The concept of "regenerative medicine" is now on everyone's lips, and the use of stem cells to treat the most complex diseases is the subject of frequent discussion in medical circles. Some claim that the use of stem cells has literally miraculous effects on the human body. Others argue that these cells can cause irreparable harm to the patient.
How safe is stem cell therapy and, in general, is regenerative medicine a "magic pill" for all diseases? Read about all this in our article.
What is regeneration
Regeneration is the ability of a living organism to regenerate damaged tissues and organs.
Why does tissue regeneration occur?
In all tissues, there is a constant renewal of cells during life. This is because the life span of a cell is limited. On average, 99% of cells live about 30 days. An epidermal skin cell lives 10 days and a red blood cell lives 4 months. This is how the living organism is programmed: to kill cells after a certain lifetime. This gets rid of aged and malfunctioning cells. The dead cells must be replaced. It turns out that there is constant cellular renewal in the body. In 70 years, about 10 tons of cells die off and are produced in the body of an average person.
How does the mechanism of creating new cells to replace the lost cells work?
1. Proliferation of terminal differentiated cells. This is the process of dividing specialized (somatic) cells that already exist.
2. Self-renewal and differentiation of stem cells, i.e. obtaining new specialized cells from stem cells.
3. The reprogramming of differentiated cells.
Now let's talk about stem cells.
Stem cells: types and properties
The efficiency of regeneration depends on the proportion of stem cells in the body. What are stem cells? They are the main participants in the process of tissue renewal and repair after damage. The main properties of stem cells:
- The ability to unlimited division. Note that normal cells have a certain limit of division (Hayflick limit), this is 52 divisions under favorable conditions. After this, division stops. At the same time the stem cell division never stops.
- The ability to divide asymmetrically, that is, part of the progeny of the stem cell will be stem cells and another part will be specialized differentiated cells. This process is called differentiation and characterizes the potency of the stem cell, that is, its ability to differentiate into other cell types. An undifferentiated stem cell can produce different types of specialized differentiated muscle, skin, fat, and cartilage cells.
There are many types of stem cells that are differentiated by potency.
- Totipotent cells (zygote) - These cells can produce any cells of the body and extra germinal tissues. The development period of these cells is very short.
- Pluripotent cells (embryonic stem cells, ESCs). One pluripotent cell can create an entire organism.
- Multipotent cells are cells which are present in a living organism after its birth (postnatal period). They have limited potency: they can differentiate only within the germ sheets: ectoderm (skin, nervous system), mesoderm (muscles, skeleton, heart and kidneys) or endoderm (gastrointestinal tract, lungs, liver).
- Progenitor cells. These are cells that can become a specialized type only within a particular tissue. In the process of specialization, multipotent cells reach the state of precursor cells. In an adult, it is precisely the progenitor cells that are present in the body.
Stem cells are present in many tissues and organs throughout human life. Usually these endogenous stem cells are responsible for the maintenance and repair of our organs and tissues.
It is important to understand that the proportion of stem cells in living organisms varies. For example, 90% of the cells in flatworm planarians are stem cells. These worms have a high capacity for regeneration. Lizards have 30% of such cells. Humans have only 1% of stem cells in their bodies. For this reason, most human diseases are associated with tissue damage and loss of tissue and organ repair ability. The vast majority of tissues cannot regenerate on their own after severe damage. This leads to internal organ dysfunction, serious illness and death.
What is regenerative medicine
In the last 3 decades, a new field of medicine - regenerative medicine - has been actively developing. It is aimed at finding approaches to restore structures and functions of damaged tissues and organs.
Cell renewal in different tissues and organs occurs at different rates and by different mechanisms, but renewal occurs in all tissues during life. Regenerative medicine is based on the ability of the living organism to renew itself. It is based on the fact that it is inherent in the organism in principle. The goal of regenerative medicine is to use the human body's ability to renew itself to treat various diseases.
What distinguishes regenerative medicine from conventional medicine? First of all, traditional methods mainly treat the symptoms, while regenerative medicine techniques are aimed at treating the cause of the patient's condition by replacing defective cells (organs) or correcting a defective gene.
