Recipes for adult stem cell plasticity: fusion cuisine or readymade?

Mesenchymal Stromal Cell Therapeutic Delivery: Translational Challenges to Clinical Application

For several decades, multipotent mesenchymal stromal cells (MSCs) have been extensively studied for their therapeutic potential across a wide range of diseases. In the preclinical setting, MSCs demonstrate consistent ability to promote tissue healing, down-regulate excessive inflammation and improve outcomes in animal models. Several proposed mechanisms of action have been posited and demonstrated across an array of in vitro models. However, translation into clinical practice has proven considerably more difficult. A number of prominent well-funded late-phase clinical trials have failed, thus calling out for new efforts to optimize product delivery in the clinical setting. In this review, we discuss novel topics critical to the successful translation of MSCs from pre-clinical to clinical applications. In particular, we focus on the major routes of cell delivery, aspects related to hemocompatibility, and potential safety concerns associated with MSC therapy in the different settings.

Bone marrow mesenchymal stem cells participate in prostate carcinogenesis and promote growth of prostate cancer by cell fusion in vivo

The tumor microenvironment is comprised of diverse stromal cells that contribute towards tumor progression. As a result, there has been a growing interest in the role of bone marrow derived cells (BMDCs) in cancer progression. However, the role of BMDCs in prostate cancer (PCa) progression still remains unclear. In this study, we established GFP bone marrow transplanted TRAMP and MUN-induced prostate cancer models, in order to investigate the role of BMDCs in prostate cancer progression. By tracing GFP positive cells, we observed that BMDCS were recruited into mouse prostate tissues during tumorigenesis. GFP+/Sca-1+/CD45− BMDCs were significantly increased in the MNU-induced PCa group, as compared to the citrated-treated control group (2.67 ± 0.25% vs 0.67 ± 0.31%, p = 0.006). However, there were no significant differences found in GFP+/Sca-1+/CD45+ cell populations between the two groups (0.27 ± 0.15% vs 0.10 ± 0.10%, p = 0.334). Moreover, co-grafting of bone marrow mesenchymal stem cells (BMMSCs) and RM1 cells were found to promote RM1 tumor growth in vivo, and cell fusion was observed in RM-1+BMMSCs xenografts. Therefore, the data suggests that BMDCs can be recruited to the prostate during carcinogenesis, and that BMMSCs may promote the growth of PCa.

[Autologous fat transplantation in the modern reconstructive surgery of breast cancer]

Autologous fat transplantation is often used in aesthetic plastic surgery, and is recently becoming increasingly popular in the reconstruction of soft tissue defects following oncological surgery. A still not standardized technique of fat transplantation for breast cancer reconstruction is rapidly getting popular. The procedure is not a passive volume replacement, but transplantation of biologically active tissue bearing endocrine, paracrine, exocrine functions and containing fat-derived stem cells, which in the tumorous environment raises many questions in relation to the oncological safety and diagnostic follow-up. Although long-term results based on prospective, randomized studies are not yet available, published clinical experience is promising and reveals an effective and surgically safe procedure if used with appropriate indications and techniques. The authors conducted a broad review of the literature, presenting indications, technique, molecular interactions, and potential risks of the clinical results of autologous fat transplantation in the breast cancer reconstructive surgery. The authors initiated that breast and plastic surgeons should promote adequate long term follow-up of breast cancer patients who underwent breast reconstruction with autologous fat transplantation by the establishment of national registries.

The safety of autologous fat transfer in breast cancer: lessons from stem cell biology

Autologous fat grafting is versatile tool in plastic surgery and is increasing used for reconstruction following breast conserving surgery for breast cancer. Part of the reconstructive qualities of the transferred fat may be due to the presence of adipose derived mesenchymal stem cells (ADMSC) playing an angiogenic and an adipogenic role. In this context it must be considered if autologously engrafted fat tissue could contribute to carcinogenesis following breast conserving surgery. In this article we review the current stem cell biology evidence on engraftment, transdifferentiation and potential carcinogenic contribution in the breast and other solid organ stem cell niches in an attempt to highlight possible areas of concern.

Cell Fusion, Drug Resistance and Recurrence CSCs

Cancer stem cells (CSCs) are a rare population of cancer cells exhibiting stem cell properties, such as self-renewal, differentiation and tissue restoration. Beside the initiation of the primary tumor, CSCs have also been associated with metastasis formation and cancer relapses. In the context of cancer relapses, we have recently postulated the existence of so-called recurrence CSCs (rCSCs). These specific CSC subtype will initiate relapses exhibiting an "oncogenic resistance" phenotype, which are characterized by a markedly increased malignancy concomitant with a drug resistance towards first line therapy. In the present chapter we will discuss the necessity of rCSCs as a distinct CSC subtype and that cell fusion could be one mechanism how rCSCs could originate.

In vitro differentiation of embryonic and adult stem cells into hepatocytes: state of the art

Stem cells are a unique source of self-renewing cells within the human body. Before the end of the last millennium, adult stem cells, in contrast to their embryonic counterparts, were considered to be lineage-restricted cells or incapable of crossing lineage boundaries. However, the unique breakthrough of muscle and liver regeneration by adult bone marrow stem cells at the end of the 1990s ended this long-standing paradigm. Since then, the number of articles reporting the existence of multipotent stem cells in skin, neuronal tissue, adipose tissue, and bone marrow has escalated, giving rise, both in vivo and in vitro, to cell types other than their tissue of origin. The phenomenon of fate reprogrammation and phenotypic diversification remains, though, an enigmatic and rare process. Understanding how to control both proliferation and differentiation of stem cells and their progeny is a challenge in many fields, going from preclinical drug discovery and development to clinical therapy. In this review, we focus on current strategies to differentiate embryonic, mesenchymal(-like), and liver stem/progenitor cells into hepatocytes in vitro. Special attention is paid to intracellular and extracellular signaling, genetic modification, and cell-cell and cell-matrix interactions. In addition, some recommendations are proposed to standardize, optimize, and enrich the in vitro production of hepatocyte-like cells out of stem/progenitor cells.

