SzS patient tumor cells are refractory to TCR/CD3 signaling. (A) PBMCs from a representative healthy donor and patient S5 were activated with anti-CD3. In patients with SzS who had a CD4⁺CD7^-tumor, nontumor (CD4⁺CD7⁺), and tumor (CD4⁺CD7^-), T cells were analyzed for induction of CD25 and CD69 membrane expression upon anti-CD3 stimulation. The counterparts in healthy donors were also analyzed. Fluorescence histograms are shown for unstimulated cells (thin lines) and anti-CD3-stimulated cells (thick lines). Dashed lines represent isotype-control staining of unstimulated cells. Similar results were obtained in 2 other patients with SzS. (B) PBMCs from a healthy donor and patient S5 were cultured in medium alone or activated with PMA/ionomycin (PI) for 6 hours. CD40L induction was monitored by flow cytometry. Dot plots for CD7 and CD40L staining are shown. The tumor T cells in the patients with SzS are contained in the CD7^- fraction. The percentage of labeled cells for each quadrant is indicated in the upper right quadrant. Similar results were obtained in 3 other patients with SzS.