of the suitability of reagents for measuring FVIII products in a one-stage clotting assay (OSA) showed variations in their FVIII activity (FVIII:C). Most studies have focused on the activated partial thromboplastin time (APTT) reagent rather than FVIII-deficient plasma (F8DP), even though the APTT-based OSA is comprised of APTT reagents and factor-deficient plasma.

AIM

A single-centre study was conducted to clarify variations in measurements of FVIII products in an OSA using a total of 12 reagent combinations, including four APTT reagents and three types of F8DP.

METHODS

FVIII:C in nine types of FVIII product-spiked plasma was measured using an OSA with four different APTT reagents and three types of F8DP.

RESULTS

F8DP-dependent variations were found in addition to differences derived from APTT reagents. Variations in target recovery (TR) were observed for NovoEight®, Eloctate®, and Jivi®. Reduced TR for Jivi was found only for Pathromtin SL in combination with congenital F8DP (F8DP-3). This lower TR was not observed with alternative manufacturing lots of F8DP-3. The reduced TR for Jivi might be related to impaired contact activation due to lower factor XI activity in F8DP-3.

CONCLUSION

In addition to APTT reagents, variations in F8DPs used for OSAs can also affect FVIII:C results. F8DPs as well as the APTT reagent used for OSA should be chosen with caution, and laboratories should evaluate reagents for F8DPs as they currently do for APTT reagents, especially when lot changes occur.

High variability in Factor IX one-stage assay in samples spiked with nonacog beta pegol among different pairs of reagent/detection system

INTRODUCTION

Haemophilia B (HB) is an X-linked hereditary bleeding disorder characterized by coagulation factor IX (FIX) deficiency. To improve the quality of life of patients and adherence to treatment, recombinant factor concentrates modified to extend their half-life have been developed, called extended half-life factors (EHL: extended half-life). Nonacog beta pegol (N9-GP) is a glycopegylated recombinant human FIX molecule that has a half-life of 93 h with a single dose and has shown a higher recovery percentage than other molecules. To diagnose and monitor the treatment of haemophiliac patients, FIX activity is determined with the one-stage clotting assay (OSA) and/or the chromogenic assay. The objective of this work, carried out in three centres, was to measure the recovery of N9-PG with 10 different activated partial thromboplastin time (APTT) reagents on three platforms, in samples spiked in vitro with N9-GP, at four different concentration levels.

METHODS

It was measured the recovery of N9-GP with 10 different APTT reagents (polyphenol, ellagic acid, silice dioxide, colloidal silica as APTT activator on three platforms, in sample spiked in vitro with N9-GP.

RESULTS

The results show heterogeneity in the activity of N9-GP measured by OSA with the different APTT reagents when the calibrations were performed with the specific calibrator of each coagulometer. A recovery percentage between 87% and 108% was obtained only with polyphenol and ellagic acid as activator in the three platforms evaluated. The other reagents studied overestimate or underestimate, with no clear profile. When a calibration curve was performed with a calibrator prepared from the N9-GP vial, all APTT reagents met the established recovery requirement.

CONCLUSION

APTT reagents with polyphenol or ellagic acid as activator would be the only ones appropriate when using the commercially available OSA with specific calibrator to monitor patients treated with N9-GP.

Hemophilia A: Emicizumab monitoring and impact on coagulation testing

Hemophilia A is an X-linked recessive bleeding disorder characterized by absent or ineffective coagulation factor VIII, a condition that could result in a severe and potentially life-threatening bleed. Although the current standard of care involves prophylactic replacement therapy of factor VIII, the development of neutralizing anti-factor VIII alloantibody inhibitors often complicates such therapeutic treatment. Emicizumab (Hemlibra®), a novel recombinant therapeutic agent for patients with hemophilia A, is a humanized asymmetric bispecific IgG4 monoclonal antibody designed to mimic activated factor VIII by bridging factor IXa and factor X thus effecting hemostasis. Importantly, this drug eliminates the need for factor VIII and complications associated with inhibitor generation. Emicizumab has been approved for use in several countries including the United States and Japan for prophylaxis of bleeding episodes in hemophilia A with and without FVIII inhibitors. Therapy is also approved in the European Union for routine prophylaxis of bleeds in hemophilia A with inhibitors or severe hemophilia A without inhibitors. Unfortunately, emicizumab therapy presents unique challenges for routine and specialty coagulation tests currently used to monitor hemophilia A. In this review, hemophilia A is presented, the biochemistry of factor VIII is discussed, and the impact of the therapeutic agent emicizumab is highlighted.

Guidance for establishing a factor VIII testing protocol for the myriad of factor VIII products

INTRODUCTION

Management of hemophilia A has changed significantly in the past few years with the expansion of new and/or modified products as treatment options. Unfortunately, many of the standard factor VIII assays do not always accurately measure all available treatment products; therefore, the laboratory must investigate various assay algorithms to ensure the reporting of the correct results.

