Transforming Growth Factor-β1 Polarizes Murine Hematopoietic Progenitor Cells to Generate Langerhans Cell-Like Dendritic Cells Through a Monocyte/Macrophage Differentiation Pathway

Ligation of E-cadherin on in vitro–generated immature Langerhans-type dendritic cells inhibits their maturation

Epithelial tissues of various organs contain immature Langerhans cell (LC)-type dendritic cells, which play key roles in immunity. LCs reside for long time periods at an immature stage in epithelia before migrating to T-cell–rich areas of regional lymph nodes to become mature interdigitating dendritic cells (DCs). LCs express the epithelial adhesion molecule E-cadherin and undergo homophilic E-cadherin adhesion with surrounding epithelial cells. Using a defined serum-free differentiation model of human CD34+hematopoietic progenitor cells, it was demonstrated that LCs generated in vitro in the presence of transforming growth factor β1 (TGF-β1) express high levels of E-cadherin and form large homotypic cell clusters. Homotypic LC clustering can be inhibited by the addition of anti–E- cadherin monoclonal antibodies (mAbs). Loss of E-cadherin adhesion of LCs by mechanical cluster disaggregation correlates with the rapid up-regulation of CD86, neo-expression of CD83, and diminished CD1a cell surface expression by LCs—specific phenotypic features of mature DCs. Antibody ligation of E-cadherin on the surfaces of immature LCs after mechanical cluster disruption strongly reduces the percentages of mature DCs. The addition of mAbs to the adhesion molecules LFA-1 or CD31 to parallel cultures similarly inhibits homotypic LC cluster formation, but, in contrast to anti–E-cadherin, these mAbs fail to inhibit DC maturation. Thus, E-cadherin engagement on immature LCs specifically inhibits the acquisition of mature DC features. E-cadherin–mediated LC maturation suppression may represent a constitutive active epithelial mechanism that prevents the uncontrolled maturation of immature LCs.

Ligation of E-cadherin on in vitro–generated immature Langerhans-type dendritic cells inhibits their maturation

Epithelial tissues of various organs contain immature Langerhans cell (LC)-type dendritic cells, which play key roles in immunity. LCs reside for long time periods at an immature stage in epithelia before migrating to T-cell–rich areas of regional lymph nodes to become mature interdigitating dendritic cells (DCs). LCs express the epithelial adhesion molecule E-cadherin and undergo homophilic E-cadherin adhesion with surrounding epithelial cells. Using a defined serum-free differentiation model of human CD34+hematopoietic progenitor cells, it was demonstrated that LCs generated in vitro in the presence of transforming growth factor β1 (TGF-β1) express high levels of E-cadherin and form large homotypic cell clusters. Homotypic LC clustering can be inhibited by the addition of anti–E- cadherin monoclonal antibodies (mAbs). Loss of E-cadherin adhesion of LCs by mechanical cluster disaggregation correlates with the rapid up-regulation of CD86, neo-expression of CD83, and diminished CD1a cell surface expression by LCs—specific phenotypic features of mature DCs. Antibody ligation of E-cadherin on the surfaces of immature LCs after mechanical cluster disruption strongly reduces the percentages of mature DCs. The addition of mAbs to the adhesion molecules LFA-1 or CD31 to parallel cultures similarly inhibits homotypic LC cluster formation, but, in contrast to anti–E-cadherin, these mAbs fail to inhibit DC maturation. Thus, E-cadherin engagement on immature LCs specifically inhibits the acquisition of mature DC features. E-cadherin–mediated LC maturation suppression may represent a constitutive active epithelial mechanism that prevents the uncontrolled maturation of immature LCs.

