CD107a mAb-based degranulation assay against primary MM cells. (A) Effector cells were incubated alone, with isotype controls, or with target cells in the presence of CD107a mAb as specified. Representative data (patient 5) demonstrating the expression of CD107a on CD3⁻ gated day-20 cells upon coculture with the K562 cell line or autologous MM cells. (B) Comparison of degranulation in different subsets of day-0, -5, and -20 effector cells upon coculture with autologous MM cells for 6 hours. The results are shown as mean percentage of CD107a⁺ cells (± SD; data from patients 2, 5, and 7).