骨髓干细胞参与小鼠急性肾小管坏死修复的实验研究

【摘要】 目的 观察在生理和病理情况下,骨髓来源的干细胞(BMSC)能否分化成肾小管上皮细胞。 方法 绿色荧光蛋白(GFP)标记的C57BL/6转基因小鼠提供骨髓细胞。同种无荧光标记的C57BL/6小鼠100只分为正常对照组、全身照射组、缺血再灌注组、骨髓移植组、骨髓移植+缺血再灌注组。受体鼠的骨髓重建经血液常规检查和流式细胞仪检测确认,并采用荧光组织化学、免疫组织化学等方法观察绿色荧光标记的BMSC在受体鼠肾脏的分布及数量。 结果 全身致死剂量γ射线照射未造成小鼠肾脏组织结构和生理功能的明显改变。骨髓移植后第56、84天的受体鼠肾小管中有少量GFP阳性细胞的存在[(78.75±5.99)%、(79.58±4.60)%],激光共聚焦显微镜进一步证实这些细胞位于肾小管,并表达肾小管上皮细胞特异性的功能蛋白megalin。 结论 在生理和病理情况下,骨髓干细胞均可以向肾小管上皮细胞转分化,参与肾小管上皮细胞的更新,并且在急性肾小管坏死的病理条件下,骨髓干细胞的肾向转化率与肾脏受损程度有关。     

小鼠骨髓干细胞参与肾小管上皮细胞更新的实验研究

目的：观察骨髓来源的干细胞能否分化成肾小管上皮细胞，深化对骨髓干细胞可塑性的认识。方法：绿色荧光蛋白标记的C57BL／6转基因小鼠提供骨髓，同种无荧光的C57BL／6小鼠经致死剂量7射线全身均匀照射后接受骨髓移植，分别在移植后第56d、84d处死，采用荧光组织化学、免疫组织化学等方法观察绿色荧光在骨髓移植小鼠肾脏肾小管的分布及数量，观察骨髓干细胞在无损伤的小鼠肾脏中的分化。结果：骨髓移植后56d、84d的小鼠肾小管中有少量绿色荧光蛋白阳性细胞存在。激光共聚焦显微镜进一步证实这些细胞位于肾小管，并表达肾小管上皮细胞特异性的功能蛋白megalin。结论：骨髓干细胞可能参与肾小管上皮细胞的更新。     

骨髓干细胞转分化为肾祖细胞并参与修复急性肾脏损伤的研究

目的 观察骨髓干细胞是否可以向肾祖细胞转分化,成为肾脏祖细胞库的肾外来源;验证粒细胞集落刺激因子(G-CSF)是否可以促进骨髓干细胞向肾脏祖细胞的转分化,提高肾脏修复的效能.方法 6周龄全身表达绿色荧光蛋白(GFP)的C57BL/6J转基因小鼠提供骨髓,6~8周龄同种无荧光标记的C57BL/6J小鼠40只作为骨髓受体.骨髓移植前,受体小鼠接受致死剂量的γ放射线137Cs照射,骨髓重建情况经流式细胞仪检测确认.骨髓重建完毕后所有小鼠均接受单侧肾脏缺血再灌注损伤.干细胞动员效果及向肾脏归巢情况经流式细胞仪检测鉴定.损伤4、8周后取肾脏标本行免疫荧光组织化学染色,观察骨髓来源的肾脏祖细胞数以及骨髓细胞在微血管形成中的作用.损伤4周后通过组织切片免疫荧光组织化学方法观察并计数微血管细胞数.结果 G-CSF动员1 d后,分别为CD29、CD34、Sca-1、c-Kit、Flk-1阳性的干细胞占外周血非红系细胞的比例均高于对照组(P<0.05).损伤4周后,G-CSF动员组的肾脏中,骨髓来源并且分别表达Sca-1/GFP、CD29/GFP的干细胞的比例均高于对照组(P<0.05);在损伤4周及8周后,肾脏切片免疫荧光组织化学显示G-CSF动员肾脏中骨髓来源的肾祖细胞即Sca-1/GFP双阳性的细胞数量高于对照组.损伤4周后,动员组肾脏中表达CD31的微血管密度高于对照组(P<0.05).损伤4周后肾脏组织中存在CD105/GFP及α-SMA/GFP双阳性的细胞.结论 ①骨髓干细胞可以转分化为器官特异性干细胞-肾脏祖细胞;②G-CSF可以加速这一转分化的过程,并使损伤肾脏得到更好的修复.     

