Dual R5- and X4-ZFN treatment confers protection in vivo. (A) Experimental timeline of the in vivo study is shown. (B) All 3 treatment groups were successfully engrafted as measured 21 days postinfusion and 3 days prior to infection with a slight decrease in CD4⁺ T-cell counts in ZFN groups compared with the GFP control. (C) Dual ZFN treatment preserves CD4⁺ T cells in the spleen compared with controls. Spleens were obtained from infected animals from all animals at the time of euthanasia. Human CD4⁺ T cells were defined as CD45⁺CD3⁺CD4⁺CD8⁻ T cells by FACS. (D) Dual ZFN treatment confers long-term protection against HIV as measured by preservation of peripheral blood CD4⁺ T-cell counts. All uninfected animals and 1 infected animal in the R5/X4-ZFN–treated group were killed 34 days postinfection due xenogeneic graft-versus-host disease. Infected animals were followed for 55 days after infection. All statistical analyses were performed using a Mann-Whitney U test. Error bars indicate the mean ± SEM.