METHODS

Requirements for factor testing, diagnosis and severity levels, product testing, factor VIII inhibitor detection and titers, are evaluated, and potential algorithms are created for optimal assessment of patients with hemophilia A.

RESULTS

The potential for inaccurate result reporting for patients with hemophilia A or those being treated with the myriad of products has left many laboratories uncertain as to which assay algorithm to implement to ensure reporting the correct results for all products used in their hemophilia program. Algorithms for using either One-stage Clotting assays or Chromogenic assays or a combination of both types of assays are presented for each laboratory to implement based on their clinical situation.

CONCLUSIONS

Several algorithms are considered based on the needs of the clinical providers and their patients. Each laboratory must select a testing algorithm that is cost-effective and within available resources, yet that encompasses the needs of their providers and patients. Laboratory personnel must consider all assay uses (factor VIII levels, different products, interfering products, and inhibitor titers) in determining the best algorithm for their laboratory. This paper is a starting guide for developing the best factor VIII testing assays and protocols for your laboratory.

Haemophilia

Haemophilia A and B are rare congenital, recessive X-linked disorders caused by lack or deficiency of clotting factor VIII (FVIII) or IX (FIX), respectively. The severity of the disease depends on the reduction of levels of FVIII or FIX, which are determined by the type of the causative mutation in the genes encoding the factors (F8 and F9, respectively). The hallmark clinical characteristic, especially in untreated severe forms, is bleeding (spontaneous or after trauma) into major joints such as ankles, knees and elbows, which can result in the development of arthropathy. Intracranial bleeds and bleeds into internal organs may be life-threatening. The median life expectancy was ~30 years until the 1960s, but improved understanding of the disorder and development of efficacious therapy based on prophylactic replacement of the missing factor has caused a paradigm shift, and today individuals with haemophilia can look forward to a virtually normal life expectancy and quality of life. Nevertheless, the potential development of inhibitory antibodies to infused factor is still a major hurdle to overcome in a substantial proportion of patients. Finally, gene therapy for both types of haemophilia has progressed remarkably and could soon become a reality.

Factor IX assay discrepancies in the setting of liver gene therapy using a hyperfunctional variant factor IX-Padua

BACKGROUND

Limited information exists regarding the factor IX (FIX) coagulant activity (FIX:C) measured by different assays following FIX-Padua gene therapy.

OBJECTIVE

Assess for the first time FIX:C in five commonly used coagulation assays in plasma samples from hemophilia B subjects receiving FIX-Padua gene transfer.

METHODS

FIX:C was compared between central (n = 1) and local laboratories (n = 5) in the study, and across four commonly used FIX:C one-stage assays and one FIX:C chromogenic assay. For comparison, samples of pooled congenital FIX-deficient plasma spiked with purified recombinant human FIX (rHFIX)-Padua protein or rHFIX (nonacog alfa) to obtain FIX:C concentrations from ~20% to ~40% were tested.

RESULTS

FIX:C results at local laboratories strongly correlated with central laboratory results. However, absolute values at the central laboratory were consistently lower than those at local laboratories. Across five different FIX:C assays, a consistent pattern of FIX:C was observed for subjects receiving fidanacogene elaparvovec-expressed gene transfer. Use of Actin FSL activated partial thromboplastin time (APTT) reagent in the central laboratory resulted in lower FIX:C values compared with other APTT reagents tested. The chromogenic assay determined lower FIX:C than any of the one-stage assays. The rHFIX-Padua protein-spiked samples showed similar results. In contrast, FIX:C results for rHFIX-nonacog alfa measured within 25% of expected for all one-stage assays and below 25% in the chromogenic assay.

CONCLUSIONS

Assay-based differences in FIX:C were observed for fidanacogene elaparvovec transgene product and rHFIX-Padua protein, suggesting the variable FIX:C determined with different assay reagents is inherent to the FIX-Padua protein and is not specific to gene therapy-derived FIX-Padua.

Laboratory testing in hemophilia: Impact of factor and non-factor replacement therapy on coagulation assays

The advent of extended half-life (EHL) recombinant clotting factors and innovative non-factor replacement therapeutics, such as emicizumab, offers several advantages over existing products for the prophylactic treatment of people living with hemophilia (PwH). These include low annual bleeding rates with less frequent dosing, higher trough plasma concentrations, and a more convenient route of administration. However, increasing use of these therapies poses challenges to clinicians and coagulation laboratories due to the lack of standardized assays for monitoring of hemostatic parameters, and the potential for misinterpretation of test results, which may jeopardize patient safety. Definitive diagnosis of hemophilia and treatment monitoring is reliant on demonstrating factor VIII (FVIII; hemophilia A) or factor IX (FIX; hemophilia B) deficiency using a functional coagulation assay. The most frequently used assays are based on activated partial thromboplastin time, using a one-stage or two-stage process. While one-stage and chromogenic assays have performed well with human-derived FVIII and FIX and full-length recombinant products, EHL recombinant factors are heterogeneous in structure and mode of action and therefore show wide variation in activity levels between different one-stage assays, and between one-stage and chromogenic assays. In the context of the recommended stepwise approach for laboratory diagnosis of hemophilia, we examine the diagnostic challenges associated with the use of EHL factors and novel non-factor therapeutics and consider the optimal diagnostic approach in PwH who are receiving these treatments. Ultimately, accurate diagnostic solutions are a prerequisite for personalized therapy to minimize treatment burden and improve quality of life in PwH.

