Clemens Esche

Tumor's other immune targets: dendritic cells.

The induction of apoptosis in T cells is one of several mechanisms by which tumors escape immune recognition. We have investigated whether tumors induce apoptosis in dendritic cells (DC) by co‐culture of murine or human DC with different tumor cell lines for 4–48 h. Analysis of DC morphological features, JAM assay, TUNEL, caspase‐3‐like and transglutaminase activity, Annexin V binding, and DNA fragmentation assays revealed a time‐ and dose‐dependent induction of apoptosis in DC by tumor‐derived factors. This finding is both effector and target specific. The mechanism of tumor‐induced DC apoptosis involved regulation of Bcl‐2 and Bax expression. Double staining of both murine and human tumor tissues confirmed that tumor‐associated DC undergo apoptotic death in vivo. DC isolated from tumor tissue showed significantly higher levels of apoptosis as determined by TUNEL assay when compared with DC isolated from spleen. These findings demonstrate that tumors induce apoptosis in DC and suggest a new mechanism of tumor escape from immune recognition. DC protection from apoptosis will lead to improvement of DC‐based immunotherapies for cancer and other immune diseases. J. Leukoc. Biol. 66: 336–344; 1999.

FLT3: receptor and ligand. Biology and potential clinical application.

Flt3 ligand (FL) is a recently identified cytokine having a central role in the proliferation, survival and differentiation of early murine and human hematopoietic precursor/stem cells. FL acts synergistically in vitro with a number of other hematopoietic growth factors such as IL-3, IL-6, IL-11, IL-12, KIT Ligand and GM-CSF. Recently, it has been shown the in vivo administration of FL results in a significant alteration of hematopoiesis in murine bone marrow (BM), spleen, peripheral blood, liver and lymph nodes. In addition, treatment with FL resulted in a significant accumulation of functionally active dendritic cells within murine lymphoid tissues. The possible applications of FL in dendritic cell-based immunotherapies are discussed.

Transduction of Dendritic Cells with Bcl-xL Increases Their Resistance to Prostate Cancer-Induced Apoptosis and Antitumor Effect in Mice

We have shown that prostate cancer (PCa) causes apoptosis of dendritic cells (DC), which might block the development of specific antitumor immune responses. Analysis of murine prostatic carcinoma tissues revealed the significant decrease in intratumoral DC number during tumor progression. We demonstrated that the cytokine-mediated increase in DC survival was accompanied by an elevated expression of the anti-apoptotic protein Bcl-xL. Next, we evaluated the resistance to tumor-induced apoptosis and the antitumor efficiency of genetically engineered DC overexpressing Bcl-xL. DC were transduced with an adenoviral vector encoding the murine Bcl-xL gene and injected intratumorally. Data analysis revealed that treatment of PCa-bearing mice with Bcl-xL-transduced DC resulted in significant inhibition of tumor growth compared with the administration of nontransduced DC. Thus, our data suggest that the protection of DC from PCa-induced apoptosis might significantly increase the efficacy of DC-based therapies in cancer even in the absence of available tumor-specific Ags.

Human prostate cancer regulates generation and maturation of monocyte-derived dendritic cells

The progression of prostate cancer is accompanied by a marked suppression of the immune system, including the apoptotic death of dendritic cells (DC) responsible for the induction of antitumor immunity. In this study, we evaluated whether prostate cancer might inhibit DC generation and maturation in vitro.

Identification of delta- and mu-type opioid receptors on human and murine dendritic cells.

The purpose of this study was to evaluate mu- and delta-opioid receptors (OR) on human and murine dendritic cells (DC). Expression of mu- and delta-OR mRNA on DC was demonstrated by RT-PCR. The immunocytochemical and Western blot analyses revealed the expression of OR protein in DC. Radioreceptor assay demonstrated the specific saturated temperature-dependent binding of [3H]-labeled opioid ligand on DC and B(max)=2.8+/-0.3 fmol/10(6) cells and K(D)=4.8+/-1.0 nM were calculated by a Scatchard analysis. Finally, OR ligands DADLE and DAGO dose-dependently modulated the capacity of DC to induce T cell proliferation in an MLR assay. Importantly, expression of functional OR on DC was significantly increased upon TNF-alpha-induced DC maturation. Thus, these data suggest a new mechanism of opioid-dependent neuroendocrine immunomodulation.

