Stem Cells and Cancer: Cure

There are three types of stem cell transplants that are used in cancer treatment: autologous, allogeneic and syngeneic. Autologous transplants entail harvesting stem cells from the cancer patient before they undergo treatment that will destroy the stem cells, freezing these cells and then transplanting them back into the patient after chemo or radiation is complete. This is a useful technique in that it leaves no chance for a negative graft vs host reaction; stem cells derived from another source might be rejected by the patient's body or cause an infection. However, autologous transplants are not always successful. They are most often used to treat leukemias, lymphomas and myeloma. One consequence of autologous transplants is that cancer cells me could potentially be collected along with stem cells when they are harvested from the body; these cancer cells would then be placed back in the patient's body. To combat this, some doctors use purging, a method of treating the harvested stem cells in order to remove any cancer cells. Purging has not proven to be effective thus far, and comes with the downside of potentially damaging or killing stem cells in the process. A more common method for removing the cancer cells from the stem cells is in vivo purging, wherein the patient is given medicine to kill cancer cells after the stem cells have been re-injected into his or her body. Sometimes, two autologous transplants will be done consecutively. This is called a tandem transplant. The tandem treatment is generally reserved for patients with advanced testicular cancer or multiple myeloma, and the risks of a single autologous transplants are compounded by the procedure.

Allogeneic transplants involve transplanting stem cells from an individual with the tissue type of the patient into the patient’s body following chemo or radiation. Occasionally, an allogeneic transplant can be performed by taking blood from the placenta and umbilical cord of a newborn and transplanting it into the cancer patient. This serves as a good source of stem cells, but is still not sufficient to fulfill an adult patient’s stem cell needs. Allogeneic transplants are beneficial in that the transplanted stem cells produce immune cells, which can aid the patient’s immune system in battling the cancerous cells. Also, in contrast with the autologous transplant, the allogeneic transplant does not involve a source that has a finite quantity of stem cells. However, allogeneic transplants are risky in that the transplant (graft) could be rejected by the host. The patient’s immune system might attack the new cells, and might damage or destroy some of its own healthy cells in the process.

The syngeneic transplant is a very specific subset of the allogeneic transplant. It can be done when a cancer patient has an identical sibling. Transplanting stem cells from one identical sibling to another is optimal; there is not a risk of the host rejecting the transplant, nor is there a chance of transplanting cancer cells into the body, which is a risk of the autologous transplant. However, the syngeneic transplant does not have the benefit that other allogeneic transplants have; the graft does not introduce new, foreign immune cells that could help attack cancer cells.