First UK Patient Treated with CSL Behring’s AAV Gene Therapy for Hemophilia B

LONDON, UK – June 24, 2025 – The National Health Service (NHS) in the UK has administered CSL Behring’s Hemgenix (etranacogene dezaparvovec), a groundbreaking AAV gene therapy for hemophiliaB, to its first patient. The treatment was provided at Guy’s & St Thomas’ NHS Foundation Trust in London to a patient from the North East of England. This one-time AAV therapy could potentially free the patient from the lifelong need for regular infusions of clotting factor IX (FIX).

Hemophilia B is a genetic bleeding disorder affecting over 2,000 people in the UK, caused by insufficient FIX levels. Current severe cases require continuous intravenous FIX, leaving patients vulnerable to breakthrough bleeds.

“This is a big step forward in our ability to manage hemophilia B and could change the lives of some of our patients,” said Pu-Lin Luo, a consultant haematologist at Guy’s and St Thomas’. “It’s also a testament to the advancement of cell and gene therapies in the UK and these are exciting times.”

Hemgenix AAV Gene Therapy Addresses Underlying Cause with Sustained Results

Hemgenix works by enabling the body to continuously produce FIX, directly addressing the underlying genetic cause of hemophilia B. This AAV-based therapy is the only one-time gene therapy approved in the UK for adults with severe or moderately severe hemophilia B without a history of FIX inhibitors.

The National Institute for Health and Care Excellence (NICE) recommended Hemgenix in June 2024, based on strong evidence from the late-stage HOPE-B trial. This trial demonstrated:

• Significant increases in mean FIX activity levels: 36.9% at 18 months, sustained at 36.7% at 24 months, and 38.6% at 36 months.
• An adjusted annualized bleed rate reduction of 64% at 24 and 36 months post-dose, compared to the pre-treatment period.

Updated four-year results, presented in February, showed mean FIX activity levels remained near normal at 37% and the mean adjusted annualized bleeding rate for all bleeds was reduced by approximately 90% from lead-in to year four.

CSL Behring confirmed its commitment to collaborate with selected gene therapy centers to ensure broader patient access to this AAV gene therapy across the country.