Ex vivo expansion of CD56+ cytotoxic cells from human umbilical cord blood

The immune-mediated effect of natural killer (NK) and cytotoxic T cells against residual tumor cells previously was shown to prevent relapse and reinduce remission after bone marrow transplantation. Human umbilical cord blood is a rich source of cytotoxic CD56+ cells including fetal NK cells (CD16(-)CD56+1) with high lytic capabilities upon activation with interleukin-2 (IL-2). Cord blood transplantations are reported to be associated with lower risk of graft-vs-host disease, which may jeopardize the graft-vs-leukemia effect. Therefore, our goal was to expand and amplify, ex vivo, cord blood-derived CD56+ cell-mediated cytotoxic activity.Cord blood-derived CD56+ cells were separated using anti-CD56 monoclonal antibody and immunomagnetic beads. The cells were expanded in the presence of irradiated feeder cells and various concentrations of IL-2. Maximal fold expansion (152 +/- 29) was achieved on day 22 by culturing the cells in the presence of irradiated autologous lymphocytes. Irradiated murine stromal cells yielded 42 +/- fourfold expansion (p < 0.05). FACS analysis at the peak of expansion revealed that the cells were 96% +/- 1% CD56+. Interferon-gamma levels significantly decreased throughout the culture period (from 1,034 +/- 34 pg/mL to 21 +/- 8 pg/mL) as did IL-6 levels (from 11,535 +/- 1,452 pg/mL to 323 +/- 161 pg/mL) whereas tumor necrosis factor-alpha levels did not change. The expanded cells manifested potent lytic capabilities against K562 and Colo-205 cell lines (70.9% +/- 2.0% and 48.2% +/- 4.0%, respectively) (n = 5) (effector-to-target ratio 25:1). Coculturing the expanded NK cells with fresh ALL blasts resulted in 85% +/- 1% inhibition of colony growth in methylcellulose (n = 2). In addition, the CD56+ expanded cells induced 44% +/- 7.5% apoptosis of K562 target cells (n = 3). It is possible to effectively expand cord blood-derived CD56+ cells, ex vivo, while maintaining their antileukemic capablilities.     

Ex vivo large-scale generation of human red blood cells from cord blood CD34+ cells by co-culturing with macrophages

We generated red blood cells (RBC) from cord blood (CB) CD34⁺ cells using a four-phase culture system. We first cultured CB CD34⁺ cells on telomerase gene-transduced human stromal cells in serum-free medium containing stem cell factor (SCF), Flt-3/Flk-2 ligand, and thrombopoietin to expand CD34⁺ cells (980-fold) and the total cells (10,400-fold) (first phase). Expanded cells from the first phase were liquid-cultured with SCF, interleukin-3 (IL-3), and erythropoietin (EPO) to expand (113-fold) and differentiate them into erythroblasts (second phase). To obtain macrophages for the next phase, we expanded CD34⁺ cells from a different donor using the same co-culture system. Expanded cells from the first phase were liquid-cultured with granulocyte-macrophage colony stimulating factor, macrophage-colony stimulating factor (M-CSF), IL-3, and SCF to generate monocytes/macrophages (75-fold), which were incubated with type AB serum and M-CSF to fully differentiate them into macrophages. Erythroblasts were then co-cultured with macrophages in the presence of EPO to expand (threefold) and fully differentiate them (61% orthochromatic erythroblasts plus 39% RBC) (third phase). RBC were purified from erythroblasts and debris through a deleukocyting filter to generate 6.0 × 10¹² RBC from 1.0 unit of CB (3.0 transfusable units). Qualitatively, these RBC showed a hemoglobin content, oxygenation of hemoglobin, and in vivo clearance similar to those of adult peripheral RBC. Finally, an almost complete enucleation of orthochromatic erythroblasts (99.4%) was achieved by the cultivation method recently described by Miharada et al. in the absence of macrophages and cytokines (fourth phase). RBC were purified from remnant erythroblasts and debris by passage through a deleukocyting filter to generate 1.76 × 10¹³ RBC from 1.0 unit of CB (8.8 transfusable units), the highest yield ever reported. Thus, this method may be useful for generating an alternative RBC supply for transfusions, investigating infectious agents that target erythroid cells, and as a general in vitro hematopoietic model system.     

