Derivation, propagation and differentiation of human embryonic stem cells

Hematopoietic Development from Human Embryonic Stem Cells

The most common human cell-based therapy applied today is hematopoietic stem cell (HSC) transplantation. HSCs can be defined by two essential properties: self-renewal and multilineage hematopoietic differentiation. These combined HSC properties allow them to differentiate into all blood cell types (multilineage) in a sustained manner for the lifetime of the animal, which requires their ability to make cellular copies of themselves (self-renewal). These features can be tested by transplantation from donor to recipient and provide a functional basis to define and identify HSCs. Currently, human bone marrow (BM), mobilized peripheral blood, and umbilical cord blood (CB) represent the major sources of transplantable HSCs, but their availability for use is limited by both quantity and compatibility. Although increasing evidence suggests that somatic HSCs can be expanded to meet current needs, their in vivo potential is concomitantly compromised after ex vivo culture. Pluripotent human embryonic stem cells (hESCs) may provide an alternative. hESCs possess indefinite proliferative capacity in vitro, and have been shown to differentiate into the hematopoietic cell fate, giving rise to erythroid, myeloid, and lymphoid lineages using a variety of differentiation procedures. In most cases, hESC-derived hematopoietic cells show similar clonogenic progenitor capacity and primitive phenotype to somatic sources of hematopoietic progenitors, but possess limited in vivo repopulating capacity when transplanted into immunodeficient mice. Although this suggests HSC function can be derived from hESCs, the efficiency and quality of these cells must be characterized using surrogate models for potential clinical applications.

Sterile and disposable fluidic subsystem suitable for clinical high speed fluorescence-activated cell sorting

BACKGROUND

Applications of fluorescence-activated cell sorting (FACS) are ideally performed under aseptic conditions so that isolated cells can be successfully cultured, transplanted, or processed for the isolation of protein and nucleic acids. However, modern "off-the shelf" flow cytometers are suboptimally designed for these purposes because nonsterile instrument hardware components directly contact sample-harboring fluids, compromising their sterility.

METHODS

We have described the design and modular modification of a cytometer with a sterile and disposable FACS fluid handling system that meets requirements of high-speed FACS and good manufacturing practice. This system was tested for functionality and its ability to maintain a clean and sterile fluid environment.

RESULTS

Our data have shown that this new fluidic subsystem completely replicated the intended function of the manufacturer's standard fluid handling system, and isolates the fluid from contaminants such as bacteria and fungus, endotoxins, mycoplasma, and helicobacter.

CONCLUSIONS

FACS has emerged as a powerful tool used to study and manipulate stem cells. However, if stem cell discoveries are to be fully utilized in clinical transplant medicine, aseptic instrument configurations must be developed. For this purpose, we have designed a disposable sterile fluid handling system.

Gut-like structures from mouse embryonic stem cells as an in vitro model for gut organogenesis preserving developmental potential after transplantation

Recently, we reported the formation of gut-like structures from mouse ESCs in vitro. To determine whether ESCs provide an in vitro model of gastrointestinal (GI) tracts and their organogenesis, we investigated the morphological features, formation process, cellular development, and regional location within the GI tract by immunohistochemistry, electron microscopy, and reverse transcription-polymerase chain reaction. We also examined the developmental potential by transplantation into kidney capsules. The results demonstrated that Id2-expressing epithelium developed first, alpha-smooth muscle actin appeared around the periphery, and finally, the gut-like structures were formed into a three-layer organ with well-differentiated epithelium. A connective tissue layer and musculature with interstitial cells of Cajal developed, similar to organogenesis of the embryonic gut. Enteric neurons appeared underdeveloped, and blood vessels were absent. Many structures expressed intestinal markers Cdx2 and 5-hydroxytryptamine but not the stomach marker H(+)/K(+) ATPase. Transplants obtained blood vessels and extrinsic nerve growth from the host to prolong life, and even grafts of premature structures did not form teratoma. In conclusion, gut-like structures were provided with prototypical tissue components of the GI tract and are inherent in the intestine rather than the stomach. The formation process was basically same as in gut organogenesis. They maintain their developmental potential after transplantation. Therefore, gut-like structures provide a unique and useful in vitro system for development and stem cell studies of the GI tract, including transplantation experiments.

Laser-assisted blastocyst dissection and subsequent cultivation of embryonic stem cells in a serum/cell free culture system: applications and preliminary results in a murine model

Background

To evaluate embryonic stem cell (ESC) harvesting methods with an emphasis on derivation of ESC lines without feeder cells or sera. Using a murine model, laser-assisted blastocyst dissection was performed and compared to conventional immunosurgery to assess a novel laser application for inner cell mass (ICM) isolation.

Methods

Intact blastocysts or isolated ICMs generated in a standard mouse strain were plated in medium with or without serum to compare ESC harvesting efficiency. ESC derivation was also undertaken in a feeder cell-free culture system.

