Isolation, characterization, and transplantation of candidate stem cells

造血干细胞在出生后存在于骨髓中，为宿主的生命提供了所有的造血谱系，在过去的几十年里，它们的广泛特性导致了临床应用，包括骨髓移植治疗影响造血室的良性和恶性疾病。基于CD34抗原表达的骨髓细胞分离丰富了原始隔室，分离CD34阳性群体的技术在临床实践中常用。最近，Goodell等人描述了一种分离小鼠骨髓细胞的方法，该方法在致命照射后能够重建造血功能，仅基于双波长流式细胞术，并用重要染料Hoechst 33342染色。这些侧群细胞的分子基础最近归因于ABC转运体ABCG2的表达。侧群（SP）细胞具有高度富集的造血再生能力，其中一个细胞能够在辐照受体小鼠中重建造血。我们推断，这种表型在具有产后再生能力的器官中是保守的。我们最近从人尸体肝脏的非实质部分分离出SP细胞，并在肝脏培养基中培养这些细胞。肝SP细胞产生的细胞集落显示出颗粒状丰富的细胞质和致密的双核，与肝细胞一致。这些肝细胞样细胞表达人肝细胞的标志物，包括HepPar、细胞角蛋白-8和人白蛋白。RT-PCR证实了肝细胞标志物的表达，包括白蛋白、细胞角蛋白-18，以及更特异性的标志物，&#61537；1抗胰蛋白酶和人类P450基因CYP2B6。我们现在已经开发了一种用亚致死剂量的四氯化碳治疗NOD/SCID小鼠的体内拯救模型，初步结果表明，与对照组相比，SP细胞能够影响肝功能测试的正常化，类似于成熟肝细胞。这些SP细胞的进一步体内表征正在进行中。此外，已从成人胰腺中分离出SP细胞，微阵列分析显示其基因表达谱与骨髓来源的SP细胞相似。将胰腺SP细胞分化为成熟β细胞表型的初步尝试只取得了有限的成功，这些研究仍在进行中，但它们在培养中的沉默提出了β细胞能否在成年宿主中再生的问题。因此，我们开发了一种利用加速器质谱法测定14C年代的方法来评估出生后的β细胞再生。初步结果表明，人员流动率有限，研究仍在进行中。最后，为了产生能够抵抗I型糖尿病特征的自身免疫的胰岛素生成细胞，我们在体内测试了几种转录因子通过病毒载体的转移是否会导致肝细胞向β细胞的转分化，有证据表明这一过程即使发生，也是低水平的。

Hematopoietic stem cells reside within the bone marrow post-natally, providing all hematopoietic lineages for the life of the host, and their extensive characterization over the last several decades has led to clinical application including bone marrow transplantation for benign and malignant disorders affecting the hematopoietic compartment. Isolation of bone marrow cells based upon expression of the CD34 antigen enriches for the primitive compartment, and techniques to isolate the CD34-positive population are commonly used in clinical practice. Recently, a method for the isolation of murine bone marrow cells capable of reconstituting hematopoiesis after lethal irradiation based solely upon dual wavelength flow cytometry after staining with the vital dye, Hoechst 33342, was described by Goodell et. al. The molecular basis of these side population cells was recently attributed to expression of the ABC transporter, ABCG2. Side population (SP) cells are highly enriched for hematopoietic repopulating ability, with one cell capable of reconstituting hematopoiesis in irradiated recipient mice. We reasoned that this phenotype is conserved among organs with the capacity for post-natal regeneration. We have recently isolated SP cells from the non-parynchymal portion of human cadaveric liver and have cultured these cells in hepatic culture media. Hepatic SP cells generated colonies of cells demonstrating granule rich cytoplasm and dense, often double nuclei consistent with hepatocytes. These hepatocyte-like cells expressed markers of human hepatocytes including HepPar, cytokeratin-8, and human albumin. RT-PCR confirmed the expression of hepatocyte markers including albumin, cytokeratin-18, along with the more specific markers, 1 antitrypsin and the human P450 gene, CYP2B6. We have now developed an in vivo rescue model in NOD/SCID mice treated with sublethal dosing of carbon-tetra-chloride, and initial results suggest that SP cells are capable of affecting a normalization of liver function test similar to mature hepatocytes when compared to controls. Further in vivo characterization of these SP cells is ongoing. Additionally, SP cells have been isolated from the adult pancreas, and microarray analysis demonstrates gene expression profile similar to that of bone marrow derived SP cells. Initial attempts to differentiate pancreatic SP cells toward a mature beta-cell phenotype have met with only limited success and these studies are ongoing, yet their quiescence in culture raises the question whether beta-cells can regenerate in adult hosts. We have thus developed a method for assessing beta cell regeneration post-natally using 14C dating by accelerator mass spectrometry. Initial results suggest limited turnover, and the study is ongoing. Finally, in an attempt to generate insulin producing cells that could resist the autoimmunity that characterizes Type I diabetes, we have tested whether the transfer of several transcription factors via viral vectors in vivo could lead to hepatocyte-to-beta cell transdifferentiation, with evidence that this process occurs a low level if at all.