Epidermal Langerhans cell development and differentiation

CCL5 and CCL20 mediate immigration of Langerhans cells into the epidermis of full thickness human skin equivalents

Epidermal Langerhans cells (LC) play a key role in initiation and regulation of immune responses. Whereas LC migration out of the epidermis upon environmental assault is extensively studied, the mechanisms involved in the (re)population of the epidermis with LC are poorly understood. Here, we investigated the immigration of LC derived from the human MUTZ-3 cell line (MUTZ-LC) into the epidermis of a full thickness skin equivalent, comprising a fully differentiated epidermis on a fibroblast-populated dermis. MUTZ-LC were used to determine which epidermis-derived chemokines play a role in mediating LC trans-dermal migration into the epidermis. We found evidence for a role of keratinocyte-derived CCL5 and CCL20 in the chemo-attraction of MUTZ-LC. Neutralizing antibodies against CCL5 and CCL20 blocked LC migration towards keratinocytes. Secretion of these two chemokines was associated with incorporation of MUTZ-LC into the epidermis of full thickness skin equivalents. In conclusion, our findings suggest that epidermis derived CCL5 and CCL20 are pivotal mediators in recruitment of LC into the epidermis.

Mutz-3-derived Langerhans cells are a model to study HIV-1 transmission and potential inhibitors

Sexual transmission is the primary route of HIV-1 infection, and DC subsets are thought to be involved in viral dissemination to T cells. In the genital mucosa, two main subsets of DCs are present: epithelial LCs capture and degrade HIV-1 through C-type lectin Langerin, whereas subepithelial DCs express DC-SIGN, which facilitates HIV-1 transmission to T cells. As there is currently no HIV-1 vaccine available, microbicides provide an alternative strategy to limit HIV-1 spread. However, research into the function of LCs is hampered by the low availability and donor differences. Here, we set out to investigate whether LCs derived from the Mutz-3 cell line (Mu-LCs) provide a valuable tool to investigate the role of LCs in HIV-1 transmission and identify suitable potential microbicides. We demonstrate that Mu-LCs phenotypically resemble human primary LCs; Mu-LCs do not transmit HIV-1 efficiently, and inhibition of Langerin enhances HIV-1 transmission to T cells. We show that carbohydrate structures blocking DC-SIGN but not Langerin are potential microbicides, as they prevent HIV-1 transmission by DCs but do not affect the antiviral function of LCs. Therefore, Mu-LCs are a suitable model to investigate the role of LCs in HIV-1 transmission and to screen potential microbicides.

Manipulation of dendritic cell functions by human cytomegalovirus

Dendritic cells are the most potent antigen-presenting cells of the mammalian immune system and are central to the initiation and maintenance of the adaptive immune response. They are crucial for the presentation of antigen to T cells and B cells, as well as the induction of chemokines and proinflammatory cytokines, which orchestrate the balance of the cell-mediated (Th1) and antibody (Th2) response. This ability of dendritic cells to present antigen and release chemokines and cytokines also bridges the innate and adaptive immune responses by driving T cell activation. These cells thus possess key immunological functions that make them the front line of defence for the targeting and clearance of any invading pathogen and, as such, they underpin the host immune response to infection. For efficient infection, invading pathogens often need to overcome these sentinel immune functions. It is therefore not surprising that pathogens have evolved numerous mechanisms to target dendritic cell functions directly or indirectly during infection, and at least one herpesvirus--human cytomegalovirus--has evolved a life cycle that hijacks dendritic cells for its long-term persistence in the infected host.

Activin A induces Langerhans cell differentiation in vitro and in human skin explants