Regenerative medicine is a very serious intervention on the body. Its use must be justified. For this reason, regenerative medicine methods are used to treat diseases whose treatment with classical methods has a low chance of success. In other words, regenerative medicine methods are now applied to patients who have a small chance of survival with other treatment methods. First of all, these are oncology, serious hereditary diseases, orphan diseases that can lead to a fatal outcome.
The main task of regenerative medicine is to fight such diseases:
- Autoimmune diseases
- Oncological diseases
- Type I Diabetes
- Heart failure
- Postinfarction myocardial fibrosis
- Massive burns and soft tissue trauma
- Liver cirrhosis
- Alzheimer's disease
- Orphan and hereditary diseases, malformations
- Cartilage, joint, and bone injuries
- Spinal trauma and peripheral nerve injuries
Today there are four interrelated areas of regenerative medicine:
1. Cell therapy - live cells are used as medicines. This is the most popular direction.
2. Gene therapy - control of genes in cells or use of genes as a healing agent. Involves introducing genetic constructs into living tissue cells or modeling the genome.
3. Regenerative pharmacology - regenerative medicine without cell culture. A new, promising field that will help create new tissue to replace dead tissue.
4. tissue engineering - creation of artificial organs or tissues from cells. Involves the use of a framework on which living cells are planted to mimic the creation of organs.
Regenerative medicine is a revolutionary field of medicine that can completely heal damaged tissues and organs. It offers solutions and gives hope to people suffering from serious life-threatening diseases.
Now a few words about the history of stem cell discovery and the development of regenerative medicine.
Brief history of research
The term "stem cell" was first used in his works by the German scientist Valentin Haacker at the end of the XIX century. At that time, this concept was not further developed. Then the term was used by the Russian scientist, professor of the Imperial Military Medical Academy Alexander Alexandrovich Maksimov. In a study published in 1909, he put forward the theoretical rationale that all blood cells develop from one progenitor. Today it is known that all blood cells originate from hematopoietic cells (hemocytoblasts) - stem cells of the bone marrow, which create blood cells in the process of differentiation.
In the 1960s the results of A. Maksimov's theoretical research were confirmed experimentally by the American scientists James Till and Ernest McCulloch. They proved the ability of bone marrow stem cells to create all types of blood cells. Based on the research, the first technology of regenerative medicine - bone marrow transplantation - was created.
The first bone marrow transplantation surgery was performed in 1968. It was performed by the American transplantologist Edward Donald Thomas, who was awarded the Nobel Prize for his work. Since the first bone marrow transplantation stem cells have been actively used to treat oncohematological diseases.
In the 1970s Russian scientists Alexander Yakovlevich Friedenshtein and Josef Lvovich Chertkov proved that besides hematopoietic cells the bone marrow contains bone marrow stromal cells - cells with mutipotent differentiation properties. Today these cells are known as mesenchymal stromal cells yielding differentiated connective tissue cells. We will describe them in detail later.
In 1981, scientists Martin Evans and Matthew Kaufman, and parallel to them Gail Martin, isolated embryonic stem cells from a mouse blastocyst that were pluripotent. Their characteristics were amazing: they could retain their properties outside the body for a long time, and when they entered the body they gave birth to new tissues.
In 1988 Eliane Gluckman isolated stem cells from umbilical cord blood. In 1998, human embryonic stem cells were isolated.
These studies have been associated with attempts to use stem cells for regeneration of human tissues.
Cell Therapy: Features and Sources
Cell therapy is the most actively developing area of regenerative medicine, which originated in the 1960s of the twentieth century. But the active development of the direction has received only after the development of methodological and methodical approaches to work with living cells outside the body, in the laboratory.
Cell therapy is used for the replacement of damaged cells and tissues; stimulation of the body's own progenitor cells and enhancement of reparative regeneration, increase of the natural ability of the body to self-regenerate; for targeted delivery of drugs, genetic constructions and biomolecules to diseased tissues or organs to restore their functions.
There are 3 sources of cell therapy:
- Autologous cells - the patient's own cells. They are isolated from the patient, grown or modified, and then injected into the same patient's body.
- Allogeneic cells are donor cells. A popular example of using such a source is bone marrow transplantation.
- Xenogenic cells are animal cells. One of the actively developing areas is the creation of chimeric animals with genetically altered cell structure in certain organs so that they are as close as possible to human cells.