利用脊柱骨来源骨髓细胞建立急性移植物抗宿主病模型

目的探讨利用脊柱骨来源骨髓细胞建立小鼠异基因造血干细胞移植(allogeneic hematopoietic stem cell transplantation,Allo-HSCT)急性移植物抗宿主病(aGVHD)模型的可行性。方法选择C57BL/6(H-2b)雄性小鼠为供体鼠,BALB/c(H-2d)雌性小鼠为受体鼠。制备供体鼠的脾细胞和脊柱骨来源骨髓细胞悬液。受体鼠采用药物加小剂量辐照的预处理方式,于移植前8d～移植前4d腹腔注射氟达拉滨(200mg/kg),接着移植前3d～移植前1d腹腔注射环磷酰胺(60mg/kg),最后在移植前进行全身照射(total-body irradiation,TBI),照射剂量为4Gy(戈瑞)。18只受体鼠经预处理后随机分为3组,每组6只:(1)骨髓移植组,只输入1×107个脊柱骨来源骨髓细胞;(2)aGVHD组,输注1×107个脊柱骨来源骨髓细胞和5×106个脾细胞,建立aGVHD模型;(3)空白对照组,不输入任何细胞。观察3组小鼠生存状态及存活率,取aGVHD组与骨髓移植组存活21d的受体鼠进行病理学检查,取aGVHD组移植后21～28d存活的小鼠的脾脏进行流式细胞术检测骨髓细胞嵌合度。结果骨髓移植组小鼠全部存活,可重建造血,单纯输注骨髓细胞不会诱发aGVHD。aGVHD组小鼠出现aGVHD表现,100%发生aGVHD相关死亡,中位生存期为18d;病理检查结果显示符合aGVHD病理表现,移植后21～28d存活的小鼠诊断为供受体混合嵌合状态,符合aGVHD诊断标准。结论用脊柱骨来源骨髓建立的aGVHD模型完全符合标准,且更加经济,适合大规模建模。     

经诱导的绿色荧光蛋白转基因C57BL雄鼠脾细胞移植重建雌鼠造血功能研究

目的探讨雄性C57BL绿色荧光蛋白（GFP）鼠诱导的脾细胞移植对造血衰竭小鼠造血重建的作用。方法建立小鼠造血衰竭模型,移植鱼卵提取物诱导的雄性C57BL荧光鼠脾细胞,检测诱导后细胞的干细胞标志抗原表达;观察受体存活时间,检测外周血白细胞计数、外周血GFP阳性细胞,进行荧光原位杂交检测Y染色体;各组受体脾和肺切片观察GFP细胞分布。结果鱼卵提取物诱导的雄性C57BL荧光鼠脾细胞比未诱导的脾细胞表达更多的干细胞标志抗原。1×106个脾细胞经尾静脉回输经致死剂量照射的雌性小鼠,明显延长小鼠存活时问,提高小鼠外周血白细胞计数。诱导组受体外周血中检测到GFP阳性细胞,骨髓中检测出60％的细胞含Y染色体。诱导组受体脾和肺切片观察到GFP阳性细胞分布。结论鱼卵提取物诱导的小鼠脾细胞中含较多的多能干细胞,回输给造血衰竭小鼠能重建其造血功能。     

放射性损伤对骨髓来源干细胞分化为实体细胞的影响

目的 观察骨髓来源干细胞(BMDSCs)能否在体分化为其他实体组织细胞.方法 野生型C57BL/6J雌性小鼠作为受体接受10 Gy的射线照射后,经尾静脉植入同等背景的转增强型绿色荧光蛋白(EGFP)基因的C57BL/6J雄性小鼠(绿鼠)骨髓细胞1×107个/只.移植受体稳定1年后检测各组织中EGFP的表达.结果 野生型小鼠各组织中EGFP的表达为0%,绿鼠各组织中EGFP的表达为100%.受体鼠各组织均有EGFP阳性细胞分布,表达率为100%,与野生型比较差异有统计学意义(P<0.01),但是表达强度均低于绿鼠组.EGFP阳性细胞主要存在于皮肤组织角质形成细胞、毛囊上皮,以及肺间质、支气管上皮、肺泡上皮中.结论 BMDSCs能在体内分化为其他实体细胞,并有组织特异性.     

