Currently, with immunomagnetic isolation the scarce nDCs can be obtained for DC vaccination. plasmacytoid DCs were administered and showed encouraging immunological and clinical outcomes. Currently, also the combination of CD1c+ myeloid and plasmacytoid DCs as well as the intratumoral use of CD1c+ myeloid DCs is usually under investigation in the clinic. Isolation and culture strategies for CD141+ myeloid DCs are being developed. Here, we summarize and discuss recent clinical developments and future prospects of natural DC-based immunotherapy. Keywords: Dendritic cells, Natural dendritic cells, Plasmacytoid dendritic cells, Myeloid dendritic cells, Conventional dendritic cells, Cross-presenting dendritic cells, Cancer, Immunotherapy, Vaccination Background In 1973 Cohn and Steinman discovered a new type of immune cell, the dendritic cell (DC) , which plays an important role in the induction of specific immunity. DCs are sentinels of the immune system, as they are deployed throughout the body and monitor their surroundings for antigens and danger signals derived from pathogens or tissue damage. They are the most potent antigen-presenting cells, able to initiate and modulate specific immune responses. In their immature state, DCs mainly reside in lymphoid and peripheral tissues where they recognize and capture antigens. Upon receiving an activating stimulus in the presence of inflammatory signals, DCs undergo maturation and migrate to lymphoid organs. DC maturation is usually associated with functional and morphological changes, an essential process for T-cell activation. The immature phenotype of DCs is mainly characterized by a low surface expression of MHC I and II molecules and co-stimulatory molecules and a high capacity for phagocytosis that mediates sampling of antigens . DCs activated by so-called danger signals become highly motile, their endocytic and phagocytic receptors are down-modulated, and chemokine receptors that foster migration to lymphoid organs are upregulated. Furthermore, cell surface expression of MHC molecules and adhesion/co-stimulatory molecules, such as CD40, CD54, CD80, CD83, and CD86 is usually upregulated, and production of specific cytokines is usually induced . In the lymphoid organs, mature DCs present processed exogenous peptides to naive CD4+ T-cells via MHC class JAK/HDAC-IN-1 II and endogenous peptides to CD8+ T-cells via MHC class I. In addition, some DCs have a superior capacity to cross-present exogenous antigens on MHC class I to CD8+ T-cells , which is usually important for the induction of cytotoxic T-cell responses against tumor cells. Effective T-cell priming in the lymphoid tissues requires three signals between DCs and T-cells: antigen presentation via the MHC-peptide complex (signal 1), stimulation via co-stimulatory molecules from the DC to the T-cell (signal 2), and immune-stimulatory cytokines in the microenvironment (signal 3) . The ability of DCs to initiate and direct adaptive immune responses is usually exploited for cancer immunotherapy, especially in DC vaccination. With DC vaccination, mature DCs loaded with tumor antigens ex vivo are injected into JAK/HDAC-IN-1 cancer patients to induce tumor-specific effector T-cells that aim to recognize and eliminate cancer cells and induce immunological memory to control tumor growth . In the majority of clinical DC vaccination trials conducted so far, DCs differentiated ex vivo from monocytes or CD34+ progenitors have been used, since naturally circulating DCs (nDCs) are present in the blood but only constitute about 1% of blood mononuclear cells. However, through the development of efficient isolation techniques, the use of nDCs has recently become feasible. In this review, we summarize JAK/HDAC-IN-1 and discuss recent clinical developments of DC-based Mst1 immunotherapy with nDC subsets, comprising completed and ongoing clinical trials. Lessons from DC vaccination with moDCs Prompted by excellent results against transplanted mouse tumors with bone marrow-derived DC cultures, the first DC vaccination trials were performed in the late nineties. The effect of various DC vaccination parameters on immunological and clinical outcome of vaccination has been studied in numerous small phase I/II clinical trials in cancer patients. Most of these studies have been performed with monocyte-derived DCs (moDCs), due to their easy differentiation protocol in vitro. Maturation of moDCs MoDCs are mostly HLA-DR+/MHC-II+ CD11c+ BDCA3? and frequently express CD16, CD14 and DC-SIGN, due to their monocytic origin . Their functions and appearance are very divers, likely due to the inflammatory context they are differentiating in and the variety of cytokine cocktails that are used for their activation ex vivo. From the first clinical.