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Stem cell transplant represents intravenous infusion of own or donated blood forming, in order to repopulate bone marrow with healthy cells, capable of forming new blood cells and restore immunity.
Blood forming stem cells, know as hematopoietic stem cells have the potential to reconstitute any blood cell type and rescue patients with blood malignancies or other certain life threatening diseases.
Patients who undergo a stem cell transplant have bone marrow or immune system damaged (mainly due to chemotherapy administered before transplant) or defective (in certain diseases).
There are 2 basic types of stem cell transplant depending on the relationship with the donor:
Autologous stem cell transplant: patient receives his/her own stem cells.
Allogeneic stem cell transplant: patient receives stem cells from a donor, which can be related with him/her or unrelated.
- Related donor can be a sibling, a parent or an identical twin sibling
- Unrelated donor can be any healthy adult person, between ages 17 to 50, who wants to offer the chance of healing / survival of a patient with severe disease. Such donor can be identified through public registries.
Searching for the matched donor is the first step mandatory to be taken, in case of an allogeneic stem cell transplant. HLA typing tests check the immunological matching between donor and the patient.
Search for a matched donor starts in the family. Between siblings there are 25 % chances for a HLA perfect match. A parent could be a donor, only in special type of blood forming stem cell transplant, known as haplotype transplant.
3 blood forming stem cell sources are currently approved and used in transplant field:
Bone marrow: is the first source of blood forming stem cell which are used for transplant since 1956. Still it is considered the "golden standard".
The bone marrow is harvested from hip bones.
The procedure is done usually in operating room, the patient or the donor, being under epidural (spinal) or general anesthesia.
Through multiple punctures taking 1-2 hours it is harvested a volume of bone marrow and blood corresponding to the patient's weight.
In case that the patient is a child the volume of harvested bone marrow will be lower in comparison with an adult patient.
About 500- 1000 ml bone marrow and blood it is usually harvested for an adult.
This represent 3-5% of the donor bone marrow and usually in few weeks the donated cells will be replaced.
Subsequently from the harvested bone marrow, stem cells are filtered and then, stored in frozen state until the transplant are performed.
Peripheral blood: was implemented in 1986 as a less invasive alternative source to bone marrow and with lower risks associated to harvest procedure.
The harvest procedure can be performed in an outpatient basis, no anesthesia being necessary.
Usually in the peripheral blood there are only a few circulating stem cells. Therefore, in order to increase the amount of cells according to the patient's needs, the donor's bone marrow has to be stimulated to produce more blood forming stem cells and progenitors. This ca be done by daily administrating a special growth factor (the drug is called colony-stimulating factor) for 4-6 days before the harvest.
As a result of highly increased number of cells in bone marrow, blood forming stem cells and progenitors (blood cells with intermediate degrees of maturation) are released into the bloodstream.
Apheresis is the procedure by which donor's cells are removed from his/her bloodstream. Usually a harvest session takes 4-5 hours. Sometimes it's necessary repetitive harvest sessions to achieve the amount of stem cells appropriate for patient.
Umbilical cord blood: the first successful umbilical cord blood transplant was done in 1988, to a 5 year old boy diagnosed with Fanconi anemia.
Since then cord blood banking has developed significantly, as the service providing the testing, processing, storage and release of cord blood units for stem cell transplant.
Since the first successful blood forming stem cells performed in 1957 by E. Donnall Thomas, in a patient with leukemia, this field has evolved and expanded worldwide.
This highly specialized and unique medical procedure has opened a new era in medicine. Severe hematological diseases once considered as incurable, started to be reevaluated in light of the new treatment.
Current standard indications for performing a blood forming stem cell transplant include over 80 diseases.
Most of them are malignant and non malignant blood diseases. Genetic metabolic diseases, inherited immune system diseases and certain form of malignant solid tumors were added progressively as stem cell transplant field had evolved.
Hematopoietic stem cells existing in the bone marrow are the resource of blood cells forming process, known as hematopoiesis.
Both hematopoietic stem cells and the progenitors (intermediate stages of cell specialization) under the influence of various factors (e.g. genetic factors, environmental factors, infections, etc.) may be affected, resulting in a number of diseases.
These factors can work towards stimulating uncontrolled proliferation of cells belonging to one or more blood cell lines (hematological malignancies e.g. Leukemia) or towards inhibiting the activity of bone marrow hematopoiesis (stem cell diseases with bone marrow failure e.g. Aplastic anemia ).
Another category of non-malignant diseases with indication of making a stem cell transplant, due to severity of evolution and prognosis are hereditary blood diseases affecting the quality or function of blood cells (e.g. in hemoglobinopathies red blood cells are affected; in chronic granulomatosis- neutrophils in immune deficits are affected – white blood cells affected populations) and hereditary metabolic diseases (e.g. Gaucher's disease, mucolipidosis).
For these diseases the hematopoietic stem cells graft has a curative, healing role, in some cases being the only saving therapy means. Hematopoietic stem cell transplant (blood cell maker) is to replace diseased cells with healthy cells after the former were destructed by prior chemoradiotherapy
Stem cell transplant may be autologous (with own stem cells) or allogeneic (with donated stem cells). If the disease has genetic determinism (is caused by an alteration of genetic information), only allogeneic transplantation (transplantation from another healthy, immunologically compatible individual) which should bring "healthy” genetic information (e.g. immunological congenital deficits or congenital metabolic diseases). can play a curative "healer" role.
We know a large number of such diseases (see table), but they have an incidence (frequency) very small population. But if the disease has no such genetic determinism, both autologous transplantation and allogeneic transplantation may be curative role.
Stem cell transplant may also play only the adjuvant role (complementary) to the fund treatment of some solid malignant tumors. In these cases, the availability of a stored graft and the chance to perform the stem cell transplant allows a therapeutic reassessment of the patient.
Thus it is possible to apply a more aggressive anti-tumor treatment, compared to the usual one (with higher doses of chemo / radiotherapy), aiming to reduce metastasis or tumor recurrence.
This aggressive treatment is accompanied by bone marrow toxic effects (destruction of bone marrow cells); therefore further administration of a hematopoietic stem cell grafts, which should thus provide bone marrow cell repopulation (e.g. malignant solid tumors: neuroblastoma, retinoblastoma) is required.