Measuring factor IX activity of nonacog beta pegol with commercially available one-stage clotting and chromogenic assay kits: a two-center study

Field Study and Correlative Studies of Factor IX Variant FIX-R338L in Participants Treated with Fidanacogene Elaparvovec

BACKGROUND

 Fidanacogene elaparvovec, an adeno-associated virus-based gene therapy vector expressing the high-activity factor IX (FIX) variant FIX-R338L, is in development for hemophilia B. One-stage clotting (OS) assays and chromogenic substrate (CS) assays are commonly used to measure FIX-R338L variant activity. Data from ongoing trials suggest FIX activity varies between different OS and CS assays.

MATERIAL AND METHODS

 To better understand FIX-R338L activity in clinical samples, an international multisite field study was conducted across a central laboratory and 18 local laboratories, using standard protocols, reagents, and instrumentation, with individual participant samples from a phase 1/2a study of fidanacogene elaparvovec.

RESULTS

 Unlike the wild-type FIX control, FIX-R338L activity was higher with the OS silica-based assay versus OS ellagic acid-based and CS assays. Variation in FIX activity was greater at the lowest activity levels. Activated FIX (FIXa) in plasma could result in higher OS assay activity or increased thrombin generation, which could overestimate FIX activity. However, FIXa was not detected in the participant samples, indicating that it was not contributing to the OS assay differences. Since individuals on gene therapy may receive exogenous replacement FIX products, replacement products were spiked into patient plasma samples to target a therapeutic concentration. Exogenous FIX was additive to endogenous FIX-R338L, with no interference from FIX-R338L.

CONCLUSION

 These results demonstrate FIX-R338L activity can be measured with OS and CS assays in clinical laboratories and provide insight into assay variability when measuring FIX with endogenously produced FIX-R338L. The findings may help establish best practices for measuring FIX-R338L activity (Clinicaltrials.gov identifier: NCT02484092).

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.

Biodistribution of recombinant factor IX, extended half-life recombinant factor IX Fc fusion protein, and glycoPEGylated recombinant factor IX in hemophilia B mice

Extended half-life recombinant FIX (rFIX) molecules have been generated to reduce the dosing burden and increase the protection of patients with hemophilia B. Clinical pharmacology studies with recombinant factor IX Fc fusion protein (rFIXFc) report a similar initial peak plasma recovery to that of rFIX, but with a larger volume of distribution. Although the pegylation of N9-GP results in a larger plasma recovery, there is a smaller volume of distribution, suggesting less extravasation of the latter drug. In this study, we set out to compare the biodistribution and tissue localization of rFIX, rFIXFc, and glycoPEGylated rFIX in a hemophilia B mouse model. Radiolabeled rFIX, rFIXFc, and rFIX-GP were employed in in vivo single-photon emission computed tomography imaging (SPECT/CT), microautoradiography (MARG), and histology to assess the distribution of FIX reagents over time. Immediately following injection, vascularized tissues demonstrated intense signal irrespective of FIX reagent. rFIX and rFIXFc were retained in joint and muscle areas through 5 half-lives, unlike rFIX-GP (assessed by SPECT). MARG and immunohistochemistry showed FIX agents localized at blood vessels among tissues, including liver, spleen, and kidney. Microautoradiographs, as well as fluorescent-labeled images of knee joint areas, demonstrated retention over time of FIX signal at the trabecular area of bone. Data indicate that rFIXFc is similar to rFIX in that it distributes outside the plasma compartment and is retained in certain tissues over time, while also retained at higher plasma levels. Overall, data suggest that Fc fusion does not impede the extravascular distribution of FIX.

Factor VIII and Factor IX Activity Measurements for Hemophilia Diagnosis and Related Treatments

Accurate measurement of clotting factors VIII (FVIII) or IX (FIX) is vital for comprehensive diagnosis and management of patients with hemophilia A or B. The one-stage activated partial thromboplastin time (aPTT)-based clotting assay is the most commonly used method worldwide for testing FVIII or FIX activities. Alternatively, FVIII and FIX chromogenic substrate assays, which assess the activation of factor X, are available in some specialized laboratories. The choice of reagent or methodology can strongly influence the resulting activity. Variation between one-stage FVIII or FIX activities has been reported in the measurement of some standard and extended half-life factor replacement therapies and gene therapy for hemophilia B using different aPTT reagents. Discrepancy between one-stage and chromogenic reagents has been demonstrated in some patients with mild hemophilia A or B, the measurement of some standard and extended half-life factor replacement therapies, and the transgene expression of hemophilia A and B patients who have received gene therapy. Finally, the measurement of bispecific antibody therapy in patients with hemophilia A has highlighted differences between chromogenic assays. It is imperative that hemostasis laboratories evaluate how suitable their routine assays are for the accurate measurement of the various hemophilia treatment therapies.

