[1] Univ Texas Med Branch, Dept Pediat, 301 Univ Blvd, Galveston, TX 77555 USA
[2] Univ Texas Med Branch, Dept Microbiol & Immunol, Galveston, TX 77555 USA
[3] Univ Texas Med Branch, Sealy Ctr Vaccine Dev, Galveston, TX 77555 USA
[4] Univ Massachusetts, Sch Med, Dept Pathol, Worcester, MA 01655 USA