Monitoring standard and extended half-life products in hemophilia: Assay discrepancies for factor VIII and IX in pre- and postinfusion samples

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.

Functional determination of emicizumab in presence of factor VIII activity

BACKGROUND

Accurate measurement of emicizumab in the presence of factor (F) VIII is required in patients with severe hemophilia A treated with emicizumab, as well as additional need for FVIII substitution or emicizumab prophylaxis in patients with acquired or moderate to mild hemophilia A. However, the presence of FVIII potentially biases the results.

OBJECTIVES

To assess the impact of plasma FVIII activity on determined emicizumab levels and evaluate different strategies for correction for or preanalytical inhibition of FVIII.

METHODS

Evaluated strategies comprised of the following: (1) calculation of actual emicizumab plasma levels based on measured FVIII activities and FVIII-affected emicizumab values, (2) preanalytical heat treatment (56 °C for 40 minutes), and (3) neutralization of FVIII activity using FVIII inhibitors. Emicizumab levels and FVIII activities were measured using a modified FVIII one-stage clotting assay and a chromogenic FVIII assay based on bovine factors, respectively.

RESULTS

Spiking experiments revealed a consistent linear association between FVIII activities and determined (FVIII-affected) emicizumab results at different emicizumab input levels (∼0.12 μg/mL per IU/dL of FVIII). This principally allowed for mathematical correction of measured emicizumab levels in the presence of FVIII. While a 40% to 50% activity loss of intrinsic plasma emicizumab through heat treatment was observed in patient samples, emicizumab spiked into FVIII-deficient plasma was not or only marginally affected. Application of inhibitor-based FVIII neutralization led to good agreement of results when compared with direct quantification of emicizumab by liquid chromatography-tandem mass spectrometry.

CONCLUSION

Inhibitor-based FVIII neutralization appears to be a feasible strategy for accurate measurement of plasma emicizumab levels in the presence of FVIII activity.

Plasma Clearance of Coagulation Factor VIII and Extension of Its Half-Life for the Therapy of Hemophilia A: A Critical Review of the Current State of Research and Practice

Factor VIII (FVIII) is an important component of blood coagulation as its congenital deficiency results in life-threatening bleeding. Current prophylactic therapy of the disease (hemophilia A) is based on 3-4 intravenous infusions of therapeutic FVIII per week. This poses a burden on patients, demanding reduction of infusion frequency by using FVIII with extended plasma half-life (EHL). Development of these products requires understanding FVIII plasma clearance mechanisms. This paper overviews (i) an up-to-date state of the research in this field and (ii) current EHL FVIII products, including recently approved efanesoctocog alfa, for which the plasma half-life exceeds a biochemical barrier posed by von Willebrand factor, complexed with FVIII in plasma, which results in ~1 per week infusion frequency. We focus on the EHL FVIII products' structure and function, in particular related to the known discrepancy in results of one-stage clotting (OC) and chromogenic substrate (CS) assays used to assign the products' potency, dosing, and for clinical monitoring in plasma. We suggest a possible root cause of these assays' discrepancy that is also pertinent to EHL factor IX variants used to treat hemophilia B. Finally, we discuss approaches in designing future EHL FVIII variants, including those to be used for hemophilia A gene therapy.

Measurement of extended half-life recombinant FVIII molecules: In vitro and ex vivo evidence of relevant assay discrepancies

Background

Extended half-life recombinant FVIII products (EHL-rFVIIIs) have been engineered to improve the pharmacokinetic profile of FVIII, enabling better hemostatic protection with a reduced number of injections in persons with hemophilia. Previous studies showed several discrepancies in FVIII activity (FVIII:C) measurements for EHL-rFVIIIs comparing one-stage clotting assay (OSA) and chromogenic assay (CSA), although a systematic investigation of this phenomenon is still lacking.

Objective

Evaluation of the accuracy and precision of measurement of all available EHL-rFVIIIs with 5 different assays both in vitro and ex vivo.

Methods

Damoctocog alfa pegol, rurioctocog alfa pegol, turoctocog alfa pegol, and efmoroctocog alfa were tested with 3 OSA types: (1) aPTT-based commercial reagents with colloidal silica (Synthasil, Werfen-IL); (2) ellagic acid, Synthafax (Werfen-IL); and (3) OSA calibrated with each EHL-rFVIII product and colloidal silica. Measurements were also carried out with 2 different commercially available CSA reagents (Coamatic Factor VIII, Chromogenix-Werfen) and Trinichrom FVIII (Tcoag-Stago). A Bland-Altman analysis was performed to compare all assays.

Results

The simple OSA showed significant discrepancies between the expected and measured EHL-rFVIII concentrations as CSA methods, whereas the calibrated OSA assay was accurate and precise in determining the activity of all EHL-rFVIIIs in the in vitro setting. Comparable results were found using ex vivo plasma samples.

Conclusion

In this study, only OSA with a calibration curve constructed with each EHL-rFVIII product showed acceptable accuracy and precision in EHL-rFVIIIs measurements.

