FDA Talk Papers are prepared by the Press Office to guide FDA personnel in responding with consistency and accuracy to questions from the public on subjects of current interest. Talk Papers are subject to change as more information becomes available.

FDA PLACES TEMPORARY HALT ON GENE THERAPY TRIALS
USING RETROVIRAL VECTORS IN BLOOD STEM CELLS

Agency Action Provides Way for Patients to Continue Therapy Under Certain Circumstances if Additional Measures Taken

In a precautionary measure, the Food and Drug Administration (FDA) today placed on "clinical hold" all active gene therapy trials using retroviral vectors to insert genes into blood stem cells.

FDA took this action after it learned that a second child treated in a French gene therapy trial has developed a leukemia-like condition. Both this child, and another who had developed a similar condition last August, had been successfully treated by gene therapy for X-linked severe combined immunodeficiency disease (X-SCID), also known as "bubble baby syndrome."

Infants with X-SCID have a gene defect that leads to a complete lack of white blood cells that can fight infection. Without treatment, they die from complications of infectious diseases during the first year of life. The only treatment for this condition is a bone marrow transplant.

In early results of the French study in which a normal gene is inserted into blood stem cells of patients with X-SCID, nine of the 11 children had promising results and could leave the hospital and lead relatively normal lives.

After notification of the first case last year, FDA identified the three U.S. gene therapy studies that most closely resembled the French trial and stopped enrollment of human subjects in those trials. They remain on clinical hold, a condition which FDA can impose when adverse events or other safety questions arise during a clinical study.

FDA's continuing review of adverse event reports from all U.S. studies involving retroviral vectors has to date found no evidence of leukemia caused by the gene therapy. Moreover, the agency has to consider the potential risks of any experimental therapy within the context of the disease it may treat - in this case a devastating disease in children.

FDA's action includes a temporary hold on the enrollment of new patients in a subset of gene therapy
trials that involve the use of retroviruses to insert new genes in blood stem cells, irrespective of the disease condition.

The temporary hold reflects FDA's appreciation that some of these trials involve patient populations and gene therapy products that may be appropriate to continue after they are updated to reflect this new risk information. FDA will consider and evaluate specific requests for clinical indications for fatal or life-threatening disorders for which there are no viable alternative treatments. In all cases, sponsors will need to inform treated and new subjects of the two adverse events, and will need to have a plan to actively monitor subjects for leukemia like events.

FDA continues to review the data from the adverse event in France, as well as the risks and potential benefits of all ongoing gene therapy trials, and will continue to work closely with the National Institute of Health's Office of Biotechnology Activities to oversee gene therapy studies in the U.S.

The agency expects to hold an advisory committee meeting late next month to discuss the new adverse event in particular and retroviral gene therapy in general.

####

Media Contacts   |   FDA News Page   |   FDA Home Page

Office of Public Affairs
Web page created by tg 2003-JAN-14.