1. Institute for Research in Immunology and Cancer and Department of Chemistry, Université de Montréal, P.O. Box 6128, Station Centre-Ville Montréal QC H3C 3J7, Canada, Merck Frosst Center for Therapeutic Research, Kirkland, Canada, Department of Internal Medicine, University of Utah, Salt Lake City, Utah 84132, and Department of Human Genetics, University of Utah, Salt Lake City, Utah 84112