Embryonic Stem Cells: Controversy, Mechanisms, and Safety (2023)

Louis A. Cona, MD
Updated on
May 23, 2023

Embryonic Stem Cells: Controversy, Mechanisms, and Safety (2023)

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Embryonic stem cells, with their exceptional potential to differentiate into diverse cell types, remain unparalleled in scientific research. This article intends to explore the realm of embryonic stem cells, highlighting their origin, functionality, and the diverse applications they promise in regenerative medicine.


Diverse Landscape of Stem Cells

In the broad spectrum of stem cells, human embryonic stem cells often steal the limelight due to their inherent pluripotency that confers them the ability to metamorphose into virtually any cell type. Alongside them, we also delve into induced pluripotent stem cells (iPS cells), a class of engineered stem cells that replicate the properties of embryonic stem cells without the associated ethical concerns.

Moreover, our focus will extend to bone marrow stem cells, a quintessential example of multipotent stem cells known for their potential in treating hematological disorders. We will also consider totipotent stem cells' capability to generate an entire organism.

A significant part of our discussion involves the role of differentiated somatic cells, mature cells that have a defined role in the human body, and the breakthrough technology of somatic cell nuclear transfer. We will contemplate how the paradigm shift from the pluripotency of embryonic cells to the induced pluripotency of iPS cells has sparked a revolution in stem cell research.

The article also promises insights into perinatal stem cells and their therapeutic applications, the significance of maintaining a robust stem cell line for research, and the potential of various cell types, including liver cells, bone cells, hematopoietic stem cells, and brain cells in the scope of regenerative medicine.

Understanding Stem Cells

Before diving into the specifics of embryonic stem cells, it's vital to get a basic understanding of stem cells themselves. Stem cells exist in the human body and are the raw materials from which all other cells with specialized functions are generated. These cells can divide to form more stem cells or become specialized cells like nerves, brain, or blood cells. Essentially, stem cells are like a blank canvas, ready to be transformed into a masterpiece of functionality and purpose.

One crucial attribute that sets stem cells apart from other cell types is their capacity for self-renewal, which means they can divide and produce more stem cells indefinitely. There are two main types of stem cells: adult stem cells and embryonic stem cells. Adult stem cells, or somatic cells, are undifferentiated cells found dispersed among differentiated cells in a tissue or organ. They can self-renew and differentiate to yield the major specialized cell types of the organ from which they originate.

What are Embryonic Stem Cells?

A human embryonic stem cell is an undifferentiated cell derived from a developing embryo, typically in the blastocyst stage. These cells can self-renew and differentiate into various specialized cell types, including those from all three germ layers (ectoderm, mesoderm, and endoderm). Due to their pluripotent nature and potential applications in tissue regeneration and medical research, they have garnered significant interest in the scientific community.

Embryonic stem cells, often abbreviated as ES cells, are pluripotent stem cells derived from the inner cell mass of a blastocyst, an early-stage preimplantation embryo. In simpler terms, embryonic stem cells come from three to five days old embryos. At this stage, an embryo is a blastocyst with about 150 cells. These cells are pluripotent, meaning they can divide into more stem cells or can become any cell type in the body. This versatility allows embryonic stem cells to regenerate or repair diseased tissue and organs. However, their use in people has been limited to eye-related disorders such as macular degeneration.


Origin and Characteristics of Embryonic Stem Cells

The main characteristics of an embryonic stem cell include:

  1. Pluripotency: Embryonic stem cells can differentiate into various specialized cell types derived from all three germ layers (ectoderm, mesoderm, and endoderm), which is known as pluripotency. This means that they can give rise to various cell types in the body, including muscle, nerve, and blood cells.
  2. Self-renewal: Embryonic stem cells can proliferate and self-renew indefinitely in culture while maintaining their undifferentiated state. This means they can constantly supply new cells for experimentation, tissue regeneration, or cell therapy.
  3. Dependency on specific growth factors: Embryonic stem cells rely on specific growth factors for their maintenance and proliferation, such as transforming growth factor-beta (TGF-beta), activin, and fibroblast growth factor (FGF). These factors help sustain the pluripotency and self-renewal ability of the cells.
  4. Expression of pluripotency markers: Embryonic stem cells express specific markers associated with pluripotency, such as Oct4, Nanog, and Sox2. These transcription factors play a crucial role in maintaining the undifferentiated state and pluripotency of the cells.
  5. Sensitivity to culture conditions: The culture conditions for embryonic stem cells are critical for maintaining their pluripotent state and preventing spontaneous differentiation or contamination. This includes using specific culture media, growth factors, feeder layers, and controlled environmental conditions such as temperature, humidity, and gas concentrations.
  6. Genetic stability: Maintaining the genetic integrity of embryonic stem cells is essential for their safe use in research and clinical applications. However, these cells can undergo spontaneous genetic modifications, such as chromosomal abnormalities and mutations, over time in culture. Therefore, monitoring the genetic stability of the cells is a vital aspect of working with them.

Where Do Embryonic Stem Cells Come From?

