Lineage-negative side-population (SP) cells with restricted hematopoietic capacity circulate in normal human adult blood: immunophenotypic and functional characterization

Overexpressing microRNA-34a overcomes ABCG2-mediated drug resistance to 5-FU in side population cells from colon cancer via suppressing DLL1

Colon cancer side population (SP) cells are a small subset of cancer cells that have cancer stemness capacity and enhanced drug resistance. ABCG2 is a multidrug resistance-related protein in SP cells and has been demonstrated to be regulated by Notch signalling pathway. Recently, microRNAs are reported to play a critical role in SP cell fate. However, their role in ABCG2-mediated drug resistance in colon cancer SP cells remains unclear. In the current study, the different expressions of miR-552, miR-611, miR-34a and miR-5000-3p were compared within SP and non-SP cells, which were separated from human colon cancer cell lines (SW480 and LoVo). We found that miR-34a was significantly down-regulated in SP cells and that overexpressing miR-34a overcame drug resistance to 5-fluorouracil (5-FU). The luciferase reporter assay indicated that miR-34a negatively regulated DLL1, a ligand of Notch signalling pathway, via binding with 3'-untranslated region of its messenger RNA. In addition, overexpressing miR-34a overcame ABCG2-mediated resistance to 5-FU via DLL1/Notch pathway in vitro, and suppressed tumour growth under 5-FU treatment in vivo. In conclusion, our findings suggest that miR-34a acts as a tumour suppressor via enhancing chemosensitivity to 5-FU in SP cells, which provides a novel therapeutic target in chemotherapy-resistant colon cancer.

Cultured circulating tumor cells and their derived xenografts for personalized oncology

Recent cancer research has demonstrated the existence of circulating tumor cells (CTCs) in cancer patient's blood. Once identified, CTC biomarkers will be invaluable tools for clinical diagnosis, prognosis and treatment. In this review, we propose ex vivo culture as a rational strategy for large scale amplification of the limited numbers of CTCs from a patient sample, to derive enough CTCs for accurate and reproducible characterization of the biophysical, biochemical, gene expressional and behavioral properties of the harvested cells. Because of tumor cell heterogeneity, it is important to amplify all the CTCs in a blood sample for a comprehensive understanding of their role in cancer metastasis. By analyzing critical steps and technical issues in ex vivo CTC culture, we developed a cost-effective and reproducible protocol directly culturing whole peripheral blood mononuclear cells, relying on an assumed survival advantage in CTCs and CTC-like cells over the normal cells to amplify this specified cluster of cancer cells.

A Functionally Superior Second-Generation Vector Expressing an Aurora Kinase-A-Specific T-Cell Receptor for Anti-Leukaemia Adoptive Immunotherapy

Aurora Kinase A is a cancer-associated protein normally involved in the regulation of mitosis. Being over-expressed in a range of cancers, it is a suitable target for cell-based immunotherapy. Gene transfer of T-cell receptor sequences cognisant of HLA-A*0201-restricted Aurora Kinase A antigen has previously been shown to transfer specific immunoreactivity against the target peptide in a Human Lymphocyte Antigen-restricted manner. While T cell receptor gene-transfer has great potential in overcoming the difficulties of isolating and expanding tumour-reactive lymphocytes from a patient’s own cells, one hurdle is potential mispairing and competition between exogenous and endogenous T cell receptor chains. We have used a retroviral vector design bearing a short-interfering RNA that downregulates endogenous T cell receptor chains, without affecting expression of the transgenic T cell receptor sequences. The T cell receptor expression cassette also includes a 2A self-cleaving peptide, resulting in equimolar expression of the T cell receptor alpha and beta chains, further enhancing formation of the desired T cell receptor. Via a simple, modular cloning method, we have cloned the alpha and beta chains of the anti-Aurora Kinase A-reactive T cell receptor into this ‘siTCR’ vector. We then compared the activity of this vector against the original, ‘conventional’ vector across a panel of assays. T cell receptors expressed from the siTCR-vector retained the cytotoxic functionality of the original vector, with evidence of reduced off-target reactivity. The rate of expression of correctly-formed T cell receptors was superior using the siTCR design, and this was achieved at lower vector copy numbers. Maintaining T cell receptor efficacy with a reduced vector copy number reduces the risk of genotoxicity. The siTCR design also reduces the risk of mispairing and cross-reactivity, while increasing the functional titre. Such improvements in the safety of T cell receptor gene-transfer will be crucial for clinical applications of this technology.

Human umbilical cord blood-mesenchymal stem cells transplantation renovates the ovarian surface epithelium in a rat model of premature ovarian failure: Possible direct and indirect effects

This study aimed to isolate mesenchymal stem cells (MSC) from human umbilical cord blood (HCB) and to explore their influence on the ovarian epithelium after paclitaxel-induced ovarian failure. Ninety-five rats were divided into 6 groups: control, paclitaxel, paclitaxel and saline, HCB-MSC-treated for 2 weeks, HCB-MSC-treated for 4 weeks, and HCB-MSC-treated for 6 weeks. HCB cells were studied for CD34, CD44, and Oct ¾ using flow cytometry. Serum levels of FSH and E2 were measured using ELISA, RT-PCR analysis for human gene; beta-actin (ACTB), immunohistochemical analysis for CK 8/18, TGF-ß, PCNA and CASP-3 were performed. We found that ACTB gene was expressed in all rats' ovaries received HCB-MSC. After 4 weeks of transplantation, there was significant reduction in FSH, elevation in E2 levels, stabilization of the surface epithelium morphostasis, an increase in the antral follicle count and increase in integrated densities (ID) of CK 8/18, TGF-ß, and PCNA expressions and decrease in ID of CASP-3 expression. We concluded that HCB-MSC can restore the ovarian function after paclitaxel injection through a direct triggering effect on the ovarian epithelium and/or indirect enrichment of ovarian niche through regulating tissue expression of CK 8/18, TGF-ß and PCNA. These molecules are crucial in regulating folliculogenesis and suppressing CASP-3-induced apoptosis.

