The basis of the functioning of a multicellular organism is the specialization of cells aimed at performing a specific function. This cell differentiation begins early in the development of the embryo. But in our body there are cells that are capable of acquiring various specializations throughout a person’s life. And this fully applies to hematopoietic stem cells, which maintain a constant quantitative and qualitative composition of blood cells.
General information
Hematopoietic stem cells (Hematopoietic Stem Cell, from the Greek words Haima - blood, Poiesis - creation) are stem cells capable of unlimited division and differentiation into blood cells.
Theyare formed in the red bone marrow and differentiate in four directions:
- Erythroid (in red blood cells).
- Megakaryocytic (in platelets).
- Myeloid (multinuclear phagocytes, leukocytes).
- Lymphoid (in lymphocytes).
Hematopoietic stem cell transplantation (allogeneic - from a donor, autologous - transplantation of own cells) restores the hematopoietic system, which can be impaired in certain diseases, chemotherapy.
The first transplantation of autogenous stem cells was carried out back in 1969 by E. Thomas (Seattle, USA). Modern techniques in 80% of cases can defeat blood cancer. At this stage, medicine has at its disposal the methods of fetal medicine, when the donation of hematopoietic stem cells is provided by cord blood, embryonic tissues, bone marrow, adipose tissue.
Features of this cellular material
Hematopoietic stem cells (hemocytoblasts) have two main properties:
- The ability to asymmetric division, during which two daughter cells are formed, identical to the mother. However, the cells do not undergo differentiation. They remain multipotent hematopoietic stem cells. This means that they can choose any of the above specialization paths.
- The presence of differentiating potential in hematopoietic stem cells. This means that the stem cells are dividing and the daughter cells begin theirspecialization, turning into highly specialized erythrocytes, platelets, lymphocytes, leukocytes.
Hematopoietic stem cells in the bone marrow, like all cells in our body, have an age - a short “childhood”, a quickly flying “youth”, when cells choose “army” or “study”, and a long period “maturity.”
I will go to red blood cells - let them teach me
Most of the hematopoietic stem cells in the bone marrow are dormant - they don't divide. But when the hemocytoblast wakes up, it makes the most important choice - to give rise to a new multipotent stem cell or to start the process of specialization of daughter cells. In the first case, the cell can prolong its “childhood” indefinitely, in the second, the cells enter the next period of their life.
Mature hematopoietic cells begin to divide asymmetrically, which leads to their differentiation and specialization. Precursors of cells are formed that choose "study" - the myeloid path of development, or "army" - the lymphoid path of development.
Myeloid hemocytoblasts develop into platelets, erythrocytes, macrophage leukocytes, granulocytes (a type of leukocyte - eosinophils, neutrophils or basophils).
Lymphoid hemocytoblasts will give rise to cells of the body's immune defense - T-lymphocytes (recognize the antigens of strangers), B-lymphocytes (produce antibodies), T-helpers (attack foreign cells), NK-lymphocytes (provide phagocytosis of foreign agents).
Realizing Potential
Hematopoietic stem cells, entering the stage of differentiation, lose their multipotency and realize their potential. Several factors influence the choice of hemocytoblast development path:
- Environment - different areas of the bone marrow differentiate in different ways.
- Factors acting at a distance. For example, the hormone erythropoietin, which stimulates the formation of red blood cells, is synthesized in the kidneys. All these biologically active substances are called cytokines and growth factors (parathyroid hormone, interleukin).
- Signals of the sympathetic nervous system that transmit information about the state of the body and the composition of the blood.
Today, the mechanisms of hematopoiesis have not been fully unraveled and are still waiting for their Nobel laureates who will learn to control the fate of hemocytoblast.
Bone marrow transplant
This is the term used most often to refer to transplantation of hematopoietic stem cells. This is a widely used method in the treatment of blood diseases, oncological and genetic pathologies. Modern methods of therapy allow using not only donor bone marrow. Today, the donor of hematopoietic stem cells is peripheral blood, umbilical cord blood, and products of fetal (embryonic) medicine.
The essence of hemocytoblast transplantation is as follows. At the initial stage, the patient undergoes a conditioning stage (irradiation or chemotherapy), in which the functioning of his own bone marrow is suppressed. The patient is then givena suspension of hematopoietic cells that populate his hematopoietic organs and restore hematopoietic functions.
Own or others
Depending on the source of stem cells for transplantation, allocate:
- Autotransplantation. With this therapy, the patient is given a suspension of his own hemocytoblasts, which are taken in advance and stored frozen. This type of transplant is used in the treatment of lymphomas, neuroblastoma, brain tumors and other solid malignancies.
- Allotransplantation. In this case, donor hematopoietic cells are used, which can be either close relatives of the patient or those selected from bone marrow donor registries.
With autotransplantation, there is no cell rejection and immune complications, but this method is not always effective. Allotransplantation is effective for many congenital (Fanconi anemia, severe combined immunodeficiencies) and acquired (leukemia, aplastic anemia, myelodysplastic syndrome) pathologies of the blood and hematopoietic system, but requires careful selection of a donor for histocompatibility.
Summing up
But in any case, bone marrow transplantation is associated with a significant risk to the he alth of the patient. That is why it is carried out only in case of vital necessity.
Modern methods of bone marrow transplantation have already saved the lives of thousands of patients with blood pathologies.
StemCord blood cells were first used in 1987, and today these techniques have already saved more than 10,000 patients. At the same time, banks of umbilical cord blood stem cells develop, because it can be taken no more than 100 ml and only once. When frozen, the cells remain viable for 20 years, and it is possible to pick up donor blood in such banks.
Another direction in the development of stem cell transplantation is fetal therapy, which uses cells from embryos. Their source is abortive material. But this is a topic for a completely different article.
