Regulation of Hematopoietic Differentiation from Pluripotent Stem Cells by HOXB4 and Niche Factors

胚胎发育过程中造血干细胞（HSCs）的生成在时间和空间上受到内在因素和外在微环境（“生态位”）的严格控制。造血干细胞似乎是从胚胎血管中的生血内皮细胞重新产生的，它们在胚胎血管中接种胎儿肝脏和成人骨髓。多能胚胎干细胞（ES-）的分化可以重演造血的许多方面，在体外，甚至可以产生细胞移植到受体小鼠后，能够长期多谱系再增殖，当同源结构域转录因子HOXB 4异位表达。因此，ES细胞分化系统对于详细了解血液形成过程具有重要价值。此外，它在造血细胞和基因治疗方面也有很好的应用前景。自从允许我们将体细胞重编程回ES细胞样状态的技术出现以来，从患者特异性的所谓诱导多能干细胞（iPS）细胞产生HSC显示出未来治疗应用的巨大前景。在这项中德联合申请中，我们将研究表达HOXB 4的分化ES细胞的特化和造血承诺，以及新型小生境衍生细胞系支持从小鼠和人类多能干细胞体外生成完全成熟HSC的能力。

Generation of hematopoietic stem cells (HSCs) during embryonic development is spatially and temporally tightly controlled by intrinsic factors and the extrinsic microenvironment, the “niche”. HSCs appear to arise de novo from hemogenic endothelial cells residing in embryonic vessels from where they seed the fetal liver and the adult bone marrow. Differentiation of pluripotent embryonic stem (ES-) cells can recapitulate many aspects of hematopoiesis, in vitro, and can even generate cells capable of long-term multilineage repopulation after transplantation into recipient mice, when the homeodomain transcription factor HOXB4 is ectopically expressed. Thus, the ES-cell differentiation system is of great value for a detailed understanding of the process of blood formation. Furthermore, it is also promising for future application in hematopoietic cell- and gene therapy. Since the arrival of techniques which allow us to reprogram somatic cells back to an ES-cell like state, the generation of HSCs from patient-specific so-called induced pluripotent stem (iPS) cells shows great promise for future therapeutic applications. In this Chinese-German joint application, we will investigate the specification and hematopoietic commitment of differentiating ES-cells expressing HOXB4 and the capability of novel niche-derived cell lines to support the in vitro generation of fully mature HSCs from mouse and human pluripotent stem cells.