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Bone marrow is the important tissue in the human body that makes red blood cells, white
blood cells, and platelets.
It is found in the center of most bones, and its functioning is essential to live.
A bone marrow transplant, also called a stem cell transplant replaces unhealthy bone marrow
with healthy cells called hematopoietic stem cells.
This medical procedure can be used to treat certain types of cancer, such as leukemia,
myeloma, lymphoma, and other blood and immune system diseases that affect the bone marrow.
There are two main types of stem cell transplants.
The first is called an autologous stem cell transplant, and uses the patient's own stem
cells.
The second type is an allogeneic stem cell transplant, which means the stem cells come
from another person, called a donor.
In an autologous stem cell transplant, we take the patient's own stem cells out of the
bone marrow, and we put them essentially in storage, in a freezer.
We then deliver very high doses of chemotherapy and rescue the patient's bone marrow with
their own stem cells that have been preserved ahead of time.
And the key there is autologous, or "auto" is the Latin root for "self."
The other type of transplant is called an allogeneic transplant and here the goal is
very different.
Here we have a donor, somebody who is not the patient, usually a brother or a sister,
sometime an unrelated donor from the International Bone Marrow Transplant Registry, or we can
sometimes have a cord, a placental cord, or even a child or parent.
After a donor is identified, the patient having an allogeneic transplant will get specific
treatments, such as high dose chemotherapy and sometimes radiation therapy beforehand,
to prepare their body to receive the donated cells.
We give them treatment that suppresses their own immune system in addition to trying to
get rid of as much of their cancer as possible.
We then take somebody else's stem cells, and give them to the patient.
And these stem cells do two things.
The first thing they do is they give back a normal bone marrow to that patient.
Normal red cells, white cells, and platelets.
The other thing those stem cells do is give the patient a new immune system, and
that new immune system recognizes the cancer as not belonging, and is able to get rid of
it.
We call that graft-versus-lymphoma, or graft-versus-leukemia, or graft-versus-malignancy effect.
They are different terms for the same process.
Now there are some side effects in that sometimes the stem cells not only attack the cancer,
but they can attack the patient themselves and some of their normal tissues.
And we call that "graft-versus-host" disease.
Trying to balance graft-versus-malignancy and graft-versus-host disease is one of the
major challenges of this procedure that we call allogeneic stem cell transplant.
The process to find a donor begins with the patient's blood being tested to find out their
HLA type.
HLA stands for Human Leukocyte Antigens, which are certain proteins on your cells.
The best donor has HLA proteins that match the patient's HLA type as much as possible.
The closer the match, the lower the risk of serious side effects.
When performing an allogeneic stem cell transplant, it's really important to have the best matched
donor possible.
In general, if there is a full brother or sister that have the same two parents, the
likelihood of somebody matching is about 1 in 4.
However many people don't have a matched sibling, and in that case, we go out to the registry,
which is an international group of volunteer donors, and we can look with very high-resolution
typing, something called molecular typing, to see if we can find somebody from around
the world who matches our patient.
If there is nobody in the registry, which can happen, there are other types of transplants
that are now really exciting, because they've opened up the opportunity for transplant to
many more patients.
This includes transplants using placental cord stem cells, or using something called
a haplo donor, which is somebody who is half-matched, and could be a child or parent or sibling.
Most transplants are done in a hospital setting, and the patient usually spends several weeks
there or longer.
The patient's recovery time after a stem cell transplant varies depending on the type of
transplant, how closely the HLA types matched if it was an allogeneic transplant, and other
factors.
Recovery starts in the hospital, and at some point the patient will transition to continue
their recovery at home.
The recovery process after an autologous stem cell transplant is usually several months,
and may be up to a year.
For an allogeneic transplant, the process is a little bit more complex because there
is a separate donor who is involved.
In an allogeneic stem cell transplant the patient will receive some type of chemotherapy
to suppress their immune system and give one last shot at getting rid of whatever leftover
cancer there is.
They then receive their stem cells from their donor, and that process again, is typically
done in the hospital, although there are some places that will do an outpatient transplant.
This is about 18-21 days in the hospital, while we wait for the new stem cells to take
hold and create the normal blood elements.
The recovery process after an allogeneic transplant is a bit more complicated and can take much
longer.
For one thing, patients have to stay on anti-rejection medications, usually for several months after
the transplant, and then that gets tapered off.
The decision to recommend a transplant for any patient is a highly complicated
one, that is best done in a setting where we have large teams that focus on stem cell transplants.
There are risks associated with transplant that include risk of infection, organ dysfunction,
and as we discussed before, graft-versus-host disease and graft-versus-cancer effects.
These are very complicated situations, and its best served in a tertiary care center.
Talk with your doctor about the type of transplant recommended for your treatment, and possible
side effects.
To learn more about bone marrow and stem cell transplantation, please visit ASCO's patient
information website, Cancer.Net.
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