Differences in wild-type- and R338L-tenase complex formation are at the root of R338L-factor IX assay discrepancies

Adeno-associated virus (AAV) gene therapy has the potential to functionally cure hemophilia B by restoring factor (F)IX concentrations into the normal range. Next-generation AAV therapies express a naturally occurring gain-of-function FIX variant, FIX-Padua (R338L-FIX), that increases FIX activity (FIX:C) by approximately eightfold compared with wild-type FIX (FIX-WT). Previous studies have shown that R338L-FIX activity varies dramatically across different clinical FIX:C assays, which complicates the monitoring and management of patients. To better understand mechanisms that contribute to R338L-FIX assay discrepancies, we characterized the performance of R338L-FIX in 13 1-stage clotting assays (OSAs) and 2 chromogenic substrate assays (CSAs) in a global field study. This study produced the largest R338L-FIX assay dataset to date and confirmed that clinical FIX:C assay results vary over threefold. Both phospholipid and activating reagents play a role in OSA discrepancies. CSA generated the most divergent FIX:C results. Manipulation of FIX:C CSA kits demonstrated that specific activity gains for R338L-FIX were most profound at lower FIX:C concentrations and that these effects were enhanced during the early phases of FXa generation. Supplementing FX into CSA had the effect of dampening FIX-WT activity relative to R338L-FIX activity, suggesting that FX impairs WT tenase formation to a greater extent than R338L-FIX tenase. Our data describe the scale of R338L-FIX assay discrepancies and provide insights into the causative mechanisms that will help establish best practices for the measurement of R338L-FIX activity in patients after gene therapy.

Advances in laboratory assessment of thrombosis and hemostasis

Technologies in laboratory diagnostics are changing fast with progress in understanding and therapy of diseases. Unfortunately, new analyzers are often needed to be installed in a clinical laboratory to implement such techniques. The demand for new hardware is a bottleneck in improving the diagnostic services for many facilities with limited resources. In this regard, hemostasis laboratories take a slightly different position. Because many in vitro diagnostic tests target the functional aspects of hemostasis, further meaningful information can be obtained from the same analyzers as in current use. Automated coagulometers are good candidates for such further utilization. Clot waveform analysis is a leading example. Behind the simple values reported as clotting time, clotting curves exist that represent the process of fibrin clot formation. Clot waveform analysis examines the clotting curves and derives new parameters other than clotting times. The clot waveform parameters are now in active use in assessing the hemostatic potential of hemorrhagic patients. Clinical application of coagulometers can also be widened by modifying the reagent formulation. For example, the chromogenic factor VIII assay with bovine source reagent compositions has recently been introduced for hemophilia A patients on emicizumab prophylaxis. Also, new immunoturbidimetric functional assays for von Willebrand factor have been developed recently. Thus, new clinically relevant information can be mined from the automated coagulometers that are based on old technology.

International consensus recommendations on the management of people with haemophilia B

