Transamniotic stem cell therapy (TRASCET) in a rabbit model of spina bifida

Purpose

Transamniotic stem cell therapy (TRASCET) with select mesenchymal stem cells (MSCs) has been shown to induce partial or complete skin coverage of spina bifida in rodents. Clinical translation of this emerging therapy hinges on its efficacy in larger animal models. We sought to study TRASCET in a model requiring intra-amniotic injections 60 times larger than those performed in the rat.

Fetal bone marrow homing of donor mesenchymal stem cells after transamniotic stem cell therapy (TRASCET)

Purpose

Donor cell engraftment patterns following transamniotic stem cell therapy (TRASCET) with amniotic fluid mesenchymal stem cells (afMSCs) are incompatible with solely direct amniotic seeding. We sought to determine whether fetal bone marrow is a component of such engraftment and to examine the chronology of afMSC placental trafficking.

A comparison of clinically relevant sources of mesenchymal stem cell-derived exosomes: Bone marrow and amniotic fluid

Background/Purpose

Exosomes may constitute a more practical alternative to live cells in select stem cell-based therapies. We sought to compare exosomes from two mesenchymal stem cell (MSC) sources relevant to perinatal and pediatric diseases.

Percutaneous fetoscopic patch closure of human spina bifida aperta: advances in fetal surgical techniques may obviate the need for early postnatal neurosurgical intervention

Background  A percutaneous minimally invasive fetoscopic approach was attempted for closure of a spina bifida aperta in two fetuses with L5 lesions. The goal was to obviate the need for postnatal neurosurgery to manage this condition. Methods and Results  The percutaneous fetoscopic procedures were performed by a two-layer approach at respectively 22 ± 2 and 22 ± 4 weeks of gestation. The fetuses were delivered respectively at 32 ± 6 and 32 + 3 weeks of gestation. Their neural cords were completely covered although in small areas skin closure was incomplete. Postnatally, complete skin closure occurred beneath an occlusive draping within 2 to 3 weeks such that neurosurgical intervention was not required. Both neonates showed reversal of hindbrain herniation, near-normal leg function, and satisfactory bladder and bowel function. For one of the two fetuses, ventriculoperitoneal shunt insertion was not required. Conclusions  Percutaneous minimally invasive fetoscopic patch closure of spina bifida aperta offers a substantially less maternal trauma than open fetal surgical repair and currently may even obviate the need for postnatal neurosurgical repair. With a little further improvement in surgical techniques and a better understanding of incorporating surgical patches into the fetus, complete skin closure seems possible in the near future.     

人羊水间充质干细胞的分离鉴定及其对抗Thy-1肾炎的治疗作用

探讨羊水间充质干细胞(amniotic fluid mesenchymal stem cells,AF-MSCs)对抗Thy-1肾炎模型的治疗作用。 方法采用差异性贴壁与机械性分离法从人孕中期羊水中分离出羊水间充质干细胞,流式细胞术鉴定其表面标志物,成脂、成骨诱导分化检测其分化能力。利用尾静脉注射抗Thy-1抗体建立SD大鼠抗Thy-1系膜增生性肾炎模型;将第5代羊水间充质干细胞通过尾静脉注射治疗抗Thy-1系膜增生性肾炎大鼠,检测大鼠尿蛋白的变化,PAS染色观察大鼠肾脏病理改变。 结果羊水间充质干细胞顺利分离,流式结果显示其表达间充质干细胞标志物(CD29、CD44、CD73、CD90、CD105)和胚胎干细胞标志物(SSEA-4)而不表达造血干细胞标志物(CD34、CD45、CD133),且在适当条件下能够被诱导分化为脂肪细胞和骨细胞。羊水间充质干细胞治疗后,与模型组相比,治疗组在第7、12天时24 h尿蛋白明显下降(P<0.01),且肾脏病理结果表明系膜细胞增殖减轻,系膜区细胞外基质积聚减少。 结论成功的从人孕中期羊水中分离出羊水间充质干细胞,羊水间充质干细胞治疗系膜增生性肾小球肾炎有效。     

