sPD-L1 inhibits CAR T-cell cytokine production in vitro in a dose-dependent manner. Human CD19 CAR T cells were generated from healthy donors (n = 3) and assayed on days 14 to 16 after the start of manufacturing. CD4⁺ CAR T cells were cocultured with CD19-expressing K562 cells at a 1:1 effector-to-target ratio and the indicated sPD-L1 concentrations or media alone for ∼24 hours. (A) The percentages of CD4⁺ CAR T cells expressing the indicated numbers of cytokines were measured by intracellular flow cytometry. IFN-γ (B) and IL-2 (C) individual production. Data are representative of at least 2 independent experiments. Figures show mean ± standard error of the mean. One-way analysis of variance tests with Tukey correction for multiple comparisons were used to compare differences between groups. IL-2, interleukin-2; ns, not significant.