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Please cite this paper as: Enhanced T-cell activation by immature dendritic cells loaded with HSP70-expressing heat-killed melanoma cells. Experimental Dermatology 2010; 19: 108–116. Vaccination protocols that utilize dendritic cells (DCs) to elicit therapeutic immunity against tumors are the subject of intense research. Given that the capacity of DCs to cross-present antigens is physiologically low, there is considerable interest to develop strategies that enhance that pathway. In order to best exploit the enhanced cross-presentation of antigens bound to heat shock protein 70 (HSP70), we analysed melanoma cell preparations for their HSP70 expression. Western blotting revealed strong upregulation of HSP70 after heat-killing in contrast to UV-B irradiation. When the uptake of heat-killed necrotic cells by DCs at various levels of maturation was assessed, 61 ± 7% of immature DCs (iDCs) internalized fluorescence-labelled necrotic material. Apoptotic material from UV-B-irradiated cells was internalized by only 48 ± 5% of iDCs. Maturation-inducing cytokines did not affect the uptake when added simultaneously with the tumor cell preparations. Loading DCs with heat-necrotic or apoptotic melanoma cells slightly reduced CD83 expression while leaving CD208 (DC-LAMP) expression unchanged. As determined by IFN-γ-detecting enzyme-linked-immunospot assays, iDCs loaded with heat-killed melanoma cells activated autologous T cells most effectively when used without any further maturation, whereas DCs loaded with apoptotic material required maturation. In conclusion, HSP70-expressing melanoma cells could be generated by heat-killing. Loading iDCs with heat-killed melanoma cells resulted in a superior priming of autologous T cells in vitro. [ABSTRACT FROM AUTHOR]

Based on their role for the induction of T-cell responses, dendritic cells (DCs) are popular candidates in cancer vaccine development. We established a novel single-step intracellular delivery of peptide/poly(I:C) complexes for antigen loading and Toll-like receptor-3 (TLR3)-mediated maturation of human DCs using a cell-penetrating peptide (tat49–57: RKKRRQRRR) as delivery vector. Towards this end, a cationic tat-sequence was fused with an antigenic, major histocompatibility complex (MHC) class I-binding melanoma epitope (Melan-A/Mart-1 sequence: ELAGIGILTV) and then mixed with negatively charged poly(I:C) dsRNA to form peptide/nucleic acid complexes. Flow cytometry and confocal laser scanning microscopy confirmed intracellular localization of TLR3 in monocyte-derived immature DCs (iDCs). Peptide/poly(I:C) complexes were readily internalized by iDCs without negatively affecting cell viability. They induced DC maturation and secretion of bioactive interleukin (IL)-12p70. When peptide/poly(I:C) complex-loaded DCs were used for autologous T cell stimulation, epitope-specific interferon-gamma secretion was quantitatively superior in comparison to peptide-loaded DCs matured by a cytokine cocktail, as detected by enzyme-linked immunospot assays. Thus, complexes of cationic antigenic peptides and poly(I:C) might be of great utility for a TLR3-mediated DC maturation and intracellular peptide targeting in a single step. Resulting DCs induce a strong expansion/activation of antigen-specific T cells in the context of an IL-12p70 secretion. [ABSTRACT FROM AUTHOR]

Dendritic cells (DC) are potent antigen-presenting cells capable to induce efficient antigen-specific T cell responses in vitro and in vivo. Herein, the maturation process is of great significance, as immature DC (iDC) are known to induce rather regulatory than effector T cell differentiation. This study was designed to characterize the role of the CD40-CD40L pathway for differentiation and function of human DC. Therefore, iDC were stimulated through CD40-CD40L interaction by transduction of DC with adenoviral vectors encoding for CD40L (Ad-CD40L). Resulting DC (CD40L-DC) were analysed concerning their phenotype, cytokine profile and T cell stimulatory capacity. Transduction induced a DC phenotype comparable to stimulation with proinflammatory cytokines as revealed by upregulation of CD83 and the costimulatory molecules CD80 and CD86. Additionally, Ad-CD40L-induced strong production of IL-12p70 not observed in cytokine-matured DC. Surprisingly, the T cell stimulatory capacity was markedly reduced in CD40L-DC. Furthermore, stimulation of CD8+ T cells by peptide-loaded CD40L-DC resulted in a substantial reduction of antigen-specific IFN-γ production. This phenomenon is due to an enhanced IL-10 production of CD40L-DC in DC-T cell coculture as well as a stabilization of the IL-10 receptor expression on activated T cells. These data demonstrate that DC stimulated through CD40-CD40L interaction differentiate into tolerogenic DC with immunomodulatory function. [ABSTRACT FROM AUTHOR]

We have demonstrated that dendritic cells (DCs) genetically modified to express tumor-associated antigens (TAAs) with retroviral vectors elicit more potential anti-tumor effect than those loaded with peptides because they can prime antigen-specific CD4+ T cells resulting in production of tumor-specific antibody. In this study, we showed the importance of antigen presentation via a major histocompatibility complex (MHC) class II molecule in cancer immunity against non-membrane bound TAAs such as the melanoma antigen gp100 by using DCs derived from MHC class II-deficient mice (C2KO). DCs were prepared by transduction of gp100 cDNA into haematopoietic progenitor cells obtained from C2KO followed by differentiation with cytokines (C2KO-gp/DCs). When C2KO-gp/DCs were inoculated into immunocompetent mice, the mice scarcely primed the antigen-specific Th1 cells and developed fewer CD8 T cells than did those inoculated with transduced DCs prepared from normal mice. The attenuated anti-tumor effect was also confirmed in a postimmunization setting where, while two of eight control mice eradicated the pre-existing melanoma cell line B16 (25%), no mice inoculated with C2KO-gp/DCs did. These results suggested not only the limitation of current protocols using MHC class I-restricted tumor peptides but also the usefulness of DCs expressing gp100 in vaccine therapy against melanoma. [ABSTRACT FROM AUTHOR]

Despite as yet limited clinical effectiveness, dendritic cell (DC)-based immunotherapy remains a promising approach for the treatment of cancer, but requires further improvement in its immunostimulatory effectiveness. Potent anti-tumor immunity often depends on the induction of type 1 (TH1) immune responses. Therefore, we combined different DC maturation stimuli that are known to induce TH1 immunity [anti-CD40, interleukin (IL)-12, IL-18], with the aim to trigger a TH1 driven anti-tumor CTL response. When compared with untreated DC or DC treated with anti-CD40 alone, DC matured with anti-CD40 plus IL-12 and IL-18 expressed significantly more IFN-γ and IL-12, induced enhanced CD8+ T-cell proliferation, prolonged synaptic interaction with T cells and increased CD8+ T-cell-mediated cytotoxicity. To analyse if these DC are able to induce efficient anti-tumor immunity, mice carrying a B16-OVA tumor were treated with tumor antigen (TA)-loaded DC that had been exposed to anti-CD40 or to anti-CD40 plus IL-12 and IL-18. Our data show that anti-CD40 plus IL-12 and IL-18 matured DC are superior to controls in retarding tumor growth. These data indicate that maturation of DC with anti-CD40 plus IL-12 and IL-18 potently stimulates the generation of an anti-tumor immune response and may lead to improved immunotherapeutic capacity of DC vaccination. [ABSTRACT FROM AUTHOR]