骨髓间充质干细胞及其诱导成骨的研究进展

间充质干细胞(MSCs)是一种多潜能成体干细胞,主要存在于骨髓,还存在于胚胎时期间充质来源的骨外组织[1],如皮肤成纤维细胞、脂肪干细胞、骨骼肌的卫星细胞和血管内皮细胞等。骨髓MSCs(BMSCs)是骨髓基质的组成成分,体外分离培养后,在一定的诱导条件下,BMSCs具有向成骨细胞、软骨细胞、神经细胞、脂肪细胞、心肌细胞等多向分化的能力[2-3],这些细胞经过20～30个培养周期,仍能保持多向分化潜能。无论是自体的还是同种异源的BMSCs,一般都不会引起宿主的免疫反应。BMSCs以其来源充足、取材简便、对供体损伤小、易于分离培养、体外增殖能…     

Development and characterization of novel clinical grade neonatal porcine bone marrow‐derived mesenchymal stem cells

Due to recent advances in research on mesenchymal stem cells (MSCs), MSCs are expected to be used in various clinical applications. However, securing adequate cadaveric donors and safety of living donors are major issues. To solve such issues, we have examined to develop clinical grade neonatal porcine bone marrow‐derived MSCs (npBM‐MSCs). Clinical grade neonatal porcine bone marrow cells were collected, frozen, and sent to our laboratory by air. The npBM‐MSCs were isolated from thawed bone marrow cells, then frozen. The thawed npBM‐MSCs were examined for CD markers and differentiated into chondrocytes, osteocytes, and adipocytes. They were compared with human bone marrow‐derived MSCs (hBM‐MSCs) for growth rate and size. To assess the robustness of proliferation, we compared culture medium with or without gelatin. The npBM‐MSCs expressed positive MSC markers CD29, CD44, and CD90 and were differentiated into chondrocytes, osteocytes, and adipocytes. The doubling time of npBM‐MSCs was significantly shorter than that of hBM‐MSCs (17.3 ± 0.8 vs 62.0 ± 19.6 hours, P < 0.01). The size of npBM‐MSCs was also significantly smaller than that of hBM‐MSCs (13.1 ± 0.3 vs 17.5 ± 0.4 μm, P < 0.001). The npBM‐MSCs showed similar proliferation characters irrespective of with or without gelatin coating. The npBM‐MSCs secreted VEGF‐A, VEGF‐C, and TGF‐β1. We have established npBM‐MSCs which show super‐rapid growth, small size, and robust proliferation profile. The np‐MSCs might be able to solve the donor issues for MSC therapy.     

诱导小鼠骨髓间充质干细胞向雄性生殖细胞的定向分化

目的探讨小鼠骨髓间充质干细胞是否能够在体外被诱导发生向雄性生殖细胞方向的分化。方法从雄性小鼠骨髓中分离能够长期贴壁生长的细胞,并鉴定其是否为间充质干细胞。对分离的细胞进行生殖细胞特异性报告基因标记(stra-8-GFP)。采用视黄酸诱导标记的细胞发生向生殖细胞方向的分化。通过观察报告基因表达和生殖细胞相关基因mRNA表达情况确定是否发生了分化。结果从小鼠骨髓中分离到的贴壁生长的细胞表达间充质干细胞的表面标志CD90、CD44、CD105和Sca-1;细胞在体外可以被诱导分化为成骨、成软骨及成脂肪细胞。报告基因标记的间充质干细胞在被视黄酸诱导2d后开始表达绿色荧光蛋白和生殖细胞相关基因Mvh、Fragilis和Stella的mRNA。未经视黄酸诱导的细胞不表达绿色荧光蛋白和生殖细胞相关基因。结论小鼠骨髓间充质干细胞在体外可以被视黄酸诱导发生向雄性生殖细胞方向的分化。     