A bispecific antibody demonstrates limited measurability in routine coagulation assays

: Accurate monitoring of coagulation, needed for optimal management of patients with haemophilia A with inhibitors, presents a challenge for treating physicians. Although global haemostatic assays may be used in this population, their utility with nonfactor therapies has yet to be established in the clinical setting. The aim of this study was to assess options for potential haemostatic activity monitoring and feasibility for factor VIII (FVIII)-equivalency measurement with a sequence identical analogue (SIA) to emicizumab using different coagulation assays. SIA was analysed using five commercial chromogenic assays and activated partial thromboplastin time (aPTT) assays including clot waveform analysis using five different triggers. Recombinant FVIII served as a comparator in all assays. Thrombin generation in haemophilia A plasma was measured using extrinsic and intrinsic trigger conditions (tissue factor or Factor XIa). Of the five chromogenic assays, a concentration-dependent increase in Factor Xa was observed with one assay, with human Factor IXa and X reagents. The SIA dose-response signal plateaued at therapeutically relevant concentrations and was nonparallel with FVIII reference, thereby not permitting FVIII-equivalence assessment. aPTT varied between reagents, with aPTT normalization occurring at low and below-therapeutic SIA concentrations. SIA [600 nmol/l (90 μg/ml)] only partially restored thrombin generation in individual haemophilia A patient plasma. FVIII-equivalence of SIA could not be determined using standard FVIII protocols and was found to be highly influenced by assay type, analytical conditions and parameters used for calculation. New and/or modified methodology and standard reagents specific for use with nonfactor therapies are required for their utilization in the clinical setting.

Laboratory issues in gene therapy and emicizumab

The treatment options for the haemostatic disorders, haemophilia A and haemophilia B, have progressed rapidly over the last decade. The introduction of extended half-life recombinant factor VIII (FVIII) and factor IX (FIX) concentrates to replace these missing clotting factors highlighted discordance between one-stage activated partial thromboplastin time (APTT)-based clotting factor assays and chromogenic factor assays with some products. This raised awareness of the importance of investigation of potential reagent or assay differences by pharmaceutical companies. In 2017, the FVIII mimetic, emicizumab, was approved as a prophylactic treatment for haemophilia A patients with anti-FVIII inhibitors. The mechanism of action of emicizumab causes interference with some commonly used haemostasis tests including the APTT and its associated one-stage APTT-based clotting assays. Chromogenic assays may also be affected but this is dependent on the particular constituents of the reagents. Chromogenic assays containing human factor IXa (FIXa) and factor X (FX) are sensitive to the presence of emicizumab but those containing bovine FIXa and FX are unaffected. Many haemostasis laboratories have been required to evaluate new assays to enable accurate monitoring of emicizumab in patient plasma. A number of gene therapy approaches have been trialled in both haemophilia A and haemophilia B but there are scant data published on the measurement of FVIII and FIX in these patients and whether there are discrepancies between reagents or assay methodologies.

Factor VIII and IX assays for post-infusion monitoring in hemophilia patients: Guidelines from the French BIMHO group (GFHT)

Replacement therapy with plasma-derived or recombinant FVIII and FIX (pdFVIII/pdFIX or rFVIII/rFIX) concentrates is the standard of treatment in patients with haemophilia A and B, respectively. Measurement of factor VIII (FVIII:C) or factor IX (FIX:C) levels can be done by one-stage clotting assay (OSA) or chromogenic substrate assay (CSA). The French study group on the Biology of Hemorrhagic Diseases (a collaborative group of the GFHT and MHEMO network) presents a literature review and proposals for the monitoring of FVIII:C and FIX:C levels in treated haemophilia A and B patients, respectively. The use of CSA is recommended for the monitoring of patients treated with pdFVIII or rFVIII including extended half-life (EHL) rFVIII. Except for rFVIII-Fc, great caution is required when measuring FVIII:C levels by OSA in patients substituted by EHL-rFVIII. The OSA is recommended for the monitoring of patients treated with pdFIX or rFIX. Large discordances in the FIX:C levels measured for extended half-life rFIX (EHL-rFIX), depending on the method and reagents used, must lead to great attention when OSA is used for measuring FIX:C levels in patients substituted by EHL-rFIX. Data of most of recent studies, obtained with spiked plasmas, deserve to be confirmed in plasma samples of treated patients.

