Participants in this study have a genetic mutation, specifically in the coagulation (blood clotting) Factor 9 gene that causes severe or moderately severe hemophilia B. This study is researching an experimental gene insertion therapy (the adding of a gene into your DNA) called REGV131-LNP1265, also called the "study drug". Gene insertion therapy aims to teach the body how to produce clotting factor long-term, without the need for factor replacement therapy. The main aim of this study is to find a safe and well-tolerated dose of the study drug by checking the side effects that may happen from taking it, both in the near term and over time. The study is looking at several other research questions including: * How much study drug is in the blood at different times * Whether the body makes antibodies against parts of the study drug, which could make the drug less effective or could lead to side effects. Antibodies are proteins produced by the body's immune system in response to a foreign substance * Whether the body makes antibodies against the clotting factor replacement therapy * How often factor replacement therapy is needed, both on a regular basis for prevention of bleeding, and as needed to treat bleeding events (and it if changes after taking study drug) * Whether there is a difference in 2 different methods for measuring Factor 9 activity in the blood
Age range
2 Years
Sex
MALE
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AI-rewrites the medical criteria so a patient or caregiver can understand them. Always confirm with the trial site.
Bring these to your next appointment. They're a starting point for a shared conversation — not a sign you qualify or a recommendation to enrol.
Generated to help you prepare — always confirm anything about your own eligibility and care with the study team and your doctor.
The trial coordinator is the person who runs the study day to day. These cover the practical side — logistics, costs, and what taking part would actually mean for your life. The study team confirms whether you meet the criteria; these are questions to ask, not a sign you qualify.
A starting point for the conversation — always confirm anything about your own eligibility, costs, and care with the study team and your doctor.
Occurrence of Treatment-Emergent Adverse Events (TEAEs)
Timeframe: Up to 2 Years
Severity of TEAEs
Timeframe: Up to 2 Years
Coagulation Factor IX (FIX) functional activity measured using the chromogenic substrate assay
Timeframe: Up to 2 Years
Change in FIX functional activity in plasma, measured using the chromogenic substrate assay
Timeframe: Up to 2 Years
Annualized Bleeding Rate (ABR) following sustained FIX functional activity among participants receiving the RDE
Timeframe: Up to 2 Years
Occurrence of Serious Adverse Events (SAEs)
Timeframe: Through Long Term Follow Up (LTFU), Up to 15 Years
Severity of SAEs
Timeframe: Through LTFU, Up to 15 Years
Occurrence of Adverse Event of Special Interests (AESIs)
Timeframe: Through LTFU, Up to 15 Years
Severity of AESIs
Timeframe: Through LTFU, Up to 15 Years
Occurrence of clinically meaningful Adverse Events (AEs)
Timeframe: Through LTFU, Up to 15 Years
Severity of clinically meaningful AEs
Timeframe: Through LTFU, Up to 15 Years