Viral loads and tetramer levels in rhesus macaques challenged with SIVmac239. Rhesus macaques were challenged i.r. with either 1,000 TCID₅₀ of cloned SIVmac239/nef-stop (A) or 3,160 TCID₅₀ (10 rhesus macaque ID₅₀) of cloned SIVmac239/nef-open (B). The concentrations of SIV RNA from plasma were measured by using Chiron's SIVmac branched DNA RNA assay (solid lines). Levels of Gag CM9-specific T-cell responses, as measured with tetramers, are also shown (bars). Time points for the MVA inoculations are indicated by downward arrows, and the number of weeks that the animals survived is indicated in the top right corner of each graph. (Animals 94004 and 96114 were selectively euthanized, as indicated, prior to signs of AIDS-associated disease.)