How is a bone marrow transplant done?
The basic principle of a bone marrow transplant is the implantation of healthy blood stem cells to the patient, in the hope that the transplanted cells will 'repair' the bone marrow and restore its normal function. The critical step in this procedure is 'engraftment', meaning that the transplanted cells thrive inside the patient and repopulate the bone marrow. If engraftment is successful, the transplanted cells will start to produce new healthy blood cells within 2-3 weeks.
In some cases the transplanted cells may be from the patient, this being known as an autologous transplant. In most cases however this is not appropriate due to this risk of putting diseased cells back into the patient. Therefore, in the majority of cases cells from a healthy donor are used. This is known as an allogeneic transplant. The key steps in an allogeneic bone marrow transplant for leukemia are as follows:
- A suitable source of donor cells is identified: this is usually from a sibling, alternatively a parent or child, or from an unrelated, volunteer donor.
- Donor cells are harvested from the bone marrow or peripheral blood.
- Patients undergo 'conditioning' such as chemotherapy: this aims to kill the malignant cells present in the bone marrow before the healthy donor cells are transferred. Sometimes complete ablation of the bone marrow is the goal (high intensity conditioning), but in older, less fit patients partial clearance may be attempted (reduced intensity conditioning).
- Donor cells are infused into the patient: this is done in a similar way to a blood transfusion i.e. through an intravenous line. The volume of cells and time taken to infuse can vary depending on the way the donor cells were collected.
- Patient is closely monitored following the transplant: the first sign of successful engraftment is usually an improved white blood cell count.