Stem cells, with their ability to transform, seem to be a wonderful remedy for many diseases. Find out what stem cells are, what diseases are stem cells currently used to treat and what are the prospects for the development of stem cell therapy? Where does the skepticism of specialists come from?

Stem cellshave the ability to transform into other types of cells. Stem cell therapy is certainly one of the catchiest and most promising concepts in modern medicine. It would seem that the list of their medical applications should be endless - repairing damaged tissues, growing replacement organs …

The facts are different, however. Although the beginnings of research on stem cells took place in the 1960s, their use has so far been limited to a few well-defined indications.

Ideas for the use of stem cells are abundant, however, introducing them to clinical use is limited by a number of factors, among which the question about the safety of this type of therapy comes to the fore.

What are stem cells?

Stem cells are essential for the formation of the human body. In the earliest stages of development, the human embryo is made up entirely of stem cells. Over time, they undergo changes, giving rise to all cell lines that make up the human body.

The second important role of stem cells is to colonize some tissues of a mature organism and act as a "storehouse". If necessary, they are able to transform into cells of a given tissue that die or are damaged. However, this is only possible for certain tissues.

Stem cells are therefore those cells that have the ability to transform into other, more specialized types of cells.

The most important feature of stem cells, which distinguishes them from other cells, is how they divide.

During division, a stem cell can differentiate itself, i.e. it creates a daughter cell of a specific type (e.g. a muscle, nerve or epithelial cell).

There are different types of stem cells, depending on their nature: some of themthey can transform into any kind of daughter cell, while others can only make cells that make up a certain type of tissue (more on that below).

The second important feature of stem cells is also related to their division. During the formation of a daughter cell, the parent cell does not disappear without a trace. In the process of division, one more stem cell is created, identical to the "mother-cell".

The result of a mother cell division is one mother cell and one specialized daughter cell.

This mechanism is called self-renewal. Thanks to it, stem cells do not "wear out" and do not allow the size of their pool to decrease.

Types of stem cells

As already mentioned, stem cells can transform into other types of cells when they divide. Can any stem cell then become any daughter cell? Well, no.

Stem cells are divided into four subgroups, depending on how wide the spectrum of cells can arise from their division.

The stem cells that build the human embryo are able to give rise to all kinds of cell lines. In turn, some stem cells that inhabit the tissues of an adult human being can transform only into a strictly defined type of cells that build a given tissue.

The division of stem cells due to the possibility of creating various daughter cells is as follows:

  • totipotent stem cells

These are cells with the widest differentiation potential that can evolve into any kind of daughter cell. Totipotent cells form a zygote (a cell resulting from the fertilization of an egg by a sperm), as well as an embryo at the earliest stages of its development. All types of cells that make up the human body can be created from totipotent cells.

  • pluripotent stem cells

Pluripotent cells can also transform into many types of cells. Placental cells are an exception, however. Pluripotent cells form the so-called embryo node, which is one of the structures formed in the first week of embryo development.

Pluripotent cells of the embryonic node give rise to three so-called the germ layers, from which all the tissues of our organism later develop. Although the names of the germ layers sound a bit complicated (ectoderm, mesoderm and endoderm), the tissues formed from them are known to everyone.

The ectoderm produces skin and structurenervous, from the mesoderm - the circulatory and musculoskeletal systems, and from the endoderm - the respiratory system and most of the digestive system.

  • multipotent stem cells

Multipotent cells are a group of stem cells with a slightly narrower differentiation potential. While they can still make several types of cells, they are usually cells of a similar type. The flagship example of cells in this subgroup are bone marrow multipotent cells, also known as hematopoietic stem cells. They can transform into any blood cell, such as red blood cells or different types of leukocytes. However, they are unable to produce the cells that build other tissues.

  • unipotent stem cells

This type of cell can only become one kind of daughter. Usually unipotent cells are a reservoir for the renewal and repair of adult tissues. An example of unipotent cells are epidermal stem cells, found in human skin.

Where to get stem cells

Obtaining stem cells is basically possible in two ways.

Their first source is a human embryo, from which the so-calledembryonic stem cellsare isolated. These are cells of the charactertotipotentorpluripotent , and therefore able to differentiate into all types of tissues.

The second type of stem cells is calledsomatic stem cells(or "adult" stem cells). This type of cell comes - as the name suggests - from the adult human body.

Normally these are cells that inhabit various organs

  • bone marrow
  • muscles
  • liver
  • skin
  • blood vessels

In these organs, stem cells act as a reservoir, enabling the regeneration of damaged tissues.

It is not hard to guess that somatic stem cells have a more limited differentiation potential than those of embryonic origin. Adult cells aremultipotentorunipotent , i.e. they can transform into cells of a similar type or even into only one type of daughter cell.

Finding and obtaining somatic stem cells in an adult body is quite a challenge. The number of these types of cells in tissues is very small.

Once collected, they are very difficult to cultivate in a laboratory setting, so it is difficult to obtain themlarger quantities.

For now, adult stem cells are only obtained from a few sources. For hematopoietic stem cells, these are:

  • bone marrow
  • peripheral blood
  • cord blood

In turn, from adipose tissue and bone marrow you can obtain the so-calledmesenchymal stem cells . They can transform into different types of tissues:

  • bone
  • chondral
  • muscle
  • fatty

Therapies with the use of mesenchymal stem cells are still in the research phase - so far their safety and effectiveness have not been confirmed.

