[1] Washington Univ, Sch Med, Med Scientist Training Program, St Louis, MO 63110 USA
[2] Washington Univ, Sch Med, Dept Pathol & Immunol, St Louis, MO 63110 USA
[3] Washington Univ, Sch Med, Dept Med, St Louis, MO 63110 USA
[4] Univ Pittsburgh, Ctr Vaccine Res, Dept Immunol, Pittsburgh, PA USA
[5] US Army, Med Res Inst Infect Dis, Virol Div, Ft Detrick, MD 21702 USA
[6] Washington Univ, Sch Med, Dept Mol Microbiol, St Louis, MO 63110 USA