1. From the Division of Hematologic Products, Center for Biologics Evaluation and Research, Food and Drug Administration, Bethesda, Maryland 20892; Department of Obstetrics and Gynecology, Johns Hopkins University, Baltimore, Maryland 21287; Laboratory of Immunopathology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland 20892; and Flow Cytometr