The binding of MEDI-507 to MET-1 ATL cells was evaluated by FACS analysis. The MET-1 ATL cells were harvested as described in “Materials and methods.” The primary mAbs used were humanized anti-CD20 and MEDI-507. The secondary antibody was a rat anti–human IgG Fc fragment conjugated with FITC. In panel A, the primary antibody was MEDI-507 directed to CD2. The isotype control is represented by the solid area, whereas the line represents the humanized anti-CD2. In panel B, the solid area is the isotype control and the line represents humanized anti-CD20.