Engraftment and tumor formation after allogeneic in utero transplantation of primate embryonic stem cells

Experimental and clinical progress of in utero hematopoietic cell transplantation therapy for congenital disorders

In utero hematopoietic cell transplantation (IUHCT) is considered a potentially efficient therapeutic approach with relatively few side effects, compared to adult hematopoietic cell transplantation, for various hematological genetic disorders. The principle of IUHCT has been extensively studied in rodent models and in some large animals with close evolutionary similarities to human beings. However, IUHCT has only been used to rebuild human T cell immunity in certain patients with inherent immunodeficiencies. This review will first summarize the animal models utilized for IUHCT investigations and describe the associated outcomes. Recent advances and potential barriers for successful IUHCT are discussed, followed by possible strategies to overcome these barriers experimentally. Lastly, we will outline the progress made towards utilizing IUHCT to treat inherent disorders for patients, list out associated limitations and propose feasible means to promote the efficacy of IUHCT clinically.

A review of application of stem cell therapy in the management of congenital heart disease

Research on stem cells has been rapidly growing with impressive breakthroughs. Although merely a few of the laboratory researches have successfully transited to the clinical trial phase, the application of stem cells as a therapeutic option for some currently incapacitating diseases hold fascinating potentials. This review emphasis the various opportunities for the application of stem cell in the treatment of fetal diseases. First, we provide a brief commentary on the common stem cell strategy used in the treatment of congenital anomalies, thereafter we discuss how stem cell is being used in the management of some fetal disorders.

In Utero Stem Cell Transplantation: Potential Therapeutic Application for Muscle Diseases

Muscular dystrophies, myopathies, and traumatic muscle injury and loss encompass a large group of conditions that currently have no cure. Myoblast transplantations have been investigated as potential cures for these conditions for decades. However, current techniques lack the ability to generate cell numbers required to produce any therapeutic benefit. In utero stem cell transplantation into embryos has been studied for many years mainly in the context of hematopoietic cells and has shown to have experimental advantages and therapeutic applications. Moreover, patient-derived cells can be used for experimental transplantation into nonhuman animal embryos via in utero injection as the immune response is absent at such early stages of development. We therefore propose in utero transplantation as a potential method to generate patient-derived humanized skeletal muscle as well as muscle stem cells in animals for therapeutic purposes as well as patient-specific drug screening.

In utero stem cell transplantation and gene therapy: rationale, history, and recent advances toward clinical application

Recent advances in high-throughput molecular testing have made it possible to diagnose most genetic disorders relatively early in gestation with minimal risk to the fetus. These advances should soon allow widespread prenatal screening for the majority of human genetic diseases, opening the door to the possibility of treatment/correction prior to birth. In addition to the obvious psychological and financial benefits of curing a disease in utero, and thereby enabling the birth of a healthy infant, there are multiple biological advantages unique to fetal development, which provide compelling rationale for performing potentially curative treatments, such as stem cell transplantation or gene therapy, prior to birth. Herein, we briefly review the fields of in utero transplantation (IUTx) and in utero gene therapy and discuss the biological hurdles that have thus far restricted success of IUTx to patients with immunodeficiencies. We then highlight several recent experimental breakthroughs in immunology, hematopoietic/marrow ontogeny, and in utero cell delivery, which have collectively provided means of overcoming these barriers, thus setting the stage for clinical application of these highly promising therapies in the near future.

Sonic hedgehog increases the skin wound-healing ability of mouse embryonic stem cells through the microRNA 200 family

BACKGROUND AND PURPOSE

To use stem cell therapy effectively, it is important to enhance the therapeutic potential of stem cells with soluble factors. Although sonic hedgehog (shh) is important in maintaining the stem cell, the recovery effect of mouse embryonic stem cells (mESCs) with shh has not yet been elucidated. The present study investigated the effect of mESCs with shh in skin recovery in vivo as well as the related intracellular signal pathways in vitro.

EXPERIMENTAL APPROACH

The healing effect of mESCs with shh on skin wounds was examined in vivo in ICR mice. The involvement of Smads, the microRNA (miR)-200 family, zinc finger E-box-binding homeobox (ZEBs) and E-cadherin on shh-induced mESC migration and self-renewal was determined in vitro.

KEY RESULTS

The mESCs with shh increased re-epithelialization and VEGF expression in skin wounds. Shh-treated mESCs increased both secreted and intracellular levels of VEGF. Shh induced dephosphorylation of glycogen synthase kinase 3β through the Smoothened receptor and increased the phosphorylation of Smad1 and Smad2/3 in mESCs. Shh-induced decrease of the mmu-miR-141, -200c, -200a, -200b and -429 expression levels was significantly reversed by Smad4 siRNA. Shh increased nuclear expression of ZEB1/ZEB2 and decreased E-cadherin expression while increasing cell migration and skin wound healing. Both these effects were reversed by mmu-miR-141 and -200b mimics.

CONCLUSIONS AND IMPLICATIONS

Mouse ESCs accelerated skin wound healing by shh through down-regulating E-cadherin, an effect dependent on mmu-miR-141 and -200b. Our data provides evidence for the effectiveness of shh in stem cell-based therapy in vivo.

