Stem cell apheresis
The peripheral stem cell transplantation (from the Greek apheresis = removal) is a process for the separation, thus filtering out of which in the blood contained blood stem cells . The resulting blood product, which contains the stem cells (the apheresis ) may be, for Therapy of various diseases, either the dispenser itself ( autologous ) or requiring feature compatible patients ( allogeneic ) transplanted be. In the latter case, it is now the preferred method of stem cell removal in the context of a transplant, as it is less invasive than bone marrow removal .
The majority of the formation and proliferation of blood stem cells take place in the large bones of the body, e.g. B. the pelvis . The so-called progenitor cells formed there have the opportunity to develop into white blood cells or red blood cells . Only a small part leaves the bone marrow without being differentiated in any way, ie being “fixed” to a specific cell type. The aim of apheresis is to extract precisely these not yet differentiated ( multipotent ) cells from the bloodstream .
Since most of the stem cells remain in the bone marrow, the patient (which can also mean the voluntary donor), depending on the type and indication of the apheresis, is given the natural growth hormone G-CSF a few days in advance started, which stimulates the production of stem cells. As a rule , it is administered subcutaneously by means of small syringes such as insulin , which is why the patient can also administer it himself. A precisely calculated amount of the drug is always dispensed and the patient is informed in detail about the (side) effects (see below) prior to the first administration in order to avoid overdosing . When used correctly, G-CSF leads to a controlled excessive production of stem cells, which also increasingly enter the bloodstream, although they have not yet reached their final stage of development.
Before a donor can donate, he must be approved for donation by the medical management of his donor database in coordination with the donor doctors. This approval is based on the findings of detailed preliminary examinations, but also other information from the donor on questionnaires (e.g. on family-related or rare diseases) or in personal conversations. (For references and further information see.)
On the day of the apheresis, the patient is connected to an apheresis machine using two venous catheters on his arms. The blood is taken from one arm and centrifuged . The blood components are spatially separated according to their density so that the required blood stem cells can be "sucked off" in a targeted manner. After filtering, the individual blood components are mixed together again and the blood is returned to the other arm. The procedure is carried out on an outpatient basis in special clinics, with blood donation services or directly with stem cell donor files.
Typically, all of the donor's blood goes through the apheresis machine about four times, which takes about 3-4 hours. The volume of the resulting apheresis depends on the concentration of the required cells in the donor's blood, but is generally lower than with a blood donation. The aforementioned concentration depends on various factors, including gender and age . If the yield of stem cells is not high enough one day, another collection can be carried out the following day.
The obtained preparations ("bags"), which contain the stem cells that are viable for only about 72 hours at normal temperatures after harvesting, are stored and transported in a cool place in order to extend the life span of the cells. Temperatures of 4–9 ° C with the help of special ice packs as well as so-called cryopreservation , in which the apheresate is stored in nitrogen tanks at temperatures of up to −196 ° C (usually −160 ° C), are suitable. The slight cooling of the cells does not increase their service life excessively, but temperatures that are too low also destroy more cells. Cryopreservation is particularly considered if the cells are not to be administered to the recipient immediately or only in partial steps.
Possible complaints and side effects
The effects of G-CSF are not limited to the bones alone. Since it acts as a hormone on the immune and blood-forming systems, a spleen sonography is often ordered beforehand in order to check the spleen as an organ that is also integrated in this system for normal function. In addition, various blood samples are taken and an ECG is made, among other things to examine the coagulation behavior of the patient's blood and to minimize circulatory problems during apheresis.
While taking medication , flu-like symptoms can occur, which can be explained by the fact that G-CSF is a natural hormone of the body, which this e.g. B. during a flu to produce more white blood cells to strengthen the immune system . Since the stem cells to be collected ( CD34pos ) belong to the white blood cells, the function of G-CSF is used to increase their number in the body. The resulting increased activity in the bone marrow leads to the well-known flu-like bone pain. In individual cases, headaches or a slightly depressed mood were also observed in the patients . However, the severity of all these complaints in response to G-CSF varies in each person, and some even feel none at all. If necessary, the pain by the administration z. B. be mitigated by paracetamol .
During the apheresis process itself , the possible complaints described above subside to some extent, but the 3 to 4 hour apheresis process inevitably leads to discomfort in some people . A citrate reaction can occur, so that the patient's arms and / or hands can begin to tingle or burn at the needle insertion points during apheresis . However, the symptoms are generally described as bearable and can also be treated during apheresis. More serious, although generally very rare, complications can range from circulatory problems up to collapse , which should, however, usually be detected early on through detailed preliminary examinations and constant monitoring of the patient during apheresis. The mobility of the arms is only restricted on one side during apheresis. This limitation results from a non-moving needle for drawing blood in one arm of the donor. Since the blood is returned with the help of a peripheral venous catheter , the other arm can be moved easily and painlessly. The toilet can be used during the entire donation. For this purpose, the immobile arm is fixed in a splint to avoid pain that can result from unintentional movement of the arm. After the apheresis, the patient is usually on sick leave for the rest of the day, as the process is a significant burden on the body.
Seriously ill cancer patients require high-dose radiation and chemotherapy . However, since these kill a large part of the cells in the patient's blood, an apheresis is carried out before treatment. The stem cells are then added to the patient's bloodstream after the therapies and begin to rebuild.
In the case of autologous donations, the donor is also the patient: he donates his own stem cells for himself. Allogeneic donors, on the other hand, donate their stem cells either to family members or to completely strangers. However, this is only possible if the HLA characteristics of the donor and patient match.
For more information on methods and procedures for stem cell transplants, see there.