Haemophilia B is a rare X-linked genetic deficiency of coagulation factor IX (FIX) that, if untreated, can cause recurrent and disabling bleeding, potentially leading to severe arthropathy and/or life-threatening haemorrhage. Recent decades have brought significant improvements in haemophilia B management, including the advent of recombinant FIX and extended half-life FIX. This therapeutic landscape continues to evolve with several non-factor replacement therapies and gene therapies under investigation. Given the rarity of haemophilia B, the evidence base and clinical experience on which to establish clinical guidelines are relatively sparse and are further challenged by features that are distinct from haemophilia A, precluding extrapolation of existing haemophilia A guidelines. Due to the paucity of formal haemophilia B-specific clinical guidance, an international Author Group was convened to develop a clinical practice framework. The group comprised 15 haematology specialists from Europe, Australia, Japan, Latin America and North America, covering adult and paediatric haematology, laboratory medicine and biomedical science. A hybrid approach combining a systematic review of haemophilia B literature with discussion of clinical experience utilized a modified Delphi format to develop a comprehensive set of clinical recommendations. This approach resulted in 29 recommendations for the clinical management of haemophilia B across five topics, including product treatment choice, therapeutic agent laboratory monitoring, pharmacokinetics considerations, inhibitor management and preparing for gene therapy. It is anticipated that this clinical practice framework will complement existing guidelines in the management of people with haemophilia B in routine clinical practice and could be adapted and applied across different regions and countries.

IDELVION: A Comprehensive Review of Clinical Trial and Real-World Data

Hemophilia B is a bleeding disorder caused by a deficiency of coagulation factor IX (FIX). Treatment with FIX replacement products can increase FIX activity levels to minimize or prevent bleeding events. However, frequent dosing with standard-acting FIX products can create a high treatment burden. Long-acting products have been developed to maintain bleed protection with extended dosing intervals. Recombinant factor IX–albumin fusion protein (rIX-FP) is a long-acting product indicated for the treatment and prophylaxis of bleeding events and perioperative management in adult and pediatric patients. This review outlines data from all previously treated patients in the Prophylaxis and On-Demand Treatment using Longer Half-Life rIX-FP (PROLONG-9FP) clinical trial program and summarizes real-world data evaluating the use of rIX-FP in routine clinical practice. In the PROLONG-9FP program, rIX-FP demonstrated effective hemostasis in all patients at dose regimens of up to 21 days in patients aged ≥ 18 years and up to 14 days in patients aged < 12 years. rIX-FP has a favorable pharmacokinetic profile and an excellent safety and tolerability profile. Extended dosing intervals with rIX-FP led to high levels of adherence and reduced consumption compared with other FIX therapies. Data from real-world practice are encouraging and reflect the results of the clinical trials.

An Update on Laboratory Diagnostics in Haemophilia A and B

Haemophilia A (HA) and B (HB) are X-linked hereditary bleeding disorders caused by lack of activity of coagulation factors VIII (FVIII) or IX (FIX), respectively. Besides conventional products, modern replacement therapies include FVIII or FIX concentrates with an extended half-life (EHL-FVIII/FIX). Two main strategies for measuring plasma FVIII or FIX activity are applied: the one-stage clotting assay (OSCA) and the chromogenic substrate assay (CSA), both calibrated against plasma (FVIII/FIX) standards. Due to the structural modifications of EHL-FVIII/FIX, reagent-dependent assay discrepancies have been described when measuring the activity of these molecules. Assay discrepancies have also been observed in FVIII/FIX gene therapy approaches. On the other hand, nonfactor replacement by the bispecific antibody emicizumab, a FVIIIa-mimicking molecule, artificially shortens activated partial thromboplastin time–based clotting times, making standard OSCAs inapplicable for analysis of samples from patients treated with this drug. In this review, we aim to give an overview on both, the currently applied and future therapies in HA and HB with or without inhibitors and corresponding test systems suitable for accompanying diagnostics.

External quality assessment for one-stage and chromogenic factor IX assays in samples containing Alprolix (rFIXFc) or Idelvion (rIX-FP) and evidence that UK National External Quality Assessment Scheme for blood coagulation samples are commutable with patient samples

INTRODUCTION

There may be clinically relevant differences between results of different FIX assays in samples containing extended half life FIX concentrates requiring regular surveillance of assay results through proficiency testing exercises. Control materials used in proficiency testing must be commutable, that is have the same inter-assay properties as those demonstrated by authentic clinical samples when measured by different analytical methods.

METHODS

We assessed relationships between results with different FIX assays and commutability of UK National External Quality Assessment Scheme (NEQAS) materials containing rIX-FP (Idelvion) or rFIXFc (Alprolix) by comparing results obtained using widely used one-stage and chromogenic assays during a proficiency testing exercise with results obtained when analysing a series of individual patient samples using the same assay systems. NEQAS samples prepared by addition of either Idelvion or Alprolix to FIX deficient plasma were sent to 76 haemophilia centres in Europe. A total of 18 Idelvion and 22 Alprolix patient samples were assayed in a single centre. Two chromogenic and two one-stage assays were compared.