CD154 inhibits tumor-induced apoptosis in dendritic cells and tumor growth

We have recently demonstrated that murine and human tumors induce apoptosis of dendritic cells (DC). Here, we evaluated the effect of CD40 ligation on the survival of tumor‐associated DC and tumor growth. Retroviral transduction of MC38 colon carcinoma cells with the CD154 gene resulted in inhibition of tumor growth. This effect was abrogated in IL‐12 knockout mice. Immunohistochemical analysis revealed an increase in CD11c+ (N418) and CD8+ but not NLDC‐145+ cells in CD154‐transfected tumors in wild‐type mice. This increase was less pronounced in IL‐12‐deficient mice. Inu2004vitro, overexpression of CD154 on tumor cells significantly decreased the level of tumor‐induced DC apoptosis. Surprisingly, the CD154‐induced protection of DC from tumor‐induced apoptosis was IL‐12 independent in vitro, suggesting an IL‐12‐dependent and an IL‐12‐independent mechanism of CD154‐induced anti‐tumor immunity. Thus, our data suggest a new strategy to improve immunotherapy of cancer by protecting DC from tumor‐induced apoptosis.

Interleukin-12 and Flt3 ligand differentially promote dendropoiesis in vivo.

Interleukin‐12 (IL‐12) and Flt3 ligand (FL) regulate hematopoiesis by stimulating proliferation, differentiation and migration of progenitor and/or stem cells. In this study, we evaluated the in vivo effect of IL‐12 alone or in combination with FL on dendritic cell (DC) generation and accumulation in murine spleen, lymph node, thymus, liver, and tumor tissues. Both cytokines induced accumulation of functional DC in lymphoid and non‐lymphoid tissues. IL‐12 promoted predominantly myeloid dendropoiesis, while FL induced both myeloid and lymphoid dendropoiesis. Combination treatment resulted in a dramatic increase in CD86+, and particularly, NLDC‐145+ cells within the liver, which was largely due to cell proliferation. Combination therapy also revealed the ability of FL to protect bone marrow cell populations from IL‐12‐induced depletion in vivo. In vitro, we found a significant FL‐induced up‐regulation of IL‐12 production by DC at both mRNA and protein levels. Thus, our study suggests that (i) the antitumor activity of IL‐12 may, at least in part, be mediated by the stimulation of dendropoiesis and (ii) IL‐12 might contribute to the antitumor activity of FL. Furthermore, induction of DC generation in vivo by a combination of IL‐12 and FL might become a new approach for immunotherapy of cancer.

Murine Dendritic Cells Express Functional Delta-Type Opioid Receptors

Dendritic cells (DC) are the most potent antigen-presenting cells (APC), and the only APC capable of presenting novel antigens to naïve T-cells. 1 Following their departure from the bone marrow, DC migrate to nonlymphoid tissues where they reside in an immature stage. The classical example is the epidermal Langerhans cell (LC) that recognizes and processes antigens in the skin. After migration to the secondary lymphoid organs, DC mature into cells that are capable of presenting antigens and stimulating T-cell proliferation. TNFα promotes DC maturation in vitro by upregulation of adhesion and costimulatory molecules, and downregulation of antigencapturing and antigen-processing molecules. DC are involved in the pathogenesis of numerous skin diseases including psoriasis, allergic contact eczema, atopic eczema, oral hairy leukoplakia, mycosis fungoides, and melanoma. The function of epidermal LC and dermal DC is likely to be regulated by neuropeptides released from nerves ending in the skin. In fact, receptors for calcitonin gene-related peptide, 2 pituitary adenylate cyclase activating polypeptide, 3 gastrin-releasing peptide, 3 and substance P 4 have been identified on epidermal LC. The aim of this work was to evaluate presence and function of δ -type opioid receptors (DOR) on DC.