Dendritic cells and natural killer cells interact via multiple TNF family molecules.

Dendritic cells (DC) and natural killer (NK) cells are essential components of the innate immune system, which rapidly sense and eliminate invading pathogens and transformed cells, mediate inflammation, and initiate adaptive immune responses. During the early immune events, DC and NK cells interact and regulate each other. The cellular "cross talk" and its molecular mediators are believed to be critical to the quality and magnitude of innate and adaptive immune responses. The goal of the present manuscript is to identify and initially assess major molecular mediators of DC-NK cell interaction. We have previously shown that DC and NK cells constitutively express several tumor necrosis factor family ligands (TNFfLs) and corresponding TNF family receptors (TNFfRs). Therefore, DC and NK cells might be able to interact via cognate interplays of TNFfLs and TNFfRs. Here, we provide initial experimental evidence supporting this possibility. We found that combined but not individual ligation of several TNFfRs induced substantial increases in secretion of interleukin-12 and interferon-gamma by DC and NK cells, respectively. In contrast, specific, individual disruptions of the engagements of the corresponding TNfL-TNFfR pairs greatly impaired DC and NK cell abilities to reciprocally mediate the increases in cytokine secretion. These findings indicate that multiple TNFfLs mediate DC-NK cell interaction.

A novel epitope of N-CAM defines precursors of human adherent NK cells.

Activated, adherent natural killer (A-NK) cells represent a distinct subpopulation of interleukin (IL)-2-stimulated NK cells, which are selectively endowed with the increased expression of integrins and ability to adhere to solid surfaces, migrate into, infiltrate, and destroy cancerous tissues. The present study defines the phenotype and functions of precursors of A-NK (pre-A-NK) cells in humans. Peripheral blood pre-A-NK cells, in contrast to the rest of NK cells, express a novel epitope of CD56 neuronal cell adhesion molecule, termed ANK-1, and increased cell-surface levels of integrins. Pre-A-NK cells also express low levels of CD56 and CD161, and some express CD162 receptor, do not express CD25 or activation markers, and are effective mediators of NK cytotoxicity. Thus, pre-A-NK cells are generally similar to CD56(dim) NK cells. However, pre-A-NK cells differ from the main NK cell subpopulation by having a lower expression level of CD16 and a lower ability to mediate redirected antibody-dependent, cell-mediated cytotoxicity. More importantly, pre-A-NK cells are preferentially endowed with the ability to rapidly respond to IL-2 by integrin-mediated adherence to endothelial cells, extracellular matrix, and plastic. This early, specific response of pre-A-NK cells to IL-2 is followed by their activation, vigorous proliferation, and differentiation into phenotypically and functionally similar A-NK cells. Pre-A-NK cells represent only approximately 26% of peripheral blood NK cells but encompass the majority of NK cells in normal and cancerous, solid tissues. We conclude that pre-A-NK cells represent a distinct subset of resting, mature NK cells with the characteristics indicative of their ability to migrate and reside in solid tissues.

Function and survival of dendritic cells depend on endothelin-1 and endothelin receptor autocrine loops.

The biologic effects of endothelin-1 (ET-1) are not limited to its potent vasoconstricting activity. The endothelin receptors, ETA and ETB, have differential tissue and functional distributions. Here we showed that dendritic cells (DCs), the major antigen-presenting cells in the adaptive limb of the immune system, produce large amounts of ET-1 and significantly increase the expression of endothelin receptors upon maturation. Selective blockade of the ETA receptor significantly reduced expression of the mature DC marker CD83, decreased the production of the immunostimulatory cytokine interleukin-12, down-regulated DC ability to stimulate T cells, and promoted DC apoptosis. Selective ETB receptor blockade, on the other hand, resulted in increased expression of CD83 and improved DC survival. Therefore, ET-1/ETA/ETB autocrine/paracrine loops on DCs appear to be essential for the normal maturation and function of human DCs, presenting a unique target for immunomodulatory therapies.

