e. CFSElow, T cells ± SD. Discussion ��-Nicotinamide in vitro Due to a growing body of knowledge about immunosurveillance – and loss thereof – anti-tumor immunotherapy has been refined [32]. Nevertheless, especially results of APC-based tumor vaccination trials often have often not met the high expectations. Lack of efficacy mainly originates from well-defined tumor escape mechanisms [2, 3, 33]. Tolerizing conditions of the tumor environment are mainly driven by tumor or bystander cell derived cytokines inducing tolerogenic DC, e.g. by triggering myeloid DC B7-H1 expression [34], and by recruitment of regulatory T cells [35], myeloid-derived

suppressor cells (MDSCs) and mesenchymal stroma cells (MSCs) [36]. IL-10, TGF-β, and VEGF all have PF01367338 been identified as key factors that mediate the inhibitory action of the tumor microenvironment. Their serum levels are frequently increased in cancer patients

and the tumor tissues of many cancer types are enriched for these immunosuppressive factors [37–39]. The main activity of IL-10 is related to downregulation of T cell function, which occurs predominantly through indirect mechanisms involving APCs [40]. IL-10 has been shown to impair antigen-presentation by DCs through reduction of the cell surface expression of adhesion and costimulatory molecules as well as MHC class II. Furthermore, IL-10 promotes DC apoptosis and inhibits DC migration to the secondary lymphoid organs [41, 42]. Ureohydrolase DCs isolated from transgenic mice that over-express IL-10 have a defect in antigen presentation and decreased capacity to induce T cell activation. Conversely, in IL-10-deficient tumor-bearing mice the defect in DC function was reversed [43]. As

a consequence IL-10-conditioned DCs are tolerogenic and induce T cell anergy [6, 44]. Like IL-10 TGF-β prevents the trafficking of DCs to the lymph nodes [45]. In addition, TGF-β impairs the maturation of DCs and thereby leads to the accumulation of immature DCs with the ability to generate regulatory T cells [8, 46]. VEGF also inhibits DC maturation leading to an accumulation of immature DCs with impaired APC function within the tumor microenvironment and the tumor-draining lymph nodes [9]. Consequently, inhibition of TGF-β, IL-10, or VEGF signaling improves DC function and enhances the efficacy of tumor vaccines [47–49]. Another strategy to address these tumor escape mechanisms in cellular tumor vaccinations is the use of alternative APC sources. In this context human CD40-activated B cells have gained increasing interest. We and others have previously shown that CD40-activated B cells are equipped with a profile of chemokine receptors that are required for the homing to the secondary lymphoid organs [31]. Furthermore, CD40-activated B cells are FRAX597 nmr potent antigen-presenting cells and are able to prime both CD4+ and CD8+ T cells in vitro.