Stem Cell Transplant: Complete Guide to Procedure & Recovery

What Is a Stem Cell Transplant?

A stem cell transplant replaces damaged or diseased bone marrow with healthy blood-forming stem cells. The procedure can use your own stem cells collected beforehand (autologous transplant) or stem cells from a matched donor (allogeneic transplant). It treats blood cancers, bone marrow failure, and severe immune disorders by essentially giving you a new blood-producing system.

A stem cell transplant is also known as a bone marrow transplant or hematopoietic stem cell transplant (HSCT). The terms are often used interchangeably because the goal is the same: to replace the stem cells in your bone marrow that produce all blood cells. These include red blood cells that carry oxygen, white blood cells that fight infection, and platelets that help your blood clot.

The procedure is sometimes called high-dose treatment with stem cell support because you receive intensive chemotherapy or radiation therapy (conditioning) before the stem cells are transplanted. This conditioning treatment serves two critical purposes: it destroys diseased cells in your bone marrow and suppresses your immune system to prevent rejection of new stem cells.

Stem cells for transplant are most commonly collected from the bloodstream after treatment with growth factors that stimulate the bone marrow to produce extra stem cells. Less commonly, stem cells may be taken directly from the bone marrow through a surgical procedure. Once collected, stem cells can be frozen and stored for extended periods until they are needed.

Autologous vs Allogeneic Transplant

The choice between autologous and allogeneic transplant depends on your specific condition and treatment goals. In autologous transplant, your own stem cells are collected before conditioning treatment and then returned to you afterward. This approach works well for conditions where the bone marrow is healthy but needs protection from intensive treatment, such as certain lymphomas and multiple myeloma.

Allogeneic transplant uses stem cells from another person, typically a sibling with matching tissue type or an unrelated donor found through international registries. This type is necessary when your bone marrow is diseased (as in leukemia) or when the transplant's therapeutic effect depends partly on the donor's immune cells attacking remaining cancer cells—a phenomenon called graft-versus-tumor effect.

The Transplant Process Overview

The entire stem cell transplant process typically takes about five weeks, though recovery continues for months afterward. Understanding each phase helps patients and families prepare mentally and practically for this intensive treatment. The process includes comprehensive medical evaluation, stem cell collection (if autologous), conditioning treatment, the transplant itself, and the engraftment period.

During the engraftment period, you remain in hospital isolation while the transplanted stem cells migrate to your bone marrow and begin producing new blood cells. This critical phase typically takes two to three weeks, during which you receive supportive care including blood transfusions, antibiotics, and nutritional support as needed.

What Conditions Does Stem Cell Transplant Treat?

Stem cell transplant treats blood cancers including leukemia, lymphoma, and multiple myeloma, as well as non-cancerous conditions like aplastic anemia, severe combined immunodeficiency (SCID), sickle cell disease, and thalassemia. The type of transplant depends on whether the patient's own bone marrow is diseased or healthy.

The decision to proceed with stem cell transplant depends on multiple factors including the specific disease, its stage, previous treatments, and the patient's overall health. For many conditions, stem cell transplant offers the possibility of cure when other treatments have failed or as part of a planned treatment strategy.

Blood cancers represent the most common indication for stem cell transplant. In acute leukemia, allogeneic transplant can provide a cure by replacing the diseased bone marrow with healthy donor cells while also providing a graft-versus-leukemia effect. For multiple myeloma and some lymphomas, autologous transplant allows delivery of higher chemotherapy doses than would otherwise be safe, potentially achieving deeper remission.

Blood Cancers

Leukemia, both acute and chronic forms, is frequently treated with allogeneic stem cell transplant. Acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL) in adults often require transplant for cure, particularly in higher-risk disease or after relapse. The transplant provides not only new healthy bone marrow but also donor immune cells that can recognize and destroy remaining leukemia cells.