RESULTS

The pattern of results obtained for NEQAS samples and patient samples was similar. In all cases, the NEQAS sample data point was within the scatter of patient sample data in plots of patient sample results showing one-stage assay results using Synthasil or Actin FS plotted against chromogenic assay results with Biophen or Rox chromogenic FIX kits.

CONCLUSION

This indicates that the NEQAS samples containing Idelvion or Alprolix were commutable and therefore suitable for use in proficiency testing exercises.

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.

Activity of transgene-produced B-domain-deleted factor VIII in human plasma following AAV5 gene therapy

Adeno-associated virus (AAV)-based gene therapies can restore endogenous factor VIII (FVIII) expression in hemophilia A (HA). AAV vectors typically use a B-domain-deleted FVIII transgene, such as human FVIII-SQ in valoctocogene roxaparvovec (AAV5-FVIII-SQ). Surprisingly, the activity of transgene-produced FVIII-SQ was between 1.3 and 2.0 times higher in one-stage clot (OS) assays than in chromogenic-substrate (CS) assays, whereas recombinant FVIII-SQ products had lower OS than CS activity. Transgene-produced and recombinant FVIII-SQ showed comparable specific activity (international units per milligram) in the CS assay, demonstrating that the diverging activities arise in the OS assay. Higher OS activity for transgene-produced FVIII-SQ was observed across various assay kits and clinical laboratories, suggesting that intrinsic molecular features are potential root causes. Further experiments in 2 participants showed that transgene-produced FVIII-SQ accelerated early factor Xa and thrombin formation, which may explain the higher OS activity based on a kinetic bias between OS and CS assay readout times. Despite the faster onset of coagulation, global thrombin levels were unaffected. A correlation with joint bleeds suggested that both OS and CS assay remained clinically meaningful to distinguish hemophilic from nonhemophilic FVIII activity levels. During clinical development, the CS activity was chosen as a surrogate end point to conservatively assess hemostatic efficacy and enable comparison with recombinant FVIII-SQ products. Relevant trials are registered on clinicaltrials.gov as #NCT02576795 and #NCT03370913 and, respectively, on EudraCT (European Union Drug Regulating Authorities Clinical Trials Database; https://eudract.ema.europa.eu) as #2014-003880-38 and #2017-003215-19.

In silico comparison of pharmacokinetic properties of three extended half-life factor IX concentrates

Purpose

Pharmacokinetic (PK) differences between the extended half-life (EHL) factor IX (FIX) concentrates for hemophilia B exist, which may influence hemostatic efficacy of replacement therapy in patients. Therefore, we aimed to evaluate the PK properties of three EHL-FIX concentrates and compare them to a standard half-life (SHL) recombinant FIX (rFIX) concentrate.

Methods

Activity-time profiles of PEGylated FIX (N9-GP), FIX linked with human albumin (rIX-FP), FIX coupled to human IgG1 Fc-domain (rFIXFc), and SHL rFIX were simulated for 10,000 patients during steady-state dosing of 40 IU/kg once weekly (EHL-FIX) and biweekly (rFIX) using published concentrate specific population PK models.

Results

Half-lives were respectively 80, 104, and 82 h for N9-GP, rIX-FP, and rFIXFc versus 22 h for rFIX. Between the EHL concentrates, exposure was different with area under the curve (AUC) values of 78.5, 49.6, and 12.1 IU/h/mL and time above FIX target values of 0.10 IU/mL of 168, 168, and 36 h for N9-GP, rIX-FP, and rFIXFc, respectively. N9-GP produced the highest median in vivo recovery value (1.70 IU/dL per IU/kg) compared with 1.18, 1.00, and 1.05 IU/dL per IU/kg for rIX-FP, rFIXFc, and rFIX, respectively.

Conclusions

When comparing EHL products, not only half-life but also exposure must be considered. In addition, variation in extravascular distribution of the FIX concentrates must be taken into account. This study provides insight into the different PK properties of these concentrates and may aid in determination of dosing regimens of EHL-FIX concentrates in real-life.