Results

Although ICM growth and dissociation was comparable irrespective of the media components, an enhanced ESC harvest was observed in our serum-free medium (p < 0.01). ESC harvest rate was not affected by ICM isolation technique but was attenuated in the feeder cell-free group.

Conclusion

Achieving successful techniques for human ESC research is fundamentally dependent on preliminary work using experimental animals. In this study, all experimentally developed ESC lines manifested similar features to ESCs obtained from intact blastocysts in standard culture. Cell/sera free murine ESC harvest and propagation are feasible procedures for an embryology laboratory and await refinements for translation to human medical research.

Banking on human embryonic stem cells: estimating the number of donor cell lines needed for HLA matching

BACKGROUND

Human embryonic stem (hES) cells are a promising source for transplantation to replace diseased or damaged tissue, but their differentiated progeny express human leucocyte antigens (HLAs) that will probably cause graft rejection. The creation of a bank of HLA-typed hES cells, from which a best match could be selected, would help reduce the likelihood of graft rejection. We investigated how many hES cell lines would be needed to make matching possible in most cases.

METHODS

The number of hES cell lines needed to achieve varying degrees of HLA match was estimated by use of, as a surrogate for hES-cell donor embryos, blood group and HLA types on a series of 10,000 consecutive UK cadaveric organ donors. The degree of blood group compatibility and HLA matching for a recipient population consisting of 6577 patients registered on the UK kidney transplant waiting list was determined, assuming all donor hES cell lines could provide a transplant for an unlimited number of recipients.

FINDINGS

A bank of 150 consecutive donors provided a full match at HLA-A, HLA-B, and HLA-DR for a minority of recipients (<20%); a beneficial match (defined as one HLA-A or one HLA-B mismatch only) or better for 37.9% (range 27.9-47.5); and an HLA-DR match or better for 84.9% (77.5-90.0). Extending the number of donors beyond 150 conferred only a very gradual incremental benefit with respect to HLA matching. A panel of only ten donors homozygous for common HLA types selected from 10,000 donors provided a complete HLA-A, HLA-B and HLA-DR match for 37.7% of recipients, and a beneficial match for 67.4%.

INTERPRETATION

Approximately 150 consecutive blood group compatible donors, 100 consecutive blood group O donors, or ten highly selected homozygous donors could provide the maximum practical benefit for HLA matching. The findings from these simulations have practical, political, and ethical implications for the establishment of hES-cell banks.

Hematopoietic development from human embryonic stem cell lines

The most common human cell-based therapy applied today is hematopoietic stem cell (HSC) transplantation. Currently, human bone marrow, mobilized peripheral blood, and umbilical cord blood represent the major sources of transplantable HSCs, but their availability for use is limited by both compatibility between donor and recipient and required quantity. Although increasing evidence suggests that somatic HSCs can be expanded to meet current needs, their in vivo potential is concomitantly compromised after ex vivo culture. In contrast, human embryonic stem cells (hESC) possess indefinite proliferative capacity in vitro and have been shown to differentiate into the hematopoietic cell fate, giving rise to erythroid, myeloid, and lymphoid lineages using a variety of differentiation procedures. Human ESC-derived hematopoietic cells emerge from a subset of embryonic endothelium expressing PECAM-1, Flk-1, and VE-Cadherin, but lacking CD45 (CD45negPFV). These CD45negPFV precursors are exclusively responsible for hematopoietic potential of differentiated hESCs. hESC-derived hematopoietic cells show similar clonogenic capacity and primitive phenotype to somatic sources of hematopoietic progenitors and possess limited in vivo repopulating capacity in immunodeficient mice, suggestive of HSC function. Here, we will review current progress in studies of hESC-derived hematopoietic cells and discuss the potential precincts and applications.

Prospective identification of cardiac progenitors by a novel single cell-based cardiomyocyte induction

Dissection of cardiomyocyte differentiation process at the cellular level is indispensable in the research for cardiac development and regeneration. Previously, we have established an embryonic stem cell differentiation system that reproduces early vascular development from progenitor cells that express Flk1, a vascular endothelial growth factor receptor, by the combinatory application of 2-dimensional culture and flowcytometry. Here we show that cardiomyocytes can be successfully induced from a single Flk1+ cell on 2-dimensional culture, enabling the direct observation of differentiating cardiomyocytes and the prospective identification of cardiac progenitor potentials. Flk1+ cells could give rise to cardiomyocytes, as well as endothelial cells, from a single cell by the co-culture on OP9 stroma cells in a fusion-independent manner. Among the cell populations in intermediate stages from Flk1+ cells to cardiomyocytes, Flk1+/CXCR4+/vascular endothelial cadherin- cells were cardiac-specific progenitors at the single cell level. Noggin, a bone morphogenetic protein inhibitor, abolished cardiomyocyte differentiation by inhibiting the cardiac progenitor induction. However, wnt inhibitors Dkk-1 or Frizzled-8/Fc chimeric protein augmented, but wnt3a inhibited, cardiomyocyte differentiation. In vitro reproduction of cardiomyocyte differentiation process should be a potent tool for the cellular and molecular elucidation of cardiac development, which would provide various targets for cardiac regeneration.