Recurrence cancer stem cells--made by cell fusion?

Within the past 10-15 years our knowledge about cancer and how cancer cells might originate has changed dramatically. It is now generally believed that a tumor has its origin in cancer stem cells (CSCs), which originated either from transformed tissue stem cells or transformed progenitor cells that have regained self-renewal activity. CSCs share several characteristics of normal stem cells, such as self-renewal capacity, slow cell cycle activity, differentiation capacity, possessing an enhanced resistance towards cytotoxic agents and radiation, as well as tissue restoration capacity. Due to the increased drug and radiation resistance and slow cell cycle activity concomitant with tumor initiation capacity it is generally assumed that recurrent cancers originate from first line therapy surviving CSCs. But how does the CSC hypothesis explain "oncogenic resistance", which describes the phenomenon that most recurrent cancers are characterized by both an increased malignancy as well as resistance towards first line cancer therapy. To us, "oncogenic resistance" can not be simply attributed to the resistance properties of normal CSCs. If so, the recurring tumor should be treatable by first line therapy, which is mostly not the case. Thus, we conclude that "oncogenic resistance" demands a new type of tumor initiating cells, the so-called recurrence CSCs (rCSCs). This type of tumor initiating cell originates during first line therapy and is characterized by giving rise to first line therapy resistant and highly malignant progenies. Because several characteristics of "oncogenic resistance", such as increased drug resistance, increased resistance to apoptosis and an enhanced malignancy have been linked to cell fusion we further conclude that rCSCs might originate from this cellular event. However, which cell types have to fuse with each other to ultimately give rise to rCSCs is not clear. In any case, tumor tissues, particularly those being destructed by first line therapy comprise of a variety of fusogenic cells including tumor cells and CSCs as well as recruited monocytes/macrophages and bone marrow-derived stem cells. The fusogenic properties of these cells concomitant with phenotypic heterogeneity, which is also a property of cell fusion, will then lead to the origin of rCSCs. In accordance with Darwinian evolution only those cells will survive that can resist best to the selection pressure first line therapy.

Human immature dental pulp stem cells' contribution to developing mouse embryos: production of human/mouse preterm chimaeras

OBJECTIVES

In this study, we aimed at determining whether human immature dental pulp stem cells (hIDPSC) would be able to contribute to different cell types in mouse blastocysts without damaging them. Also, we analysed whether these blastocysts would progress further into embryogenesis when implanted to the uterus of foster mice, and develop human/mouse chimaera with retention of hIDPSC derivates and their differentiation.

MATERIALS AND METHODS

hIDPSC and mouse blastocysts were used in this study. Fluorescence staining of hIDPSC and injection into mouse blastocysts, was performed. Histology, immunohistochemistry, fluorescence in situ hybridization and confocal microscopy were carried out.

RESULTS AND CONCLUSION

hIDPSC showed biological compatibility with the mouse host environment and could survive, proliferate and contribute to the inner cell mass as well as to the trophoblast cell layer after introduction into early mouse embryos (n = 28), which achieved the hatching stage following 24 and 48 h in culture. When transferred to foster mice (n = 5), these blastocysts with hIDPSC (n = 57) yielded embryos (n = 3) and foetuses (n = 6); demonstrating presence of human cells in various organs, such as brain, liver, intestine and hearts, of the human/mouse chimaeras. We verified whether hIDPSC would also be able to differentiate into specific cell types in the mouse environment. Contribution of hIDPSC in at least two types of tissues (muscles and epithelial), was confirmed. We showed that hIDPSC survived, proliferated and differentiated in mouse developing blastocysts and were capable of producing human/mouse chimaeras.

Stem cells for skin tissue engineering and wound healing

The tremendous ability of the skin's epidermis to regenerate is due to the presence of epidermal stem cells that continuously produce keratinocytes, which undergo terminal differentiation to a keratinized layer that provides the skin's barrier properties. The ability to control this process in vitro has made it possible to develop various types of tissue-engineered skin grafts, some of which are among the first tissue-engineered products to ever reach the market. In the past 30 years, these products have been applied with some success to the treatment of chronic skin wounds such as diabetic and venous ulcers and deep, acute wounds such as burns. Current technologies remain partially effective in their ability to restore other skin structures, for example, the dermis, which is critical to the overall long-term appearance and function of the skin. As yet, none of these approaches can regenerate skin appendages (e.g. hair follicles and sweat glands). The use of earlier progenitor and stem cells, including embryonic stem cells, is gaining interest in the attempt to overcome such limitations. Furthermore, recent evidence suggests that "adult" stem cells, which are present in the circulation, target areas of injury and likely participate in the wound-healing process. In this paper, we start with an overview of the wound-healing process and current methods used for wound treatment, both conventional and tissue-engineering based. We then review current research on the various types of stem cells used for skin tissue engineering and wound healing, and provide future directions.

