Detection of BRAF mutation-bearing GMODP in the BM of high-risk LCH patients. (A) Scheme depicting the position of GMODP in the hematopoietic tree. The GMODP is a redefinition of the GMP, based on defined oligopotency, as determined by dedicated in vitro differentiation cultures.²⁶  CLP, common lymphoid progenitor; EMP, erythroid-myeloid progenitor; HSC, hematopoietic stem cell; LMPP, lymphoid-primed myeloid progenitor; MPP, multipotent progenitor. (B) The frequencies (%) of (G)MODP (Lin⁻CD34⁺c-Kit⁺Flt3⁺) cells among total live cells in BM samples of MS-RO⁺ LCH patients (LCH_002, 005, and 013) and 4 age-matched HDs, as determined by flow cytometry. For the gating strategy used, see supplemental Figure 2A. (C) Culturing scheme. (D-I) (G)MODP cells were sorted from BM of LCH_005 and cultured under DC-differentiation conditions (Flt3L; D-F) or LC-differentiation conditions (TGF-β and TNF-α; G-I) and analyzed for appearance by light microscopy (D,G), cell-surface phenotype by flow cytometry (E,H), and BRAF^V600E mutation status by ddPCR (F,I). (F) Droplets containing BRAF^WT or BRAF^V600E PCR products are depicted by the green and blue dots, respectively. Orange dots represent droplets containing both PCR products. The numbers of droplets analyzed are indicated in the quadrants. (I) BRAF mutation scoring method (−, ±, +, ++, and +++) is explained in supplemental Materials and methods and supplemental Figure 1B. RFU, relative fluorescence units.