Embryonic stem cells originate from human embryos. But where do these embryos come from? Most embryonic stem cells are derived from embryos that develop from eggs fertilized in vitro—in an in vitro fertilization clinic—and then donated for research purposes with the informed consent of the donors. They are not derived from eggs fertilized in a woman's body. The process of deriving embryonic stem cells involves the destruction of the blastocyst stage of the embryo, which raises a host of ethical and moral issues that have been the source of much debate.

Harvesting Embryonic Stem Cells

Harvesting embryonic stem cells involves a complex process. The initial steps are carried out in a laboratory. It involves removing cells from the donated embryo in cell line derivation. This process usually takes six months to a year to establish a cell line. Once embryonic stem cell lines are established, the cells can be grown in the laboratory indefinitely. Different batches of cells can be frozen and shipped to other laboratories for further growth and experimentation.

Features of Embryonic Stem Cells

Embryonic stem cells exhibit two unique properties: pluripotency and the ability to replicate indefinitely. Combining these traits makes embryonic stem cells uniquely valuable to medical research. As they are pluripotent, embryonic stem cells have the potential to become any cell type in the body, making them a vital component in the field of regenerative medicine. Their ability to replicate indefinitely allows researchers to produce limitless quantities of these cells for research purposes.

Applications and Uses of Embryonic Stem Cells

  1. Regenerative medicine: Embryonic stem cells have great potential for treating various degenerative diseases, such as Parkinson's, multiple sclerosis, spinal cord injuries, heart diseases, and diabetes. They can be directed to differentiate into specific cell types, which can be used for cell replacement therapy.
  2. Drug discovery and development: Embryonic stem cells can be used to create cellular models for studying the molecular mechanisms of diseases and for drug screening. This approach allows researchers to identify and test the safety and efficacy of potential therapeutic compounds.
  3. Toxicity testing: Embryonic stem cell-derived cell types can study the potentially toxic effects of drugs and other chemicals on human tissues and organs, contributing to more accurate testing and safer drug development.
  4. Developmental biology research: Studying embryonic stem cells provides valuable insights into the mechanisms of cell differentiation, tissue formation, and organ development, contributing to a better understanding of human development and congenital disorders.


Medical Use of Embryonic Stem Cells

Embryonic stem cells hold immense potential for use in various medical treatments. Researchers believe that with the help of embryonic stem cells, they can transform the field of medicine by treating a host of diseases that were once considered incurable. From neurodegenerative diseases like Parkinson's and Alzheimer's to heart disease, diabetes, and spinal cord injuries, the potential of embryonic stem cells is vast.

A clear example of the potential of embryonic stem cells can be seen in treating Type 1 diabetes. Researchers aim to replace the pancreas's insulin-producing cells that are lost in this disease. This approach would, in theory, provide a renewable source of cells for transplantation and eliminate the need for lifelong insulin administration for people with this condition.

Embryonic Stem Cells in Disease Treatment

There are several diseases that embryonic stem cells can potentially cure. This is mainly due to their pluripotent nature, meaning they can develop into any cell type in the body. Some diseases that could benefit from stem cell therapy include Parkinson's disease, Alzheimer's disease, heart disease, spinal cord injury, and burns. They can also help in treating conditions like stroke and arthritis. It's important to mention, however, that while the potential of embryonic stem cells in these treatments is vast, the actual use is still under investigation, and many treatments are currently in the experimental stage or clinical trials.

Current State of Embryonic Stem Cell Usage

Despite the vast potential of embryonic stem cells, their use in treatment is currently limited. Most of the embryonic stem cell research is still in the experimental stage. There have been some successful treatments, especially in eye-related disorders, but there's still a long way to go before these treatments become mainstream.

Adult stem cell art image

Adult Stem Cells are Safer for Clinical Practice

  1. Ethical considerations: Adult stem cells can be derived from the patient's body or external sources such as umbilical cord tissue and do not involve the destruction of embryos, thus avoiding the ethical controversies surrounding embryonic stem cells.
  2. Reduced risk of tumorigenesis: Embryonic stem cells have a higher risk of forming tumorous growths called teratomas due to their pluripotent nature, whereas adult stem cells typically have more limited differentiation potential, reducing the risk of tumor formation.
  3. More available sources: Adult stem cells can be derived from various tissue sources, including bone marrow, adipose tissue, and dental pulp, making them more readily available for clinical applications compared to embryonic stem cells, which require the use of embryos.
  4. Proven clinical success: Adult stem cells have been successfully used in clinical practice for decades, such as bone marrow transplants for leukemia and other blood disorders. This highlights the benefits and safety of using adult stem cells in medical treatments.

Cell Division and Differentiation

One of the key features of embryonic stem cells is their ability to divide and differentiate. But how exactly does this process work? When a stem cell divides, it can either remain a stem cell or become another type with a more specific function, like a muscle cell, a red blood cell, or a brain cell. This process is known as differentiation. During differentiation, specific genes get activated while others get deactivated, leading to changes in the cell's DNA that cause it to develop specific physical and functional traits.