Exogenous bone marrow cells do not rescue non-irradiated mice from acute renal tubular damage caused by HgCl2, despite establishment of chimaerism and cell proliferation in bone marrow and spleen

OBJECTIVE

Various studies have shown that bone marrow stem cells can rescue mice from acute renal tubular damage under a conditioning advantage (irradiation or cisplatin treatment) favouring donor cell engraftment and regeneration; however, it is not known whether bone marrow cells (BMCs) can contribute to repair of acute tubular damage in the absence of a selection pressure for the donor cells. The aim of this study was to examine this possibility.

MATERIALS AND METHODS

Ten-week-old female mice were assigned into control non-irradiated animals having only vehicle treatment, HgCl(2)-treated non-irradiated mice, HgCl(2)-treated non-irradiated mice infused with male BMCs 1 day after HgCl(2), and vehicle-treated mice with male BMCs. Tritiated thymidine was given 1 h before animal killing.

RESULTS

Donor BMCs could not alleviate non-irradiated mice from acute tubular damage caused by HgCl(2), deduced by no reduction in serum urea nitrogen combined with negligible cell engraftment. However, donor BMCs could home to the bone marrow and spleen and display proliferative activity. This is the first report to show that despite no preparative myeloablation of recipients, engrafted donor BMCs can synthesize DNA in the bone marrow and spleen.

CONCLUSIONS

Exogenous BMCs do not rescue non-irradiated mice from acute renal tubular damage caused by HgCl(2), despite establishment of chimerism and cell proliferation in bone marrow and spleen.

Haematopoietic lineage-committed bone marrow cells, but not cloned cultured mesenchymal stem cells, contribute to regeneration of renal tubular epithelium after HgCl 2 -induced acute tubular injury

OBJECTIVE

Our previous studies have demonstrated that endogenous bone arrow cells (BMCs) contribute to renal tubular regeneration after acute tubular injury. The aim of this study was to examine which fraction of BMCs, haematopoietic lineage marrow cells (HLMCs) or mesenchymal stem cells (MSCs), are effective.

MATERIALS AND METHODS

Six-week-old female mice were lethally irradiated and were transplanted with female enhanced green fluorescent protein-positive (GFP(+)), plastic on-adherent marrow cells (as a source of HLMCs) plus cloned cultured male GFP(-) MSCs. Four weeks later, they were assigned into two groups: control mice with vehicle treatment and mice treated with HgCl2. Tritiated thymidine was given 1 h before animal killing which occurred at intervals over 2 weeks. Kidney sections were stained for a tubular epithelial marker, cell origin indicated by GFP immunohistochemistry or Y chromosome in situ hybridization; periodic acid-Schiff staining was performed, and samples were subjected to autoradiography. One thousand consecutive renal tubular epithelial cells per mouse, in S phase, were scored as either female (indigenous) GFP+(HLMC-derived) or male (MSC-derived).

RESULTS

Haematopoietic lineage marrow cells and MSCs stably engrafted into bone marrow and spleen, but only HLMC-derived cells, not MSCs, were found in the renal tubules and were able to undergo DNA synthesis after acute renal injury. A few MSCs were detected in the renal interstitium, but their importance needs to be further explored.

CONCLUSION

Haematopoietic lineage marrow cells, but not cloned cultured MSCs, can play a role not only in normal wear-and-tear turnover of renal tubular cells, but also in repair after tubular injury.

Plasticity after allogeneic hematopoietic stem cell transplantation

The postulated almost unlimited potential of transplanted hematopoietic stem cells (HSCs) to transdifferentiate into cell types that do not belong to the hematopoietic system denotes a complete paradigm shift of the hierarchical hemopoietic tree. In several studies during the last few years, donor cells have been identified in almost all recipient tissues after allogeneic HSC transplantation (HSCT), supporting the theory that any failing organ could be accessible to regenerative cell therapy. However, the putative potential ability of the stem cells to cross beyond lineage barriers has been questioned by other studies which suggest that hematopoietic cells might fuse with non-hematopoietic cells and mimic the appearance of transdifferentiation. Proof that HSCs have preserved the capacity to transdifferentiate into other cell types remains to be demonstrated. In this review, we focus mainly on clinical studies addressing plasticity in humans who underwent allogeneic HSCT. We summarize the published data on non-hematopoietic chimerism, donor cell contribution to tissue repair, the controversies related to the methods used to detect donor-derived non-hematopoietic cells and the functional impact of this phenomenon in diverse specific target tissues and organs.

The role of bone marrow-derived cells in fibrosis

There is a growing realization that bone marrow-derived cells (BMDCs) are a potential therapy for many diseases including ischemic heart disease, arterial stenosis and osteogenesis imperfecta. On the other hand, the fact that BMDCs may also contribute to fibrosis in many solid organs as well as to fibrosis surrounding tumours suggests that BMDCs are also involved in disease progression. This review focuses on the contribution of bone marrow cells to organ and tumour fibrosis, noting the utility of BMDCs as a potential new portal through which to direct anti-tumour therapies. Conversely, bone marrow cell therapy has been claimed to reduce fibrosis in some organs, highlighting a seemingly beneficial as opposed to a detrimental effect of BMDCs on organ fibrosis.

Metaplasia and transdifferentiation: from pure biology to the clinic

Transformations from one tissue type to another make up a well established set of phenomena that can be explained by the principles of developmental biology. Although these phenomena might be rare in nature, we can now imagine the possibility of deliberately reprogramming cells from one tissue type to another by manipulating the expression of transcription factors. This approach could generate new therapies for many human diseases.

Liver chimerism after allogeneic blood stem cell transplantation

Blood stem cells can mature into elements of many different lineages. We investigated the presence and nature of donor-derived (chimeric) cells within the liver after allogeneic stem cell transplantation.

