1. From the Departments of Medicine, Microbiology, and Immunology, University of North Carolina School of Medicine, the Lineberger Comprehensive Cancer Center, and the University of North Carolina Neurosciences Center, Chapel Hill, NC; the Schering Plough Research Institute, Kenilworth, NJ; and the Department of Pediatrics, Division of Blood and Marrow Transplantation, University of Minnesota Cancer Center, Minneapolis, MN.