Bone marrow transplant is a revolutionary procedure in medicine, and has opened new perspectives in the management of many blood disorders. It can be curative in some conditions such as thalassemia, acute leukemias, hemoglobin disorders, some immunodeficiency disorders, and some autoimmune diseases. But like all medical procedures, it comes with its share of side effects and complications. The most significant is the graft versus host disease or GVHD.
What is GVHD?
Living organisms are fascinating, and the most fascinating part of their existence is the presence of a complex system of cooperation between multiple cells. According to evolutionary theory, the most important step of evolution is the transformation of unicellular organisms into multicellular organisms, and they key to reach this level of understanding between cells can be explained by antigens. If you walk into a building that has some form of security, the porter or security officer will ask for an ID, a method to make sure that you belong to that building. Our cells identify each other by a unique set of proteins placed on their surface. This mechanism doesn’t only serve to help cells identify each other, but also acts as a defense barrier against foreign cells or substances. Then, what the body doesn’t identify, it attacks.
Our immune system is complex and has some static components in the form of natural barriers like the skin, mucous membranes, stomach acidity and some adaptive mechanisms including the white blood cells. White blood cells are formed mainly in the bone marrow and if this bone marrow is transplanted to another patient, white blood cells and their “coding system” will transfer along with it. During the bone marrow transplantation process, the old bone marrow is usually ablated using chemotherapy or radiotherapy and the new one becomes the backbone of the patient’s immunity. In case of transplanted organs like the liver or the kidney, if the antigens are not similar between the donor and the recipient, tissue rejection will occur and that tissue or organ will be destroyed, sometimes even before closing the surgical wound. In the case of bone marrow transplantation, it is the transplanted bone marrow that attacks the recipient’s body, making the condition more severe.
It is worth knowing, however, that GVHD doesn’t only occur due to stem cell transplantation of the bone marrow, but can theoretically occur with the transplantation of any tissue containing white blood cells including blood products which have not undergone external irradiation – a standard procedure that aims to paralyze white blood cells of transfused blood- and in the case of particular types of tissue like the small intestines, which may contain a type of lymphoid tissue called Peyer’s patches.