As expected, treatment with autologous CAR T cells led to a reduction of CD19+ malignant B cells in both models, which was more pronounced in the core of ALL‐derived co‐cultures than in the CLL setting (mean difference: −17.2% ± 5.5 ALL; 9.3% ± 5.0 CLL; Figure 2A, left panels). The gene discussed is CD19; the disease is B-cell chronic lymphocytic leukemia.