Lymphoma patients may receive autologous transplant to enable high-dose chemotherapy that destroys lymphoma cells. This is particularly common for Hodgkin lymphoma and aggressive non-Hodgkin lymphoma that has responded to initial treatment but has high risk of recurrence. Some lymphoma patients with resistant disease may benefit from allogeneic transplant instead.

Multiple myeloma, a cancer of plasma cells, is commonly treated with autologous transplant as part of initial therapy in eligible patients. This allows for more intensive treatment than would be possible without stem cell rescue and typically leads to deeper and more durable remission.

Non-Cancerous Blood Disorders

Aplastic anemia, a condition where the bone marrow fails to produce sufficient blood cells, can be cured with allogeneic transplant. This is particularly effective in younger patients with a matched sibling donor. The transplant replaces the failing bone marrow with healthy donor stem cells capable of normal blood production.

Inherited blood disorders such as sickle cell disease and thalassemia major can also be treated with allogeneic transplant. In these conditions, the patient's bone marrow produces abnormal hemoglobin. Replacing it with donor stem cells allows production of normal red blood cells, potentially curing the disease. However, the risks of transplant must be weighed against the chronic illness burden of these conditions.

Severe combined immunodeficiency (SCID), sometimes called "bubble boy disease," represents one of the most dramatic success stories for stem cell transplant. Children born with SCID have virtually no immune system and cannot survive without either transplant or emerging gene therapy approaches.

How Do I Prepare for Stem Cell Transplant?

Preparation includes comprehensive medical testing of heart, lung, kidney, and liver function, dental examination and treatment, insertion of a central venous catheter, and discussion of fertility preservation options. The evaluation ensures your body can tolerate the intensive treatment and identifies any conditions requiring attention before transplant.

The pre-transplant evaluation is one of the most thorough medical assessments you may ever undergo. This comprehensive testing serves to confirm that transplant is appropriate for your condition and that your body can handle the intensive treatment. The evaluation typically takes several days and involves multiple specialists.

Your medical team will assess your heart function with electrocardiogram (ECG) and echocardiogram, lung function with breathing tests, and kidney and liver function with blood tests. These organs must work well enough to tolerate conditioning therapy and support recovery. Any existing problems will be optimized before proceeding.

Medical Evaluation

Blood tests form the foundation of pre-transplant assessment. These include complete blood counts, chemistry panels to evaluate organ function, and tests for infectious diseases like hepatitis and HIV. If you're receiving an allogeneic transplant, tissue typing confirms compatibility with your donor and screens for antibodies that might cause complications.

Heart assessment is crucial because the conditioning regimen can stress the cardiovascular system. An echocardiogram measures how well your heart pumps blood, while an ECG checks for rhythm abnormalities. Some patients may need additional cardiac testing or medication adjustments before proceeding.

Pulmonary function tests measure lung capacity and efficiency. Good lung function is essential because some conditioning drugs can affect the lungs, and you'll need adequate respiratory reserve to recover from treatment. Patients with pre-existing lung disease may need modified conditioning or enhanced supportive care.

Dental Care

Dental health receives special attention before transplant because mouth infections can become life-threatening when your immune system is suppressed. You'll see a dentist familiar with transplant preparation who will treat any cavities, gum disease, or other dental problems. Teeth that cannot be adequately treated may need extraction to prevent later complications.

This preventive dental care is not optional—untreated dental infections can spread to the bloodstream (bacteremia) during the period when you have almost no immune defenses. Taking care of dental issues beforehand dramatically reduces this risk.

Central Venous Catheter

A central venous catheter (central line) is placed before conditioning begins. This specialized intravenous access allows delivery of chemotherapy, stem cells, antibiotics, blood products, and nutrition without repeatedly needling peripheral veins. The catheter is typically placed in a large vein in your chest and can remain in place for weeks to months.

Having the central line simplifies the many procedures you'll need. Blood samples can be drawn through the catheter rather than with needle sticks, and multiple medications can be given simultaneously through separate ports. You'll learn to care for the catheter to prevent infection.

