Anti-third-party CTLs induce apoptotic death in B-CLL leukemic cells. Fresh or frozen 2.5 × 10⁶ B-CLL cells obtained from patients in stage IV were cultured alone (▵), or together (○) with 5 × 10⁵ allogeneic (A) or autologous (B) anti-third-party CTLs. At different time points, wells were sampled and stained with the corresponding fluorescent Abs as described in “Materials and methods.” Subsequently, samples were analyzed by FACS for annexin staining. Values are expressed as annexin-positive cells from total CD19⁺ cells (n = 6).