PB1178 - Validation of a neutralizing antibody (NAb) assay with extended reportable range for etranacogene dezaparvovec, an adeno-associated virus serotype 5 (AAV5)-based gene therapy for adult hemophilia B

Tuesday, June 25, 2024

13:45 – 14:45 ICT

Room: Exhibition Hall

Presenting Author(s)

Jacqueline Tarrant, BVSc DACVP PhD

Senior Director, Global Lead, Clinical Biomarkers, Clinical Development
CSL Behring
philadelphia, Pennsylvania, United States

Co-Author(s)

HL

Haiying Liu

Director, Clinical Biomarker
CSL Behring
King of Prussia, Pennsylvania, United States
DB

Debbie Bensen-Kennedy

Vice President Medical Affairs
CSL Behring
King of Prussia, Pennsylvania, United States
JM

Joseph Monforte

Precision Medicine & Genomics Advisor
Wild Type Advisors
Berkeley, California, United States
AF

Annette Feussner

Research and Clinical Bioanalytics
CSL Behring
Marburg, Hessen, Germany
DZ

Detlev Zwingmann-Cornelius

Lead Quality Engineer Combination Products & Medical Devices
CSL Behring
Marburg, Hessen, Germany
TH

Travis Harrison

Vice President, Diagnostic Development
Precision for Medicine
Redwood City, California, United States
CS

Crystal Sung

Vice President, Companion Diagnostics
Precision for Medicine
Frederick, Maryland, United States
VG

Vivian Goodell

Senior Biostatistician
Precision for Medicine
Temecula, California, United States
DP

Deborah Phippard

Chief Scientific Officer
Precision for Medicine
Frederick, Maryland, United States
SB

Soraya Benchikh El Fegoun

Global Medical Director, Global Medical Affairs Hematology TA
CSL Behring, Bern, Switzerland
Bern, Bern, Switzerland

Background: Preexisting NAbs to AAV5 are a consideration for decisions to treat adult hemophilia B patients with etranacogene dezaparvovec (EDZ). NAbs are measured with an in vitro cell-based transduction inhibition assay specific for EDZ.

Aims: As patients with preexisting NAbs may benefit from EDZ, we modified the clinical trial assay to extend the reportable measuring range.

Methods: Validation studies were conducted on a revised NAb assay with the same principle as the phase 3 clinical trial assay with a modified sample dilution scheme. The NAb assay was performed in microtiter plates coated with reporter vector cells. Nine serial dilutions of serum samples were prepared with 3-fold dilution intervals, with a starting dilution of 1:2 in the initial test and at 1:18 for reflex testing. Following incubation with the reporter vector, test samples were added onto the reporter cells and reporter gene expression was assessed by luminescence. NAb titer was determined from the sample titration curve and transduction controls using a four-parameter non-linear regression.

Results: Validation of the modified assay confirmed a linear measuring range from 18.5 to 1100 (and up to 4400 titer with reflex testing). Analytical variability met acceptance criteria, with intra-assay precision < 13% and total precision ≤25% CV. A method comparison study established that 678 in the original clinical trial NAb assay, a titer demonstrated to have a safe and efficacious response to EDZ, is equivalent to 898 in the modified method.

Conclusion(s): A modified EDZ NAb assay that is based on a similar principle as the original clinical trial assay has an extended measuring range with improved linearity and accuracy at high NAb titers. This does not represent a change in the amount of the AAV5 NAb, rather the improved assay response curve of the new method yields a comparatively higher titer than the original assay.