Comparative analysis of dendritic cells transduced with different anti-apoptotic molecules: sensitivity to tumor-induced apoptosis.

BACKGROUND: Tumors develop mechanisms to escape recognition by the immune system. It has recently been demonstrated that tumors cause apoptotic death of key immune cells, including the major antigen-presenting cells, dendritic cells (DC). Elimination of DC from the tumor environment significantly diminishes development of specific immunologic responses. We have recently demonstrated that tumor-induced DC apoptosis could be prevented by overexpression of the anti-apoptotic molecule Bcl-x(L). The aim of this study was to identify extrinsic and intrinsic tumor-induced apoptotic pathways in DC by targeting different anti-apoptotic molecules, including FLIP, XIAP/hILP, dominant-negative procaspase-9 and HSP70. METHODS: Murine bone marrow derived DC were transduced with adenoviral vectors carrying different anti-apoptotic molecules and co-incubated with tumor cells in a Transwell system. Apoptosis of DC was assessed by Annexin V and PI staining. RESULTS: We have demonstrated that adenoviral infection of DC with genes encoding different anti-apoptotic molecules exhibits different degrees of resistance to melanoma-induced apoptosis. Furthermore, we have shown that anti-apoptotic molecules other than the Bcl-2 family of proteins are able to protect DC and prevent tumor-induced apoptosis in DC. CONCLUSIONS: The results show that tumor-induced apoptosis of DC is not limited to the mitochondrial pathway of cell death and open additional possibilities for targeted molecular protection of DC longevity in cancer. Therefore, effective protection of DC from tumor-induced apoptosis may significantly improve the efficacy of DC-based therapies for cancer.

Lung cancer-derived bombesin-like peptides down-regulate the generation and function of human dendritic cells.

Development of tumors is regulated by tumor-derived neuroendocrine factors, including bombesin-like peptides (BLP). We have evaluated neuroendocrine regulation of dendritic cell (DC) maturation and function by both tumor-derived and purified bombesin (BOM), neuromedin B (NMB), gastrin-releasing peptide (GRP), and a BOM antagonist D-Phe-bombesin (DPB). BOM, NMB and GRP dose-dependently inhibited maturation of DC assessed as down-regulation of CD40, CD80 and CD86 expression on DC. BOM and GRP also inhibited interleukin-12 (IL-12) production by DC and their ability to activate T cells. DPB partly abrogated immunosuppressive effect of tumor cells on DC. These data are a first evidence for the role of BLP in the regulation of DC maturation and function, demonstrating that BLP inhibit DC maturation and longevity in the lung cancer microenvironment. This suggests a new mechanism of tumor escape and provides new targets for the immunopharmacological correction of immune effectors in cancer.

Increased function and survival of IL-15-transduced human dendritic cells are mediated by up-regulation of IL-15Ralpha and Bcl-2.

It has been recently demonstrated that dendritic cells (DC) coincubated with interleukin (IL)-15 express high levels of the Bcl-2 family of proteins and display an increased resistance to tumor-induced apoptotic death. Here, the phenotype, functions, and survival of human DC transduced with adenoviral vector encoding the human IL-15 gene were studied. The transduction of DC with the IL-15 gene resulted in a significant elevation of expression of CD83, CD86, and CD40 molecules, which was blocked by anti-IL-15 monoclonal antibodies. This effect was also accompanied by an increased production of IL-12 and stimulated ability of DC to induce T cell proliferation. Furthermore, transduction of DC with the IL-15 gene significantly increased their resistance to prostate cancer-induced apoptosis: Overexpression of IL-15 on DC blocked tumor-induced inhibition of Bcl-2 expression and prolonged DC survival after coincubation with tumor cells. Finally, overexpression of IL-15 in DC was associated with a higher level of expression of IL-15 receptor alpha chain mRNA. In summary, these results suggest that transduction of DC with the IL-15 gene markedly stimulates DC function and protects them from tumor-induced apoptosis.