急性肝损伤小鼠体内的骨髓源性肝细胞研究

目的观察在急性肝损伤小鼠体内是否存在骨髓来源肝细胞。方法使用CCL4诱导小鼠急性肝损伤，24h内移植入绿色荧光蛋白转基因小鼠骨髓细胞，移植后不同时间采用免疫荧光方法检测肝脏中的骨髓来源肝细胞。结果骨髓移植后在8周的观察期内肝脏中始终存在骨髓来源的造血干细胞，移植后1、2、4、6、8周肝脏中存在现骨髓来源的表达AFP的未成熟肝细胞，移植后4、6、8周时肝脏中检测到骨髓来源表达ALB的成熟肝细胞。结论急性肝损伤小鼠体内存在骨髓来源肝细胞，骨髓可能是急性肝损伤后肝再生途径之一。     

竹叶青蛇毒诱导不同品系小鼠系膜增生性肾炎模型的比较研究

目的：探讨竹叶青蛇毒（habu snake venom,HSV）诱导C57BL/6小鼠和FVB/N小鼠系膜增生性肾炎模型的病理差异,为实验动物模型的选择提供科学依据。方法：取8周龄雄性C57BL/6小鼠（n=33）和FVB/N小鼠（n=52）,单次尾静脉注射2.5 mg/kg竹叶青蛇毒建立模型。定期检测血尿素氮和肌酐水平,观察肾组织病理改变并进行病理评分,观察肾小球内PCNA免疫组化染色情况。结果：FVB/N小鼠的存活率（53.2%）明显低于C57BL/6小鼠（89.3%）。肾组织病理表现为C57BL/6小鼠在蛇毒注射后的第1和3天肾小球内出现显著系膜溶解病变,第7天肾小球系膜细胞增殖和系膜基质积聚,第14、21天病变肾小球逐渐恢复正常。FVB/N小鼠注射后第1和3天系膜溶解病变不显著,第7天存在系膜细胞增生,但病变程度低于同期C57BL/6小鼠。病理评分结果示C57BL/6小鼠在模型建立后系膜溶解指数和肾小球硬化指数均高于同期FVB/N小鼠。免疫组化结果显示两种小鼠肾小球内PCNA阳性率在第3、7天均显著高于对照组,其中C57BL/6小鼠肾小球内PCNA表达在第3天高于FVB/N小鼠。结论：静脉注射HSV能诱导小鼠发生系膜增生性肾炎病理改变,C57BL/6小鼠对该模型的耐受性和易感性均优于FVB/N小鼠。     

外源性骨髓细胞在体诱导形成毛囊上皮细胞的研究

目的 观察外源性骨髓细胞能否在体诱导形成皮肤的上皮细胞.方法 获取转增强型绿色荧光蛋白基因的C57BL/6J小鼠原代骨髓细胞和野生型C57BL/6J小鼠原代表皮干细胞,植入野生型C57BL/6J小鼠背部创面并打包.分A、B两组各10只,A组每只植入1.0×107个单纯骨髓细胞,B组每只植入混合骨髓细胞、表皮干细胞各1.0×107个.创面痊愈后应用荧光法和免疫组织化学技术检测新生皮肤内EGFP的表达.结果 两组动物3个月后创面痊愈并有完整的毛发生长.A组新生皮肤内未见EGFP的表达;B组所有新生皮肤(100%)均可见EGFP阳性细胞群,多分布在毛囊内.结论 创伤后小鼠毛囊的再生过程中,骨髓细胞-表皮干细胞接触诱导对骨髓来源细胞向毛囊上皮细胞转化至关重要.     

