Stem Cell Transplantation Overview

A stem cell transplant (SCT) is the best treatment available for many kinds of cancer. The SCT procedure was considered such a major development of biomedical science that the individuals responsible were awarded the Nobel Prize in Medicine in 1989. Continued refinement has made SCT safer, widely available, and part of the overall management strategy for several kinds of cancer.

Stem cells are early blood-forming cells that grow and mature in the bone marrow, but can circulate in the blood. Blood Stem Cell Transplants are used to either treat a disease with a dysfunctional stem cell like leukemia, or to restore bone marrow blood cell production when the very high doses of chemotherapy or radiation used to treat the cancer kill the stem cells and they need to be replaced like in Hodgkin Disease.

Stem cell transplants work to treat cancer by utilizing very high doses of chemotherapy or take advantage of the donor immunologic cells to treat the cancer. Higher doses of chemotherapy drugs and radiation therapy may kill more cancer cells than lower doses. When higher doses of therapy kill more cancer than lower doses, doctors say there is a “dose response effect.” The delivery of higher doses of therapy is referred to as “dose intensive or high-dose therapy”. Unfortunately, the higher doses of therapy used to destroy cancer cells also cause damage to normal cells. The body’s normal cells that are most sensitive to destruction by high-dose therapy are the blood-producing stem cells in the bone marrow and these can be effectively replaced with a stem cell transplant. When donor cells are used from someone other than the patient the transplanted immune system also treats the cancer.

Stem cell transplants are classified based on which individual donates the stem cells and from where the stem cells are collected. Stem cells may be collected from the bone marrow, peripheral blood or umbilical cord. Therefore, the terms bone marrow transplantationperipheral blood stem cell transplantation, and umbilical cord transplantation are utilized. There are important advantages and disadvantages to utilizing stem cells collected from these different sources. The second part of stem cell transplant classification is determined by who donates the stem cells. Stem cells may come from the patient (autologous), an identical twin (syngeneic), or someone other than the patient (allogeneic). Allogeneic stem cells are further classified by whether the individual donating the stem cells is related or unrelated to the patient and the degree of genetic similarity. Donors may either be HLA identical, mismatched or haplo-identical or “half” matched to the patient.

Autologous Stem Cell Transplant

Allogeneic Stem Cell Transplant

Stem Cell Transplant-Key Terms to Know

Allogeneic transplant
An allogeneic stem cell transplant is a procedure in which a person receives blood-forming stem cells (cells from which all blood cells develop) from a genetically similar but not identical donor. This may also be called an allogeneic stem cell transplant.

Autologous transplant
Means tissue taken from a patient and returned to the same patient. A transplant that uses stem cells taken previously from the patient (rather than stem cells from a donor is called an autologous stem cell transplant).

Bone marrow harvesting
A surgical procedure in which doctors insert long needles through the skin to withdraw bone marrow from the crests of the pelvic bones. Donors receive general or spinal anesthesia for the procedure.

Central line
This is also called a central venous catheter. It is a small, flexible tube inserted into a large vein near the heart to administer medications and draw blood. It is also used to give the stem cells that you receive during your transplant.

Conditioning
The process of preparing the patient to receive donated stem cells collected front the blood or bone marrow.  Often done through the use of chemotherapy, radiation therapy or both, conditioning is intended to do one of three things:

  • Eliminate cancer cells
  • Disable the immune system in people with an autoimmune disease
  • Destroy the bone marrow in people with other marrow-related diseases

High-dose conditioning leaves patients without an immune system or the ability to form new blood cells.  Alternatively, some patients may receive (RIC) reduced-intensity conditioning which is designed to weaken, but not destroy, their bone marrow and immune system so their body can more readily accept the donor’s stem cells.

Cord blood transplant The injection of umbilical cord blood to restore a patient’s blood production system that has been suppressed by chemotherapy and/or radiation therapy used in treating severe blood disorders such as aplastic anemia or cancer. Cord blood contains high concentrations of stem cells needed to produce new blood cells.

