CD23.CAR⁺ T lymphocytes lack cytotoxic activity against normal B lymphocytes. (A) MFI of CD23 antigen on B cells isolated from the peripheral blood of healthy donors and CLL patients is shown. Percentages of double-positive CD19/CD23 cells were comparable in healthy donors and CLL patients at levels ≥ 90% (data not shown), as expected. **P ≤ .005 comparing healthy donors and CLL-derived B cells. (B) Cytotoxic activity of control NT, CD19.CAR⁺, and CD23.CAR⁺ T lymphocytes obtained from healthy donors against purified CD20⁺ B cells obtained from the peripheral blood of healthy donors. Cytotoxic activity was evaluated in a ⁵¹Cr-release assay, and results are shown at E:T ratios of 40:1, 20:1, 10:1, and 5:1. Data represent the means ± SD for 3 different T-cell lines. *P ≤ .05 comparing CAR⁺ with NT T lymphocytes. (C) Cytotoxic activity of control NT, CD19.CAR⁺, and CD23.CAR⁺ T lymphocytes obtained from CLL patients against purified CD20⁺ B cells labeled with CFSE. Cytotoxic activity was evaluated in a 24-hour coculture experiment, and results are shown at an E:T ratio of 3:1. The experiment shown is representative of 3 different experiments.