Functional evidence for derivation of systemic histiocytic neoplasms from hematopoietic stem/progenitor cells

Langerhans Cell Histiocytosis (LCH) and the non-LCH neoplasm Erdheim-Chester Disease (ECD) are heterogeneous neoplastic disorders marked by infiltration of pathologic macrophage-, dendritic cell-, or monocyte-derived cells in tissues driven by recurrent mutations activating MAP kinase signaling. Although recent data indicate that at least a proportion of LCH and ECD patients have detectable activating kinase mutations in circulating hematopoietic cells and bone marrow-based hematopoietic progenitors, functional evidence of the cell-of-origin of histiocytosis from actual patient materials has long been elusive. Here we provide evidence for mutations in MAP kinase signaling intermediates in CD34 + cells from patients with ECD and LCH/ECD, including detection of shared origin of LCH and acute myelomonocytic leukemia driven by TET2 -mutant CD34 + cell progenitors in one patient. We also demonstrate functional self-renewal capacity for CD34 + cells to drive the development of histiocytosis in xenotransplantation assays in vivo. These data indicate that the cell-of-origin of at least a proportion of patients with systemic histiocytoses resides in hematopoietic progenitor cells prior to committed monocyte/macrophage or dendritic cell differentiation and provide the first example of a patient-derived xenotransplantation model for a human histiocytic neoplasm.