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Embryonic hematopoiesis is a complex process. Elucidating the mechanism regulating hematopoietic differentia- tion from pluripotent stem cells would allow us to establish a strategy to efficiently generate hematopoietic cells. How- ever, the mechanism governing the generation of hematopoietie progenitors from human embryonic stem cells （hESCs） remains unknown. Here, on the basis of the emergence of CD43＋ hematopoietic cells from hemogenic endothelial （HE） cells, we demonstrated that VEGF was essential and sufficient, and that bFGF was synergistic with VEGF to specify the HE cells and the subsequent transition into CD43＋ hematopoietic cells. Significantly, we identified TGFI5 as a novel signal to regulate hematopoietic development, as the TGFβ inhibitor SB 431542 significantly promoted the transition from HE cells into CD43＋ hematopoietic progenitor cells （HPCs） during hESC differentiation. By defining these critical signaling factors during hematopoietic differentiation, we can efficiently generate HPCs from hESCs. Our strategy could offer an in vitro model to study early human hematopoietic development.

Dendritic cells （DCs） and monocyte subpopulations present in the human spleen were analyzed by flow cytometry in an attempt to identify the presence of a novel dendritic-like cell subset described previously in mice and named L-DCs. In this study, an equivalent of this novel murine subset was characterized in the human spleen, thus increasing our knowledge of the antigen-presenting cell types present in the human spleen. Human L-DCs were identified as a hCD11c~hCD11b＋HLA-DR-hCD86＋ subset in the spleen, along with the previously described subsets of hCDlc＋ DCs, hCD123＋ plasmacytoid DCs （pDCs）, hCD16＋ DCs and hCD141＋ DCs. Three subsets of monocytes were also characterized. DC and monocyte subsets in human spleen had phenotypes similar to those of subsets in human blood. In line with murine studies, the presence of L-DC progenitors within the spleen was also investigated. When human splenocytes depleted of T and B cells were cocultured with the murine stromal line 5G3, hematopoiesis ensued and hCD11c＋HLA-DR＋ and hCD11c＋HLA-DR- cells were produced. The latter resemble L-DCs, which are also produced in murine spleen cocultures. Both subsets expressed hCDSO and hCD86, which identifies them as antigen-presenting cells, particularly DCs, and were highly endocytic. It is noteworthy that murine splenic stroma can serve as a support matrix for human hematopoiesis and DC production. These results support the hypothesis that 5G3 must express both cell-associated and soluble factors that can signal hematopoiesis in human and murine progenitors.

Human embryonic stem cells （hESCs） have been successfully differentiated into hematopoietic progenitor cells with colony formation capacity and further into various kinds of blood cells including erythrocytes, megakaryocytes, neutrophils, nature killer cells and T lymphocytes . Nevertheless, the differentiation efficiency is extremely low. The differentiation usually involves complex steps such as embryonic body formation or co-culture with stromal cells, causing inconsistencies and difficulties in dissection of its molecular mechanisms [8,9]. Therefore, it is essential to establish a well-defined hematopoietic differentiation model that is independent of serum and stromal cells and much easier to manipulate genes for functional screening, thus the underlying molecular mechanism of hematopoietic differen- tiation of hESCs could be dissected more easily.

血小板生成素（thrombopoietin,TPO）是近年来发现的造血生长因子,参与巨核细胞增殖、分化、成熟并分裂成有功能的血小板的全部过程,是相对特异性调节巨核细胞系的细胞因子。还可以与G-CSF、EPO、IL-3等协同作用，促进红系与粒系祖细胞增殖，促进干细胞进入增殖周期。目前国内外均报道重组人血小板生成素（rhTPO）可减少白血病化疗后的血小板减少。但尚无rhTPO在老年急性髓细胞白血病（Acute Myelogenous Leukemia，AML）中应用的报道。我们应用rhTPO治疗老年AML患者完全缓解（CR）后巩固化疗导致的血小板减少症，观察其疗效及不良反应，报告如下。