An Update on Laboratory Diagnostics in Haemophilia A and B

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).

Measurement of recombinant porcine factor VIII in patients with congenital haemophilia A and inhibitors in the presence of emicizumab

INTRODUCTION

Recombinant porcine factor VIII (rpFVIII) is a treatment option for break-through bleeds in patients with congenital haemophilia A with inhibitors (CHAwI) on emicizumab. However, there are limited data about the measurement of rpFVIII in the presence of emicizumab.

AIM

To analyse whether rpFVIII can be measured with a chromogenic assay with bovine component (bCSA) in plasma from CHAwI on emicizumab treatment.

METHODS

In the first part of the study, FVIII deficient plasma was spiked with rpFVIII, in the second part, commercial plasma from CHAwI was spiked with emicizumab and rpFVIII, and in the third part, plasma from CHAwI on emicizumab treatment was spiked with rpFVIII. FVIII was then measured with bCSA and a chromogenic assay with human component (hCSA). Thrombin generation (TG) and clot-waveform analysis (CWA) were also carried out.

RESULTS

The recovery of rpFVIII measured with bCSA is approximately 80% and is further influenced by the presence of an anti-porcine inhibitor. rpFVIII assessed with hCSA was influenced by emicizumab. CWA and TG showed a weak correlation with baseline emicizumab concentration, but peak thrombin and CWA correlated well with increasing emicizumab concentrations and rpFVIII activities.

CONCLUSION

This study indicates that rpFVIII can be measured in the presence of emicizumab with a bCSA. A calibration curve for the measurement of rpFVIII with bCSA should be established.

A global comparative field study to evaluate the factor VIII activity of efanesoctocog alfa by one-stage clotting and chromogenic substrate assays at clinical haemostasis laboratories

INTRODUCTION

Structural and chemical modifications of factor VIII (FVIII) products may influence their behaviour in FVIII activity assays. Hence, it is important to assess the performance of FVIII products in these assays. Efanesoctocog alfa is a new class of FVIII replacement therapy designed to provide both high sustained factor activity levels and prolonged plasma half-life.

AIM

Evaluate the accuracy of measuring efanesoctocog alfa FVIII activity in one-stage clotting assays (OSAs) and chromogenic substrate assays (CSAs).

METHODS

Human plasma with no detectable FVIII activity was spiked with efanesoctocog alfa or a full-length recombinant FVIII product comparator, octocog alfa, at nominal concentrations of 0.80 IU/mL, 0.20 IU/mL, or 0.05 IU/mL, based on labelled potency. Clinical haemostasis laboratories (N = 35) tested blinded samples using in-house assays. Data from 51 OSAs (14 activated partial thromboplastin time [aPTT] reagents) and 42 CSAs (eight kits) were analyzed.

RESULTS

Efanesoctocog alfa activity was reliably (±25% of nominal activity) measured across all concentrations using OSAs with Actin FSL and multiple other aPTT reagents. Under- and overestimation of FVIII activity occurred with some reagents. No specific trend was observed for any class of aPTT activators. A two- to three-fold overestimation was consistently observed using CSAs and the OSA with Actin FS as the aPTT reagent across evaluated concentrations.

CONCLUSION

Under- or overestimation occurred with some specific OSAs and most CSAs, which has been previously observed with other modified FVIII replacement products. Efanesoctocog alfa FVIII activity was measured with acceptable accuracy and reliability using several OSA methods and commercial plasma standards.

Efanesoctocog alfa for the prevention and treatment of bleeding in patients with hemophilia A

INTRODUCTION

Hemophilia A is an inherited bleeding disorder due to a deficiency of coagulation factor VIII (FVIII). Prevention and treatment of bleeding is traditionally through intravenous infusion of a FVIII concentrate. Modifications of recombinant FVIII (rFVIII) with an aim to prolong the half-life have been modest, thought because FVIII is dependent on plasma von Willebrand factor (VWF) for its half-life. Efanesoctocog alfa (ALTUVIIIO), approved by the Federal Drug Administration (FDA) in February 2023, was made independent of endogenous VWF by linking of the FVIII-binding D'D3 domain of VWF to B-domain deleted single chain FVIII.

AREAS COVERED

This review will outline the development of efanesoctocog alfa and the pharmacokinetic and safety data from clinical trials, as well as efficacy data from the phase 3 trials. These data formed the basis for the FDA approval.

EXPERT OPINION

Efanesoctocog alfa is a new type of FVIII replacement with an extended half-life allowing once weekly dosing to achieve hemostasis and FVIII trough levels of 13-15 IU/dL. This provides a highly effective option for treatment and prevention of bleeding in hemophilia A, where FVIII levels are easily measured. It also provides an option for treatment of bleeding and coverage for surgery with few infusions.

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.

A Review of Factor VIII and Factor IX Assay Methods for Monitoring Extended Half-Life Products in Hemophilia A and B

Clinical trials have used a variety of coagulation factor assay methods to assess treatment with recombinant Factor VIII (rFVIII) and recombinant Factor IX (rFIX) extended half-life (EHL) products. However, diagnostic laboratories may use different reagent combinations for routine use or for field trials of EHL products. The focus of this review is on the choice of one-stage clotting and chromogenic Factor VIII and Factor IX methods and the influence that assay principle and components may have on results, including the effects of different activated partial thromboplastin time reagents and factor-deficient plasma. Our aim is to tabulate the findings for each method and reagent group to give laboratories practical guidance as to how the reagent combinations used in their local laboratory compare to others, for the various EHLs available.

PEGylated drug delivery systems in the pharmaceutical field: past, present and future perspective

Target-site drug delivery systems are gaining interest in the pharmaceutical field due to their great advantages, such as higher drug dosing capacity and better bioavailability. However, some existing problems need to be overcome. As an example, interaction between blood proteins and drug delivery systems. A potent candidate to approach the mentioned problem is based on polyethylene glycol (PEG) surface modifications. This polymer acts as a protector towards the external possible interactions with other compounds, making targeted delivery possible. Diseases such as cancer, diabetes, haemophilia and pain treatment can benefit from these new systems.This review aims to give an overview of drug delivery systems based on PEGylation as surface modification as pharmaceutical approach. Moreover, a deeper insight of the properties of PEG and its advantages is given, as well as brief overview of present therapies based on this technology.