AgAb can stimulate the ex vivo activation and expansion of EBV-specific memory T-cell clones from an EBV-positive donor. (A) PBMCs were obtained from an EBV-positive donor who expressed the restricting HLA allele of the T-cell clone EBNA3C 5H11. These cells were subjected to 7 consecutive rounds of stimulation with 1.3 ng of αCD21 fused with 5H11. We obtained 10 T-cell clones by limiting dilution. A T-cell recognition assay was then performed with 4 of these clones using LCLs pulsed with the αCD21-5H11 AgAb. The results of assays performed in triplicate with 2 independent clones are shown here with obtained means and standard deviations. (B) Intracellular IFN-γ staining of PBMCs from the same donor. Freshly isolated PBMCs were incubated with the indicated concentrations of the 963-bp CD21-EBNA3C AgAb or α-CD21 control antibody. The percentage of IFN-γ positive CD3⁺CD4⁺ T cells was determined by intracellular cytokine staining 1 day later.