Meeting Report. From December 8 to 11, 2012 at Atlanta, GA, U.S.A

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1 Meeting Report Affiliation Department of Transfusion Medicine and Cell Therapy Name Hisayuki Yao Name of the meeting Period and venue Type of your presentation Title of your presentation The 54 th Annual Meeting of the American Society of Hematology From December 8 to 11, 2012 at Atlanta, GA, U.S.A 1) Invited lecture 2) Poster presentation 3) Workshop / Symposium 4) Others (Please explain specifically below ( ) Mesenchymal stem cells skewed their phenotype toward the osteogenic lineage support the hematopoietic cell differentiation 1. Summary of your presentation (Include what you learned from discussions with audience) The interaction between hematopoietic cells and bone marrow microenvironment is important for the regulation of hematopoiesis. Recent studies have identified the specific bone marrow microenvironment for the hematopoietic stem cells, the endosteal niche and the vascular niche, in which mesenchymal stem cells (MSCs) and their progenies including osteoblasts are demonstrated to be major cellular constituents. We found that osteogenesis-induced MSCs by the combinations of ascorbic acid, dexamethasone, and potassium dihydrogen phosphate have unique capabilities of both expanding CD34 + hematopoietic progenitor cells and of differentiating CD34 + hematopoietic progenitor cells into mature cells. The osteogenesis-induction was achieved by treating human MSCs with ascorbic acid, dexamethasone, and potassium dihydrogen phosphate (osteogenesis-inducing cocktails: OICS). When human MSCs were osteogenesis-induced by OICS for 4 weeks, MSCs differentiated into mature osteoblasts with abundant calcium accumulation assessed by Alizarin red S staining. However, when human MSCs were treated with OICS for short periods, they did not show apparent calcium accumulation but expressed early-stage osteogenic marker, osterix, and maintain differentiation capability to adipocytes. Intriguingly, purified CD34 + hematopoietic cells (5.0x10 3 cells/dish) were expanded to the number of 12.6±1.01x10 4 in 10 day co-cultures with the osterix positive osteogenesis-induced cells in StemSpan Medium (StemCell Technologies) supplemented with 100ng/mL SCF, 100ng/mL Flt-3 ligand, 50ng/mL TPO, and 20ng/mL IL-3. As a control, CD34 + hematopoietic cells were expanded to the number of 6.2±0.4x10 4 in co-cultures of pg. 1

2 unstimulated MSCs. Moreover, although the most of the hematopoietic cells expanded on unstimulated MSCs showed an immature blast-like morphology, the hematopoietic cells expanded in the co-cultures with OICS-stimulated MSCs showed a tendency to differentiate into the mature hematopoietic cells, which was supported by the expression of glycophorin-a and CD14 on the hematopoietic cells by FACS analysis. When purified CD34 + hematopoietic cells were co-cultured with OICS-stimulated MSCs in the transwell, the number of expanded CD34 + hematopoietic cells was decreased to 21.7%. In contrast, there was no apparent difference in the expression of differentiation markers in the expanded hematopoietic cells between the co-cultures in the presence and in the absence of transwell. Therefore, cell-cell interactions through surface membrane molecules were involved in CD34 + hematopoietic cells expansion mediated by OICS-stimulated MSCs, and soluble factors were mainly involved in the enhancement of hematopoietic differentiation. Real-time PCR analysis showed that the expression of CXCL12 and LIF was reduced in OICS-stimulated MSCs. Given that osteogenic stimulation of MSCs by OICS enhances the expansion and differentiation of CD34 + hematopoietic cells in vitro, we tested the possibility of in vivo administration of OICS to mice receiving bone marrow transplantation after myeloablative conditioning for obtaining quick hematopoietic recover. Lethally irradiated (9Gy) C57BL/6 mice were injected with OICS on day 1-7 after receiving total bone marrow transplantation. The number of leukocytes was decreased to bottom level around 7 days after transplantation in both OICS-treated and non-treated (control) mice. However, the number of leukocyte showed a rapid increase in OICS-treated mice compared with that in control mice. These results suggested that short-term osteogenic stimulation supports the hematopoietic recovery in vivo, probably in part, through acting on MSCs in bone marrow microenvironment. In conclusion, osteogenesis-induced, osterix positive MSCs have unique capabilities to enhance both expansion of CD34 + hematopoietic cells through surface membrane molecules, and differentiation of CD34 + hematopoietic cells into mature cells through soluble factors. This work suggests a possibility that pharmacological stimulation of MSCs could modify the bone marrow microenvironment through enhancement of biological potency of MSCs. Further studies are needed whether this strategy may be applied in the clinical settings. There is growing interest in bone marrow stromal cells. I was asked many questions from researchers. The questions were mainly about the techniques of handling MSCs. One researcher asked about the safety and predicted clinical effects of OICS. OICS are combination of clinically approved drugs and their safety is ensured. In mouse model, the number of leukocyte showed a rapid increase in OICS-treated mice. This result indicated pg. 2