CCl4慢性肝损致无白蛋白受体鼠对移植骨髓细胞肝细胞增殖的影响

目的 观察和研究F344来源的骨髓细胞(bone marrow cells,BMCs)能否驻存于γ-全身照射的先天性无白蛋白大鼠的骨髓,进而转化为产白蛋白肝细胞,移植后给予四氯化碳(carbon tetracholoride,CCl4)后对这些细胞增殖的影响.方法 雄性F344大鼠为供体,而雄性F344alb(先天性无白蛋白大鼠)为受体,分为4组:组Ⅰ(n=10)为正常对照组,不接受肝损处理,无全身射线照射和阴茎静脉骨髓细胞移植;组Ⅱ(n=10)为肝损无移植组,只接受肝损处理,无全身射线照射和阴茎静脉骨髓细胞移植;组Ⅲ(n=1O)为正常移植组,全身射线照射后阴茎静脉移植骨髓细胞1×107;组Ⅳ(n=10)为肝损移植组,接受CCl4注射肝损,全身射线照射后阴茎静脉骨髓细胞移植1×107BMCs,其中,γ-照射剂量为7.5 Gy,F344大鼠的BMCs经受体的阴茎静脉注入.移植后四周,CCl4腹腔内注射铸成大鼠慢性肝损模型,细胞移植12周后,处死大鼠.肝脏切片用抗白蛋白抗体行白蛋白免疫染色,检测从受体骨髓细胞和肝脏切片中呈多于6个白蛋白阳性簇状分布的肝细胞群中提取的DNA和血清中白蛋白的水平.结果 ①尽管组Ⅰ肝脏切片可发现少量散在的1个或2个白蛋白阳性肝细胞,但是白蛋白阳性肝细胞呈多于6个的簇状分布仅发现于γ-射线全身照射后接受BMCs移植的肝切片中(组Ⅲ和组Ⅳ),而且组Ⅳ中呈多于6个的簇状分布的肝细胞数明显多于组Ⅲ,有统计学意义.②从F344alb受体(组Ⅲ和组Ⅳ)骨髓细胞及肝脏切片中微切的呈多于6个白蛋白阳性簇状分布的肝细胞群中提取的DNA中可检测到正常的白蛋白基因序列.③组Ⅳ较组Ⅲ血清中白蛋白水平显著升高.结论 ①F344来源的骨髓细胞移植入全身射线照射的F344alb受体,可驻存于F344alb受体的骨髓内,进而转化为产白蛋白的肝细胞.②F344来源的骨髓细胞移植入全身射线照射的F344alb受体,4周后CCh腹腔内注射铸成大鼠慢性肝损模型可明显增加骨髓细胞的增殖.③全身射线照射后移植F344供体骨髓细胞,之后CCl4腹腔内注射铸成大鼠慢性肝损模型的F344alb受体的外周血中白蛋白水平可明显提高.     

Generation of donor hematolymphoid cells after rat-limb composite grafting

BACKGROUND: Composite tissue allografts are unique because they provide the vascularized bone marrow with stroma, which is the supportive microenvironment. In this study, we investigated the beneficial effect of donor-derived bone marrow cells within the long-surviving recipient rats after limb transplantation. METHODS: Green fluorescent protein (GFP) transgenic rats developed for paramount cell marking were donors, and wild Wistar rats were recipients. Orthotopic hind-limb transplantation was performed using a microsurgical technique. Tacrolimus (1.0 mg/kg) was intramuscularly injected for 14 days postoperatively. The skin graft from GFP donor onto the GFP recipient was performed as a control. Flow cytometric analyses of recipient peripheral blood and bone marrow were carried out at 4 to 6 days, 18 to 21 days, 6 weeks, and 2, 4, 6, 9, and 12 months after transplantation. RESULTS: The rats that received tacrolimus therapy achieved prolonged composite graft acceptance more than 12 months, whereas GFP skin grafts were rejected at 47 days under the same immunosuppressive protocol. Numerous GFP lymphocytes and granulocytes were detected within the recipient bone marrow for the first 6 weeks post limb transplantation. These cells remained relatively stable for more than 12 months. CONCLUSIONS: The results showed that donor-derived hematopoietic stem cells engrafted in recipient bone marrow and differentiated to lymphocytes and granulocytes after limb transplantation. The vascularized bone marrow, transplanted as a part of the hind limb, could have contributed to mixed chimerism and worked as the bone-marrow source in the recipients.     

The potential of bone marrow-derived cells to differentiate to glomerular mesangial cells.

Bone marrow stem cells (BMC) develop into hematopoietic and mesenchymal lineages but have not been known to differentiate into glomerular cells. To investigate whether such differentiation is possible, a search was made for donor glomerular cells in lethally irradiated C57BL/6j (B6) mice given transplants of BMC from syngeneic mice transgenic for green fluorescence protein (GFP) ([GFP-->B6] mice). After the recipients of donor BMC manifested GFP-positive cells in their glomeruli, the numbers of such cells increased markedly, in a time-dependent manner, from 2 wk to 24 wk after bone marrow transplantation. Immunohistochemical analyses revealed that most GFP-positive cells in the glomeruli were neither macrophages nor T cells. With the use of a laser-scanning confocal microscope, GFP-positive cells were observed within the mesangium of [GFP-->B6] mice. Furthermore, indirect immunofluorescence assays demonstrated that desmin-positive cells in the glomeruli of these chimeric mice were also positive for GFP. Among glomerular cells isolated from [GFP-->B6] mice 24 wk after bone marrow transplantation and then cultured, the majority of cells (approximately 84%) stained for desmin and approximately 60% of the desmin-positive cells expressed GFP. In addition, these GFP-positive cells in the cultures contracted in response to angiotensin II stimulation. These results suggest that bone marrow-derived cells may have the potential to differentiate into glomerular mesangial cells.     

