Blood GMODP frequency is elevated in low-risk LCH patients and their myeloid cells contain the BRAF mutation. (A) The frequencies (%) of (G)MODP in blood from unifocal bone (UFB), multifocal bone (MFB), MS-RO⁻, and MS-RO⁺ LCH patients and age-matched HD. See supplemental Table 1 for clinical details of the patients. Error bars indicate median and interquartile range; P values according to statistical testing by Mann-Whitney U test (*P < .05; **P < .01, ***P < .001). (B-C) (G)MODP cells were sorted from blood, cultured under DC (B) or LC (C) differentiation, and counted and analyzed for cell-surface phenotype by flow cytometry. Live-cell yield from 500 (G)MODP and the frequencies (%) of DC (HLA-DR⁺CD11c⁺CD14⁻) or LC-like cells (HLA-DR⁺CD11c⁺CD1a⁺CD207⁺) among live (G)MODP-derived offspring cells are represented for HDs (n = 5) and patients LCH_002, 005, 006, 013 (MS-RO⁺), 014 (MFB), and 019 (UFB) (n = 6) (supplemental Table 1). P values according to statistical testing by Mann-Whitney U test (**P < .01). (D) GMODP from BM and blood of the indicated BRAF^V600E genotyped high-risk MS-RO⁺ LCH patients were seeded at 1500 to 2000 cells per well and cultured under DC-differentiation conditions, and the BRAF mutation was assessed by ddPCR in offspring cells. (E) BRAF mutation status of DCs, Mo’s, B cells, T cells, and granulocytes (Gr) from indicated LCH patients (supplemental Table 1).