骨折后外周血间充质干细胞浓度变化的实验研究

[目的]观察骨折后不同时间点外周血间充质干细胞(MSCs)浓度变化,并比较其与骨髓间充质干细胞生物学特性的异同.[方法]根据不同处理条件将SD大鼠分为:对照组和骨折组(骨折后1、3、7d共3组),每组20只.分别于骨折后1、3、7d抽取外周血,密度梯度离心法分离培养外周血MSCs,计数成纤维细胞集落形成单位(CFU-Fs)数.流式细胞仪检测细胞表面标记(CD44、CD90、CD34、CD45).成骨、成脂诱导,碱性磷酸酶、茜素红和油红染色检测其分化特性.[结果]原代外周血MSCs呈集落生长,骨折组集落数明显多于对照组,其中以骨折后3d组形成的集落数最多,具有显著差异(27.25±11.52 CFU-Fs/cuhure vs 2.80±3.96 CFU-Fs/culture,P＜0.01).外周血MSCs高表达CD44、CD90,低表达CD34、CD45,不同的是CD34小部分呈阳性(＜20％).与对照组骨髓MSCs的诱导结果相同,外周血MSCs成骨诱导后28 d出现钙结节,茜素红染色阳性;成脂诱导后21 d有大量脂滴出现,油红染色阳性.[结论]外周血体外密度梯度离心法分离培养的细胞具有多潜能分化的MSCs表面标记且可以向成骨、成脂分化.骨折后外周循环中MSCs数量明显增多,呈一定的时序性变化,可能参与骨折修复.     

A comparative analysis of human mesenchymal stem cell response to hypoxia in vitro: Implications to translational strategies

Purpose

Mesenchymal stem cells (MSCs) are particularly valuable for structural tissue replacement. We compared the response to hypoxia among human MSCs derived from four different clinically relevant sources as an adjunct to translational developments.

Methods

Immunophenotypically indistinguishable human MSC lineages derived from bone marrow (bmMSCs), adipose tissue (adMSCs), amniotic fluid (afMSCs), and umbilical cord blood (cbMSCs) were submitted to either room air or 1% O₂, under otherwise standard culture conditions. Cell expansion and quantitative RT-PCR data were obtained at different time points. Statistical analysis was by two-way mixed model and the F-test (P < 0.05).

Results

The effect of hypoxia on expansion kinetics was dependent on cell source. Only prenatal sources of MSCs – afMSCs (P = 0.002) and cbMSCs (P < 0.001) – proliferated significantly faster under hypoxia than normoxia. Increased HIF1-alpha expression correlated consistently with increased cell expansion only among afMSCs. There were no significant variabilities in Survivin, Oct-4, and VEGF expressions.

Conclusions

Mesenchymal stem cell tolerance to hypoxia in vitro varies with cell source. Prenatal cells, particularly those derived from amniotic fluid, are more robust than their postnatal counterparts. HIF1-alpha may play a role in the amniotic fluid-derived cells’ enhanced response. These findings should inform the choice of mesenchymal stem cells for prospective regenerative strategies.     

LncRNA DANCR调控骨髓间充质干细胞成骨分化在骨质疏松症中的研究进展

骨质疏松症(osteoporosis,OP)是一种中老年人易患的骨代谢性疾病,以骨密度减低和骨微结构破坏为特征,可导致骨脆性增加和骨折风险增大。随着OP分子机制研究的深入,针对相关细胞调控通路的治疗靶点被陆续发现,通过这些靶点可研发出新的靶向治疗方案。lncRNA分化拮抗非蛋白编码RNA(differentiation antagonizing non-protein coding RNA,DANCR)能够通过竞争结合、作为转录辅助因子等方式作用于Wnt/β-catenin、MAPK及NF-κB等信号通路调控BMSC成骨分化,影响OP的发生与进展。DANCR具有作为OP临床诊断标志物的潜力,并有希望作为药物干预的靶点参与OP的精准医疗。     

BMSCs向心肌分化的基因表达谱分析

目的分析hBMSCs经5-氮杂胞苷(5-azacytidine,5-aza)诱导向心肌样细胞分化过程中基因表达谱的改变。方法取胸外科非血液病患者手术中废弃的肋骨骨髓分离培养hBMSCs,5-aza诱导第2代hBMSCs。取诱导前及诱导后的细胞,免疫细胞化学法检测α-actin、肌钙蛋白T(cardiac troponin T,cTnT)和连接蛋白43(connexin 43)表达,流式细胞仪检测cTnT阳性细胞百分率;利用人表达谱基因芯片技术筛选分化过程中的差异表达基因,对部分基因进行功能分类和分层聚类分析。结果 hBMSCs经5-aza诱导后,部分呈肌细胞样形态。免疫细胞化学染色检测示诱导前细胞α-actin、cTnT染色呈弱阳性,connexin 43染色呈阴性;诱导后3周细胞α-actin、cTnT、connexin 43染色均呈阳性。流式细胞仪检测示诱导前cTnT阳性细胞百分率为7.43%±0.02%,诱导后3周为49.64%±0.05%。分化过程中共检测到1 814个显著差异表达基因,对其中647个基因分层聚类,聚为5类,生物功能包括信号传导、细胞代谢、增殖分化、发育以及形态发生等。结论 hBMSCs经5-aza诱导向心肌样细胞分化过程受信号传导通路、转录基因、生长因子等多种因素在不同时间点上的共同调控。     

