Stem cell transplant, also called as peripheral blood stem cell transplant, is a treatment to cure some types of cancers like leukemia, lymphoma, and myeloma. You have very high doses of chemotherapy, sometimes with the whole body radiotherapy. It has a better chance of killing the cancer cells but also destroys the stem cells present in bone marrows.
We require stem cells to survive. Surgeons can collect stem cells from your blood or a donor's. Following high-dose treatment, you have the stem cells into a vein through a drip to restore those that the cancer treatment has been destroyed.
Stem cell transplant means that you can have excessive doses of treatment. So there may be more possibility of curing cancer than with conventional chemotherapy.
Types of Stem Cell Transplants
In a usual stem cell transplant for cancer, very excessive doses of chemo are used, at times along with radiation therapy, to try to destroy all the cancer cells. This treatment also destroys the stem cells in the bone marrow. Following the treatment, stem cells are given to restore those that were destroyed. These stem cells are disposed into a vein, like a blood transfusion. As time passes, they settle in the bone marrow and start to grow and make healthy blood cells. This procedure is called engraftment.
There are three basic types of transplants. They are named based on who provides the stem cells.
1. Autologous– (the cells come from you)
In this kind of transplant, your stem cells are separated, or harvested, from your blood before you get treatment that kills them. Your stem cells are taken out either from your bone marrow or your blood and then frozen. After you get excessive doses of chemo and radiation, the stem cells are defrosted and returned to you. The only benefit of autologous stem cell transplant is that you are getting your cells back. You need not have to worry about the new stem cells attacking your body or about getting a new infection from another person.
2. Allogeneic– (the cells originate from a matched related or unrelated donor)
Allogeneic stem cell transplants use cells from a donor. In the most standard type of allogeneic transplant, the stem cells come from a donor whose tissue type closely matches the patients. The best donor is a nearby family member, generally a brother or sister. If you do not have a better match in your family, then a donor might be endowed in the general public through a national registry. It is sometimes called a MUD (matched unrelated donor) transplant. Transplants with a MUD are riskier than those with a relative who is a better match.
3. Syngeneic– (the cells coming from your identical twin or triplet)
It is a particular type of allogeneic transplant that can be used when the patient has an identical sibling – someone who has the same kind of tissue. The benefit of syngeneic stem cell transplant is that graft-versus-host disease will not be an issue. Also, no cancer cells are present in the transplanted stem cells, as there might be in an autologous transplant.
The only disadvantage is that because the new immune system is so much like the recipient’s immune system, there is no graft-versus-cancer effect. Every single effort must be made to kill all the cancer cells before the transplant is performed to help keep cancer from returning.
Sources of Stem Cells
Depending on the type of transplant that’s performed, there are three possible sources of stem cells to use it for transplant:
- Bone marrow ( either from you or someone else)
- The bloodstream (peripheral blood – from you or anyone)
- Umbilical cord (blood from newborns)
Significance of a Matched Stem Cell Donor
It is very vital that the donor and recipient are a close tissue match to avoid graft rejection. Graft rejection occurs when the recipient’s immune system identifies the donor cells as foreign and tries to kill them as it would a bacteria or virus. Graft refusal can lead to graft failure, but it is rare when the donor and recipient are well matched.
The more common trouble is that when the donor stem cells make their immune cells, the new cells may observe the patient’s cells as foreign and attack their new “home.” It is called graft-versus-host disease. The new, grafted stem cells strike the body of the person who got the transplant. It is another reason it is so important to find the closest match possible.