Role of endothelial progenitors and other bone marrow-derived cells in the development of the tumor vasculature

Increasing evidence suggests the importance of bone marrow-derived cells for blood vessel formation (neovascularization) in tumors, which can occur in two mechanisms: angiogenesis and vasculogenesis. Angiogenesis results from proliferation and sprouting of existing blood vessels close to the tumor, while vasculogenesis is believed to arise from recruitment of circulating cells, largely derived from the bone marrow, and de novo clonal formation of blood vessels from these cells. Although bone marrow-derived cells are crucial for neovascularization, current evidence suggests a promotional role of these cells on the existing blood vessels rather than de novo neovascularization in tumors. This is believed to be due to the highly proangiogenic features of these cells. The bone marrow-derived cells are heterogeneous, consisting of many different cell types including endothelial progenitor cells, myeloid cells, lymphocytes, and mesenchymal cells. These cells are highly orchestrated under the influence of the specific tumor microenvironment, which varies depending on the tumor type, thereby tightly regulating neovascularization in the tumors. In this review, we highlight some of the recent findings on each of these cell types by outlining some of the essential proangiogenic cytokines that these cells secrete to promote tumor angiogenesis and vasculogenesis.     

Ex vivo expansion of human umbilical cord blood and peripheral blood CD34(+) hematopoietic stem cells

The proliferation and expansion of human hematopoietic stem cells (HSC) in ex vivo culture was examined with the goal of generating a suitable clinical protocol for expanding HSC for patient transplantation.HSC were derived from umbilical cord blood (UCB) and adult patient peripheral blood stem cell collections. HSC were stimulated to proliferate ex vivo by a combination of two growth factors, flt-3 ligand (FL) and thrombopoietin/c-mpl ligand (TPO/ML), and assessed for expansion by flow cytometry.Ex vivo expansion cultures of UCB were maintained for prolonged periods (up to 16 weeks), and sufficient HSC were generated for adult transplantation. In contrast to UCB, FL + TPO/ML did not significantly increase CD34(+) peripheral blood stem cell (PBSC) numbers.UCB-HSC can be expanded in culture to numbers theoretically adequate for safe, rapid engraftment of adult patients. Additional studies are needed to establish the functional activity of expanded UCB-HSC.     

应用粒细胞集落刺激因子动员的外周血体外扩增内皮祖细胞

目的探讨从正常人经粒细胞集落刺激因子(granulocyte colony simulating factor,G-CSF)动员的外周血中分离扩增内皮祖细胞(endothelial progenitor cells,EPCs)。方法经G-CSF动员后,富集的外周血单个核细胞(peripheralblood mononuclear cells,PBMNC)贴壁培养法定向扩增EPCs,免疫组织化学染色和荧光标记鉴定其内皮细胞特性。流式细胞仪检测细胞表面标记物变化。结果获得的贴壁细胞数为(8.825±2.958)个/100个PBMNC,具有多种内皮细胞特征,血管性假血友病因子阳性,同时结合荆豆凝集素I并内吞乙酰化低密度脂蛋白呈红绿荧光双染色。培养后血细胞标记物减少,内皮细胞标记物增加(P<0.01)。结论从G-CSF动员的外周血中可获得较多数量EPCs,并具有多种内皮细胞特征。     

Ex vivo expansion of megakaryocyte progenitors from cryopreserved umbilical cord blood. A potential source of megakaryocytes for transplantation

OBJECTIVE: Umbilical cord blood (CB) provides an alternative source of hematopoietic progenitor cells for transplantation; however, prolonged thrombocytopenia remains a major obstacle due to the low numbers of megakaryocyte progenitor (Mk-prog) cells and their subsequent delayed engraftment. In this study, we improved techniques for enrichment, cryopreservation, and ex vivo expansion of Mk-prog cells from CB. MATERIALS AND METHODS: CB mononuclear cells (MNC) were isolated and Mk-prog enriched by sedimentation on gelatin followed by centrifugation with Ficoll-Hypaque and cryopreserved. The capacity of MNC to produce Mk-prog cells, assessment of CD34(+) and Mk-prog expansion in liquid culture, and analysis of the cell populations by flow cytometry were studied in cryopreserved separated CB and compared to whole CB and freshly separated samples. RESULTS: Excellent viability of greater than 85% was maintained after cryopreservation of separated CB. The number of colony-forming Mk-prog, myeloid, and erythroid progenitor cells did not decrease with cryopreservation. Flow cytometric analysis of cryopreserved cells revealed significant removal of the residual red blood cells while maintaining complete recovery of CD34(+), CD41(+) (Mk), myeloid, and T and B cells compared to noncryopreserved CB cells. There was no difference in the ability of separated cryopreserved MNC CB cells to be expanded in short-term liquid cultures. CONCLUSIONS: The conditions defined here for cryopreservation of gelatin/Ficoll-Hypaque separated CB, followed by ex vivo expansion of MNC, allowed complete recovery of proliferating CD41(+), CD34(+), Mk-prog cells, and other hematopoietic progenitors. Mk-prog cell expansion just before the scheduled transplantation is easily applicable by this technically simple and economical procedure that requires only an aliquot of red cell cell-depleted MNC to be separated from the CB unit before cryopreservation.     