In the future, xenogenic cells could be very much in demand, but now cell therapy operates in practice with human cells - autologous and allogeneic cells.
How cells are grown in the laboratory
Skin cells are extracted in small quantities from a living organism and grown in a specialized laboratory. Millions of cells can be grown in a relatively short time.
Growing cells is a labor-intensive task. This is due to the fact that in order to grow cells in special nutrient media (the composition of the media can simulate future cell functions) it is necessary to create sterile aseptic conditions in the laboratory, excluding the contamination by microorganisms.
Automated stations are used to grow a large number of cells.
Examples of cell preparations developed using stem cells
One of the most important developments in recent years is cell therapy for diabetes. Scientists have developed a capsule for subcutaneous administration. Inside the capsule: human embryonic stem cells. The capsule is designed in such a way that it receives nutrients and secreted substances come out of it. The embryonic stem cells inside the capsule are protected from the cells of the human immune system.
A certain amount of time after the capsule is placed under the skin of a diabetic patient, the embryonic stem cells differentiate into pancreatic progenitor cells that produce insulin, glucagon, and somatostatin, hormones produced by the pancreas. As a consequence, the patient's glucose levels are maintained at normal levels.
The drug is now in clinical trials. What does the successful testing and registration of the drug mean for millions of diabetics? A return to normal sugar metabolism and the elimination of insulin injections. Consequently, an improvement in the quality of human life.
Mesenchymal stromal cells: characteristics, features, applications
Stem cells are present in all adult organs, but the largest source of stem cells is the bone marrow, which contains 2 types of stem cells. We have already mentioned hematopoietic stem cells, which are used in oncoimmunology, transplantology and other fields. Bone marrow also contains mesenchymal stem cells (mesenchymal stromal cells, MSCs) - the most sought-after type of stem cells in cell therapy.
What is the peculiarity of MSCs?
MSCs have an important feature: they work very closely with the resident tissue-specific stem cells, regulating their bioenvironmental function through the secretion of bioactive (paracrine) factors. Today scientists consider MSCs as key regulators of tissue renewal and repair after damage.
The secretion products of these cells can stimulate angiogenesis and neurogenesis (growth of blood vessels and nerve endings), two necessary conditions for full tissue repair.
MSCs are easy to isolate and multiply, so they are the most commonly used cells in regenerative medicine. Due to their immunomodulatory properties, these cells offer promising treatment options for autoimmune, inflammatory and hematological diseases, as well as for use in transplantology.
Applications of cell preparations based on MSCs
- - Bone regeneration in case of injuries, after surgical operations. In this situation, the multipotency of MSCs, their ability to turn into bone cells, is used.
- - Cartilage regeneration of joints, including osteoarthritis.
- - Restoration of soft tissues lost as a result of trauma, surgery or disease development.
- - Healing of skin wounds of different genesis.
- - Plastic surgery.
Regenerative medicine continues to evolve, and now there are many studies related to the properties of MSCs. There are a lot of such properties: differentiation, vascular growth and stabilization, nerve growth, activation of stem cells in tissues, stroma remodeling, immunity regulation. They have unique self-renewal abilities and are able to differentiate.
MSCs are able to secrete extracellular vesicles, controlling the damaged cellular environment, activating the regenerative program, possible processes of cell dedifferentiation (transformation into less specialized cells) with subsequent redifferentiation into the desired type. Given that extracellular vesicles can mimic the functions of stem cells, today, in addition to classical cell-based cell therapy, cell therapy without cells is also distinguished, which uses various products secreted by cells for disease therapy. The principle of production of these products is very similar to that of cell therapy products. It involves isolating material from a donor, culturing it and obtaining the product.
Where can MSCs be isolated from? They can be isolated from bone marrow, adipose tissue, umbilical cord matrix, tendons, lungs and periosteum.
To obtain a sufficient number of cells for therapeutic purposes, MSCs are multiplied in a laboratory setting. Multilayer cell factories, bioreactors can be used to increase the scale of cell cultivation. It is known that 2D systems can limit the quality of MSCs, while the use of 3D systems to grow cells can improve their survival as well as their stem, anti-inflammatory and angiogenic properties. Culturing in bioreactors yields large volumes of MSCs, ensures compliance with good manufacturing practices, and guarantees high quality standards.
Now let's talk about preparations based on mesenchymal stromal cells.
