1. Experimental Transplantation and Immunology Branch, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892-1203.
2. Division of Experimental Hematology, Department of Hematology, St. Jude Children's Research Hospital, Memphis, TN 38105.
3. Division of Veterinary Resources, Office of Research Services, National Institutes of Health, Bethesda, MD 20892.