1. Gene Therapy Program, Division of Medical Genetics, Department of Medicine, University of Pennsylvania Medical Center, Philadelphia, Pennsylvania.
2. Present address: Departement d'anatomie et physiologie, Université Laval, Centre de recherche du CHUL (CHUQ), Local 4–52, 2505, boulevard Laurier, Sainte-Foy, Quebec, Canada G1V 4G2.
3. Department of Surgery, University of Pennsylvania, Philadelphia, Pennsylvania.