Factor VIII expression was detected on liver biopsies at more than 2 years after a single infusion of adeno-associated virus (AAV) gene therapy for hemophilia A in two patients who were part of a recent phase 1/2 study and who participated in an optional liver biopsy substudy.
The persistent factor VIII (FVIII) expression seen in the two patients was consistent with the presence of circularized, full-length human FVIII-SQ DNA in the biopsy samples and was observed in one patients at week 201 after infusion with 6 x 1012 vg/kg of the AAV serotype 5 human FVIII-SQ gene therapy(valoctocogene roxaparvovec) and in another at week 140 after infusion with 4×1013 vg/kg, Sylvia Fong, PhD, reported during the International Society of Thrombosis and Haemostasis virtual congress.
The first patient had no FVIII detected in the plasma at the time of biopsy. The second had 28.4% of normal FVIII activity detected at the time of biopsy, said Dr. Fong of BioMarin Pharmaceutical, noting that alanine aminotransferase levels were normal at the time of biopsy for both subjects.
“Valoctocogene roxaparvovec is currently being evaluated in a phase 3 clinical study,” Dr. Fong said. “Data from the phase 1/2 trial have demonstrated preliminary proof of concept that valoctocogene roxaparvovec treatment, in many cases, eliminated spontaneous bleeds and the need for prophylactic factor VIII replacement.
“In addition, an acceptable safety profile was observed.”
Data from that trial were presented at the World Federation of Hemophilia virtual summit in June.
Liver biopsy for factor VIII expression
The current exploratory liver biopsy substudy – the first-in-human liver biopsy study after gene therapy for hemophilia A – was open to all phase 1/2 study participants and was initiated in September 2019 with multiple aims, including improved understanding of the durability and variability of AAV gene therapy, she explained.
Histopathological examination revealed normal liver architecture with mild steatosis and no evidence of steatohepatitis or significant inflammation in either participant. In the 6×1012 vg/kg– and 4×1013 vg/kg–treated participants, a dose-dependent increase was seen in the percentage of hepatocytes that stained positive for vector genomes (1.3% and 32%, respectively), she said.
“This was very exciting to see,” she said, referring to the 32% stain-positive rate in the patient who received the 4x1013 vg/kg dose. “Not only were we able to detect vector genomes more than 2 years post-dose, there seems to be quite a bit of signals in this patient sample.”
The findings were similar to those seen in preclinical nonhuman primate models, she noted.
liver hFVIII-SQ RNA levels were 7.67×102 copies/mcg and 6.77×104 copies/µg in the 6×1012 vg/kg–treated participant the 4×1013 vg/kg–treated participant, respectively.
The circularized genomes were present as monomers and concatemers in both participants, and “were presumably associated with long-term expression,” Dr. Fong said.
Both participants are clinically stable with no long-term hepatic issues, she said, noting that analyses of results from additional participants in the substudy will be shared as they become available.
To date, because of “precious small amounts” of tissue available from the biopsy samples, Dr. Fong said she and her colleagues had not looked for degradation of the vectors.
Session moderator Sebastien Lacroix-Desmazes, MD, of Centre de recherche des Cordeliers, Paris, asked: “Is there a plan [to do so] or not, because I guess it’s a very important point,” to which Dr. Fong said that it is a possibility if adequate samples become available.
Dr. Fong is an employee of BioMarin Pharmaceuticals.
SOURCE: Fong S. 2020 ISTH Congress, Abstract OC 03.4.