Performance of factor IX extended half-life product measurements in external quality control assessment programs

BACKGROUND

Patients with hemophilia B are increasingly treated with extended half-life (EHL) factor IX (FIX) concentrates. For the laboratory, introduction of these EHL concentrates presents a major challenge. To understand the variation in FIX activity levels, all available diagnostic assays need to be directly compared.

METHODS

The ECAT, UKNEQAS, and RCPAQAP have collaboratively performed a global survey to evaluate the quality of FIX measurements using FIX deficient plasma samples spiked with recombinant FIX (rFIX), rFIXFP, rFIXFc, and N9-GP to levels at typical FIX trough (6 IU/dL) and peak levels (60 IU/dL). Participants were asked to use their routine protocols, using one-stage assays (OSA) or chromogenic assays (CA).

RESULTS

In samples spiked with 6 IU/dL product, median (25%-75% range) FIX activity levels (OSA), were 8.0 IU/dL (7.0-9.2) for rFIX, 6.0 IU/dL (4.0-7.1) for rFIXFP, 6.6 IU/dL (5.5-8.0) for rFIXFc, and 4.9 IU/dL (3.5-8.4) for N9-GP. In samples spiked with 60 IU/dL, FIX activity levels measured (using OSA) was 63.0 IU/dL (59.9-67.0) for rFIX, 42.5 IU/dL (28.2-47.0) for rFIXFP, 50.0 IU/dL (45.0-55.0) for rFIXFc, and 34.0 IU/dL (24.8-67.5) for N9-GP. Considerable differences were observed between reagents for all samples. With CA, there was also quite some variation, but no differences between reagents.

CONCLUSION

Large variation is observed in the measurement of FIX activity levels after administration of rFIX and EHL FIX products. For N9-GP, most silica-based assays show especially high levels. It is essential to standardize and improve reliability of measurements of these concentrates as diagnosis and treatment monitoring is based on these results.

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.

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.

Measurements of eftrenonacog alfa by 19 different combinations reagents/instrument: A single-centre study

INTRODUCTION

Recombinant factor IX Fc fusion protein (rFIXFc) is an extended half-life concentrate for the treatment of haemophilia B (HB). rFIXFc activity monitoring is crucial in several clinical situations. However, differences were observed between one-stage clotting (OSC) and chromogenic assays, but not for all factor IX (FIX) concentrations.

AIMS

To compare rFIXFc measurements obtained using different instruments and common OSC and chromogenic asssays.

METHODS

FIX:C measurements were performed in rFIXFc-spiked plasma aliquots (targeted FIX levels of 1.5, 1, 0.5, 0.2, 0.05, 0.02 and 0.01 IU/mL) and plasma samples collected from two patients with HB at various time points after rFIXFc infusion, using three instruments (STA-R MAX, ACLTOP700 and CS2100i) and common clotting and chromogenic FIX:C assays.

RESULTS

The same reagent could give different FIX:C measurements when adapted to different instruments. Moreover, the same reagent/instrument combination could give different results depending of the FIX concentration. For OSC assays, only STA-Cephascreen on STA-R MAX and CS2100i, SynthAFax on ACLTOP 700 and Actin on CS2100i provided acceptable recoveries for all rFIXFc concentrations. The chromogenic assays ROX-FIX and Biophen FIX:C underestimated rFIXFc for concentrations lower than 0.05 and 0.2 IU/mL, respectively.

CONCLUSIONS

Our study demonstrates that the same reagent adapted to different instruments could lead to different rFIXFc values. As rFIXFc under/overestimation could be associated with inappropriate treatment or biased calculation of pharmacokinetic parameters, the reagent/instrument combination used by haemostasis laboratories should be considered and regularly evaluated by external quality assessment programmes.

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.

Real-world assay variability between laboratories in monitoring of recombinant factor IX Fc fusion protein activity in plasma samples

Introduction

Monitoring of factor IX (FIX) replacement therapy in haemophilia B relies on accurate coagulation assays. However, considerable interlaboratory variability has been reported for one‐stage clotting (OSC) assays. This study aimed to evaluate the real‐world, interlaboratory variability of routine FIX activity assays used in clinical haemostasis laboratories for the measurement of recombinant FIX Fc fusion protein (rFIXFc) activity.