Langerhans cells (LC) represent a well characterized subset of dendritic cells located in the epidermis of skin and mucosae. In vivo, they originate from resident and blood-borne precursors in the presence of keratinocyte-derived TGFbeta. In vitro, LC can be generated from monocytes in the presence of GM-CSF, IL-4 and TGFbeta. However, the signals that induce LC during an inflammatory reaction are not fully investigated. Here we report that Activin A, a TGFbeta family member induced by pro-inflammatory cytokines and involved in skin morphogenesis and wound healing, induces the differentiation of human monocytes into LC in the absence of TGFbeta. Activin A-induced LC are Langerin+, Birbeck granules+, E-cadherin+, CLA+ and CCR6+ and possess typical APC functions. In human skin explants, intradermal injection of Activin A increased the number of CD1a+ and Langerin+ cells in both the epidermis and dermis by promoting the differentiation of resident precursor cells. High levels of Activin A were present in the upper epidermal layers and in the dermis of Lichen Planus biopsies in association with a marked infiltration of CD1a+ and Langerin+ cells. This study reports that Activin A induces the differentiation of circulating CD14+ cells into LC. Since Activin A is abundantly produced during inflammatory conditions which are also characterized by increased numbers of LC, we propose that this cytokine represents a new pathway, alternative to TGFbeta, responsible for LC differentiation during inflammatory/autoimmune conditions.

Human CD34+ CD11b- cord blood stem cells generate in vitro a CD34- CD11b+ subset that is enriched in langerin+ Langerhans dendritic cell precursors

OBJECTIVE

We investigated whether the expression of CD11b on precursors derived in vitro from CD34+ hematopoietic stem cells was related to their ability to generate CD11b- and CD11b+ Langerhans dendritic cells (LC).

METHODS

Human CD34+ cells purified from cord blood were cultured with FLT3 ligand, thrombopoietin, and stem cell factor (FTS) for 2 weeks, analyzed, and sorted by FACS. Sorted fractions were cultured as above, or differentiated into LC with GM-CSF, IL-4, and TGF-beta1 (G4-TGF) for 6 days. The capacity of LC to internalize langerin and dextran was assessed.

RESULTS

Ex vivo, human CD34+ cells were CD11b- and mostly CLA+. After 2 weeks of culture with FTS, CD34- CLA- CD11b- and CD34- CLA- CD11b+ cells emerged. CD11b- cells were the most ancestral because they were the only ones to proliferate with FTS, and constantly generated CD11b+ cells. Both CD11b- and CD11b+ sorted cells generated E-cadherin+ langerin+ LC after incubation with G4-TGF. The former fraction contained 46% +/- 15% of E-cadherin+ and 10% +/- 5% of langerin+ cells, whereas in the latter fraction these values reached respectively 66% +/- 23% and 30% +/- 16% (mean +/- SD, n = 7, p < 0.056). Looking at functional properties, CD11b- and CD11b+ LC were similar in terms of langerin and dextran endocytosis. By contrast, only CD11b+ LC internalized fluorescent LPS.

CONCLUSION

Human CD34+ CD11b- cells differentiate in FTS culture into a CD34- CD11b- precursor that in turn generates CD34- CD11b+ cells. These cells are enriched in LC precursors compared to CD34- CD11b- cells. Both CD11b- and CD11b+ LC are generated in vitro, and each fraction may assume different functions in inflammatory situations.

Physiological concentrations of transforming growth factor beta1 selectively inhibit human dendritic cell function

In this study the effects of different in vitro conditioning with transforming growth factor (TGF) beta1 on human monocyte-derived DC maturation (hMo-DC) were investigated. hMo-DC differentiated in the presence of physiologically relevant concentrations of TGFbeta1 (2 ng/ml) failed to undergo complete maturation despite adequate stimulation with LPS or LPS+IFNgamma. These hMo-DC did not produce IL-12p70 or PGE2, and showed decreased IL-10 and IL-18 production and HLA-DR expression. However, the expression of these molecules, except for IL-12p70, was not significantly affected in hMo-DC differentiated in the presence of lower concentrations of TGFbeta1 (0.2 and 0.02 ng/ml). Exposure of hMo-DC to TGFbeta1 (2 ng/ml) after they had completed differentiation had minimal effects. Thus, the functional response of hMo-DC to LPS or LPS+IFNgamma depended on the stage of hMo-DC differentiation at which cells were first exposed to TGFbeta1 and on the concentration of TGFbeta1. These results suggest that in the in vivo micro-environment, the concentrations and the timing of monocyte exposure to TGFbeta1 may be crucial in the differentiation of DC toward more or less mature phenotypes, and this may have important implications for DC functions. The decrease in T-cell proliferation and a small increase in IL-5 production by T cells co-cultured with hMo-DC that had been treated with TGFbeta1, suggest the possibility that in vivo such DC may provide chronic, but incomplete signals to T cells, and this could be a potential mechanism underlying polarisation of T cells towards anergy.