Fertility Preservation

Conditioning treatment frequently causes permanent infertility, so fertility preservation should be discussed before treatment begins. This applies to both adults and children receiving transplant, as the effects on reproductive organs are often irreversible.

Options for fertility preservation depend on age, sex, and time available before treatment. Men and adolescent boys can bank sperm, which can be stored indefinitely. Women may be able to undergo egg retrieval or ovarian tissue preservation, though these require more time and may not be possible in all cases. Discuss options thoroughly with your medical team, as not all patients recover fertility naturally.

How Are Stem Cells Collected?

Stem cells are most commonly collected from the bloodstream through a process called apheresis after receiving growth factor injections for 8-10 days. The procedure takes 3-4 hours as blood passes through a machine that separates and collects stem cells before returning the remaining blood. Less commonly, stem cells can be surgically harvested from the bone marrow.

If you're having an autologous transplant, your stem cells must be collected before conditioning destroys your bone marrow. This process, called harvesting or apheresis, requires preparation to move stem cells from the bone marrow into circulating blood where they can be collected.

For approximately 8-10 days before collection, you'll receive daily injections of a growth factor called G-CSF (granulocyte colony-stimulating factor). This medication stimulates your bone marrow to produce large numbers of stem cells and release them into the bloodstream. The dose used for stem cell mobilization is higher than for other purposes, which helps achieve adequate cell counts.

Side Effects of Growth Factor

Growth factor injections commonly cause bone pain, particularly in the back, hips, and legs. This discomfort occurs because of the intense cell division happening in your bone marrow. While uncomfortable, it's actually a sign that the medication is working. Over-the-counter pain relievers or antihistamines usually provide adequate relief, and the discomfort resolves within a few days of completing the injections.

Other possible side effects include headache, fatigue, and low-grade fever. These are generally mild and manageable. Your team will monitor you closely during this period with blood tests to track when stem cells are optimally mobilized for collection.

The Apheresis Procedure

On collection day, thin tubes (catheters) are inserted into blood vessels, typically in the arms, groin, or neck. Your blood then flows through a specialized machine called a cell separator. This machine spins the blood to separate its components, collecting the layer rich in stem cells while returning the rest (red cells, plasma, and most white cells) to your body.

The apheresis procedure itself takes approximately 3-4 hours. You'll be awake throughout and can watch television, read, or rest. Most people don't find the procedure painful, though you may notice tingling around your mouth or fingertips from the anticoagulant medication used to prevent clotting in the collection lines. This sensation is harmless and resolves when collection is complete.

For most patients, collection is completed in a single day. However, some people require two consecutive days of collection to obtain sufficient stem cells. The collected cells are then frozen and stored until transplant day.

Bone Marrow Harvest

Although less common, stem cells can also be collected directly from the bone marrow through a surgical procedure. This is done under general anesthesia, with stem cells extracted through multiple needle insertions into the back of the pelvis (hip bone). The marrow regenerates naturally within a few weeks.

Bone marrow harvest is more commonly used for allogeneic donors rather than patients receiving their own cells. Recovery involves soreness at the collection site for several days, but serious complications are rare.

What Is Conditioning Treatment?

Conditioning is high-dose chemotherapy and/or radiation therapy given over 2-7 days before transplant. It destroys cancer cells and diseased bone marrow, suppresses the immune system to prevent rejection of donor cells, and creates space in the bone marrow for new stem cells to grow. The intensity varies based on the type of transplant and patient factors.

Conditioning treatment is the most intensive phase of stem cell transplant, serving multiple essential purposes. It eliminates as many cancer or diseased cells as possible, destroys the existing bone marrow to make room for transplanted cells, and suppresses the immune system (especially important in allogeneic transplant to prevent rejection).

The specific conditioning regimen depends on your disease, type of transplant, age, and overall health. Regimens range from myeloablative (fully destroying the bone marrow) to reduced-intensity (partially destroying the bone marrow). Your medical team selects the approach that balances effectiveness against tolerability for your situation.

