CTL-mediated upregulation of CD54 in B-CLL is contact dependent. Fresh or frozen 2.5 × 10⁶ B-CLL cells obtained from patients in stage IV were cultured alone (▪) or with 5 × 10⁵ allogeneic anti-third-party CTLs in the absence (□) or presence of LFA-1 blocking (▨). Three days later, different wells were sampled and stained with the corresponding fluorescent Abs as described in “Materials and methods.” Values are expressed as the percentage of CD54⁺ cells from total CD19⁺ cells (n = 3). Error bars indicate SD.