Allogeneic transplant patients: generally enter a sterile warehouse and need to be pre-treated with high dose chemotherapy or radiotherapy for about 5 days to kill as many leukemia cells and immunosuppression as possible and to vacate the bone marrow. After reaching bone marrow suppression transfusion of donor donated HSCs, which can be derived from bone marrow, mobilized peripheral blood stem cells, or cord blood stem cells. The person who donates blood stem cells is called the donor and is physically qualified after examination. For donors who donate bone marrow, on the day of stem cell transfusion, they go to the operating room to have the bone marrow drawn under local anesthesia. Generally, an adult patient of 60 kg needs 600-800 ml of bone marrow, which requires many needles in the body and is more painful for the donor, and this method is rarely used now; the most used method now is to donate peripheral blood stem cells mobilized by granulocyte stimulating factor (GCSF). The donor needs to be mobilized with GCSF injection for 4 days (in parallel with the patient pretreatment), the purpose is to let the hematopoietic stem cells grow rapidly, the excess stem cells will run from the bone marrow to the blood, so that through a machine can filter enough stem cells from the blood stream, the volume is about 100-200ml, and return to the patient who has been pretreated can be, the total number of their own hematopoietic stem cells The total number and proportion of blood stem cells will generally return to normal within a week, and work, study and life will not be affected. As long as the donor is physically qualified, there is really no effect on health or leukemia (there is no way to talk about it). There are about 50,000 transplants done every year in the world, and there is no reported increase in the disease rate compared to people who do not donate cells. This is essentially the method used by donors to the Chinese Bone Marrow Bank. Umbilical cord blood stem cells. Cord blood is collected from newborns after birth, frozen in a liquid nitrogen tank after passing a series of tests, and stored for a long time (the quality of storage should be fine for 10 years). Patients who need transplantation go to the cord blood bank to find cord blood that matches both their blood type and HLA mapping, and if there is, they make an appointment to pay the fee, and the patient undergoes pretreatment. After the treatment, the cord blood is taken out and transfused back into the patient at the agreed time. The advantages of cord blood are that it is available in the bank at any time; the incidence of post-transplant rejection is very low; however, the disadvantages are also obvious, the main one being that the amount of cells is too small, which is generally considered for patients under 50 kg body weight and more commonly used for children. Secondly, the small amount of cord blood cells brings about a particularly slow recovery of patients after transplantation, some need to stay in the warehouse for 1-3 months, and individual patients have been unable to recover, which increases the cost and risk. Also, cord blood is less powerful, has less rejection rate, and has less ability to control leukemia, so the relapse rate after transplantation is higher than that of peripheral blood HSCT. In conclusion: for acute leukemia, peripheral blood stem cells are the best source of hematopoietic stem cells; for non-malignant hematologic diseases and children, cord blood is more appropriate; for patients with heavy aplastic anemia, bone marrow can be chosen.