Autologous Transplant Conditioning

For autologous transplants, conditioning typically involves high-dose chemotherapy given over several days, most commonly five days. Since you're receiving your own cells back, the goal is primarily to deliver maximum anti-cancer treatment. There's no need for intense immune suppression because your body won't reject its own cells.

Side effects during autologous conditioning are similar to regular chemotherapy but often more pronounced due to the higher doses. Nausea, fatigue, and temporary hair loss are common. However, many patients tolerate autologous conditioning reasonably well because the side effects are manageable with modern supportive medications.

Allogeneic Transplant Conditioning

Allogeneic transplant conditioning is typically more intensive because it must not only treat disease but also suppress your immune system enough to accept donor cells. This often involves 2-7 days of high-dose chemotherapy, sometimes combined with total body irradiation (TBI)—a form of radiation that treats the entire body.

Total body irradiation, when used, is given in multiple fractions (individual treatments) over 2-4 days. This helps minimize side effects while achieving adequate bone marrow suppression. Common side effects include nausea, fatigue, and parotid (salivary gland) swelling. Long-term effects may include increased risk of cataracts and second cancers.

Reduced-intensity conditioning (RIC) uses lower doses of chemotherapy and/or radiation. This approach is appropriate for older patients or those with other health conditions who might not tolerate full-intensity treatment. RIC relies more heavily on the donor immune system's graft-versus-tumor effect to control disease.

What Happens on Transplant Day?

On transplant day, frozen stem cells are thawed (if previously stored) and infused through your central line into your bloodstream, similar to a blood transfusion. The process takes 1-2 hours. You may notice a strong taste resembling corn or garlic from the preservative, and some experience facial flushing, coughing, or chest tightness, which can be managed with medication.

Transplant day itself is often anticlimatic compared to the intensive preparation leading up to it. The actual infusion of stem cells is straightforward—a bag of cells is hung like an IV solution and drips into your central line. The cells naturally find their way to your bone marrow, a process called homing.

If your stem cells were frozen (as is always the case for autologous and sometimes for allogeneic transplants), they're thawed at the bedside immediately before infusion. The entire infusion process typically takes one to two hours, depending on the volume of cells.

What You May Experience

The preservative used to freeze stem cells (DMSO) can cause noticeable side effects during infusion. Many patients report a strong taste in their mouth described as similar to corn, garlic, or creamed corn. This unusual taste is harmless but can be unpleasant. Sucking on hard candy or breathing through your mouth may help.

Some patients experience facial flushing, throat irritation, coughing, or a sensation of pressure in the chest during infusion. These reactions relate to the preservative and are generally mild. Your team can slow the infusion rate or give medications to ease discomfort. Serious reactions are rare but the medical team monitors you closely throughout.

The room may develop a strong garlic-like odor from the preservative, which some patients and visitors find bothersome. This smell clears within a day or two as the preservative is metabolized and exhaled through your lungs.

Fresh vs Frozen Cells

In some allogeneic transplants, particularly when the donor is nearby, cells may be infused fresh rather than frozen. Fresh cells avoid preservative-related side effects but require precise coordination with the donor's collection. The medical team decides whether fresh or frozen infusion is most appropriate for your situation.

What Happens After Transplant?

After transplant, you remain in hospital isolation for 2-3 weeks while waiting for engraftment (when new stem cells start producing blood cells). During this time, you're vulnerable to infections and may need blood and platelet transfusions. Most patients are ready for discharge 3-4 weeks after transplant, with full recovery taking up to one year.

The period immediately following transplant is called the aplastic phase because your bone marrow is essentially empty, unable to produce blood cells. The transplanted stem cells need time to engraft (establish themselves in the bone marrow) and begin producing new cells. This critical period typically lasts two to three weeks.

