Considering that a large fraction (>65%) of BEKO thymoma cells containing pSIRΔ-NFkB-destEGFP-CMV-Puro potently upregulate GFP expression upon stimulation, we were wondering why only a small fraction of T cells (and B cells) from KappaBle mice upregulate GFP upon PMA/Ionomycin stimulation. This evidence concerns the gene NFKB1 and thymoma.