Counts
When your doctor or nurse talks about monitoring your counts, they are talking about your “blood counts” or the numbers of blood cells, including white blood cells, red blood cells, and platelets that are measured in your blood. Your transplant  team monitors your absolute neutrophil count (or ANC) while watching for signs of engraftment and your platelets closely.

Engraftment
A process in which a stem cell transplant becomes successfully integrated into the body. For example, bone marrow begins to manufacture new white blood cells, red blood cells, and platelets in the patient’s marrow cavities after bone marrow transplantation.  Signs of engraftment usually appear about 10 to 28 days after the transplant. The first sign is a rising white blood count.

Graft-versus-host disease (GVHD)
GVHD is a common side effect in people who receive cells from a donor (allogeneic transplant). It occurs when the transplanted cells recognize the recipient’s tissues as foreign and attack the tissues. This can cause a variety of problems, including skin rashes, liver problems, and diarrhea. There are two types of GVHD: acute GVHD, which often happens in the first three months after a transplant, and chronic GVHD, which can develop any time between three months and three years after the transplant. Both acute and chronic GVHD can be mild to serious. Medications and other treatments that suppress the immune system are used to prevent and treat GVHD until the donor cells stop attacking.

Haploidentical transplant
A transplant using stem cells from a donor whose HLA type is a half-match for the recipient. This may be an option for people who need a transplant but have not been able to find a more closely matched donor in typically occurs from a family member.

Hematopoietic cell transplant (HCT)
HCT is the general term for all transplants of stem cells, regardless of the source of the stem cells. Stem cells used in transplants may be collected from bone marrow; from blood circulating around the body, called peripheral blood; or from blood collected from an umbilical cord donated by a mother right after her baby’s birth.

HLA typing
HLA stands for human leukocyte antigen. Human leukocyte antigens are protein molecules that are inherited. HLA typing is the process of testing blood or other tissue samples from a patient who needs a transplant and from any potential donor to see how closely they match. The more HLA molecules two people share, the better the match. When two people share the same HLA molecules, their immune systems will not see each other as foreign and are less likely to attack each other.

Mini-transplant
See reduced-intensity transplant.

Minimally mismatched donor
In an optimal HLA match, the patient and donor share all eight or 10 HLA (human leukocyte antigen) markers (genes or proteins) tested. This is ideal for bone marrow or stem cell transplantation because it minimizes risks of rejection or graft-versus-host disease. New techniques allow effective transplantation using stem cells from a donor who matches the patient in only seven of eight or nine of 10 HLA markers—a minimally mismatched donor. Using these donors allows many more people to benefit from a potentially life-saving transplant.

Mucositis
Mucositis means inflammation of mucous membranes that line the digestive tract. It may occur as a side effect of chemotherapy or radiation, which can break down the rapidly dividing cells in these membranes. This can lead to ulcers and infection. Mucositis can occur anywhere along the digestive tract from the mouth to the anus. It can be mild to severe.

Non-myeloablative transplant
See reduced-intensity transplant.

Reduced-intensity transplant
A type of hematopoietic stem cell transplant where the patient receives reduced-dose conditioning that is designed to weaken, but not destroy, their bone marrow and immune system so their body will accept the donor’s stem cells.

Sinusoidal obstruction syndrome (SOS)

SOS, also called veno-occlusive disease (VOD), is a complication of transplants. In SOS, your liver cannot remove waste products from your body as well as it should. This is most likely to occur during the first month after a transplant.

Stem cell mobilization and collection
Stem cell mobilization means receiving medicine that causes stem cells to leave the tissues they normally occupy and to circulate in the bloodstream. Typically it takes a few days after receiving the medicine for the stem cells to mobilize. Then the stem cells are collected using a machine similar to those used for blood donation at blood banks. A catheter (tube) is placed in a donor’s large vein so blood can flow out of the body and into the machine, which separates the stem cells from the blood and returns the blood through another catheter. Collection typically takes a few hours, and donors leave the same day.

Veno occlusive Disease of the Liver-see sinusoidal obstruction syndrome (SOS)

Total body irradiation (TBI)
TBI is a radiation treatment to the entire body. It is used to destroy cancer cells and bone marrow cells in preparation for a bone marrow or peripheral stem cell transplantation.