During aplasia, you have virtually no immune system and are extremely vulnerable to infection. You'll stay in a private hospital room with special air filtration and strict visitor policies. Healthcare workers follow rigorous hand hygiene and may wear protective equipment. These precautions, while sometimes feeling isolating, are essential for your safety.

Isolation Period

The isolation experience affects people differently. Some find it boring or lonely; others appreciate the quiet time to rest and recover. Hospital staff make every effort to meet your needs, and in most cases, one designated caregiver can visit daily. Children typically have a parent present throughout the hospitalization.

Staying physically active is important even during isolation. A physiotherapist may visit daily to guide exercises you can do in your room. Many hospitals provide stationary bikes or other exercise equipment. Walking in the corridors may be possible depending on your counts and hospital policies. Maintaining activity helps preserve strength and may speed recovery.

Home-based isolation is sometimes possible for autologous transplant patients who live close to the hospital and have appropriate home support. This option reduces infection exposure from the hospital environment and may improve quality of life during recovery. Discuss with your team whether home isolation might work for your situation.

Supportive Care During Recovery

Until your new bone marrow produces sufficient blood cells, you'll likely need transfusions. Red blood cell transfusions address anemia and related fatigue. Platelet transfusions help prevent bleeding when counts are dangerously low. These transfusions are routine parts of post-transplant care.

Prophylactic antibiotics, antivirals, and antifungals are given to prevent infections during the vulnerable period. Even with these precautions, many patients develop fevers that require evaluation and sometimes stronger antibiotics. Fever in a transplant patient is taken very seriously given the lack of immune defenses.

Eating and drinking often becomes difficult after transplant. Conditioning treatment causes mouth sores (mucositis), nausea, and sometimes diarrhea. Pain medication helps manage mouth discomfort. Nutritional support through IV nutrition (TPN) ensures adequate calories and nutrients when oral intake is insufficient.

Signs of Engraftment

Blood counts are monitored daily to watch for engraftment. Rising neutrophil counts (a type of white blood cell) indicate the new bone marrow is starting to function—this is cause for celebration. Most patients achieve neutrophil engraftment within 14-21 days, though the timeline varies.

Once counts recover adequately and you're medically stable, you can be discharged from the hospital. This typically occurs 3-4 weeks after transplant. Going home can feel both exciting and anxiety-provoking after weeks of intensive medical supervision. Detailed discharge instructions help guide the transition.

What Are the Common Side Effects and Complications?

Common side effects include fatigue, mouth sores, difficulty eating, nausea, and diarrhea in the weeks after transplant. Longer-term effects may include GVHD (for donor transplants), infections due to suppressed immunity, hormonal deficiencies, cognitive changes ("chemo brain"), and emotional adjustment challenges. Most side effects improve over time with appropriate management.

Understanding potential side effects and complications helps you recognize problems early and work effectively with your medical team. While the list of possible complications may seem overwhelming, remember that not everyone experiences all of them, and most are manageable with proper care.

Early Side Effects

In the first weeks after transplant, mouth sores (mucositis) are among the most challenging side effects. The conditioning treatment damages fast-dividing cells, including those lining your mouth and digestive tract. Pain management with medications makes this more tolerable, and the sores heal as new cells regenerate.

Nausea, vomiting, and diarrhea are common as the digestive system responds to chemotherapy. Modern anti-nausea medications are very effective, but some discomfort is often unavoidable. These symptoms typically improve within the first few weeks as conditioning effects wear off.

Fatigue during and after transplant is profound. Your body is recovering from intensive treatment while simultaneously working to produce new blood cells. This is not ordinary tiredness—it requires significant rest while gradually building activity as tolerated. Fatigue improves over months but may persist to some degree for a year or longer.

GVHD (Graft-Versus-Host Disease)

GVHD is a significant complication specific to allogeneic (donor) transplants. It occurs when donor immune cells recognize your body tissues as foreign and attack them. Despite preventive medications, GVHD affects many allogeneic transplant recipients to some degree.