Stem cell transplantation for neuroprotection in stroke

Stem cell-based therapies for stroke have expanded substantially over the last decade. The diversity of embryonic and adult tissue sources provides researchers with the ability to harvest an ample supply of stem cells. However, the optimal conditions of stem cell use are still being determined. Along this line of the need for optimization studies, we discuss studies that demonstrate effective dose, timing, and route of stem cells. We recognize that stem cell derivations also provide uniquely individual difficulties and limitations in their therapeutic applications. This review will outline the current knowledge, including benefits and challenges, of the many current sources of stem cells for stroke therapy.

Preclinical stem cell therapy in Chagas Disease: Perspectives for future research

Chagas cardiomyopathy still remains a challenging problem that is responsible for high morbidity and mortality in Central and Latin America. Chagas disease disrupts blood microcirculation via various autoimmune mechanisms, causing loss of cardiomyocytes and severe impairment of heart function. Different cell types and delivery approaches in Chagas Disease have been studied in both preclinical models and clinical trials. The main objective of this article is to clarify the reasons why the benefits that have been seen with cell therapy in preclinical models fail to translate to the clinical setting. This can be explained by crucial differences between the cellular types and pathophysiological mechanisms of the disease, as well as the differences between human patients and animal models. We discuss examples that demonstrate how the results from preclinical trials might have overestimated the efficacy of myocardial regeneration therapies. Future research should focus, not only on studying the best cell type to use but, very importantly, understanding the levels of safety and cellular interaction that can elicit efficient therapeutic effects in human tissue. Addressing the challenges associated with future research may ensure the success of stem cell therapy in improving preclinical models and the treatment of Chagas disease.

Molecular imaging of induced pluripotent stem cell immunogenicity with in vivo development in ischemic myocardium

Whether differentiation of induced pluripotent stem cells (iPSCs) in ischemic myocardium enhances their immunogenicity, thereby increasing their chance for rejection, is unclear. Here, we dynamically demonstrated the immunogenicity and rejection of iPSCs in ischemic myocardium using bioluminescent imaging (BLI). Murine iPSCs were transduced with a tri-fusion (TF) reporter gene consisting of firefly luciferase-red fluorescent protein-truncated thymidine kinase (fluc-mrfp-tTK). Ascorbic acid (Vc) were used to induce iPSCs to differentiate into cardiomyocytes (CM). iPSCs and iPS-CMs were intramyocardially injected into immunocompetent or immunosuppressed allogenic murine with myocardial infarction. BLI was performed to track transplanted cells. Immune cell infiltration was evaluated by immunohistochemistry. Syngeneic iPSCs were also injected and evaluated. The results demonstrated that undifferentiated iPSCs survived and proliferated in allogenic immunocompetent recipients early post-transplantation, accompanying with mild immune cell infiltration. With in vivo differentiation, a progressive immune cell infiltration could be detected. While transplantation of allogenic iPSC-CMs were observed an acute rejection from receipts. In immune-suppressed recipients, the proliferation of iPSCs could be maintained and intramyocardial teratomas were formed. Transplantation of syngeneic iPSCs and iPSC-CMs were also observed progressive immune cell infiltration. This study demonstrated that iPSC immunogenicity increases with in vivo differentiation, which will increase their chance for rejection in iPSC-based therapy.

Stem cell therapy in heart diseases: a review of selected new perspectives, practical considerations and clinical applications

Degeneration of cardiac tissues is considered a major cause of mortality in the western world and is expected to be a greater problem in the forthcoming decades. Cardiac damage is associated with dysfunction and irreversible loss of cardiomyocytes. Stem cell therapy for ischemic heart failure is very promising approach in cardiovascular medicine. Initial trials have indicated the ability of cardiomyocytes to regenerate after myocardial injury. These preliminary trials aim to translate cardiac regeneration strategies into clinical practice. In spite of advances, current therapeutic strategies to ischemic heart failure remain very limited. Moreover, major obstacles still need to be solved before stem cell therapy can be fully applied. This review addresses the current state of research and experimental data regarding embryonic stem cells (ESCs), myoblast transplantation, histological and functional analysis of transplantation of co-cultured myoblasts and mesenchymal stem cells, as well as comparison between mononuclear and mesenchymal stem cells in a model of myocardium infarction. We also discuss how research with stem cell transplantation could translate to improvement of cardiac function.

In utero hematopoietic cell transplantation for the treatment of congenital anomalies

In utero hematopoietic cell transplantation (IUHCTx) is a promising strategy for the treatment of common hematopoietic disorders and for inducing immune tolerance in the fetus. Although the efficacy of IUHCTx has been demonstrated in multiple small and large animal models, the clinical application of this technique in humans has had limited success. Recent studies in mice have demonstrated that the maternal immune system plays a critical role in limiting engraftment in the fetus. This article reviews the therapeutic rationale of IUHCTx, potential barriers to its applications, and recent experimental strategies to improve its clinical success.