Isolation and phenotypic characterization of cancer stem-like side population cells in colon cancer

Previous studies in cancer biology suggest that chemotherapeutic drug resistance and tumor relapse are driven by cells within a tumor termed 'cancer stem cells'. In the present study, a Hoechst 33342 dye exclusion technique was used to identify cancer stem‑like side population (SP) cells in colon carcinoma, which accounted for 3.4% of the total cell population. Following treatment with verapamil, the population of SP cells was reduced to 0.6%. In addition, the sorted SP cells exhibited marked multidrug resistance and enhanced cell survival rates compared with non‑SP cells. The SP cells were able to generate more tumor spheres and were CD133 positive. Subsequent biochemical analysis revealed that the levels of the adenosine triphosphate‑binding cassette sub‑family G member 2 transporter protein, B‑cell lymphoma anti‑apoptotic factor and autocrine production of interleukin‑4 were significantly enhanced in the colon cancer SP cells, which contributed to drug resistance, protection of the cells from apoptosis and tumor recurrence. Therefore, the findings suggested that treatment failure and colon tumorigenesis is dictated by a small population of SP cells, which indicate a potential target in future therapies.

Effect of human umbilical cord blood derived lineage negative stem cells transplanted in amyloid-β induced cognitive impaired mice

Alzheimer's disease (AD) is pathologically characterized by extracellular deposition of insoluble amyloid-β (Aβ) plaques and intracellular tangles made up of phosphorylated tau in brain. Several therapeutic approaches are being carried out in animal AD models for testing their safety and efficacy in altering disease pathology and behavioral deficits. Very few studies have examined the effect of human umbilical cord blood (hUCB) derived stem cells in degenerative disease models despite growing number of cord blood banks worldwide. Here we have examined the therapeutic efficacy of hUCB derived lineage negative (Lin -ve) stem cells in alleviating behavioral and neuropathological deficits in a mouse model of cognitive impairment induced by bilateral intrahippocampal injection of Aβ-42. Lin -ve cells were transplanted at two doses (50,000 and 100,000) at the site of injury and examined at 10 and 60 days post transplantation for rescue of memory deficits. These cells were found to ameliorate cognitive impairment in 50,000-60 days and 100,000-10 days groups whereas, 50,000-10 days and 100,000-60 days groups could not exert any significant improvement. Further, mice showing spatial memory improvement were mediated by up-regulation of BDNF, CREB and also by concomitant down regulation of Fas-L in their brain. The transplanted cells were found in the host tissue and survived up to 60 days without expressing markers of neuronal differentiation or reducing Aβ burden in mouse brain. We suggest that these undifferentiated cells could exert neuroprotective effects either through inhibiting apoptosis and/or trophic effects in the brain.

SP/drug efflux functionality of hematopoietic progenitors is controlled by mesenchymal niche through VLA-4/CD44 axis

Hematopoiesis is orchestrated by interactions between hematopoietic stem/progenitor cells (HSPCs) and stromal cells within bone marrow (BM) niches. Side population (SP) functionality is a major characteristic of HSPCs related to quiescence and resistance to drugs and environmental stresses. At steady state, SP cells are mainly present in the BM and are mostly absent from the circulation except in stress conditions, raising the hypothesis of the versatility of the SP functionality. However, the mechanism of SP phenotype regulation is unclear. Here we show for the first time that the SP functionality can be induced in lin(-) cells from unmobilized peripheral blood after nesting on mesenchymal stromal cells (MSCs). This MSC-induced SP fraction contains HSPCs as demonstrated by their (i) CD34(+) cell percentage, (ii) quiescent status, (iii) in vitro proliferative and clonogenic potential, (iv) engraftment in NSG (NOD SCID gamma chain) mice and (v) stemness gene expression profile. We demonstrate that SP phenotype acquisition/reactivation by circulating lin(-) cells is dependent on interactions with MSCs through VLA-4/α4β1-integrin and CD44. A similar integrin-dependent mechanism of SP phenotype acquisition in acute myeloid leukemia circulating blasts suggests an extrinsic regulation of ATP-binding cassette-transporter activity that could be of importance for a better understanding of adhesion-mediated chemoresistance mechanisms.

The mouse ovarian surface epithelium contains a population of LY6A (SCA-1) expressing progenitor cells that are regulated by ovulation-associated factors

The ovarian surface epithelium, a single layer of poorly differentiated epithelial cells, covers the surface of the ovary and is ruptured during ovulation. Little is known about the changes that occur in this layer before or during ovulation, and even less is known about the regenerative processes that occur after the surface is ruptured to release a mature oocyte. Recently, a population of mouse ovarian surface epithelial (MOSE) cells that exhibit progenitor/stem cell characteristics has been identified, though neither a genetic marker nor how these cells are regulated has been determined. We have identified a defined population of MOSE cells with progenitor cell characteristics that express the stem cell marker lymphocyte antigen 6 complex, locus A (LY6A; also known as stem cell antigen-1 [SCA-1]). By testing the effect of factors found in the follicular fluid at ovulation on proliferation, sphere formation, and LY6A expression, we have determined that the size of the LY6A-expressing (LY6A+) progenitor cell population is regulated by at least two ovulation-associated factors present in the follicular fluid: transforming growth factor beta 1 and leukemia-inhibitory factor. Our work has identified a population of LY6A+ MOSE progenitor cells on the surface of the ovary that may play a role in ovulatory wound healing.

