A stem cell transplant replaces damaged or destroyed blood-forming cells in your bone marrow with healthy ones. It’s most commonly used to treat blood cancers like leukemia and lymphoma, but also treats certain immune disorders and other conditions where the bone marrow stops working properly. The transplant itself isn’t a surgery. Healthy stem cells are infused into your bloodstream through a catheter, much like a blood transfusion, and those cells find their way to your bone marrow where they begin producing new blood cells.
Types of Stem Cell Transplants
There are three main types, defined by where the stem cells come from.
In an autologous transplant, you are your own donor. Your stem cells are collected, stored, and returned to you after intensive treatment destroys your existing bone marrow. The advantage is that your body won’t reject its own cells, and there’s no risk of the transplanted immune cells attacking your healthy tissue. The downside is that the transplanted cells can’t help fight any remaining cancer the way a donor’s immune cells can, and there’s a small chance cancer cells survive the collection process and get reinfused.
In an allogeneic transplant, the stem cells come from another person, usually a sibling or an unrelated donor whose tissue type closely matches yours. Donor cells carry a powerful benefit: they can recognize and kill remaining cancer cells in your body, a phenomenon called the graft-versus-cancer effect. That immune advantage comes with a trade-off, though. The donor’s immune cells may also attack your healthy tissues, a complication called graft-versus-host disease.
A syngeneic transplant is a special case where the donor is your identical twin. Because your tissue types are a perfect match, there’s no risk of graft-versus-host disease, but there’s also no graft-versus-cancer benefit.
How Donors Are Matched
Your immune system identifies cells as “self” or “foreign” using proteins called human leukocyte antigens, or HLA. You have 12 unique HLA markers, and the possible combinations number in the millions. Matching starts with a blood draw or cheek swab sent to a lab for HLA typing. Your results are then compared against family members and the national donor registry.
A full match means the donor shares all the same HLA markers. A partial match shares most but not all. A haploidentical match, where donor and patient share only half of their HLA markers, is increasingly common thanks to advances in post-transplant medications that suppress rejection. This has dramatically expanded the pool of eligible donors, since a biological parent, child, or half-matched sibling can serve as a donor. One study of haploidentical transplants for acute lymphoblastic leukemia found five-year overall survival of 64%, comparable to results from fully matched donors in well-resourced medical centers.
Closer HLA matches improve the odds of successful engraftment, reduce complication risk, and lower the chance of graft-versus-host disease.
Where the Stem Cells Come From
Stem cells can be harvested from three sources: bone marrow, peripheral (circulating) blood, and umbilical cord blood. Bone marrow is collected through a needle inserted into the donor’s hip bone under anesthesia. Peripheral blood stem cells are collected after the donor takes medication for several days that pushes stem cells out of the marrow and into the bloodstream, where they’re filtered out through a process similar to donating blood. Cord blood is collected from the umbilical cord and placenta after a baby is born and banked for future use.
Each source has trade-offs. Peripheral blood stem cells tend to engraft faster. Cord blood requires a less precise HLA match, making it useful when no well-matched adult donor exists. Recent research combining cord blood with partially matched donor cells showed one-year disease-free survival of 82%, compared to 66% when bone marrow was used in the same setting, with lower rates of severe infection and transplant-related death.
The Transplant Process, Step by Step
The process unfolds in distinct phases, typically requiring several weeks in the hospital.
Conditioning
Before you receive new stem cells, your existing bone marrow needs to be cleared out. This phase, called conditioning, uses high-dose chemotherapy and sometimes radiation to destroy cancer cells and suppress your immune system so it won’t reject the transplant. Conditioning typically lasts one to several days, counted backward from transplant day (Day -4, Day -3, and so on). Some treatment plans include a rest day between the last dose of chemotherapy and the transplant to give the drugs time to clear your body so they don’t harm the incoming stem cells.
Conditioning intensity varies. Full-intensity (myeloablative) conditioning completely wipes out the bone marrow and is more common in younger patients who can tolerate the side effects. Reduced-intensity conditioning uses lower doses, which causes less tissue damage and fewer complications but carries a somewhat higher risk of cancer relapse. In one comparison, severe graft-versus-host disease occurred in about 19% of patients receiving full-intensity conditioning versus just 2% of those receiving reduced-intensity treatment. Reduced-intensity regimens are often used for older patients or those with other health conditions.
Transplant Day
Day 0 is transplant day. The stem cells, previously collected and stored, are infused into your bloodstream through a catheter at your bedside. It looks and feels similar to receiving a blood transfusion. You’ll receive medications about 30 minutes beforehand to reduce potential side effects during the infusion. The stem cells then travel through your bloodstream to your bone marrow on their own.
Engraftment
Once the stem cells reach your bone marrow, they begin dividing and producing new blood cells. This process, called engraftment, typically takes 10 to 14 days but can take up to 30 days depending on the disease and treatment. During this waiting period, your blood cell counts are dangerously low, leaving you highly vulnerable to infection and bleeding. Your medical team monitors your blood counts daily, and you’ll likely need transfusions and antibiotics until your new marrow takes hold.
Graft-Versus-Host Disease
Graft-versus-host disease is the most significant complication of allogeneic transplants. It happens when the donor’s immune cells see your body’s cells as foreign and attack them. The donated blood cells carry HLA markers from your donor, not from you, and if the mismatch is large enough, those cells treat your own tissues as threats.
The acute form usually appears within the first 100 days and commonly affects the skin, gut, and liver. Symptoms include rash, itching, diarrhea, nausea, abdominal cramping, and jaundice. The chronic form can develop months or even years later and affects a wider range of organs. It can cause skin tightness and swelling, hair loss, dry mouth, mouth sores, dry or gritty eyes, shortness of breath, muscle weakness, joint stiffness, and fatigue.
Prevention starts with the closest possible HLA match. After the transplant, you’ll take immune-suppressing medications to keep the donor cells in check. Even so, some degree of graft-versus-host disease is common with allogeneic transplants, and mild cases may actually be beneficial because the same immune activity that causes the disease also fights remaining cancer cells.
Survival and Outlook
Outcomes vary widely depending on the type of transplant, the disease being treated, your age, and how well the donor matches. For autologous transplants, five-year overall survival is roughly 72% for conditions like AL amyloidosis, with younger patients (under 60) faring better at around 80% compared to 66% for those 60 and older. Treatment-related mortality in the first year was about 3% for younger patients and 11% for older ones.
For haploidentical allogeneic transplants in acute leukemia, five-year overall survival of around 64% has been reported, with relapse and non-relapse mortality rates of roughly 17% and 22% respectively. Early transplant-related death (within 30 days) in that setting was essentially zero, rising to 7% at 100 days.
Recovery and Daily Life After Transplant
Recovery is measured in months, not weeks. Your immune system is essentially rebuilt from scratch, and until it matures, you’re vulnerable to infections that a healthy person would easily fight off. Most people avoid eating at restaurants for about three months after transplant. Food safety becomes a daily concern: raw or undercooked meat, poultry, seafood (including sushi), and eggs are off the table, along with unpasteurized dairy, unwashed produce, raw sprouts, and cold deli meats. You should never drink untreated water from natural sources, and well water should be boiled for 15 to 20 minutes before drinking.
Dietary supplements, probiotics, herbal products, and traditional remedies can interact with your post-transplant medications or affect your recovering immune system, so these need to be discussed with your transplant team before use. Energy levels rebuild gradually, and many people describe the first several months as a slow return to normalcy, with good days and setbacks mixed together. Physical stamina, appetite, and emotional well-being all tend to improve over time, but the timeline is different for everyone.