XmAb5574 gave a sustained reduction in NK-cell levels in blood compared with vehicle or anti-CD19 IgG1. XmAb5574 administration at either 3 mg/kg (A) or 10 mg/kg (B) produced a substantial and sustained drop in NK-cell levels with recovery beginning by day 4 and complete by day 15. Vehicle and anti-CD19 IgG1 treatment also reduced NK-cell levels after administration, but the levels quickly recovered to baseline by days 2 to 3. NK cells were measured using flow cytometry with a gate for CD20⁻CD3⁻ (A) or CD16⁺CD3⁻ (B) and are expressed as a percentage of baseline. Values shown are the mean (± SE) at each time point.