Gene therapy for hemophilia B
A single peripheral-vein infusion of an AAV8 vector expressing factor IX raised clotting-factor activity in men with severe hemophilia B in an early-phase trial.
What the study found
Hemophilia B is an X-linked bleeding disorder caused by deficiency of clotting factor IX. In this study (New England Journal of Medicine, 2011), six patients with severe hemophilia B — factor IX activity under 1 percent of normal — received a single infusion into a peripheral vein of a self-complementary AAV vector (serotype-8 pseudotyped) carrying a codon-optimized human factor IX gene. Participants were enrolled in three dose cohorts. The infusion raised circulating factor IX activity, reducing the deficiency that causes bleeding, without routine immunosuppression at the time of dosing.
How it works
The AAV vector delivers a working factor IX gene mainly to liver cells, which then produce the clotting factor the body cannot make on its own. A single dose is meant to provide a lasting supply, replacing frequent factor infusions. Because the vector prompts an immune response in some patients, a transient rise in liver enzymes was watched closely.
Analysis — the pattern
This sits within a broader pattern (analysis): AAV-delivered gene transfer targets single-gene disorders where adding one working gene can change the disease, and the liver is a favored destination for secreted proteins like clotting factors. Durability and immune responses to the vector are the recurring questions the field tracks.
What is still uncertain
This was a small, early-phase trial. How long factor IX expression lasts, the immune response to the vector, the best dose, and long-term safety were all still being studied, and results depend on careful patient selection.