CD28 costimulation enhances growth of primary T lymphocytes.

PBLs from 4 different donors were stimulated with anti-CD3 alone (■) or both anti-CD3 and anti-CD28 (▪), transduced with the LV'VFas retroviral vector, and cultured in the presence of low doses of IL-2 (25-50 U/mL). Proliferation of viable cells was measured by numerical expansion and trypan blue exclusion. The proliferation index was calculated by the ratio of total cell number at days 13 to 14 of the culture to the starting cell number at day 0. Means and standard deviations are displayed.