Morphologic appearance of BM-engrafted ROSA^{KIT WT} and ROSA^{KIT D816V} cells in NSG mice. Whole BM cells from NSG mice engrafted intravenously with (A) ROSA^{KIT WT} or (B) ROSA^{KIT D816V} cells were analyzed for their content of CD117⁺/CD45⁺ engrafted human MCs (A and B, top panels). The cells were also cytocentrifuged on glass slides, stained with MGG and then observed by using light microscopy (bottom panels). Note the presence of spindle-shaped MCs with an abnormal distribution of granules in the BM of mice engrafted with ROSA^{KIT D816V} cells (B, black arrows), whereas the BM MCs from mice engrafted with ROSA^{KIT WT} cells presented with a rounded shape, similar to the one observed in culture (A, gray arrows). Magnification is ×200. FL2-H, FL2 peak emission values; PerCP, peridinin chlorophyll.