PB0221 - Persistent and stable therapeutic levels of transgenic FVIII expression following AAV delivery to adult and infant hemophilic dogs

Sunday, June 23, 2024

13:45 – 14:45 ICT

Room: Exhibition Hall

Presenting Author(s)

Paul Batty, MBBS PhD

Associate Professor
Cancer Institute, University College London, London, UK
London, England, United Kingdom

Co-Author(s)

AI

A. M. Ismail

Senior Scientist
BioMarin Pharmaceutical, Novato, United States
Novato, California, United States
BY

Bridget Yates

Associate Director
BioMarin Pharmaceutical, Novato, United States
Novato, California, United States
LS

Laura Swystun

Medical Writer
Department of Pathology and Molecular Medicine, Queen's University, Kingston, Canada
Kingston, Ontario, Canada
AM

Aomei Mo

Research Technologist
Department of Pathology and Molecular Medicine, Queen's University, Kingston, Canada
Kingston, Ontario, Canada
LH

Lori Harpell

Veterinary Technologist
Department of Pathology and Molecular Medicine, Queen's University, Kingston, Canada
Kingston, Ontario, Canada
AP

Abbey Pender

Veterinary Technologist
Department of Pathology and Molecular Medicine, Queen's University, Kingston, Canada
Kingston, Ontario, Canada
AM

Alex Menard

Assistant Professor
Kingston Health Sciences Centre, Kingston, Canada
Kingston, Ontario, Canada
AW

Andrew Winterborn

Veterinarian
Animal Care Services, Queen's University, Kingston, Canada
Kingston, Ontario, Canada
SS

Sandra Salcido

Senior Research Associate II
BioMarin Pharmaceutical, Novato, United States
Novato, California, United States
AG

Alyssa Gonazlez

Research Associate II
BioMarin Pharmaceutical, Novato, United States
Novato, California, United States
CK

Chan Kyu Kim

Research Associate II
BioMarin Pharmaceutical, Novato, United States
Novato, California, United States
SB

Sebastian Brennan

Senior Principal Pathologist
BioMarin Pharmaceutical, Novato, United States
Novato, California, United States
Sylvia Fong

Executive Director, Head of Hematology Research
BioMarin Pharmaceutical
Novato, California, United States
David Lillicrap, MD

Professor Department of Pathology and Molecular Medicine
Molecular Hemostasis Research Group, Department of Pathology and Molecular Medicine, Queen's University, Kingston, ON, Canada.
Kingston, Ontario, Canada

Background: Adeno-associated viral-factor VIII (AAV-FVIII) gene therapy is approved for treatment of adults with severe hemophilia A. Factors influencing hepatocyte transduction and AAV-FVIII vector processing kinetics remain unknown.

Aims: To evaluate the influence of age, codon-optimization, and vector dose on AAV-FVIII genome processing kinetics and FVIII expression in a hemophilia dog model.

Methods: Neonatal (2-weeks, n=2), infant (2-months, n=3) and adult (mean=4.7 years, n=10) severe hemophilia A dogs received a single infusion of codon-optimized (co) or wild-type (wt) AAV-canine FVIII (AAV-cFVIII) (dose=6.0e13-2.0e14 vg/kg). Serial liver biopsies (0.4-18 months post-AAV-cFVIII) underwent droplet digital PCR and histological analyses.

Results: Stable therapeutic FVIII:C expression (one-stage) was seen in adult (8.1-27.0%) and infant (11.8-15.5%), but not neonatal (0-2%) dogs, 12-18 months post-co-AAV-cFVIII (Figure 1). For infant and adult treated dogs, vector hepatocyte transduction measured by in situ hybridization was efficient (>80%), declined in the early months, and remained stable for 12-18 months (29-67%). Significant decline in hepatocyte transduction to < 10% was seen at 6 months for neonatal-treated dogs.

Similarly, full-length circular vector genomes (vg) were highest at early time points, declined, and remained stable for the duration of the study (Figure 2). Neonatal dogs had low levels of circular full-length AAV-cFVIII for 3 months. cFVIII mRNA correlated with plasma FVIII:C for adult (r=0.92) and infant/neonatal dogs (r=0.88).

In adult dogs, codon-optimization and dose were associated with increased FVIII:C. Circular full-length vg levels displayed dose-dependency 3-12 months post-treatment. Although treatment with wt-AAV-cFVIII showed persistent circular full-length AAV-cFVIII, cFVIII mRNA and plasma FVIII:C remained low.

Histopathological analyses were normal. There was no evidence of ER stress or increased GRP78 in FVIII-expressing hepatocytes.

Conclusion(s): Adult and infant co-AAV-cFVIII-treated dogs displayed efficient dose-dependent hepatocyte transduction. Hepatocyte transduction and circular full-length AAV-cFVIII copies were highest early post-treatment and maintained for 12-18 months with therapeutic FVIII expression.