In this procedure, the patient's own blood stem cells are collected and frozen ahead of therapy that would normally be too intensive without backup blood stem cells. After the intensive therapy, the previously collected stem cells are transplanted back into the patient in a manner similar to a regular blood transfusion. The return of the blood stem cells helps patients overcome the destruction of white and red blood cells and platelets. Without new stem cells, patients would have too few white cells to ward off a life-threatening infection. They would also develop anemia because of low numbers of red cells and bleeding problems caused by too few platelets, which help the blood to clot.
Why High-Dose Therapy?
Certain cancers can respond to chemotherapy with a decrease in the number of cancerous cells with every cycle of chemotherapy. For some cancers, a point is reached where a small number of residual cancer cells remain that do not respond as well to the standard repeated doses of chemotherapy, particularly those of blood cancers: leukemia, lymphoma and multiple myeloma. However, these residual cells may be destroyed by higher doses of chemotherapy. As long as patients receive adequate blood stem-cell support, chemotherapy doses several times higher than the conventional maximum can be tolerated. Some blood cancers can be cured this way.
Even when high doses of chemotherapy with blood stem cell support do not "cure" certain cancers, they often can cause the cancer cells to be severely depleted and suppressed. Clinical trials have shown that diseases like multiple myeloma and follicular lymphoma, which usually involve the bone marrow, can be controlled for longer periods using higher doses of chemotherapy. This also can help in certain forms of amyloidosis where the overproduction of protein by plasma cells in the bone marrow leads to systemic disease. As a result, you may hear that the goal of some autologous transplant procedures is disease "control" rather than “cure."
Allogenic (Non-self donor) Stem Cell Transplant
In this procedure, a donor's HLA-matched blood stem cells are collected and transplanted into the patient. HLA matching is the process of determining if the donor and the patient share certain critical genes that educate the immune system which is different than a blood type. The safest allogeneic transplants occur when donors and patients share the same HLA genes. Because these genes are all on chromosome 6 and because we inherit a chromosome 6 from each parent, there is a 25% chance that any one brother or sister will have the same HLA genes. Recent advances in our understanding of immune recovery after an allogeneic transplant have allowed us to also use donors who only match at one chromosome 6 or "haplo" donors in patients without other donor options. This is still an experimental procedure in our program, offered on a protocol basis. When there is not a full or haplo match donor in the family, we may need to refer the patient to a center than can find a match among the millions of volunteer donors in the international HLA registry.
Before an allogeneic transplant, the patient is admitted to the hospital to undergo “conditioning” therapy to prepare them to receive the cells from the donor. In some cases, where the blood cancer needs to be suppressed more, intensive treatment with chemotherapy or radiation are used. However, often the goal is to simply replace the patient's bone marrow and immune system with new cells from the donor rather than kill huge numbers of cancer cells. In this case, less intensive therapy can be used in a "mini" allogeneic transplant.
The Engrafted Immune System
After an allogeneic stem cell transplant, the patient's bone marrow cells are replaced with new, healthy donor cells. These cells will produce the white blood cells, red blood cells and platelets that the patient needs for a healthy blood system. Moreover, all of the cells that comprise the patient's immune system are replaced, resulting in a completely new immune system. These new donor immune cells often can recognize any residual cancer cells in the patient as "foreign invaders" and directly attack and kill them. This is a very useful therapy for patients that do not respond well to other standard therapies. Every cancer has a different sensitivity to this immune attack, so this treatment does not work with all cancers. Fortunately, most blood cancers do respond.
Graft versus Host Disease (GVHD)
Unfortunately, there is a potential downside to allogeneic transplant in that the new immune cells may recognize some normal parts of the patient as "foreign invaders" and attack these normal cells. This complication is called "graft versus host disease," where "graft" refers to the donor cells and "host" refers to the patient. The better the HLA match between the donor and patient, the lower the chances of severe GVHD. However, with newer techniques even “haplo” donors can be used successfully as noted above. Graft versus host disease can be a life-threatening problem and is the major complication of an allogeneic transplant. If an allogeneic transplant is part of your therapy, we will discuss this issue with you in detail.