Association of uterine activity and maternal volatile anesthetic exposure during open fetal surgery for spina bifida: a retrospective analysis

BackgroundRecent warnings postulate a possible damaging effect of volatile anesthetics on the fetus. In our archive of fetal surgeries, we found wide variation in dosing of volatile anesthetics during spina bifida surgeries. We hypothesized that there was an association between volatile anesthetic exposure and uterine activity.MethodsSixty anesthesia records from spina bifida operations were assessed. We analyzed the course of the administered volatile anesthetic during surgery and calculated from each patient’s anesthesia record the volatile anesthetic exposure expressed in vol%h. We divided the records into two post hoc groups of the 20 lowest exposure (Group L) versus the 20 highest exposure (Group H), and compared them for uterine activity and fetal heart rate.ResultsThe number of contractions per hour was significantly greater in Group H (mean 1.3, SD ± 1.2) compared with Group L (mean 0.5, SD ± 0.6, P=0.049). There was no difference between the groups for the administration of the tocolytic drug atosiban (P=0.29). The course of the mean arterial pressure did not significantly differ but group H needed significantly more vasoactive medication (P <0.05).ConclusionsWe found that a lower intra-operative volatile anesthetic exposure than recommended in the MOMS-trial (i.e. <2.0 minimum alveolar concentration [MAC]) was not associated with an increase in intra-operative uterine activity. This is an indication that during spina bifida surgery, 2.0 MAC may not be necessary to avoid potentially harmful uterine activity.     

骨髓间充质干细胞来源的外泌体对骨再生机制研究

目的本研究旨在检测骨髓间充质干细胞外泌体(BMSC-Exos)的特征,并通过体内体外实验探讨其对成骨分化的影响及对骨再生的机制。方法①原代培养人骨髓间充质干细胞(BMSCs),并对其表面抗原和多系分化潜能进行鉴定;②收集BMSC的P4～P6代细胞培养的培养上清液,应用试剂盒提取BMSC-Exos;③透射电镜观察BMSC-Exos的形态结构,免疫电泳检测BMSC-Exos的表面抗原;④茜素红、ALP染色验证BMSC-Exos在体外成骨分化中的作用;⑤通过大鼠颅骨缺损动物模型验证BMSC-Exos在体内骨再生的作用;⑥通过免疫电泳和qRT-PCR检测加入BMSC-Exos后的成骨细胞中相关蛋白和基因的表达情况。结果①分离培养的BMSCs形态呈多角形或长梭形,表面抗原CD90、CD29、CD44为阳性,符合间充质干细胞的特征;②BMSC-Exos呈双面凹的圆形或椭圆形,直径约40～120 nm(81.7±19.9),表面抗原与BMSC一致;③经茜素红染色和ALP染色后,染色强度与Exo浓度呈正相关;④通过对大鼠颅骨缺损模型拍摄X片、组织学分析,外泌体可促进大鼠颅骨缺损的修复和新生骨的形成;⑤免疫电泳显示经外泌体处理后,BMSC中的OCN、Runx2、β-catenin蛋白含量增加,qRT-PCR结果显示Runx2、β-catenin的基因表达上调。结论 BMSC-Exos有促进骨再生的能力,并与上调Wnt/β-catenin通路有关。     

