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.
BMT-info Guide to transplants
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)
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. In general the risk of dying from this procedure is quite high and is in the range of 20-40%. 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 not controlled properly.
In 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 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.