1. Department of Clinical Studies, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA 19104.
2. Laboratory of Host Defenses, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892.
3. Division of Experimental Hematology, St. Jude Children's Research Hospital, Memphis, TN 38105.
4. Clinical Research Division, Fred Hutchinson Cancer Research Center, Seattle, WA 98109.
5. Department of Medicine, University of Washington, Seattle, WA 98109.