Hypoxia modulates adenosine receptors in human endothelial and smooth muscle cells toward an A2B angiogenic phenotype

We previously reported that adenosine A2B receptor activation stimulates angiogenesis. Because hypoxia is a potent stimulus for the release of both adenosine and angiogenic factors, we tested the hypothesis that hypoxia alters the expression of adenosine receptors toward an "angiogenic" phenotype. We used human umbilical vein endothelial cells (HUVECs) and bronchial smooth muscle cells (BSMCs) because, under normoxic conditions, adenosine does not release vascular endothelial growth factor (VEGF). HUVECs expressed a characteristic A2A phenotype (the selective A2A agonist CGS21680 was as potent as the nonselective agonist 5'-N-ethylcarboxamidoadenosine [NECA] in generating cAMP). Hypoxia (4.6% O2, 3 hours) decreased A2A mRNA from 1.56+/-0.3% to 0.16+/-0.01% of beta-actin expression but increased A2B mRNA from 0.08+/-0.01% to 0.27+/-0.05%. Consistent with changes in receptor expression, CGS21680 failed to increase cAMP in hypoxic HUVECs, whereas NECA remained active (A2B phenotype), and NECA increased VEGF release from 9.5+/-1.0 to 14.2+/-1.2 pg/mL (P<0.05), indicating that increased A2B receptors were functionally coupled to upregulation of VEGF. Hypoxia had similar effects on BSMCs, increasing A2B mRNA by 2.4+/-0.3-fold, from 0.42+/-0.04% to 1.00+/-0.13% of beta-actin. Whereas NECA had no effect on VEGF release in normoxic BSMCs, it increased VEGF release in hypoxic BSMCs, from 74.6+/-9.6 to 188.3+/-16.7 pg/mL (P<0.01), and a selective A2B antagonist, CVT-6694, inhibited this increase. A2B receptors activated a VEGF reporter made unresponsive to hypoxia by mutating its hypoxia-inducible factor-1 (HIF-1) binding element, indicating a mechanism independent of HIF-1. In conclusion, hypoxia modulates the expression of adenosine receptors in human endothelial and smooth muscle cells toward an A2B"angiogenic" phenotype.     

Vascular progenitor cells isolated from human embryonic stem cells give rise to endothelial and smooth muscle like cells and form vascular networks in vivo

We report that human embryonic stem cells contain a population of vascular progenitor cells that have the ability to differentiate into endothelial-like and smooth muscle (SM)-like cells. Vascular progenitor cells were isolated from EBs grown in suspension for 10 days and were characterized by expression of the endothelial/hematopoietic marker CD34 (CD34+ cells). When these cells are subsequently cultured in EGM-2 (endothelial growth medium) supplemented with vascular endothelial growth factor-165 (50 ng/mL), they give rise to endothelial-like cells characterized by a cobblestone cell morphology, expression of endothelial markers (platelet endothelial cell-adhesion molecule-1, CD34, KDR/Flk-1, vascular endothelial cadherin, von Willebrand factor), incorporation of acetylated low-density lipoprotein, and formation of capillary-like structures when placed in Matrigel. In contrast, when CD34+ cells are cultured in EGM-2 supplemented with platelet-derived growth factor-BB (50 ng/mL), they give rise to SM-like cells characterized by spindle-shape morphology, expression of SM cell markers (alpha-SM actin, SM myosin heavy chain, calponin, caldesmon, SM alpha-22), and the ability to contract and relax in response to common pharmacological agents such as carbachol and atropine but rarely form capillary-like structures when placed in Matrigel. Implantation studies in nude mice show that both cell types contribute to the formation of human microvasculature. Some microvessels contained mouse blood cells, which indicates functional integration with host vasculature. Therefore, the vascular progenitors isolated from human embryonic stem cells using methods established in the present study could provide a means to examine the mechanisms of endothelial and SM cell development, and they could also provide a potential source of cells for vascular tissue engineering.     

