Hematopoietic stem cells are the “seeds” of blood cells, from which all blood cells in the body, including red blood cells, white blood cells, platelets, etc., differentiate and develop. Hematopoietic stem cells have the ability of self-replication, i.e., they produce new stem cells to replenish themselves and thus live on. Hematopoietic stem cells are mainly found in bone marrow, peripheral blood and umbilical cord blood. It refers to the transplantation of normal hematopoietic stem cells from various sources into the recipient by intravenous infusion after the patient has received an overdose of chemotherapy (radiation) to replace the original pathological hematopoietic stem cells, thus allowing the patient’s normal hematopoietic and immune functions to be reestablished. Principle of Stem Cell Transplantation for Malignant Diseases Since the response of malignant tumor cells to chemotherapy (radiation) is closely related to their dose, the patient is given an overdose of chemotherapy (radiation) to kill as many tumor cells as possible, and then allogeneic or autologous bone marrow collected beforehand and preserved in vitro is injected to rebuild the patient’s normal hematopoietic system. Hematopoietic stem cell transplantation can be used to treat oncologic diseases such as leukemia and certain malignant solid tumors, as well as non-oncologic diseases such as aplastic anemia, severe immunodeficiency disease, acute radiation sickness, and thalassemia. What is HLA and why is HLA typing necessary? What is the HLA compatibility rate of siblings? HLA is the human leukocyte antigen, which is found on the surface of various nucleated cells in the human body. It is the biological “identity card” of the human body, inherited from parents; it can recognize “self” and “non-self” and exclude “non-self” through immune response, thus maintaining the integrity of the individual. It can recognize “self” and “non-self” and exclude “non-self” through immune response, thus maintaining the integrity of the individual. Therefore, HLA plays an important role in the success or failure of HSCT, and HSCT requires HLA matching between the donor and the recipient. Since HLA varies greatly from race to race and from individual to individual, certain methods must be used to determine the HLA type of the donor and the patient, so that a donor who is compatible with the patient’s HLA can be selected for transplantation, which is the key to successful HSCT treatment. It is 100% for identical (homozygous) twin siblings and 1/4 for non-identical (heterozygous) twin or biological siblings. What is pretreatment? The purpose of preconditioning Preconditioning is the treatment of patients with intense chemotherapy and radiation therapy prior to transplantation to destroy the patient’s own tumor or diseased bone marrow in order to facilitate the permanent replacement of the “old bone marrow” with “new bone marrow” (or hematopoietic cells). In the design of the pretreatment program, the doctor will make a reasonable plan depending on the type of disease and the main purpose of the patient. The purpose of pretreatment is 1) to prepare the “space” for the transplanted stem cells; 2) to remove as thoroughly as possible the malignant cells remaining in the body; 3) to suppress the immune cells in the body so that the stem cells can be easily implanted. Donor sources for allogeneic transplantation twin siblings; HLA matched siblings; partially matched and semi-matched relatives; HLA matched unrelated donors. Hematopoietic stem cell transplantation typology 1. Allogeneic hematopoietic stem cell transplantation: Histocompatibility antigens (HLA) of the donor and recipient are basically the same, as seen in transplantation between identical twins. This kind of transplantation is the most ideal method to treat severe aplastic anemia, but the chance of homozygous donor is extremely rare and it is not suitable for the treatment of hereditary diseases. 2. Allogeneic hematopoietic stem cell transplantation: The donor and recipient are of the same race, and although the donor and recipient are not genetically identical, the major histocompatibility antigens are required to be identical. This kind of transplantation is suitable for the treatment of various types of leukemia and malignant diseases of the hematopoietic system, severe hereditary immunodeficiency diseases, and bone marrow failure caused by various reasons, such as aplastic anemia, etc. It is the most widely used hematopoietic stem cell transplantation technique with the best efficacy. It is usually divided into allogeneic HSCT with sibling donor and unrelated donor according to the source of the donor. 3.Autologous hematopoietic stem cell transplantation: Before pretreatment with overdose radiotherapy and chemotherapy, a part of the patient’s own hematopoietic stem cells are collected, separated and preserved at deep low temperature. After the overdose radiotherapy and chemotherapy, the cells are then transfused back to the patient to rebuild the hematopoietic function. Suitable for patients with lymphoma and solid tumors. Patients with acute leukemia who have achieved complete remission after treatment may also be considered for autologous HSCT if no suitable allogeneic donor is available. Choosing the type of HSCT The physician will consider the patient’s disease priority, HLA matching results, donor age, health status and other factors to choose the donor and the HSCT collection method. At present, most of the allogeneic HSCTs are between siblings of the same type, between semi-identical parents and children, and between semi-identical siblings. In recent years, the number of allogeneic HSCT from unrelated donors has been increasing with the increase and expansion of the bone marrow pool of unrelated donors worldwide and in China. Various types of transplantation have different advantages and disadvantages. The advantages of autologous HSCT are that it is not restricted by the donor, no graft-versus-host disease occurs after transplantation, less serious complications such as interstitial pneumonia, and lower cost; however, tumor cells may remain in the collected autologous HSCT, and the treatment of leukemia, myeloma, and tumor with infiltration of bone marrow and blood system has a high recurrence rate; moreover, it