HEMATOPOETIC STEM CELL TRANSPLANTATION (HSCT)
Hematopoietic stem cells, or HSCs for short, are the stem cells from which blood cells (e.g. erythrocytes) develop through cell division and increasing differentiation. This is a complex process in which errors can also occur, resulting in various diseases of the blood and immune system (also known as hematological diseases).
Many malignant hematological diseases can be either successfully cured or kept under long-term control using chemotherapeutic regimens. In some (high risk) cases, hematopoietic stem cell transplantation (HSCT) is potentially the only curative therapy. This process involves the intravenous infusion of hematopoietic stem cells from a donor to a recipient in order to reestablish production of healthy blood cells in patients. HSCT can be used for a wide spectrum of diseases: e.g. malignant hematological disorders (e.g. leukemias), non-malignant hematological disorders (e.g. sickle cell disease), immunological and metabolic disorders. (Bernardo et al. 2012; del Campo et al. 2014; McCune und Bemer 2016; Strocchio et al. 2015)
TYPES OF HSCT
In stem cell transplantation, the donor and recipient can be the same person (autologous transplantation), two different people (allogeneic transplantation) or - in extremely rare cases - an identical twin (syngeneic transplant).
Stem cells can be obtained either directly from the blood or from the bone marrow of a donor. Stem cells in the umbilical cord blood of newborns can also be used. However, this last option is not used as frequently as the first two.
Autologous transplantation is a transplantation using the patient’s own stem cells. Stem cells are collected from the patient, purified from tumor cells and frozen. The patient then undergoes a so called conditioning treatment (for further detail see also section allogeneic transplantation), consisting of high-dose chemotherapy and/or radiation, followed by reinfusion of their own stem cells.
For allogeneic (alloHSCT) transplantations, stem cells are collected from a healthy person (the donor) and reinfused into a patient who had been prepared with a conditioning regimen using high-dose chemotherapy and/or radiation treatment. This conditioning treatment is intended to fulfil 3 functions:
- weakening of the patient’s immune system to secure engraftment and to help keep the body from rejecting the donated cells after the transplant
- anti-leukemic efficacy to eliminate as many malignant cells as possible
- „making room“ for the transplanted donor stem cells to allow the donor cells to grow in the bone marrow and produce new blood cells
Since the patient’s own bone marrow cells are destroyed by the conditioning therapy, no new blood cells are formed during this period (bone marrow aplasia). The number of all types of blood cells in the blood decreases. The blood stem cells infused into the bloodstream find their way into the patient’s bone marrow, settle there and begin to form new functional blood cells. This process, called engraftment, takes two to three weeks. After successful formation of a new hematopoietic system, the patient can leave the hospital. However, regular medical controls are necessary for several weeks and months, as the immune system is not yet fully functional and must first learn to defend itself against various infections.
An optimal match of the tissue characteristics of the recipient and donor is important for the success of an allogeneic stem cell transplant. Matching stem cell donors can be found in close relatives (=related donor). For the majority of patients, however, an unrelated donor must be sought, e.g. through donor registries.
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REFERENCES Bernardo ME, Piras E, Vacca A, Giorgiani G, Zecca M, Bertaina A, et al. Allogeneic hematopoietic stem cell transplantation in thalassemia major: results of a reduced-toxicity conditioning regimen based on the use of treosulfan. Blood. 2012;120(2):473-6.
del Campo L, León NG, Palacios DC, Lagana C, Tagarro D. Abdominal complications following hematopoietic stem cell transplantation. Radiographics 2014; 34(2):396–412.
McCune JS, Bemer MJ. Pharmacokinetics, Pharmacodynamics and Pharmacogenomics of Immunosuppressants in Allogeneic Haematopoietic Cell Transplantation: Part I. Clin Pharmacokinet 2016; 55(5):525–50.
Strocchio L, Zecca M, Comoli P, Mina T, Giorgiani G, Giraldi E et al. Treosulfan-based conditioning regimen for allogeneic haematopoietic stem cell transplantation in children with sickle cell disease. Br J Haematol 2015; 169(5):726–36.