Histologic analysis of human fetal BM sections engrafted with WM cells. Analysis was performed on decalcified fetal bone chips implanted in SCID-hu mice and directly injected with patient unsorted WM cells. Bone chips were retrieved from mice after detection of rising levels of human paraprotein in murine serum and then stained with H&E. Four representative sections show infiltration with small lymphocytes, lymphoplasmacytoid cells, and plasma cells in the context of intramedullary fibrosis and scant residual fetal hematopoiesis. Original magnifications are (A) × 100, (B) × 100, (C) × 100, and (D) × 400.