Endogenous production of TGF-beta is essential for osteoclastogenesis induced by a combination of receptor activator of NF-kappa B ligand and macrophage-colony-stimulating factor

Differentiation of osteoclasts, the cells primarily responsible for bone resorption, is controlled by a variety of osteotropic hormones and cytokines. Of these factors, receptor activator of NF-kappaB (RANK) ligand (RANKL) has been recently cloned as an essential inducer of osteoclastogenesis in the presence of M-CSF. Here, we isolated a stroma-free population of monocyte/macrophage (M/Mphi)-like hemopoietic cells from mouse unfractionated bone cells that were capable of differentiating into mature osteoclasts by treatment with soluble RANKL (sRANKL) and M-CSF. However, the efficiency of osteoclast formation was low, suggesting the requirement for additional factors. The isolated M/Mphi-like hemopoietic cells expressed TGF-beta and type I and II receptors of TGF-beta. Therefore, we examined the effect of TGF-beta on osteoclastogenesis. TGF-beta with a combination of sRANKL and M-CSF promoted the differentiation of nearly all M/Mphi-like hemopoietic cells into cells of the osteoclast lineage. Neutralizing anti-TGF-beta Ab abrogated the osteoclast generation. These TGF-beta effects were also observed in cultures of unfractionated bone cells, and anti-TGF-beta blocked the stimulatory effect of 1, 25-dihydroxyvitamin D(3). Translocation of NF-kappaB into nuclei induced by sRANKL in TGF-beta-pretreated M/Mphi-like hemopoietic cells was greater than that in untreated cells, whereas TGF-beta did not up-regulate the expression of RANK, the receptor of RANKL. Our findings suggest that TGF-beta is an essential autocrine factor for osteoclastogenesis.

Transforming growth factor-β: pleiotropic role in the regulation of hematopoiesis

Hematopoiesis is a remarkable cell-renewal process that leads to the continuous generation of large numbers of multiple mature cell types, starting from a relatively small stem cell compartment. A highly complex but efficient regulatory network is necessary to tightly control this production and to maintain the hematopoietic tissue in homeostasis. During the last 3 decades, constantly growing numbers of molecules involved in this regulation have been identified. They include soluble cytokines and growth factors, cell–cell interaction molecules, and extracellular matrix components, which provide a multifunctional scaffolding specific for each tissue. The cloning of numerous growth factors and their mass production have led to their possible use for both fundamental research and clinical application.

Differentiation of myeloid dendritic cells into CD8α-positive dendritic cells in vivo

Bone marrow-derived dendritic cells (DC) represent a family of antigen-presenting cells (APC) with varying phenotypes. For example, in mice, CD8α+ and CD8α− DC are thought to represent cells of lymphoid and myeloid origin, respectively. Langerhans cells (LC) of the epidermis are typical myeloid DC; they do not express CD8α, but they do express high levels of myeloid antigens such as CD11b and FcγR. By contrast, thymic DC, which derive from a lymphoid-related progenitor, express CD8α but only low levels of myeloid antigens. CD8α+ DC are also found in the spleen and lymph nodes (LN), but the origin of these cells has not been determined. By activating and labeling CD8α− epidermal LC in vivo, it was found that these cells expressed CD8α on migration to the draining LN. Similarly, CD8α− LC generated in vitro from a CD8 wild-type mouse and injected into the skin of a CD8αKO mouse expressed CD8α when they reached the draining LN. The results also show that CD8α+ LC are potent APC. After migration from skin, they localized in the T-cell areas of LN, secreted high levels of interleukin-12, interferon-γ, and chemokine-attracting T cells, and they induced antigen-specific T-cell activation. These results demonstrate that myeloid DC in the periphery can express CD8α when they migrate to the draining LN. CD8α expression on these DC appears to reflect a state of activation, mobilization, or both, rather than lineage.

Differentiation of myeloid dendritic cells into CD8α-positive dendritic cells in vivo

Bone marrow-derived dendritic cells (DC) represent a family of antigen-presenting cells (APC) with varying phenotypes. For example, in mice, CD8α+ and CD8α− DC are thought to represent cells of lymphoid and myeloid origin, respectively. Langerhans cells (LC) of the epidermis are typical myeloid DC; they do not express CD8α, but they do express high levels of myeloid antigens such as CD11b and FcγR. By contrast, thymic DC, which derive from a lymphoid-related progenitor, express CD8α but only low levels of myeloid antigens. CD8α+ DC are also found in the spleen and lymph nodes (LN), but the origin of these cells has not been determined. By activating and labeling CD8α− epidermal LC in vivo, it was found that these cells expressed CD8α on migration to the draining LN. Similarly, CD8α− LC generated in vitro from a CD8 wild-type mouse and injected into the skin of a CD8αKO mouse expressed CD8α when they reached the draining LN. The results also show that CD8α+ LC are potent APC. After migration from skin, they localized in the T-cell areas of LN, secreted high levels of interleukin-12, interferon-γ, and chemokine-attracting T cells, and they induced antigen-specific T-cell activation. These results demonstrate that myeloid DC in the periphery can express CD8α when they migrate to the draining LN. CD8α expression on these DC appears to reflect a state of activation, mobilization, or both, rather than lineage.

