Reduction and recovery of NK cells after daratumumab treatment. (A) Rapid, dose-dependent reduction of NK cells was observed upon daratumumab treatment at all dose levels except for 0.1 mg/kg. Recovery of NK cells was slower with increasing dose. The centered curves and shaded areas represent smoothing lines and the 95% confidence intervals around the smoothing curves, respectively. (B) Longitudinal data representation of absolute NK-cell counts over time in peripheral blood. Peripheral blood was obtained from 21 patients during treatment with daratumumab (16 mg/kg) in GEN501 at the time of progression, and at 3 and 6 months after development of progressive disease. Data are presented as mean ± standard error of the mean. (C) Reduction and recovery of NK-cell counts in the peripheral blood after daratumumab treatment. Patients received daratumumab 16 mg/kg on the recommended dosing schedule or 8 mg/kg (given once every 4 weeks); NK cells showed some recovery in patients treated with daratumumab 8 mg/kg. The lines and shaded areas represent the medians of those doses per time point and their interquartile range, respectively. P values between the indicated groups were calculated by using a paired Student t test. **P < .01; ****P < .0001. ns, not significant.