Dendritic cells (DCs) have been shown to be potent in inducing cytotoxic T cell (CTL) response leading to the efficient anti-tumor effect in active immunotherapy. Myeloid DCs are conventionally generated from human peripheral blood monocytes in the presence of interleukin (IL)-4 and granulocyte/macrophage colony-stimulating factor (GM-CSF). Streptococcal preparation OK-432, which is known to be a multiple cytokine inducer, has been extensively studied as to its maturation effects on immature DCs using an in vitro culture system. The purpose of this study was to examine whether it could be possible to generate mature DCs directly from peripheral monocytes using OK-432. We specifically focused on the possibility that recombinant cytokines, which are considered to be essential for in vitro DC generation, could be substituted by OK-432. Human peripheral monocytes, which were obtained from patients with advanced cancer, were cultured with IL-4 and OK-432 for 7 days. Cultured cells were compared with DCs generated in the presence of IL-4 and GM-CSF with or without OK-432 with regard to the surface phenotype as well as the antigen-presenting capacity. As a result, the culture of monocytes in the presence of IL-4 followed by the addition of OK-432 on day 4 (IL-4/OK-DC) induced cells with a fully mature DC phenotype. Functional assays also demonstrated that IL-4/OK-DCs had a strong antigen-presenting capacity determined by their enhanced antigen-specific CTL response and exerted a Th1-type T cell response which is critical for the induction of anti-tumor response. In conclusion, human peripheral blood monocytes cultured in the presence of IL-4 and OK-432 without exogenous GM-CSF demonstrated a fully mature DC phenotype and strong antigen-presenting capacity. This one-step culture protocol allows us to generate fully mature DCs directly from monocytes in 7 days and thus, this protocol can be applicable for DC-based anti-tumor immunotherapy.

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