1. Institute for Research in Immunology and Cancer, and Department of Chemistry, Université de Montréal, P.O. Box 6128, Station Centre-ville, Montréal, Canada H3C 3J7, and Blood and Marrow Transplant Program, Maisonneuve-Rosemont Hospital, 5415, Assomption Blvd., Montreal QC, Canada H1T 2M4