# Embryonic Stem Cells: Definition, Properties, Sources, Uses, and Ethical Issues

> Learn what embryonic stem cells are, where they come from, how pluripotency and self-renewal work, their research uses, limitations, and ethical issues.

Canonical URL: https://biologynotesonline.com/embryonic-stem-cells/
Author: Sourav Pan
Last updated: September 14, 2026

![Embryonic Stem Cells: Definition, Properties, Sources, Uses, and Ethical Issues](https://biologynotesonline.com/wp-content/uploads/2023/09/Embryonic-Stem-Cells-Definition-Properties-Applications.jpg)

Embryonic stem cells (ESCs) are [pluripotent stem cells](https://biologynotesonline.com/stem-cell-definition-types-application-advantages/) that are obtained from the inner cell mass (ICM) of an early embryo, known as the blastocyst. In humans, this blastocyst stage is formed about 5-6 days after fertilization. These cells have two major properties, self-renewal and pluripotency. They can divide continuously for a long period while remaining in the undifferentiated state.

Embryonic stem cells have the ability to differentiate into cells of the three embryonic germ layers, i.e. ectoderm, mesoderm, and endoderm. From these germ layers, different specialized cells of the body can be formed. However, embryonic stem cells are referred to as pluripotent, and not totipotent, because they normally cannot form all the extra-embryonic tissues required for development of a complete organism.

## Origin and Derivation of Embryonic Stem Cells

- Embryonic stem cells (ESCs) are mainly obtained from the inner cell mass (ICM) of the blastocyst. The blastocyst is an early stage embryo, which contains an outer trophoblast layer, fluid-filled cavity and the inner cell mass. The inner cell mass forms the embryo proper.

- In humans, blastocyst is formed approximately 5 days after fertilization. For the derivation of human embryonic stem cells, blastocysts produced during [in vitro fertilization (IVF)](https://biologynotesonline.com/in-vitro-fertilization-definition-principle-procedure-applications/) are commonly used. The first human embryonic stem cell lines were also derived from the inner cell mass of IVF-produced blastocysts.

- The inner cell mass is first separated from the surrounding trophoblast cells. Different methods can be used for its isolation such as mechanical dissection, laser-assisted isolation and immunosurgery. In immunosurgery, the trophoblast cells are selectively destroyed and the inner cell mass is retained.

- After isolation, the inner cell mass is placed in suitable culture medium and allowed to grow. The cells attach to the culture surface, start growing out and divide repeatedly. Earlier, mouse embryonic fibroblasts (MEFs) were commonly used as feeder layer for culturing these cells. Feeder-free culture systems are also used.

- During this process, the growing cells are subcultured repeatedly. Colonies showing the characteristics of embryonic stem cells are selected and maintained in the undifferentiated condition. Cells which continue self-renewal during repeated culture are then established as an embryonic stem cell line.

- Embryonic stem cells have also been derived from morula-stage embryos, developmentally arrested embryos and from individual blastomeres. However, the inner cell mass of blastocyst is the major source used for ESC derivation, while these alternative methods generally show variable or lower derivation efficiency.

![Human blastocyst showing the trophectoderm, blastocoel and inner cell mass, followed by isolation and culture of inner-cell-mass cells to establish an embryonic stem cell line.](https://biologynotesonline.com/wp-content/uploads/2024/04/Embryonic-Stem-Cell-Origin-and-Derivation-from-the-Blastocyst-1024x576.webp)Human blastocyst showing the trophectoderm, blastocoel and inner cell mass, followed by isolation and culture of inner-cell-mass cells to establish an embryonic stem cell line.

## Properties of Embryonic Stem Cells

- Self-renewal- Embryonic stem cells can divide again and again and still remain as stem cells. When proper culture condition is maintained, these cells continue their growth for a long period without differentiation. This capacity of producing similar undifferentiated cells is called self-renewal.

- Pluripotency- ESCs are pluripotent cells. They can form different cell types belonging to all the [three germ layers](https://biologynotesonline.com/formation-and-fate-of-germ-layers/), ectoderm, mesoderm and endoderm. But they normally do not form all extra-embryonic tissues. Therefore, these cells are not totipotent.

- Undifferentiated nature- Under suitable conditions, embryonic stem cells are maintained in an undifferentiated state. They continue cell division without changing immediately into any specialized cell. Differentiation can take place when suitable signals are provided.

- Stem cell markers- Embryonic stem cells show some characteristic pluripotency markers. Important transcription factors include OCT4, SOX2 and NANOG. Human ESCs also express surface markers such as SSEA-3, SSEA-4, TRA-1-60 and TRA-1-81, which are used during their characterization.

