1. From the New York Blood Center and Mount Sinaı̈ Medical Center, NY; the Lawrence Berkeley National Laboratory, Life Sciences Division, Berkeley, CA; The Jackson Laboratory, Bar Harbor, ME; and the Laboratoire d'Hématologie, AP-HP, Faculté de Médecine Paris XI, INSERM U473, Hôpital de Bicêtre, Le Kremlin Bicêtre, France.