The process of hematopoietic stem cell transplantation is similar to blood transfusion, i.e. the donor’s hematopoietic stem cells are transfused to the patient through a tube, and the imported hematopoietic stem cells will “take root” like seeds in the patient’s body and divide into many new blood cells, thus replacing the original hematopoietic system in the patient’s body. There is no incision and suturing process like common surgical procedures. Before talking about hematopoietic stem cells, we must first understand what is bone marrow. Bone marrow is a soft, spongy substance located inside the bones that has hematopoietic functions and is also the center of the immune system. Bone marrow is rich in hematopoietic stem cells, which gradually differentiate into leukocytes (anti-infective cells), red blood cells (oxygen-carrying cells) and platelets (blood clotting-promoting cells), so a bone marrow transplant is essentially a transplant of hematopoietic stem cells from the bone marrow. Therefore, according to the source of hematopoietic stem cells, there are several types of hematopoietic stem cell transplantation: cord blood hematopoietic stem cell transplantation, peripheral blood hematopoietic stem cell transplantation, and bone marrow hematopoietic stem cell transplantation. Since bone marrow transplantation is the first one used in hematopoietic stem cell transplantation, it is customary to refer to hematopoietic stem cell transplantation as bone marrow transplantation in general. Second, the classification of hematopoietic stem cell transplantation type 1, allogeneic hematopoietic stem cell transplantation. Transplantation using healthy hematopoietic stem cells from another person is called allogeneic hematopoietic stem cell transplantation. If the donor is related to you, it is called a related donor transplant; if it is provided by a non-related donor, it is called a non-blood donor transplant. Either type of allogeneic transplant requires a human leukocyte antigen test, which will test to see if the antigens on the surface of your leukocytes match those of the donor. If you and your donor match at these major antigenic loci, i.e., a mismatched transplant, the donor’s stem cells will blend well in your body and the risk of transplantation will be low. We call this phenomenon as graft-versus-host disease. 2. Umbilical cord blood HSCT. The umbilical cord blood of newborns is also rich in hematopoietic stem cells and can be used for hematopoietic stem cell transplantation. However, because of the small amount of hematopoietic stem cells it contains, cord blood transplantation is currently mainly used for children. The collection of umbilical cord blood has no effect on the fetus and the mother, and is a waste to treasure. 3.Autologous hematopoietic stem cell transplantation. In autologous transplantation, your own normal hematopoietic stem cells are collected and stored first, because chemotherapy and radiotherapy destroy a large number of normal hematopoietic stem cells while destroying diseased cells in your body. The purpose of transplantation is to protect your normal blood stem cells before radiation and chemotherapy, and then re-infuse the previously stored blood stem cells after treatment is completed. Usually, autologous transplants are collected when your own bone marrow is normal. However, sometimes your own bone marrow is infiltrated and the extracted bone marrow cells will need to be purified outside of the body to remove the cancer cells and then the “clean” bone marrow will be returned to you after your chemotherapy or radiation treatment. Each bone marrow transplant center in the world has its own method of bone marrow decontamination, and the need for bone marrow decontamination is determined by the disease itself. The need for bone marrow decontamination is determined by the disease itself, but fewer people are currently choosing this type of transplant due to the disease. Indications for transplantation 1. Neoplastic diseases. Acute leukemia, chronic leukemia, lymphoma, myelodysplastic syndrome, multiple myeloma and other malignant hematologic diseases. There are also certain solid tumors, such as small cell lung cancer, breast cancer, testicular cancer, neuroblastoma, ovarian cancer, melanoma, etc. 2. Non-neoplastic diseases. Severe aplastic anemia, immunodeficiency diseases, certain congenital hemolytic anemias, such as maritime anemia and other hematological diseases, as well as autoimmune diseases such as systemic lupus erythematosus, etc. Four, transplant timing 1, most patients with acute leukemia need to achieve complete remission after chemotherapy, according to the condition of intensive treatment for 2-3 courses, and then choose allogeneic transplantation. If 2-3 courses of chemotherapy cannot achieve remission, it is also necessary to improve the preparation before transplantation as soon as possible and perform salvage transplantation as soon as possible. 2. Transplantation in chronic leukemia patients should be performed in the chronic phase, preferably within 1 year after the onset of the disease. However, with the advent of new drugs, more patients are relying on drug therapy for long-term survival, and only those patients who are not sensitive to drugs should be considered for allogeneic transplantation. 3. Patients with lymphoma usually need chemotherapy to achieve complete remission and then 2-3 courses of intensive treatment before transplantation. In case of refractory relapsed patients, allogeneic transplantation is usually considered. 4. For myelodysplastic syndromes, especially MDS-RAEB and MDS-RAEBT, as long as there is an HLA-matched donor, allogeneic transplantation is recommended as early as possible, and autologous transplantation is not considered. 5. Patients with multiple myeloma must be transplanted after chemotherapy to achieve complete remission or near remission. 6. Certain solid tumors, such as breast cancer, lung cancer, testicular cancer, etc. Transplantation is generally required after chemotherapy to achieve complete remission or near remission. Usually autologous transplantation is performed, and autologous transplantation cannot be performed if there is bone marrow metastasis. For patients with severe aplastic anemia, allogeneic transplantation is recommended as soon as there is an HLA-matched donor. 8. Patients with autoimmune diseases, which are not well controlled by conventional drugs, may be considered for transplantation, with specific advice from the doctor. Once transplantation is considered, excessive transfusion of blood products should be avoided as much as possible. Since many transplant centers include whole body radiation in their transplant protocols, it is best to avoid radiation therapy prior to transplantation. You can consult your transplant physician for more information.