What are Stem Cells?

Stem cells are unique cells, which can be considered to be the ancestors of all human tissues and organs. The main characteristic of these cells is their ability of maintaining their number by dividing and differentiating into different cell types. It means that every human body has the ability of self-renewal. 
Over time, the number of stem cells in the human body inevitably decreases.  Stem cell reserves are diminished as the body ages, suffers from serious diseases and its owner’s bad habits (smoking and alcohol use), which, in turn, decreases the body's ability of self-renewal. Such changes in the body interfere with the normal functioning of different organs.

Human stem cell sources (after birth):

Human stem cells can be divided into hematopoietic and mesenchymal stem cells.

Hematopoietic (blood-forming) stem cells form a variety of blood cells, participate in the shaping process of the immune system, fight various infections, supply oxygen to organs and tissues, as well as facilitate blood clotting.  The history of hematopoietic stem cell clinical use dates back to more than 60 years ago, and now hematopoietic stem cell transplantation is the first choice in treatment of hematologic, several oncologic, immunologic and hereditary diseases.

Hematopoietic stem cells can be obtained from bone marrow, peripheral blood (after administering certain substances) and from umbilical cord blood. While in the early decades bone marrow was considered to be the only source of stem cells, since 1988, from the first (and immediately successful) umbilical cord blood transplantation, which was performed by prof. E. Gluckman on a boy with Fanconi anemia, umbilical cord blood has earned a notable place in modern transplantology.
 
Often, patients do not have the time to wait for a bone marrow donor, as the lengthy process requires repeated tests and preparation for the bone marrow harvest procedure. Additionally, given the strict requirements for HLA genotype compatibility between the patient and the donor, not everyone is able to find a suitable bone marrow sample. In these cases, umbilical cord blood transplant not only presents an alternative to a bone marrow transplant, but it is the patient's only option.

But even in less "extreme" situations, where there is a possibility of finding a bone marrow donor, doctors prefer umbilical cord blood transplantation, as the procedure presents a significantly lower risk of rejection and graft versus host disease. Therefore, umbilical cord blood is increasingly becoming a popular source of hematopoietic stem cells, and, according to World Marrow Donor Association (WMDA), there have been more than 30 000 umbilical cord blood transplants done around the world.

Mesenchymal (stromal) stem cells are capable of differentiating (transforming) into bone cells, cartilage cells, connective tissue cells, as well as form into elements of blood vessels.  
Due to these biological functions, mesenchymal stem cells have become a very popular source of regenerative therapy. By the end of 2017, more than 780 different studies using mesenchymal stem cells were registered in the international clinical trials database clinicaltrials.gov. The promising results of mesenchymal stem cell use for tissue regeneration were obtained from cases of musculoskeletal trauma, ulcers and burns, graft-versus-host reaction and/or treatments, oncological diseases, lower limb ischemia, vascular system pathologies, as well as degenerative cartilage cases and even restorative dentistry.  It is important to note, that according to clinical research data, the use of mesenchymal stem cells does not lead to serious side effects.

The main sources of mesenchymal stem cells are bone marrow, fatty tissue and umbilical cord tissue. Unlike bone marrow and fatty tissue stem cells, mesenchymal stem cells are new cells, which have not been exposed to negative external environment effects, therefore they possess a higher functional activity. A notable advantage of mesenchymal stem cells is the easy umbilical cord tissue collection process, which is completely harmless and safe. In case of umbilical cord tissue storage, stem cells can be thawed at any time and used faster than stem cells from other sources (bone marrow and fatty tissue).