METHODS

Liver biopsy autopsy specimens were examined from nine female patients who had undergone allogeneic bone marrow (n = 6) or peripheral stem cell (n = 3) transplantation from a male donor. To identify the male origin of cells within the liver, in-situ hybridization for Y-chromosomes was performed in conjunction with CD45 staining to identify leucocytes.

RESULTS

Hematopoietic stem cell engraftment was confirmed in all nine recipients. Histologic examination of the liver tissue sections revealed 5.6-fold more Y-chromosome-positive than CD45-positive staining cells (P < .02), indicative of considerable nonleucocytic chimerism. This was particularly observed in patients who had developed graft-versus-host disease.

CONCLUSIONS

Donor-derived cells can be found in liver tissue specimens after allogeneic stem cell transplantation. A considerable fraction of chimeric (donor-derived) cells appeared to be of nonlymphohematopoietic origin. This finding supports the theory of blood stem cells developing into liver cells of mesenchymal origin.

Liver repair by intra- and extrahepatic progenitors

Despite its remarkable capacity for endogenous regeneration, the mammalian liver is vulnerable to a number of chronic or acute conditions that exceed or circumvent the proliferative capabilities of its mature cell complement. Bipotential hepatic progenitors, or "oval cells," have been shown to contribute to organ regeneration under such circumstances, both in human patients and in animal models. These progenitors are attractive agents for cell therapy, but have thus far proven challenging to isolate and manipulate. New reports indicating that transplanted bone marrow cells (BMCs) can also generate hepatocytes and contribute to liver repair have attracted considerable attention, because these cells are familiar and accessible to both clinicians and scientists. Recently, the issue of whether nuclear transfer (via cell fusion between donor BMC and recipient hepatocyte) or previously unrecognized differentiation potential (i.e., plasticity/transdifferentiation of BMC) is the primary origin of donor-derived hepatocytes has generated considerable controversy. In the liver, most evidence supports cell fusion as the key agent in the reversal of hepatopathology. However, regardless of their origin, the frequency of hepatocyte correction events is low. As is the case for the delivery of intrahepatic progenitors, substantial improvements in the understanding of this process will be needed before clinical application becomes practical.

Donor-derived myofibroblasts in the ocular surface after allogeneic haematopoietic stem cell transplantation

PURPOSE

To identify and characterize cells of donor origin in the ocular surface of female recipients who have undergone allogeneic haematopoietic stem cell transplantation (allo-SCT) from a male donor.

METHODS

Cytological impressions from the eyes of nine allografted patients (17 eyes) were analysed. Donor cells were identified using sex-chromosome-specific fluorescence in situ hybridization (FISH). Cells were characterized by immunohistochemistry (IHC) using the CK3 and CK19 epithelial markers, the panleucocytic marker CD45 and the myofibroblast marker alpha-SMA.

RESULTS

No epithelial cells of donor origin were observed in the corneal or conjunctival samples. Cells of donor origin were found in the corneal samples, although these were often too degraded to allow characterization by IHC. In the conjunctiva, a median of 86% of the total number of cells were of recipient origin, including a subgroup (2%) of giant cells exhibiting polyploidy (range 4-18 n), found in the limbal region. Donor cells were detected in the conjunctiva of all nine patients at a median ratio of 9%, of which two-thirds were CD45+/alpha-SMA+.

CONCLUSIONS

We observed superficially located myofibroblasts of donor origin in all allografted patients, but not in samples from healthy controls. Whether myofibroblasts are implicated in ocular graft-versus-host disease requires further studies.

Bone marrow-derived mesenchymal stem cells for regenerative medicine in craniofacial region

The craniofacial region contains many specified tissues including bone, cartilage, muscle, blood vessels and neurons. Defect or dysfunction of the craniofacial tissue after post-cancer ablative surgery, trauma, congenital malformations and progressive deforming skeletal diseases has a huge influence on the patient's life. Therefore, functional reconstruction of damaged tissues is highly expected. Bone marrow-derived mesenchymal stem cells (BMMSCs) are one of the most well characterized postnatal stem cell populations, and considered to be utilized for cell-based clinical therapies. Here, the current understanding and the potential applications in craniofacial tissue regeneration of BMMSCs are reviewed, and the current limitations and drawbacks are also discussed.

Embedding of bone samples in methylmethacrylate: a suitable method for tracking LacZ mesenchymal stem cells in skeletal tissues

Considerable research has been focused on the use of bone marrow-derived mesenchymal stem cells (MSCs) for the repair of non-unions and bone defects. To date, the question of whether transplanted MSCs survive and engraft within newly formed tissue remains unresolved. The development of an easy and reliable method that would allow cell fate monitoring in transplant recipients is a pressing concern for the field of tissue engineering. To demonstrate the presence of transplanted cells in newly formed bone, we established a xenograft nude rat model allowing the detection of murine LacZ MSCs in vivo. MSCs were isolated from transgenic lacZ mice, seeded onto bioabsorbable collagen sponges, and transplanted to repair a calvarial defect in nude rats. As a preliminary step, the histological procedure was adapted to optimize the detection of LacZ cells in bone tissue embedded in methylmethacrylate (MMA). Four fixatives and four fixation times were evaluated. Among all the fixatives tested, 2% formaldehyde/0.2% glutaraldehyde at 4C for 4 days gave the best results for X-gal staining at pH 7.4 on both cell cultures and bone explants. All fixatives were effective for immunodetection of beta-gal. In the chimeric LacZ/nude rat animal model, MSCs were detected in vivo for up to 4 weeks after implantation and contributed to the repair and the neovascularization of the bone defect. LacZ is a suitable phenotypic marker to track MSCs in skeletal tissues embedded in MMA.

