[1] Scripps Res Inst, DEPT IMMUNOL, IMM7, LA JOLLA, CA 92037 USA
[2] SALK INST BIOL STUDIES, LA JOLLA, CA 92037 USA
[3] UNIV PENN, DEPT MED, PHILADELPHIA, PA 19104 USA
[4] UNIV CALIF SAN FRANCISCO, DEPT MED, CANC RES INST, SAN FRANCISCO, CA 94143 USA