Patient-derived bone marrow successfully engrafts primarily and secondarily in immunodeficient mice. (A) Representative flow cytometry scatterplots of human (h; x-axis) vs mouse (m; y-axis) engraftment of xenograft recipients following transplant of bone marrow from either RO-positive patients with hematopoietic involvement (BM+, right) or from an LCH patient without bone marrow involvement (BM−, left). (B) Survival curves of xenografted experimental animals. Survival between control and NSGS mice was statistically significant (*P < .01) by log-rank test. (C) Comparison between spleen sizes in control and experimental groups, with representative spleen images. (D) Hematologic abnormalities observed in BM+ and BM− transplanted animals. Error bars represent mean ± standard deviation. Statistical significance determined by Student t test. (E) Bone marrow histology from representative animals (original magnification ×400). (F) Representative flow scatterplots of bone marrow and spleens from a secondary transplant recipient animal. (G) Bone marrow from secondary transplant NSGS mouse shows a similar infiltration of histiocytes with abundant eosinophilic cytoplasm (left, original magnification ×400) and cytospins of splenocytes demonstrate frequent hemophagocytosis (white arrowheads) with numerous large, activated and vacuolated macrophages (right, original magnification ×1000). H&E, hematoxylin and eosin stain; WBC, white blood cell.