Activity measurements of dalcinonacog alfa

INTRODUCTION

Many recombinant and modified FIX products have been, and continue to be, developed with the aim of improving treatment for patients with haemophilia B. One such new product is dalcinonacog alfa, a recombinant FIX with modifications to provide improved features such as subcutaneous administration.

AIM

In view of previously observed assay discrepancies with modified FIX therapeutics, the aim of this study was to assess potential discrepancies in potency measurement of dalcinonacog alfa between and within different assay methods.

METHODS

Potency of dalcinonacog alfa was measured against the 5th International Standard (IS) for FIX Concentrate and the 4th IS for FIX Plasma by One-Stage Clotting Assay, using 9 different APTT reagents and 2 commercially available FIX chromogenic kits. Plasma-derived concentrate and recombinant FIX samples were also included for comparison in every assay.

RESULTS

Substantial discrepancies were observed when assaying dalcinonacog alfa using the one-stage clotting assay against both standards. No statistically valid results were obtained when testing dalcinonacog alfa using either chromogenic kit. Increasing the incubation time with the activation reagent in both chromogenic kits resulted in valid assays and increased the potency to become more in line with potencies by one-stage clotting assays. Increasing the incubation time in the chromogenic kits had no effect on the potencies of the plasma-derived or recombinant samples. However, incubation time influenced in the one-stage clotting assay using Dapttin.

CONCLUSIONS

Within and between assay method discrepancy was found when assaying dalcinonacog alfa. Methods for potency labelling and clinical monitoring should be given careful consideration.

An overview of turoctocog alfa pegol (N8-GP; ESPEROCT® ) assay performance: Implications for postadministration monitoring

Factor replacement therapy with factor VIII (FVIII) concentrates is the current standard of care for patients with haemophilia A. Postadministration monitoring of FVIII activity during on‐demand or prophylactic treatment is important, for example to guide a suitable dosing regimen. While the use of two‐stage chromogenic substrate (CS) assays is increasing, activated partial thromboplastin time (APTT)‐based one‐stage clotting (OSC) assays are most commonly used to measure FVIII activity in clinical laboratories. Substantial variations in activity measurements have been observed in association with some OSC assay reagents when assessing extended half‐life FVIII molecules. Certain silica‐based APTT reagents have previously been shown to underestimate FVIII activity with the polyethylene glycol (PEG)‐conjugated product turoctocog alfa pegol (N8‐GP [ESPEROCT^®]; Novo Nordisk A/S). As a wide range of assay reagents are used in clinical laboratories worldwide, it is essential to establish which can be used to accurately measure activity with modified FVIII concentrates. Here, we describe the approach taken by Novo Nordisk to determine the suitability and accuracy of assays and reagents to measure FVIII activity in samples that contain N8‐GP. While accurate activity measurements were possible with all tested CS assays and most of the OSC APTT reagents tested, three APTT reagents that contain silica as a contact activator were found to underestimate N8‐GP recovery (APTT‐SP, TriniCLOT™, STA^® PTT‐Automate). The data demonstrate the importance of characterizing the accuracy of each FVIII activity assay. Any limitations should be communicated to treating physicians and the clinical laboratories that test samples containing N8‐GP.

Clinical utility and impact of the use of the chromogenic vs one-stage factor activity assays in haemophilia A and B

Treatment of haemophilia A/B patients comprises factor VIII (FVIII) or factor IX (FIX) concentrate replacement therapy, respectively. FVIII and FIX activity levels can be measured in clinical laboratories using one‐stage activated partial thromboplastin time (aPTT)‐based clotting or two‐stage chromogenic factor activity assays. We discuss strengths and limitations of these assays, providing examples of clinical scenarios to highlight some of the challenges associated with their current use for diagnostic and monitoring purposes. Substantial inter‐laboratory variability has been reported for one‐stage assays when measuring the activity of factor replacement products due to the wide range of currently available aPTT reagents, calibration standards, factor‐deficient plasmas, assay conditions and instruments. Chromogenic activity assays may avoid some limitations associated with one‐stage assays, but their regulatory status, perceived higher cost, and lack of laboratory expertise may influence their use. Haemophilia management guidelines recommend the differential application of one or both assays for initial diagnosis and disease severity characterisation, post‐infusion monitoring and replacement factor potency labelling. Efficient communication between clinical and laboratory staff is crucial to ensure application of the most appropriate assay to each clinical situation, correct interpretation of assay results and, ultimately, accurate diagnosis and optimal and safe treatment of haemophilia A or B patients.

Evaluation of an automated chromogenic assay for Factor VIII clotting activity measurement in patients affected by haemophilia A

INTRODUCTION

The original one-stage clotting assay is still the most widely used method to measure Factor VIII clotting activity (FVIII:C) in patients with haemophilia A (HA), although the use of chromogenic assays is increasing significantly.

AIM

Evaluation of the analytical performance and diagnostic accuracy of BIOPHEN™ FVIII:C (HYPHEN BioMed, Neuville-sur-Oise, France) assay on Sysmex CS-2400 (Sysmex, Kobe, Japan) analyser.

