What are the procedures and steps involved in a bone marrow (hematopoietic stem‑cell) transplant?

Bone Marrow (Hematopoietic Stem Cell) Transplant: Key Procedures and Steps

A bone marrow transplant involves three essential phases: (1) stem cell collection from either the patient (autologous) or a matched donor (allogeneic), (2) high-dose chemotherapy ± radiation to destroy diseased marrow and suppress immunity, and (3) infusion of healthy stem cells to re-establish normal blood cell production. 1

Type Classification

The procedure differs fundamentally based on cell source:

• Autologous transplant: Uses the patient's own stem cells, harvested before high-dose therapy, then reinfused to rescue the bone marrow after treatment 1
• Allogeneic transplant: Uses stem cells from an HLA-compatible donor to replace the patient's diseased marrow entirely 1

Step 1: Stem Cell Mobilization and Collection

For Autologous Transplants

Stem cells must first be mobilized from bone marrow into peripheral blood using high-dose cyclophosphamide followed by filgrastim (G-CSF). 2 This mobilization phase typically causes manageable toxicity—less severe than the actual transplant itself. 2

After mobilization, cells are collected via leukapheresis, where blood is processed through a machine that separates and collects the stem cells. 2 The target is collecting at least 2 × 10⁶ CD34+ cells/kg of recipient body weight to ensure reliable engraftment within approximately 14 days post-transplant. 3

For Allogeneic Transplants

Donors receive G-CSF or GM-CSF to mobilize their stem cells, which are then collected by apheresis. 3 Some centers perform ex vivo immunomagnetic selection to deplete lymphocytes from the graft. 2

Cell Source Options

Stem cells can be obtained from three sources 1:

• Peripheral blood stem cells (PBSCs): Now the predominant source, especially for autologous transplants, due to easier collection (no general anesthesia needed), faster engraftment, lower graft failure risk, and reduced transplant-related mortality 1
• Bone marrow: Still preferred for severe aplastic anemia and certain nonmalignant disorders due to lower graft-versus-host disease (GVHD) risk 1
• Umbilical cord blood: Offers rapid procurement and lower GVHD risk despite HLA mismatch 1

Critical caveat: While PBSCs engraft faster, allogeneic PBSC transplants carry increased GVHD risk compared to bone marrow grafts. 1

Step 2: Graft Processing and Storage

After collection, the stem cell graft undergoes:

• Quality testing to ensure sterility and adequate stem cell/progenitor content 2
• Cryopreservation until needed for transplant 2
• Potential lymphocyte depletion via immunomagnetic selection (center-dependent) 2

All procedures must meet national regulatory standards and international accreditation requirements. 2

Step 3: Conditioning (Preparative Regimen)

Prior to stem cell infusion, patients receive chemotherapy, serotherapy, and/or radiation—the intensity depends on transplant type. 1

Allogeneic Conditioning

The preparative regimen serves dual purposes:

• Eradicate malignant cells in the bone marrow (if using myeloablative intensity)
• Induce immunosuppression to prevent rejection and allow donor cell engraftment 1

Autologous Conditioning

High-dose myeloablative chemotherapy is used to treat the underlying malignancy, with subsequent stem cell rescue to restore blood cell production and immune function. 1

Step 4: Stem Cell Infusion

The collected and processed stem cells are infused intravenously, similar to a blood transfusion. 1 The cells naturally home to the bone marrow cavity where they begin regenerating all blood cell lineages. 3

Step 5: Engraftment and Recovery

Engraftment—when transplanted cells begin producing new blood cells—typically occurs around 14 days post-transplant when adequate CD34+ cells (≥2 × 10⁶/kg) were infused. 3 During this period, patients require intensive supportive care and monitoring for complications.

Common Disease Indications

Allogeneic transplants most commonly treat: acute myeloid leukemia (AML), acute lymphoblastic leukemia (ALL), and myelodysplastic syndromes (MDS) 1

Autologous transplants most frequently used for: multiple myeloma, non-Hodgkin lymphoma, and Hodgkin lymphoma 1

Outcome Determinants

Success varies based on 1:

• Disease type and stage at transplant
• Patient's overall health and comorbidities
• Degree of HLA-mismatch between donor and recipient (allogeneic only)
• Stem cell source chosen
• Urgency of transplantation

Critical pitfall: The choice between peripheral blood and bone marrow grafts requires balancing faster engraftment (favoring PBSCs) against GVHD risk (favoring bone marrow), particularly for allogeneic transplants. 1