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Juvenile myelomonocytic leukemia (JMML) is a mixed myeloproliferative and myelodysplastic disorder that occurs in early childhood. The clinical course of JMML is highly variable. A third of patients follow a relatively indolent course, although approximately 15 % cases are thought to develop acute myeloid leukemia, referred to as blast crisis. The etiology and clinical characteristics of blast crisis remain unclear. We document the case of a 27-month-old boy who presented with hepatosplenomegaly, skin rash, and lymphadenopathy. An initial diagnosis of acute erythroid leukemia was made according to the French–American–British classification. Following estimation of hypersensitivity to GM-CSF and genetic analysis of PTPN11, he was diagnosed with JMML in the blast crisis phase. Although he had several poor prognostic factors, including monosomy 7 and high HbF percentage, he achieved partial remission after treatment with acute myeloid leukemia-oriented chemotherapy followed by allogeneic hematopoietic stem cell transplantation. He has been in complete remission for over 6 years.

Aplastic anemia (AA) is characterized by a reduced number of hematopoietic stem cells (HSCs), resulting in peripheral pancytopenia. Several pathogeneses for AA have been hypothesized, and among these, the autoimmune-associated hypothesis is considered to be the most likely [1, 2]. Mesenchymal stem cells (MSCs) have been shown to exert immunosuppressive capacity both in vitro and in vivo. Normal bone marrow (BM)-derived MSCs suppress T cell function and may provide an immunoprotected environment for HSCs [3, 4]. Bacigalupo et al. [5] reported that MSCs derived from the BM of adult AA patients are defective in their ability to suppress T cell proliferation and cytokine release. They hypothesized that these defects may result in increased activation/proliferation of BM T cells, which suppress HSCs in AA patients. The aim of the present study was to investigate whether MSCs from pediatric AA patients also exert decreased suppressive activity on T cells when compared with those derived from normal individuals. Bone marrow samples from 34 AA children (16 males, 18 females) and 15 healthy volunteers were obtained following informed consent from either patients or parents. Median patient age was 10 years (range 2–21 years). The timing of sampling was at diagnosis in 15 patients and after immunosuppressive therapy (IST) with anti-thymocyte globulin and cycrosporin A in 19 patients. Eleven of these were IST responders and eight were non-responders. Aplasia was secondary to acute hepatitis in four patients and the cause was unknown in 30 patients. Seven patients had very severe AA, 19 patients had severe AA and eight patients had moderate AA. Bone marrow mononuclear cells (MNCs) were isolated and cultured as reported previously [5]. Briefly, MNCs were plated in a 25-cm tissue culture flask with complete MesenCult Basal Medium (Stem cell technologies, Vancouver, Canada) containing human MSC supplements. Adherent cells were expanded to the third generation. Characterization of MSCs was determined by flow cytometry and their differentiation into adipogenic and osteoblastic lineages. Surface markers of the MSCs were CD29?, CD44?, CD90?, CD105?, CD73?, CD34-, CD45and CD14-. To demonstrate capacity of MSCs to differentiate to adipocytes, cells were further cultured at 2 9 10 cells/flask with MesenCult basal medium supplemented with human adipocytogenic supplements (Stem cell technologies). Adipogenic differentiation was confirmed by the presence of lipid droplets under optical microscopy after 3 weeks. Similarly, for differentiation to osteoblasts, MSCs were cultured with MesenCult basal medium supplemented with an osteogenic differentiation kit (Stem cell technologies) containing dexamethasone (0.1 lmol/l), ascorbic acid (0.05 mmol/l) and glycerophosphate (10 mmol/l). After 5 weeks of culture, cell layers were stained with silver nitrate (Von Kossa method) in order to detect calcium deposition, which indicates osteogenesis. There were no differences in the expression of MSC surface markers and the differentiation capacity between AA patients and normal individuals. Immunosuppressive activity of MSCs from pediatric patients with AA was tested by their inhibitory effects on PHA-induced T cell proliferation. Peripheral blood MNCs from normal adult volunteers (2 9 10) were dispensed Y. Xu Y. Takahashi A. Yoshimi M. Tanaka H. Yagasaki S. Kojima (&) Department of Pediatrics, Nagoya University Graduate School of Medicine, 65 Tsurumai-cho, Showa-ku, Nagoya 466-8550, Japan e-mail: kojimas@med.nagoya-u.ac.jp