METHODS

Sixty patients with haemophilia A (HA; any severity) and 120 healthy Italian subjects were included. All the assays were performed on citrate platelet-poor plasmas stored at -80°C. Chromogenic BIOPHEN™ FVIII:C was compared with the one-stage assay using Actin FS and Factor VIII deficient plasma (Siemens Healthcare Diagnostics, Marburg, Germany) on Sysmex CS-2400 and with another chromogenic automated assay (COAMATIC™ Factor VIII, CHROMOGENIX on ACL TOP analyzer; Instrumentation Laboratory, Milan, Italy).

RESULTS

Intra-assay and inter-assay coefficient of variation were <6%. Linearity was good up to 1/128 dilution (r = 0.99); mean recovery was 91.7% and limit of detection was 0.2%. BIOPHEN™ FVIII:C assay showed a good correlation and diagnostic agreement with the chromogenic COAMATIC™ assay: the Spearmen's Rank correlation coefficient was 0.98 and the inter-rate agreement K Cohen coefficient was 0.61. The K coefficient was 0.91 when BIOPHEN™ FVIII:C was compared with the historical classification of the patients, demonstrating an optimal diagnostic accuracy in HA.

CONCLUSIONS

BIOPHEN™ FVIII:C showed good analytical performance and diagnostic accuracy and could be considered suitable for the introduction in routine analytical panel of coagulation for the diagnosis of HA patients.

Performance of a recombinant fusion protein linking coagulation factor IX with recombinant albumin in one-stage clotting assays

Essentials Performance of the one-stage clotting (OSC) assay varies with the clotting activator used. Recombinant FIX-albumin fusion protein (rIX-FP) was reliably monitored with most OSC reagents. rIX-FP shows comparable reagent-dependent variability to other rFIX products in the OSC assay. Actin® FS and kaolin-based reagents underestimated rIX-FP activity by around 50% in the OSC assay. SUMMARY: Background Measuring factor IX activity (FIX:C) with one-stage clotting (OSC) assays, based on the activated partial thromboplastin time (APTT), is the current mainstay of diagnostic techniques for hemophilia B. Assessing the performance of new recombinant FIX (rFIX) products in OSC assays is essential, as APTT reagents from different manufacturers yield different potency estimates for rFIX. Objectives To evaluate the extent to which choice of reagent composition influences rFIX potency measurements of recombinant FIX-albumin fusion protein (rIX-FP, IDELVION) activity in OSC assays. Methods rIX-FP was added to FIX-deficient plasma, and FIX:C was assessed centrally and locally in a multicenter international field study with a variety of commercial OSC APTT reagents. Paired sample analysis of clinical samples was performed to compare values of FIX:C from local and central laboratories. In-house bioanalytical investigations with spiked samples were conducted to compare the APTT-reagent dependent variability of rIX-FP with unmodified rFIX and rFIX Fc fusion protein (rFIXFc). Results Central and local assessments of FIX:C from 10 countries and 21 participating centers showed comparable results to those from the central laboratory across the majority of 18 different APTT reagents from both clinical and spiked samples. There was a consistent underestimation of rIX-FP activity of ≈ 50% with OSC assays using Actin FS or kaolin-based APTT reagents. In the bioanalytical study, rIX-FP showed comparable variability in OSC assays to unmodified rFIX and rFIXFc. Conclusions rIX-FP activity can be accurately measured by the use of OSC assays with the majority of commercial reagents. Actin FS or kaolin-based reagents will probably lead to a 50% underestimation of activity.

Reagent-specific underestimation of turoctocog alfa pegol (N8-GP) clotting activity owing to decelerated activation by thrombin

BACKGROUND

Factor VIII (FVIII) procoagulant activity is commonly assessed by measuring the activated partial thromboplastin time (APTT) to clot formation using one of the many available but differently composed reagents. The majority of APTT reagents also accurately recover the activity of the extended half-life molecule N-glycoPEGylated FVIII (N8-GP; turoctocog alfa pegol), while a few silica-based reagents give a low recovery.

OBJECTIVE

To identify the cause of N8-GP activity underestimation in the presence of certain silica-based APTT reagents.

METHODS

Development of FVIIIa-dependent tenase activity and appearance of FVIIIa from N8-GP and its non-PEGylated counterpart (N8) were compared using clotting assays, a factor Xa (FXa) activity assay mimic thereof, and thrombin activation time courses.

RESULTS

A strong correlation was demonstrated between clotting and FXa activity assays based on similar recoveries of N8-GP activity and equal responses to an altered duration of the contact activation phase, validating the latter as a useful clotting assay mimic. Contact activation phase duration influenced, and could even eliminate, N8-GP activity underestimation. Thrombin-catalyzed conversion of N8-GP to FVIIIa was considerably slower than that of N8 despite similar extents of adsorption to silica particles in APTT-SP, suggesting different modes and/or orientations of adsorption.