Acute GVHD typically develops within the first 100 days after transplant and most commonly affects the skin, liver, and gastrointestinal tract. Symptoms may include skin rash or redness, nausea, vomiting, diarrhea, and liver function abnormalities. Treatment involves intensifying immunosuppressive medications.

Chronic GVHD develops later and can affect many organ systems. Common manifestations include skin changes (thickening, color changes, dryness), dry eyes and mouth, joint stiffness, and liver inflammation. Chronic GVHD may require prolonged immunosuppressive treatment but often eventually resolves.

Long-Term Complications

Infection risk persists for months to a year after transplant as the immune system slowly rebuilds. You'll take preventive antibiotics and antivirals during this period and need to avoid crowds and sick contacts. Vaccinations are eventually renewed once immune function recovers sufficiently.

Hormonal changes are common after transplant. Women frequently experience early menopause from conditioning treatment, with symptoms including hot flashes, mood changes, and vaginal dryness. Hormone replacement therapy can help manage symptoms. Men may have low testosterone. Thyroid hormone deficiency can also develop and requires monitoring.

Cognitive changes, often called "chemo brain," affect memory, concentration, and mental processing speed. These changes are usually subtle but can be frustrating. Most patients experience gradual improvement over 6-12 months, though some changes may persist. Strategies like keeping lists and minimizing distractions can help compensate.

There is a slightly increased long-term risk of second cancers due to the chemotherapy and/or radiation received during conditioning. This risk is relatively small but real, underscoring the importance of long-term follow-up care and recommended cancer screenings.

What Follow-Up Care Is Needed?

After discharge, you'll have frequent clinic visits (several times weekly initially) for blood tests and monitoring, gradually decreasing as you recover. You'll take immunosuppressive medications if you had a donor transplant, and will need to renew your childhood vaccinations starting at least 6 months after transplant once your immune system has recovered sufficiently.

Transplant is not a single event but the beginning of a recovery journey that continues for months to years. Regular follow-up ensures complications are caught early and your recovery stays on track. The intensity of monitoring decreases over time as your condition stabilizes.

Early Post-Discharge Follow-Up

In the first weeks after leaving the hospital, you'll visit the transplant clinic frequently—often several times per week. Blood tests monitor your counts, organ function, and medication levels. The medical team watches for signs of infection, GVHD, or other complications.

Allogeneic transplant recipients take immunosuppressive medications to prevent GVHD. These require careful monitoring and dose adjustments based on blood levels and any GVHD symptoms. The goal is to use enough medication to prevent severe GVHD while allowing some immune function to recover and fight cancer.

Follow-up visits gradually space out as you recover—from weekly, to biweekly, to monthly, and eventually several times yearly. However, you should contact your transplant team immediately if you develop fever, new symptoms, or other concerns between scheduled visits.

Vaccination Renewal

Conditioning treatment destroys not only your bone marrow but also the immune memory cells that protect you from diseases you've been vaccinated against or previously had. After transplant, you are essentially an immunological "blank slate" regarding vaccination.

Revaccination begins after your immune system has recovered sufficiently to respond to vaccines—typically at least 6 months after transplant, though timing varies. You'll repeat the childhood vaccination series including tetanus, diphtheria, pertussis, polio, pneumococcus, and others. Live vaccines (like measles, mumps, rubella) require longer delays and aren't given until at least 2 years post-transplant when immunosuppression has ended.

Your transplant team and primary care physician coordinate vaccination schedules. Family members and close contacts should ensure their vaccinations are up to date to protect you during recovery, particularly for influenza and COVID-19.

Long-Term Monitoring

Even years after transplant, ongoing monitoring remains important. This includes surveillance for disease relapse, screening for late effects like second cancers or organ damage, and management of any chronic GVHD. Many transplant centers have specialized long-term follow-up clinics for survivors.

Children and adolescents who undergo transplant require special long-term attention. Growth, development, and puberty should be monitored, with intervention if needed. Educational support helps manage any cognitive effects that impact learning.