Differential in vivo potential of endothelial progenitor cells from human umbilical cord blood and adult peripheral blood to form functional long-lasting vessels

Tissue engineering requires formation of a de novo stable vascular network. Because of their ability to proliferate, differentiate into endothelial cells, and form new vessels, blood-derived endothelial progenitor cells (EPCs) are attractive source of cells for use in engineering blood vessels. However, the durability and function of EPC-derived vessels implanted in vivo are unclear. To this end, we directly compared formation and functions of tissue-engineered blood vessels generated by peripheral blood- and umbilical cord blood-derived EPCs in a model of in vivo vasculogenesis. We found that adult peripheral blood EPCs form blood vessels that are unstable and regress within 3 weeks. In contrast, umbilical cord blood EPCs form normal-functioning blood vessels that last for more than 4 months. These vessels exhibit normal blood flow, perm-selectivity to macromolecules, and induction of leukocyte-endothelial interactions in response to cytokine activation similar to normal vessels. Thus, umbilical cord blood EPCs hold great therapeutic potential, and their use should be pursued for vascular engineering.     

Platelet-derived growth factor enhances ex vivo expansion of megakaryocytic progenitors from human cord blood.

Infusion of ex vivo expanded megakaryocytic (MK) progenitor cells is a strategy for shortening the duration of thrombocytopenia after haematopoietic stem cell transplantation. The cell dose after expansion has emerged as a critical factor for achieving the desired clinical outcomes. This study aimed to establish efficient conditions for the expansion of the MK lineage from enriched CD34(+) cells of umbilical cord blood and to investigate the effect of platelet-derived growth factor (PDGF) in this system. Our results demonstrated that thrombopoietin (TPO) alone produced a high proportion of CD61(+)CD41(+) cells but a low total cell count and high cell death, resulting in an inferior expansion. The addition of interleukin-1 beta (IL-1 beta), Flt-3 ligand (Flt-3L) and to a lesser extent IL-3 improved the expansion outcome. The treatment groups with three to five cytokines produced efficient expansions of CFU-MK up to 400-fold with the highest yield observed in the presence of TPO, IL-1 beta, IL-3, IL-6 and Flt-3L. CD34(+) cells were expanded by five to 22-fold. PDGF improved the expansion of all cell types with CD61(+)CD41(+) cells, CFU-MK and CD34(+) cells increased by 101%, 134% and 70%, respectively. On day 14, the CD61(+) population consisted of diploid (86.5%), tetraploid (11.8%) and polyploid (8N--32N; 1.69%) cells. Their levels were not affected by PDGF. TPO, IL-1 beta, IL-3, IL-6, Flt-3L and PDGF represented an effective cytokine combination for expanding MK progenitors while maintaining a moderate increase of CD34(+) cells. This study showed, for the first time, that PDGF enhanced the ex vivo expansion of the MK lineage, without promoting their in vitro maturation. PDGF might be a suitable growth factor to improve the ex vivo expansion of MK progenitors for clinical applications.     

The role of angiopoietins in the development of endothelial cells from cord blood CD34+ progenitors

Circulating endothelial progenitors contribute to neovascularization at sites of injury and tumorigenesis in postnatal life. Yet, the molecular mechanisms initiating the endothelial developmental program of these precursors remain elusive. Here we provide evidence that endothelial development from progenitors circulating in human cord blood requires angiopoietins, a set of growth factors also involved in vascular branching during embryogenesis. We show that cord blood cells with the potential for endothelial development reside in a CD34⁺CD11b⁺ subset capable of autonomously producing and binding angiopoietins. Functionally, endogenous angiopoietin-1 regulates initial endothelial cell commitment, whereas angiopoietin-2 enhances expansion of the endothelial cell progeny. These findings suggest a role for angiopoietins as regulators of endothelial development from circulating progenitors and imply a function of angiopoietins at distinct developmental steps in postnatal angiogenesis.      

