Naïve mice were challenged with 0.1 LD50 of VACV-WR by the i.n. route following adoptive transfer of PBS, CD8 T cells or immune sera from NYCBH mice as described in Materials and Methods. Data shown are PFU/gm of lung tissue four days following challenge in mice that received PBS (open circles, n=12), CD8 T cells (open squares, n=8) or immune sera (open triangles, n=6) prior to challenge. Each symbol represents viral titers obtained in lungs of individual mice; mean values are denoted by horizontal lines. p values <0.05 were considered to be significant.