cannot be used to treat hereditary blood immune system diseases, aplastic anemia and other diseases with abnormal or failing hematopoietic stem cells. Allogeneic HSCT has fewer complications and is less expensive than allogeneic HSCT; it can be used for leukemia, some solid tumors, hereditary hematologic immune system diseases, aplastic anemia, and other HSC abnormalities or failures; however, it lacks the anti-tumor effect of the graft; and there are few donor sources. Allogeneic HSCT can be used for all the aforementioned indications and has the lowest recurrence rate among all types of transplantation for the treatment of malignant diseases, but complications such as graft-versus-host disease and interstitial pneumonia are higher than other types of transplantation, and therefore the cost is also higher, with the highest complications occurring with unmatched unrelated transplants, so try to use matched transplants. Stages of HSCT 1. Pre-transplant preparation: The pretreatment stage is completed mainly in the outpatient clinic: the patient (recipient) receives high doses of chemotherapy or/and radiotherapy, during which the recipient’s blood leukocytes gradually drop to 0 or near 0, and other blood cells also gradually drop to lower levels. The recipient lives in a laminar flow clean room with class 100 cleanliness. The air in the room is filtered to remove microorganisms and other particles before being imported, and all items in the clean room are sterilized before entering. 2.Transplantation stage: Blood stem cells from the donor are transfused back to the recipient through a vein; the recipient lives in a laminar flow clean room. 3.Middle post-transplantation period: After the donor’s hematopoietic stem cells are implanted in the recipient’s body, the recipient is in the observation period in the general ward. During this period, the main observation or treatment of post-transplantation complications, if the recipient is in good general condition and has no serious complications, he can be discharged from the hospital. Dietary guidance after hematopoietic stem cell transplantation Pay attention to dietary hygiene, fruits and vegetables should be washed well. Meals should be fresh, do not eat spoiled food to avoid digestive tract infection. Before pretreatment, eat a diet high in protein and vitamins. Pre-treatment and early transplantation (within one month after transplantation) eat light, less residue, easy to digest and less irritating food, avoid greasy, rough, spiny and spicy food to avoid damage to the oral cavity and digestive tract mucosa. If you feel nauseous during chemotherapy, you can eat a small amount of food, but not without food. If there are oral chemotherapy drugs, the meal time should be at least 2 hours apart from the time of taking the drugs. Between meals, you can eat some auxiliary food that is not easy to cause nausea, and chew slowly to avoid damaging the mucous membrane in front of the mouth. Rinse your mouth with antiseptic solution after eating. When you feel nauseous, you can take deep breaths repeatedly to reduce discomfort. When mouth ulcers occur, the diet should be mainly semi-liquid or liquid food. Drink more water or non-irritating fluids during chemotherapy to promote the excretion of metabolites in the body and reduce side effects. During the middle and late stages of transplantation (from one month to six months after transplantation), gradually increase the amount of food intake, gradually increase the intake of high protein, high vitamin and nutrient-rich food, but do not eat food that is not easily digested and absorbed, so as not to cause diarrhea. Eat more fruits and vegetables. Vegetables should be cooked and eaten, fruits should be peeled and eaten, and the skin of the eaten fruits should be unbroken, undecayed and easily cleaned and disinfected. Discharge guidance after hematopoietic stem cell transplantation After a period of treatment and care, the disease is better controlled and the patient will be discharged to recuperate at home. To further consolidate the therapeutic effect, prevent relapse, and maintain a happy and healthy body and mind, patients are requested to pay attention to the following matters Living environment to keep indoor air fresh, open windows for 30 minutes each morning and evening daily, reduce family gatherings, wear masks when going out (within six months after transplantation or when blood white blood cell count is lower than normal), and do not keep pets to avoid bacterial reproduction. Nutritional support Patients in the process of receiving hematopoietic stem cell transplantation, energy consumption, most patients have a certain degree of malnutrition, physical decline, so we need to supplement nutrition, can enter a high-calorie, high-protein, high vitamin diet, light semi-liquid or pasta-based, such as ribs soup, chicken soup, fish soup, etc. (such diet is easy to digest), and then add vegetables, fruits, etc. After transplantation, patients not only have low immunity but also most of them have slightly atrophied muscles in both lower limbs, so they should increase their activities indoors first and then outdoors gradually to recover their strength and enhance their resistance. Adjust your mind, keep a relaxed and happy mood, and ensure sufficient sleep. Prevent infection, pay attention to hygiene, try not to eat cold food; within six months after transplantation or when the blood white blood cell count is lower than normal, wear a mask when you go out or come into contact with the outside world, and pay attention to keeping warm to avoid catching a cold or other infectious diseases. Review on time In order to keep track of your condition and have a good idea, you should follow the doctor’s instructions to come to the hospital regularly to review the blood routine and biochemical indicators, if you have any discomfort (such as rash, cold, fever, diarrhea), please come to the outpatient clinic for examination in a timely manner, and must be treated under the guidance of the physician. After the condition is stabilized, you can return to the local hospital for regular review. Return to the transplantation hospital for a comprehensive review six months, one year, or two years after transplantation to listen to the physician’s opinion.