What Is a Stem Cell Transplant? Which Cancers Is It Used to Treat?

Blood cells are made in the bone marrow. Hematopoietic, or blood-forming, stem cells within the marrow produce blood cells throughout life. A stem cell transplant uses blood-forming stem cells to treat certain diseases.

Stem cell transplants are mainly used to treat cancers arising from the blood and bone marrow, such asmultiple myeloma, leukemia, and certain lymphomas . They are also used for aplastic anemia and myelodysplastic syndrome, which involve bone marrow failure, and for thalassemia, known as Mediterranean anemia. They are additionally used for certain rare solid tumors, including germ cell cancers. In recent years they have also been investigated for some immune system disorders known as autoimmune diseases.

Figure: Formation of other blood / immune system cells from a hematopoietic, or blood-forming, stem cell.

What Is the Difference Between a Stem Cell Transplant and a Bone Marrow Transplant?

Stem cell transplantation is not actually a new treatment: its history goes back to the 1960s. Initially, however, blood-forming stem cells could only be obtained from bone marrow, so the procedure was called a bone marrow transplant or marrow transplant . Today, stem cells can also be obtained from other sources. For example, certain drugs cause stem cells in the bone marrow to enter the bloodstream, and we collect them from the blood using devices for apheresis . When the collected product is used for treatment, the procedure is called a peripheral blood stem cell transplant (currently the most frequently preferred method in adults). Cord blood also contains a high concentration of stem cells. When these are collected and used for a transplant, the procedure is called a cord blood stem cell transplant . Thus, whether collected from bone marrow, blood, or cord blood, all procedures that collect stem cells and use them for treatment fall under the heading of stem cell transplantation.

The procedure is also named according to whose stem cells are used.

According to the donor, stem cell transplants are divided into allogeneic and autologous transplants

When the cells used are the patient’s own stem cells, the procedure is called an autologous stem cell transplant. If the patient’s own cells cannot be used and cells from another healthy person are used instead, it is called an allogeneic stem cell transplant.

What Is an Allogeneic Stem Cell Transplant?

An allogeneic transplant requires another person, a donor , to provide suitable stem cells. The donor’s tissue type must be compatible with the recipient’s, and the donor is usually a close relative. If no suitable relative is available, other matched donors through blood banks may be used. However, tissue types, medically called HLA, are so diverse that the likelihood of 2 randomly chosen people matching is between one in 100 thousand and one in a million. Siblings are therefore checked first because they share the same parents. Although Türkiye does not have its own bone marrow bank, requests can be made to international blood banks.

What Is an Autologous Stem Cell Transplant?

An autologous transplant does not require a matched donor, because the stem cells are collected from the patient. The cells are cleaned and frozen before being returned to the individual after chemotherapy drugs are given.

When treating cancers of the blood and bone marrow, stem cell transplantation is a means of allowing high-dose chemotherapy and radiotherapy, which are the main treatment; it is not the treatment itself. It therefore forms part of treatment for blood cancers but is not used for every blood cancer. It is not given as initial treatment: it is performed after treatments such as chemotherapy and radiotherapy have brought the cancer under control. Autologous and allogeneic transplants also serve different purposes. For example, autologous transplantation is mainly used for multiple myeloma and lymphoma, whereas allogeneic transplantation is the first choice in acute leukemias.

How Is a Stem Cell Transplant Performed?

For this potentially demanding treatment to be used, the disease must be serious enough to justify its risks or must not respond to other options. In autologous stem cell transplants using the patient’s own cells, the goal is to deliver very high-dose chemotherapy and/or radiotherapy. Higher doses of chemotherapy kill cancer cells more effectively. However, healthy cells are also affected by this intensive treatment, and the marrow becomes unable to produce blood cells. Survival is impossible without functioning marrow. Therefore, before high-dose treatment, the patient’s stem cells are collected and stored. Treatment resets the marrow and immune system, and patients stay in special bone marrow units to protect them against infection. After high-dose treatment finishes, the stored stem cells are transplanted back into the patient, settle in the marrow, and begin producing blood cells again. This process takes at least 2-3 weeks.

In an allogeneic transplant , the process is similar, but after high-dose chemotherapy and radiotherapy, the stem cell source is another donor with a compatible tissue type. Transferring another person’s blood stem cells has 2 important effects:

• first, the healthy donor’s immune cells destroy cancer cells, a beneficial effect;
• second, donor-derived cells may damage the patient’s own cells and cause graft-versus-host disease (GVHD), an adverse effect. The poorer the tissue match between donor and patient, the greater the GVHD risk. To reduce this effect, the patient needs prolonged treatment with immunosuppressive drugs that suppress the immune system. Allogeneic transplantation is therefore somewhat more intensive and complicated.

Donors may experience lower back pain, fatigue, and weakness for several days after stem cell collection. These mild symptoms can be relieved with nonsteroidal anti-inflammatory drugs .

Stem Cell Transplants for Autoimmune Diseases

Stem cell transplants are also being investigated for some autoimmune diseases. The most promising is multiple sclerosis, frequently known as MS, or “em-es,” multiple sclerosis, a disease of the protective myelin sheath around nerve fibers in the brain and spinal cord. Because MS affects both brain and spinal cord, it causes varied symptoms and is generally a progressive disease beginning between ages 20-40, with relapses. In Canada, people with multiple sclerosis who underwent autologous stem cell transplantation were reported to be able to walk, cycle, and even ski after treatment. Their story made headlines worldwide.

In conclusion, stem cell transplants are important medical procedures used for many diseases, especially blood cancers. They are also performed in our country to international standards, with high success rates.