[1] Univ Calif San Francisco, Gladstone Inst Virol & Immunol, San Francisco, CA 94141 USA
[2] Univ Calif San Francisco, Dept Med, San Francisco, CA 94141 USA
[3] Univ Calif San Francisco, Dept Microbiol, San Francisco, CA 94141 USA
[4] Univ Calif San Francisco, Dept Immunol, San Francisco, CA 94141 USA