XmAb5592 induced NK degranulation activity is resistant to dexamethasone pretreatment of MM cells, and is enhanced by IL-2 pretreatment of effector cells. (A) CD138⁺ patient MM cells were pretreated with 0.1μM dexamethasone or PBS overnight, followed by incubation with purified NK cells and serial dilutions of indicated mAbs. The percentage of CD107a⁺ NK cells was determined by flow cytometry. Strong XmAb5592-induced NK degranulation is not affected by dexamethasone treatment of MM cells. (B) Patient NK cells were pretreated overnight with 100 units/mL IL-2 or PBS before incubation with autologous patient MM cells, in the presence of indicated mAbs (10 μg/mL). IL-2 augments CD107a⁺ expression on patient NK cells specifically induced by XmAb5592.