[1] Stanford Univ, Sch Med, Howard Hughes Med Inst, Beckman Ctr, Stanford, CA 94305 USA
[2] Stanford Univ, Sch Med, Dept Microbiol & Immunol, Stanford, CA 94305 USA
[3] Univ New Mexico, Dept Pathol, Albuquerque, NM 87131 USA
[4] Univ New Mexico, Canc Res & Treatment Ctr, Albuquerque, NM 87131 USA