Up-regulation of phospho-ERK after stimulation in primary T cells transduced with the TCRs constructs and stimulated with pTax/HLA-A2 tetramer. (A) Primary T cells transduced with the Tax TCRs and having undergone 5 rounds of weekly peptide stimulation had the following percentages of CD8⁺tetramer⁺ T cells: Tax TCR = 83%; M1-TCR = 88%; M2-TCR = 92%; and M3-TCR = 94%. T cells (2 × 10⁵) were stimulated with pTax-MHC tetramer for the stated times, and then immediately fixed, permeabilized, and stained with anti-pERK antibodies. FACS plots of tetramer binding and pERK expression at the stated times (the axis of the FACS plots range from 10¹ to 10⁵). (B) Mean fluorescent intensity of pERK at the stated times. These figures are representative of 4 individual experiments that showed similar results.