Stem Cells: Definition, Properties, Types, Applications, and Challenges

Unique cells found in the body called stem cells have the capacity to develop into multiple cell types or to proliferate endlessly to make more stem cells.

Stem cells are vital cells that replenish lost or damaged cells as a result of illnesses.
These cells, which may be found in both embryonic and adult animals, are the earliest cells in the cell lineage in all tissues.
The tissues and organs of animals and plants are made up of new cells that are continuously produced by these cells.
Stem cells have attracted a lot of attention as a potential treatment approach for a number of illnesses and ailments.
The core cell mass of the blastocyte, which divides into all other cells in the body, contains the embryonic organism's stem cells.
Adults' stem cells, however, are restricted to certain parts of the body, such as the gonads and bone marrow.

Properties of Stem Cells

All stem cells in all biological systems have three crucial characteristics. Through a procedure known as clonogenic tests, where a single cell is tested for its capacity to differentiate, these characteristics may be shown in vitro.

These are a few characteristics of stem cells:

All stem cells have the capacity to divide and replenish themselves over an extended length of time. These cells maintain their undifferentiated condition throughout a period of cell growth.
All stem cells are undifferentiated or unspecialized. These are a mass of cells that differentiate later in the course of their cell cycle.
The capacity of stem cells to develop into specialised cells that collectively make up various tissue types is another crucial characteristic of these cells. These cells have the potential to be multipotent or pluripotent.

Stem Cell Culture

In addition to the fact that cell culture is frequently employed in fundamental research to understand stem cell biology, there is growing interest in improving stem cell culture due to the potential therapeutic uses of cultured stem cells.
These cells are cultivated in artificial environments to create more of them due to their capacity to replace injured cells.
Since embryonic stem cells may differentiate into multiple cell types, they are more powerful than adult stem cells.
However, because adult stem cells can only develop into certain lineages, they are less powerful and more constrained.
Consequently, the primary goal of cultivating embryonic stem cells is to produce additional embryonic stem cells.
Depending on the kind of stem cell, specific requirements for the cultivation of embryonic stem cells (ES) or various adult stem cell types may need to be adjusted.
Similar to this, cell culture conditions must be adjusted in accordance with the stem cell cultivation's ultimate goal.
Since stem cells always strike a balance between self-renewal and differentiation, the procedure of stem cell cultivation should be improved over time.
As certain stem cells require non-standard cell culture reagents such feeder cell layers, conditioned medium, or growth matrices, the culture of stem cells may differ from that of other cells.
Different media and conditions should be used depending on the objective of the culture, with some cultures aiming to maintain the stem-state of the cells while others may desire differentiation of the cells.
Cells are typically maintained in incubators that are at atmospheric partial oxygen pressure while being passaged under a laminar flow hood.
Controlling and maintaining precise cell culture conditions, particularly the pH and oxygen pressure, is a difficult task.

Types/ Sources of Stem Cells

stem cells are categorised into many categories depending on where they are found or where they come from;

1. Embryonic stem cells

An embryo's inner cell mass, or blastocyst, contains a collection of cells known as embryonic stem cells during a very early stage of development.
Within 4-5 days following fertilisation, the blastocyst stage of embryonic development is reached. At this stage, there are around 50–150 cells.
Since these cells are pluripotent, they can multiply and differentiate into a variety of cell types (about 250 kinds). However, unlike the placenta, they do not contribute to the extraembryonic cells.
The embryo contains embryonic stem cells, which divide and differentiate into germ layers as they specialise.
These cells have been culture increasingly as they can be artificially cultured to produce cells of different types.
Embryonic stem cell culture is important as they perform as a new source for regenerative medicine and genetic disease and toxicology test in vitro.
The embryonic germ cells in the gonadal region in animals also act like embryonic stem cells. These cells, also called primordial cells, later differentiate and divide to form male and female gametes.

2. Adult stem cells (Somatic or Tissue-specific stem cell)

Adult stem cells, also known as somatic stem cells, are cells that can only be found in certain tissues and have the ability to repair and create new cells in those tissues.
Due to their inability to develop into multiple cell types, these cells are thought to be less potent than embryonic stem cells.
Adult stem cells are found in niches or regions made by other cells, which exude nutrients and fluids to keep the stem cells alive.
These cells can be found in some tissues where there is constant cell turnover. However, only when the tissue is harmed can certain tissue, such as the liver tissue, go through modest division.
Both children and adults have adult stem cells, which are mostly located in tissues like the lining of the colon, bone marrow, and the epidermis.
As the keratinocytes fall off, the cells in the epidermal layer constantly divide to create new cells.
Hematopoietic cells, or adult stem cells, are found in bone marrow and may develop into three different types of blood cells and immune cells.
The brain contains stem cells as well, which after birth differentiate to produce very few nerve cells.

