Therapies

Stem cell

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When stem cell In general, one refers to the transfer of stem cells of one organism to another. Most of these are blood-forming stem cells from the bone marrow (bone marrow donation). Read all about this type of stem cell transplantation, procedure and side effects and what you need to consider after stem cell transplantation.

Article overview stem cell transplantation

  • What is a stem cell transplant?
  • When do you perform a stem cell transplant?
  • What do you do with a stem cell transplant?
  • What are the risks of stem cell transplantation?
  • What do I have to consider after a stem cell transplant?

What is a stem cell transplant?

A transplant basically refers to the transfer of tissue between two organisms, the donor and the recipient. So also in the case of stem cell transplantation.

Stem cells are very specialized cells in the body, which have two special characteristics: they can renew themselves (regeneration) and they can develop further to other cells (differentiation). Stem cells are found in most human tissues. The exact origin of various stem cell types is still the subject of intensive research. Treatment with stem cells, except for bone marrow donation (hematopoietic stem cell transplantation), has largely been done only in experimental studies.

Hematopoietic stem cells

Hematopoietic stem cells are found in the bone marrow of various bones, especially the so-called long bones, the pelvis, and the sternum. From the stem cells there, the organism forms the three cell types that occur in human blood:

  • the red blood cells for oxygen transport (erythrocytes)
  • blood platelets for blood clotting (platelets)
  • the cells of the immune system (leukocytes)

The formation of these cells (hematopoiesis) is coordinated in the bone marrow by a variety of different hormones. The finished cells are then flushed out into the blood.

In stem cell transplantation, hematopoietic stem cells are taken from a human (donor) and administered to another human (recipient). Nowadays, this is routinely used for diseases of the blood cells.

Every year, doctors perform approximately 40,000 hematopoietic stem cell transplantations worldwide. There are two main forms of hematopoietic stem cell transplantation: autologous stem cell transplantation and allogeneic stem cell transplantation.

Autologous stem cell transplantation

In autologous stem cell transplantation, the patient is his own donor. First of all, blood stem cells are taken from him and these are processed: Various methods are used to "purging" the tumor cells so that they do not return to the organism. Then the patient experiences a so-called myeloablation: High-dose chemotherapeutics and whole-body irradiation destroy the entire bone marrow and therefore the cancer cells present in it. Subsequently, the previously removed stem cells are returned to the patient.

Allogeneic stem cell transplantation

Allogeneic stem cell transplantation is the transfer of hematopoietic stem cells between two individuals (donor and recipient). As with autologous stem cell transplantation, myeloablation is performed here, where the stem cell tissue of the recipient is withdrawn from circulation. In addition to destroying the bone marrow, the recipient's immune system is suppressed to prevent rejection.

The allogeneic stem cell transplantation, however, has one drawback: the selection of a suitable donor. By means of the complex human leukocyte antigen (HLA) system, a person and their bone marrow can be typed, similar to the ABO blood group system. The goal is to find a donor that has the most consistent HLA characteristics possible with the recipient.

Mini-transplants

New is the development of a non-myeloablative stem cell transplantation ("mini-transplantation"). A significantly weaker myeloabalation is performed, which does not completely destroy the bone marrow. These methods are used for example in patients who suffer from a poor general condition.

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When do you perform a stem cell transplant?

There are different fields of application for autologous and allogeneic stem cell transplantation. In some cases the indications overlap, here the decision on the type of stem cell transplantation depends on various factors, such as disease stage, age, general condition or suitable HLA-compatible donor. Mostly:

Autologous stem cell transplantation:

  • Hodgkin's and non-Hodgkin's lymphomas
  • Multiple myeloma
  • testicular tumor
  • Chronic leukemia: chronic myeloid leukemia (CML) and chronic lymphocytic leukemia (CLL)

Allogeneic stem cell transplantation:

  • Acute leukemia: acute lymphoblastic leukemia (ALL) and acute myeloid leukemia (AML)
  • CML
  • Osteomyelofibrosis (OMF)
  • Lymphoma or multiple myeloma
  • Less common: Aplastic anemia, thalassemia, paroxysmal nocturnal hemoglobinuria (PNH) and severe combined immunodeficiency (SCID)
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What do you do with a stem cell transplant?

A stem cell transplantation takes place during in-patient hospitalization, usually in a specialized oncology center. First, the stem cells are harvested, either from an appropriate donor (allogeneic transplant) or from the recipient himself (autologous transplantation). Until transplantation, the stem cells are then stored frozen. Hematopoietic stem cells can be obtained from three sources:

  • Bone marrow: The stem cells can be taken directly from the bone marrow (hence the original term "bone marrow donation"). This is done by puncturing the pelvic bone and sucking out the bone marrow. Since this procedure is complex and painful, it is usually no longer used today.
  • Blood: Stem cells can also be obtained from the blood that is not in the bone marrow (peripheral blood). Since the proportion of stem cells is lower there than in the bone marrow, the stem cells are previously mobilized by growth factors. The stem cells are then filtered out from the remaining blood cells (stem cell phages). Since this method is technically relatively simple, it is mainly used. However, the rate of side effects (especially graft versus host disease, see below) is higher compared to other stem cell sources.
  • Umbilical cord: Hematopoietic stem cells can also be obtained from umbilical cord blood. However, the content of stem cells is low, so that this method has not been routinely enforced.

The course of a stem cell transplantation is roughly divided into three phases:

  1. conditioning phase
    First of all, the bone marrow with the tumor cells is destroyed by chemotherapeutic agents or whole body irradiation, thus "conditioning" the organism for the new stem cells. It lasts between 2 and 10 days.
  2. transplantation periodAbout 2 days after the end of the conditioning phase, the stem cells are transplanted. This happens via a normal venous access, similar to a blood transfusion. The actual transplant takes only 1 to 2 hours.
  3. aplasiaSince it takes about 10 days for new blood cells to form from the transplanted stem cells, the blood cells (erythrocytes, platelets, leukocytes) initially drop significantly. This phase is also called the aplasia phase. While erythrocytes and platelets can be supplied by blood transfusions, one must wait for the leukocytes until they are independently produced by the bone marrow again. Therefore, for the immunocompromised recipient organism at this stage, any infection is potentially life-threatening. A strict hygiene (hand disinfection, mouth protection), a germ-free as possible environment and possibly preventive antibiotics are therefore essential for survival. If the blood formation sets in as intended, one can be released from the hospital after three to four weeks.
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What are the risks of stem cell transplantation?

In all phases of stem cell transplantation, characteristic and sometimes serious complications can occur.

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