Vector integration and fate in the hemophilia dog liver multiple years after AAV-FVIII gene transfer
Paul Batty, Sylvia Fong, Matteo Franco, Choong‐Ryoul Sihn, Laura L. Swystun, Saira Afzal, L. Harpell, David Hurlbut, Abbey Pender, Cheng Su, Hauke Thomsen, Christopher Wilson, Loubna Youssar, Andrew Winterborn, Irene Gil-Fariña, David Lillicrap
Abstract
ABSTRACT: Gene therapy using adeno-associated virus (AAV) vectors is a promising approach for the treatment of monogenic disorders. Long-term multiyear transgene expression has been demonstrated in animal models and clinical studies. Nevertheless, uncertainties remain concerning the nature of AAV vector persistence and whether there is a potential for genotoxicity. Here, we describe the mechanisms of AAV vector persistence in the liver of a severe hemophilia A dog model (male = 4, hemizygous; and female = 4, homozygous), more than a decade after portal vein delivery. The predominant vector form was nonintegrated episomal structures with levels correlating with long-term transgene expression. Random integration was seen in all samples (median frequency, 9.3e-4 sites per cell), with small numbers of nonrandom common integration sites associated with open chromatin. No full-length integrated vectors were found, supporting predominant episomal vector-mediated long-term transgene expression. Despite integration, this was not associated with oncogene upregulation or histopathological evidence of tumorigenesis. These findings support the long-term safety of this therapeutic modality.