Jonuleit and colleagues directly compared within each of eight patients the immunogenicity of immature DCs (generated according to Nestle and colleagues in FCS-containing media using GM-CSF and IL-4) to mature DCs generated in the absence of FCS and matured by a cocktail consisting of TNF-α, IL-1β, IL-6 and PGE2 mimicking the composition of monocyte conditioned medium. These two different DC populations were administered intranodally into opposite inguinal lymph nodes. FCS-free mature DCs induced stronger T-cell responses, both to the two recall antigens used (tetanus toxoid and PPD/tuberculin) and to tumor peptides. Interestingly, however, both immature and mature DCs showed an expansion of peptide-specific T cells by tetramer staining; yet, only mature DCs induced IFN-γ-producing and lytic CD8 T cells. These findings suggest the interesting possibillity that the immature DCs might have induced regulatory T cells rather than effector T cells, an observation previously noted in studies with normal volunteers.