Figure 4.

Reconstitution of CD28 expression in CD28⁻ CD8⁺ T cells provides costimulation for IL-2 production. CD28⁻ CD8⁺ T cells were isolated from PBMCs, and an aliquot was transduced with the CD28 retrovirus. After selection, >80% of the transduced T cells expressed CD28. CD28-transduced (bottom panels) and nontransduced (top panels) CD28⁻ CD8⁺ T cells were stimulated with αCD3 mAb (10 ng/ml), with both αCD3 mAb (10 ng/ml) and αCD28 mAb (10 μg/ml), or with PMA and ionomycin, and then stained for intracellular IL-2.