Methods

Human FIX‐depleted plasma was spiked with rFIXFc at 0.80, 0.20 or 0.05 IU/mL based on label potency. Participating laboratories tested samples using their own routine OSC or chromogenic substrate (CS) assay protocols, reagents and FIX plasma standards. Laboratories could perform more than one measurement and method, and were not fully blinded to nominal activity values.

Results

A total of 142 laboratories contributed OSC results from 175 sample kits using 11 different activated partial thromboplastin time (aPTT) reagents. The median recovered FIX activity for the 0.80, 0.20 and 0.05 IU/mL samples was 0.72 IU/mL, 0.21 IU/mL and 0.060 IU/mL, respectively. Across all OSC reagents, interlaboratory variability (% CV) per aPTT reagent ranged from 9.4% to 32.1%, 8.2% to 32.6% and 12.2% to 42.0% at the 0.80, 0.20 and 0.05 IU/mL levels, respectively. CS results showed excellent median recoveries at all nominal levels (87.5% to 115.0%; n = 11) with low interlaboratory variability (CV 3.6% to 15.4%).

Conclusion

This large, real‐world data set indicates that rFIXFc activity in plasma samples can be accurately measured with the majority of routine OSC and CS assay methods. Given the variation in FIX assay procedures between sites, it is important that individual laboratories qualify their in‐house methods for monitoring of rFIXFc activity.

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.

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.

Updates in clinical trial data of extended half-life recombinant factor IX products for the treatment of haemophilia B

Whilst the global prevalence of haemophilia B is less than that of haemophilia A, rapid and remarkable innovations have been made in the development of haemophilia B therapies in the last decade. The most recent developments are the evolution of extended half-life haemophilia B replacement therapies which are designed to reduce the treatment burden associated with prophylactic infusion of factor IX (FIX) to prevent bleeding in haemophilia B participants. Clinical development programmes have culminated in the completion of three phase III studies on extended half-life (EHL) recombinant FIX (rFIX) products and subsequent approval and registration of these in many countries around the world. Current data from the three EHL rFIX clinical studies indicate that these products have acceptable safety profiles with no allergic reactions, thromboembolic phenomena or neutralizing antibodies when given to previously treated adolescent and adults for the prevention of bleeds, for the treatment of bleeds and in the perisurgical haemostasis use. Studies in previously untreated paediatric participants are currently ongoing. The EHL rFIX products have the potential impact to reduce the treatment burden associated with prophylactic infusion of replacement FIX, to treat and prevent bleeds in participants with haemophilia B and to improve the participant's health-related quality of life. The impact of EHL rFIX is likely to be modified by current development of other haemophilia B therapy such as antitissue factor pathway inhibitors and haemophilia B gene therapy. In this review, we aim to provide an update on the safety and efficacy data from the three EHL rFIX clinical studies and to consider their roles in the face of novel haemophilia B therapy currently evolving.

Advances in the Treatment of Hemophilia: Implications for Laboratory Testing

BACKGROUND

Until recently, clinical laboratories have monitored hemophilia treatment by measuring coagulation factors before/after infusion of human-derived or recombinant factors. Substantial changes are expected in the near future based on new therapeutic approaches that have been or are being developed.

CONTENT

Hemophilia treatment includes replacement therapy with human-derived/recombinant factors or treatment with bypassing agents for patients without or with inhibitors, respectively. Accordingly, laboratory methods for monitoring include one-stage clotting or chromogenic assays meant to measure either factor VIII/IX or global coagulation tests to measure the effect of bypassing agents. Recently, modified long-acting coagulation factors have been introduced for which discrepant results may be expected when measurement is performed with one-stage clotting or chromogenic assays. Currently, novel drugs not based on coagulation factors are under development and are being tested in clinical studies. These drugs do require new methods and therefore laboratory evaluation of hemophilia will undergo dramatic changes in the near future.

SUMMARY

From the analysis of the current practice and literature, we draw the following conclusions: (a) Thrombin generation or thromboelastometry are the logical candidate assays to monitor bypassing agents. (b) Considerable differences are expected when measuring modified long-acting coagulation factors, depending on whether one-stage or chromogenic assays are used. Although no definitive conclusions can presently be drawn, chromogenic assays are probably more suitable than one-stage clotting. (c) Novel drugs not based on coagulation factors such as emicizumab, fitusiran, or concizumab that are entering the market do require alternative methods that are not yet well established.

