This page was reviewed under our medical and editorial policy by
F. Marc Stewart, MD, Hematologist-Oncologist, City of Hope | Duarte
This page was reviewed on June 15, 2023.
Bone marrow transplants and stem cell transplants replenish stem cells in bone marrow that were destroyed by high doses of chemotherapy and/or radiation therapy to kill cancer or treat another disease.
The main difference between the two procedures is the origin of the transplanted stem cells.
Stem cell transplants are more common than bone marrow transplants because stem cells are easier to collect from the body. They also may be collected more quickly, and the recovery process may be faster than with a bone marrow transplant.
However, if doctors are unable to collect stem cells from the patient, bone marrow may be used.
Stem cells are cells that don’t yet serve a particular function, but have the ability to become specialized and turn into different types of cells. There are two overarching categories of stem cells—embryonic stem cells, which develop into all the different cell types needed to form a baby, and adult stem cells, which repair and replace dead or damaged cells. Adult stem cells are located all over the body. The stem cells used in transplants are found in the bone marrow (hematopoietic stem cells) or blood (peripheral blood stem cells) and are responsible for restoring and renewing blood cells.
Bone marrow is the soft, spongy material inside bones. Immature hematopoietic or blood-forming stem cells are in bone marrow. Hematopoietic stem cells divide to form more blood-forming stem cells or mature into:
Bone marrow and stem cell transplants may help treat certain types of cancer and other diseases, including:
There are two main types of stem cell and bone marrow transplants:
Autologous transplant: An autologous transplant uses stem cells removed from a patient’s own bloodstream or bone marrow and stored while the patient receives chemotherapy or radiation therapy. After treatment, the patient’s healthy stem cells are thawed and reintroduced into the bloodstream to help replace the blood cells destroyed during the treatment.
Allogeneic transplant: An allogeneic transplant uses stem cells harvested from a matched donor. These cells may be collected from a donor’s blood, bone marrow or from donated umbilical cord blood that was frozen and stored after a birth. The donated cells may come from a family member of the patient or an unrelated donor with genetically similar blood cells. After the patient undergoes treatment, the donated cells are infused into the patient’s bloodstream.
The bone marrow and stem cell transplant process is complex and takes time. Here are the general steps used in the procedure are listed below.
Collection or harvesting of stem cells: The first step is collecting stem cells from the patient or harvesting them from a donor. Medication is given to increase stem cell production, and stem cells are then collected from the bloodstream or bone marrow. To collect blood stem cells, a vein is used. If bone marrow is being used, cells are gathered through a long needle via a procedure called a bone marrow harvest.
Pretransplant conditioning of cells. Before the transplant procedure, chemotherapy is administered as a pretransplant treatment, sometimes along with radiation therapy. This treatment helps make the body more receptive to the transplanted cells.
Transplant procedure. During the transplant procedure, the stem cells or bone marrow are infused into the patient’s bloodstream via a catheter.
Recovery. During the recovery process, patients are closely monitored and treated for any side effects. Antibiotics are also given to reduce the chance of an infection.
The process for collecting cells varies depending on whether the transplant is autologous or allogeneic and whether the cells come from the bloodstream or bone marrow.
For autologous transplants, the doctor gathers the cells before the conditioning phase of treatment. This phase involves high-dose chemotherapy or radiation therapy, which may destroy healthy cells in addition to cancer cells, so it’s important that the doctor collects healthy cells for the transplant prior to treatment.
For allogeneic transplants, the doctor needs to secure suitable donor cells before treatment. Suitable donor cells have the same human leukocyte antigen (HLA) markers as the patient’s cells. HLA markers indicate whether cells belong in a body, so if the HLA markers match, the patient’s body is more likely to accept the donor cells.
To collect stem cells, the patient (for an autologous transplant) or the donor (for an allogeneic transplant) undergoes a procedure called apheresis. This procedure starts with a five-day course of injections of the drug filgrastim, which stimulates the growth of stem cells. Next, a machine collects blood from the patient (or donor) via an IV (an intravenous line), spins the blood to separate and collect the stem cells, then recirculates the blood back into the patient (or donor).
The stem cells are frozen until needed. Following chemotherapy or radiation therapy, the doctor infuses these cells into the patient’s bloodstream, where they form more blood cells.
To collect stem cells, bone marrow is removed from the back of each hip of the patient (for an autologous transplant) or the donor (for an allogeneic transplant) with a large needle. The amount of bone marrow collected varies based on the recipient’s weight. During this procedure, the patient or the donor is under general anesthesia.
There’s no one-size-fits-all treatment to ready a recipient for a bone marrow or stem cell transplant. Treatment is based on the type of cancer and chemotherapy or radiation therapy patients may have had in the past.