3 that OICS have the potential for clinical use. 2. Other topics of your interest I have been interested in works related to the bone marrow microenvironment for hematopoietic cells. Aruna Kode, from Columbia University, presented her work on the relationship between Wnt signaling activity in osteoblast precursors and leukemogenic transformation of hematopoietic cells. They showed that constitutive activation of canonical Wnt signaling in osteoblast precursors disrupts hematopoiesis in mice by shifting the differentiation potential of hematopoietic stem cells (HSCs) progenitors to the myeloid lineage which results in accumulation of granulocyte/monocyte progenitors and concomitant development of acute myeloid leukemia (AML). The AML phenotype is associated with clonal evolution at the cytogenetic level since clonal abnormalities could be detected in leukemic blasts from mice with constitutive activation of the canonical Wnt target β-catenin in osteoblast precursors (β-catenin osb mice). Bone marrow transplantation experiments from β-catenin osb mice to wild type lethally irradiated mice resulted in development of AML within 8 weeks following transplantation, demonstrating progression towards AML. At the molecular level, cell-specific gene inactivation mouse models demonstrate that β-catenin interacts with FoxO1 in osteoblasts to induce development of AML. Downstream signaling events that confer osteoblast signaling to normal HSCs and lead to their leukemogenic transformation will be presented. Importantly, malignancy-inducing osteoblasts, detected by nuclear accumulation of β-catenin in bone marrow biopsies, were identified in > 25% of patients with myelodysplasia (MDS), AML or AML arising from a prior MDS. Specifically, 15 out of 53 patients with MDS (n=17 patients), AML (n=20 patients), or MDS that had transformed to AML (n=16) chosen at random showed nuclear localization of β-catenin in osteoblasts. Of note, 12 of the 15 (80%) patients with nuclear localization of β-catenin in osteoblasts had abnormalities of chromosome 5 and/or 7, very common cytogenetic abnormalities in patients with MDS and AML. The same signaling pathways mediating AML development in β-catenin osb mice were also found to be activated in osteoblasts and hematopoietic cells from the patients with nuclear accumulation of β-catenin in osteoblasts. These findings demonstrate that genetic alterations in osteoblast precursors can induce AML in mice and are associated with AML development in humans. They also provide a molecular basis for the leukemogenic transformation. Dr. Yen-Michael S. Hsu, Washington University School of Medicine, presented his work on the stromal cells composing HSCs. CXCL12 is a key component of the stem cell niche that regulates HSC trafficking and function. CXCL12 is constitutively expressed by several pg. 3

4 stromal cell populations, including endothelial cells, osteoblasts, and perivascular stromal cells. They generated a floxed allele of Cxcl12 to conditionally delete Cxcl12 from candidate niche cells in the bone marrow and assess the effect on HSCs. Deletion of Cxcl12 in endothelial cells and mature osteoblasts was mediated by the Tie2-Cre recombinase (Cre) and osteocalcin (Oc)-Cre transgenes, respectively. To target Cxcl12 deletion in CXCL12-abundant reticular (CAR) cells and osteoprogenitors, they used the osterix (Osx)-Cre transgene. Finally, to target multipotent mesenchymal progenitors, they used the Prx1-Cre transgene. Prx1 is a transcription factor expressed early during limb bud mesoderm development, and Prx1-Cre targets all cells derived from limb bud mesoderm. They first performed lineage mapping studies using transgenic mice carrying a knock-in of the green fluorescent protein (GFP) gene into the Cxcl12 locus. As reported previously, the highest CXCL12 expression was observed in CAR cells, which is a heterogeneous perivascular stromal cell population that contains osteoprogenitors. Lineage mapping with Osx- and Prx1-Cre show that both transgenes mediate efficient and equivalent recombination in nearly all mature osteoblasts, osteoblast progenitors, and CAR cells. Prx1-Cre, but not Osx-Cre, also targets a novel subset of PDGFRα Sca mesenchymal progenitors. They showed that deletion of Cxcl12 from mature osteoblasts has no effect on HSC number or function. Deletion of Cxcl12 from Osx-Cre-targeted stromal cells, which includes osteoprogenitors and CAR cells, results in constitutive mobilization of hematopoietic progenitors; however, HSC number and function are normal. Cxcl12 deletion in endothelial cells results in a modest loss of long-term repopulating activity. Strikingly, deletion of Cxcl12 in mesenchymal progenitors is associated with a marked loss of HSCs and HSC quiescence. In addition to endothelial cells, they thus identified a novel Prx1-Cre targeted subset of mesenchymal progenitors that appears to be necessary to support HSCs. These data showed that expression of CXCL12 from stromal cells in the perivascular region is required for HSC maintenance. pg. 4

5 3. Your impression of the meeting (e.g., major trends in the field, status and contribution of your study and/or studies in Japan to the field, etc.) American Society of Hematology (ASH) is the world leading organization in the hematology all over the world. The four-day meeting consists of a superb educational program and cutting-edge scientific sessions. Though these programs and the oral sessions started from early morning and lasted long time, every hall was filled with excitement. In addition to these programs and the oral sessions, there were many poster presentations. These oral and poster sessions were highly beneficial in my research. I got the latest knowledge of bone marrow microenvironment and transplantation therapy. I can utilize the expertise acquired from this meeting to develop my up-coming research activity. Finally, I would like to express my gratitude to global-coe for giving me an opportunity to attending the ASH meeting. pg. 5