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Bone marrow transplantation is a life-saving medical process that has the potential to save many lives. Therefore, I will summarize the mechanism of bone marrow transplantation in two parts. In the first part, we will introduce diseases that require transplants, donor conditions, number of registrants, and matching.

Blood plays many important roles in the body, including transporting oxygen and nutrients, excreting waste products, and protecting against infection. Bone marrow, a spongy tissue inside bones, produces blood that plays these important roles. Bone marrow contains abundant hematopoietic stem cells that produce three types of blood cells: red blood cells, white blood cells, and platelets. Hematopoietic stem cells undergo repeated cell division and differentiate into red blood cells, white blood cells, platelets, etc. However, when abnormalities occur in hematopoietic stem cells, normal blood cannot be produced, leading to the development of blood diseases. Typical blood diseases include leukemia, aplastic anemia, and malignant lymphoma. Radiotherapy and anticancer drugs are commonly used to treat blood disorders, but hematopoietic stem cell transplantation is also an effective treatment. In this transplant, abnormal blood-forming stem cells affected by disease are replaced with healthy ones, restoring normal blood-forming function. Bone marrow transplantation is one of the typical methods of such treatment.

Suitable donors for bone marrow transplants must be between the ages of 18 and 54 and in good health. In addition, men must weigh at least 45 kg and women at least 40 kg. When a bone marrow transplant is required, blood-related family members are often the donors, but due to various reasons such as incompatibility, bone marrow may be donated to a donor other than the family. A bone marrow bank is an organization that acts as an intermediary between patients and unrelated donors. The bone marrow bank started accepting donor and patient registration in 1992, and in 2019, the number of new donor registrations reached a record high of 59,994, but since 2020, due to the impact of the coronavirus, the annual number has decreased. The number of new registrants has decreased, reaching 33,132 in 2022. Currently, more than half of the registrants are in their 40s or older, and people up to the age of 55 can become donors, so there are concerns that there will be a shortage of donors in the future.

Bone marrow bank donor registration is accepted at blood donation rooms, blood centers, health centers, etc. 2ml of blood will be drawn from your arm, the HLA type (white blood cell type) will be checked, and the data will be registered. A match search with the patient is performed using the registered data, and you will be contacted when you are selected as one of the donor candidates.

Bone marrow transplantation requires matching white blood cell types (HLA types) between the patient and the donor. The HLA type matching rate is said to be 1 in 4 (25%) among siblings. If there is no blood relation, the probability is said to be 1 in several hundred to tens of thousands of people. Furthermore, even if a donor is a match, it cannot be donated unless the donor is available or in good health, so only about half of the patients waiting for a transplant actually receive one. The most recent number of bone marrow transplant cases (between unrelated individuals) in 2022 was 1,055. The highest percentage of donors in their 30s is in their 30s, but the number of transplants performed by elderly people has been increasing in recent years, with about half of the annual transplants being performed by people over 50 years old.