Cardiac side population cells: moving toward the center stage in cardiac regeneration

Over the past decade, extensive work in animal models and humans has identified the presence of adult cardiac progenitor cells, capable of cardiomyogenic differentiation and likely contributors to cardiomyocyte turnover during normal development and disease. Among cardiac progenitor cells, there is a distinct subpopulation, termed "side population" (SP) progenitor cells, identified by their unique ability to efflux DNA binding dyes through an ATP-binding cassette transporter. This review highlights the literature on the isolation, characterization, and functional relevance of cardiac SP cells. We review the initial discovery of cardiac SP cells in adult myocardium as well as their capacity for functional cardiomyogenic differentiation and role in cardiac regeneration after myocardial injury. Finally, we discuss recent advances in understanding the molecular regulators of cardiac SP cell proliferation and differentiation, as well as likely future areas of investigation required to realize the goal of effective cardiac regeneration.

Left atrium of the human adult heart contains a population of side population cells

Cardiac "side population" (SP) cells have previously been found to differentiate into both endothelial cells and cardiomyocytes in mice and rats, but there are no data on SP cells in the human adult heart. Therefore, human cardiac atrial biopsies were dissociated, stained for SP cells and analyzed with FACS. Identified cell populations were analyzed for gene expression by quantitative real-time PCR and subjected to in vitro differentiation. Only biopsies from the left atrium contained a clearly distinguishable population of SP cells (0.22 ± 0.08%). The SP population was reduced by co-incubation with MDR1 inhibitor Verapamil, while the ABCG2 inhibitor FTC failed to decrease the number of SP cells. When the gene expression was analyzed, SP cells were found to express significantly more MDR1 than non-SP cells. For ABCG2, there was no detectable difference. SP cells also expressed more of the stem cell-associated markers C-KIT and OCT-4 than non-SP cells. On the other hand, no significant difference in the expression of endothelial and cardiac genes could be detected. SP cells were further subdivided based on CD45 expression. The CD45-SP population showed evidence of endothelial commitment at gene expression level. In conclusion, the results show that a SP population of cells is present also in the human adult heart.

Is it time to revisit our current hematopoietic progenitor cell quantification methods in the clinic?

In the clinical practice of hematopoietic SCT, the minimum numbers of cells required for a successful engraftment are defined on the basis of their CD45 and CD34 expression profiles. However, the quantity of earlier progenitors or CD34-positive cells at different differentiation stages within stem cell grafts is not generally taken into consideration. During the last decade, various teams have quantified the number of cells expressing various combinations of CD34, CD38, CD133, CD90 co-expression and/or aldehyde dehydrogenase functional capacity using flow cytometry. Some of these studies resulted in the greater appreciation that combinations of these Ags were associated with varied myeloid, erythroid and platelet engraftment rates whereas others showed that the relative absence or presence of these markers could define cells responsible for either short- or long-term engraftment. These findings were also extended to differences between progenitor cell populations found within BM vs peripheral or cord-blood grafts. Cells harvested from donors are also generally frozen and stored; thawed cells have variable levels of viability and functional capacity based on the time tested post thaw, which also can be assessed by flow cytometry. Finally, flow cytometry has the potential for analysis of cells carrying a mesenchymal stem cell phenotype, which may be quiescent within some of the stem cell products. This review will address the need for stem cell subpopulation quantification and summarize existing published data to identify some Ags and functional characteristics that can be applicable to daily clinical practice.

Stem cells in endometrium and their role in the pathogenesis of endometriosis

The human endometrium is a dynamic tissue that undergoes cycles of growth and regression with each menstrual cycle. Adult progenitor stem cells are likely responsible for this remarkable regenerative capacity; these same progenitor stem cells may also have an enhanced capacity to generate endometriosis if shed in a retrograde fashion. The progenitor stem cells reside in the uterus; however, less-committed mesenchymal stem cells may also travel from other tissues such as bone marrow to repopulate the progenitor population. Mesenchymal stem cells are also involved in the pathogenesis of endometriosis and may be the principle source of endometriosis outside of the peritoneal cavity when they differentiate into endometriosis in ectopic locations. Finally, besides progenitor stem cells, recent publications have identified multipotent stem cells in the endometrium. These multipotent stem cells are a readily available source of cells that are useful in tissue engineering and regenerative medicine. Endometrial stem cells have been used to generate chondrocytes, myocytes, neurons, and adiposites in vitro as well as to replace dopaminergic neurons in a murine model of Parkinson's disease.

Breaking the dimensionality barrier

Recent advances in biotechnology have resulted in cytometers capable of performing numerous correlated measurements of cells, often exceeding ten. In the near future, it is likely that this number will increase by fivefold and perhaps even higher. Traditional analysis strategies based on examining one measurement versus another are not suitable for high-dimensional data analysis because the number of measurement combinations expands geometrically with dimension, forming a kind of complexity barrier. This dimensionality barrier limits cytometry and other technologies from reaching their maximum potential in visualizing and analyzing important information embedded in high-dimensional data.This chapter describes efforts to break through this barrier and allow the visualization and analysis of any number of measurements with a new paradigm called Probability State Modeling (PSM). This new system creates a virtual progression variable based on probability that relates all measurements. PSM can produce a single graph that conveys more information about a sample than hundreds of traditional histograms. These PSM overlays reveal the rich interplay of phenotypic changes in cells as they differentiate. The end result is a deeper appreciation of the molecular genetic underpinnings of ontological processes in complex populations such as found in bone marrow and peripheral blood.Eventually these models will help investigators better understand normal and abnormal cellular progressions and will be a valuable general tool for the analysis and visualization of high-dimensional data.