Local and systemic effects after adenoviral transfer of the murine granulocyte-macrophage colony-stimulating factor gene into mice

Vectors encoding immunostimulatory genes are under investigation for their use as adjuvants for immunotherapy. Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a prominent candidate gene for this approach because this cytokine can prime immune responses to 'self' tumour or other weak antigens. Prior studies suggested that GM-CSF induces accumulation and differentiation of antigen-presenting cells, particularly dendritic cells that can initiate immunity. To evaluate this model in vivo, we performed i.m. and i.p. injections of an adenovirus vector encoding murine GM-CSF (Ad-mGM-CSF) and evaluated local and systemic effects. After intramuscular injection, local changes were characterized by the accumulation of myeloid cells, a subsequent infiltration of lymphocytes and then myonecrosis. Intraperitoneal injection also induced an accumulation of myeloid cells, an increase in CD3-positive T and a decrease in B220-positive B lymphocytes. Expression of the dendritic cell marker CD11c on 48 +/- 9% of the peritoneal cells (n = 6) along with high levels of surface MHC class II, a characteristic morphology, and endocytosis of FITC-dextran suggested in vivo differentiation of dendritic cells after i.p. injection of Ad-mGM-CSF. Systemic effects were observed after i.m. and i.p. injection of Ad-mGM-CSF. All mice developed hepatosplenomegaly resulting from extramedullary haematopoiesis. These changes were specific to GM-CSF as they were not seen in mice injected with an adenovirus vector without a transgene. Our observations indicate that adenoviral transfer of GM-CSF is a powerful tool for inducing local and systemic expansion of haematopoietic cells. The local expansion of myeloid cells displaying signs of dendritic cell differentiation, as characterized for the peritoneal cell compartment, can explain the potency of GM-CSF when used as an adjuvant in genetic immunotherapy.

TGF-beta 1 reciprocally controls chemotaxis of human peripheral blood monocyte-derived dendritic cells via chemokine receptors

We examined the effect of TGF-beta 1 on the chemotactic migratory ability of human monocyte-derived dendritic cells (DCs). Treatment of immature DCs with TGF-beta 1 resulted in increased expressions of CCR-1, CCR-3, CCR-5, CCR-6, and CXC chemokine receptor-4 (CXCR-4), which were concomitant with enhanced chemotactic migratory responses to their ligands, RANTES (for CCR-1, CCR-3, and CCR-5), macrophage-inflammatory protein-3 alpha (MIP-3 alpha) (for CCR-6), or stromal cell-derived growth factor-1 alpha (for CXCR-4). Ligation by TNF-alpha resulted in down-modulation of cell surface expressions of CCR-1, CCR-3, CCR-5, CCR-6, and CXCR-4, and the chemotaxis for RANTES, MIP-3 alpha, and stromal cell-derived growth factor-1 alpha, whereas this stimulation up-regulated the expression of CCR-7 and the chemotactic ability for MIP-3beta. Stimulation of mature DCs with TGF-beta 1 also enhanced TNF-alpha-induced down-regulation of the expressions of CCR-1, CCR-3, CCR-5, CCR-6, and CXCR-4, and chemotaxis to their respective ligands, while this stimulation suppressed TNF-alpha-induced expression of CCR-7 and chemotactic migratory ability to MIP-3 beta. Our findings suggest that TGF-beta 1 reversibly regulates chemotaxis of DCs via regulation of chemokine receptor expression.

