BRAF-V600E expression in precursor versus differentiated dendritic cells defines clinically distinct LCH risk groups

Area of Science:

• Immunology
• Oncology
• Genetics

Background:

• Langerhans cell histiocytosis (LCH) is a rare clonal disorder of dendritic cells (DCs) with unknown causes.
• BRAF-V600E mutations are frequently found in LCH lesions.

Purpose of the Study:

• To investigate the role of BRAF-V600E mutations in LCH pathogenesis and clinical risk stratification.
• To differentiate the cellular origin of high-risk versus low-risk LCH.

Main Methods:

• Genotyping of LCH lesions from 100 patients.
• Analysis of BRAF-V600E mutation presence in circulating cells and bone marrow progenitors.
• Induction of LCH-like disease in mice by expressing BRAF-V600E in DCs.

Main Results:

• BRAF-V600E mutation was found in 64% of LCH lesions, specifically within CD207(+) DCs.
• High-risk LCH patients showed BRAF-V600E in circulating cells and bone marrow progenitors, unlike low-risk patients where it was restricted to lesional DCs.
• Mouse models confirmed BRAF-V600E expression in DCs can cause LCH-like disease, with progenitor mutations mimicking high-risk LCH.

Conclusions:

• LCH may be classified as a myeloid neoplasia.
• High-risk LCH likely arises from somatic mutations in hematopoietic progenitors, whereas low-risk LCH originates from tissue-restricted DC precursors.