Advances in complex multiparameter flow cytometry technology: Applications in stem cell research

Flow cytometry and cell sorting are critical tools in stem cell research. Recent advances in flow cytometric hardware, reagents, and software have synergized to permit the stem cell biologist to more fully identify and isolate rare cells based on their immunofluorescent and light scatter characteristics. Some of these improvements include physically smaller air-cooled lasers, new designs in optics, new fluorescent conjugate-excitation pairs, and improved software to visualize data, all which combine to open up new horizons in the study of stem cells, by enhancing the resolution and specificity of inquiry. In this review, these recent improvements in technology will be outlined and important cell surface and functional antigenic markers useful for the study of stem cells described.

Uterine leiomyomas exhibit fewer stem/progenitor cell characteristics when compared with corresponding normal myometrium

Uterine leiomyomas (also known as uterine fibroids) are the most common benign tumors of female reproductive tract and are the single most common indication for hysterectomies. Despite their high prevalence, the exact pathogenesis of these benign tumors is still unknown. One possible mechanism for leiomyoma formation is dysregulation of mesenchymal stem cell activity. Mesenchymal stem cells have been identified in both human and murine uteri and cancer stem cells have been identified in female reproductive malignancies. We compared stem/progenitor cell characteristics in both normal myometrium and the corresponding leiomyoma of patient's undergoing hysterectomies. We found that leiomyoma cells form fewer mesenchymal stem cell colonies and exhibit less Hoechst dye-excluding side population (SP) activity, which is a function associated with progenitor cells in other tissues, than cells isolated from normal myometrium. Whereas in normal myometrium, we observed heterogeneous expression of CD90, a cell surface marker associated the with differentiation potential of uterine fibroblasts, in leiomyomas, we observed homogenous expression of CD90, suggesting leiomyoma cells are more terminally differentiated. Furthermore, we found that while leiomyoma cells could only produce CD90 expressing cells, both CD90+ and CD90- myometrial cells could reestablish their original heterogeneous CD90 profile when expanded in vitro. These results suggest that normal myometrium contains cells with stem/progenitor cell activities that are absent in leiomyomas.

Systems-level modeling of cancer-fibroblast interaction

Cancer cells interact with surrounding stromal fibroblasts during tumorigenesis, but the complex molecular rules that govern these interactions remain poorly understood thus hindering the development of therapeutic strategies to target cancer stroma. We have taken a mathematical approach to begin defining these rules by performing the first large-scale quantitative analysis of fibroblast effects on cancer cell proliferation across more than four hundred heterotypic cell line pairings. Systems-level modeling of this complex dataset using singular value decomposition revealed that normal tissue fibroblasts variably express at least two functionally distinct activities, one which reflects transcriptional programs associated with activated mesenchymal cells, that act either coordinately or at cross-purposes to modulate cancer cell proliferation. These findings suggest that quantitative approaches may prove useful for identifying organizational principles that govern complex heterotypic cell-cell interactions in cancer and other contexts.

From the fetal liver to spleen and gut: the highway to natural antibody

The film of sIgA lining the intestinal epithelium plays a role in the regulation of the commensal microflora and prevention of pathogen invasion. We show that, in the absence of intentional immunization, all sIgA in the gut is produced by B-1a B cells. We also show that B-1a B cells and sIgA derive from lineage-negative precursors found in the fetal liver and located in the spleen after birth. The splenic precursors do not generate B cells of the adaptive immune system in bone marrow, spleen, and lymph nodes, but efficiently replenish the cells producing the natural antibodies. Therefore, B-1a B cells with their splenic progenitors and their progeny of plasma cells fill the same function of the primordial immune system of lower vertebrates. The natural antibodies in the serum and on the intestinal epithelium may be an evolutionary ancient tool for the immediate protection against commensal and pathogenic bacteria.

The tumor stem cell concept-implications for endocrine tumors?

The cancer stem cell hypothesis has recently evolved from an increasing body of evidence suggesting that in some cancers a small population of tumor cells with stem cell-like properties represents a critical component that dictates the malignant behavior of a given tumor. These observations challenge classical cancer biology and its theory, that tumor growth is mainly based on genomic alterations followed by modulation of cell cycle pathways, which finally result in uncontrolled clonal proliferation. Over the last few years, much progress in the field of tumor stem cells has been achieved in non-endocrine malignancies. In this review, we summarize the existing evidence regarding the tumor stem cell concept for tumor pathophysiology in general and highlight current models that have the potential to further impact research on endocrine tumors.

Normal ovarian surface epithelial label-retaining cells exhibit stem/progenitor cell characteristics

Ovulation induces cyclic rupture and regenerative repair of the ovarian coelomic epithelium. This process of repeated disruption and repair accompanied by complex remodeling typifies a somatic stem/progenitor cell-mediated process. Using BrdU incorporation and doxycycline inducible histone2B-green fluorescent protein pulse-chase techniques, we identify a label-retaining cell population in the coelomic epithelium of the adult mouse ovary as candidate somatic stem/progenitor cells. The identified population exhibits quiescence with asymmetric label retention, functional response to estrous cycling in vivo by proliferation, enhanced growth characteristics by in vitro colony formation, and cytoprotective mechanisms by enrichment for the side population. Together, these characteristics identify the label-retaining cell population as a candidate for the putative somatic stem/progenitor cells of the coelomic epithelium of the mouse ovary.

