Background. Fibrosis is the common end stage of most liver diseases, for which, unfortunately, there is no effective treatment available currently. It has been shown that mesenchymal stem cells (MSCs) from bone marrow (BM) could engraft in the lung after bleomycin exposure and ameliorate its fibrotic effects. This study was designed to evaluate the effect of Flk1+ MSCs from murine BM (termed here Flk1+ mMSCs) on fibrosis formation induced by carbon tetrachloride (CCl4). Methods. A CCl4-induced hepatic fibrosis model was used. Flk1+ mMSCs were systemically infused immediately or 1 week after mice were challenged with CCl4. Control mice received only saline infusion. Fibrosis index and donor-cell engraftment were assessed 2 or 5 weeks after CCl4 challenge. Results. Wefound that Flk1+ mMSCs transplantation immediately, but not 1 week after exposure to CCl4, significantly reduced CCl4-induced liver damage and collagen deposition. In addition, levels of hepatic hydroxyproline and serum fibrosis markers in mice receiving immediate Flk1+ mMSCs transplantation after CCl4 challenge were significantly lower compared with those of control mice. More importantly, histologic examination suggested that hepatic damage recovery was much better in these immediately Flk1+ mMSCs-treated mice. Immunofluorescence, polymerase chain reaction, and fluorescence in situ hybridization analysis revealed that donor cells engrafted into host liver, had epitheliumlike morphology, and expressed albumin, although at low frequency. Conclusion. These results suggest that Flk1+ mMSCs might initiate endogenous hepatic tissue regeneration, engraft into host liver in response to CCl4 injury, and ameliorate its fibrogenic effects.

Overwhelming evidence from leukemia research has shown that the clonal population of neoplastic cells exhibits marked heterogeneity with respect to proliferation and differentiation. There are rare stem cells within the leukemic population that possess extensive proliferation and self-renewal capacity not found in the majority of the leukemic cells. These leukemic stem cells are necessary and sufficient to maintain the leukemia. Interestingly, the BCR/ABL fusion gene, which is present in chronic myelogenous leukemia (CML), was also detected in the endothelial cells of patients with CML, suggesting that CML might originate from hemangioblastic progenitor cells that can give rise to both blood cells and endothelial cells. Here we isolated fetal liver kinase-1-positive (Flk1+) cells carrying the BCR/ABL fusion gene from the bone marrow of 17 Philadelphia chromosomepositive (Ph+) patients with CML and found that these cells could differentiate into malignant blood cells and phenotypically defined endothelial cells at the single-cell level. These findings provide direct evidence for the first time that rearrangement of the BCR/ABL gene might happen at or even before the level of hemangioblastic progenitor cells, thus resulting in detection of the BCR/ABL fusion gene in both blood and endothelial cells. (Blood. 2005; 105: 2733-2740)

Mesenchymal stem cells (MSCs) reportedly inhibit the mixed lymphocyte reaction. Whether this effect is mediated by dendritic cells (DCs) is still unknown. In this study, we used an in vitro model to observe the effects of MSCs and their supernatants on the development of monocyte-derived DCs. Phenotypes and the endocytosic ability of harvested DCs were determined by flow cytometry; interleukin 12 (IL-12) secreted by DCs was evaluated by enzyme-linked immunosorbent assay (ELISA); and the antigen-presenting function of DCs was evaluated by MLR. Our results show that MSCs inhibit the up-regulation of CD1a, CD40, CD80, CD86, and HLA-DR during DC differentiation and prevent an increase of CD40, CD86, and CD83 expression during DC maturation. MSCs supernatants had no effect on DCs differentiation, but they inhibited the up-regulation of CD83 during maturation. Both MSCs and their supernatants interfered with endocytosis of DCs, decreased their capacity to secret IL-12 and activate alloreactive T cells. Thus, effects of MSCs on DCs contribute to immunoregulation and development.

Objective. To investigate whether Flk1＋CD31-CD34-cells islated from fetal bone marrow (BM) have characteristies of hemanghioblasts, i. e., progenitors of endothlial and hemato-poietic cells. Materials and Methods. Mononuclear cells from fetal BM were negatively sorted by CD45, Gly A, and Cd34 micromagnetic beads, then cultured to form cell colonies. Asingle colony was harvested. Culture-expanded cells were seeded on ECM gel or semisolid media supplemented with endothelial and hematopoietic trowth factors, respectively. Immuno-chemistry staining and RT-PCR were performed for cell characterization. Results. 99% of cells from the single colony maintained Flk1＋and CD31/CD34-during passaging. On ECM gel, Flk1＋CD31－CD34－cells could grow into vascular structure that was positive for CD31 and v WF. Tgere were round CD34＋cells around the vascular structure. When angiogenesis inhibitor suramin was added before tube formation, formation of vascular structure was blocked, Additionally, Flk1＋CD31-CD34-cells cultured on hematopietic condition could differentiate into hematopoietic cells which expressed GATA-1, 2, and γ, β globin gene. After being replated in methylcellulose medium. they formed typical erythroid colonies. Conclusions. Flk1＋CD31-CD34-cells derived from fetal BM could differentiate into endothelial and hematopoietic cells The rresults suggested that these Flk1＋CD31-CD34-cells after embryo stage bear characteristies of hemangioblast and mayhave potential application for the hematopoietic and vascular diseases.

Mesenchymal stem cells (MSCs) have been cultured from many sources, including bone marrow and liver. To further support our hypothesis that MSCs exist in most postnatal tissues, we isolated a clonogenic, multipotent, rapidly proliferating population of cells from a fetal pancreas and termed them "pancreas-derived mesenchymal stem cells" (PMSCs). They withstood being passaged as many as 30 times without sustaining significant structural changes. In this study, we showed that PMSCs are positive for CD44, CD29, and CDI3 but negative for CD34 and HLA-DR and that they stained with collagen I and III but not with von Willebrand factor antibody. During the log phase of growth, PMSCs proliferated, doubling in population in about 30 hours. Cell-cycle analysis showed that more than 90% of cells were in the G0 and G1 phases, whereas a small subpopulation of cells were actively engaged in proliferation (S＋G2＋M＝3.55%). Under differentiation culture conditions, PMSCs differentiated into cells of osteogenic, chondrogenic, and adipogenic lineages. These results demonstrate that PMSCs can be isolated from human fetal pancreas by means of their adherent ability and that they are capable of self-renewal, propagation, and multipotent differentiation. (J Lab Clin Med 2003; 141: 342-9)