Allogeneic stem cell transplantation
Allogeneic stem cell transplantation is an established form of treatment of leukemias, some other serious hematological illnesses and some rare illnesses of the immunological system. The most common indication for allogeneic stem cell transplantation for adults is acute myelogeneic leukemia (AML). The transplanted tissue in allogeneic stem cell transplantation is collected from another person whose tissue type is compatible with the tissue type of the patient (recipient).
In allogeneic stem cell transplantation, the diseased bone marrow of the patient is first destroyed with the use of what is called a conditioning regimen and the patient’s immune system is blocked with the use of medication. This is done to avoid the stem cells of the donor from becoming rejected. The purpose is to have the allogeneic stem cells engrafted and to have them populate the recipient’s bone marrow. The immunological cells in the donor cell transplant will replace the patient’s original bone marrow and destroy any remaining malignant cells. The intention of an allogeneic stem cell transplantation is always cure.
Donor of stem cell transplant
More than 90% of the patients who need an allogeneic stem cell transplant will have a donor that fulfils the criteria for donating a stem cell transplant. The optimal donor is a sibling of the patient with an appropriate tissue type (HLA-identical match). It is also possible to have a child, either of the parents of the patient as stem cell donors or donor can also be from extended family members such as aunts, uncles or even cousins; such a donor is called a haploidentical donor. Since not all who need an allogeneic stem cell transplant have a matching donor in the family, most patients will have a matching donor in the domestic Red Cross registry of stem cell donors and in international donor registries. Once a suitable donor has been identified, the donor and the patient will undergo the necessary preparatory steps before the actual procedure. Today, the donors of allogeneic stem cell transplants undergo collection of stem cells from the circulating blood more often than from the bone marrow.
Allogeneic stem cell transplantation: procedure and subsequent treatment
The timing of the allogeneic stem cell transplantation is always managed so that it is optimal from the point of view of the phase of the patient’s disease. The time the patient spends in the hospital is usually 4–6 weeks; of these, the conditioning regimen requires 1–2 weeks. The conditioning regimen depends on the disease being treated, the patient’s age and concomitant illnesses and on previous treatments. The conditioning regimen includes chemotherapy and, possibly, radiation treatment to reduce the tumour burden. The conditioning regiment will also stun the patient’s immune system for a time. This guarantees the undisturbed function of the transplanted cells and the production of new, healthy blood cells. During the conditioning regimen the patient may experience nausea and mucous membrane problems. After completion of the conditioning regimen, the collected stem cells are infused (transplanted) to the patient in a procedure that is like a blood transfusion.
A central problem for patients who have received an allogeneic stem cell transplant is the risk of infections. This risk prevails as long as the blood count is low. An allogeneic stem cell transplantation is an advanced and demanding medical procedure associated also with other risks. The most common treatment-related complications are severe graft-versus-host rejection reactions and posttransplant virus infections. Also, the blood disease may recur. The patient needs meticulous follow-up within the open care and often follow-up of a very long duration. Most problems post transplantation emerge only after the transplantation period in the hospital is over. New treatments and cell therapies are constantly being developed to prevent and combat the complications of allogeneic stem cell transplantation.