Multipotent Adult Progenitor Cell Lines Originating from the Peripheral Blood of Green Fluorescent Protein Transgenic Swine

Multipotent self-renewing stem cell lines have been established using peripheral blood mononuclear cells from adult green fluorescent protein transgenic swine. These cells proliferate as nonadherent spheroids in primordial-specific culture media and readily differentiate into angiogenic, osteogenic, adipogenic, and neurogenic phenotypes when cultured under the appropriate conditions. These cells are designated peripheral blood-derived multipotent adult progenitor cells (PBD-MAPCs). When differentiated in endothelial-specific media, these cells exhibit a cobblestone morphology and express von Willebrand factor (vWF), take up 1,1'-dioctadecyl-3,3,3',3'-tetramethyl-indocarboxyanine-labeled acetylated low-density lipoprotein DiI-Ac-LDL, and form tubes with lumens when grown on pads of Matrigel. Under different culture conditions, the cells appear whorl-like in appearance and express alpha-actin, indicative of smooth muscle phenotype. In the presence of dexamethasone and ascorbic acid, PBD-MAPCs differentiate into cells that produce Alizarin Red-staining extracellular mineral, consistent with an osteogenic potential. Under different conditions the cells produce Oil Red O-staining lipid vacuoles, suggestive of an adipocyte phenotype. We have also developed conditions that induce PBDMAPCs to differentiate into neural cells, confirmed by the expression of specific neuron- and glial-specific markers. Upon transplantation into rat brain, the neurogenic cells survive and migrate throughout the striatum and corpus callosum. The cells remain brightly fluorescent throughout their time in culture, during in vitro differentiation, and after in vivo transplantation. PBD-MAPCs have been maintained in primordial cell media for more than 100 doublings, yet can be induced to differentiate rapidly and efficiently into distinct cell types. PBD-MAPCs are ideal tools to study the mechanisms of differentiation and may be superior to embryonic stem cells as cellular therapeutics.

Stem cell plasticity and tumour formation

Stem cell plasticity refers to the ability of certain stem cells to switch lineage determination and generate unexpected cell types. This review applies largely to bone marrow cells (BMCs), which appear to contribute positively to the regeneration of several damaged non-haematopoietic tissues. This beneficial effect on regeneration may be a direct result of BMCs giving rise to organ parenchymal cells. Alternatively, it could be due to BMCs fusing with existing parenchymal cells, or providing paracrine growth factor support, or contributing to neovascularisation. In the context of oncology, BMC derivation of the tumour stroma and vasculature has profound biological and therapeutic implications, and there are several examples of carcinomas seemingly being derived from BMCs.

Bone marrow-derived stromal cells express lineage-related messenger RNA species

Evidence has emerged that bone marrow cells have a greater degree of plasticity than previously thought. However, there has been a call to establish proof that these bone marrow-derived cells function appropriately in their new environment. We have already shown that the bone marrow contributes to myofibroblasts in multiple organs and that this is exacerbated by injury and occurs in a mouse tumor model. Here, we provide evidence that these cells are functioning appropriately by showing that bone marrow-derived myofibroblasts are expressing mRNA for the alpha(1) chain of type I (pro)collagen using a new customized technique. This provides evidence that the bone marrow-tumor stroma axis is functionally relevant and may therefore subsequently be exploited to develop new strategies for anticancer therapy.

From embryos to embryonic stem cells: biopolitics and therapeutic potential

The inner cell mass of the preimplantation blastocyst, from which all the cells of the body develop, is a source of embryonic stem cells. These cells can be maintained in their undifferentiated state over long periods in culture and yet retain their pluripotency. The generation of human stem cells capable of differentiating into all the cell types of the human body opens the way for the use of these cells in therapeutic transplantation for a myriad of diseases. However, as discussed here, there are a number of logistical, biological, and clinical hurdles that must be overcome prior to the use of these cells in routine clinical practice.

The gastrointestinal tract stem cell niche

The gastrointestinal epithelium is unique in that cell proliferation, differentiation, and apoptosis occur in an orderly fashion along the crypt-villus axis. The intestinal crypt is mainly a proliferative compartment, is monoclonal and is maintained by stem cells. The villus represents the differentiated compartment, and is polyclonal as it receives cells from multiple crypts. In the small intestine, cell migration begins near the base of the crypt, and cells migrate from here emerging onto the villi. The basal crypt cells at position 5 are candidate stem cells. As the function of stem cells is to maintain the integrity of the intestinal epithelium, it must self-renew, proliferate, and differentiate within a protective niche. This niche is made up of proliferating and differentiating epithelial cells and surrounding mesenchymal cells. These mesenchymal cells promote the epithelial- mesenchymal crosstalk required to maintain the niche. A stochastic model of cell division has been proposed to explain how a single common ancestral stem cell exists from which all stem cells in a niche are descended. Our group has argued that these crypts then clonally expand by crypt fission, forming two daughters' crypts, and that this is the mechanism by which mutated stem cells or even cancer stem cell clones expand in the colon and in the entire gastrointestinal tract. Until recently, the differentiation potential of stem cells into adult tissues has been thought to be limited to cell lineages in the organ from which they were derived. Bone marrow cells are rare among adult stem cells regarding their abundance and role in the continuous, lifelong, physiological replenishment of circulating cells. In human and mice experiments, we have shown that bone marrow can contribute to the regeneration of intestinal myofibroblasts and thereby after epithelium following damage, through replacing the cells, which maintain the stem cells niche. Little is known about the markers characterizing the stem and transit amplifying populations of the gastrointestinal tract, although musashi-1 and hairy and enhancer of split homolog-1 have been proposed. As the mammalian gastrointestinal tract develops from the embryonic gut, it is made up of an endodermally-derived epithelium surrounded by cells of mesoderm origin. Cell signaling between these two tissue layers plays a critical role in coordinating patterning and organogenesis of the gut and its derivatives. Many lines of evidence have revealed that Wnt signaling is the most dominant force in controlling cell proliferation, differentiation, and apoptosis along the crypt-villus axis. We have found Wnt messenger RNAs expression in intestinal subepithelial myofibroblasts and frizzled messenger RNAs expression in both myofibroblasts and crypt epithelium. Moreover, there are many other factors, for example, bone morphogenetic protein, homeobox, forkhead, hedgehog, homeodomain, and platelet-derived growth factor that are also important to stem cell signaling in the gastrointestinal tract.

