SB-FIX, developed by Sangamo Therapeutics, is an investigative gene therapy for hemophilia B that, by making changes to the DNA sequence, may allow hemophilia B patients to make their own factor IX protein. (Factor IX is missing or present at low levels only in patients with hemophilia B, compromising their ability to form blood clots.)

How SB-FIX works

SB-FIX uses the so-call zinc-finger-nucleases approach. Zinc-finger-nucleases are like molecular scissors that cut DNA at a specific site where a therapeutic gene can be inserted.

SB-FIX cuts the DNA in a region that is under the control of the albumin promoter and includes a normal copy of the F9 gene, which provides instructions to build clotting factor IX. The albumin promoter is highly active in liver cells, so clotting factor IX encoded by the healthy F9 gene will be made in the liver and then released into the bloodstream. (A promoter is a region in the DNA that controls the activity of associated genes).

SB-FIX is delivered with a single infusion into the bloodstream using adeno-associated viral vectors (AAVs). AAVs often are used as transport agents in gene therapy and are modified to be harmless and non-infectious.

SB-FIX in clinical trials

A Phase 1/2 clinical trial (NCT02695160) assessing the safety, tolerability, and effectiveness of SB-FIX is recruiting up to 12 adults with severe hemophilia B at several sites in the U.S. and the United Kingdom. Participants are being divided into three groups and will receive either a low, medium or high dose of SB-FIX.

The trial will look primarily at side effects and changes in clotting factor IX levels, with patients monitored for 36 months after SB-FIX treatment.

Additional information

SB-FIX was designated an orphan drug by the U. S. Food and Drug Administration (FDA) in 2016 to speed its development as a potential treatment for hemophilia B.

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