Freshly isolated and cultured mature dendritic cells (DQ rapidly lose their high capacity to activate T cells. This diminished T cell activation activity is due, in part, to dramatically reduced expression of the costimulation ligands B7-1 (CD80) and B7-2 (CD86). Here we show that cultivation of mature DC with the lymphokines TNF alpha, GM-CSF, or TNF alpha plus GM-CSF, fully restored and enhanced their T-cell stimulation activity by two to threefold, four to fivefold, or six to sevenfold, respectively. The restored T-cell stimulation activity was directly correlated with induced and increased levels of CD80 (16-fold) and CD86 (10-fold) expression by the lymphokine-cultured DC. These results should facilitate many current DC-vaccination efforts towards generating more potent T cell responses.