- Cell morphology- Human embryonic stem cells usually grow in closely packed colonies with distinct colony boundaries. The cells contain a large nucleus with relatively less cytoplasm. Prominent nucleoli are also present.

- Genetic stability- ESCs can maintain normal karyotype during continuous culture when suitable culture conditions are provided. This property is checked while characterizing a stable embryonic stem cell line.

- High proliferation- Embryonic stem cells have a high rate of cell proliferation. They can pass through repeated cell divisions for long periods. High telomerase activity is also associated with this prolonged self-renewal.

![Embryonic stem cells undergoing self-renewal or differentiating through ectoderm, mesoderm and endoderm lineages into representative neurons, cardiomyocytes, blood cells and pancreatic cells.](https://biologynotesonline.com/wp-content/uploads/2024/04/Embryonic-Stem-Cell-Pluripotency-and-Three-Germ-Layers-1024x576.webp)Embryonic stem cells undergoing self-renewal or differentiating through ectoderm, mesoderm and endoderm lineages into representative neurons, cardiomyocytes, blood cells and pancreatic cells.

## Culture and Differentiation

- Culture conditions- Embryonic stem cells are grown under controlled culture conditions. Earlier, human ESCs were maintained on mouse embryonic fibroblast (MEF) feeder layer. The feeder cells provide suitable support for attachment and also help to maintain the cells in undifferentiated condition. [Feeder-free culture system](https://biologynotesonline.com/stem-cell-culture-definition-types-application-preparation/) can also be used with defined culture medium and extracellular matrix.

- Growth factors- Some growth factors are required for maintaining the growth of embryonic stem cells. Fibroblast growth factor 2 (FGF2 or bFGF) is commonly used for maintaining self-renewal and undifferentiated condition of human ESCs. Activin A and TGF-β signalling are also involved in maintaining pluripotency.

- Subculturing- During culture, the growing colonies are transferred into fresh medium after a particular period. This process is called passaging or subculturing. Proper culture condition is maintained during this process, otherwise spontaneous differentiation of the cells can take place.

- Spontaneous differentiation- When the conditions required for pluripotency are removed, embryonic stem cells start to differentiate. In suspension culture, the cells can aggregate and form three-dimensional structures called embryoid bodies (EBs). Different types of cells can develop within these structures. Cells belonging to ectoderm, mesoderm and endoderm may be formed.

- Directed differentiation- Embryonic stem cells can also be [differentiated into a selected cell lineage](https://biologynotesonline.com/cell-differentiation-definition-process-examples/). In this method, culture condition is changed and specific growth factors or signalling molecules are added. The cells then gradually move from the pluripotent condition towards a differentiated cell type.

- Embryoid body differentiation- Embryoid body formation is one of the methods used for differentiation of ESCs. First, the cells are allowed to aggregate in suspension and embryoid bodies are formed. After their formation, specific factors or chemicals can be added according to the required cell lineage.

- Differentiated cells- Depending on the culture condition and the differentiation signals, embryonic stem cells can form different specialized cells. These include neural cells, cardiac cells, blood-forming cells and other cell types developed from the three germ layers.

![Human embryonic stem cells maintained in self-renewing culture or directed toward spontaneous embryoid-body formation and controlled differentiation into specialized cells.](https://biologynotesonline.com/wp-content/uploads/2024/04/Embryonic-Stem-Cell-Culture-and-Differentiation-Pathways-1024x768.webp)Human embryonic stem cells maintained in self-renewing culture or directed toward spontaneous embryoid-body formation and controlled differentiation into specialized cells.

## Research Uses and Clinical Potential of ESCs

- Study of development- Embryonic stem cells are used to study the early stages of human development. Their differentiation in culture helps to understand how different cell types and tissues are formed from pluripotent cells. The genes and signalling pathways involved during this process can also be studied.

- Disease modelling- ESCs can be differentiated into particular cell types and used for making laboratory models of different diseases. Genetically modified ESC lines can also be prepared to study the effect of specific gene defects. These models are useful for understanding cellular and molecular changes involved in disease.

- Drug screening- Embryonic stem cell-derived cells are used for screening different drugs and chemical compounds. The effect of a drug on particular human cell types can be examined in vitro. They can also be used during toxicity and safety testing of new compounds.

- Regenerative medicine- ESCs can produce many specialized cell types, therefore they have potential use in cell replacement therapy. The required cells are first differentiated under controlled conditions and then considered for transplantation to replace damaged or lost cells.