It is worth mentioning one more type of stem cells, which is, in a way, a hybrid of the above two. This is calledinduced pluripotent stem cells .

These are stem cells obtained from an adult organism that have been reprogrammed in a laboratory to give them the characteristics of germ cells.

Current uses of stem cells

Since we already know the types and differentiation possibilities of stem cells, the question remains - which of them and how are they used in medicine?

  • embryonic stem cells

Embryonic stem cells are not approved for any type of therapy. Why? Here are some reasons.

First of all, their use involves ethical dilemmas. Embryonic stem cells are obtained from embryos intended for research purposes, most often created during in vitro fertilization procedures. Ethical issues are one of the factors limiting the progress of research into stem cells obtained in this way.

The second obstacle to the use of germ cells is purely scientific. They are cells with great differentiation potential and can transform into any kind of daughter cells. So far, no method has been found to control their behavior.

Embryonic stem cells, after implanting into the human body, create tumors composed of various, chaotically arranged cells. These types of tumors are called teratomas (Latin teratoma). We are constantly looking for ways to direct germ cells in such a way that they transform into the desired tissue.

The use of embryonic stem cells also carries the risk of rejection - they are foreign material (similar to an organ transplant from an unrelated donor).

The risk is theremuch less when using adult stem cells donated and received by the same patient. We call this procedure an autologous transplant.

  • adult stem cells

Although the use of adult stem cells is also associated with many limitations, only this type of stem cells is currently used in medicine. Obtaining adult stem cells does not require embryo culture, so it raises far fewer moral dilemmas. Adult stem cells are used in the following types of therapy:

  • Hematopoietic stem cell transplantation

Hematopoietic stem cell transplantation is currently the only routine stem cell therapy that is successfully used all over the world. The so-called bone marrow transplants are a method of treating many hematological diseases.

First, they are used in patients with primary immunodeficiencies, that is, inherited abnormalities in the immune system. Bone marrow transplantation is often the only way for them to obtain properly functioning immune cells.

The second group of patients who may require a haematopoietic stem cell transplant are those whose bone marrow has been damaged, for example as a result of aggressive anti-cancer treatment.

Such a situation may be desirable in the case of blood cancers (e.g. leukemias), when the goal of the therapy is to destroy the hematopoietic system covered by the neoplastic process, and then its reconstruction with the help of implanted stem cells.

  • treatment of extensive wounds with epidermal stem cells

Epidermal stem cells are one way to heal extensive wounds, such as burns.

The entire procedure is as follows: first, epidermal stem cells are collected from a fragment of the patient's he althy skin.

Then these cells are subjected to laboratory culture in conditions enabling their intensive multiplication.

Once the correct number of cells has been obtained, they are placed on the wound surface.

An additional advantage of the therapy is that the patient's body cannot reject such a "dressing" - it was made of his own cells.

  • ophthalmic treatment with the use of corneal limbal stem cells

Another therapy with the use of stem cells has been approved relatively recently. It is about a drug containingcorneal limbal stem cells, allowing the reconstruction of the corneal epithelium (the front, outer layer of the eyeball).

As in the previous case, the "source" of cells is the patient himself, and more specifically his he althy eye.

After the stem cells are collected, they are multiplied in the laboratory and then administered to the affected eye. An indication for the use of the therapy is a deficiency of corneal limbal stem cells, for example due to damage by a chemical substance.

The future of stem cells

The above text briefly presents the current and - as you can see - very limited uses of stem cells in medicine.

Research in this area is very complex, and stem cells still pose more questions than answers.

From time to time in the scientific world there is information about the breakthrough discoveries related to them, but unfortunately in many cases it turns out that the published research results are not true.

This was the case, for example, in the case of the loud attempt to implant bone marrow stem cells into the post-infarction scar in the heart muscle. The allegedly positive results of such therapy triggered an avalanche of further trials in other clinical centers, but all experiments ultimately ended in failure.

Many more years of research are needed to be able to use stem cells effectively and safely in medicine.

Scientists are constantly trying to learn more about the unusual mechanisms of their functioning.

What factors influence the process of stem cell differentiation?

Is this process controllable?

What to do to be able to effectively multiply them?

Which of the so far incurable diseases really have a chance to be cured with such therapy?

These and many other questions are constantly the subject of ongoing scientific research.

At this point, it is worth mentioning that while the therapeutic uses of stem cells are limited, they are useful in other areas of medicine.

One example is research into cancer processes. Stem cells make it possible to simulate such a process in laboratory conditions, and then test potential therapies on them (e.g. new anti-cancer drugs).

The directions of the ongoing research on stem cells are, for example, applications in:

  • neurodegenerative diseases (e.g. Alzheimer's disease)
  • spinal cord injuries
  • injuries of the musculoskeletal system

orfinally, attempts to reconstruct entire organs (e.g. pancreas in type I diabetes).

We must be aware that stem cells are not a cure-all, and that each potential application is independently researched and must undergo a series of clinical trials prior to approval.

Finally, it is also worth warning against "clinics" offering stem cell therapy without any authorization.

These types of experiments end up losing money at best, and at worst - your he alth and even your life.

About the authorKrzysztof BialaziteA medical student at Collegium Medicum in Krakow, slowly entering the world of constant challenges of the doctor's work. She is particularly interested in gynecology and obstetrics, paediatrics and lifestyle medicine. A lover of foreign languages, travel and mountain hiking.

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