Transplant Definitions

Allogeneic transplant
A transplant that uses stem cells taken from a donor (rather than using the recipient’s own stem cells).

Autologous transplant
A transplant that uses stem cells taken previously from the patient (rather than stem cells from a donor).

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. Most bone marrow donors are able to leave the hospital the same day. 

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

Conditioning therapy
This is radiation and/or chemotherapy given before a bone marrow or stem cell transplant. High- or moderate-dose conditioning is intended to do one of three things:

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

High- or moderate-dose conditioning leaves patients without an immune system or the ability to form new blood cells.

Alternatively, some patients (typically those who are older or have additional health problems) get low-dose conditioning in preparation for a mixed chimerism transplant. It’s 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
In this type of transplant, doctors use stem cells removed from blood taken from an umbilical cord donated by a mother right after her baby’s birth.

Counts
When your doctor or nurse talks about “monitoring your counts,” they are talking about levels of blood cells, including white blood cells, red blood cells and platelets. For instance, after your transplant, the team monitors your absolute neutrophil count (or ANC) while watching for signs of engraftment. Neutrophils are a type of white blood cell.

Engraftment
This is the process of transplanted stem cells starting to grow and develop. It means your bone marrow function and immune system—which were weakened or destroyed by conditioning—are beginning to recover. 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 treat GVHD symptoms until the donor cells stop attacking the body.

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 come from bone marrow; from blood circulating around the body, called peripheral blood; or from blood taken from an umbilical cord donated by a mother right after her baby’s birth, called cord blood. You may see or hear transplants called by one of these names based on the source of the stem cells: bone marrow transplant; peripheral blood stem cell transplant, or PBSC transplant; or cord blood transplant. The first HCTs were done using bone marrow. Many people are most familiar with the term “bone marrow transplant” and use this term regardless of the source of the stem cells. For simplicity, this is the term we use throughout this site.

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, they are said to be a good match. That is, their immune systems will not see each other as foreign and are less likely to attack each other.

Mixed chimerism transplant
For this type of transplant, patients get low-dose conditioning, designed to weaken, but not destroy, their bone marrow and immune system so their body will accept the donor’s stem cells. After conditioning, doctors infuse stem cells into the patient’s blood stream and wait for them to engraft, which means a new immune system develops alongside the patient’s remaining immune system. So for a time, the patient has a mixed immune system. The goals are for the new (transplanted) immune system to attack cancer cells that survived conditioning (called the graft-versus-tumor effect) and for this new system eventually to take over completely. A mixed chimerism transplant is an intensive procedure, but in some ways it is less intensive than a transplant with high- or moderate-dose conditioning (designed to destroy the bone marrow and immune system). This is why a mixed chimerism transplant is sometimes referred to as a mini-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.

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 blood stream. Typically it takes a few days after receiving the medicine for the stem cells to mobilize. Then the stem cells are collected using a pheresis machine: 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 are able to leave the same day.

Syngeneic transplant
This is the term for a transplant in which the donor and recipient are identical twins.

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 stem cell transplant.