Hematopoietic stem cells
Hematopoietic stem cells (HSCs) are adult stem cells; in other words, they are immature cells with the ability to self-renew combined with the potential to produce highly specialized (differentiated) cells.
Adult stem cells are capable of giving rise to all cell types of the tissue to which they belong, thus contributing to the maintenance of its structure and function, by replacing damaged or dead mature cells.
In the adult, HSCs are found in the bone marrow, in specific regions called niches, where they are in close contact with other types of cells (mesenchymal, bone, blood vessels) which, together with the factors they produce, are responsible for maintaining of the balance between self-renewal and differentiation.
HSCs are able to give rise to all types of blood cells through the gradual passage from the undifferentiated stem cell to the mature cell (hematopoiesis) belonging to one of the following types:
- Red blood cells, which carry oxygen to all organs and tissues of the body
- White blood cells, which help fight infections
- platelets, which help stop bleeding
Mature blood cells migrate from the bone marrow to the peripheral blood.
The HSCs on their surface have a molecule, the CD34 antigen, which characterizes them and allows their identification and quantification using flow cytometry techniques.
To date, three main sources of hematopoietic stem cells have been identified:
- bone marrow, spongy tissue found inside long bones and in the central part of flat bones (pelvis, sternum, skull, vertebrae, ribs). It produces blood cells (red blood cells, white blood cells and platelets), which are then released in peripheral blood
- peripheral blood, the number of HSCs is generally very low, but it is possible to increase their number by stimulating the marrow to produce them and release them into the circulation with particular drugs, called growth factors
- umbilical cord blood, present in the umbilical vein of the cord, is rich in ESCs with characteristics similar to those of the bone marrow and peripheral blood
Hematopoietic stem cell (HSC) transplantation
HSC transplantation currently represents the main cure for numerous blood diseases such as, for example, leukemia and lymphomas. The good results obtained in the last decades have pushed to refine more and more the transplant techniques, continuously improving the survival of the sick.
There are three main types of HSC transplant: autologous, allogeneic and syngenic. We talk about transplantation autologous when the cells are taken from the person who receives it (donor and recipient in this case coincide); allogeneic transplantation when the cells are taken from a donor (therefore a subject other than the recipient), a brother / sister, a family member, or an unfamiliar, compatible with the patient; of syngeneic transplantation, very rare, when the donor and the recipient are monovular twins.
Unfamiliar donors are entered in national registers, real archives connected to each other, in which the genetic characteristics of potential donors available to transplant centers around the world are reported. In Italy, the register of bone marrow donors, called IBMDR (Italian Bone Marrow Donor Registry), is based in Genoa, at the Galliera Hospital. Based on the type of transplant and the source of stem cells chosen, the recipient is subjected to high-dose chemotherapy and / or radiotherapy, which aims to destroy the diseased cells present and to create "space" for the new cells to come. transplanted. This is a very delicate phase since there is a decrease (aplasia) of all blood cells, exposing the recipient to the risk of contracting infectious diseases due to the reduction of white blood cells, of anemia due to the reduction of red blood cells and bleeding due to the reduction of platelets. For this reason, during this phase, the hospitalized patient must be carefully monitored in order above all to avoid exposure to infectious diseases.
After the end of the chemotherapy / radiotherapy, the recipient undergoes the infusion of HSC collected through a large vein, a procedure very similar to a blood transfusion.
The infused ESCs, after a time that can vary from 2-3 weeks, are able to repopulate the bone marrow destroyed by chemotherapy / radiotherapy and begin to produce new blood cells, allowing the patient a full recovery and discharge from the hospital.
Since this is a complex treatment, it is necessary to obtain a cure that the recipient is able to tolerate high-dose chemotherapy / radiotherapy, that the disease to be treated is sensitive to drugs and in the case of an allogeneic transplant a genetically compatible donor is available.
Stem cell donation
Until a few years ago, the possibility of carrying out a transplant was linked to the availability of a donor, perfectly compatible with the patient, present in the family environment, an event that occurs with a frequency of about 30% in siblings (Video).
The continuous advancement of knowledge and techniques has progressively expanded the possibility of applying this procedure both as regards treatable diseases and the characteristics of the sick. This has led to the need to have a greater number of donors to meet the requests.
To cope with this situation, international registers have been created in which the references of voluntary donors are inserted which, to date, are estimated at almost 30 million. Among the registers, we recall the Italian Bone Marrow Donor Registry (known as the Italian Bone Marrow Donor Registry or IBMDR) which contains the references of all potential adult donors and umbilical cord blood units donated in solidarity. This is an important register because, often, those who need a transplant cannot find a compatible donor in their family; In these cases, the research moves to the national level with the IBMDR registry and, if necessary, to the international level.
The collection of hematopoietic stem cells (HSCs), based on the source chosen by the physician in charge of the person, can take place in different ways: in the case of a bone marrow transplant, the bone marrow is aspirated directly from the hip, under general or spinal anesthesia, in case of peripheral blood transplant, stem cells are collected from the veins of the arm (staminoapheresis), after having stimulated their production (mobilization) with the administration of growth factors and finally in case cord blood transplant, the blood contained in the umbilical cord vein is collected after the child is born.In the latter case, once collected, the blood is frozen and stored in laboratories called "banks".
What is stem cell transplantation for?
Stem cell transplantation is done when the bone marrow is damaged and is no longer able to produce healthy blood cells (hematopoiesis).
Sometimes it is done to replace blood cells that are damaged or destroyed as a result of cancer treatments.
HSC transplantation can be used to treat:
- severe aplastic anemias (marrow diseases)
- leukemia (type of cancer affecting white blood cells)
- lymphomas (type of cancer affecting white blood cells)
- hemoglobinopathies (sickle cell anemias, thalassemias)
- myeloma (cancer affecting cells in the bone called plasma cells)
- disorders of the immune system and metabolism such as, for example, combined immunodeficiency and Hurler's syndrome
Stem cell transplantation takes place in several stages:
- verify that the patient is suitable for undergoing the transplant
- assess the suitability of the donor: compatibility test (histocompatibility), general state of health, negative serological tests
- treatment of the donor with growth factors / chemotherapy that induce the reproduction (proliferation) of hematopoietic stem cells and their migration from the bone marrow to the blood (mobilization phase)
- collection of hematopoietic stem cells from the blood (apheresis procedure) or from the bone marrow (bone marrow removal procedure) of the donor and their possible cryopreservation
- preparation of the patient's body for transplantation with chemotherapy or radiotherapy to destroy all cancer cells (conditioning regimen)
- infusion of stem cells into the patient
- hospitalization of the patient until the transplant takes root
A hospitalization for a month is generally required before the transplant starts to take effect, while full physical recovery can take up to a couple of years.
Risks of a stem cell transplant
Before undergoing a stem cell transplant it is important that people are aware of both the risks and the benefits it entails. Transplantation is the main cure in many diseases and has allowed many people to recover.
Possible problems that can appear during or after the transplant include:
- medullary aplasia (a functional insufficiency of the bone marrow), which can lead to anemia, bleeding or bruising and an increased risk of infections
- graft versus host disease (GvHD, Graft versus Host Disease) which occurs in allogeneic transplantation when the transplanted cells, particularly those of the immune system, begin to attack the organs of the patient who received the transplant
- side effects of chemotherapy such as, for example, hair loss and infertility
NHS Choices. Stem cell and bone marrow transplants (English)
Mayo Clinic. Bone marrow transplant (English)