Cytotoxicity of different effector cell populations from the same donor redirected against EpCAM-positive Kato cells by the bispecific single-chain antibody (bscAb) EpCAM x CD3 as measured in a ⁵¹Cr-release assay. Effector cells: unseparated PBMC (empty columns), purified naive CD8+ T cells (hatched columns) and CD8+ T cells primed for 6 days in the presence of 500 ng/ml heterodimeric B7-1 construct and 250 ng/ml bscAb EpCAM x CD3 (black columns). The concentration of bscAb EpCAM x CD3 during the ⁵¹Cr-release assay is given in ng/ml. (*) indicates the presence of 500 ng/ml heterodimeric B7-1 construct during the ⁵¹Cr-release assay.