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Epigenomics and Single-cell Sequencing Define a Developmental Hierarchy in Langerhans Cell Histiocytosis

ABSTRACT: Langerhans cell histiocytosis (LCH) is a rare neoplasm predominantly affecting children. It occupies a hybrid position between cancers and inflammatory diseases, and it provides an attractive model for studying cancer development. To explore the molecular mechanisms underlying the pathophysiology of LCH and its characteristic clinical heterogeneity, we investigated the transcriptomic and epigenomic diversity in primary LCH lesions. Using single-cell RNA sequencing, we identified multiple recurrent types of LCH cells within these biopsies, including putative LCH progenitor cells and several subsets of differentiated LCH cells. We confirmed the presence of proliferative LCH cells in all analysed biopsies using immunohistochemistry, and we defined an epigenomic and gene-regulatory basis of the different LCH cell subsets by chromatin accessibility profiling. In summary, our single-cell analysis of LCH uncovered an unexpected degree of cellular, transcriptomic, and epigenomic heterogeneity among LCH cells, indicative of complex developmental hierarchies in LCH lesions.

PROVIDER: EGAS00001003822 | EGA |

REPOSITORIES: EGA

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Project description:Langerhans-cell histiocytosis (LCH) is characterized by heterogeneous lesions containing CD207+ Langerhans cells (LCs) and lymphocytes. In this study, we isolated CD207+ cells and CD3+ T cells from LCH lesions to determine cell-specific gene expression. Compared to control epidermal CD207+ cells, the LCH CD207+ cells yielded 2113 differentially-expressed genes (FDR<0.01). Surprisingly, expression of many genes previously associated with LCH, including cell-cycle regulators, pro-inflammatory cytokines and chemokines were not significantly different from control LCs in our study. However, several novel genes whose products activate and recruit T cells to sites of inflammation, including SPP1 (osteopontin), were highly over-expressed in LCH CD207+ cells. Furthermore, several genes associated with immature myeloid dendritic cells were over-expressed in LCH CD207+ cells. Compared to the peripheral CD3+ cells from LCH patients, the LCH lesion CD3+ cells yielded only 162 differentially-regulated genes (FDR<0.01), and the expression profile of the LCH lesion CD3+ cells was consistent with an activated regulatory T cell phenotype with increased expression of FOXP3, CTLA4 as well as SPP1. Based on these results, we propose a new model of LCH pathogenesis in which lesions do not arise from epidermal Langerhans cells, but from accumulation of bone-marrow derived immature myeloid dendritic cells that recruit activated lymphocytes. Cell-specific gene expression from LCH biopsy specimens was evaluated by comparing hybridization signal from amplified cDNA on Affymetrix gene chips (U133A Plus 2.0) (Table1). Three sets of comparisons were performed: 1) Thirteen LCH CD207+ samples were compared to 12 control skin LCH CD207+ samples. 2) Seven LCH lesion CD3+ samples were compared to 7 peripheral blood CD3+ samples from the same patients. 3) Twelve LCH lesion CD3+ samples were compared to 4 pooled control tonsil CD3+ samples (5 individual tonsil CD3+ samples/pool).

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Epigenomics and Single-cell Sequencing Define a Developmental Hierarchy in Langerhans Cell Histiocytosis

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