TGN1412 requires interaction with FcγRIIb for activity and this can be provided by B cells and monocytes. (A) T-cell proliferation in response to OKT3, UCHT1 and TGN1412 in the presence of anti-FcγRI, IIa, IIb, and IIIa mAb. PBMCs were incubated with stimulating mAb as described in Figure 1 in the absence or presence of anti-FcγRI, IIa, IIb, and IIIa blocking mAb (50 μg/mL). Error bars show mean and range of duplicate wells. (B) Effect of anti-FcγRIIa and IIb on response to TGN1412. Results are expressed as % of division with TGN1412 alone and error bars represent mean and SD from 7 donors. (C) Responsiveness of isolated T cells to TGN1412 is restored by B cells and monocytes. T cells, monocytes and B cells were isolated from PBMCs after 48 h HD preculture. T cells were incubated with OKT3, UCHT1 and TGN1412 either alone, or in coculture with B cells or monocytes at a monocyte or B cell:T cell ratio of 0.3:1; TGN1412 responses were determined in the absence or presence of anti-FcγRIIb blocking mAb (50 μg/mL). Results show mean and range of 2 donors. (D) B cells and monocytes were added to isolated T cells at mono or B:T cell ratios from 0.02:1 to 0.5:1. Results show mean and range from 2 donors.