地塞米松干预人骨髓间充质干细胞分化的表观遗传学修饰

目的观察高浓度地塞米松(dexamethasone, Dex)作用于人骨髓间充质干细胞(human bone marrow mesenchymal stem cells, hBMSCs)的表观遗传修饰及对其分化作用的影响。方法①人骨髓间充质干细胞培养于ɑ-MEM完全培养基中,体外扩增,传至第4代,拍摄显微电镜图片评估细胞生长状态;②通过Real-time PCR检测经不同地塞米松浓度(1、10μmol/L)作用细胞3 d后Runx2、ALP、OPG、RANKL、Dnmt1(DNA methyltransferase 1)的mRNA表达;③Western-blot检测经1μmol/L浓度地塞米松作用的细胞7 d后Dnmt1、H3K4me3 (trimethylation of lysine 4 on histone H3)、H3K27me3(trimethylation of lysine27 on histone H3)蛋白表达;免疫荧光检测细胞核内H3K4me3、H3K27me3抗原-抗体复合物的表达;加予DNA甲基化抑制剂5-氮杂-2’-脱氧胞苷(5-Aza-2'-deoxycytidine, 5-aza-dC)干预,观察Runx2、OPG、RANKL、Col1a1、Dnmt1的mRNA表达,分析表观遗传相关基因在其中的作用。结果①Real-time PCR示高浓度(1、10μmol/L)地塞米松对骨髓间充质干细胞干预早期有促进其成骨分化的作用,Runx2、ALP、OPG、DNMT1基因表达增加;②Real-time PCR和Western-blot示中晚期1μmol/L地塞米松抑制间充质干细胞向成骨细胞分化;同时Dnmt1、H3K27me3蛋白表达增加,H3K4me3表达下降;免疫荧光检测示细胞核内H3K4me3、H3K27me3抗原-抗体复合物表达情况与Western-blot结果类似;③DNA甲基化抑制剂5-aza-dC可影响地塞米松对骨髓间充质干细胞的分化效应。结论地塞米松对骨髓间充质干细胞分化的效应具有双向性,与干预时间有关,表观遗传相关因子修饰也参与其作用的发生发展,这有助于从表观遗传学角度寻找治疗激素性骨质疏松的新方法。     

双份脐血移植后受者骨髓间充质干细胞嵌合情况

目的 研究双份脐血移植(DCBT)受者骨髓间充质干细胞(MSC)的嵌合状态.方法 急性粒细胞白血病M2a型男性患者1例,接受改良白消安环磷酰胺方案+抗胸腺细胞球蛋白(ATG)预处理,输注5个抗原(5/6)相合和4个抗原(4/6)相合的非血源脐血各1份,移植后19 d粒系造血重建.移植后87 d,采用密度梯度离心法分离DCBT后受者及正常供者的骨髓单个核细胞,分别培养MSC,用流式细胞术检测细胞表面标志,诱导其向成脂肪细胞和成骨细胞分化,应用逆转录聚合酶链反应法检测MSC表面造血及免疫相关分子的表达,短串联重复序列聚合酶链反应检测受者MSC、外周血、骨髓中供者细胞嵌合率.结果 移植后受者MSC与正常供者MSC具有相似的细胞形态、免疫表型以及分化潜能,均能表达白细胞介素6、干细胞因子、白血病抑制因子和粒-巨噬细胞集落刺激因子等造血及免疫相关分子的mRNA.DCBT后受者骨髓优势脐血嵌合度达96.4％,外周血嵌合度达95.7％,MSC的优势脐血嵌合度为5.4％,MSC中受者本身部分占94.6％.结论 DCBT后,受者造血重建仅来自于其中1份脐血.移植后骨髓MSC大部分来源受者本身,部分嵌合的供者MSC来源于植入的单份脐血.     

兔骨髓基质干细胞体外分离培养及生物学特性研究

目的：研究兔骨髓基质干细胞（bone marrow-derived mesenchymal stem cells,BMSC）体外分离、诱导培养及增殖特点,探讨其生物学特性。方法：抽取兔骨髓,密度梯度离心结合贴壁培养法分离BMSC,诱导培养液定向诱导传代细胞向成骨细胞分化。倒置显微镜下观察细胞生长及增殖情况,流式细胞仪检测细胞表面标志物的表达,免疫组织化学观察Ⅰ型胶原表达,并检测碱性磷酸酶活性及细胞矿化作用。结果：体外培养的兔BMSC贴壁生长,10～14天后形成克隆。细胞形态为均一的长梭形并呈漩涡状排列,流式细胞仪检测CD34,CD45阴性,CD44阳性。免疫组化可检测到Ⅰ型胶原表达,碱性磷酸酶活性明显增高,并且出现矿化结节。结论：密度梯度离心结合贴壁培养BMSC,操作简单,细胞易于成活,诱导条件下成骨能力肯定,适合作为骨组织工程的种子细胞。     

Donor variation and loss of multipotency during in vitro expansion of human mesenchymal stem cells for bone tissue engineering.