CONCLUSIONS

Some contact activators reduce thrombin's ability to cleave N8-GP more than native FVIII. Decelerated thrombin activation of N8-GP is reflected in delayed FVIIIa-dependent appearance of FXa activity in plasma, in turn leading to prolonged clotting time. This forms the basis for underestimation of N8-GP activity as measured by one-stage clotting assay against a FVIII standard.

Novel assays in the coagulation laboratory: a clinical and laboratory perspective

The ability to monitor Factor VIII (FVIII) and Factor IX (FIX) levels is integral to the clinical management of hemophilia A and B patients, respectively. Factor activity levels are checked during regular follow-up, post-infusion of factor concentrates, during pre- and post-operative assessments, and when the presence of an inhibitor is suspected. However, the ability to accurately and reproducibly measure factor activity levels with standard coagulation assays has been challenging due to the emergence of recombinant factor concentrates with extended half-lives. Similarly, special considerations must be given to the type of inhibitor assay used in patients with acquired hemophilia receiving recombinant porcine FVIII replacement. Alternative approaches to achieve hemostasis with clotting factor mimetics and interference of endogenous anticoagulants lack standardized assays for monitoring hemostatic efficacy. Laboratory assays measuring dynamic clotting parameters such as thrombin generation or whole blood viscoelasticity may provide a way forward, but have yet to enter routine clinical use. This review highlights the role of specialized coagulation assays in an era where multiple new hemostatic therapeutics for hemophilia are available, and underscores the need for clear communication between bedside and laboratory clinicians.

Postanalytical considerations that may improve the diagnosis or exclusion of haemophilia and von Willebrand disease

von Willebrand disease (VWD) and haemophilia represent the most common inherited or acquired bleeding disorders. However, many laboratories and clinicians may be challenged by their accurate diagnosis or exclusion. Difficulties in diagnosis/exclusion may include analytical issues, where assays occasionally generate an incorrect result (ie representing an analytical error) or have limitations in their measurement range of and/or low analytical sensitivity. Also increasingly recognized is the influence of preanalytical issues on the diagnosis of VWD or haemophilia. Unfortunately, postanalytical considerations are often not well considered in the diagnostic process. Therefore, this narrative review aims to provide an overview of some important postanalytical considerations that may help improve the diagnosis of VWD and haemophilia. This review primarily discusses aspects around reporting of test results. However, we also discuss other less well-recognized postanalytical considerations, including the use of assay ratios to help identify differential diagnoses and then guide further investigation.

Evaluation of recombinant factor VIII Fc (Eloctate) activity by thromboelastometry in a multicenter phase 3 clinical trial and correlation with bleeding phenotype

The aim of this study was to compare the hemostatic efficacy of recombinant factor VIII Fc (rFVIIIFc) (Eloctate) and Advate by ex-vivo rotation thromboelastometry (ROTEM) of whole blood and to explore potential ROTEM parameters that may be more predictive of a patient's bleeding tendency than plasma FVIII activity. Thirteen clinical sites were selected to perform ROTEM on freshly collected blood samples from 44 patients in the phase 3 study for rFVIIIFc, including 16 patients undergoing sequential pharmacokinetic assessment of Advate and rFVIIIFc. Equivalent hemostatic activity was observed for rFVIIIFc and Advate in postinfusion samples, followed by improvements for rFVIIIFc in clotting time, clot formation time and alpha angle (α) for a longer duration than Advate, consistent with the pharmacokinetic improvements reported previously for rFVIIIFc. Our study did not demonstrate a statistical correlation between a patient's ROTEM activity at baseline or at trough and the occurrence of spontaneous bleeds while on prophylactic therapy. However, an association was observed between postinfusion clotting time and the occurrence of one or more spontaneous bleeds vs. no bleeds over a follow-up period of 1 year (P = 0.003). How well a patient's whole blood clotting deficiency is corrected after a dose of FVIII may be an indicator of subsequent bleeding tendency in patients with otherwise equivalent FVIII peak and trough levels. The technical challenges of standardizing the ROTEM, largely overcome in the current study, may however preclude the use of this method for widespread assessment of global hemostasis unless additional assay controls or normalization procedures prove to be effective.

Usefulness of chromogenic assays for potency assignment and recovery of plasma-derived FVIII and FIX concentrates or their recombinant long acting therapeutic equivalents with potential application in treated pediatric hemophiliac patients

