Pharmacokinetics of rhIL-15 and inflammatory cytokines. (A) Mean and serum IL-15 levels measured in IV and SC rhIL-15 cohorts at the specified time points are compared (standard error of the mean shown). Peak IL-15 levels were significantly higher 1 hour after dosing in the IV vs SC cohorts. Immediately before dose 2 (dashed box), patients in the SC cohort had significantly higher residual IL-15 levels than those in the IV cohort. Cytokine levels associated with IV rhIL-15 (B) and SC rhIL-15 (C). IL-6 levels are significantly increased at 4 hours after dose 6 in SC compared with IV dosing (P = .04).