New challenges and best practices for the laboratory monitoring of factor VIII and factor IX replacement

Several recombinant factor VIII and factor IX concentrates with extended half-life (EHL) have recently been validated by clinical studies. The availability of these novel concentrates is expected to significantly facilitate the treatment of patients with hemophilia A and B. However, the modification applied to these molecules has introduced variations in their activity measurement in routine coagulation assays. Depending on the assays, underestimations of up to 10-fold or overestimations of up to approximately 30-fold in the measurements of the recovery have been reported in some factor concentrates. Such biases in monitoring may lead to major under- or overtreatment, as well as unnecessary searching for inhibitor antibodies. In this review, we discuss the guidelines and recommendations that allow the selection of optimal strategies to monitor patients treated with these novel factor concentrates. Based on the specificities of the assays and on local regulations, different chromogenic substrate assays in addition to one-stage clotting assays may be validated to allow the accurate measurement of all novel products. An efficient communication between the clinical laboratory and the clinicians is essential to ensure that the appropriate assays are carried out in laboratories and that the clinicians correctly evaluate the data. Further laboratory and clinical studies are still required for the optimization of the laboratory assays that can be used in the measurement of novel factor VIII and factor IX concentrates with EHL.

Potency estimates for recombinant factor IX in the one-stage clotting assay are influenced by more than just the choice of activated partial thromboplastin time reagent

The activated partial thromboplastin time (APTT) one-stage clotting (OSC) assay is used to potency label factor IX (FIX) therapeutics and to monitor the treatment of deficient patients. Studies have highlighted differences in potency estimates for FIX therapeutics depending on what activator type the APTT reagent contains. During the study to replace the 4th International Standard (IS) for FIX Concentrate, it was noted that for the recombinant FIX (rFIX) candidates, a potency difference of 20% was obtained by some between laboratories using the reagent DAPTTIN. This study was designed to investigate this discrepancy. Two plasma-derived (pdFIX) and 2 rFIX materials were assayed against the 4th IS for FIX concentrate (07/182) using the OSC assay. Three different APTT reagents were used (DAPTTIN, SynthAFax and SynthASil), plus 4 different activation times. The pdFIX samples were not affected by activation time or APTT reagent, with expected potencies recovered in all assays and at all activation times. For rFIX, expected potencies were recovered using SynthASil, but SynthAFax generated potencies around 20% lower. This was consistent across the activation times. For DAPTTIN, potencies for rFIX dropped progressively and by up to 30% as activation time increased from 120 to 300 seconds. This study demonstrates that activation time as well as choice of APTT reagent can result in discrepancies in the potency estimation of rFIX. These factors should be taken into account when assaying rFIX.

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.

Shifting Landscape of Hemophilia Therapy: Implications for Current Clinical Laboratory Coagulation Assays

Clinical coagulation assays are an integral part of diagnosing and managing patients with hemophilia; however, in this new era of bioengineered factor products and non-factor therapeutics, problems have arisen with use of traditional coagulation tests for the quantification of several of these new products. Discussion over the use of one-stage clotting assays versus chromogenic substrate assays for clinical decision making and potency labeling has been ongoing for many years. Emerging factor concentrates have heightened concern over assay selection and availability. Emicizumab interferes with all aPTT based assays, rendering them unreliable and potentially falsely reassuring to the unaware provider. This review explores considerations for coagulation assays in the clinical setting and highlights how awareness of institutional coagulation assays and potential limitations have never been more critical for providers caring for patients with bleeding disorders. This article is protected by copyright. All rights reserved.

Advances and innovations in haemophilia treatment

Haemophilia is a rare disease for which the approved therapeutic options have remained virtually unchanged for 50 years. In the past decade, however, there has been an explosion of innovation in the treatment options that are either in development or have been approved for haemophilia, including engineered clotting factors and an extensive pipeline of new approaches and modalities. Several of these new modalities, especially gene therapy, demonstrate proof of principle in haemophilia but could have broader applications. These advances, in combination with better diagnostics, are now enabling clinicians to improve the standard of care for people with haemophilia. The different mechanisms of action and modifications used in these therapies have implications for their safe and efficacious use, which must be balanced with their therapeutic utility. This Review focuses on the biological aspects of the most advanced and innovative approaches for haemophilia treatment and considers their future use.