3. Induced pluripotent stem cells (iPSCs)

Due to the limits of adult stem cells, new pluripotent cells known as induced pluripotent cells were produced from adult cells through the process of gene reprogramming.
When adult cells and embryonic stem cells are cultivated together, new cells with characteristics of stem cells are created. These new cells are known as induced pluripotent stem cells.
Other somatic cells can occasionally also be reprogrammed to develop pluripotency.
Similar to embryonic stem cells, induced pluripotent stem cells have the ability to be encouraged to develop into several cell types.
They differ from embryonic stem cells, nevertheless, in terms of the degree of gene expression and the state of the cells' chromatin.
These cells are very important because they may be employed in therapeutic treatment, which will allow doctors to create cells for almost every organ in the body specifically for each patient.
Additionally, they stop the use of additional embryonic stem cells, which might raise ethical concerns.
By creating induced pluripotent stem cells from the disease's adult or somatic cells, it also aids in the investigation of novel genetic illnesses.
In order to transplant cells during severe heart and eye disorders, induced stem cells from the heart and eyes can be utilised.

4. Perinatal stem cells

Perinatal stem cells are an intermediate cell type that exhibit traits of both adult and embryonic stem cells. They come from foetal membrane, umbilical cord, and amniotic fluid extra-embryonic cells.
Prenatal stem cells are known to have extensive multipotent plasticity and immune-privileged features.
Additionally, these cells escape any participation with moral dilemmas by being just extracted from extraembryonic tissues that are normally eliminated after birth.
These cells may develop into endothelial, hepatic, adipose, and even brain tissues and are multipotent, active, and non-tumorigenic.
Even though they are not immortal, foetal membrane cells have a great capacity for division.
Additionally, perinatal stem cells have medicinal and research uses in the treatment of renal, cardiac, inflammatory, and bone diseases, as well as spinal cord injuries.
Because of these uses, perinatal stem cells have been artificially cultivated to produce a significant quantity of these cells.

5. Mesenchymal stem cells (MSCs)

Adult stem cells, also known as somatic stem cells, such as mesenchymal stem cells, are most frequently found in the tissues of the muscles, liver, and bone marrow.
Human MSCs (hMSCs) are multipotent stem cells that can develop into ectodermal (neurocytes) and endodermal cell lines as well as mesodermal (osteocytes, adipocytes, and chondrocytes) cell lines (hepatocytes).
The most prevalent kind of mesenchymal stem cells is found in the bone marrow, where they undergo differentiation to produce the bones and cartilages that make up the skeletal system.
Not only in foetal tissues but also in many adult tissues are mesenchymal stem cells present.
These are typically present in little amounts, but they are significant because they let blood stem cells survive in the bone marrow.
Mesenchymal stem cells are important in cell proliferation, cell differentiation, and tissue regeneration under challenging immunological settings because they are very simple to separate and yield more than other stem cells.
As they release cytokines and immune-receptors that control the milieu in the host tissue, MSCs also exhibit immunomodulatory properties.
This stem cell is a helpful tool in the treatment of chronic illnesses due to its capacity to create cells of various cell lines, immunomodulation, and release of anti-inflammatory chemicals.

Stem cell research with examples

The study of stem cells' characteristics and their potential for use in therapeutic and medical procedures is known as stem cell research.
In order to someday utilise these cells for medical applications, researchers have shown a significant deal of interest in this field of study.
Understanding the formation and equilibrium of the healthy and diseased body is also aided by research on these cells.
However, because of the ethical issues surrounding how stem cells are collected, stem cell research has generated considerable controversy.
Knowing that an embryo's stem cells would ultimately be removed from it and destroyed creates moral concerns.
The usage of embryonic stem cells has diminished, and with it the ethical concerns, as a result of the discovery and use of adult stem cells and induced pluripotent stem cells.

The following are a few typical and well-known applications of stem cell research:

1. The process of cell differentiation

The investigations made to understand how undifferentiated stem cells multiply and differentiate into specialised cells are among the most significant instances of stem cell research.
The process of managing stem cell differentiation involves a lot of research as well.
Many scientists and researchers have worked on strategies to control stem cell differentiation to create specialised cells over the years.

