[1] Cornell Univ, Weill Med Coll, Dept Microbiol & Immunol, New York, NY 10021 USA
[2] Univ Calif Los Angeles, David Geffen Sch Med, UCLA AIDS Inst, Dept Med, Los Angeles, CA 90095 USA
[3] Univ Calif Los Angeles, David Geffen Sch Med, UCLA AIDS Inst, Dept Microbiol Immunol & Mol Genet, Los Angeles, CA 90095 USA