On demand and prophylaxis usage of FVIII/ FIX concentrates for the therapeutic management of hemophilia has greatly changed quality of life, and healthy life span of affected patients. Availability of recombinant therapeutic FVIII and FIX products, and of their long-acting variants, further improves the treatment constraints, and progressively permits to hemophiliacs to have an almost normal way of life. Unlimited amounts of recombinant or engineered substitutive products become available, and open new avenues for extending the benefits of prophylaxis to all hemophiliac patients, not only in economically advanced territories, but also in emerging and developing countries, worldwide. Pharmacokinetics of injected products can be variable among treated patients, and dependent on age. In addition, patient medical status, existing diseases, and the nature of joint damages can impact protective effect of substitutive products, and risks associated to way of life and activity. Product requirements and half-life of infused products are therefore patient specific. Monitoring recoveries of injected products thus provide useful information for the most appropriate treatment adjustment. FVIII and FIX measurements in plasma of treated patients helps to establish the optimal interval between injections for each treated patient, and the overall therapeutic cost. Due to the high variability from reagent to reagent, and the different behavior from plasma derived products, clotting methods are not ideal for recombinant and long-acting products. They require to be performed only in association with a drug specific calibrator. They are not recommended for patients' survey, due to the high variety of reagents available. Chromogenic assays (2-stage methods) offer a standard reactivity to all available FVIII or FIX products in drugs, whether the way they are obtained, or in plasma. In a subset of treated patients, inhibitory antibodies to FVIII or FIX develop and can be measured with inhibition assays (Bethesda units), or by Elisa. Unfortunately, FVIII or FIX substitutive therapies cannot be used in patients with inhibitors, and alternative clinical management is requested, such as the use of FEIBA or FVIIa for their bypassing activity. A new treatment is being introduced in the form of a bispecific antibody (Emicizumab) targeted to both FIXa and FX, and which allows activating FX by FIXa without the need for FVIII. Some chromogenic assays (Biophen FVIII), designed with human proteins, offer the possibility to measure the activity and recovery of this new drug. Chromogenic methods are then useful for establishing potency of therapeutic products or monitoring recovery and kinetics in treated patients, through plasma measurements. Availability of International Standards for FVIII and FIX, in concentrates or plasma, allows harmonization of assay results.

Educational needs of hematologists and laboratory professionals regarding factor activity assays

Introduction

Diagnosis and management of hemophilia require accurate and precise measurements of factor activity levels. Activity is traditionally measured via one-stage (OS) clot-based assay; however, chromogenic substrate (CS) assays may be needed for certain cases. A survey was performed to understand assay-related knowledge gaps among hematologists and laboratory professionals.

Methods

Separate web-based surveys were administered to hematologists who manage hemophilia and to laboratory professionals and queried practice patterns, knowledge of/attitudes toward CS assays, and interest in continuing education.

Results

A total of 51 hematologists participated in this study; 67% managed hemophilia patients for ≥10 years and 24% were affiliated with a hemophilia treatment center (HTC). Most (80%) stated familiarity with general assay interpretation. Majorities of non-HTC and HTC respondents agreed that CS assays are more accurate than OS assays (62%/67%), although non-HTC hematologists indicated less understanding of when to order a CS assay (49%/67%). Fewer non-HTC respondents expressed concerns regarding the reliability of OS assays for diagnosis (38%/67%) and monitoring (38%/75%). Most (80%) expressed an interest in factor assay education, especially on available assays, efficacy, and best practices (39%). A total of 57 laboratory professionals participated, averaging 10 years in their current position; most (88%) were hospital based. More performed OS (72%) than CS (10%) or both (17%) assays; only 11% reported confidence with the interpretation of CS results. Few expressed concerns regarding the reliability of OS for diagnosis (9%) or monitoring (12%). Reported barriers to CS use included infrequent need (68%), lack of US Food and Drug Administration (FDA) approval (61%), and need for validation work (56%). Most (70%) were interested in CS assay education; top interests included advantages over traditional assays, general information on CS assays, and indications for testing (each 18%).

Conclusion

Future educational efforts may focus on limitations of OS assays, indications for CS assay diagnosis/monitoring, and support for clinic-laboratory dialog.

Long-term tolerability, immunogenicity and efficacy of Nuwiq® (human-cl rhFVIII) in children with severe haemophilia A

INTRODUCTION

Nuwiq^® (human-cl rhFVIII, simoctocog alfa) is a 4th generation recombinant human FVIII, without chemical modification or fusion with any other protein, produced in a human cell line.

AIM/METHODS

This study (GENA-13) was an extension of the GENA-03 study in which previously treated children aged 2-12 years with severe haemophilia A received Nuwiq^® prophylaxis for ≥6 months. GENA-13 examined long-term tolerability, immunogenicity and efficacy of Nuwiq^® prophylaxis in children.

RESULTS

Of 59 patients enrolled in GENA-03, 49 continued Nuwiq^® prophylaxis in GENA-13 for a median (range) of 30.0 (9.5-52.0) months. No patient withdrew due to drug-related adverse events or developed inhibitors. Only 2 of 20 518 infusions were associated with possibly related adverse events (dyspnoea, fever). The estimated annualized bleeding rate (ABR) was 0.67 (95% CI: 0.44, 1.02) for spontaneous and 2.88 (95% CI: 1.86, 4.46) for all bleeds. Younger children (2-5 years) had lower ABRs than children aged 6-12 years. Annualized bleeding rates were reduced in GENA-13 vs GENA-03, especially for spontaneous bleeds in younger children (71% reduction; ABR ratio 0.29 [95% CI: 0.11, 0.74]). Nuwiq^® efficacy was rated as excellent/good in the treatment of 83.0% of 305 evaluated breakthrough bleeds. Surgical prophylaxis with Nuwiq^® was rated as excellent for all 17 assessed procedures.