Cellular but not humoral immune responses generated by vaccination with dendritic cells protect mice against leukaemia

Dendritic cells (DC) are extremely efficient at generating both prophylactic and therapeutic anti-tumour immunity. We aimed to analyse the respective roles of humoral and cellular immune responses generated in mice vaccinated with bone marrow (BM)-derived DC in terms of in vivo anti-leukaemia effect. We used the murine L1210 B lymphocytic leukaemia genetically modified to express on the cell surface of human CD4 (hCD4) (L1210/hCD4) as a model tumour-associated antigen (TAA). DC cultures were loaded with either purified soluble hCD4 (shCD4) protein or unfractionated L1210/hCD4 extracts and injected as vaccine into mice. The efficacy of these vaccinations was compared with that of vaccination with shCD4 protein emulsified in Freund's adjuvant (FA). We evaluated the immune responses generated after these vaccinal protocols and the survival rate of vaccinated mice subsequently challenged with a lethal injection of L1210/hCD4 cells. Our results demonstrated that vaccination with shCD4 protein or tumour extract-loaded DC mainly generated an hCD4 antigen-specific cell-mediated cytotoxic immune response that was associated with a specific protection against leukaemia. In contrast, vaccination with the protein emulsified in FA only generated potent humoral immune responses that were not protective against leukaemia. Altogether, our results indicate that the unique property of loaded DC to trigger an anti-leukaemia protective effect is mainly associated with cellular immune responses.

Development of dendritic cells in vitro from murine fetal liver–derived lineage phenotype-negative c-kit+hematopoietic progenitor cells

We describe here that lineage phenotype- negative (Lin)−c-kit+ hematopoietic progenitor cells (HPCs) from day 13 postcoitus (dpc) murine fetal liver (FL) can generate dendritic cell (DC) precursors when cultured in vitro in the presence of PA6 stromal cells plus granulocyte/macrophage colony-stimulating factor (GM-CSF) + stem cell factor (SCF) + Flt3 ligand (Flt3L) for 12 to 14 days, and develop into mature DCs when stimulated with GM-CSF plus mouse tumor necrosis factor  (mTNF) for an additional 3 to 5 days. A transwell culture system showed that the generation of DC precursors depended on the support of PA6 cell-secreted soluble factor(s). The mature DCs derived from 13 dpc FL Lin−c-kit+ HPCs showed characteristic morphology and function of DCs and expressed high levels of Ia, CD86, and CD40 molecules, low levels of DEC205, E-cadherin, and F4/80 molecules, but barely detectable CD11c antigen. Once FL-derived HPCs were cultured without GM-CSF, NK1.1+ cells developed in the presence of PA6 cells + SCF + Flt3L. These NK1.1+ cells could develop into DC precursors at an earlier stage of differentiation by reculturing with PA6 cells + SCF + Flt3L + GM-CSF, but they would be irreversibly committed to NK cell precursors without GM-CSF after 3 days, suggesting that GM-CSF plays a critical role in controlling the transition of DC and NK cell precursors from 13 dpc FL-derived Lin−c-kit+ HPCs. This study represents the first success in generating mature DCs in vitro from murine FL HPCs. (Blood. 2000;95:138-146)

Development of dendritic cells in vitro from murine fetal liver–derived lineage phenotype-negative c-kit+hematopoietic progenitor cells

We describe here that lineage phenotype- negative (Lin)−c-kit+ hematopoietic progenitor cells (HPCs) from day 13 postcoitus (dpc) murine fetal liver (FL) can generate dendritic cell (DC) precursors when cultured in vitro in the presence of PA6 stromal cells plus granulocyte/macrophage colony-stimulating factor (GM-CSF) + stem cell factor (SCF) + Flt3 ligand (Flt3L) for 12 to 14 days, and develop into mature DCs when stimulated with GM-CSF plus mouse tumor necrosis factor  (mTNF) for an additional 3 to 5 days. A transwell culture system showed that the generation of DC precursors depended on the support of PA6 cell-secreted soluble factor(s). The mature DCs derived from 13 dpc FL Lin−c-kit+ HPCs showed characteristic morphology and function of DCs and expressed high levels of Ia, CD86, and CD40 molecules, low levels of DEC205, E-cadherin, and F4/80 molecules, but barely detectable CD11c antigen. Once FL-derived HPCs were cultured without GM-CSF, NK1.1+ cells developed in the presence of PA6 cells + SCF + Flt3L. These NK1.1+ cells could develop into DC precursors at an earlier stage of differentiation by reculturing with PA6 cells + SCF + Flt3L + GM-CSF, but they would be irreversibly committed to NK cell precursors without GM-CSF after 3 days, suggesting that GM-CSF plays a critical role in controlling the transition of DC and NK cell precursors from 13 dpc FL-derived Lin−c-kit+ HPCs. This study represents the first success in generating mature DCs in vitro from murine FL HPCs. (Blood. 2000;95:138-146)