Beta-galactosidase of ROSA26 mice is a useful marker for detecting the definitive erythropoiesis after stem cell transplantation

BACKGROUND: Hematopoietic reconstitution after stem cell transplantation has been analyzed by using stem cells of Ly5 congenic mice. However, the early erythropoiesis has never been analyzed because this marker is not expressed on all of the erythroid lineage cells. The transgenic mouse expressing beta-galactosidase (beta-gal) or green fluorescent protein (GFP) has been reported. Using these markers, we analyzed the early erythropoiesis after stem cell transplantation. METHODS: The beta-gal activity and GFP were examined in the hematopoietic cells of ROSA26 and GFP transgenic mice, respectively, by flow cytometry. The primitive hematopoietic stem cell fraction (Lin(-)c-kit(+)Sca-1(+)) in bone marrow (BM) cells of ROSA26 mice was transferred into lethally irradiated mice. The kinetics of hematopoietic reconstitution was analyzed in the BM and spleen after transplantation. RESULTS: The beta-gal activity, but not the GFP and Ly5, was detected in all of the erythroid (TER119+) cells. The beta-gal activity was also detected in the donor-derived myeloid (Mac-1+), B lymphoid (B220+), and T lymphoid (Thy-1+) cells in the BM and spleen after stem cell transplantation. The kinetics of the hematopoietic reconstitution demonstrated that early erythroid (TER119(low)CD71(med)) cells were developed in the BM and spleen within 2 days after transplantation before development of proerythroblasts (TER119(+)CD71(high)), and that massive erythropoiesis and myelopoiesis were observed in the spleen until 2 and 4 weeks after transplantation, respectively. Conclusions. The beta-gal of ROSA26 mice can be a useful marker to identify the donor-derived hematopoietic cells, including early erythroid cells, and the first major wave of erythropoiesis occurring in the spleen after stem cell transplantation.     

Bone mass and microarchitecture of irradiated and bone marrow-transplanted mice: influences of the donor strain

Summary  Total body irradiation and bone marrow transplantation induced dramatic trabecular bone loss and cortical thickening in mice. Transplanted cells were engrafted in bone marrow, along trabeculae, and in periosteal and endosteal envelopes. None of the osteocytes were of donor origin. Bone microarchitecture of transplanted mice changed to tend toward the donor phenotype. Introduction  Osteopenia and osteoporosis are complications of bone marrow transplants (BMT) attributed to related chemotherapy. However, the specific influence of total body irradiation (TBI) is unknown. Methods  We investigated the effects of TBI and BMT on bone mass and microarchitecture by micro-CT. Eighteen C57Bl/6 (B6) mice receiving lethal TBI had a BMT with marrow cells from green fluorescent protein--transgenic-C57Bl/6 (GFP) mice. Transplanted (T^GFPB6), B6, and GFP mice were euthanized 1, 3, and 6 months after BMT or at a related age. Results  T^GFPB6 presented a dramatic bone loss compared with B6 and did not restore their trabecular bone mass over time, despite a cortical thickening 6 months after BMT. Serum testosterone levels were not significantly reduced after BMT. During aging, GFP mice have less trabeculae, thicker cortices, but a narrower femoral shaft than B6 mice. From 3 months after BMT, cortical characteristics of T^GFPB6 mice differed statistically from B6 mice and were identical to those of GFP mice. GFP⁺ cells were located along trabecular surfaces and in periosteal and endosteal envelopes, but none of the osteocytes expressed GFP. Conclusion  Our findings suggest that engrafted cells did not restore the irradiation-induced trabecular bone loss, but reconstituted a marrow microenvironment and bone remodeling similar to those of the donor. The effects of irradiation and graft on bone remodeling differed between cortical and trabecular bone.     

