The exclusive ability of dendritic cells (DCs) to stimulate primary and secondary immune responses favors the use of antigen-loaded human monocyte-derived DCs (MoDCs) in vaccinations against tumors. Previous studies demonstrated that PGE(2) is fundamental during MoDC maturation to facilitate migration toward lymph node-derived chemokines. A recent study challenged the use of PGE(2), as PGE(2) induced IDO in mature MoDCs. In MoDCs compatible for clinical use, we now demonstrate that PGE(2) is responsible for IDO induction if matured by soluble CD40 ligand, LPS, or cytokines. In contrast, IDO expression in MoDCs matured by TLR3 triggering occurs independently of PGE(2). It is surprising that despite active IDO protein, MoDCs matured with PGE(2) display a greater potential to stimulate naïve CD4(+) and CD8(+) T cell proliferation, which is not increased further by IDO inhibition. Moreover, we found elevated levels of tryptophanyl-tRNA-synthetase (TTS) in T cells cultured with PGE(2)-matured MoDCs. Our data demonstrate that PGE(2) induces IDO in MoDCs but that T cell-stimulating capacities of PGE(2)-matured MoDCs overcome IDO activity, probably through TTS induction. As PGE(2) is critical for DC migration and enhances the capability of MoDCs to induce T cell proliferation, we highly recommend supplementing DC maturation stimuli with PGE(2) for use in clinical trials.