Non-cultured adipose-derived CD45- side population cells are enriched for progenitors that give rise to myofibres in vivo

Side population (SP) cells are highly able to exclude the Hoechst 33342 dye through membrane transporters, a feature associated with cell immaturity and therefore proposed as a marker of stem cells. Herein we demonstrate that the adipose tissue derived stromal vascular fraction (SVF) contains a novel population of non-haematopoietic "side population" (SPCD45(-)) cells. Simultaneous qRT-PCR of 64 genes revealed that the freshly isolated SPCD45(-) was highly enriched for cells expressing genes related to stem cells, the Notch pathway, and early vascular precursors. Notably, the expression of smooth muscle actin, C-met and Cd34 together with Angpt2, Flk1, VE-cadherin, and Cd31 suggested a phenotypic resemblance to pericytes and aorta-derived mesoangioblasts. Recent evidence suggests that cells residing within the vascular niche may participate in regeneration of skeletal muscle and although skeletal muscle repair mainly relies on the satellite cell, several reports have shown that vessel-associated cells may adopt a myogenic phenotype when exposed to a muscle environment. In accordance with these findings, we also observed in vitro myogenic specification of SPCD45(-) cells when cocultured with myoblasts. Furthermore, immediate intramuscular engraftment of non-cultured SPCD45(-) cells gave rise to myofibres and cells lining blood vessels, whereas the SVF only provided donor derived mononuclear cells. We therefore conclude that the SPCD45(-) fraction of adipose-derived SVF is enriched for cells expressing vascular associated markers and that the myogenic differentiation potential of these cells does not depend on prior in vitro expansion.

Stem cells and the pathogenesis of endometriosis

Endometriosis is a common gynecological disorder that is defined by the presence of endometrial tissue outside the uterine cavity. This disease often results in extensive morbidity, including chronic pelvic pain and infertility. The pathogenesis of endometriosis is likely multifactorial, and extensive investigation has explored the role of genetics, environmental factors, and the immune system in predisposing patients to developing endometriosis. A series of recent publications have described the identification of endometrial stem/progenitor cells. Such cells have long been speculated to function in the cyclic regeneration of the endometrium during the menstrual cycle and in the pathogenesis of several gynecological disorders. This narrative review will (i) examine the evidence for endometrial stem cells, (ii) examine their potential role in the pathogenesis of endometriosis, and (iii) identify important unanswered questions with suggestions for future investigation.

Adult mouse myometrial label-retaining cells divide in response to gonadotropin stimulation

Conditional deletion of beta-catenin in the Müllerian duct mesenchyme results in a degenerative uterus characterized by replacement of the myometrial smooth muscle with adipose tissue. We hypothesized that the mouse myometrium houses somatic smooth muscle progenitor cells that are hormonally responsive and necessary for remodeling and regeneration during estrous cycling and pregnancy. We surmise that the phenotype observed in beta-catenin conditionally deleted mice is the result of dysregulation of these progenitor cells. The objective of this study was to identify the mouse myometrial smooth muscle progenitor cell and its niche, define the surface marker phenotype, and show a functional response of these cells to normal myometrial cycling. Uteri were labeled with 5-bromo-2'-deoxyuridine (BrdU) and chased for up to 14 weeks. Myometrial label-retaining cells (LRCs) were observed in the myometrium and stroma throughout the chase period. After 12 weeks, phenotypic analysis of the LRCs by immunofluorescence demonstrated that the majority of LRCs colocalized with alpha-smooth muscle actin, estrogen receptor-alpha, and beta-catenin. Flow cytometry of myometrial cells identified a myometrial Hoechst 33342 effluxing "side population" that expresses MISRII-Cre-driven YFP. Functional response of LRCs was investigated by human chorionic gonadotropin stimulation of week 12 chase mice and demonstrated sequential proliferation of LRCs in the endometrial stroma, followed by the myometrium. These results suggest that conventional myometrial regeneration and repair is executed by hormonally responsive stem or progenitor cells derived from the Müllerian duct mesenchyme. Disclosure of potential conflicts of interest is found at the end of this article.

Fibronectin and laminin enhance engraftibility of cultured hematopoietic stem cells

To test the hypothesis that extracellular matrix (ECM) components maintain stem cell property, murine bone marrow (BM) cells were expanded in fibronectin and laminin coated plate in the presence of cytokines. We observed significant phenotypic and functional improvement of expanded cells. In 10 days, 800-fold expansion of colony-forming unit-granulocyte erythrocyte monocyte megakaryocyte (CFU-GEMM) was observed in the cultured cells. No apparent activation of cell cycle was observed, but CD29 and very late antigen-4 (VLA-4) expression was increased, as compared to the normal BM cells. A fraction of the expanded cells became verapamil sensitive, suggesting upregulation of multi-drug resistant gene(s), as found in the primitive hematopoietic stem cells (HSCs). Competitive repopulation assay confirmed that HSCs compartment was amplified during culture. Overall, our study clearly demonstrated that ex vivo culture of murine HSCs in the presence of fibronectin and laminin resulted in expansion of primitive stem cells and improvement in the marrow engraftibility.

Optimization of immunomagnetic separation for cord blood-derived hematopoietic stem cells

BACKGROUND

There is a growing interest in cord blood as a source of primitive stem cells with the capacity for multilineage differentiation. Pure cell fractions are needed for the characterization and in vitro expansion of stem cells as well as for their use in preclinical research. However, enrichment of stem cells is challenging due to the lack of stem cell-specific markers and gentle protocols for the isolation of highly pure stem cell fractions. Protocols developed for the enrichment of peripheral blood-derived stem cells have been found to be suboptimal for cord blood.

RESULTS

In this study, immunomagnetic cell sorting protocols to purify CD34+, CD133+ and Lin- cells from fresh and cryopreserved cord blood were optimized. Reproducible purities of up to 97% were reached. The selected cells were highly viable having substantial colony-forming potential.

CONCLUSION

The optimized protocols enable rapid enrichment of highly pure hematopoietic stem cells from both fresh and cryopreserved cord blood.

