What is bone marrow? Bone marrow is the center of the immune system and is rich in hematopoietic stem cells, which gradually differentiate into white blood cells (anti-infective cells), red blood cells (oxygenated cells) and platelets (hemostatic cells). What are hematopoietic stem cells? Hematopoietic stem cells are cells that are capable of self-renewal, have strong differentiation and regenerative abilities, and can produce various types of blood cells. Hematopoietic stem cells are derived from red bone marrow and can migrate into the peripheral blood circulation through the blood stream without damaging the hematopoietic function through blood donation or hematopoietic stem cell donation. What is hematopoietic stem cell transplantation? Replacement of hematopoietic stem cells from patients damaged by radiotherapy with fresh normal human hematopoietic stem cells. This is called hematopoietic stem cell transplantation, in which normal human hematopoietic stem cells are infused intravenously into the patient’s body to rebuild the patient’s hematopoietic and immune functions for the purpose of treating certain diseases. In fact, HSCT includes bone marrow transplantation, peripheral HSCT and cord blood transplantation. What are the diseases that can be treated by HSCT? Hematopoietic stem cell transplantation is an effective treatment for two main types of diseases: (a) Malignant diseases, such as refractory and recurrent acute leukemia, chronic leukemia, malignant lymphoma, myelodysplastic syndrome and other malignant hematologic diseases, and is even the only cure for some hematologic tumors. In addition some solid tumors: malignant teratoma, neuroblastoma, malignant osteosarcoma, some brain tumors, retinoblastoma, etc. can be treated by one or even multiple hematopoietic stem cell transplantation. (ii) Non-malignant diseases congenital or secondary bone marrow failure diseases, congenital immunodeficiency diseases (combined immunodeficiency disease, chronic eosinophilic granuloma, etc.), certain genetic metabolic diseases (e.g. marble bone disease, adrenal cerebral leukodystrophy, mucopolysaccharidosis, etc.), certain benign but malignant proliferative diseases (e.g. refractory Langerhans cell histiocytosis, familial/refractory hemophagocytic syndrome, etc.) Certain congenital hemolytic diseases (thalassemia, etc.) autoimmune diseases (refractory systemic lupus erythematosus/scleroderma, etc.).