Immunologic activity of EBV-CTLs. Panel A shows the frequency of EBV-specific T cells in the peripheral blood as measured by the number of IFN-γ–secreting PBMCs upon stimulation with irradiated autologous LCLs in an IFN-γ ELISPOT assay before and after one single dose of CTLs. Bars represent the mean of triplicate wells ± SD. A transient but significant increase of CTL precursors compared with the pretreatment level was observed. Panel B shows in vivo expansion of the infused cells. Patients 1 (top graph) and 3 (bottom graph) received CTLs mainly containing CD3⁺CD4⁺ cells. The figure shows the frequency of T cells responding to autologous LCLs assessed by IFN-γ ELISPOT assay on CD4⁺ (▪) and on CD8⁺ (▦) selected cells before and 4 and 2 weeks after CTL infusion, respectively. An increase in the number of CD4⁺ T cells was observed, whereas CD8⁺ T-cell frequencies remained unchanged.