How Do I Protect Myself During Recovery?

During the recovery period, protect yourself by practicing meticulous hand hygiene, avoiding crowds and sick people, taking prescribed preventive medications, eating safely prepared foods, staying physically active within your limitations, and promptly reporting any fever or new symptoms to your medical team.

Your behavior during recovery significantly impacts your outcomes. The precautions may feel restrictive, but they protect you during the vulnerable period when your new immune system is still developing. Most restrictions ease as your immunity recovers.

Infection Prevention

Hand hygiene is your most important defense against infection. Wash your hands frequently with soap and water or use alcohol-based hand sanitizer, especially before eating or touching your face. Ask visitors to do the same, and don't hesitate to remind healthcare workers.

Avoid crowds and people who are sick. Large gatherings increase infection exposure during your vulnerable period. Similarly, avoid close contact with anyone who has respiratory symptoms, diarrhea, or rash. This includes staying away from children who recently received live vaccines.

Take all prescribed preventive medications as directed. These antibiotics, antivirals, and antifungals provide crucial protection against organisms your depleted immune system cannot fight effectively. Don't skip doses or stop medications early.

Food Safety

Food safety takes on extra importance after transplant. Your reduced immunity makes you more susceptible to foodborne illness. General guidelines include avoiding raw or undercooked meat, fish, and eggs; washing fruits and vegetables thoroughly; avoiding unpasteurized dairy products and juices; and ensuring proper food storage and reheating.

Specific restrictions vary among transplant centers and may ease as your immunity recovers. Your medical team will provide detailed dietary guidelines appropriate for your situation.

Staying Active

Physical activity is encouraged during recovery, adapted to your energy level and blood counts. Exercise helps maintain strength, improve mood, and may speed recovery. Start gently—even short walks help—and gradually increase as tolerated.

Balance activity with rest. Your body is doing enormous work rebuilding itself, and fatigue is both common and valid. Listen to your body, rest when needed, and don't compare your recovery pace to others. Every patient's journey is different.

How Can I Receive Donor Stem Cells?

For allogeneic transplant, the best donor is usually a sibling with matching tissue type (HLA matching). If no sibling matches, donors can be found through international registries, or a partially matched family member (haploidentical transplant) may be used. Finding a matched unrelated donor can take time, so the search typically begins early in treatment planning.

The success of allogeneic transplant depends significantly on the match between donor and recipient. Human leukocyte antigen (HLA) typing determines compatibility. The more closely matched the HLA markers, the lower the risk of severe GVHD and graft rejection.

Sibling Donors

Full siblings have a 25% chance of being an HLA-identical match because HLA types are inherited from parents. When available, a matched sibling donor typically provides the best outcomes. Siblings who are potential donors undergo HLA typing early in the transplant evaluation process.

Even when siblings don't fully match, they may still serve as donors in certain circumstances. Haploidentical transplant uses a half-matched family member (parent, child, or sibling). Advances in GVHD prevention have made haploidentical transplant increasingly successful, expanding donor options significantly.

Unrelated Donors

When no suitable family donor is available, international bone marrow registries can be searched for unrelated donors. These registries contain millions of volunteers who have had HLA typing performed and agreed to donate if matched with a patient.

Finding an unrelated donor can take weeks to months depending on the patient's HLA type. Some HLA types are common and easier to match; others are rare. Ethnic background affects the likelihood of finding a match, as HLA types vary among populations. Registry diversity efforts aim to improve match rates for underrepresented groups.

Cord Blood Transplant

Umbilical cord blood, collected and banked after birth, provides another source of stem cells. Cord blood has advantages including ready availability (no need to schedule donor collection) and more flexibility in matching requirements. Disadvantages include smaller cell doses and slower engraftment.

Cord blood transplant may be particularly useful when no adult donor match is available or when transplant needs to proceed quickly. Some transplants use double cord blood units to provide adequate cell doses for adults.