Fas knock down in EBV-CTLs is stable and increases their survival in the presence of aberrant activation of the Fas/FasL pathway. EBV-CTLs transduced with GFP-siRNA10 or GFP-CsiRNA were stimulated weekly with autologous LCLs and rhIL-2 without selection. The percentage of GFP⁺ (▦) and GFP^- (□) cells was stable over time for both CTLs transduced with GFP-CsiRNA (A) and GFP-siRNA10 (B). However, the addition of CH-11 antibody (40 ng/mL) to the culture induced selective growth advantage for GFP⁺ CTLs transduced with GFP-siRNA10 (D) compared with those transduced with GFP-CsiRNA (C). (E-G) The expression is shown of Fas in GFP⁺ CTLs transduced with GFP-siRNA10 (bold solid lines) and GFP-CsiRNA (thin solid lines), respectively, over time with or without the addition of CH-11 to the culture. Dashed lines indicate the profile of the isotype control. The analysis was performed on gated GFP⁺ cells. Data illustrate a representative donor of 5 independent experiments.