Factor IX assay discrepancies in the setting of liver gene therapy using a hyperfunctional variant factor IX‐Padua. (28th March 2021)

• Record Type: Journal Article
• Authors: Robinson, Mary M.; George, Lindsey A.; Carr, Marcus E.; Samelson‐Jones, Benjamin J.; Arruda, Valder R.; Murphy, John E.; Rybin, Denis; Rupon, Jeremy; High, Katherine A.; Tiefenbacher, Stefan
• Is Part Of: Journal of thrombosis and haemostasis. Volume 19:Number 5(2021)
• Page Start: 1212
• Page End: 1218
• Publication Date: 2021-03-28
• Subjects: blood coagulation tests -- biological assay -- fidanacogene elaparvovec -- genetic therapy -- hemophilia B; Thrombosis -- Periodicals; Hemostasis -- Periodicals; Blood coagulation disorders -- Periodicals; 616.1
• DOI: 10.1111/jth.15281
• Languages: English
• ISSNs: 1538-7933

Abstract

Abstract: 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.