1. From the Center for Biologics Evaluation and Research, Bethesda, MD; the Laboratory of Clinical Investigation, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD; the Department of Hematology/Oncology, Children's National Medical Center, Washington, DC; and the Laboratory of Pathology, Hematopathology Section, National Cancer Institutes, Bethesda, MD.