Expansion and cytotoxicity of modified T cells. (A) Schematic representation of the αCD20-28-BB-ζ chimeric receptor, not to scale. (B-C) Growth curves of ex vivo expanded T cells for the 3 treated patients (B) and of the 2 attempts to expand cells from patient UPN-01 (C). PBMCs collected by apheresis were stimulated with anti-CD3 Ab and IL-2, transfected by electroporation by the plasmid encoding the CAR shown in panel A, selected with G418, and restimulated every 12 to 15 days in a rapid expansion protocol. Black bars represent periods of G418 selection; and gray bar, the target cell dose range. (D) CD20-specific cytotoxicity of G418-selected autologous patient T cells was assessed with 5-hour chromium-release assays using the following ⁵¹Cr-labeled target cells: Granta cells (MCL), Daudi cells (Burkitt NHL), EL4 cells transfected to express CD20, or the parental EL4 cell line lacking CD20 expression. The cells were tested after G418 selection (top panels) and 54, 27, and 40 days later for the 3 patients at the time of T-cell infusions (bottom panels). Data represent the mean of triplicate values, and error bars represent SEM.