Differential resistance to CD3/TCR-dependent activation-induced cell death of ILT2⁺CD4⁺CTCL cells and autologous ILT2⁻ CD4⁺ T cells.

(A) Upper panel: PBMCs from a patient with 30% circulating Sézary cells were stained with anti-ILT2 GHI/75 mAb followed by FITC-conjugated GAM Ig. After extensive washing to remove the excess of GAM Ig and blocking with normal mouse Ig, TRI-conjugated anti-CD4 mAb was added. The CD4⁺ILT2⁺ and CD4⁺ILT2⁻ subpopulations were sorted. Lower panel: The ILT2⁺CD4⁺ and ILT2⁻CD4⁺ cell fractions were incubated for 9 hours with 10 μg/mL immobilized anti-CD3 (unshaded histogram) or isotype control mAb (shaded histogram) and analyzed for binding of annexin V and PI exclusion by flow cytometry. Percentages indicated for each fraction correspond to anti-CD3–stimulated apoptotic cells and were calculated after exclusion of PI-stained cells. (B) PBMCs from a different SS patient with 20% circulating Sézary cells were separated into CD4⁺ILT2⁺ and CD4⁺ILT2⁻ subpopulations and tested for their resistance to cell death induced through CD3/TCR engagement, as described above.