Switching from standard to extended half-life FVIII prophylaxis in haemophilia A: Comparison of factor product use, bleed rates and pharmacokinetics

INTRODUCTION

Majority of haemophilia A patients in our comprehensive care centre have switched from standard half-life (SHL) to extended half-life (EHL) FVIII products in a short time.

AIM

We compared the clinical and laboratory outcomes between SHL and EHL FVIII prophylaxis in product switchers.

METHODS

This is a retrospective inception cohort of all adult haemophilia A patients switched to EHL (rFVIIIFc or rFVIII-PEG) prophylaxis in our centre. Dosing, product utilization, annualized bleed rates (ABR), treatment regimen and pharmacokinetics by Web Accessible Population Pharmacokinetic Service (WAPPS)-Hemo were compared between SHL and EHL.

RESULTS

We included 38 patients, whose median age was 38 years (range 17-75). Median FVIII dose was 23 IU/kg for SHL versus 25 IU/kg for EHL. After switching, weekly infusions decreased by 29% from median 2.8 (every 2.5 days) to 2.0 (every 3.5 days) (P = <.001) and factor consumption for prophylaxis by 17% from 60 to 50 IU/kg/week (P = <.001). Weekly infusions decreased in 71% and FVIII utilization in 55% of patients. ABR remained low (1.0 for SHL and .5 for EHL, respectively). In pharmacokinetics, the half-life of FVIII increased from median 13 to 21 h after switching. Times above .01 and .03 IU/ml improved from 85 to 131 h and from 65 to 106 h. Half-lives of the SHL products and von Willebrand factor levels predicted half-lives with the EHL products.

CONCLUSIONS

Our cohort study confirms the successful experience of switching to EHL FVIII products, with decreased infusion frequency, factor consumption and excellent clinical efficacy.

Evaluation of the Atellica COAG 360 coagulation analyzer in a specialized coagulation laboratory

Background

Diagnosis of bleeding disorders includes correct analysis of coagulation factors VIII, IX, XI, XII, XIII, II, V, VII, and X and von Willebrand antigen and activity. The aim of this study was to evaluate the analytical performance of the Atellica COAG 360 analyzer in a specialized coagulation laboratory with focus on specific coagulation parameters involved in the diagnosis of bleeding disorders.

Methods

Verification included assessment of precision, reference interval, and method comparison according to local guidelines. For FVIII (Chromogenix) and FIX (Rossix), extended verifications were performed with additional assessment of linearity, detection limit, and comparability to BCS‐XP.

Results

The precision was below 5% (normal levels) and below 10% (abnormal levels) and either improved or similar when compared to expected target values from a BCS‐XP. The locally established reference range agreed well (≥80% of measured values within manufacturer's assigned ranges) for most of the methods. The lower limit of quantification was calculated to below 0.01 IU/ml for FVIII chromogenic (Chromogenix) and FIX chromogenic (Rossix), both with acceptable linearity. Bland–Altman analyses revealed generally good agreement between Atellica COAG 360 and BCS‐XP in the determination of coagulation parameters, and differences between the two instruments did not result in any diagnostic change.

Conclusions

The results of the evaluation show that the Atellica COAG 360 analyzer performs as expected to target values and equivalent to BCS‐XP for the diagnosis of bleeding disorders in a specialized coagulation laboratory providing service to a hemophilia treatment center (HTC).

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.

Validation of factor VIII activity for monitoring standard and extended half-life products and correlation to thrombin generation assays

INTRODUCTION

Monitoring replacement therapy with standard and extended half-life (EHL) products is challenging, since one-stage assay (OSA) and chromogenic substrate assay (CSA) results may differ significantly. Recent recommendations include local validation of each new product with recovery within 20-30%, depending on activity level.

AIM

To validate factor VIII (FVIII) activity for monitoring products in clinical use on Atellica Coag and to correlate it with thrombin generation.

METHODS

Plasma samples spiked with Advate^® , Elocta^® , Adynovi^® , Nuwiq^® , NovoEight^® and Afstyla^® (0.05, 0.20, 0.50 and 0.80 IU/ml) were analysed using Atellica Coag 360 with CSA-1 (Coatest SP) and CSA-2 (FVIII chromogenic), and OSA (Actin FS). Thrombin generation was performed using two thrombin generation assays (TGA-1 (Thrombinoscope) and TGA-2 (Technothrombin).

RESULTS

All products at levels above 0.05 IU/ml, except Adynovi, showed acceptable recovery using CSA-1, whereas measurements using CSA-2 gave more results outside the target level. All products, except Afstyla, showed acceptable recovery using OSA. Correlation between CSA-1 and OSA was excellent (r² =1.0) with biases of 6-3​2%, depending on FVIII product. A clear dose-response was seen for all thrombin generation parameters and products using both methods, except at low levels for lag time using TGA-1. With CSA-1 as an independent variable, the correlations to thrombin peak (measured with TGA-2) were good (r²  = .8-.9).

CONCLUSION

Our data revealed good correlation and acceptable bias between CSA and OSA using our sets of reagents, methods and analyser in spiked samples. Thrombin generation gave good correlation to CSA-1 factor activity and is a possible complement to factor activity assays.