Effects of histocompatibility and host immune responses on the tumorigenicity of pluripotent stem cells

Pluripotent stem cells hold great promises for regenerative medicine. They might become useful as a universal source for a battery of new cell replacement therapies. Among the major concerns for the clinical application of stem cell-derived grafts are the risks of immune rejection and tumor formation. Pluripotency and tumorigenicity are closely linked features of pluripotent stem cells. However, the capacity to form teratomas or other tumors is not sufficiently described by inherited features of a stem cell line or a stem cell-derived graft. The tumorigenicity always depends on the inability of the recipient to reject the tumorigenic cells. This review summarizes recent data on the tumorigenicity of pluripotent stem cells in immunodeficient, syngeneic, allogeneic, and xenogeneic hosts. The effects of immunosuppressive treatment and cell differentiation are discussed. Different immune effector mechanisms appear to be involved in the rejection of undifferentiated and differentiated cell populations. Elements of the innate immune system, such as natural killer cells and the complement system, which are active also in syngeneic recipients, appear to preferentially reject undifferentiated cells. This effect could reduce the risk of tumor formation in immunocompetent recipients. Cell differentiation apparently increases susceptibility to rejection by the adaptive immune system in allogeneic hosts. The current data suggest that the immune system of the recipient has a major impact on the outcome of pluripotent stem cell transplantation, whether it is rejection, engraftment, or tumor development. This has to be considered when the results of experimental transplantation models are interpreted and even more when translation into clinics is planned.

Embryonic stem cell (ESC)-mediated transgene delivery induces growth suppression, apoptosis and radiosensitization, and overcomes temozolomide resistance in malignant gliomas

High-grade gliomas are among the most lethal of all cancers. Despite considerable advances in multimodality treatment, including surgery, radiotherapy and chemotherapy, the overall prognosis for patients with this disease remains dismal. Currently available treatments necessitate the development of more effective tumor-selective therapies. The use of gene therapy for malignant gliomas is promising, as it allows in situ delivery and selectively targets brain tumor cells while sparing the adjacent normal brain tissue. Viral vectors that deliver proapoptotic genes to malignant glioma cells have been investigated. Although tangible results on patients' survival remain to be further documented, significant advances in therapeutic gene transfer strategies have been made. Recently, cell-based gene delivery has been sought as an alternative method. In this paper, we report the proapoptotic effects of embryonic stem cell (ESC)-mediated mda-7/IL-24 delivery to malignant glioma cell lines. Our data show that these are similar to those observed using a viral vector. In addition, acknowledging the heterogeneity of malignant glioma cells and their signaling pathways, we assessed the effects of conventional treatment for high-grade gliomas, ionizing radiation and temozolomide, when combined with ESC-mediated transgene delivery. This combination resulted in synergistic effects on tumor cell death. The mechanisms involved in this beneficial effect included activation of both apoptosis and autophagy. Our in vitro data support the concept that ESC-mediated gene delivery might offer therapeutic advantages over standard approaches to malignant gliomas. Our results corroborate the theory that combined treatments exploiting different signaling pathways are needed to succeed in the treatment of malignant gliomas.

Improved efficacy and safety of in utero cell transplantation in sheep using an ultrasound-guided method

In the present study, we investigated the suitability of two methods for the transplantation of cells into ovine fetuses. The first method was an ultrasound-guided cell injection via the uterine wall. The second involved hysterotomic cell injection with an incision in the uterine wall exposing the amnion. Monkey embryonic stem (ES) cell-derived hematopoietic cells were used as donor cells. After transplantation, the abortion rate associated with the hysterotomic injection method was significantly higher than that of the ultrasound-guided injection method (8/13 versus 4/24; P < 0.01). The fetuses were delivered to examine the engraftment of transplanted monkey hematopoietic cells. Monkey cells were detected in one of the five animals (20%) in the hysterotomic injection group, and 14 of 20 animals (70%, P < 0.05) in the ultrasound-guided injection group. Therefore, the ultrasound-guided method was effectively shown to be minimally invasive for in utero transplantation and can produce a higher rate of engraftment for transplanted cells.

Variation in the Incidence of Teratomas after the Transplantation of Nonhuman Primate ES Cells into Immunodeficient Mice

Embryonic stem (ES) cells have the ability to generate teratomas when transplanted into immunodeficient mice, but conditions affecting the generation remain to be elucidated. Nonhuman primate cynomolgus ES cells were transplanted into immunodeficient mice under different conditions; the number of transplanted cells, physical state (clumps or single dissociated cells), transplant site, differentiation state, and immunological state of recipient mice were all varied. The tumorigenicity was then evaluated. When cynomolgus ES cells were transplanted as clumps into the lower limb muscle in either nonobese diabetic/severe combined immunodeficiency (NOD/SCID) or NOD/SCID/?cnull (NOG) mice, teratomas developed in all the animals transplanted with 1 × 105 or more cells, but were not observed in any mouse transplanted with 1 × 103 cells. However, when the cells were transplanted as dissociated cells, the number of cells necessary for teratomas to form in all mice increased to 5 × 105. When the clump cells were injected subcutaneously (instead of intramuscularly), the number also increased to 5 × 105. When cynomolgus ES cell-derived progenitor cells (1 × 106), which included residual pluripotent cells, were transplanted into the lower limb muscle of NOG or NOD/SCID mice, the incidence of teratomas differed between the strains; teratomas developed in five of five NOG mice but in only two of five NOD/SCID mice. The incidence of teratomas varied substantially depending on the transplanted cells and recipient mice. Thus, considerable care must be taken as to tumorigenicity.