Potential role of bone marrow-derived cells in the turnover of mesothelium

Background: Bone marrow cell has been proposed as a source of new mesothelium, but supporting evidence is rare. This study examines the validity of this hypothesis by using green fluorescent protein (GFP) and Y-chromosome trackers to identify the presence of donor marrow cells in peritoneal membrane of bone marrow transplant recipient mice. Methods: Cross-gender and GFP-mismatched bone marrow transplantation was undertaken in 20 FVB mice. Five recipients were killed 2, 4, and 6 weeks and 6 months later. Peritoneal tissues were obtained for the detection of GFP and Y chromosome by immunohistochemical staining (IHC) and chromogenic in situ hybridization (CISH). Results: GFP+ cells could be found in the peritoneal membrane of bone marrow transplant recipients. However, the level of engraftment was low, accounting for 0.9%, 0.8%, 0.7%, and 2.2% of the total counted mesothelial cells in intestinal serosa at 2, 4, and 6 weeks and 6 months post-transplantation, respectively. The presence of donor marrow cells within mesothelium was again confirmed by the detection of Y-chromosome-containing cells. Moreover, Y-chromosome+ cells incorporated within the mesothelium were positively stained by anticytokeratin antibody. Conclusions: Donor marrow cells could attach to mesothelium and exhibit mesothelial marker cytokeratin in bone marrow transplant recipients. This finding suggests that bone marrow-derived cells might participate in the turnover of mesothelium.     

Adult endothelial progenitor cells retain hematopoiesis potential

Hematopoietic stem cells (HSCs) are derived from endothelium in the aortic-gonado-mesonephric (AGM) region during embryogenesis. But little is known about whether endothelial progenitor cells (EPCs) retain hematopoiesis potential after birth. In this study, we isolated adult EPCs from the bone marrow of C57BL/6 mice and identified them with an endothelial functional assay and by the CD31(+) CD133(+) CD45(-/dim) VEGFR2(+) phenotype. EPCs isolated from green fluorescence protein (GFP) transgenic C57BL/6 mice were cotransfused with bone marrow cells from wild-type C57BL/6 mice into lethally irradiated BABL/c mice. One month after transplantation, granulocytes (25.73 ± 5.43%) and lymphocytes (12.68 ± 3.26%) in peripheral blood showed GFP(+), referred to as donor EPC-derived blood cells. After an additional month, the percentage of GFP(+) granulocytes decreased to (3.69 ± 1.43%), whereas the percentage of GFP(+) lymphocytes showed no significant difference. Most of the GFP(+) elements showed a diffuse distribution in the spleen; but some were present as aggregates forming lymphoid nodules. GFP(+) endothelial cells were observed in the liver sinusoids, intestinal villi, and lung of recipient mice. These results indicated that adult EPCs not only took part in vasculogenesis, but also retained hematopoietic ability.     

Xenotransplant cardiac chimera: immune tolerance of adult stem cells

BACKGROUND: Bone marrow stromal cells have been shown to engraft into xenogeneic fetal recipients. In view of the potential clinical utility as an alternative source for cellular and gene therapies, we studied the fate of xenogeneic marrow stromal cells after their systemic transplantation into fully immunocompetent adult recipients without immunosuppression. METHODS: Bone marrow stromal cells were isolated from C57B1/6 mice and retrovirally transduced with LacZ reporter gene for cell labeling. We then injected 6 x 10(6) labeled cells into immunocompetent adult Lewis rats. One week later, the recipient animals underwent coronary artery ligation and were sacrificed at various time points ranging from 1 day to 12 weeks after ligation. Hearts, blood, and bone marrow samples were collected for histologic and immunohistochemical studies. RESULTS: Labeled mice cells engrafted into the bone marrow cavities of the recipient rats for at least 13 weeks after transplantation without any immunosuppression. On the other hand, circulating mice cells were positive only for the animals with 1-day-old myocardial infarction. At various time points, numerous mice cells could be found in the infarcted myocardium that were not seen before coronary ligation. Some of these cells subsequently showed positive staining for cardiomyocyte specific proteins, while other labeled cells participated in angiogenesis in the infarcted area. CONCLUSIONS: The marrow stromal cells are adult stem cells with unique immunologic tolerance allowing their engraftment into a xenogeneic environment, while preserving their ability to be recruited to an injured myocardium by way of the bloodstream and to undergo differentiation to form a stable cardiac chimera.