In general, once a patient has been deemed a suitable candidate for a transplant and cells have been collected, the patient will begin the conditioning phase of treatment with chemotherapy, radiation therapy or both. This is done to make room for the transplanted stem cells, suppress the immune system to lessen the chance of transplant rejection and destroy remaining cancer cells.
If the stem cells were frozen, they must first be thawed. Since the freezing process involves the use of preservatives, the recipient may need to take medication to reduce the risk of reacting to the preservatives.
During the actual transplant, the stem cells are infused into the recipient’s bloodstream. This process is similar to getting a blood transfusion. Once infused, the stem cells travel through the bloodstream into the bone marrow. If a donor was used, the recipient’s new blood cells contain the DNA or genetic material of the donor.
A bone marrow transplant is usually performed in a specialty hospital or medical center. Recipients will stay in a special transplant area to reduce the risks of developing an infection—though the stay may vary in length. Infection risk is heightened for at least the first six weeks after the transplant until the new stem cells start making infection-fighting white blood cells.
The bone marrow transplant process isn’t painful, and the patient is awake during the procedure, which takes several hours. Because side effects are always possible after any medical procedure, it’s important for patients to follow their doctor’s instructions during and after the procedure.
Bone marrow and stem cell transplants may come with a number of side effects before the procedure, shortly after and further down the road.
Conditioning with chemotherapy and radiation therapy before a bone marrow or stem cell transplant may cause mouth sores, nausea, vomiting and/or infection. There’s also a risk of bleeding and the need for blood transfusions because the conditioning treatment destroys the body’s ability to make platelets. Other side effects include pneumonitis (inflammation of the lung tissue) and other lung conditions.
Some of the more serious complications may include:
GVHD occurs when donated stem cells (the “graft”) misfire against the healthy tissues in the body (the “host”). This may only happen with a donor transplant, not the patient’s own cells. It may be acute (occurring within the first 90 days after a transplant) or chronic (starting anywhere after the first three months and up to several years later.
SOS, previously known as hepatic veno-occlusive disease (VOD), may occur when tiny veins and other blood vessels inside the liver become blocked after an allogeneic transplant. This is a rare but serious complication, and it tends to happen within three weeks after transplant.
Graft failure occurs when the body doesn’t accept the graft. As a result, the stem cells don’t enter into the bone marrow and multiply. This is more likely to occur when the patient and donor aren’t well matched.
Bone marrow and stem cell transplant complications may occur much later, too, and may include:
Recovery is a process of stages that may take weeks to months. Most patients report feeling tired after a transplant. Patients must meet certain criteria to be discharged from the hospital. For instance, patients must be fever-free for 48 hours and be able to keep medication down.
In addition, any nausea, vomiting and diarrhea should have abated, and blood counts need to reach certain levels, according to the American Cancer Society. Specifically:
It may take a year or longer for blood counts to get close to normal and the immune system to be healthy.
The risk of infection is the greatest immediately after the transplant, when counts are at their lowest. The doctor may prescribe antibiotics to help keep infections at bay. It takes about two to six weeks to begin seeing a steady return to normal blood counts.
It’s important to take many precautions during this time:
Some bone marrow and stem cell transplant recipients may need to stay in the hospital or very close to the transplant center for the first three months, since there will likely be daily or weekly exams and other tests during this time.
A trusted caregiver for a bone marrow or stem cell transplant recipient is essential to the recovery process. This person will need to be on call during the hospital stay and after discharge to get a patient to and from follow-up appointments, make sure he or she takes medications as directed, monitor him or her for complications, and support him or her during recovery.
Bone marrow and stem cell transplant survival rates vary depending on the type of disease, age, overall health and disease progression. Most often, transplant outcomes data is grouped by disease.
A 2021 study in JAMA Oncology found that among a cohort of 4,741 patients, after an allogeneic bone marrow or stem cell transplant, about 8.7 years of life were lost compared to the general population. Yet, over the past 40 years, fewer people died in the later decades following a bone marrow transplant. Advances have helped patients live longer. The reduction in death rates is a positive trend, but having had a bone marrow transplant at some point puts patients at higher risk for disease recurrence, infections, other cancers, heart disease, lung disease and earlier mortality compared to the general population.
Various studies have compared outcomes between stem cell transplants and bone marrow transplants. While some studies have revealed slight differences in outcomes, more research is needed.
Detailed information on transplant outcome data may be found at the National Marrow Donor Program.
With recovery, 100 days post-transplant is considered a key milestone. This is when the greatest risks may be greatly reduced and the stem cells have started to do their job.