Cross-reactivity of the induced leukemic CTLs. Immature monocyte-derived DCs generated from the peripheral blood of patient no. 1 were electroporated with 10 μg total tumor RNA isolated from CLL cells. After further incubation with 10 ng/mL TNF-α for 24 hours DCs were used as APCs for in vitro CTL induction. Cytolytic activity of the CTL was determined on day 5 after the last restimulation by using autologous monocyte-derived DCs transfected with autologous CLL-RNA or RNA isolated from 3 other patients with CLL (patients no. 2 to no. 4) and from one patient with AML (patient no. 5) as targets in a standard ⁵¹Cr-release assay (A). DCs electroporated with in vitro–transcribed EGFP RNA were included as a control. The cytolytic activity of CTLs induced from patient no. 1 in a similar fashion was tested in a subsequent experiment (B) against autologous DCs electroporated with RNA isolated from 3 patients with AML (patients no. 6 to no. 8) and from 2 patients with ALL (patients no. 9 and no. 10). Autologous DCs electroporated with allogeneic PBMNC-RNA were used as a control to exclude allo-MHC reactivity.