AML blasts exhibit defective APC function with healthy T cells in mixed allogeneic experiments. Healthy T cells were allowed to conjugate with allogeneic (allo) healthy CD34⁺ cells, healthy B cells, or AML blasts ± sAg acting as APCs (CMAC dyed, blue). Conjugates were then fixed and stained with rhodamine phalloidin to detect F-actin (red). Conjugates were selected at random for imaging and were scored for F-actin polarization at the immune synapse. Each dataset is the mean ± SD from 10 independent patient experiments with at least 50 conjugates analyzed per experiment. Arrows indicate F-actin accumulation at the T-cell–APC synapse site. Note the equivalent APC function of healthy B cells and healthy CD34⁺ cells acting as control cells. Original magnification × 63. Statistical differences between experimental groups were evaluated by 2-tailed Student t test. P < .05 was considered statistically significant.