Findings from our group and others demonstrate that SHIV-C leads to depletion of peripheral blood CD4+ T-cell counts within 6 months of infection in approximately one-third of challenged animals, and progression to simian AIDS in 88–270 weeks.34,38 We did not observe either of these parameters in A11199 over ~44 weeks postchallenge (Figure 4b). Here, CD4 is linked to infection.