The function of stem cells and their future roles in healthcare

Adult stem cells from bone marrow have been used in the treatment of cancer for many years. Recently, however, interest has developed in the isolation and growth of adult, cord and embryonic stem cells for use in regenerative medicine. Their therapeutic use will undoubtedly be implemented in nursing practice in a variety of clinical areas. This article is a brief introduction to stem cells and addresses the biology of these cells and their potential clinical applications, looking at three possible diseases as examples: myocardial infarction, type 1 diabetes and osteoarthritis.

Stem cells in gynaecology

Currently, there is enormous interest in stem cells as a new treatment modality for regenerative medicine, commencing when human embryonic stem (hES) cells were first cultured from spare in vitro fertilisation-derived embryos. Emerging evidence also suggests that somatic stem cells may have greater differentiation potential. Stem cell research is now in an exciting phase of development and has the potential to dramatically influence therapeutics as hES cell derivatives and/or adult stem cells are applied to regenerative medicine or to deliver gene therapy. Human ES cells show apparently limitless proliferative potential and differentiation capacity into all tissue types. Adult stem cells are rare cells, which maintain the tissue in which they reside. The challenges facing the use of hES cells and adult stem cells in medicine are highlighted and examples of their use in laboratory studies and the clinic are given. Adult stem cells have been identified in diverse tissues, including human bone marrow, breast, prostate, brain and liver. We hypothesised that adult stem cells reside in the endometrium, a highly proliferative, cyclically regenerating tissue. Our research has demonstrated, for the first time, that human endometrium contains a small population of epithelial cells (0.22%) and stromal cells (1.25%) that exhibit stem/progenitor cell behaviour in vitro; clonogenicity. The progeny in these colonies have been characterised and growth factors supporting clonogenicity identified. The goal is to examine the role of putative endometrial stem/progenitor cells in proliferative disorders of human endometrium, such as endometriosis, adenomyosis, endometrial hyperplasia and endometrial cancer, and the action of hormone-replacement therapy on the post-menopausal endometrium.

Administrative and research policies required to bring cellular therapies from the research laboratory to the patient's bedside

The research process is a balance between the inherent risks of new discoveries and the risks of research participant safety. Conflicts of interest, inherent to the research process, as well as those introduced by emerging cellular therapies, have the potential to compromise safety. The relationship of trust between the researcher and the clinical trial participant facilitates objective decision making, in the best interest of both parties. In the setup of each clinical trial, investigators incorporate ethical, political, legal, financial, and regulatory considerations as protocols are established. Responsibility to abide by these decisions ensures a systematic process and safeguards participants in this process. The integrity of the research process is strengthened by identifying potential conflicting issues with the guiding principles established in the protocols, which may threaten the objectivity of involved parties and jeopardize safety of the participants. The rapid pace and changing paradigms of new discoveries in cellular therapies exaggerate existing conflicts and introduce new ones. Ethical issues raised by emerging cellular therapies include the division of opinions regarding the use of embryonic and fetal tissue to develop stem cell lines for research, the individual versus professional conscience of a researcher, overselling of outcomes as a result of the researcher's desire to be the first to discover a cellular therapy, and therapeutic misconception resulting from a participant's desire for a miracle cure. The basic ethical issue of whether stem cells should be utilized as a cellular therapy raises heated debates because some believe that it is not acceptable to use fetal material as a source of research material for future cures and others feel equally as strong that inaction is unethical because it results in needless suffering and death owing to the absence of this research. Political issues include the divergent position statements of presidential administrations on cellular therapy, variations in individual state laws, and states becoming involved in research funding, such as California's Proposition 71. Legal concerns include expanding private litigation with diversity of lawsuits, expanding lists of defendants, and the use of class-action lawsuits in research cases. Ownership issues also arise in terms of intellectual property, patents, and ownership of stem cells collected from minors, as in umbilical cord blood donations. Situations that challenge the regulatory processes established to ensure participant safety include differences in reporting requirements for private- and public-funded research and the lack of adequate funding and resources to implement and support the institutional review board (IRB) process. Financial considerations influence the development of clinical protocols, because funding is often limited. Financial incentives, personal investment in companies funding research activities, and fundraising pressures may present potential conflicts. In addition, the increasing role of emerging biotechnology start-up companies and pharmaceutical companies in clinical research introduces additional financial considerations. Administrative policies are needed to address these possible conflicts and ensure research participant safety as cellular therapies progress from the research laboratories to the patient's bedside. Administrative policies to ensure minimum standards of quality for emerging products before human clinical trials, policies to enforce consistent reporting requirements for private and public cellular research, policies to minimize financial conflicts of interest, policies to strengthen implementation of the existing IRB process and to structure into the process a consistent, systematic review of these identified conflicts, and policies to limit private litigation will help to preserve the objectivity of the review process and ultimately increase participant safety.