CONCLUSION

Long-term treatment with Nuwiq^® for the prevention of bleeds in children with severe haemophilia A was well tolerated, effective and reduced spontaneous bleeding by up to 70% compared with GENA-03.

Evaluation of chromogenic factor IX assays by automated protocols

INTRODUCTION

Chromogenic substrate assays (CSA) to measure Factor IX (FIX) have recently become commercially available. However, information on their performance characteristics and use in diagnostic haemostasis laboratories remains limited.

AIM

To evaluate the Hyphen Biomed (Hyphen) and Rossix FIX CSAs on fully automated coagulation analysers and compare them to the FIX one-stage assay (OSA). This study was conducted in a tertiary referral haemostasis laboratory associated with a haemophilia treatment centre.

METHODS

Automated CSA protocols were adapted to the Sysmex CS2500 (CS2500) and Diagnostica Stago STA-R (STA-R) analysers. Samples assayed were from healthy volunteers, haemophilia B patients and FIX deficient plasma spiked with either plasma derived, recombinant or extended half-life FIX products.

RESULTS

Reference intervals for Hyphen and Rossix assays were 73 IU/dL to 164 IU/dL and 73 IU/dL to 168 IU/dL, respectively, on the CS2500 analyser; and 84 IU/dL to 165 IU/dL for the Rossix assay on the STA-R. Repeatability across all method/analyser combinations resulted in CVs ranging from 0.8% to 5.4%. Between run reproducibility gave CVs <6.7% for all method/analyser combinations. In spiked samples, FIX recoveries were mostly within an acceptable limit of 100 ± 25% for BeneFIX^® , Rixubis^® and Alprolix^® with some differences between CSAs.

CONCLUSION

Both commercial factor FIX CSA kits can be adapted for Stago and Sysmex automated coagulation analysers. Reagent cost and workflow practices will need to be considered. These assays are potentially more consistent than OSA in measurement of replacement FIX products in haemophilia B patients.

Lonoctocog alfa (rVIII-SingleChain) for the treatment of haemophilia A

INTRODUCTION

The administration of factor VIII (FVIII) concentrates on-demand or on long-term prophylaxis is the effective and safe standard of care of patients with hemophilia A (HA). Development of neutralizing antibodies against exogenous FVIII and the short half-life of the current available products remain major challenges. There is currently a great interest towards newer FVIII products with the goal of reducing the inhibitor risk and increasing the half-life. Area covered: In this review, the authors describe the efficacy and safety of rVIII-SingleChain (Lonoctocog alfa), the first and only single chain recombinant FVIII (rFVIII) molecule developed for the prevention and treatment of bleeding episodes in HA patients. The pre-clinical and clinical studies of rVIII-SingleChain as well as the results of the AFFINITY trial program in previously treated patients both adults and pediatric are presented and discussed. Expert opinion: The results from PTP studies document the efficacy and safety profile of the rVIII-SingleChain. However, even if rFVIII-SingleChain presents advantageous pharmacokinetic features compared to conventional rFVIII, it should not be considered as an EHL-FVIII while its immunogenicity is currently being studied in PUPs. The slightly better PK profile of rFVIII-SingleChain could however allow a small number of selected patients to be treated with a less intensive regimen.

Lonoctocog Alfa: A Review in Haemophilia A

Lonoctocog alfa (rVIII-SingleChain; Afstyla^®) is a novel single-chain recombinant factor VIII (FVIII) molecule, with a truncated B-domain and the heavy and light chains covalently linked to form a stable and homogenous drug that binds with high affinity to von Willebrand factor (VWF). Intravenous lonoctocog alfa is approved for the prophylaxis and treatment of bleeding in patients with haemophilia A in several countries worldwide. In two pivotal, multicentre trials, lonoctocog alfa was effective in the treatment of bleeding episodes and as prophylaxis, including for perioperative management in adults, adolescents and children. In terms of haemostatic efficacy in controlling bleeding episodes, overall treatment and investigator-assessed success rates were high across all age groups, with the majority of these bleeds controlled with a single injection of lonoctocog alfa. Low median spontaneous, overall and traumatic annualized bleeding rates were evident with prophylactic lonoctocog alfa regimens in both trials. Lonoctocog alfa was generally well-tolerated, with very low rates of injection-site reactions. No previously treated patient experienced an anaphylactic reaction or developed an inhibitor. In conclusion, lonoctocog alfa is an effective and generally well-tolerated alternative to conventional FVIII products for the treatment and prophylaxis of bleeding, including in the surgical setting, in adults, adolescents and children with haemophilia A.