Cytotoxicity of modified T cells. Standard chromium release assays were performed using preinfusion-modified T cells at 8 to 12 days after restimulation, using the following MHC-mismatched target cells: EL4-CD20, a murine T-cell lymphoma line transfected to express the human CD20 molecule (----), the parental EL4 nontransfected CD20⁻ line (…), and the Daudi CD20⁺ Burkitt lymphoma cell line (—), at the E:T ratios shown. The calculated specific cytolysis values are displayed as percentages. (A) The CD20-specific cytotoxicity of the reinfused T cells. Data shown represent the mean combined data from all treated patients (± 1 SD). Triplicate assays were performed for each patient. (B) CD20 expression of the target cell lines of EL4, EL4-CD20, and Daudi, as determined by flow cytometry using PE-labeled mouse anti–human CD20 Ab.