CD200, CD274, CD276, and CD270 mediate F-actin polymerization dysfunction at the T-cell synapse in CLL. (A) Mean synapse area ± SD from 6 healthy donor allogeneic T-cell functional screens with siRNA-treated MEC1 cells, with selected target molecules on the x-axis. CD54 siRNA and nontargeting siRNA (Control) treated cells acted as positive and negative controls, respectively. (B) Mean T-cell F-actin synapse area ± SD from 20 CLL patient cells pretreated with neutralizing Abs (α) before primary coculture with healthy donor allogeneic T cells. T cells were then negatively selected and used in conjugation assays with sAg-pulsed third-party healthy donor allogeneic B cells as APCs. (C) Mean T-cell synapse area ± SD from 6 CLL patient autologous functional screens. T cells from CLL patients were cocultured with autologous CLL cells. T cells were then negatively selected and used in conjugation assays with autologous CLL cells pulsed with sAg as APCs. T-cell/CLL(+sAg) and age-matched healthy donor T-cell/B cell (+sAg) autologous conjugates without primary coculture were included as controls. *P < .05; **P < .01. The confocal images show T-cell/APC conjugates after primary coculture with treated tumor cells. Original magnification, 63×.