CD34+ cells in the peripheral blood transport herpes simplex virus DNA fragments to the skin of patients with erythema multiforme (HAEM)

Herpes simplex virus (HSV)-associated erythema multiforme (HAEM) is a recurrent disease characterized by the presence and expression of HSV DNA fragments in lesional skin. Our studies examined the mechanism of viral DNA transport to the skin of HAEM patients. CD34+ cells were isolated from the blood of normal subjects and HSV and HAEM patients during acute lesions and at quiescence. They were cultured with cytokines that favor their differentiation into Langerhans cells (LC) precursors (CD1a+/CD14-) and examined for HSV replication, HSV-induced cellular alterations, viral DNA fragmentation, and clearance. CD34+ cells from all study groups were non-permissive for HSV replication but infection favored their differentiation into CD1a+/CD14- LC precursors and upregulated E-cadherin expression, thereby assisting LC targeting to the skin. Only HAEM patients had CD34+ cells that retained viral DNA fragments, notably polymerase DNA, for at least 7 d of in vitro culture. The percentages of circulating CD34+ (and CD34+/CLA+) cells were significantly higher in HAEM patients at the time of acute lesions. A similar increase was not seen for HSV patients. The data are the first report implicating CD34+ cells in HAEM pathogenesis, likely by transporting HSV DNA fragments to lesional skin.

IL-3 in dendritic cell development and function: a comparison with GM-CSF and IL-4

Dendritic cells (DC) develop in vivo from hematopoietic precursor cells. This process can be mimicked in vitro by growth factor stimulation. Among those factors granulocyte-macrophage colony-stimulating factor (GM-CSF) is the best known and most widely used for generation of rodent and human DC of the myeloid lineage. GM-CSF is often combined with interleukin-4 (IL-4) to suppress macrophage (Mph) outgrowth in cultures of human cells, but this does not apply to the mouse, and detailed analyses on the role of IL-4 are rare. Despite evidence for the importance of GM-CSF for DC development derived from in vitro data, GM-CSF-deficient mice are largely normal with respect to their DC populations. This raised the interest in other growth factors for DC. IL-3 can also support DC growth in vitro, but has been neglected for some years. Now it has been revived by a series of publications. In this review, some new features of myeloid DC regarding their early developmental stages, the GM-CSF/IL-4-interplay, and the role of IL-3 are summarized.

Dendritic cells: friend or foe in autoimmunity?

The large amount of information that has been acquired from human and animal models substantiates that the DC lineage system represents a double-edged sword in the immune system. Presumably, in normal physiology, tolerizing DCs guard against autoimmunity and control established immune reactions, whereas immunogenic DCs provide active host defenses. In autoimmune diseases, there is strong evidence to support the idea that tolerance is overridden by the development of immunogenic DCs that favor cross-priming. Based on the wide range of possible clinical applications, it is not surprising that manipulation of DCs for clinical benefit is rampant. Indeed, multiple clinical strategies are currently underway, including the development of DC immunotherapy for cancer vaccines and graft survival. In cancer, DC-based vaccines for solid tumors, such as melanoma, were well-tolerated and produced beneficial antitumor responses, even in patients who had advanced disease. Although initial trials such as these are highly promising, the ultimate goal is to develop DC-based strategies that will lead to highly specific, long-lasting immunity against the cancer cells. In autoimmune diseases and transplant settings, the goal is to devise strategies that will block the initiation and maintenance of autoreactive and antigraft responses, respectively. Specific strategies for autoimmune diseases might include interference with cross-priming events that activate autoreactive T cells and genetic engineering to introduce molecules that have immunosuppressive functions, such as IL-10, TGF3, Fas ligand, ILT3, and ILT4. Successful application to these diseases will necessitate high specificity. In this regard, recent preliminary studies that described antigen-specific suppression of a primed immune response by tolerogenic DCs are especially informative.

