Kaplan-Meier survival plot of MET-1 FcRγ knock-out and FcRγ intact ATL-bearing NOD/SCID mice. (A) FcR intact mice. (B) FcR knock-out mice. MET-1 ATL cells were transferred into mice. Once the mice developed sIL-2Rα levels of 20 000 to 90 000 pg/mL (reflecting a very large tumor burden), therapy with MEDI-507 antibody was initiated. The groups (10 mice/group) included those receiving PBS (□) or 4 weeks of 100 μg per week of MEDI-507 (○) in the FcRγ knock-out ATL-bearing mice. In the parallel FcRγ intact ATL-bearing NOD/SCID mice, the groups (10 mice/group) included those receiving PBS (□) or 4 weekly intraperitoneal doses of 100 μg MEDI-507 (○). Event-free survival was followed for 40 days. There was no significant statistical difference in the survival between the group receiving 4 weekly doses of MEDI-507 and that receiving PBS in the FcRγ knock-out mice. In contrast, in FcRγ intact ATL-bearing NOD/SCID mice the survival of the group receiving 4 weekly doses of MEDI-507 was prolonged when compared with the control group.