[1] UNIV CALIF SAN FRANCISCO, DEPT MED, SAN FRANCISCO, CA 94143 USA
[2] HOWARD HUGHES MED INST, SAN FRANCISCO, CA 94143 USA
[3] HARVARD UNIV, SCH MED, DANA FARBER CANC INST, DEPT MEMBRANE IMMUNOCHEM, BOSTON, MA 02115 USA
[4] INSERM, F-13258 MARSEILLE 09, FRANCE