Malignant T cells have deficient expression and function of the TCR/CD3 complex. (A) Nonmalignant (MyLa 1885) and malignant (MyLa 2039) T-cell lines from skin from a patient with tumor-stage MF and malignant T cells from blood of a patient with Sezary syndrome (SeAx) were stained with anti-CD3 mAb, anti–MHC class I (HLA-A, HLA-B, and HLA-C) mAb, or isotype IgG control. Flow cytometry results are shown for viable cells gated from Fsc/Ssc-scatter plots. The data are representative of 3 independent experiments. (B) Nonmalignant (P1183) and malignant (MyLa 2039) T cells were grown in microtiter plates coated with or without anti-CD3 mAb or isotype control mAb and with or without cyclosporine A (10 nM final concentration) or with rIL-2 (100 U/mL) for 48 hours at 37°C in a humidified 5% CO₂ atmosphere. Twelve hours prior to harvest, ³H-thymidine (1 μCi [0.037 MBq]/well) was added, the cells were harvested onto glass fiber filters, and ³H-thymidine incorporation was measured. The proliferation was expressed as mean counts per minute (+ SD) of triplicate cultures. The data are representative of 5 independent experiments with 3 malignant and 3 nonmalignant T-cell lines.