Function of iCasp9_M in vivo. NOD/SCID mice were irradiated and injected subcutaneously with 10 × 10⁶ to 15 × 10⁶ LCLs. After 14 days, mice bearing tumors of 0.5 cm in diameter received a total of 15 × 10⁶ EBV-CTLs (50% of these cells were nontransduced and 50% were transduced with iCasp9_M.I.GFP and sorted for high GFP expression). On day 3 after CTL administration, mice received either CID (50 μg AP20187; ▴, n=6) or carrier only (▪, n=5) and on day 6 the presence of human CD3⁺/GFP⁺ T cells in the tumors was analyzed. Human CD3⁺ T cells isolated from the tumors of a control group of mice that received only nontransduced CTLs (15 × 10⁶ CTLs; n= 4) were used as a negative control for the analysis of CD3⁺/GFP⁺ T cells within the tumors.