Gingival organotypic culture and langerhans cells: a tool for immunotoxicologic experiments

Langerhans cells (LCs) are dendritic cells localized in epidermis and mucosal tissues, where they are responsible for triggering the immune response. To study LCs in the oral epithelium, organotypic cultures were prepared using gingival explants. Immunochemical techniques using anti-CD1a, anti-HLA-DR, and anti-Langerin antibodies were used to detect and quantify LCs at various times. Observations were made by light and confocal microscopy. Quantification studies showed that there is a statistically significant drop in LC numbers in the epithelial tissue after 96 h of incubation. Gingival organotypic cultures thus are a good model for studying the migration of LCs and their involvement in contact hypersensitivity and periodontal diseases. The model offers potential utility as a tool for the study of periodontal tissue in the presence of different stimuli and for conducting immunotoxicologic experiments.

The role of antigen presenting cells at distinct anatomic sites: they accelerate and they slow down allergies

It has been repeatedly demonstrated that allergic reactions are driven by the continuous flow of antigen uptake and presentation processes, which are perpetuated mainly by dendritic cells (DC). The ability of allergens to cause allergic inflammation is contingent upon the presence of an immunological milieu and microenvironment that either privileges Th2 responses or prohibits these reactions by the induction of contraregulatory anti-inflammatory activities of the immune system. In the light of recent developments it appears that DC have to manage two opposing tasks: on the one hand they can favor pro-inflammatory reactions and actively induce a T-cell response, yet on the other hand they serve an important function as 'silencers' in the immune system by sending out anti-inflammatory, tolerance inducing signals. This unique capacity of DC has opened several exciting possibilities for a role of DC in both - accelerating and slowing down allergic reactions. It is therefore a challenge to understand in which way DC subtypes located at distinct anatomic sites with frequent allergen exposure, such as the skin, the nasal mucosa, the respiratory tree or the mucosa of the intestinal tract can have an impact on mechanisms involved in tolerance induction or effective immunity.

Susceptibility of immature and mature Langerhans cell-type dendritic cells to infection and immunomodulation by human cytomegalovirus

Human cytomegalovirus (CMV) infection initiates in mucosal epithelia and disseminates via leukocytes throughout the body. Langerhans cells (LCs), the immature dendritic cells (DCs) that reside in epithelial tissues, are among the first cells to encounter virus and may play important roles in the immune response, as well as in pathogenesis as hosts for viral replication and as vehicles for dissemination. Here, we demonstrate that CD34(+) progenitor cell-derived LC-type DCs exhibit a differentiation state-dependent susceptibility to CMV infection. In contrast to the small percentage (3 to 4%) of the immature LCs that supported infection, a high percentage (48 to 74%) of mature, LC-derived DCs were susceptible to infection with endotheliotropic strains (TB40/E or VHL/E) of CMV. These cells were much less susceptible to viral strains AD169varATCC, TownevarRIT(3), and Toledo. When exposed to endotheliotropic strains, viral gene expression (IE1/IE2 and other viral gene products) and viral replication proceeded efficiently in LC-derived mature DCs (mDCs). Productive infection was associated with downmodulation of cell surface CD83, CD1a, CD80, CD86, ICAM-1, major histocompatibility complex (MHC) class I, and MHC class II on these cells. In addition, the T-cell proliferative response to allogeneic LC-derived mDCs was attenuated when CMV-infected cultures were used as stimulators. This investigation revealed important characteristics of the interaction between CMV and the LC lineage of DCs, suggesting that LC-derived mDCs are important to viral pathogenesis and immunity through their increased susceptibility to virus replication and virus-mediated immune escape.

Reduced virus specific T helper cell induction by autologous dendritic cells in patients with chronic hepatitis B - restoration by exogenous interleukin-12

Insufficient stimulatory capacities of autologous dendritic cells (DC) may contribute in part to impaired T cell stimulation and therefore viral persistence in patients with chronic hepatitis B virus (HBV) infection. In order to characterize the antigen presenting functions of DC from chronic HBV carriers and controls antigen specific T cell responses were analysed. CD34+ peripheral blood progenitor cells were differentiated to immature DC in the presence of GM-CSF, IL-6/IL-6R fusion protein and stem cell factor. Proliferative CD4+ T cell responses and specific cytokine release were analysed in co-cultures of DC pulsed with HBV surface and core antigens or tetanus toxoid and autologous CD4+ T cells. Cultured under identical conditions DC from chronic HBV carriers, individuals with acute resolved hepatitis B and healthy controls expressed similar phenotypical markers but chronic HBV carriers showed less frequent and weaker HBV antigen specific proliferative T helper cell responses and secreted less interferon-gamma while responses to the tetanus toxoid control antigen was not affected. Preincubation with recombinant IL-12 enhanced the HBV specific immune reactivities in chronic HBV patients and controls. In conclusion, the weak antiviral immune responses observed in chronic hepatitis B may result in part from insufficient T cell stimulating capacities of DC. Immunostimulation by IL-12 restored the HBV antigen specific T cell responses and could have some therapeutical benefit to overcome viral persistence.

