Figure 4.

Recapitulating the human bone marrow microenvironment in mouse: A subcutaneous ossicle with mesenchymal components derived from human mesenchymal stromal cells is seeded by murine trilineage hematopoiesis and provides an easily accessible niche for xenotransplanted human myeloid neoplasms. (A) The overall ossicle architecture is similar to adult human bone marrow architecture, including trilineage hematopoiesis admixed with significant mature adipose tissue, interspersed trabecular bone (T), and visible sinusoids (S); the chondroid cap (Ch) which is the residuum of the initial chondrogenic MSC outgrowth is visible at the end of the ossicle; original magnification 40×; scale bar 25 μm; (B) Double immunofluorescence (DIF) for species non-specific vimentin (green), human-specific vimentin (red) and nuclei (blue) in a subcutaneous ossicle. The partially calcified chondroid cap (Ch) abuts admixed murine hematopoiesis visible as blue nuclei (H) and mature adipose tissue (A). All mesenchymal-derived cells, including chondrocytes and bipolar cells, are human vimentin-positive as well as species-nonspecific vimentin-positive, resulting in a yellow-green color; no red mouse-derived mesenchymal population is present, confirming that the microenvironment is entirely human-derived; original magnification 40×; scale bar 25 μm; (C) Immunohistochemistry for human vimentin in an ossicle seeded with human acute myeloid leukemia. Human vimentin-positive arborizing stromal cells are visible within residual murine hematopoiesis, as are numerous human-vimentin positive leukemic blasts; original magnification 40×; scale bar 25 μm; (D) DIF for species human CD45 (green), human CD271 (red) and nuclei (blue) in a subcutaneous ossicle with xenotransplanted acute myeloid leukemia. Recapitulating the situation in human bone marrow, human myeloid blasts are associated with human-derived CD271+ MSCs original magnification 20×; scale bar 50 μm.