The tumorigenicity of human embryonic stem cells

Human embryonic stem cells (HESCs) are the in vitro descendants of the pluripotent inner cell mass (ICM) of human blastocyst stage embryos. HESCs can be kept undifferentiated in culture or be differentiated to tissues representing all three germ layers, both in vivo and in vitro. These properties make HESC-based therapy remarkably appealing for the treatment of various disorders. Upon transplantation in vivo, undifferentiated HESCs rapidly generate the formation of large tumors called teratomas. These are benign masses of haphazardly differentiated tissues. Teratomas also appear spontaneously in humans and in mice. When they also encompass a core of malignant undifferentiated cells, these tumors are defined as teratocarcinomas. These malignant undifferentiated cells are termed embryonic carcinoma (EC), and are the malignant counterparts of embryonic stem cells. Here we review the history of experimental teratomas and teratocarcinomas, from spontaneous teratocarcinomas in mice to induced teratomas by HESC transplantation. We then discuss cellular and molecular aspects of the tumorigenicity of HESCs. We also describe the utilization of HESC-induced teratomas for the modeling of early human embryogenesis and for modeling developmental diseases. The problem of HESC-induced teratomas may also impede or prevent future HESC-based therapies. We thus conclude with a survey of approaches to evade HESC-induced tumor formation.

Collection and culture of primordial germ cells from cynomolgus monkeys (Macaca fascicularis)

Aim:  To clarify the location of primordial germ cells (PGC) in an embryo of target-age and to examine the culture environment of the PCG. Methods:  The days of ovulation and fertilization were estimated by measuring the serum concentration of estrogen. Pregnancy was confirmed by measurement of the serum concentration of the beta subunit of macaque chorionic gonadotropin and by ultrasonography. We also examined the location of PGC in the embryo at the time of retrieval. Results:  Results showed that PGC in an embryo were in the hindguts at day 30 postfertilization, arrived at the genital ridges via mesenteries at approximately day 33 postfertilization, and colonized the gonads by day 36 postfertilization. Conclusions:  In conclusion, embryos collected on day 33 postfertilization are more suitable for obtaining PGC from cynomolgus monkeys. The PGC collected from cynomolgus monkey fetuses were cultured under conditions for the derivation and culture of human embryonic germ cells; enzymatically dispersed single cells were cultured on a SIM thioguanine-resistant ouabain-resistant cells (STO) feeder layer with recombinant human leukemia inhibitory factor, recombinant human basic fibroblast growth factor and forskolin. The cells from genital ridges and mesenteries at day 33 postfertilization had alkaline phosphatase (ALP) activity in vitro for a maximum of 13 days. In contrast, ALP activity had been held for 2 months under the same culture condition when the cells were derived from the gonads at day 66 postfertilization. Derivation of an embryonic germ cell from a cynomolgus monkey was not achieved from these cultures. (Reprod Med Biol 2007; 6: 203-210).

Human embryonic stem cell-derived cardiomyocytes: inducing strategies

Cell-based therapy is emerging as an innovative approach for the treatment of degenerative diseases, and stem cells appear to be an ideal source of cells for this. In cardiology, in particular, human embryonic stem cell (hESC)-derived cardiomyocytes theoretically fulfill most, if not all, of the properties of an ideal donor cell, but several critical obstacles need to be overcome. Many research projects are focusing on set-up strategies for directing hESC differentiation toward the cardiac lineage. It is one of the main difficulties in the search to provide a valuable source of cells to effect regeneration of myocardial tissue in patients with severe heart failure. To date, there are no easy and efficient protocols for the induction of hESC differentiation toward the cardiac lineage. Discovering new molecules or tools capable of doing this is imperative.

Differential requirements for hematopoietic commitment between human and rhesus embryonic stem cells

Progress toward clinical application of ESC-derived hematopoietic cellular transplantation will require rigorous evaluation in a large animal allogeneic model. However, in contrast to human ESCs (hESCs), efforts to induce conclusive hematopoietic differentiation from rhesus macaque ESCs (rESCs) have been unsuccessful. Characterizing these poorly understood functional differences will facilitate progress in this area and likely clarify the critical steps involved in the hematopoietic differentiation of ESCs. To accomplish this goal, we compared the hematopoietic differentiation of hESCs with that of rESCs in both EB culture and stroma coculture. Initially, undifferentiated rESCs and hESCs were adapted to growth on Matrigel without a change in their phenotype or karyotype. Subsequent differentiation of rESCs in OP9 stroma led to the development of CD34(+)CD45(-) cells that gave rise to endothelial cell networks in methylcellulose culture. In the same conditions, hESCs exhibited convincing hematopoietic differentiation. In cytokine-supplemented EB culture, rESCs demonstrated improved hematopoietic differentiation with higher levels of CD34(+) and detectable levels of CD45(+) cells. However, these levels remained dramatically lower than those for hESCs in identical culture conditions. Subsequent plating of cytokine-supplemented rhesus EBs in methylcellulose culture led to the formation of mixed colonies of erythroid, myeloid, and endothelial cells, confirming the existence of bipotential hematoendothelial progenitors in the cytokine-supplemented EB cultures. Evaluation of four different rESC lines confirmed the validity of these disparities. Although rESCs have the potential for hematopoietic differentiation, they exhibit a pause at the hemangioblast stage of hematopoietic development in culture conditions developed for hESCs.

