Dissecting the Transcriptomic Landscape of Circulating Mononuclear Phagocytes in Langerhans Cell Histiocytosis at Single-cell Level

Langerhans cell histiocytosis (LCH) is a rarely clonal disorder caused by aberrant activation of MAPK pathway, which predominantly affects the mononuclear myeloid lineages. Many efforts have been devoted to tracking precursor cells in circulating blood and bone marrow by detection of BRAFV600E alleles and to exploring the differentiation potential of LCH-related myeloid cells in vitro. However, their cellular and molecular alterations remain unclear. Here, we constructed a single-cell transcriptional landscape of more than 3,000 monocytes and DCs from treatment-naïve pediatric LCH and targeted-therapy pediatric LCH cohorts, unraveling patient to patient heterogeneity and underlying molecular mechanisms of BRAF inhibitor, respectively. In parallel, we further investigated the precise relationship between circulating potential precursors and pathological LCH clusters based on unbiased joint analysis. In addition, we found that the proportion of pDC in Lin-HLA-DR+ population is closely linked with the severity of the disease, providing a novel promising indicator to optimize the stratification strategy. Taken together, our data update the molecular understanding of LCH biology, which might contribute to improvement of clinical therapeutics and promotion of the personalized medicine. We performed the STRT-seq of 3,271 cells to generate transcriptomic landscapes of circulating monocytes and DCs closely related to tissue pathological cells in LCH patients.