The use of multipotent human mesenchymal stem cells (hMSCs) for tissue engineering has been a subject of extensive research. The donor variation in growth, differentiation and in vivo bone forming ability of hMSCs is a bottleneck for standardization of therapeutic protocols. In this study, we isolated and characterized hMSCs from 19 independent donors, aged between 27 and 85 years, and investigated the extent of heterogeneity of the cells and the extent to which hMSCs can be expanded without loosing multipotency. Dexamethasone-induced ALP expression varied between 1.2- and 3.7-fold, but no correlation was found with age, gender, or source of isolation. The cells from donors with a higher percentage of ALP-positive cells in control and dexamethasone-induced groups showed more calcium deposition than cells with lower percentage of ALP positive cells. Despite the variability in osteogenic gene expression among the donors tested, ALP, Collagen type 1, osteocalcin, and S100A4 showed similar trends during the course of osteogenic differentiation. In vitro expansion studies showed that hMSCs can be effectively expanded up to four passages (approximately 10-12 population doublings from a P0 culture) while retaining their multipotency. Our in vivo studies suggest a correlation between in vitro ALP expression and in vivo bone formation. In conclusion, irrespective of age, gender, and source of isolation, cells from all donors showed osteogenic potential. The variability in ALP expression appears to be a result of sampling method and cellular heterogeneity among the donor population.     

白茅苷对去卵巢大鼠骨髓间充质干细胞功能和骨量的影响

目的观察白茅苷治疗去卵巢大鼠骨髓间充质干细胞功能和骨量的影响并初步探索可能机制。方法通过双侧去卵巢建立骨质疏松大鼠模型;随后随机分为假手术组(Sham)、去卵巢组(OVX)以及白茅苷组(BMG),每组10只;其中BMG组去卵巢大鼠每天给予白茅苷(20 mg/kg)灌胃治疗;待12周治疗结束后分离培养各组大鼠骨髓间充质干细胞(BMSCs),使用碱性磷酸酶(ALP)和茜素红(ARS)染色并使用蛋白质印迹检测BMP-2、Runx2、OPN、OCN、ALP和Col1蛋白表达;进一步使用Micro-CT和骨生物力学检测观察治疗效果。结果 OVX组大鼠BMSCs向成骨细胞分化后ALP和ARS染色阳性面积以及BMP-2、Runx2、OPN、OCN、ALP和Col1表达较Sham组明显降低(P0.05);而经过BMG治疗,BMG组大鼠BMSCs向成骨细胞分化后ALP和ARS染色阳性面积以及BMP-2、Runx2、OPN、OCN、ALP和Col1表达较OVX组明显增加(P0.05)。OVX组股骨最大载荷和弹性模量、BMD、BV/TV、Tb.N和Tb.Th较Sham组明显降低,而Tb.Sp则明显升高(P0.05)。BMG组左侧股骨最大载荷和弹性模量、BMD、BV/TV、Tb.N和Tb.Th均明显高于OVX组(P0.05),而Tb.Sp明显低于OVX组(P0.05)。结论白茅苷通过促进BMSCs诱导成骨分化来减少去卵巢大鼠骨骨密度、骨量和骨强度下降。     

In utero transplantation of human bone marrow-derived multipotent mesenchymal stem cells in mice.

Mesenchymal stem cells (MSCs) are multipotent cells that can be isolated from human bone marrow and possess the potential to differentiate into progenies of embryonic mesoderm. However, current evidence is based predominantly on in vitro experiments. We used a murine model of in utero transplantation (IUT) to study the engraftment capabilities of human MSCs. MSCs were obtained from bone marrow by negative immunoselection and limiting dilution, and were characterized by flow cytometry and by in vitro differentiation into osteoblasts, chondrocytes, and adipocytes. MSCs were transplanted into fetal mice at a gestational age of 14 days. Engraftment of human MSCs was determined by flow cytometry, polymerase chain reaction, and fluorescence in situ hybridization (FISH). MSCs engrafted into tissues originating from all three germ layers and persisted for up to 4 months or more after delivery, as evidenced by the expression of the human-specific beta-2 microglobulin gene and by FISH for donor-derived cells. Donor-derived CD45+ cells were detectable in the peripheral blood of recipients, suggesting the participation of MSCs in hematopoiesis at the fetal stage. This model can further serve to evaluate possible applications of MSCs.