Differentiation of encapsulated embryonic stem cells after transplantation

BACKGROUND

Embryonic stem cells (ESC) when transplanted into recipients with different major histocompatibility antigens may be rejected, especially as cells differentiate and expression of these antigens increases. One method to prevent rejection is to place the developing ESC in microcapsules. It is currently unknown what effect encapsulation has on the ability of ESC to differentiate.

METHODS

Human ESC (hESC; hES03 line) and mouse ESC (mESC; R1 line) were encapsulated in 2.2% barium alginate and transplanted intraperitoneally in SCID and BALB/c mice respectively. Cell morphology, viability, and gene characterization were assessed after retrieving the capsules up to four weeks from SCID mice and three months from BALB/c mice.

RESULTS

Encapsulation prevented hESC and mESC from forming teratomas up to four weeks and three months, respectively. mESC but not hESC formed aggregates within the capsules, which remained free of fibrosis. Some but not all the transplanted encapsulated hESC differentiated towards all three lineages, but more so towards an endodermal lineage as shown by increased expression of alpha fetoprotein. This was similar to what occurred when encapsulated and non-encapsulated hESC were cultured in vitro for two weeks. In contrast to the hESC, transplanted encapsulated mESC differentiated mostly towards an ectodermal lineage as shown by increased expression of nestin and glial fibrillary acidic protein. In vitro, encapsulated and nonencapsulated mESC also began to differentiate, but not down any specific lineage.

CONCLUSIONS

Encapsulated ESC do differentiate, although along multiple pathways, both when transplanted and maintained in culture, just as nonencapsulated ESC do when removed from their feeder layer.

Acidic fibroblast growth factor promotes hepatic differentiation of monkey embryonic stem cells

Embryonic stem (ES) cells can replicate indefinitely and differentiate into all cell types, including hepatocytes. Research using primate ES cells is considered to be important for studies of potential cell therapies. Recently, we established cynomolgus monkey ES cells designated as CMK6. The CMK6 cell line is a useful tool for investigating the mechanism of differentiation in primate ES cells and developing cell therapies, because of its biological similarity to human ES cells. To examine whether cynomolgus monkey ES cells differentiate into hepatocytes, CMK6 cells were cultured with or without acidic fibroblast growth factor (aFGF). Evaluation of the hepatic differentiation was performed by analysis of the mRNA expression in early hepatic marker genes using the reverse transcriptase-polymerase chain reaction (RT-PCR). The protein expression of albumin (ALB) was also studied by immunocytochemistry. RT-PCR analyses revealed mRNA expressions of alpha-fetoprotein, transthyretin, and ALB in the presence of aFGF at 3 wk of differentiation, whereas no mRNA expression of these genes was detected in cells without aFGF. The protein expression of ALB in the presence of aFGF at 3 wk of differentiation was also confirmed by immunocytochemistry. However, tyrosine aminotransferase, which is a mature hepatic marker, was not detected in the presence or absence of aFGF at any stage of differentiation. These results suggested that aFGF successfully promoted in vitro differentiation of cynomolgus monkey ES cells to an early hepatic lineage.

Human neural stem cell differentiation following transplantation into spinal cord injured mice: association with recovery of locomotor function

Stem cells are under intense investigation as potential therapeutics for central nervous system (CNS) injury and disease. However, several reports have suggested that stem cells grown as neurospheres and transplanted into an injured environment preferentially differentiate into astrocytes, contributing to glial scar. Further, the relationship between functional recovery and cell transplantation has not been empirically investigated in early studies. Using severe combined immunodeficient (scid) mice to minimize xenograft rejection, we report that prospectively isolated human fetal CNS-derived stem cells grown as neurospheres (hCNS-SCns) survive, migrate and express differentiation markers for neurons and oligodendrocytes after long-term engraftment in spinal cord injured (SCI) NOD-scid mice. Only rarely do these cells differentiate into glial fibrillary acidic protein (GFAP)-positive astrocytes, with no apparent contribution to glial scar. hCNS-SCns engraftment was associated with recovery of locomotor function. After long-term engraftment and stable behavioral plateaus in recovery were achieved (4 months post-transplantation), locomotor improvements were abolished by selective ablation of human cells with diphtheria toxin (DT). These data suggest that hCNS-SCns survival is required for locomotor recovery, possibly via differentiation and integration of human cells in the mouse host or continuous supply of trophic or other support necessary for gains in host cell function.

Gene-enhanced tissue engineering for dental hard tissue regeneration: (1) overview and practical considerations

Gene-based therapies for tissue regeneration involve delivering a specific gene to a target tissue with the goal of changing the phenotype or protein expression profile of the recipient cell; the ultimate goal being to form specific tissues required for regeneration. One of the principal advantages of this approach is that it provides for a sustained delivery of physiologic levels of the growth factor of interest.

