In vitro cytotoxicity. Relative number of surviving Raji cells treated with increasing activities of ²²⁷Th-p-benzyl-DOTA-rituximab. The relative cell number was calculated by dividing the number of treated cells by the number of control cells at day 8 after start of incubation. On days 1, 4, and 6, half of the medium was changed to simulate the elimination of RIC that occurs in the body and to supply the cells with nutrients. ○ shows that binding of ²²⁷Th-p-benzyl-DOTA-rituximab to the cells was blocked by incubation with cold rituximab (10 μg/mL). ● indicats without cold rituximab. *Significantly different from corresponding blocked cells (t test, P < .05). Error bars represent SE from 3 to 5 experiments.