Before a donor stem cell transplant, you’ll be given treatment to get you ready for your donor’s cells. This is called conditioning treatment. During this time, the doctors may talk about days as numbers. The day of your transplant (stem cell infusion) is Day 0. The days before the transplant are counted as Day -8, Day -7, and so on, until Day 0 when you have the transplant. The days after the transplant are counted as Day +1, Day +2, and so on.
Your conditioning treatment will be completed 24–48 hours before the transplant (Day -2 or Day -1).
You will usually have several different chemotherapy drugs for your conditioning treatment. These can be given in different combinations. Some people also have radiotherapy to the whole body, which is known as total body irradiation, or TBI.
The conditioning treatment is given:
- to prepare your immune system to accept the donor stem cells
- to reduce the risk of your immune system attacking the donor stem cells
- to remove any remaining cancer cells from your body.
Conditioning treatment can take up to a week. The conditioning treatment starts before the donor’s stem cells are collected. If your donor is a relative, their cells will be collected on Day -1 (the day before the transplant). If the donor is not related, their cells will be collected on Day -2 (two days before the transplant date). This is to make sure you’re ready for the transplant soon after the stem cells are available.
There are different ways of giving conditioning treatment and also different levels of intensity (strength) of treatment. The treatment you have will depend on the type of cancer or leukaemia you have, your general health and any chemotherapy or radiotherapy treatment you’ve had in the past.
High-dose chemotherapy, sometimes with total body irradiation, is given to destroy your bone marrow and immune system. You are then given donor stem cells to replace your immune system and to attack any remaining cancer cells in your body.
This uses less intense doses of chemotherapy or radiotherapy, which should mean fewer complications. Reduced-intensity conditioning weakens your immune system enough to allow the donor stem cells to grow in your bone marrow. When both your donor’s cells and your own cells are in your system, this is called mixed chimerism. The donor stem cells will gradually replace your immune system and attack any remaining cancer cells in your body.