Maturation of thyroidal dendritic cells in Graves' disease

Because thyroidal dendritic cells (t-DC) may be implicated in the pathogenesis of Graves' disease (GD), we compared t-DC in thyroid sections of patients with GD (n = 15) and control patients with toxic (TG; n = 12) or non-toxic goitre (NG; n = 12). Goitres in GD, but not TG or NG, were populated with three discernible t-DC phenotypes. (i) Immature t-DC (major histocompatibility complex (MHC) II+/CD40-/CD80-) were located perifollicularly (95% of the patients with GD, but only 55% of TG and 51% of NG patients); numbers of such t-DC were significantly elevated in GD (P < 0.001). (ii) Partially matured CD80+ t-DC were present in connective tissue (73% of the patients) and focal interstitial clusters (40% of the patients). In 53% of the patients with GD, single as well as clustered interstitial t-DC expressed CD40. (iii) However, phenotypically mature t-DC (MHC II+/CD40+/CD80+/RFD1+) were only present in clusters and colocalized with activated CD4+/MHC class II+ T-helper (Th) cells. Expression of CD54 and CD83 did not significantly differ among the groups. The phenotype of intrathyroidal DC in GD thus supports their role as potential (co)stimulators of thyroid autoimmunity.

Appearance of Langerhans cells in the epidermis of Tgfb1(-/-) SCID mice: paracrine and autocrine effects of transforming growth factor-beta 1 and -beta 2(1)

A striking immunologic abnormality of normal and SCID Tgfb1(-/-) mice is the total absence of Langerhans cells in their epidermis. Here we show that transfer of Tgfb1(+/-) SCID bone marrow causes, within a few weeks, the appearance of Langerhans cells in the epidermis of gamma-irradiated and unirradiated Tgfb1(-/-) SCID recipients. In addition, local injection of 2 x 10(5) latent transforming growth factor-beta1 cDNA-transduced cloned CD4+ T lymphocytes causes the appearance of Langerhans cells in the ear epidermis of Tgfb1(-/-) SCID mice. This effect is enhanced by antigen-specific activation of these T cells. Injection of recombinant active transforming growth factor-beta 2 into the ear of Tgfb1(-/-) SCID mice also results in the migration of Langerhans cells into the epidermis locally, but no epidermal Langerhans cells are seen after systemic injections of transforming growth factor-beta 2. Our results suggest that transforming growth factor-beta can act in paracrine as well as autocrine fashion to induce the differentiation of precursors into Langerhans cells. Furthermore, these results indicate that the relative roles of different transforming growth factor-beta isoforms in vivo may be influenced by their local availability and/or the regulation of their conversion from latent into active form.

Dermal-resident CD14+ cells differentiate into Langerhans cells

Epidermal Langerhans cells (LCs) show extraordinary immunostimulatory capacity and play a key role in the initiation and regulation of immune responses. Studies of LC biology are currently the focus of efforts to engineer immune responses and to better understand the immunopathology of cutaneous diseases. Here we identified and characterized a population of LC precursors that were resident in human skin. These immediate precursors expressed CD14, langerin and functional CCR6. When cultured with transforming growth factor-beta1 alone, they had the potential to differentiate into epidermal LCs; when cultured in the presence of granulocyte macrophage-colony-stimulating factor and interleukin 4 they differentiated into functionally mature dendritic cells. Identification and characterization of these LC precursors provided insight into LC biology and the mechanism(s) through which LCs repopulate the epidermis.