This manuscript will review the principals of gene-enhanced tissue engineering and the techniques of introducing DNA into cells. Part 2 will review recent advances in gene-based therapies for dental hard tissue regeneration, specifically as it pertains to dentin regeneration/pulp capping and periodontal regeneration.

Generation and Characterization of Functional Cardiomyocytes from Rhesus Monkey Embryonic Stem Cells

Embryonic stem cells (ESCs) from mice and humans (hESCs) have been shown to be able to efficiently differentiate toward cardiomyocytes (CMs). Because murine ESCs and hESCs do not allow for establishment of pre-clinical allogeneic transplantation models, the aim of our study was to generate functional CMs from rhesus monkey ESCs (rESCs). Although formation of ectodermal and neuronal/glial cells appears to be the default pathway of the rESC line R366.4, we were able to change this commitment and to direct generation of endodermal/mesodermal cells and further differentiation toward CMs. Differentiation of rESCs resulted in an average of 18% of spontaneously contracting embryoid bodies (EBs) from rESCs. Semiquantitative reverse transcription-polymerase chain reaction analyses demonstrated expression of marker genes typical for endoderm, mesoderm, cardiac mesoderm, and CMs, including brachyury, goosecoid, Tbx-5, Tbx-20, Mesp1, Nkx2.5, GATA-4, FOG-2, Mlc2a, MLC2v, ANF, and alpha-MHC in rESC-derived CMs. Immunohistological and ultrastructural studies showed expression of CM-typical proteins, including sarcomeric actinin, troponin T, titin, connexin 43, and cross-striated muscle fibrils. Electrophysiological studies by means of multielectrode arrays revealed evidence of functionality, electrical coupling, and beta-adrenergic signaling of the generated CMs. This is the first study demonstrating generation of functional CMs derived from rESCs. In contrast to hESCs, rESCs allow for establishment of pre-clinical allogeneic transplantation models. Moreover, rESC-derived CMs represent a cell source for the development of high-throughput assays for cardiac safety pharmacology.

Embryonic stem cell immunogenicity increases upon differentiation after transplantation into ischemic myocardium

BACKGROUND

We investigated whether differentiation of embryonic stem cells (ESCs) in ischemic myocardium enhances their immunogenicity, thereby increasing their chance for rejection.

METHODS AND RESULTS

In one series, 129/SvJ-derived mouse ESCs (ES-D3 line) were transplanted by direct myocardial injection (1 x 10(6) cells) into murine hearts of both allogeneic (BALB/c, n=20) and syngeneic (129/SvJ, n=12) recipients after left anterior artery ligation. Hearts were procured at 1, 2, 4, and 8 weeks after ESC transplantation and analyzed by immunohistochemistry to assess immune cell infiltration (CD3, CD4, CD8, B220, CD11c, Mac-1, and Gr-1) and ESC differentiation (hematoxylin and eosin). In a second series (allogeneic n=5, sham n=3), ESC transplantation was performed similarly; however after 2 weeks, left anterior descending artery-ligated and ESC-injected hearts were heterotopically transplanted into naive BALB/c recipients. After an additional 2 weeks, donor hearts were procured and analyzed by immunohistochemistry. In the first series, the size of all ESC grafts remained stable and there was no evidence of ESC differentiation 2 weeks after transplantation; however, after 4 weeks, both allogeneic and syngeneic ESC grafts showed the presence of teratoma. By 8 weeks, surviving ESCs could be detected in the syngeneic but not in the allogeneic group. Mild inflammatory cellular infiltrates were found in allogeneic recipients at 1 and 2 weeks after transplantation, progressing into vigorous infiltration at 4 and 8 weeks. The second series demonstrated similar vigorous infiltration of immune cells as early as 2 weeks after heterotopic transplantation.

CONCLUSIONS

In vivo differentiated ESCs elicit an accelerated immune response as compared with undifferentiated ESCs. These data imply that clinical transplantation of allogeneic ESCs or ESC derivatives for treatment of cardiac failure might require immunosuppressive therapy.

Improved Safety of Hematopoietic Transplantation with Monkey Embryonic Stem Cells in the Allogeneic Setting

Cynomolgus monkey embryonic stem cell (cyESC)-derived in vivo hematopoiesis was examined in an allogeneic transplantation model. cyESCs were induced to differentiate into the putative hematopoietic precursors in vitro, and the cells were transplanted into the fetal cynomolgus liver at approximately the end of the first trimester (n = 3). Although cyESC-derived hematopoietic colony-forming cells were detected in the newborns (4.1%-4.7%), a teratoma developed in all newborns. The risk of tumor formation was high in this allogeneic transplantation model, given that tumors were hardly observed in immunodeficient mice or fetal sheep that had been xeno-transplanted with the same cyESC derivatives. It turned out that the cyESC-derived donor cells included a residual undifferentiated fraction positive for stage-specific embryonic antigen (SSEA)-4 (38.2% +/- 10.3%) despite the rigorous differentiation culture. When an SSEA-4-negative fraction was transplanted (n = 6), the teratoma was no longer observed, whereas the cyESC-derived hematopoietic engraftment was unperturbed (2.3%-5.0%). SSEA-4 is therefore a clinically relevant pluripotency marker of primate embryonic stem cells (ESCs). Purging pluripotent cells with this surface marker would be a promising method of producing clinical progenitor cell preparations using human ESCs.

