CD4 and infection: We found that the mean AUC for all the infections performed with the mutant viruses in CD4+ cells (1.37x108 pg SIV p27/106 cells) was significantly higher (p=0.0008, paired t-test) than infections in PBMC with the same mutant viruses (3.22x106 pg SIV p27/106 cells) (Figure 7A).