Functional impairment of dendritic cells (DC) appears to be one of the mechanisms responsible for tumor escape from the control of the immune system. DC isolated from tumor-bearing animals and cancer patients with solid or with hematological malignancies have phenotypic and functional abnormalities. In addition, supernatants from in vitro cultured tumor cells have been shown to interfere with DC differentiation from CD34+ and monocyte precursors. Primary effusion lymphoma (PEL) is a Human Herpesvirus-8 (HHV-8)-associated tumor, which releases several cytokines such as IL-6, IL-10 and VEGF and its growth seems to be dependent on them in vitro or in vivo. In the present study, we found that these cytokines released by PELs have also an important role in interfering with the in vitro differentiation of immature DC (iDC) from CD14+ monocytes. The iDC obtained in the presence of PEL supernatants showed reduction of FITC-dextran uptake, reduction of MLR allostimulatory activity and altered expression of surface molecules, suggesting that cytokines released by PEL adversely affect DC differentiation.