Drugs based on MSCs
Today in the U.S. there are about 20 registered cell-based drugs for the treatment of various diseases. In 2018, Alofisel was registered in Europe for the treatment of perianal fistulas in Crohn's disease.
The fact that these drugs were registered proves their effectiveness and safety for patients.
With cell preparations, some modifications can be made in the laboratory to give them new properties. This is how gene-cell therapy drugs are developed. They are based on the genetic modification of cells in order to fight malignant diseases. The cells in such preparations are capable of recognizing malignant cells and triggering their death processes. Such drugs have found wide application in the treatment of leukemia (blood cancer).
Examples of gene-cell therapy drugs: KYMRIAH (Tisagenlecleucel) for the treatment of leukemia, and Zynteglo (Betibeglogene autotemcel) for the treatment of beta-thalassemia.
Scientist Shinya Yamanaka's revolutionary discovery
As we said before, cellular potency decreases as the body gradually matures. Is it possible to get the level of potency back? Is it possible to return cells to a pluripotent state? Yes, it is possible. In 2006 the Japanese scientist Shinya Yamanaka proved that by introducing several transcription factors it is possible to turn a mature cell into an induced pluripotent cell, from which any cells of the body can be obtained.
How does it work? A number of transcription factors are used to transdifferentiate cells. Mature cells of the body become induced pluripotent cells, which after differentiation become blood cells, heart and vascular cells, cells of the nervous system and all other organs.
Today there are already several protocols for the clinical use of cell therapy drugs for the treatment of severe diseases such as Parkinson's disease and diabetes based on induced pluripotent cells.
In addition to creating drugs, reprogramming, that is, the process of returning mature specialized cells to the state of induced pluripotent stem cells, allows the creation of individual cellular models of disease. This makes it possible to study the peculiarities of disease development and select an effective treatment.
Regenerative Medicine and Cell Therapy: Development Prospects
There are big and small players on the market of regenerative medicine products creation - representatives of pharmaceutical and medical industry who are constantly working on the search and implementation of new methods of treatment.
Cell therapy is one of the most promising areas of modern science. The market for cellular products is constantly growing.
Obviously, both patients and product manufacturers can benefit greatly from regenerative medicine. But first we need to solve the problem of the huge costs of producing such products. Now the manufacturers of cell therapy drugs face an important task: to increase the affordability of products by reducing the costs of their production. It is important to understand that lowering the price should not reduce the effectiveness of the drug products offered.
Pitfalls of regenerative medicine
Without a doubt, regenerative medicine and, in particular, cell therapy using MSCs is a real breakthrough in health care. It is an opportunity to deal with the cause of disease by repairing, replacing or regenerating damaged cells in the body.
Scientists agree that this field of medicine has great potential.
The methods of regenerative medicine can, firstly, increase the life expectancy of patients and, secondly, improve the quality of life of people suffering from chronic diseases. However, to date, regenerative medicine techniques have not been incorporated into mainstream medical practice in most fields of medicine.
Why is this the case? Because in many experimental studies regenerative medicine and cell therapy have had temporary or limited effects.
Despite the arguments in favor of introducing MSCs for cell therapy, there is still a risk that these cells could cause irreparable harm to the patient. In particular, they can cause tumors, inflammatory reactions and fibrosis. In some cases, MSCs can transform into malignant cells or contribute to tumor formation. Because MSCs suppress the immune system and promote the formation of new blood vessels, these properties can also support tumor growth and metastasis. During the repair processes, there is a possibility of fibrotic reactions because MSCs can differentiate into fibroblasts.
But this is not about rejecting regenerative medicine techniques as potentially dangerous. It's about the fact that stem cells need further study.
That's not the only problem scientists have to solve. Growing MSCs in a laboratory setting is extremely expensive. This is because there are different culturing processes for different diseases. Each procedure requires a specific protocol, which makes production much more expensive.
And another obstacle to large-scale production of stem cells is the lack of uniform quality control standards. This makes it impossible to standardize the bioprocesses of cell production.
Now it is impossible to say when cell therapy will enter general medical practice and whether it will happen in the coming decades. One thing is clear: regenerative medicine requires the close attention of scientists and further research. Will it become a magic cure for all diseases? There is no unequivocal answer yet.