TGF-beta1 regulation of dendritic cells

Dendritic cells (DCs) represent antigen-presenting cell (APC) populations in lymphoid and nonlymphoid organs which are considered to play key roles in the initiation of antigen-specific T-cell proliferation. According to current knowledge, the net outcome of T-cell immune responses seems to be significantly influenced by the activation stage of antigen-presenting DCs. Several studies have shown that transforming growth factor-beta 1 (TGF-beta1) inhibits in vitro activation and maturation of DCs. TGF-beta1 inhibits upregulation of critical T-cell costimulatory molecules on the surface of DCs and reduces the antigen-presenting capacity of DCs. Thus, in addition to direct inhibitory effects of TGF-beta1 on effector T lymphocytes, inhibitory effects of TGF-beta1 at the level of APCs may critically contribute to previously characterized immunosuppressive effects of TGF-beta1. In contrast to these negative regulatory effects of TGF-beta1 on function and maturation of lymphoid tissue type DCs, certain subpopulations of immature DCs in nonlymphoid tissues are positively regulated by TGF-beta1 signaling. In particular, epithelial-associated DC populations seem to critically require TGF-beta1 stimulation for development and function. Recent studies established that TGF-beta1 stimulation is absolutely required for the development of epithelial Langerhans cells (LCs) in vitro and in vivo. Furthermore, TGF-beta1 seems to enhance antigen processing and costimulatory functions of epithelial LCs.

Dendritic cell origins: puzzles and paradoxes

In the present review, a series of studies on the origins of dendritic cells of mice and humans are summarized. Several subsets of mature dendritic cells found in vivo are described and these may correspond to distinct lineages. There is evidence that some dendritic cells are myeloid-derived and that others are lymphoid-derived. The different ways of generating dendritic cells are examined and an attempt to reconcile the differences seen using mouse and human culture models is made. The particular case of Langerhans cells is discussed and an historical overview of the biology of the plasmacytoid T cells, which may represent a distinct 'lymphoid-related' dendritic cell lineage, is given. It is concluded that three or four different pathways lead to the development of different subtypes of dendritic cells.

Chemotactic Response Toward Chemokines and Its Regulation by Transforming Growth Factor-β1 of Murine Bone Marrow Hematopoietic Progenitor Cell-Derived Different Subset of Dendritic Cells

Dendritic cells (DCs) are highly specialized antigen-presenting cells that distribute widely in all organs. DCs initiate the primary immune response and activate naive T cells and B cells responsible for the acquired immunity. In this study, CCR7 mRNA was proved to be expressed in DCs and their precursors derived from murine bone marrow-derived hematopoietic progenitor cells (HPCs), whereas CCR1 mRNA was expressed in both CD11b−/dullCD11c+ and CD11b+hiCD11c+ DC precursors. CCR6 mRNA was not detected in any murine DC populations. In agreement with the chemokine receptor mRNA expression by each population in the DC differentiation pathway, SLC (also termed as MIP-3β), one of the ligands for CCR7, strongly and selectively chemoattracted both CD11b−/dullCD11c+ and CD11b+hiCD11c+ DC precursors (days 6 to 7) and more mature DCs (days 13 to 14). We have recently found that transforming growth factor-β1 (TGF-β1), a cytokine that is essential for the appearance of Langerhans cells in the skin, polarizes murine HPCs to generate Langerhans-like cells through monocyte/macrophage differentiation pathway. We observed here that TGF-β1 not only inhibited the expression of CCR7 in DCs and DC precursors derived from HPCs, but also inhibited the migration of these cells in response to SLC. This is the first report describing the chemokine and chemokine receptors responsible for murine DC migration and downregulation of DC migration by TGF-β1.