Cardiac stem cells and mechanisms of myocardial regeneration

This review discusses current understanding of the role that endogenous and exogenous progenitor cells may have in the treatment of the diseased heart. In the last several years, a major effort has been made in an attempt to identify immature cells capable of differentiating into cell lineages different from the organ of origin to be employed for the regeneration of the damaged heart. Embryonic stem cells (ESCs) and bone marrow-derived cells (BMCs) have been extensively studied and characterized, and dramatic advances have been made in the clinical application of BMCs in heart failure of ischemic and nonischemic origin. However, a controversy exists concerning the ability of BMCs to acquire cardiac cell lineages and reconstitute the myocardium lost after infarction. The recognition that the adult heart possesses a stem cell compartment that can regenerate myocytes and coronary vessels has raised the unique possibility to rebuild dead myocardium after infarction, to repopulate the hypertrophic decompensated heart with new better functioning myocytes and vascular structures, and, perhaps, to reverse ventricular dilation and wall thinning. Cardiac stem cells may become the most important cell for cardiac repair.

Biological implications of cell fusion

Until recently, cells were thought to be integral and discrete components of tissues, and their state was determined by cell differentiation. However, under some conditions, stem cells or their progeny can fuse with cells of other types, mixing cytoplasmic and even genetic material of different (heterotypic) origins. The fusion of heterotypic cells could be of central importance for development, repair of tissues and the pathogenesis of disease.

Optimizing techniques for tracking transplanted stem cells in vivo

The potential for bone marrow-derived cells (BMDCs) to contribute to nonhematopoietic tissues has generated considerable debate in recent years. Causes for the controversies include disparities in the techniques used to track engraftment of BMDCs, inappropriate tissue preparation, a lack of appropriate positive and negative controls, and basic misunderstandings about how to properly collect and interpret images from epifluorescent and confocal microscopes. Our laboratory was among the first to use bone marrow transplants from transgenic mice constitutively expressing enhanced green fluorescent protein (GFP) to study the ability of BMDCs to give rise to nonhematopoietic tissue types, a system that is now in widespread use. During our 6 years of experience using GFP, as well as beta-galactosidase and the Y chromosome, to track BMDCs in vivo, we have identified many difficulties and have developed techniques to resolve them. We discuss several of these methods, and, in particular, we describe ratiometric analysis techniques for improving detection of transplanted cells derived from genetically modified bone marrow. Finally, to help resolve reported discrepancies regarding the frequency with which BMDCs contribute to skeletal myofibers, we demonstrate that the pattern of highly autofluorescent myofibers in skeletal muscle is clearly distinct from that of GFP-expressing myofibers and describe how unambiguous conclusions can be drawn from such data.

A perspective on pancreatic stem/progenitor cells

The prevalence of both type 1 and type 2 diabetes mellitus is increasing throughout the world along with the ensuant morbidity and early mortality because of premature microvascular and macrovascular disease. Current insulin and drug therapies control diabetes, but do not cure it. Cell-based therapies offer the possibilities of a permanent cure for diabetes. Recently, success in the transplantation of pancreatic islets in the livers of type 1 diabetics has afforded the opportunity for a potential cure. However, the severe shortage of donor islets for transplantation limits the usefulness of this therapy. One approach is to exploit the use of stem cells, either embryo-derived or adult tissue-derived, as substrates to create islet tissue suitable for transplantation. Cells isolated from embryo blastocysts and from adult pancreas, liver, and bone marrow can be expanded extensively in vitro and differentiated into islet-like clusters that produce insulin, and, in some instances, can achieve glycemic control when transplanted into streptozotocin-induced diabetic mice. It is, now, also possible to envision the direct systemic administration of stem cells that would home in on and regenerate injured islets, or to administer stem cell stimulators that would enhance endogenous pancreatic stem cells to expand and differentiate into functional, insulin-producing beta-cells. This perspective discusses the potential applications of cellular medicines, in the new discipline of regenerative medicine, to achieve a cure for diabetes.

Proliferation of bone marrow-derived cells contributes to regeneration after folic acid-induced acute tubular injury

Studies of tissue from recipients of bone marrow transplantation or organ allograft suggest that bone marrow-derived cells (BMDC) may differentiate into a variety of nonhematologic tissues, including renal tubular epithelium. The aims of this study were to examine whether BMDC contribute to recovery after acute renal injury and to assess the effects of cytokine mobilization on regeneration. Female mice (6 wk old) were lethally irradiated and transplanted with male bone marrow (BM) cells and later assigned into control, folic acid-treatment, and folic acid-treatment with granulocyte-colony stimulating factor (G-CSF), and control with G-CSF. Tritiated thymidine was given 1 h before death. Kidney sections were stained for a tubular epithelial marker, Y chromosome (in situ hybridization), periodic acid-Schiff staining, and subjected to autoradiography. Renal tubular epithelial cells in S-phase were scored as female (indigenous) or male (BM-derived). This is the first report to show that BMDC can respond by engrafting the renal tubules and undergo DNA synthesis after acute renal injury. BMDC contributed to the renal tubular epithelial cell population, although most (90%) renal tubular regeneration came from female indigenous cells. Some evidence was found for cell fusion between indigenous renal tubular cells and BMDC, but this was infrequent and the significance and consequences of cell fusion in the kidney are unresolved. G-CSF treatment nearly doubled the frequency of thymidine-labeled BM-derived tubular cells and might facilitate the recovery of renal tubular epithelium.

