Killing of B-CLL by anti-third-party CTLs is not inhibited by OKT3. EBV B cells (1.5 × 10⁵) used as CTL stimulators (A) or fresh B-CLL cells obtained from patients in stage IV (B) were cultured alone (▪) or with 5 × 10⁴ allogeneic anti-third-party CTLs that were previously incubated with (▨) or without (□) blocking anti-CD3 Ab. Three days later, cells divided into aliquots from different wells were counted and stained with the corresponding fluorescent Abs as described in “Materials and methods.” Values are expressed as the number of CD19⁺ cells (n = 4). P values are referred to the control untreated group. Error bars indicate SD.