- Retinal diseases- Retinal pigment epithelial (RPE) cells can be produced from human ESCs. These cells have been studied clinically for retinal disorders such as age-related macular degeneration and Stargardt disease. Clinical studies mainly examine the safety and possible therapeutic effect of transplanted RPE cells.

- Diabetes- Embryonic stem cells can be differentiated towards pancreatic cell lineages, including insulin-producing cells. ESC-derived pancreatic cells are being studied as a possible source of replacement cells for diabetes.

- Neurological disorders- Neural cells can also be produced from ESCs. Such cells are used in research related to neurological diseases and for studying the possibility of replacing damaged neural cells. Pluripotent stem cell-based therapies have entered clinical studies for some neurodegenerative conditions.

- Cardiac research- ESCs can be differentiated into cardiomyocytes, which are used for studying heart development, cardiac disease and drug responses. ESC-derived cardiac cells are also being examined for their possible use in repairing damaged heart tissue.

## Limitations of ESCs

- Ethical issues- Human embryonic stem cells are generally derived from early-stage embryos. During their derivation, the embryo is destroyed and therefore, the use of ESCs has raised ethical and legal issues in different countries.

- Immune rejection- ESC-derived cells may not be genetically matched with the recipient. After transplantation, these cells can be recognized as foreign by the immune system and immune rejection may take place. Immunosuppressive treatment may therefore be required in some cases.

- Tumor formation- Undifferentiated embryonic stem cells can form teratomas after transplantation. Even a small number of remaining pluripotent cells in the differentiated cell population can create a safety problem. For this reason, removal of undifferentiated cells is important before transplantation.

- Control of differentiation- ESCs can differentiate into many types of cells, but directing all the cells towards one required cell type is difficult. The differentiated population may contain unwanted or incompletely differentiated cells. This heterogeneity is one of the problems during their clinical use.

- Genetic instability- During prolonged culture, embryonic stem cells can acquire genetic and epigenetic abnormalities. Such changes may affect their normal properties and can also increase safety concerns for transplantation. Regular genetic analysis is therefore required during culture.

- Culture difficulties- Maintenance of ESCs requires carefully controlled culture conditions. Changes in culture medium, passage method or growth conditions can result in spontaneous differentiation and changes in cell characteristics.

- Clinical safety- ESC-derived cells need proper characterization before their use in patients. Tumorigenicity, immune compatibility, purity of the differentiated cells and genetic stability have to be checked. These requirements make their clinical application more complex.

![ESC-derived cell therapy workflow showing residual pluripotent cells and teratoma risk, heterogeneous differentiation, possible genomic changes during culture, and immune rejection after transplantation.](https://biologynotesonline.com/wp-content/uploads/2024/04/Safety-Challenges-of-Embryonic-Stem-Cell-Derived-Therapies-1024x768.webp)ESC-derived cell therapy workflow showing residual pluripotent cells and teratoma risk, heterogeneous differentiation, possible genomic changes during culture, and immune rejection after transplantation.

## Ethical and Research Oversight of ESCs

- Embryo use- Human embryonic stem cells are derived from early-stage embryos, therefore their use involves important ethical consideration. Research using embryos and derivation of new ESC lines are generally subjected to specialized scientific and ethical review.

- Informed consent- Embryos used for ESC research should be obtained with proper informed consent from the donors. The donors must be informed about the research use of the embryos and derivation of stem cell lines before consent is given.

- Research oversight- Research involving human embryos and some related stem cell studies are reviewed through a specialized scientific and ethics oversight process. The review can be carried out by committees such as Embryo Research Oversight (EMRO), ESCRO or other appropriate institutional committee having scientific and ethical expertise.

- Scientific justification- The proposed research should have a clear scientific purpose. During review, the scientific value of the work, ethical issues and the number of embryos required are considered. Unnecessary use of human embryos is avoided.

- Embryo culture limit- Human embryo research has traditionally been restricted to about 14 days after fertilization or before formation of the primitive streak, depending upon the regulations followed in a particular region. Current guidelines have opened discussion of research beyond this period only under strict specialized review, public support and where local law permits it.

- Donor privacy- Information related to embryo and tissue donors should be handled carefully. Proper consent procedures and protection of donor information form an important part of ethical stem cell research oversight.

- Local regulations- Rules for human embryonic stem cell research are not the same in every country. Researchers have to follow the applicable institutional requirements, national laws and ethical regulations before starting the work. Some types of embryo and stem cell research may require additional review or may not be permitted.

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