Clinical trials of active immunotherapy strategies against viral infections and malignancies are increasingly using dendritic cells (DC) generated in vitro from peripheral blood mononuclear cells (PBMC) in media supplemented with granulocyte macrophage colony-stimulating factor (GM-CSF) plus interleukin-4 (IL-4). Although GM-CSF appears necessary, it is not well established whether other cytokines have advantages or could replace IL-4 in clinical preparations. IL-13 is a Th2-derived cytokine that shares a variety of biologic functions with IL-4, such as inhibition of monocyte differentiation and upregulation of major histocompatibility complex (MHC) molecules on cell surfaces. In the present study, the authors compared IL-4 and IL-13 in their abilities to induce DC differentiation and found that adherent PBMC cultured in GM-CSF and IL-13 displayed features characteristic of DC generated in media containing IL-4. They formed cellular clumps and had extensive dendrites. Fluorescence-activated cell sorter analysis showed that they expressed a high level of MHC class II and the costimulatory molecule CD86, and did not express the lineage markers CD3, CD14, CD16, or CD20. They were also equally potent stimulators of allogeneic lymphocytes in the mixed lymphocyte reaction. Moreover, the authors demonstrated that they were capable of inducing antigen-specific CD8+ cytotoxic T cells efficiently.