Interleukin-3 induces hepatocyte-specific metabolic activity in bone marrow-derived liver stem cells

Bone marrow-derived adult liver stem cells (BALSC) are a promising target for the development of future cell-based therapies for a variety of liver disorders. However, the ability of stem cells to fully function, as hepatocytes, is limited and differentiation is time dependent. Therefore, it will be conducive to find a growth factor that is able to enhance liver-specific metabolic activity in freshly isolated liver stem cells. Recently, a subpopulation of BALSC was isolated and characterized (beta2-microglobulin-negative/ Thy-1-positive cells). We hypothesized that using interleukin-3 (IL-3), a hematopoietic differentiation growth factor, we may be able to enhance liver-specific metabolic activity in freshly isolated BALSC. Rat BALSC from normal and injured livers (bile duct ligated) were isolated and stimulated with IL-3 in culture. Cells were co-cultured with or without hepatocytes, separated by a semipermeable membrane. We measured the effect of IL-3 on BALSC to metabolize ammonia into urea (a liver-specific metabolic activity). IL-3 increased the ability of BALSC, purified from normal animals, to metabolize ammonia into urea by several folds. Interestingly, no such effect was found in cell cultures from bile duct-ligated animals. Additionally, co-cultures of BALSC with hepatocytes induced higher rate of ammonia metabolism, which was further enhanced by IL-3. Our study indicates that IL-3 may be used as an agent to enhance differentiation of BALSC, both qualitatively and quantitatively. It is conceivable that stem cells may undergo IL-3 priming before their clinical application in cell transplantation or bioartificial liver systems.

Directing stem cells into the keratinocyte lineage in vitro

A major area of research in regenerative medicine is the potential application of stem cells in skin grafting and tissue engineering. This would require well defined and efficient protocols for directing the commitment and differentiation of stem cells into the keratinocyte lineage, together with their selective purification and proliferation in vitro. The development of such protocols would reduce the likelihood of spontaneous differentiation of stem cells into divergent lineages upon transplantation, as well as reduce the risk of teratoma formation in the case of embryonic stem cells. Additionally, such protocols could provide useful in vitro models for studying skin tissue biology, as well as facilitate the genetic manipulation of stem cells for therapeutic applications. The development of pharmacokinetic and cytotoxicity/genotoxicity screening tests for skin-related biomaterials and drugs could also utilize protocols developed for the commitment and differentiation of stem cells into the keratinocyte lineage. Hence, this review critically examines the various strategies that could be employed to direct the commitment and differentiation of stem cells into the keratinocyte lineage in vitro.

Liver biopsies from human females contain male hepatocytes in the absence of transplantation

Fetal cells derived from pregnancy can persist in a woman's blood and tissues for decades and have been implicated in the pathogenesis of autoimmune disease. Transplantation studies based on donor sex mismatch suggest that circulating stem cells can lead to liver regeneration with donor-derived hepatocytes. However, male cells in female liver could derive from pregnancy. We investigated male cells in liver biopsies from women with sons and asked whether they were hematopoietic cells or hepatocytes. Fluorescence in situ hybridization for X- and Y-chromosomes with concomitant immunohistochemistry was employed to study 28 female liver biopsies: 14 with the autoimmune disease primary biliary cirrhosis (PBC), eight with Hepatitis C, and six with other diseases. Total male cells and those expressing hematopoietic (CD45) or hepatocyte (CAM-5.2) markers were quantified. None of the male cells were hematopoietic in origin, as shown by lack of CD45 expression. Instead, male cells with hepatocyte morphology expressing the hepatocyte marker CAM 5.2 were found in 25% of all biopsies (36% of PBC and 14% of others). Overall, male cells were found in 36% of female liver biopsies. Of the PBC livers 43% had male cells compared to 25% of Hepatitis C biopsies and 33% of others. There was a trend toward increased numbers of male cells in PBC compared to others (mean 1 per 30,000 host cells vs 0.17 in Hepatitis C and 0.35 in others). Thus, male cells found in livers of women with sons include cells that express hepatocyte antigens. Therefore, transplantation and stem cell differentiation studies using sex difference to conclude that donor cells regenerate liver may be confounded by fetal microchimerism. Whether fetal cells play a role in autoimmune diseases like PBC merits further investigation.

A human umbilical cord stem cell rescue therapy in a murine model of toxic liver injury

BACKGROUND

Several studies have demonstrated that bone marrow contains a subpopulation of stem cells capable of participating in the hepatic regenerative process, even if some reports indicate quite a low level of liver repopulation by human stem cells in the normal and transiently injured liver.

AIMS

In order to overcome the low engraftment levels seen in previous models, we tried the direct intraperitoneal administration of human cord blood stem cells, using a model of hepatic damage induced by allyl alcohol in NOD/SCID mice.

METHODS

We designed a protocol based on stem cell infusion following liver damage in the absence of irradiation. Flow cytometry, histology, immunohistochemistry and RT-PCR for human hepatic markers were performed to monitor human cell engraftment.

RESULTS

Human stem cells were able to transdifferentiate into hepatocytes, to improve liver regeneration after damage and to reduce the mortality rate both in both protocols, even if with qualitative and quantitative differences in the transdifferentiation process.

CONCLUSIONS

We demonstrated for the first time that the intraperitoneal administration of stem cells can guarantee a rapid liver engraftment. Moreover, the new protocol based on stem cell infusion following liver damage in the absence of irradiation may represent a step forward for the clinical application of stem cell transplantation.