Responses to CD19 CAR T cells with concurrent ibrutinib were associated with better in vivo expansion of CAR T cells. CAR T-cell transgene peak in blood was measured by quantitative polymerase chain reaction (FLAP-EF1α copies per microgram of genomic DNA in blood) according to response by the 2018 iwCLL criteria (A) and marrow response by flow cytometry (sensitivity 10⁻⁴) (B). Bold horizontal lines represent the median, the box represents the interquartile range (IQR), and the vertical lines represent quartiles ± 1.5 × IQR. Data are from patients evaluable for response (n = 18). The P values were calculated using the Wilcoxon rank-sum test (2-sided).