Ovarian cancer side population defines cells with stem cell-like characteristics and Mullerian Inhibiting Substance responsiveness

The recent identification of "side population" (SP) cells in a number of unrelated human cancers and their normal tissue sources has renewed interest in the hypothesis that cancers may arise from somatic stem/progenitor cells. The high incidence of recurrence attributable to multidrug resistance and the multiple histologic phenotypes indicative of multipotency suggests a stem cell-like etiology of ovarian cancer. Here we identify and characterize SP cells from two distinct genetically engineered mouse ovarian cancer cell lines. Differential efflux of the DNA-binding dye Hoechst 33342 from these cell lines defined a human breast cancer-resistance protein 1-expressing, verapamil-sensitive SP of candidate cancer stem cells. In vivo, mouse SP cells formed measurable tumors sooner than non-SP (NSP) cells when equal numbers were injected into the dorsal fat pad of nude mice. The presence of Mullerian Inhibiting Substance (MIS) signaling pathway transduction molecules in both SP and NSP mouse cells led us to investigate the efficacy of MIS against these populations in comparison with traditional chemotherapies. MIS inhibited the proliferation of both SP and NSP cells, whereas the lipophilic chemotherapeutic agent doxorubicin more significantly inhibited the NSP cells. Finally, we identified breast cancer-resistance protein 1-expressing verapamil-sensitive SPs in three of four human ovarian cancer cell lines and four of six patient primary ascites cells. In the future, individualized therapy must incorporate analysis of the stem cell-like subpopulation of ovarian cancer cells when designing therapeutic strategies for ovarian cancer patients.

Hematopoietic stem cells

Hematopoietic stem cells (HSCs) have the capacity to self-renew and the potential to differentiate into all of the mature blood cell types. The ability to prospectively identify and isolate HSCs has been the subject of extensive investigation since the first transplantation studies implying their existence almost 50 years ago. Despite significant advances in enrichment protocols, the continuous in vitro propagation of human HSCs has not yet been achieved. This chapter describes current procedures used to phenotypically and functionally characterize candidate human HSCs and initial efforts to derive permanent human HSC lines.

p57Kip2 is expressed in quiescent mouse bone marrow side population cells

Hematopoietic stem cells can be accurately identified by the side population (SP) phenotype. It has been previously shown that hematopoietic stem cells are cell cycle arrested, but the mechanisms involved are currently poorly understood. In the present study, results from quantitative real-time RT-PCR show that while SP cells have increased expression of various cyclins and cyclin-dependent kinases, the increased expression of cyclin-dependent kinase inhibitors, in particular p57(Kip2), is responsible for the observed cell cycle arrest. In addition, gene expression analysis of c-kit(+/)/Sca-1(+)/Lineage- SP (KSL-SP) cells demonstrates that only p57(Kip2) shows both higher expression compared to both SP and non-SP cells. Furthermore, immunostaining also demonstrates significantly higher protein expression in KSL-SP cells. These results demonstrate that the maintenance of bone marrow SP cells in G0/G1 may be carefully controlled by p57(Kip2).

Murine side population cells contain cobblestone area-forming cell activity in mobilized blood

Primitive hematopoietic stem cells (HSCs) can be purified from murine bone marrow by sorting Hoechst 33342-effluxing side population (SP) cells. The aim of this study was to establish whether SP cells from peripheral blood contain primitive HSCs and whether this is altered in mice following mobilization. SP cells were analyzed and isolated from bone marrow and blood of mice after mobilization; the HSC content of isolated SP cells was determined through surrogate cobblestone area-forming cell (CAFC) assays. SP cells in normal blood were not found in the high Hoechst dye effluxing portion of the SP tail, did not express the stem cell markers c-Kit and CD34, and did not have measurable CAFC activity. In contrast, SP cells in mobilized blood expressed both stem cell markers, contained cells in the high dye efflux portion of the SP tail, and displayed significant day- 28 to day-35 CAFC activity with 165- to 334-fold enrichment. In comparison to mobilized blood SP cells, normal marrow SP cells contained a higher proportion of cells expressing c-Kit and CD34 and had a greater percentage of cells in the high Hoechst dye-effluxing portion of the SP tail. Analysis of SP cells in the bone marrow after mobilization revealed a decrease in the frequency of SP cells, in expression of c-Kit and Sca+ CD34(+)/CD34(-), and in day-7 to day-35 CAFC activity, consistent with mobilization into blood. We conclude that murine SP cells mobilized into blood contain primitive hematopoietic stem cell activity (day-28 to day-35 CAFC activity). This model offers a means to study the mechanisms of mobilization of primitive stem cells directly in a murine model.

Human umbilical cord matrix stem cells: preliminary characterization and effect of transplantation in a rodent model of Parkinson's disease

The umbilical cord contains an inexhaustible, noncontroversial source of stem cells for therapy. In the U.S., stem cells found in the umbilical cord are routinely placed into bio-hazardous waste after birth. Here, stem cells derived from human umbilical cord Wharton's Jelly, called umbilical cord matrix stem (UCMS) cells, are characterized. UCMS cells have several properties that make them of interest as a source of cells for therapeutic use. For example, they 1) can be isolated in large numbers, 2) are negative for CD34 and CD45, 3) grow robustly and can be frozen/thawed, 4) can be clonally expanded, and 5) can easily be engineered to express exogenous proteins. UCMS cells have genetic and surface markers of mesenchymal stem cells (positive for CD10, CD13, CD29, CD44, and CD90 and negative for CD14, CD33, CD56, CD31, CD34, CD45, and HLA-DR) and appear to be stable in terms of their surface marker expression in early passage (passages 4-8). Unlike traditional mesenchymal stem cells derived from adult bone marrow stromal cells, small populations of UCMS cells express endoglin (SH2, CD105) and CD49e at passage 8. UCMS cells express growth factors and angiogenic factors, suggesting that they may be used to treat neurodegenerative disease. To test the therapeutic value of UCMS cells, undifferentiated human UCMS cells were transplanted into the brains of hemiparkinsonian rats that were not immune-suppressed. UCMS cells ameliorated apomorphine-induced rotations in the pilot test. UCMS cells transplanted into normal rats did not produce brain tumors, rotational behavior, or a frank host immune rejection response. In summary, the umbilical cord matrix appears to be a rich, noncontroversial, and inexhaustible source of primitive mesenchymal stem cells.