Dendritic cells (DCs) in rheumatoid arthritis (RA): progenitor cells and soluble factors contained in RA synovial fluid yield a subset of myeloid DCs that preferentially activate Th1 inflammatory-type responses

There is evidence that mature dendritic cells (DCs) present in the rheumatoid arthritis (RA) joint mediate immunopathology in RA. In this study, we indicate that early myeloid progenitors for DCs and DC growth factors existing in RA synovial fluid (SF) are also likely participants in the RA disease process. A fraction of cells lacking markers associated with mature DCs or DC precursors and enriched in CD34(negative) myeloid progenitors was isolated from RA SF. These cells proliferated extensively when cultured in vitro with cytokines that promote the growth of myeloid DCs (GM-CSF/TNF/stem cell factor/IL-4) and, to a lesser degree, when cultured with monocyte/granulocyte-restricted growth factors (M-CSF/GM-CSF). Mature DCs derived from RA SF progenitors with CD14-DC cytokines known to be prevalent in the inflamed RA joint (GM-CSF/TNF/stem cell factor/IL-13) were potent stimulators of allogeneic T cells and inflammatory-type Th1 responses and included CD14-DC subtypes. Cell-free RA SF facilitated DC maturation from myeloid progenitors, providing direct evidence that the inflamed RA joint environment instructs DC growth. Enhanced development of CD14-derived DCs was correlated with the presence of soluble TNFR (p55), raising the possibility that soluble TNFR also regulate CD14-derived DC growth in vivo. SF from patients with osteoarthritis contained neither myeloid DC progenitors nor DC growth factors. The existence of DC progenitors and myeloid DC growth factors in RA SF supports the concept that RA SF may be a reservoir for joint-associated DCs and reveals a compelling mechanism for the amplification and perpetuation of DC-driven responses in the RA joint, including inflammatory-type Th1 responses.

Langerhans cells in Dupuytren's contracture

We have examined biopsies of Dupuytren's contracture palmar fascia, overlying subcutis and skin, and have correlated the distribution of gross macroscopic changes in the hand, mapped pre- and intraoperatively, with light microscopic immunohistochemical findings. We report increased numbers of S100 positive Langerhans cells (an epidermal cell of dendritic lineage) and CD45 positive cells, both in "nodules" and at dermo-epidermal junctions, in the biopsied tissues. This suggests that Langerhans cells migrate from the epidermis into Dupuytren's contracture tissue, possibly in response to local changes in levels of inflammatory cytokines within the tissue. Our findings, together with other reports of increased numbers of dermal dendrocytes and inflammatory cells in Dupuytren's contracture tissue, lend circumstantial support to the "extrinsic theory" of the pathogenesis of Dupuytren's contracture. However, the earliest stages of the disease process have not been defined, and therefore the events which ultimately produce fibrosis in the palmar fascial complex in susceptible individuals could begin in the skin and/or within deeper tissues, especially where there is dysregulation of the immune system.

Phenotypic and functional outcome of human monocytes or monocyte-derived dendritic cells in a dermal equivalent

The dermis harbors a true dendritic cell population that could elicit primary allogeneic T cell responses in vitro and contact hypersensitivity reactions in vivo. The origin of dermal dendritic cells remains poorly understood, however. In this study, we analyzed the fate of monocytes or monocyte-derived dendritic cells in a dermal equivalent. Freshly isolated monocytes or monocytes cultured for 6 d with either GM-CSF/IL-4 or GM-CSF/IL-4/TGF-beta 1 (TGF-DC) were seeded in a collagen solution with normal human fibroblasts. The lattices were cultured for 7--14 d in the presence, or absence, of the exogenous cytokines, before phenotypic and functional studies were performed. Supply of exogenous cytokines allows the appearance of typical CD1a(+)/CD14(-)/CD68(low) dendritic cells with significant allostimulatory property, regardless of the cell type incorporated into the lattices. In cytokine-free conditions, monocytes and GM-CSF/IL-4-derived dendritic cells give rise to a CD1a(-)/CD14(+)/CD68(high) monocyte/macrophage population with no allostimulatory property. When incorporated into the lattices in the absence of exogenous cytokines the TGF-DC express few CD68 and FXIIIa. Interestingly, these cells do not all convert into the CD14(+)/CD1a(-) population. Indeed, a small HLA-DR(+)/CD1a(+)/CD14(-) subset was consistently found, which represents about one-third of the HLA-DR(+) cells. Moreover, TGF-DC recovered from the lattices after culture without cytokines do display a significant allostimulatory function. Thus, in the absence of exogenous cytokines, only Langerhans-cell-like dendritic cells can retain the typical dendritic cell features when inserted in a dermal environment. Taken together, these results may provide evidence supporting an epidermal origin of dermal dendritic cells.

