A 0.5 mg/kg dose of Hu-Mikβ1 does not maintain saturation of the IL-2/IL-15Rβ, whereas 1.5 mg/kg is sufficient to maintain saturation for 3 weeks. (A) Three patients with T-LGL leukemia were evaluated for saturation of their IL-2/IL-15R between 6 and 72 hours after administration of 0.5 mg/kg of Hu-Mikβ1 and were shown to have saturated receptors. However this receptor saturation was not maintained in 2 patients at 7, 14, and 21 days. To evaluate saturation, FACS analysis was performed at these time points with fluorochrome-labeled Hu-Mikβ1 and fluorochrome-labeled Mikβ3, which define non-cross-competing epitopes on IL-2/IL-15Rβ, as described in “Methods.” Different symbols represent the results for different patients. (B) Three patients with T-LGL leukemia were evaluated for saturation of their receptors after a 1.5 mg/kg IV infusion of Hu-Mikβ1. This dose of Hu-Mikβ1 was sufficient to provide prolonged saturation of the IL-2/IL-15R. In particular, saturation of CD122 was achieved at the 6- to 72-hour time point and was maintained at 100% saturation at the 7- and 14-day time points and at 80% saturation for the cells at the 21-day time point. Different symbols reflect the results for different patients.