This clinical trial is focused on studying the long-term safety and effectiveness of a gene therapy treatment for adults with Hemophilia B, a genetic disorder that affects the blood’s ability to clot properly. The treatment being studied is called AAV5-hFIX, which is a type of gene therapy. It uses a harmless virus to deliver a modified version of the human factor IX gene, which is important for blood clotting, into the patient’s liver cells. This therapy aims to help the body produce more of the factor IX protein, potentially reducing bleeding episodes in patients with severe or moderately severe Hemophilia B.

The purpose of this study is to assess the long-term safety of the AAV5-hFIX treatment over a period of 6 to 10 years after it has been administered. Participants in this study have previously received this gene therapy in an earlier phase of the trial. Throughout the study, researchers will monitor participants for any side effects that may be related to the treatment, as well as changes in liver function and the presence of any antibodies that might affect the treatment’s effectiveness. Additionally, the study will evaluate how well the treatment works in terms of increasing factor IX activity, reducing the need for additional factor IX treatments, and decreasing the frequency of bleeding events.

Participants will undergo regular check-ups and assessments to track their health and the impact of the gene therapy on their quality of life. This includes monitoring for any bleeding episodes, evaluating joint health, and assessing overall well-being through quality of life questionnaires. The study aims to provide valuable information on the long-term benefits and safety of AAV5-hFIX for individuals living with Hemophilia B.