Specific LCH mutations have differential sensitivity to BRAF and MEK inhibitors. (A,B) HE293 cells transiently transfected with expression plasmids encoding various cDNAs (A) or c.302_307del MAP2K1 lesion biopsy cell suspension (B) were treated with BRAF or MEK inhibitor for 1 hour, and corresponding lysates were subjected to immunoblotting with the indicated antibodies. (C) Median fluorescent intensity (MFI) of p-ERK1/2 in CD207⁺ cells determined through IFC analyses in patients harboring BRAFV600E (patients LCH5, LCH7, and LCH13) and MAP2K1 c.302_307del (patient LCH24) mutations, and patients with no somatic mutations (LCH30, LCH32, LCH37, LCH38, and LCH40) posttreatment with BRAF or MEK inhibitor.