Hematopoietic stem cell transplantation is divided into autologous hematopoietic stem cell transplantation and allogeneic hematopoietic stem cell transplantation.
- After autologous HSCT, oral anti-rejection drugs are not required.
- After allogeneic HSCT, anti-rejection medication is required.
Allogeneic hematopoietic stem cell transplantation is the process of taking stem cells from the donor, entering the patient’s body, and then these stem cells, growing within the patient’s bone marrow, can develop and form, mature hematopoietic cells. In this process, at the early stage of HSCT, when the donor’s stem cells are first introduced into the patient’s body, the immune cells of the patient will consider the patient’s immune cells as a foreign body and want to destroy them because the markings on the surface of the donor’s stem cells are different from those of the patient’s cells, and this will cause a rejection reaction. So in the early stages of transplantation, we must use anti-rejection drugs in order to allow the donor’s stem cells to grow smoothly in the patient’s bone marrow.
The second stage is that after the donor stem cells grow in the patient’s body, they generate immune cells, mainly lymphocytes, which have different surface markers than the patient’s cells, and they think the patient’s cells are rejection, so they have to be eliminated, so there is also rejection.
There are two types of immune reactions that can occur in hematopoietic stem cell transplantation:
- Grafts are recognized as “foreign” by the patient’s immune system, resulting in rejection and graft failure;
- Immunologically active cells in the donor’s bone marrow or hematopoietic stem cells attack the patient’s cells and tissues, causing graft versus host disease (GVHD).
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Graft versus host disease usually occurs after transplantation and can be classified as hyperacute, acute, or chronic depending on the timing:
- Acute graft-versus-host disease occurring within 10 days of transplantation is called hyperacute or fulminant graft-versus-host disease and is more aggressive;
- Acute graft-versus-host disease occurring within 100 days of transplantation is characterized by rash, diarrhea, and jaundice;
- Chronic graft-versus-host disease occurring 100 days after transplantation.
Anti-rejection drugs can prevent or reduce the occurrence of graft-versus-host disease by attenuating the rejection reaction in the body. Depending on the patient’s primary medical condition and the severity and duration of graft-versus-host disease, the physician may choose different anti-rejection drugs and the amount to take.
After bone marrow transplantation in patients with hematologic disease, it can take as early as 6 months to stop the anti-rejection medication if there is no significant rejection, and most patients can stop the anti-rejection medication in about 6 months to a year. If the rejection reaction persists, the medication will need to be taken all the time.