Stem Cell TransplantsStem cell transplants have been used increasingly over the past decade as novel new drugs are discovered, and researchers learn better ways to prevent or manage toxicity and side effects. Once, the last treatment of choice they are now frequently used in first relapse or even up front for patients with high risk disease.
Please check out the various SCT topics of importance on the left menu. Below are some additional topics of interest. If you can't find what you are looking for please click on the Questions link at the top to ask us a question.
On this page we will attempt to bring to you the most important information
that you want to know about when contemplating your own SCT. If you are looking
for a very detailed look at transplants then you should check out the BMT-Info
on-line book on the subject.
Many of you will be familiar with the term "Bone Marrow Transplant" and
essentially that is the same thing as a Stem Cell Transplant. The difference is
the source of the stem cells.
In a Stem Cell Transplant, the stem cells are collected from the circulating blood. This procedure is called aphaeresis. It is accomplished by inserting an IV into both arms of the donor. Blood is drawn out of one arm and pumped through a machine which separates out the stem cells, then the remaining blood is pumped back into the donor through an IV in the other arm. In many cases instead of using an IV in both arms they will use a central line similar to a Hickman catheter. Under normal circumstances there are usually very few stem cells circulating in the blood, therefore it is necessary to "mobilize" the stem cells out of the marrow and into the blood. This is done by giving the patient chemotherapy. Giving the patient chemotherapy kills many of the normal red and white blood cells. When this happens your bone marrow must go into overdrive to replace them which means the stem cells go to work. Stem cells are the cells which can become any type of blood cell, and which normally reside in the bone marrow. This sudden drop in red and white counts causes many of them to be pushed out into the circulating blood at this time. Then they can be collected by aphaeresis.
Allogeneic (al-o-gen-ay-ic)In this transplant someone else is the donor. Most often it will be a sibling
who has HLA
matched blood. When a sibling match is not available another relative may be
a candidate or the bone marrow registry may
be searched. Allogeneic transplants have the highest chance of curing the
patient, and in fact even those who have indolent varieties which are generally
not curable, may be cured with an allogeneic transplant. Unfortunately along
with this excellent chance of cure, also comes a corresponding risk of death.
Although the risk of death has been dropping over the past decade it is still
quite high and is in the range of 20-35%. The risks can be even higher for
patients already in poor health. This risk comes primarily from the Graft Versus Host Disease (GVHD). This is
caused by the donors immune cells mounting a response against the patient. This
is quite opposite to what you may be used to thinking. Most of us are familiar
with a typical transplant rejection where the patients body tries to reject the
donated organ. However since an SCT involves transplanting a new donor immune
system into the patient it is the donated immune system that is trying to reject
the patient. This can be fatal if it gets out of hand. There is a great deal of
research being done to find better ways to deal with GVHD. Check out the
ASH abstracts for lots of medical abstracts
about GVHD. GVHD is not all bad. In fact GVHD is part of what can cure the patient and a limited amount of it is a good thing for patients undergoing an allogeneic transplant. When the donors immune system mounts its attack on the patient, it also mounts an attack on the patients cancer because this healthy new immune system works properly and recognizes cancer as more foreign than the patient. If controlled properly the new immune system will kill the cancer and not the patient. The good aspect of Graft Versus Host Disease is often called Graft Versus Lymphoma (or Leukaemia ) in recognition of the beneficial effect that it has.
Min-AllogeneicA mini-allogeneic transplant is called by many names: Mini-allogeneic Reduced intensity allogeneic Non-myeloablative allogeneic
The procedure is the same as for a standard allogeneic transplant, but the chemotherapy they give is lower doses and therefore does not entirely wipe out the bone marrow (hence the term non-myeloablative). More and more studies are showing that you don't need to give a myeloablative dose of chemotherapy because the donors immune system does a lot of the work killing the lymphoma. This is the Graft versus Lymphoma effect which is part of the GVHD discussed above. It is the "good" part of the GVHD. Therefore lower (safer) doses of chemotherapy is all that is needed, which drastically lowers the mortality rate, down to about 5-10% and still provides the potential for a cure.
AutologousIn this transplant the patient donates their own stem cells/marrow. You might
think this sound strange since the patient already has cancer. However there are
two characteristics of NHL that are important to understand. First the patient
who has NHL has cancer of the white blood cells that circulate in the lymphatic
system. Therefore very few if any cancer cells are in the blood. Second, the
aphaeresis procedure collects only stem cells not white blood cells. In theory
there should not be any risk of collecting any cancer cells, but unfortunately
theory and fact don't quite match. The fact is that we have not perfected the art of separating the stem cells
from the blood during the aphaeresis procedure so some other blood products will
be collected. And although NHL does not normally circulate in the blood there
are always a few roaming cancer cells in the blood. This means that there is a
pretty good risk of getting some cancer cells in the stem cell harvest. Many
cancer centres are experimenting with various techniques to eliminate this
problem. There are some mechanical filtering systems in use in which the harvest
is run through a machine which is able to detect and eliminate the cancer cells.
However one of the more promising techniques for "purging" the harvest is to use
monoclonal antibodies such as Rituxan to purge the patient before the harvest is
collected. There is no risk of Graft vs Host Disease (GVHD) with this type of transplant since the patient is only getting their own stem cells. For this reason the risk of death is far lower (only 2%-5%). SyngeneicThere is also a third type of transplant which you might think of a a
combination of the two mentioned above. The syngeneic
transplant is a transplant where the donor and patient are identical twins.
Obviously this type of transplant is not very common because NHL alone is
uncommon enough, but someone who has an identical twin to get it would be even
less common. The advantage to this type of transplant is that the identical twin
is 100% guaranteed to match so there is no chance of Graft Versus Host Disease.
The disadvantage is that since there is no GVHD there is also no GVLE (graft
versus lymphoma effect). GVHD and GVLE are actually the same thing, it is just a
matter of degree. You must keep in mind that in a typical allogeneic transplant,
the donated stem cells recognized the patient as being "different" and they
attempt to attack the patient. This is GVHD and it can kill the patient if it
gets out of hand. While it is risky for the patient it is necessary because
those same stem cells will recognize any remaining cancer cells as VERY
different and attack them even more than normal cells. Graft versus Lymphoma
Effect (GVLE) is referring to this phenomenon where the donated cells attack any
remaining cancer cells and with some luck all the cancer cells, without
attacking too many normal cells and killing the patient.
With an identical twin as the donor neither phenomenon can happen. The donated stem cells are identical to the original ones the patient had, and both of them will fail to recognize the cancer cells as bad bad bad cells that should be killed. Luckily the donor cells also will not try to kill the patient so the risk of GVHD is eliminated. The reason for doing this type of transplant is that it means you can still give the patient extremely high doses of chemotherapy to kill all the cancer, and then rescue them with brand new stem cells that are guaranteed to match their blood type and also guaranteed not to be contaminated with any residual cancer cells. TriviaJust in case you are interested in trivia, SCT is a really shortened form of
what the procedure's proper name is. The proper name is "Peripheral Blood Stem
Cell Transplant" or PBSCT. This name reflects the fact that the stem cell
transplant came from the peripheral blood and not the bone marrow.
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