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Non Hodgkin's Lymphoma |
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Stem Cell Transplant information |
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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 traditional Bone Marrow Transplant, the stem cells are collected by placing the donor under a general anaesthetic, then using a surgical procedure to extract bone marrow directly from the bones. This consists of a number of needle insertions to extract the marrow. The patient feels no pain since they are asleep, but after waking up they will in all likelihood be very sore for a number of days. 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. For patients with NHL, Bone Marrow Transplants are largely being abandoned in favour of Stem Cell Transplants. This is because the patient will recover significantly faster with an SCT. They engraft faster, have fewer complications and the death rate appears to be lower. Yet in some cases a bone marrow transplant is the only choice. Some donors are just not able to mobilize enough stem cells into the circulating blood to be collected. When this happens the Bone Marrow Transplant becomes necessary. Whether the stem cells come directly from the bone marrow or from the circulating blood, there are two main types of transplant. 1. Allogeneic (al-o-gen-ay-ic) 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. 2. Autologous 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%). 3. Syngeneic 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. Just 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. But even that is a short form. A really really formal long name is:
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