The bone marrow inside our bones is characterized by high manufacturing activity.
Every day, the bone marrow produces millions of blood cells.
These are first of all red blood cells (erythrocytes). They contain a protein - hemoglobin, thanks to which they have the ability to carry oxygen from the lungs to the tissues. Second - white blood cells (leukocytes). Their function is to protect against bacterial, viral, fungal and parasitic infections, as well as to recognize and destroy abnormal cells (including neoplastic cells) arising in the body. Third, platelets (thrombocytes). They are responsible for the inhibition of bleeding in case of damage to blood vessels. The appropriate level of each of the above types of blood cells is essential for human life.
The marrow also contains a pool of so-called stem cells.
Although they represent only about 0.1% of all cells are extremely important. Some of them have the ability to self-reconstruct, and part, dividing, gives rise to the next generations of cells from which mature blood cells are finally formed. They leave the marrow and get into the blood. It is assumed that the number> 2x106 stem cells calculated per kilogram of body weight is able to restore bone marrow and permanently ensure the necessary production of blood cells. Reconstructing the necessary number of blood cells is a daily, exhausting task. Each man's heart produces hundreds of millions of blood cells a day.
The bone marrow is easily damaged!
The high activity of the bone marrow makes it very sensitive to harmful chemical and physical factors, for example chemo and radiotherapy necessary in the treatment of cancer. A particularly drastic problem is the treatment of advanced malignant tumors by using very high doses of toxic chemotherapeutics. This is not always possible, because by destroying cancer cells, we damage the blood cell maker too much.
Toxic bone marrow chemotherapy is therefore the main limiting factor in the treatment of many malignancies.
This obstacle can be bypassed by an autograft or bone marrow transplant from a healthy person - e.g. someone from the sick person's family. Having previously, i.e. before surgery, a sufficient number of own stem cells or a transplant from a healthy person, we can apply a very strong chemotherapy, which would be lethal in normal conditions, and then transplant to ensure bone marrow recovery. The bone marrow reconstructed due to the transplant relatively quickly undertakes intensive leukocyte production. Because some cancer cells have molecules (antigens) on their membranes that distinguish them from the normal cells of the body, they can be recognized and destroyed by leukocytes. Bone marrow transplantation is therefore a form of immunotherapy, i.e. treatment that uses natural immune mechanisms. In the case of congenital bone marrow defects or when it is permanently damaged by external factors (ionizing radiation, environmental toxins, some viruses), the only salvation is the transplantation of hematopoietic stem cells from a healthy donor.
How do we obtain hematopoietic cells?
The classic method is to retrieve the marrow from the hip plate. This is done under general anesthesia in the operating room. The bone marrow is mixed with blood at a rate of about 1-1.5 liters using a trepan (needle with a handle). It is usually enough to make only a few skin punctures, thanks to which the procedure leaves no scars. The mere fact of collecting does not harm the donor, because the bone marrow regenerates itself in a short time, filling in the cavity. Usually the donors are discharged the next day and can return to a normal life. Complications are extremely rare.They may result from the anesthesia itself, involve breaking the treadmill during the collection or infection. The source of stem cells may also be blood. Under normal conditions, their blood content is about 100 times lower than in the bone marrow. However, this number can be increased many times by means of special mobilization techniques. The transition of hematopoietic cells from the bone marrow to the blood is forced by giving the so-called growth factors (cytokines) alone or in combination with cytostatics (chemotherapy). After a few to a dozen or so days, the donor is subjected to leukapheres. It involves connecting to the apparatus that draws blood, isolates the appropriate cells from it and then returns it to the donor. The treatment does not require anesthesia and can be repeated for two consecutive days if necessary.
What happens to the marrow after collection?
The collected material is directly transplanted, depending on the type of procedure, stored at 40C for a maximum of 3-5 days or frozen and transplanted at any time. There is the possibility of engineering bone marrow processing. It may consist of removal of erythrocytes (in the case of incompatibility of donor and recipient blood groups), removal of certain types of leukocytes or, in the case of autotransplantation (see below) purification of cancer cells. Special techniques also allow selection of almost exclusively stem cells, ie those from which the marrow after transplantation is to be reborn. The material prepared for the transplant has a volume of just a few tens of milliliters and is contained in a large syringe. Transplantation itself takes place through the intravenous route and resembles blood transfusion, so it does not require anesthesia, but only close observation.
Who can be a bone marrow donor?
- Autotransplantation.
The donor is sick himself. Such a transplant is intentional in patients who are in remission of cancer, i.e. when due to prior treatment a condition is obtained in which the disease is completely or almost undetectable by available methods, it is known that after some time it can be converted. Autotransplantation involves the collection of hematopoietic cells, the use of high doses of chemotherapy and the return of cells to the patient. The main goal here is to reduce the risk of relapse.
- Allotransplantation.
The donor may be a person having the same HLA-compatible tissue compatibility antigens. Almost always this condition is met for identical twins. For siblings, the compatibility probability is 1: 4; for an unrelated person 1: several hundred thousand (this is due to the huge diversity of HLA antigens in the human population).
Due to the fact that the probability of genetic compatibility of two unrelated individuals is so small, registers of potential bone marrow donors are being created all over the world.
Registries of potential bone marrow donors
Volunteers are asked to give a blood sample, which is then tested for HLA, and the data entered into the international database. Entering the register does not automatically mean that the person will be asked to donate the marrow. This will happen only when somewhere in the world there is a patient with features closely matching the HLA of a potential donor (according to statistics, the odds are 1: 250). Even then, compliance has yet to be confirmed in an independent laboratory using very high resolution techniques. In this context, the creation of national registers is of particular importance. The chance of genetic compatibility of two people is much greater within one nation than outside its borders. The number of registered donors in the world is over 3 million, in Poland - several hundred. Bone marrow donation is free, based on honorary principles. Only own costs incurred in connection with participation in the program are reimbursed. The principle of anonymity is also adopted. For at least a year, it is impossible to contact the donor and recipient, which is to guarantee unselfishness.
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