In 1956, American medical scientist E.D. Thomas successfully performed the world’s first human bone marrow transplantation operation, for which he won the 1990 Nobel Prize in Medicine. After more than half a century of development, with the deepening of research on hematopoietic stem cells (HSC) and the influence of various factors such as the development and progress of science and technology, the technology of hematopoietic stem cell transplantation (HSCT) has become increasingly mature and has gradually developed into a relatively complete treatment system. At present, about 60,000 cases of HSCT are performed every year worldwide, providing hope to ten thousand patients.
What are HSC and HSCT?
HSCs are pluripotent stem cells with both self-renewal ability and multi-differentiation potential, and they are the initial cell of various blood cells and immune cells.
HSCs have two important characteristics: high self-renewal and self-replication ability, and the ability to differentiate into all types of blood cells, including red blood cells, white blood cells, platelets, and others. While HSCT involves the injection of HSC of a healthy human into the recipient through intravenous injection (IV) to rebuild the recipient’s hematopoietic ability and immune ability. HSCs can be obtained from various sources, including bone marrow hematopoietic stem cell transplantation (BMT), peripheral blood hematopoietic stem cell transplantation (PBSCT), umbilical cord blood hematopoietic stem cell transplantation (UCBT) and fetal liver hematopoietic stem cell transplantation (FLT). At present, HSCT is considered the best choice for the radical cure of certain hematological malignancies and genetic diseases.
Why HSCT can treat disease?
HSCT removes abnormal cells in the recipient through high-dose radiotherapy and chemotherapy pretreatment, and then transplants HSC to the recipient to rebuild the normal hematopoietic function and immune system in the recipient, so as to achieve the purpose of treating the disease.
The role of HLA in HSCT
HLA molecules are present on the surface of various nucleated cells in the human body, serving as the ‘ID card’ of human biology, inherited from parents. HLA molecules are capable of identifying ‘self’ and ‘non-self’. The HLA genes of different individuals are highly diverse, and successful transplantation requires the matching of HLA-A, HLA-B, and HLA-DR of the donor and recipient. This matching process is crucial to the success of HSCT.
The 5 phases of HSCT
1. A conditioning phase
Usually last for one week, radiation and chemotherapy are used to eliminate any existing disease and prevent rejection.
2. The transplant phase
A day of rest is usually given after radiotherapy and chemotherapy to ensure that the cytotoxic drug has been cleared from the body before HSC transplantation into the recipient.
3. The neutropenic phase
Usually lasting 2-4 weeks, at this time, the recipient is not overtly immunocompetent, and endogenous fungal infection is addressed with broad-spectrum antibiotics and antifungal therapy. Blood transfusion support is usually needed at this phase.
4. The engraftment phase
During this phase, the patient begins to experience healing from the damaged mucosa, resolution of the bacterial infection, and the development of acute graft-versus-host disease ( aGVHD). At the same time, it is also necessary to prevent opportunistic protozoan and fungal infections and reduce the incidence rate.
5. The postengraftment phase
Immunodeficiency persists during this phase until immune reconstitution is complete and graft tolerance develops. Lymphocyte function remains poor, and the ratio of T cell helper/suppressor does not normalize until 8-10 months after transplantation. Once the immune function has recovered, the recipient can begin the process of reimmunization.
What are the impacts of HSCT?
The most common effect of HSCT is the change in blood type. Unlike Leukemia or blood transfusions, which do not affect the patient’s blood type. The root cause of the blood type change is the use of donor stem cells with different blood types. If the donor stem cells are type O, for example, the recipient’s blood type will gradually shift towards type O regardless of their original blood type. This process can take some time to complete. Once the transplantation is successful, the donor’s stem cells will gradually replace the recipient’s original cells, leading to a permanent change in the recipient’s blood type.
What other diseases can be treated by HSCT?
In addition to leukemia, HSCT can also treat other blood cancers, such as multiple myeloma, lymphoma, myelodysplastic syndrome, and so on. Moreover, hereditary blood diseases and immune system diseases, such as thalassemia major, and severe combined immunodeficiency disease, can also be treated with HSCT. Furthermore, hematopoietic failure diseases, such as severe aplastic anemia. Non-hematopoietic diseases, such as solid tumors, can also be treated with HSCT.
Hoping that this article can give you a better understanding of HSCT.
 Moore, T. B., & Sakamoto, K. M. (2005). Topics in Pediatric Leukemia -- Hematopoietic Stem Cell Transplantation. Medscape. Retrieved from https://www.medscape.com/viewarticle/499049_3
神采干细胞. (2022, August 25). 造血干细胞移植成功后，血型也会发生改变？[After successful hematopoietic stem cell transplantation, will blood type also change?]. 中国医疗器械信息网 [China Medical Device Information Network]. https://www.cn-healthcare.com/articlewm/20220825/content-1424528.html