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Hematopoietic stem cells -CSH- cells of all hopes ! (EN)

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      Since their discovery in the early twentieth century, hematopoietic stem cells have aroused great interest from the scientific community. Their ability to differentiate and self-renew, totally new, quickly made them the cells of all hopes.



What is a stem cell ? A stem cell is an undifferentiator capable of self-renewing or differentiating into any cells of the human body and is derived from either the embryo, fetus or adult tissue.

                                  

There are 4 types of stem cells according to their ability to differentiate into specialized cells:



Totipotent Stem Cells: Cells that give a whole individual (all tissues).

Pluripotent Stem Cells (Embryonic): Embryonic cells derived from divisions of a totipotent cell (blastula) they have the ability to differentiate into all tissues of the body (from the 3 embryonic leaves) except the placenta.
Unipotent stem cells: Cells that give a single cell type such as hepatocytes.
Multipotent stem cells: Stem cells of a tissue capable of differentiating into several cells such as hematopoietic stem cells.
                             


What is a hematopoietic stem cell ? A CSH is a cell that produces all the cells of the blood (red blood cells, white blood cells, platelets), it is at the origin of the hematopoiesis (it describes the successive stages of the proliferation and the differentiation of the stem cells multipotent, generating several generations of progenitors and precursors (intermediate cells between HSCs and differentiated and specialized cells) whose terminal differentiation provides the three mature blood cell lines).




HSCs are differentiated into two types of progenitors:




• Myeloid progenitor that gives erythrocytes (red blood cells), platelets and leucocytes.

• Lymphoid progenitor that gives lymphocytes and NK cells "Natural killer" (which are leukocytes too).



They can be obtained from umbilical cord blood, circulating blood, or bone marrow.

These HSCs are used extensively in cell therapy, which consists in sustainably treating the patient through a single injection of HSCs from the patient himself (autograft) or from a donor (Allograft) in order to restore the function of the bone marrow.
                                    


As HCC-related diseases, acute leukemia is a form of cancer that affects bone marrow cells, where red blood cells, platelets and white blood cells are produced, this disease does not prevent HSCs to differentiate themselves in progenitors or precursors but it prevents the obtaining of some mature cells from the precursors and progenitor so we will have an accumulation of these thanks to their great ability to multiply, but we will also have a deficiency in mature blood cells and functional. There are two types of acute leukemia: acute lymphoblastic leukemia and myeloid.


                                 
How can we diagnose this disease ? There are several diagnostic techniques including flow cryometry (This method is used to measure and identify lymphoblasts (immature cells) involved in acute lymphoblastic leukemia according to their specific marker present on the plasma membrane or nucleus or cytoplasm using monoclonal antibodies. fluorescents directed against these markers) and counting peripheral blood cells (The diagnosis of acute leukemia depends on the number of white blood cells from 25,000 to 35,000 / microliter, of which more than 30% are immature lymphoblasts).



The treatment of this disease is done by hematopoietic stem cell transplants, either by autograft (or autologous transplant is a transplant where the patient receives his own CSH, at present, CSH used for autologous grafts come from the peripheral blood ) or by allograft (the most common grafts, in cases where the donor and the recipient belong to the same biological species but are two distinct individuals).


For the autograft we use what is called cytapheresis which is an apparatus where we separate the stem cells from the other components of the blood and this is done first by the injection of growth factors either alone or linked to a drug to increase the number of stem cells and to free them from the bone marrow to the peripheral blood, this is called "Mobilization", 
                                  

Second, the blood will be circulated in a machine that will allow separate the SCs from the other blood elements (the machine sorts the necessary stem cells and reinjects the unused blood components) and then chemotherapy to treat  this disease, this treatment will destroy cancer cells but will also disrupt the immune system and in the mean time SC are stored in pockets until the treatment is completed, after finishing with chemotherapy is reinjected stem cells that will regain the spinal cord Bone, this is called "Homing" and after 10 to 30 days they will be able to make all the blood cells and restore our immune system.
                                    


And for the allograft that is more complex autograft because of the difference in gene pool between the donor and the recipient there must be compatibility from the point of view of the HLA system for the transplant can be considered it is in the immediate family of the recipient that one is most likely to find a compatible HLA donor. If there is insufficient family compatibility, physicians will use unrelated donor banks.




                                                                         Zahra .G Dean and Aspirant of the LRS project


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