Types of stem cell or bone marrow transplants are classified by the source of the donor cells.
In syngeneic stem cell transplants, the donor of the stem cells is the identical twin of the recipient. In this type of allogeneic transplant, stem cells are collected from the donor twin, and infused into the other twin following high dose chemotherapy.
Since the donor and the recipient have identical genetics, syngeneic transplants are in many ways more similar to an autologous transplant than allogeneic. As a result, there are both advantages and disadvantages to this type of transplant.
The main advantage to syngeneic transplants is that the recipient of the cells will likely not experience graft versus host disease (GVHD) because the donor cells will not identify the genetically identical tissues as being “foreign.” This usually eliminates the need for ongoing immune suppression. While there have been reported cases where recipients did experience GVHD after syngeneic transplant, the reasons for this are not completely understood.
There are two main disadvantages to this type of transplant. First, since the donor has identical genetics to the recipient, there may be concern that they are at higher risk of developing the same or similar cancers over time. In this case, the recipient would be no further ahead, since the new marrow may also eventually begin to produce abnormal cells and cause a relapse. This phenomenon would be more likely in the instance of childhood cancers.
The second, and most important, disadvantage to syngeneic transplants is that without graft versus host response there is no graft versus leukemia/tumor response either. This principle is based on the ability of the donor cells to recognize any cancer cells that remain in the recipient after high dose chemotherapy to be abnormal or foreign and attack them.
Despite the disadvantages to syngeneic transplants, the option of having a sibling that is closely matched enough to be a stem cell donor is advantage in itself.
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