Cells were stimulated with the following combination of mAbs to T cell surface molecules (Meiler et al., 2008): anti-CD2 (clone 4B2 and 6G4; 0.5 µg/ml), anti-CD3 (clone OKT3; 0.5 µg/ml), and anti-CD28 mAb (clone B7G5; 0.5 µg/ml; all from Sanquin) and cultured in serum-free AIM-V medium (Life Technologies) with the addition of 1 nmol/liter IL-2 (Roche).