Human melanoma cells inhibit the earliest differentiation steps of human Langerhans cell precursors but failed to affect the functional maturation of epidermal Langerhans cells

Tumour-derived factors suppress differentiation and function of in vitro generated DC. Here, we investigate the effect of two melanoma clones differing in their invasive and metastatic properties on the generation and/or functional maturation of human epidermal LC. LC were generated from CD34+ cord blood progenitors under GM-CSF/TNF-α/TGF-β1. CD34+ cells were co-cultured with or without melanoma cells using Transwell dishes. After 11 days of co-culture, CD34+-derived cells display a non-adherent undifferentiated morphology, a high level of monocytic CD14 marker, a down-regulated expression of LC markers (CD1a, E-cadherin) and DC markers (CD40, CD80, CD54, CD58, CD83, CD86, HLA-DR, HLA-class I). These cells were less potent than control LC in inducing allogeneic T cell proliferation. The generation of the CD14+ population was correlated with a decrease in the CD1a+ population, without any statistical differences between the two clones. Melanoma cells diverted the differentiation of CD34+ cells towards a dominant CD14+ population only if the progenitors were in an early growth phase. IL-10, TGF-β1 and VEGF were not responsible for these effects, as assessed by using blocking antibodies. By contrast, co-culture of fresh epidermal LC with melanoma cells did not affect their phenotype and function. Our data demonstrate that melanoma cells inhibit the earliest steps of LC differentiation, but failed to affect the functional maturation of epidermal LC. This suggests that melanoma cells participate in their own escape from immunosurveillance by preventing LC generation in the local cutaneous microenvironment. © 2001 Cancer Research Campaign http://www.bjcancer.co

Dysregulated Expression of Glycolipids in Tumor Cells: From Negative Modulator of Anti-tumor Immunity to Promising Targets for Developing Therapeutic Agents

Glycolipids are complex molecules consisting of a ceramide lipid moiety linked to a glycan chain of variable length and structure. Among these are found the gangliosides, which are sialylated glycolipids ubiquitously distributed on the outer layer of vertebrate plasma membranes. Changes in the expression of certain species of gangliosides have been described to occur during cell proliferation, differentiation and ontogenesis. However, the aberrant and elevated expression of gangliosides has been also observed in different types of cancer cells, thereby promoting tumor survival. Moreover, gangliosides are actively released from the membrane of tumor cells, having a strong impact on impairing anti-tumor immunity. Beyond the undesirable effects of gangliosides in cancer cells, a substantial number of cancer immunotherapies have been developed in recent years that have used gangliosides as the main target. This has resulted in successful immune cell- or antibody-responses against glycolipids, with promising results having been obtained in clinical trials. In this review, we provide a general overview on the metabolism of glycolipids, both in normal and tumor cells, as well as examining glycolipid-mediated immune modulation and the main successes achieved in immunotherapies using gangliosides as molecular targets

CD40 Ligation Alters the Cell Cycle of Differentiating Keratinocytes

CD40 is expressed in normal human keratinocytes, especially in the basal cell layer. We have recently reported that CD40 ligation strongly inhibits keratinocyte proliferation and induces their differentiation. In this study, the CD40 pathway that prevents keratinocyte growth was investigated. We first reported that interferon-γ treatment potentiated the CD40-mediated inhibition of keratinocyte proliferation. CD40–CD40 ligand interactions, in the presence or absence of interferon-γ, neither enhanced spontaneous keratinocyte apoptosis, nor did it enhance apoptosis induced by various agents. More importantly, we showed that CD40 signaling altered the keratinocyte cell cycle, as demonstrated by a decreasing number of cells in the G1 and S phases and an accumulation in G2/M phase of the cell cycle. Furthermore, western blot analysis of cell cycle regulatory proteins, showed a decrease in cyclin A and E expression in CD40-activated keratinocytes. Collectively, these results indicate that CD40 ligation inhibits keratinocyte renewal by a mechanism independent of cell apoptosis and that modulation of the keratinocyte cell cycle is an additional outcome of CD40 signaling

Poly(I:C)-Treated human langerhans cells promote the differentiation of CD4+ T cells producing IFN-gamma and IL-10.

International audienceEpidermal Langerhans cells (LCs) are the first dendritic cells to encounter skin pathogens. However, their function has recently been challenged, especially in the initiation of T-cell responses to viral antigens. We have previously reported that fresh immature human LCs express mRNA encoding TLR3. Here we analyze the response of highly purified human LCs to poly(I:C), a synthetic mimetic of viral dsRNA recognized by TLR3. We show that LCs exposed for 2 days to poly(I:C) under serum-free conditions up-regulated co-stimulatory molecules, a process associated with increased allostimulatory capacity. Furthermore, poly(I:C) significantly enhanced LC survival and induced them to produce CXCL10, IL-6, and IL-12 p40. Bioactive IL-12 p70, IL-1beta, IL-15, IL-18, and IL-23 were never detected, even after CD40 ligation. LC incubation in the presence of bafilomycin completely reversed the effect of poly(I:C) on LC phenotypic activation and survival, indicating that endosomal TLR3 is involved in this process. Most interestingly, we report here that poly(I:C)-treated LCs favored alloreactive CD4(+) T-cell differentiation toward a Th1 profile and concomitant differentiation of IL-10-producing CD4(+) T cells that might limit, at another time, the inflammatory response and subsequent tissue damage

: Gangliosides impair Langerhans cell function

Gangliosides are ubiquitous, membrane-associated, glycosphingolipids, the composition and production of which is altered in many tumour cells. They have been shown to inhibit the in vitro generation and differentiation of dendritic cells (DCs) from progenitors, but their effect on human tissue-residing DCs is yet to be investigated. In the present study, we analysed the effect of GM3 and GD3 gangliosides purified from human melanoma tumours on the phenotypic and functional maturation of human epidermal Langerhans cells (LCs), the first immune barrier against the tumour cells. We showed that both gangliosides impaired spontaneous LC maturation induced by a short in vitro culture, as assessed by significant down-regulation of co-stimulation (CD40, CD54, CD80, CD86) and maturation markers (CD83, CCR7), which correlated to an impaired ability of the cells to mount allogeneic T cell proliferation. Furthermore, the ganglioside-treated cells displayed less ability to migrate towards CCL19/macrophage inflammatory protein 3 beta, the chemokine that specifically binds CCR7 and mediates LC migration to lymph nodes. Lastly, we showed that both GM3 and GD3 gangliosides enhance LC spontaneous apoptosis. Globally, these in vitro results might explain, at least in part, the altered number and distribution of LCs in melanoma-bearing patients. They underscore a new mechanism for gangliosides to impede the host immune response by inducing LC dysfunction in the tumour microenvironment