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.

Qualification of a select one-stage activated partial thromboplastin time-based clotting assay and two chromogenic assays for the post-administration monitoring of nonacog beta pegol

Essentials Nonacog beta pegol (N9-GP) is an extended half-life, recombinant human factor IX (FIX). One-stage clotting (OSC) and chromogenic FIX activity assays were assessed for N9-GP recovery. OSC STA® -Cephascreen® , ROX FIX and BIOPHEN FIX chromogenic assays were qualified for N9-GP. Other extended half-life factor products should be assessed in a similar way prior to approval.

SUMMARY

Background Nonacog beta pegol (N9-GP) is an extended half-life, glycoPEGylated recombinant human factor IX that is under development for the prophylaxis and treatment of bleeding episodes in hemophilia B patients. Considerable reagent-dependent variability has been observed when one-stage clotting assays are used to measure the recovery of recombinant FIX products, including N9-GP. Objective To qualify select one-stage clotting and chromogenic FIX activity assays for measuring N9-GP recovery. Methods The accuracy and precision of the one-stage clotting assay (with the STA-Cephascreen activated partial thromboplastin [APTT] reagent) and the ROX Factor IX and BIOPHEN Factor IX chromogenic assays for measuring N9-GP recovery were assessed in N9-GP-spiked hemophilia B plasma samples in a systematic manner at three independent sites, with manufacturer-recommended protocols and/or site-specific assay setups, including different instruments. Results For each of the three FIX activity assays qualified on five different reagent-instrument systems, acceptable intra-assay and interassay accuracy and precision, dilution integrity, reagent robustness and freeze-thaw and short-term sample stabilities were demonstrated. The STA-Cephascreen assay showed a limited reportable range at one of the three qualification sites, and the BIOPHEN Factor IX assay showed suspect low-end sensitivity at one of the three qualification sites. An individual laboratory would account for these limitations by adjusting the assay's reportable range; thus, these findings are not considered to impact the respective assay qualifications. Conclusion The one-stage clotting assay with the STA-Cephascreen APTT reagent, the ROX Factor IX chromogenic assay and the BIOPHEN Factor IX chromogenic assay are considered to be qualified for the measurement of N9-GP in 3.2% (0.109 m) citrated human plasma.

Underestimation of N-glycoPEGylated factor IX one-stage clotting activity owing to contact activator-impaired activation

BACKGROUND

In clinical practice, factor IX (FIX) activity is routinely quantified by measurement of the activated partial thromboplastin time (APTT) in a one-stage (OS) FIX clotting assay. APTT reagents provide a contact activator and phospholipid surfaces required for triggering and sustaining the plasma clotting process. The large diversity in reagent components is reflected in the variable recovery of nonacog beta pegol (N9-GP; N-glycoPEGylated recombinant FIX) activity when assayed against a FIX standard. This variation warrants mechanistic studies and is plausibly attributable to the nature and amount of contact activator.

OBJECTIVE

To identify the cause of the N9-GP activity underestimation observed with a heterogeneous group of APTT reagents.

METHODS

Experiments mimicking the clotting phase (omitting the contact activation phase) of the OS assay, complemented by measurements of activated factor XI (FXIa) activity, were performed to characterize and explain the influence of APTT reagents/contact activators on the conversion of N9-GP and regular FIX (N9) to activated FIX (FIXa).

RESULTS

In the presence of an intact underestimating APTT reagent or the isolated contact activator, clotting phase activation of N9-GP proceeded at a reduced rate compared with that of N9. APTT reagent and contact activator negatively affected the activity of FXIa, conceivably as a consequence of FXIa adsorption. Thus, activation of FIX apparently poses a greater steric challenge after polyethylene glycol (PEG) conjugation.

CONCLUSIONS

Some OS clotting assay contact activators reduce FXIa-mediated activation of N9-GP to a larger degree than that of N9, causing underestimation of N9-GP activity of potential clinical significance.