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A gene therapy for hemophilia aims to restore a protein called factor that stabilizes fibrin (yellow), a component of blood clots.


Experimental gene therapy for hemophilia probably did not cause patient’s liver tumor

The company uniQure has concluded that a virus used widely in gene therapy was very unlikely to have caused liver cancer in a hemophilia patient in a clinical trial.

The tumor, detected in December 2020, raised concerns that the adeno-associated virus (AAV) used to carry a loop of DNA into the patient’s liver cells had inadvertently switched on a cancer gene. But uniQure’s tests of the patient’s tumor cells showed the AAV inserted into the genome in only a tiny fraction (0.027%) of the cells, and when it did, it landed in randomly scattered spots. If the AAV had triggered a single cell to grow out of control, the viral DNA would have shown up in the same spots in lots of the tumor cells.

The patient also had several known cancer mutations in his tumor cells, as well as risk factors for liver cancer including long-term hepatitis B and C infections.

The findings “support the conclusion that an AAV integration event was not likely responsible” for the liver tumor, says hemophilia gene therapy researcher Denise Sabatino of the Children’s Hospital of Philadelphia. “This is good news for the field.”

UniQure’s announcement today comes less than 3 weeks after another company, bluebird bio, found that a different virus called a lentiviral vector probably did not play a role in a patient’s leukemia in a gene therapy trial for sickle cell disease. Both companies are now hoping the U.S. Food and Drug Administration will lift holds on their trials.