Embryonic stem cells infographic

Embryonic Stem Cells vs. Adult Cells

Embryonic and adult stem cells serve essential roles in our bodies but have some key differences. While both types of cells can divide and renew themselves, they differ in their ability to differentiate into different cell types. Embryonic stem cells are pluripotent and can become all body cell types. In contrast, adult stem cells are generally limited to differentiating into different cell types of their tissue of origin.

While embryonic stem cells have wide-ranging potential applications, adult stem cells offer a more ethical, safer, and practical approach to stem cell therapies. The use of adult stem cells in clinical practice is supported by their lower risk of immune rejection, reduced tumorigenesis, availability, and proven clinical success.

Transformative Potential of Embryonic Stem Cells

The transformative potential of embryonic stem cells lies in their pluripotency and ability to replicate indefinitely. These cells could be used to regenerate and repair diseased tissue and organs. Moreover, they can serve as a valuable tool in drug discovery and understanding the complex events that occur during human development.

The Controversy and Ethics of Embryonic Stem Cells

Research predominantly revolves around the issue of obtaining and using human embryos for research purposes. Embryonic stem cells are derived from the inner cell mass of the 5- to 7-day-old blastocyst, and the process of extracting these cells involves the destruction of human embryos. This has led to intense ethical debates, as specific individuals and groups view embryos as having rights and interests that must be respected.

One central argument in this controversy is the belief held by some that "human life begins at conception," and therefore, embryos have the same rights as fully developed humans. From this perspective, deriving embryonic stem cell lines is seen as equivalent to murder. This belief is often rooted in religious faith and moral conviction, and arguments stemming from it contribute significantly to the ethical debate surrounding embryonic stem cell research.

On the other side of the controversy, proponents of embryonic stem cell research argue that the potential benefits of these cells in terms of medical advancements and therapies outweigh the ethical concerns related to the destruction of embryos. They view embryos at the blastocyst stage as not having the same moral status as fully developed humans, and they believe that the advancements in regenerative medicine, drug development, toxicity testing, and developmental biology research made possible by embryonic stem cells justify their use.

The ethical debate has also driven advancements in stem cell research, leading to the development of induced pluripotent stem (iPS) cells, which do not involve embryos or oocytes. While iPS cells offer a less controversial alternative to embryonic stem cells, unresolved issues with their use require further research.


Ethical Concerns Surrounding Embryonic Stem Cells

Using embryonic stem cells in research and medicine has sparked a significant ethical debate. The primary concern revolves around the moral status of the embryo. Some argue that the embryo deserves the same rights as a human being, while others contend that the potential benefits of stem cell research outweigh any moral concerns. The debate is further complicated by varying beliefs about when life begins.

Addressing the Controversial Aspects

Addressing the ethical concerns surrounding embryonic stem cells involves carefully balancing the potential benefits of this research against moral concerns. In many countries, there are regulations to oversee stem cell research and ensure that it is carried out responsibly and ethically.

Legal Status of Embryonic Stem Cells

The legal status of embryonic stem cells varies from country to country. Some countries allow embryonic stem cell research, while others have strict laws prohibiting it. In the United States, for example, federal funds can be used for research on embryonic stem cells, but creating new stem cell lines using federal funds is not allowed.


In conclusion, the fascinating world of embryonic stem cells—pluripotent cells that can develop into virtually any type of human cells—continues to captivate the scientific community. The embryonic development stages, driven by the intricate choreography of the three embryonic germ layers, serve as the foundational blueprint for all human cells.

These cells, often sourced from in vitro fertilization clinics during the early stages of development, can give rise to diverse cell types, including neural cells, muscle cells, and even healthy heart muscle cells, given the appropriate feeder cells and conditions. The versatility of embryonic stem cells enables their use in cell transplantation strategies to treat diseases, setting the stage for breakthroughs in regenerative medicine.

Interestingly, efforts to induce stem cells from mature cells, such as mouse embryonic fibroblasts and human foreskin fibroblasts, have yielded another type of pluripotent cells known as induced pluripotent stem cells, expanding our understanding of the stem cell landscape.

As we continue to uncover the capabilities of these cells, from peripheral blood to egg cell differentiation, the hope for leveraging human stem cells—especially embryonic stem cells—to address previously untreatable diseases is ever more compelling. Our journey into the microscopic world of embryonic stem cells is just beginning.


(1) Lo B, Parham L. Ethical issues in stem cell research. Endocr Rev. 2009 May;30(3):204-13. doi: 10.1210/er.2008-0031. Epub 2009 Apr 14. PMID: 19366754; PMCID: PMC2726839.

(2) National Research Council (US) and Institute of Medicine (US) Committee on the Biological and Biomedical Applications of Stem Cell Research. Stem Cells and the Future of Regenerative Medicine. Washington (DC): National Academies Press (US); 2002. CHAPTER THREE, Embryonic Stem Cells. Available from: https://www.ncbi.nlm.nih.gov/books/NBK223690/

(3) Vazin T, Freed WJ. Human embryonic stem cells: derivation, culture, and differentiation: a review. Restor Neurol Neurosci. 2010;28(4):589-603. doi: 10.3233/RNN-2010-0543. PMID: 20714081; PMCID: PMC2973558.

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