Expansion of virus-specific cells in SIVmac239Δnef-vaccinated macaques at 2 wk p.c. with SIVsmE660. Expansion in vaccinated macaques of the number of SFC above prechallenge levels in IFN-γ ELISPOT assays at 2 wk p.c. with SIVsmE660. To determine the expansion of SFC p.c., we subtracted the number of SFC per pool before challenge from the number of SFC detected p.c. The sum of the expanded cells per protein is displayed in the graph.