LV'VFas⁺ T cells can be ablated by AP1903 in vivo. (A-B) Analysis of PBMCs for the in vivo persistence of LV'V⁺ and LV'VFas⁺ T cells after simultaneous transfer to macaque no. 2. Dosing of AP1903 (0.2 mg/kg) was begun 1 day after the T-cell infusion and was then given every other day for a total of 5 doses. (A) DNA was isolated from PBMCs collected 1 day (□) and 3 days (▪) after the T-cell infusion and assayed for the frequency of LV'V or LV'VFas-containing cells by TaqMan PCR. (B) The in vivo persistence of LV'V⁺ (⋄) and LV'VFas⁺ (♦) T cells was examined for the frequency of vector-containing cells by TaqMan PCR. The 100% value was assigned to the frequency of LV'V⁺ or LV'VFas⁺ T cells among PBMCs at day 1, prior to the initial dose of AP1903. Values for subsequent dates are calculated as the percent change in transduced cells among PBMCs compared with the day 1 value. The arrow indicates the day of the T-cell infusion. (C) Transgene product-specific cytolytic T-cell responses after the transfer of LV'V⁺ and LV'VFas⁺ T cells. PBMCs were collected from macaque no. 2 on the indicated days and stimulated with autologous γ-irradiated LV'V or LV'VFas-modified T cells twice 1 week apart. Specific cytotoxicity was examined in a chromium release assay for recognition of either parental (□), or LV'VFas⁺ (▪) target cells. Data are shown for an E/T ratio of 20:1.