Challenges of Primate Embryonic Stem Cell Research

Embryonic stem (ES) cells hold great promise for treating degenerative diseases, including diabetes, Parkinson's, Alzheimer's, neural degeneration, and cardiomyopathies. This research is controversial to some because producing ES cells requires destroying embryos, which generally means human embryos. However, some of the surplus human embryos available from in vitro fertilization (IVF) clinics may have a high rate of genetic errors and therefore would be unsuitable for ES cell research. Although gross chromosome errors can readily be detected in ES cells, other anomalies such as mitochondrial DNA defects may have gone unrecognized. An insurmountable problem is that there are no human ES cells derived from in vivo-produced embryos to provide normal comparative data. In contrast, some monkey ES cell lines have been produced using in vivo-generated, normal embryos obtained from fertile animals; these can represent a "gold standard" for primate ES cells. In this review, we argue a need for strong research programs using rhesus monkey ES cells, conducted in parallel with studies on human ES and adult stem cells, to derive the maximum information about the biology of normal stem cells and to produce technical protocols for their directed differentiation into safe and functional replacement cells, tissues, and organs. In contrast, ES cell research using only human cell lines is likely to be incomplete, which could hinder research progress, and delay or diminish the effective application of ES cell technology to the treatment of human diseases.

Magnetic Cell Sorting Purification of Differentiated Embryonic Stem Cells Stably Expressing Truncated Human CD4 as Surface Marker

Embryonic stem (ES) cells offer great potential in regenerative medicine and tissue engineering. Clinical applications are still hampered by the lack of protocols for gentle, high-yield isolation of specific cell types for transplantation expressing no immunogenic markers. We describe labeling of stably transfected ES cells expressing a human CD4 molecule lacking its intracellular domain (DeltaCD4) under control of the phosphoglycerate kinase promoter for magnetic cell sorting (MACS). To track the labeled ES cells, we fused DeltaCD4 to an intracellular enhanced green fluorescent protein domain (DeltaCD4EGFP). We showed functionality of the membrane-bound fluorescent fusion protein and its suitability for MACS leading to purities greater than 97%. Likewise, expression of DeltaCD4 yielded up to 98.5% positive cells independently of their differentiation state. Purities were not limited by the initial percentage of DeltaCD4(+) cells, ranging from 0.6%-16%. The viability of MACS-selected cells was demonstrated by reaggregation and de novo formation of embryoid bodies developing all three germ layers. Thus, expression of DeltaCD4 in differentiated ES cells may enable rapid, high-yield purification of a desired cell type for tissue engineering and transplantation studies.

Gene delivery to embryonic stem cells

Since the establishment of embryonic stem (ES) cells and the identification of tissue-specific stem cells, researchers have made great strides in the analysis of the natural biology of such stem cells for the development of therapeutic applications. Specifically, ES cells are capable of differentiating into all of the cell types that constitute the whole body. Thus, ES cell research promises new type of treatments and possible cures for a variety of debilitating diseases and injuries. The potential medical benefits obtained from stem cell technology are compelling and stem cell research sees a bright future. Control of the growth and differentiation of stem cells is a critical tool in the fields of regenerative medicine, tissue engineering, drug discovery, and toxicity testing. Toward such a goal, we present here an overview of gene delivery in ES cells, covering the following topics: significance of gene delivery in ES cells, stable versus transient gene delivery, cytotoxicity, suspension versus adherent cells, expertise, time, cost, viral vectors for gene transduction (lentiviruses, adenoviruses, and adeno-associated viruses, chemical methods for gene delivery, and mechanical or physical gene delivery methods (electroporation, nucleofection, microinjection, and nuclear transfer).

Human embryonic stem cells express an immunogenic nonhuman sialic acid

Human embryonic stem cells (HESC) can potentially generate every body cell type, making them excellent candidates for cell- and tissue-replacement therapies. HESC are typically cultured with animal-derived 'serum replacements' on mouse feeder layers. Both of these are sources of the nonhuman sialic acid Neu5Gc, against which many humans have circulating antibodies. Both HESC and derived embryoid bodies metabolically incorporate substantial amounts of Neu5Gc under standard conditions. Exposure to human sera with antibodies specific for Neu5Gc resulted in binding of immunoglobulin and deposition of complement, which would lead to cell killing in vivo. Levels of Neu5Gc on HESC and embryoid bodies dropped after culture in heat-inactivated anti-Neu5Gc antibody-negative human serum, reducing binding of antibodies and complement from high-titer sera, while allowing maintenance of the undifferentiated state. Complete elimination of Neu5Gc would be likely to require using human serum with human feeder layers, ideally starting with fresh HESC that have never been exposed to animal products.