Fig. 4. Cross-reactivity of virus-specific polyclonal CD8⁺ T cells assessed by lytic activity.To assess the degree of lytic activity a gating strategy was used to determine the number of viable CFSE positive target cells in the (a) absence and (b) presence of virus-specific T cells using FlowJo software. (c) B/Victoria/2/1987 and (d) B/Yamagata/16/1988 virus-specific polyclonal CD8⁺ T cells from study subjects 6888, 8801 and 9465 were isolated after stimulation of PBMCs with the respective virus. Lytic activity against HLA-matched CFSE-labeled BLCLs infected with B/Victoria/2/1987, B/Netherlands/455/201, B/Yamagata/16/1988 and B/Netherlands/712/2011 was assessed. Uninfected BLCLs were used as negative controls. Experiments were performed in triplicate; bar, sd.