Ag presentation by dendritic cells (DC) is essential to effective antitumor T cell responses in cancer patients. Depending on their origin, maturation state, and the ambient cytokine milieu, DC can differentiate into distinct subpopulations, which preferentially either induce Th1 cell activation (CD11c+,CD123- myeloid DC (MDC)) or immunosuppressive T cell development (CD11c-,CD123+ plasmacytoid DC (PDC)). The present study was undertaken to characterize the effects of pancreatic carcinoma cell-derived cytokines on immature monocyte-derived DC (iMo-DC) in vitro and in vivo. Medium conditioned by human pancreatic carcinoma cells inhibited iMo-DC proliferation, expression of costimulatory molecules (CD80 and CD40) and of HLA-DR, and functional activity as assessed by MLR and IL-12p70 production. iMo-DC generated from pancreatic carcinoma patients in advanced stages of the disease similarly showed decreased levels of HLA-DR expression and reduced ability to stimulate MLR in response to CD40L and IFN-gamma. Moreover, in tumor-patient peripheral blood, the ratio of MDC to PDC cells was lower than in healthy controls due to reduced numbers of MDC CD11c+ cells. Importantly, rather than a single cytokine, a combination of tumor-derived cytokines was responsible for these effects; these were primarily TGF-beta, IL-10, and IL-6, but not vascular endothelial growth factor. In summary, we have identified an array of pancreatic carcinoma-derived cytokines that cooperatively affect iMo-DC activation in a manner consistent with ineffective antitumor immune responses.