2. Stem cell-based therapies

Studies on controlling stem cell differentiation have also been conducted in an effort to employ them to treat various ailments.
One instance of this is the differentiation of stem cells into cells that produce insulin so that these cells may be transplanted into people with type 1 diabetes.
There are also several additional initiatives being carried out with a variety of illnesses and ailments in mind.

3. Stem cells to test new drugs

To test novel medications without testing them on human cells, stem cells are cultivated in labs.
This is one of the more recent stem cell research fields.

Application/ Uses of Stem cell Research

Because of their characteristics, stem cells have been exploited in several fields of study. The following are some typical uses for stem cell research:

Regenerative medicine, which deals with the regeneration of tissues or organs in patients suffering from serious injuries or certain chronic diseases, has made use of stem cell research.
The development of stem cell research has paved the way for alternative cell-based treatments for illnesses that are resistant to traditional medication.
Studies using human stem cells have a great deal of promise to further our knowledge of basic physiology.
Hematopoietic stem cells may now be transplanted into patients following their cancer therapies thanks to years of study on stem cells.
Prior to being tested on animals or people, novel medications have also been examined through stem cell research.
For cell transplants for a variety of disorders, such as bone marrow for leukaemia, nerve cells for Parkinson's and Alzheimer's disease, heart muscle for heart disease, and pancreatic islets for diabetes, cultured stem cells are employed.

Limitations/ Challenges of Stem cell Research

There are several restrictions or difficulties with stem cell research due to various ethical and other related considerations. Among them are:

The moral dilemma surrounding the use of embryonic stem cells is the most significant obstacle to stem cell research. These problems have led to political and religious barriers to stem cell research.
Some stem cell lines' origins may include mutations, which raises the possibility of transplant-related mutations.
The transplantation of stem cells made in labs into target cells is similarly challenging.
Additionally, embryonic stem cells quickly specialise into various lineage progenitor cells of the three embryonic germ layers rather than continuously renewing themselves in vivo.
These cells may be made to self-renew in vitro under artificial circumstances that prevent their differentiation.
A adequate supply of stem cells that can develop into the required cell type is likewise difficult to come by.
Even when directed by the addition of differentiation factors, the differentiation of embryonic and adult stem cells requires a certain degree of spontaneous differentiation into distinct cell types.
Furthermore, the differentiation has not yet been synchronised, resulting in a variety of cells that are at different stages of development.

Stem Cell lines

A stem cell line is a collection of certain stem cells that have been cultivated in vitro so they may be repeated endlessly for different uses.
These cell lines come from either humans or animals, and they can be either adult stem cells, induced stem cells, or embryonic stem cells.
For genetic research and regenerative medicine, stem cell lines are widely employed.
They can proliferate indefinitely thanks to their capacity for renewal, which makes them extremely important.
Even after acquiring the capacity to divide endlessly, the stem cell lines maintain their original genetic characteristics.
Depending on the origin of the stem cells, there are three different types of stem cell lines: induced stem cell lines, adult stem cell lines, and embryonic stem cell lines.
Compared to embryonic cell lines, adult stem cell lines are less efficient in proliferating and producing differentiated cells.
The induced stem cell lines, on the other hand, have the capacity to develop into derivatives of all three germ layers while being able to self-renew indefinitely in vitro.
These cell lines have been the subject of studies that are helpful for cellular transplantation treatments, drug screening, understanding the differentiation and function of human tissues, and toxicity testing.

Stem Cell Therapy

One use for stem cells that encourages the repair of damaged and dysfunctional tissues and their derivatives is stem cell therapy, sometimes referred to as regenerative medicine.
Because some of these cells may unintentionally lead to the production of uncommon solid tumours known as teratomas, pluripotent stem cells are not frequently employed therapeutically in people.
However, it has been applied to cure spinal wounds and blindness in animals.
On the other hand, multipotent stem cells taken from bone marrow have been employed to treat leukaemia, myeloma, and lymphoma since the 1960s.
The potential of mesenchymal stem cells to regenerate whole joints may also help treat other illnesses.
Pluripotent cells should not be used in place of multipotent stem cells as the latter would result in the immune system of the recipient's body rejecting the transplant.
Therefore, stem cell therapy is a great way to enhance the facilities and methods for treating a variety of chronic illnesses.
Before their full therapeutic promise can be realised, however, much more research on their biology, manipulation, and safety is still required.

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Stem Cells: Definition, Properties, Types, Applications, and Challenges

Table of Contents

Stem Cells Definition

Properties of Stem Cells

Stem Cell Culture