Inhibition of the growth of MET-1 ATL cells in NOD/SCID mice by ²¹¹At-7G7/B6, daclizumab, and the combination of these agents. MET-1 ATL cells were transferred into mice intraperitoneally. The groups (11-12 mice/group) included those receiving PBS, 4 weekly doses of 4 mg/kg (100 μg/mouse) daclizumab (Dac), a single dose of 12 μCi (0.444 MBq) ²¹¹At-7G7/B6 (10 μg/mouse), the combination 100 μg of 4-weekly doses of daclizumab with a single dose of 12 μCi (0.444 MBq) ²¹¹At-7G7/B6, and a single dose of 12 μCi (0.444 MBq) ²¹¹At-11F11 (10 μg/mouse). The data represent the mean serum concentrations of the surrogate tumor marker human β₂μ in μg/mL. The group receiving a single dose of 12 μCi (0.444 MBq) ²¹¹At-7G7/B6, the group receiving 4-week daclizumab, and the group receiving the combination of 12 μCi (0.444 MBq) ²¹¹At-7G7/B6 with 4-week daclizumab had significantly decreased values of β₂μ (0.24 μg/mL at day 50) when compared with those of the PBS and ²¹¹At-11F11 control groups (P < .001). There was no significant difference in β₂μ levels between the group receiving a single dose of 12 μCi (0.444 MBq) ²¹¹At-11F11 and that receiving PBS (P = .43).