Understanding Stem Cell Transplant VICC Momentum

Vanderbilt-Ingram Cancer Center performs around 215 stem cell and bone marrow transplants each year, providing care leading up to the transplant, through all aspects of the procedure, and indefinitely after the transplant to monitor for complications. To address some common questions about the procedure, we spoke with Madan Jagasia, M.D., director of the Outpatient Transplant Program and section chief for Hematology and Stem Cell Transplant at Vanderbilt-Ingram.

What is a stem cell? (click to enlarge)

Stem cells or more specifically, in this case, hematopoietic stem cells are cells that can give rise to all the different types of mature blood cells the red blood cells that carry oxygen, the platelets involved in blood clotting, and a host of white blood cells, which are part of the bodys immune system and provide defense against infectious agents. Stem cells are self-renewing (i.e., they can produce more of themselves) and reside primarily in the bone marrow but also circulate in the blood.

For a stem cell transplant, the stem cells can come from a related or unrelated donor, from umbilical cord blood, or from the patient him/herself.

No, these are adult stem cells, from the blood or bone marrow. Even when the source of stem cells is umbilical cord blood, these are still adult stem cells and have nothing to do with embryonic stem cells.

Most of the stem cell transplants we do in adult patients are for bone marrow, blood or lymph node cancers. For example, in acute leukemia, the DNA of immature white blood cells is somehow damaged, which causes one or more of the white blood cell types to grow rapidly and accumulate in the blood. These abnormal cells do not function properly and crowd out normally functioning blood cells.

With a stem cell transplant (SCT), the patients stem cells are replaced with stem cells from either a healthy donor (called an allogeneic transplant) or with the patients own stem cells (called an autologous transplant). The goal is for the new stem cells to begin producing a new, properly functioning set of circulating blood cells.

Transplants can also be used to treat other blood and bone marrow diseases, like sickle cell anemia or thalassemia, for example.

An autologous transplant is more like a stem cell rescue than a true transplant it is just removing the stem cells and giving them back to the patient. We do bone marrow biopsies as part of the transplant process to make sure that the marrow is not heavily contaminated (with malignant cells). And from previous research, we know that if/when the cancer comes back, it is because of residual cancer cells in the patient that were not killed by the chemotherapy, not from the stem cells that were infused back.

Stem cell transplant illustration (click to enlarge)

In an autologous transplant, we collect the patients stem cells, treat the patient with high-dose chemotherapy and/or radiation to hopefully kill the cancer and destroy the existing bone marrow, and then infuse the stem cells back intravenously, which become the new marrow.

In donor (allogeneic) transplants, we dont always need as high a dose of chemotherapy for adult patients. The goal of the chemotherapy (in some patients, radiation is used along with chemotherapy) is to kill the recipients immune system, so that the donor cells wont be rejected. The donor immune system then fights the tumor a phenomenon that is called graft-versus-tumor effect.

The infused stem cells find their way to the bone marrow, where they will start producing blood cells. This generally takes around two weeks, but can take longer (three to four weeks) for stem cells from umbilical cord. By monitoring blood cell counts, we know when this engraftment of the stem cells has occurred.

In time, the donor cells which we call the graft begin attacking the patients remaining tumor cells. We call this graft-versus-tumor effect, and thats what leads to remission or cure.

Possibly. The challenge in allogeneic transplants is something called graft-versus-host disease (GVHD). The graft doesnt really know the difference between a patients tumor cells and healthy cells, so the donor cells may attack healthy tissue. GVHD is the bottleneck of transplantation today, so we try to limit or treat the damage done by the donors immune cells with steroids and other therapies. (See When the Treatment Fights Back)

The success rate or cure rate the percentage of patients living five years or more beyond transplant just depends on the disease for which the transplant was done and the source of the cells transplanted. To give examples of the extremes: for a person in their 20s with aplastic anemia (a bone marrow failure syndrome) receiving a related donor transplant, the cure rate is about 90 percent; on the other extreme, for someone with advanced relapsed leukemia receiving stem cells from umbilical cord blood, the cure rate might be between 10 percent and 15 percent.

Categories Summer 2012

Tags allogeneic transplant autologous bone marrow hematology Madan Jagasia Outpatient Transplant Unit stem cell transplant stem cells Summer 2012

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Understanding Stem Cell Transplant VICC Momentum