The first experiments to reverse a human disease by transplanting genes into a patient's blood cells moved a step closer last week when a federal review panel voted unanimously to approve the controversial project.

The Human Gene Therapy Subcommittee voted provisional approval; a final vote is scheduled for July 30. The Food and Drug Administration also must approve the project.

In the experiment, scientists from the National Heart, Lung and Blood Institute and the National Cancer Institute will remove white blood cells from four children suffering a genetic disease called severe combined immune deficiency syndrome, or SCID -- best remembered as the disease that afflicted David, the Boy in the Bubble.

These children are missing the gene that makes adenosine deaminase, or ADA, an enzyme. Without ADA, a toxic compound builds up in the children's blood and destroys the immune system.

NCI's R. Michael Blease and NHLBI's W. French Anderson plan to use a genetically engineered virus to carry a normal copy of the ADA gene into the T cells, a type of white blood cell, from the afflicted children. The repair gene will become part of the cell and begin making ADA -- enough, the researchers hope, to reverse the disease.

The T cells then will be grown in the laboratory until there are large numbers of them. They will then be returned to the children. The scientists, however, will not immediately be able to determine whether the genetically altered T cells make enough of the enzyme to cure the disease.

For that reason, the children will continue to receive injections of ADA in a preparation called PEG-ADA, which boosts their immune system.