Side population/ABCG2-positive cells represent a heterogeneous group of haemopoietic cells: implications for the use of adult stem cells in transplantation and plasticity protocols

Murine side population (SP) cells may have an increased ability to engraft lethally irradiated mice and lack CD34 expression. Strategies using CD34 as a primary marker of haemopoietic stem cells may therefore result in the exclusion of a primitive stem cell population. The molecular basis for the murine SP phenotype has been attributed to the multidrug-resistance transporter ABCG2. This study aimed to investigate ABCG2 expression from a variety of human sources and investigate the relationship between ABCG2 expression, the SP phenotype, and expression of markers such as CD34 and CD133. SP cells were observed in different haemopoietic sources, but a significant increase in the number of SP cells was observed in PB following granulocyte colony-stimulating factor mobilisation. No direct correlation between the frequency of SP cells and the expression of ABCG2 was observed. SP cells were identified in both lineage-positive and lineage-negative population and ABCG2 expression was enriched in lineage-negative SP cells. Lineage-negative SP cells were devoid of CD34 expression but enriched for CD133. Subsequent analysis revealed that ABCG2 and CD133 are coexpressed. Together, these data suggest that the ABCG2 transporter is neither required nor responsible for the SP phenotpye in many human blood cells.

Ponce de Leon's Fountain: stem cells and the regenerating heart

Despite current pharmacologic and whole organ transplantation strategies, advanced heart failure remains a common and deadly disease. Limited availability of donor organs for use in orthotopic heart transplantation has prompted the examination of alternative therapies, including cell transfer strategies. Stem cell populations have been identified in virtually all postnatal tissues with the exception of the heart, and these stem cells function in the maintenance and regeneration of the respective tissues. Recent studies challenge preexisting notions regarding cardiac repair and suggest that the heart is capable of limited regeneration through the activation of resident cardiac stem cells or the recruitment of stem cell populations from other tissues such as the bone marrow. This review highlights animal models that have the capacity for myocardial regeneration and examines potential sources of stem cell populations that may participate in tissue regeneration. While some authors view these cell-based strategies as a Fountain of Youth for the myopathic heart, future studies will decipher the regulatory mechanisms of stem cell populations and serve as a prelude to stem cell-based strategies.

Phenotypic characterization and preclinical production of human lineage-negative cells for regenerative stem cell therapy

BACKGROUND

Regenerative stem cell therapy (SCT) is currently being tested in clinical trials. The ideal type and source of cells have not yet been defined. Lineage (Lin) depletion is an experimental procedure capable of enriching all recently recognized SC types with regenerative potency. This study was performed to define a practicable monoclonal antibody (MoAb) cocktail for Lin depletion and to test whether clinical-scale Lin depletion is possible.

STUDY DESIGN AND METHODS

MoAbs (CD2/14/15/19/41/56/glycophorin A) were selected to mark seven mature hematopoietic lineages. Lin7-negative (Lin7NEG) cells were analyzed in peripheral blood (PB, n = 9), mobilized PB (MPB, n = 5), umbilical cord blood (UCB, n = 5), and marrow aspirates (BM, n = 4) by flow cytometry. Preclinical Lin depletion was tested with leukapheresis products from PB following good manufacturing practice (GMP) principles.

RESULTS

Lin7NEG cells comprised 0.23 +/- 0.04, 0.27 +/- 0.03, 0.53 +/- 0.07, and 0.49 +/- 0.03 percent of PB, MPB, UCB, and BM, respectively. Basophils, CD34+, and dendritic cells constituted the major Lin7NEG subpopulations (84 +/- 2, 90 +/- 3, 40 +/- 3, and 80 +/- 3% in PB, MPB, UCB, and BM, respectively). Minor populations included CD7- and CD45- cells. Preclinical CD2/14/15/19/56 (Lin5) depletion after automated red blood cell and platelet reduction resulted in up to a 16.7-fold enrichment of CD34+ and CD34-/Lin5NEG cells.

CONCLUSIONS

A seven-MoAb cocktail is sufficient to label more than 99 percent of nucleated cells in PB, MPB, UCB, and BM. Preclinical Lin depletion can be performed under GMP conditions from PB apheresis procedures.

Rare Incorporation of Bone Marrow-Derived Cells Into Kidney After Folic Acid-Induced Injury

Results obtained in recent experiments suggest that bone marrow-derived cells (BMDCs) engraft into tissues and differentiate into various somatic cell types. However, it is unclear whether injury is required for the phenomenon to occur at appreciable frequencies. In this study we tested whether BMDCs engraft into kidneys and differentiate into renal cells in the absence or presence of toxic injury. Renal damage was induced by delivery of folic acid (FA) to bone marrow (BM)-recipient mice 1 or 9 months after bone marrow transplant, and kidneys were examined for donor-derived cells 2,4, or 8 weeks after injury. Donor-derived cells were abundant in the renal interstitium of injured kidneys and were detected in glomeruli of vehicle- and FA-treated mice. Most of these cells expressed the common leukocyte antigen CD45 and display morphological characteristics of white blood cells. No donor-derived renal tubule cells (RTCs) were detected in kidney sections of BM-recipient mice. However, in cell culture, a cluster of seven donor-derived cells of 4 x 10(6) RTCs examined (approximately 0.0002%) displayed morphological characteristics of RTCs. CD45+ cells of donor origin were also detected in glomeruli and glomerular outgrowths. Nested polymerase chain reaction analysis for the male-specific Sry gene in cultured RTCs and glomerular outgrowths confirmed the presence of donor-derived cells. These results suggest that BMDCs may incorporate into glomeruli as specialized glomerular mesangial cells; however, BMDCs rarely contribute to the repair of renal tubules in uninjured or FA-treated mouse kidneys.

