To better understand the consequences of AAV gene transfer patients will be recruited to undergo a liver biopsy. Patients will be from a unique cohort of successfully treated patients, who are at least 6 months post gene transfer (patients will be at varying timepoints post gene transfer, with the current maximum time post gene transfer being 9.5 years) and have been treated with self-complementary and over-sized AAV vectors will advance the state-of-the-art, in the following aspects:~Provide a clearer insight into the AAV life cycle in human liver~Define the number of human hepatocytes that are transduced~Improve our understanding at the human hepatocyte level of long-term consequences of AAV mediated transgene expression from the liver that will include (i) changes in the pattern of gene expression in human hepatocytes following AAV mediated gene transfer, (ii) information on the epigenetic signature in the liver following AAV mediated gene transfer and how this changes with time and (iii) the consequences of transgene expression in hepatocytes including the endoplasmic reticulum stress response This study will provide new data addressing several unknowns with AAV mediated gene transfer in humans that will better inform on safety and efficacy following AAV gene transfer for patients who have already participated in gene therapy studies as well as those considering this treatment option.
To perform a liver biopsy in haemophilia A and B patients stably expressing human FVIII/FIX for a period of at least 6 months following AAV mediated gene transfer. This is to obtain tissue for analysis, to understand if FIX/FVIII transgenic protein expression is mediated by AAV proviral DNA that is integrated into the host cell DNA or if stable expression in humans is mediated by episomal maintained AAV genome.