Granulocyte-macrophage colony-stimulating factor priming plus papillomavirus E6 DNA vaccination: effects on papilloma formation and regression in the cottontail rabbit papillomavirus--rabbit model

A cottontail rabbit papillomavirus (CRPV) E6 DNA vaccine that induces significant protection against CRPV challenge was used in a superior vaccination regimen in which the cutaneous sites of vaccination were primed with an expression vector encoding granulocyte-macrophage colony-stimulating factor (GM-CSF), a cytokine that induces differentiation and local recruitment of professional antigen-presenting cells. This treatment induced a massive influx of major histocompatibility complex class II-positive cells. In a vaccination-challenge experiment, rabbit groups were treated by E6 DNA vaccination, GM-CSF DNA inoculation, or a combination of both treatments. After two immunizations, rabbits were challenged with CRPV at low, moderate, and high stringencies and monitored for papilloma formation. As expected, all clinical outcomes were monotonically related to the stringency of the viral challenge. The results demonstrate that GM-CSF priming greatly augmented the effects of CRPV E6 vaccination. First, challenge sites in control rabbits (at the moderate challenge stringency) had a 0% probability of remaining disease free, versus a 50% probability in E6-vaccinated rabbits, and whereas GM-CSF alone had no effect, the interaction between GM-CSF priming and E6 vaccination increased disease-free survival to 67%. Second, the incubation period before papilloma onset was lengthened by E6 DNA vaccination alone or to some extent by GM-CSF DNA inoculation alone, and the combination of treatments induced additive effects. Third, the rate of papilloma growth was reduced by E6 vaccination and, to a lesser extent, by GM-CSF treatment. In addition, the interaction between the E6 and GM-CSF treatments was synergistic and yielded more than a 99% reduction in papilloma volume. Finally, regression occurred among the papillomas that formed in rabbits treated with the E6 vaccine and/or with GM-CSF, with the highest regression frequency occurring in rabbits that received the combination treatment.

Functional involvement of E-cadherin in TGF-beta 1-induced cell cluster formation of in vitro developing human Langerhans-type dendritic cells

Epithelial Langerhans cells (LC) represent immature dendritic cells that require TGF-beta 1 stimulation for their development. Little is known about the mechanisms regulating LC generation from their precursor cells. We demonstrate here that LC development from human CD34+ hemopoietic progenitor cells in response to TGF-beta 1 costimulation (basic cytokine combination GM-CSF plus TNF-alpha, stem cell factor, and Flt3 ligand) is associated with pronounced cell cluster formation of developing LC precursor cells. This cell-clustering phenomenon requires hemopoietic progenitor cell differentiation, since it is first seen on day 4 after culture initiation of CD34+ cells. Cell cluster formation morphologically indicates progenitor cell development along the LC pathway, because parallel cultures set up in the absence of exogenous TGF-beta 1 fail to form cell clusters and predominantly give rise to monocyte, but not LC, development (CD1a-, lysozyme+, CD14+). TGF-beta 1 costimulation of CD34+ cells induces neoexpression of the homophilic adhesion molecule E-cadherin in the absence of the E-cadherin heteroligand CD103. Addition of anti-E-cadherin mAb or mAbs to any of the constitutively expressed adhesion molecule (CD99, CD31, LFA-1, or CD18) to TGF-beta 1-supplemented progenitor cell cultures inhibits LC precursor cell cluster formation, and this effect is, with the exception of anti-E-cadherin mAb, associated with inhibition of LC generation. Addition of anti-E-cadherin mAb to the culture allows cell cluster-independent generation of LC from CD34+ cells. Thus, functional E-cadherin expression and homotypic cell cluster formation represent a regular response of LC precursor cells to TGF-beta 1 stimulation, and cytoadhesive interactions may modulate LC differentiation from hemopoietic progenitor cells.

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.