Nonhuman primate embryonic stem cells as a preclinical model for hematopoietic and vascular repair

Stem cell-based regenerative medicine therapies have been touted recently as a novel therapeutic approach to treat and cure a wide range of diseases. Both adult and embryonic stem (ES) cells can serve as important sources of precursor cells to derive more mature cells potentially utilized for clinical applications. Nonhuman primates have proven useful as a preclinical model, as demonstrated in studies of hematopoietic cell transplantation, gene therapy, and other areas. The derivation of nonhuman primate ES cells now provides an optimal resource to characterize and test ES cell-based therapies prior to trials with human ES cells. This review describes work to define strategies and mechanisms to derive blood and endothelial cells from nonhuman primate ES cells isolated from various species. Preclinical testing that solely relies on studies of putative therapeutic cells derived from mouse ES cells transplanted into other mice, or analyses of human ES cell-derived cells transplanted into immunodeficient or immunosuppressed rodents may not be predictive of efficacy in subsequent human trials. However, future testing using nonhuman primate ES cell-derived therapeutic cells done as an allogeneic transplant may best predict success for subsequent studies using human ES cells. Therefore, additional research on nonhuman primate ES cells, in addition to work on mouse and human ES cells, is greatly needed to facilitate clinical translation of new stem cell treatments.

Large animal models for stem and progenitor cell analysis

Extrapolation of an understanding regarding hematopoiesis and, in particular, hematopoietic stem cells (HSCs) from rodent models or in vitro human cell models to applications in humans has proven very difficult. This is not surprising, given the differences between rodent and human hematopoietic physiology and the lack of true in vitro assays for HSCs. Therefore, translational preclinical development of genetic and cellular therapies is dependent on the utilization of practical and well-defined large animal models. This chapter will introduce the most commonly used model species, including macaques, baboons, dogs, cats, and sheep, and explain the particular advantages and limitations of each. Specific protocols for the support of macaques through ablative cell and gene therapy procedures will be included to introduce investigators to the types of resources and support required to maintain a large animal facility dedicated to high-intensity experimentation, and also to introduce investigators to the types of procedures that are possible.

Designer blood: creating hematopoietic lineages from embryonic stem cells

Embryonic stem (ES) cells exhibit the remarkable capacity to become virtually any differentiated tissue upon appropriate manipulation in culture, a property that has been beneficial for studies of hematopoiesis. Until recently, the majority of this work used murine ES cells for basic research to elucidate fundamental properties of blood-cell development and establish methods to derive specific mature lineages. Now, the advent of human ES cells sets the stage for more applied pursuits to generate transplantable cells for treating blood disorders. Current efforts are directed toward adapting in vitro hematopoietic differentiation methods developed for murine ES cells to human lines, identifying the key interspecies differences in biologic properties of ES cells, and generating ES cell-derived hematopoietic stem cells that are competent to repopulate adult hosts. The ultimate medical goal is to create patient-specific and generic ES cell lines that can be expanded in vitro, genetically altered, and differentiated into cell types that can be used to treat hematopoietic diseases.

Embryonic stem cell–derived astrocytes: a novel gene therapy vector for brain tumors

Object

For gene therapy strategies currently in clinical trials, viral vectors are used to deliver transgenes directly to normal and tumor cells within the central nervous system (CNS). The use of viral vectors is limited by several factors. The aim of this study was to assess whether embryonic stem cell (ESC)–derived astrocytes expressing a doxycycline-inducible transgene can be used as a vector for gene therapy.

Methods

The authors generated a pure population of ESC-derived astrocytes carrying a transgene, tumor necrosis factor–related apoptosis-inducing ligand (TRAIL), inserted in the chromosome under the control of a highly regulated doxycycline-inducible expression system. Fully differentiated ESC-derived astrocytes were stereotactically transplanted in the mouse brain, and then cell migration and transgene expression were studied.

Results

The ESC-derived astrocytes started to migrate from the transplant site 48 hours after the procedure. They were found to have migrated throughout the brain tissue by 6 weeks. Transplanted ESC-derived astrocytes expressed the TRAIL transgene after doxycycline induction throughout the duration of the experiment. Teratoma formation was not observed in long-term experiments (12 weeks).

Conclusions

These data show that ESC-derived astrocytes can be used as delivery vectors for CNS tumors. This technique might have a major impact on the treatment of patients with malignant gliomas and a wide spectrum of other neurological diseases.

