Impaired CD40L induction on SzS tumor cells. (A) PBMCs from healthy donors and patients with SzS were double-stained for CD4 and CD7 expression. Representative dot plots are shown for a healthy donor (left panel), patients S1 (middle panel), and S5 (right panel), which both have a CD4⁺CD7^- tumor. The percentage of labeled cells for each quadrant is indicated in the upper right quadrant. (B) PBMCs were activated with anti-CD3 as in Figure 1. After 6 hours, cells were immunostained for CD40L and analyzed by flow cytometry. Fluorescence histograms are shown for unstimulated (thin lines) and anti-CD3-stimulated (thick lines) gated CD4⁺CD7^-cells.