Characterization of a lineage-negative stem-progenitor cell population optimized for ex vivo expansion and enriched for LTC-IC

Current hematopoietic stem cell transplantation protocols rely heavily upon CD34+ cells to estimate hematopoietic stem and progenitor cell (HSPC) yield. We and others previously reported CD133+ cells to represent a more primitive cell population than their CD34+ counterparts. However, both CD34+ and CD133+ cells still encompass cells at various stages of maturation, possibly impairing long-term marrow engraftment. Recent studies demonstrated that cells lacking CD34 and hematopoietic lineage markers have the potential of reconstituting long-term in vivo hematopoiesis. We report here an optimized, rapid negative-isolation method that depletes umbilical cord blood (UCB) mononucleated cells (MNC) from cells expressing hematopoietic markers (CD45, glycophorin-A, CD38, CD7, CD33, CD56, CD16, CD3, and CD2) and isolates a discrete lineage-negative (Lin-) cell population (0.10% +/- 0.02% MNC, n=12). This primitive Lin- cell population encompassed CD34+/- and CD133+/- HSPC and was also enriched for surface markers involved in HSPC migration, adhesion, and homing to the bone marrow (CD164, CD162, and CXCR4). Moreover, our depletion method resulted in Lin- cells being highly enriched for long-term culture-initiating cells when compared with both CD133+ cells and MNC. Furthermore, over 8 weeks in liquid culture stimulated by a cytokine cocktail optimized for HSPC expansion, TPOFLK (thrombopoietin 10 ng/ml, Flt3 ligand 50 ng/ml, c-Kit ligand 20 ng/ml) Lin- cells underwent slow proliferation but maintained/expanded more primitive HSPC than CD133+ cells. Therefore, our Lin- stem cell offers a promising alternative to current HSPC selection methods. Additionally, this work provides an optimized and well-characterized cell population for expansion of UCB for a wider therapeutic potential, including adult stem cell transplantation.

Systemic delivery of human microdystrophin to regenerating mouse dystrophic muscle by muscle progenitor cells

Cell-based therapy for Duchenne muscular dystrophy patients and mdx mice has proven to be a safe but ineffective form of treatment. Recently, a group of cells called muscle side population (SP) cells have been isolated based on their ability to efflux the DNA-binding dye Hoechst. To understand the potential of skeletal muscle SP cells to serve as precursors for muscle, SP cells from the two mice strains mdx(5cv) and C57BL/6N were isolated, transduced, and transplanted. Under coculture conditions with myogenic cells, some cells within the SP cell population can give rise to early Pax7-positive satellite cells and other later stage myogenic cells. Transduced SP cells were transplanted via the tail vein and were shown to successfully deliver enhanced GFP and human microdystrophin to the skeletal muscle of nonirradiated mdx(5cv) mice, thus demonstrating their ability to travel through the capillaries and enter into damaged muscle. These results demonstrate that i.v. delivery of genes via SP cells is possible and that these SP cells are capable of recapitulating the myogenic lineage. Because this approach shows definitive engraftment by using autologous transplantation of noninjured recipients, our data may have substantial implications for therapy of muscular dystrophy.

Stem cell-mediated muscle regeneration is enhanced by local isoform of insulin-like growth factor 1

We investigated the mechanism whereby expression of a transgene encoding a locally acting isoform of insulin-like growth factor 1 (mIGF-1) enhances repair of skeletal muscle damage. Increased recruitment of proliferating bone marrow cells to injured MLC/mIgf-1 transgenic muscles was accompanied by elevated bone marrow stem cell production in response to distal trauma. Regenerating MLC/mIgf-1 transgenic muscles contained increased cell populations expressing stem cell markers, exhibited accelerated myogenic differentiation, expressed markers of regeneration and readily converted cocultured bone marrow to muscle. These data implicate mIGF-1 as a powerful enhancer of the regeneration response, mediating the recruitment of bone marrow cells to sites of tissue damage and augmenting local repair mechanisms.

Stem cell biology and therapeutic applications

PURPOSE OF REVIEW

Chronic diseases are common and deadly. Stem cell therapies have received intense interest for the repopulation of damaged or diseased tissues. A detailed understanding of the similarities and differences between embryonic stem cells and somatic stem cells will enhance our understanding of mechanisms of tissue repair or cellular augmentation. In addition, emerging technologies will be useful in the definition of the molecular regulation of the respective stem cell populations.

RECENT FINDINGS

A number of postnatal tissues have a population of somatic stem cells, which function in the maintenance and repair of tissues. Using molecular technologies these somatic stem cell populations have been shown to be pluripotent when placed in a permissive environment. Recent studies have utilized emerging technologies to define a molecular signature of embryonic stem cells and selected somatic stem cell populations. These strategies will be useful for the definition of a molecular program that promotes a stem cell phenotype (i.e. stemness phenotype).

SUMMARY

Recent studies suggest that embryonic and somatic stem cell populations hold promise as sources for tissue engineering. The use of cell biological and molecular technologies will enhance our understanding of embryonic and somatic stem cell populations and their molecular regulatory events that promote multipotentiation.