Liver tumor in gene therapy recipient raises concerns about virus widely used in treatment

It’s troubling news that gene therapy researchers have long anticipated: A hemophilia patient injected with a virus carrying a therapeutic gene in a clinical trial has developed a liver tumor. The U.S. Food and Drug Administration (FDA) has halted the associated clinical trials, and uniQure, the Dutch firm behind the studies, is now investigating whether the virus itself caused the cancer.

Gene therapy experts say that’s unlikely. The patient had underlying conditions that predisposed him to liver cancer. Still, scientists say it’s crucial to rule out any role for adeno-associated virus (AAV), the viral delivery system, or vector, that is used in hundreds of other gene therapy trials. “Everyone will want to know what happened,” says physician-scientist David Lillicrap of Queen’s University, a hemophilia researcher who was not involved with the uniQure study.

Gene therapy for various forms of the blood-clotting disorder hemophilia has been one of the field’s latest success stories. UniQure’s hemophilia B treatment appears to be among the treatments working, with 52 of 54 patients no longer needing injections of factor IX after 6 months in its...