1. Gene Therapy Program, Department of Pathology and Laboratory Medicine, University of Pennsylvania, Philadelphia, PA 19104.
2. Present address: Gene Therapy Center, University of Massachusetts Medical School, Worcester, MA 01605.
3. Present address: Vaccine Research Institute, Third Affiliated Hospital, Sun Yat-Sen University, Guangzhou, China 510630.
4. Department of Pathology and Laboratory Medicine, University of Pennsylvania, Philadelphia, PA 19104.