Abstract Number: OC 75.2
Meeting: ISTH 2021 Congress
Theme: Hemophilia and Rare Bleeding Disorders » Hemophilia Gene Therapy
Background: Long term expression of Factor VIII (FVIII) following adeno-associated viral (AAV) gene therapy has been reported in clinical studies. There is uncertainty on the mechanisms resulting in variable FVIII expression and early liver toxicity.
Aims: To evaluate early changes affecting the liver and factors affecting FVIII expression following AAV gene therapy in a hemophilia A dog model.
Methods: Severe hemophilia A dogs were treated using one of three AAV5-B-domain deleted canine FVIII vectors with a hybrid liver promoter (AAV5-HLP-cFVIII). Hemostatic outcomes were measured using FVIII:C, whole blood clot time (WBCT) and ROTEM/TEG. Ultrasound-guided liver biopsies were performed at baseline, 3, 12 and 18 months.
Results: Five male dogs were treated with a single infusion of AAV5-HLP-cFVIII at doses of 6.8e13 – 2e14 vector genomes/kg (Table 1). FVIII expression was seen for both dogs treated with codon-optimized constructs (JA2013 & K2015) and is sustained at six months (co-cFVIII-SQ=6.3% and co-cFVIII-V3=4.3%) with normalization of the WBCT. Although no significant cFVIII-SQ expression was seen for dogs (n=3) treated with the non-codon-optimized-AAV5-cFVIII-SQ vector, improvement in WBCT and TEG R-time was seen. The co-cFVIII-V3 treated dog (K2015) developed two episodes of transaminitis and an episode of transient loss of FVIII expression (Figure 1). Ultrasound imaging and liver biopsies to investigate these episodes demonstrated no significant underlying liver histopathology. Liver MRI at baseline and at 12-18 months in non-codon-optimized-AAV5-cFVIII treated dogs (n=3) demonstrated no significant changes. End-point post-mortem liver examination of two dogs (AU2010 and BA2011) demonstrated sparse sub-centimeter foci of benign nodular hyperplasia (seen in untreated dogs), with no evidence of inflammation, fibrosis or neoplasia.
| ID | Vector (dose vg/kg) |
Age at treatment (years) |
Follow-up (Weeks) |
WBCT mins (pre) |
WBCT mins (6 months) |
R Time*or CT # mins (pre) |
R Time*or CT # mins (6 months) |
FVIII:C % OSA (6 months) |
|---|---|---|---|---|---|---|---|---|
| AU2010 | HLP-nco-cFVIII-SQ 8.0e13 |
9.0 | 76 | 17.7 | 10.6 | 102.1 * | 140.4 * | 0.6 |
| BR2018 | HLP-nco-cFVIII-SQ 8.2e13 |
0.8 | 75 | 15.6 | 9.7 | 353.7 * | 26.8 * | 2.1 |
| BA2011 | HLP-nco-cFVIII-SQ 2.1e14 |
8.3 | 52 | 15.2 | 8.3 | 141.4 * | 43.3 * | 2.3 |
| K2015 | HLP-co-cFVIII-V3 6.8e13 |
5.2 | 25 | 13.5 | 4.1 | 89.9 # | 15.2 # | 4.3 |
| JA2013 | HLP-co-cFVIII-SQ 6.8e13 |
6.9 | 24 | 9.9 | 3.9 | 89.9 # | 20.6 # | 6.8 |
Hemostatic outcomes six months following AAV5-HLP-cFVIII treatment in severe hemophilia dogs. WBCT = Whole blood clot time (normal: 4-6 minutes); R-Time (TEG, normal: 1.7-8.2 mins) and Clotting Time (CT) (ROTEM, normal: 8.2-11.0 mins). OSA=One stage FVIII:C. nco=non-codon-optimized. co=codon optimized.
Episodes of transaminitis at Days 79 (post 3 month biopsy) and 116, and transient loss of FVIII expression in K2015 treated with AAV5-HLP-co-cFVIII-V3 (6.8e13 vg/kg). ALT upper limit of normal (118U/L) indicated by horizontal line.
Conclusions: Factor VIII expression was seen using co-AAV5-HLP-cFVIII vectors in a hemophilia dog model. This is the first description of transaminitis and loss of FVIII expression in a preclinical model. Further investigation of mechanisms leading to transient transaminitis and variation in FVIII levels are ongoing.
To cite this abstract in AMA style:
Batty P, Yates B, Hurlbut D, Siso-Llonch S, Menard A, Akeefe H, Christianson T, Colosi P, Harpell L, Liu S, Mo A, Pender A, Veres G, Vitelli C, Winterborn A, Bunting S, Fong S, Lillicrap D. Investigation of Early Outcomes Following Adeno-associated Viral Gene Therapy in a Canine Hemophilia Model [abstract]. Res Pract Thromb Haemost. 2021; 5 (Suppl 2). https://abstracts.isth.org/abstract/investigation-of-early-outcomes-following-adeno-associated-viral-gene-therapy-in-a-canine-hemophilia-model/. Accessed January 26, 2022.« Back to ISTH 2021 Congress
ISTH Congress Abstracts - https://abstracts.isth.org/abstract/investigation-of-early-outcomes-following-adeno-associated-viral-gene-therapy-in-a-canine-hemophilia-model/