Myeloid lineage of high proliferative potential human smooth muscle outgrowth cells circulating in blood and vasculogenic smooth muscle-like cells in vivo

Emerging experimental data supports a circulating precursor origin for some smooth muscle cells that participate in vasculogenesis but uncertainty exists on the precise phenotype and lineage of these vascular precursors. We determined the lineage of human smooth muscle outgrowth cells (SOC) derived from circulating blood mononuclear cells and smooth muscle-like cells present in regions of vasculogenesis in diseased arteries. Immunophenotypic characterization of SOC was performed using FACS and immunofluorescence (IF). An SOC hierarchy was determined based on in vitro clonogenic and proliferative potential. Lineage of smooth muscle-like cells in vasculogenic regions in vivo was also determined by dual IF for myeloid and smooth muscle specific markers combined with FISH for the X and Y chromosome in diseased vessel of human subjects who had undergone gender mismatched cardiac transplantation. We show here that primary high proliferative potential smooth muscle outgrowth cells (HPP-SOC) expanded in culture from human peripheral blood mononuclear cells (PBMC) and recipient-derived chimeric smooth muscle cells participating in vasculogenesis in vivo share a myeloid phenotype (CD68 and CD14 positivity). Moreover, HPP-SOC in vitro are distinct in being negative for several myeloid markers such as CD11b, CD13 and CD33, and CD45 surface antigens and chimeric SMC in vivo show no evidence of cell fusion propensity. This study provides evidence of a possible myeloid subpopulation origin for smooth muscle outgrowth cells in blood and vasculogenic smooth muscle-like cells in the intima and adventitial microvasculature of diseased arteries. These data have significant implications for understanding the role myeloid cells play in smooth muscle cell biology and vascular remodelling.     

Ex vivo expansion of umbilical cord blood stem cells for transplantation: growing knowledge from the hematopoietic niche

Umbilical cord blood transplantation (UCBT) in adults is limited by the small number of primitive hematopoietic stem cells (HSC) in each graft, resulting in delayed engraftment post transplant, and both short- and long-term infectious complications. Initial efforts to expand UCB progenitors ex vivo have resulted in expansion of mature rather than immature HSC, confounded by the inability to accurately and reliably measure long-term reconstituting cells. Ex vivo expansion of UCB HSC has failed to improve engraftment because of resulting defects that promote apoptosis, disrupt marrow homing and initiate cell cycling. Here we discuss the future of ex vivo expansion, which we suggest will include the isolation of immature hematopoietic progenitors on the basis of function rather than surface phenotype and will employ both cytokines and stroma to maintain and expand the stem cell niche. We suggest that ex vivo expansion could be enhanced by manipulating newly discovered signaling pathways (Notch, Wnt, bone morphogenetic protein 4 and Tie2/angiopoietin-1) and intracellular mediators (phosphatase and tensin homolog and glycogen synthase kinase-3) in a manner that promotes HSC expansion with less differentiation. Improved methods for ex vivo expansion will make UCBT available to more patients, decrease engraftment times and allow more rapid immune reconstitution post transplant.     

Construction of an artificial blood vessel wall from cultured endothelial and smooth muscle cells.

Cloned bovine endothelial cells were grown on a preformed layer of cultured rat smooth muscle cells that contained large amounts of connective tissue proteins. The successful growth of the endothelial cells was dependent upon the addition of more than 2.5 x 10(4) cells per cm2, and the final density reached was approximately 2.5 times higher than that obtained for the same cells growing on plastic. The endothelial cells anchored more firmly to the smooth muscle cells than to plastic, and electron microscopy showed the existence of an irregular, dense, basal lamina-like structure between the two cell types. Biochemical analysis of the lamina produced by the endothelial cells in isolation demonstrated the presence of collagen and two fucosylated glycoproteins. The structure produced, which has some of the characteristics of a blood vessel wall, was stable for several months in culture and has many potential applications.     

Ex vivo rapamycin treatment of human cord blood CD34+ cells enhances their engraftment of NSG mice

Since cord blood (CB) has become a commonly used source of transplantable hematopoietic stem (HSC) and hematopoietic progenitor cells (HPC), there has been a need to overcome the limited HSC and HPC numbers available to transplant from a single CB, especially for adult recipients. Our laboratory previously demonstrated that Rheb2 overexpression significantly impaired the repopulating ability of HSC. Since overexpression of Rheb2 leads to increased signaling through mTOR, we examined the effect of the mTOR inhibitor rapamycin ex vivo on cytokine expanded CD34(+) CB cells for the engraftment of these cells in non-obese diabetic, severe combined immunodeficient, IL-2 receptor γ chain null (NSG) mice. We observed significant enhancement in engraftment of the CB treated ex vivo with cytokines in the presence of rapamycin prior to transplant, effects seen in primary as well as secondary transplants. These pre-clinical results suggest a positive role for rapamycin during ex vivo culture of CB SCID repopulating cells/HSC.