Antitumor reactivity and proliferation capacity of human T cells and NK cells induced by a mAb/B-BiTE complex. (A) CD19⁺ B-cell–depleted human PBMCs (CD19^– PBMCs) derived from 6 different donors were incubated with K562 or K562/CD38 cells in the presence of the indicated antibodies. Multiple cytokine production by peripheral blood CD8⁺ T cells, CD4⁺ T cells, and NK cells was assessed using intracellular cytokine assays. The concentration of daratumumab and B-BiTE was 7.5 μg/mL and 2.5 μg/mL, respectively. Each dot represents each donor. (B-C) CD19^– PBMCs derived from 5 different donors were labeled with CFSE and stimulated as above. After 5 days of incubation with the indicated antibodies, the MFI of CFSE–labeled human CD8⁺ T cells, CD4⁺ T cells (B), and NK cells (C), which were designated as CD16⁺CD56⁺ cells among CD4^–CD8^– population, was examined, and their proliferation (percentage) against K562/CD38 cells is summarized. Each dot represents each donor. (D-E) CD19^– PBMCs from the same patient were incubated with isolated myeloma cells in the presence of the indicated antibodies including daratumumab/B-BiTE (daratumumab, 7.5 μg/mL; B-BiTE, 2.5 μg/mL). Cytokine production by CD8⁺ T cells, CD4⁺ T cells, and NK cells against target cells was assessed. Representative data (triplicate) and CD38 expression of CD138⁺ myeloma cells isolated from a patient are shown (D). This analysis was performed using samples obtained from 7 different patients including the patient in panel D, and the results are summarized (E). Each dot represents each donor. All data were evaluated statistically by a paired t test (2-sided) or a Welch t test (2-sided), and error bars show the SD. ∗P  < .05; ∗∗P  < .01; ∗∗∗P  < .001; ∗∗∗∗P  < .0001. CFSE, carboxyfluorescein diacetate succinimidyl ester; MFI, mean fluorescence intensity; n.s., not significant; SD, standard deviation.