1. Immunobiology Research Center, Department of Surgery, Beth Israel Deaconess Medical Center, Harvard Medical School, 02115 Boston, MA, U.S.A. and Instituto Gulbenkian de Ciência, Apartado 14, 2781-901 Oeiras, Portugal
2. Department of Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, 02115 Boston, MA, U.S.A.
3. Immunobiology Research Center, Department of Surgery, Beth Israel Deaconess Medical Center, Harvard Medical School, 02115 Boston, MA, U.S.A.