Embryonic stem cell—derived astrocytes expressing drug-inducible transgenes: differentiation and transplantion into the mouse brain

OBJECT

Embryonic stem cell (ESC)-derived astrocytes have many theoretical and practical advantages as vectors for delivery of gene therapy to the central nervous system (CNS). The aim of this study was to generate highly pure populations of ESC-derived astrocytes expressing drug-inducible transgenes, while minimizing contamination by undifferentiated ESCs

METHODS

Embryonic stem cells carrying a doxycycline-inducible green fluorescent protein (GFP) transgene were induced to differentiate into astrocytes by using feeder cell-free conditions that are completely defined. More than 95% of these cells expressed the astrocyte markers glial fibrillary acidic protein and GLT-1 glutamate transporter, and the morphological characteristics of these cells were typical of astrocytes. The expression of additional astrocyte markers was detected using reverse transcription-polymerase chain reaction. Undifferentiated ESCs comprised fewer than 0.1% of the cells after 10 days in this culture. Positive and negative selection techniques based on fluorescence-activated cell sorting were successfully used to decrease further the numbers of undifferentiated ESCs. Fully differentiated astrocytes expressed a GFP transgene under the tight control of a doxycycline-responsive promoter, and maintained their astrocytic phenotype 24 hours after transplantation into the mouse brain.

CONCLUSIONS

This study shows that transgenic ESCs can be induced to differentiate into highly pure populations of astrocytes. The astrocytes continue to express the transgene under the tight control of a drug-inducible promoter and are suitable for transplantation into the mouse brain. The number of potentially hazardous ESCs can be minimized using cell-sorting techniques. This strategy may be used to generate cellular vectors for delivering gene therapy to the CNS.

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.

Hematopoietic microchimerism in sheep after in utero transplantation of cultured cynomolgus embryonic stem cells

BACKGROUND

Although directed differentiation of human embryonic stem (ES) cells would enable a ready supply of cells and tissues required for transplantation therapy, the methodology is limited. We have developed a novel method for hematopoietic development from primate ES cells. We first cultured cynomolgus monkey ES cells in vitro and transplanted the cells in vivo into fetal sheep liver, generating sheep with cynomolgus hematopoiesis.

METHODS

Cynomolgus ES cells were induced to mesodermal cells on murine stromal OP9 cells with multiple cytokines for 6 days. The cells (average 4.8 x 10 cells) were transplanted into fetal sheep in the liver (n=4) after the first trimester (day 55-73, full term 147 days). The animals were delivered at full term, and two of them were intraperitoneally administered with human stem-cell factor (SCF).

RESULTS

Cynomolgus hematopoietic progenitor cells were detected in bone marrow at a level of 1% to 2% in all four sheep up to 17 months posttransplant. No teratoma was found in the lambs. After SCF administration, the fractions of cynomolgus hematopoiesis increased by several-fold (up to 13%). Cynomolgus cells were also detected in the circulation, albeit at low levels (<0.1%).

CONCLUSIONS

Long-term hematopoietic microchimerism from primate ES cells was observed after in vitro differentiation to mesodermal cells, followed by in vivo introduction into the fetal liver microenvironment. The mechanism of such directed differentiation of ES cells remains to be elucidated, but this procedure should allow further investigation.

Chimerism of metanephric adenoma but not of carcinoma in kidney transplants

Recipient-derived cells integrate into renal allografts inducing organ-specific microchimerism. Circulating pluripotent progenitor cells with high plasticity for differentiation were suggested as a potential source of allograft chimerism. Whether or not these cells also contribute to tumor formation in renal transplants is unknown. We analyzed six histologically different tumors in renal allografts for the presence of recipient-derived cells. To circumvent dependency on gender mismatch, a polymerase chain reaction assay for highly polymorphic short tandem repeat marker (DNA fingerprinting) in combination with laser microdissection was applied. Pure tumor cell populations were harvested by laser microdissection after immunohistochemical (CD45/CD68) marking of contaminating leukocytes. In cases of gender mismatch (n = 2), results were confirmed by sex chromosome in situ hybridization. Two metanephric adenomas demonstrated microchimerism comprising both donor- and recipient-derived tumor cells. Two clear cell carcinomas, one transitional cell carcinoma, and one renal cortical adenoma were all of donor origin without chimerism. We conclude that except for metanephric adenomas, tumors arising in renal transplants originate completely from graft cells. The mixed derivation of metanephric adenomas indicates an incorporation of recipient-derived progenitor cells. This finding suggests that adult stem cells can assume neoplastic phenotypes.

Progress with Nonhuman Primate Embryonic Stem Cells1

Embryonic stem cells hold potential in the fields of regenerative medicine, developmental biology, tissue regeneration, disease pathogenicity, and drug discovery. Embryonic stem (ES) cell lines are now available in primates, including man, rhesus, and cynomologous monkeys. Monkey ES cells serve as invaluable clinically relevant models for studies that can't be conducted in humans because of practical or ethical limitations, or in rodents because of differences in physiology and anatomy. Here, we review the current status of nonhuman primate research with ES cells, beginning with a description of their isolation, characterization, and availability. Substantial limitations still plague the use of primate ES cells, such as their required growth on feeder layers, poor cloning efficiency, and restricted availability. The ability to produce homogenous populations of both undifferentiated as well as differentiated phenotypes is an important challenge, and genetic approaches to achieving these objectives are discussed. Finally, safety, efficiency, and feasibility issues relating to the transplantation of ES-derived cells are considered.