Treating cancer via chemotherapy and radiotherapy inevitably leads to the death of some stem cells in the patient’s bone marrow. When the treatment is completed, stem cells are given to the patient intravenously so that they may replace the ones that were destroyed through a process called engraftment. These stem cells will settle in the marrow and eventually start to produce healthy blood cells.
There are three types of stem cell transplants, which are named based on the donor of the cells. We briefly outline some of the main differences between these transplants below:Autologous stem cell transplants are based on cells collected from the patient, before he had the cancer treatment. These stem cells are collected from blood or bone marrow tissue, and frozen. When the chemo and radiation therapy is completed, the cells are thawed and engrafted.The main advantage with this form of transplant is that there are no chances of having an infection passed on, or of the graft attacking your body through a condition called graft-versus-host disease.There may still be a possibility of graft failure. Also, autologous transplants don’t yield a ‘graft-versus-cancer’ effect, like other types of transplant do. Another disadvantage is that some of the stem cells harvested from your body through whichever method you choose, even the most advanced, could also have been cancerous. Studies are underway to determine how to best purge those cancerous cells before or after they were transplanted. Additionally, as the immune system is the same throughout the process and cancer cells were able to develop once, they may be able to do so again, even after the transplant.Autologous transplants of stem cells are used for conditions such as: leukaemia, multiple myeloma, lymphoma, neuroblastoma and testicular cancer, as well as some cancers children may suffer from.Tandem transplants or double autologous transplants are two consecutive treatments as described above. Two courses of chemo are followed by two stem cell transplants; both performed using cells collected from the patient before chemo started. They are usually performed within a 6-month time-frame.These transplants are occasionally used to treat multiple myeloma or advanced testicular cancer, but much research is required to minimise the risks, which are higher than those for single transplants.Allogeneic transplants are performed using stem cells harvested from a matching donor, usually a sibling. More recently, stem cells have been collected using blood from a newborn’s umbilical cord and placenta. Cord blood is very rich in stem cells with a tendency to multiply quickly, but the harvest from one cord is usually too low for an adult to use.The advantage of this technique is that the stem cells from the new donor produce their own immune cells, which could destroy any post-chemo cancer cells (graft-versus-cancer), or prevent new cancer cells from developing. Additionally, the donor’s stem cells don’t have the potential to include cancerous cells, and more can be donated at leisure.On the other hand, the graft might not take because the stem cells can be destroyed by the patient’s immune system before settling into the bone marrow. Otherwise, the patient may suffer from graft-versus-host disease. Another complication is that the patient is more vulnerable to infections, either from the donour, or from himself, which would have been kept in check under normal conditions. However, due to immunosuppressive drugs taken to allow the graft to take, infections can arise at any moment.This type of transplant is used to treat multiple myeloma, leukaemia, lymphoma, myelodysplastic syndrome and even aplastic anaemia.Mini transplants, or non-myeloablative transplants are used with patients who would not withstand complete bone marrow cells destruction during chemotherapy. Only some of the cancel cells and bone marrow cells are destroyed, just enough to allow the donor stem cells to settle.Because the donor stem cells thrive, they eventually have a graft-versus-cancer effect. Another advantage is the fact that blood cell counts aren’t decreased so drastically as with full-blown chemotherapy.A disadvantage is that the risk of graft-versus-host disease is the same as with other forms of transplant. Also, the chances of recurrence may be slightly higher, although studies are still under way. Syngeneic transplants are only limited to identical twins or triplets, where the sibling is the donor.The obvious advantage is that graft-versus-host disease will pose no threat, seeing as the new tissue is identical to the patient’s. Additionally, as the donor has no cancer cells, the chances of survival of the new stem cells are much greater.The main disadvantage is that the patient’s immune system is very much like that of the donor’s. So much so, in fact, that there will be no graft-versus-cancer effect.Half-matched transplants, or haploidentical transplants, are usually performed for people with no siblings to donate viable stem cells. In this case, parents or children of the patient will usually be the donors, but graft-versus-host disease is unavoidable as only half of the genetic content of the transplant is identical to the patient’s.
