A bone marrow transplant—more precisely, hematopoietic stem cell transplantation—is a medical procedure that replaces or rescues blood‑forming stem cells to reconstitute hematopoiesis and immunity. It is used to treat malignant and non‑malignant disorders, including leukemias, lymphomas, myelodysplastic syndromes, aplastic anemia, thalassemia, and sickle cell disease. Modern practice encompasses autologous, allogeneic, and syngeneic approaches with grafts sourced from peripheral blood, marrow, or umbilical cord blood, with outcomes continually improving through advances in conditioning, donor selection, and graft‑versus‑host disease prophylaxis.
Last updated October 31, 2025
Bone marrow transplant (hematopoietic stem cell transplantation, HSCT) replaces or rescues the recipient’s blood‑forming system using hematopoietic progenitors to restore normal hematopoiesis and immune function after cytotoxic conditioning or marrow failure. According to the National Cancer Institute, HSCT can be autologous (patient’s own cells) or allogeneic (donor cells) and is used in cancers and inherited or acquired marrow failure syndromes. National Cancer Institute.
Terminology and scope
HSCT encompasses autologous, allogeneic, and syngeneic procedures, with grafts obtained from bone marrow, mobilized peripheral blood, or umbilical cord blood; mobilization for peripheral blood collection typically uses granulocyte colony‑stimulating factor. StatPearls; Encyclopaedia Britannica. The procedure is distinct from solid‑organ transplantation in that donor hematolymphoid cells engraft, potentially mediating both graft‑versus‑host disease (GVHD) and graft‑versus‑tumor effects. National Cancer Institute.
Modern HSCT was pioneered by E. Donnall Thomas, whose work—from early twin transplants and canine models to clinical protocols—culminated in the 1990 Nobel Prize in Physiology or Medicine for discoveries enabling therapeutic organ and cell transplantation. Nobel Prize; Fred Hutchinson Cancer Center. Reports of early successful human marrow transplants in the late 1950s informed later clinical implementation. Nobel Prize.
Indications
Allogeneic HSCT is indicated for high‑risk or relapsed acute leukemias, myelodysplastic syndromes, myeloproliferative neoplasms, aplastic anemia, and selected congenital immune or marrow failure states; autologous HSCT is used primarily in lymphomas and multiple myeloma. National Cancer Institute; EBMT 2025 practice recommendations. In sickle cell disease, HSCT remains the only established curative therapy, with formal practice guidelines published by the American Society of Hematology in 2021. NHLBI; ASH Blood Advances guideline.
Donor types include HLA‑matched related donors, matched unrelated donors, haploidentical related donors, and mismatched unrelated donors; umbilical cord blood provides an alternative source with more permissive HLA matching requirements. StatPearls; NMDP donor selection guidance. The U.S. NMDP (formerly Be The Match) connects patients to a worldwide pool exceeding 42 million potential donors and emphasizes the effect of ancestry on 8/8 match likelihood; modeling shows that allowing 7/8 or 5/8 mismatches plus modern prophylaxis greatly expands access. NMDP (organization overview); NMDP modeling; NMDP Donor for All. In FY2024 the U.S. government’s C.W. Bill Young Cell Transplantation Program reported facilitating 7,550 unrelated donor or cord blood transplants (6,457 for U.S. patients). HRSA CWBYCTP.
Conditioning regimens
Conditioning ranges from myeloablative (e.g., high‑dose busulfan‑ or cyclophosphamide‑based, often with total body irradiation) to reduced‑intensity or non‑myeloablative regimens, balancing relapse risk against non‑relapse mortality. StatPearls; J Clin Oncol randomized AML/MDS trial. Systematic reviews suggest similar long‑term survival between regimen intensities in several diseases, with differing profiles of relapse and toxicity. Biol Blood Marrow Transplant systematic review; Meta‑analysis AML/MDS.
Procedure and peri‑transplant course
Work‑up includes disease assessment, performance status, organ function, infectious disease screening, and donor/HLA selection. Cells are collected by apheresis for peripheral blood or harvested from marrow under anesthesia; filgrastim is used to mobilize peripheral blood stem cells in donors. National Cancer Institute; Mayo Clinic; Encyclopaedia Britannica. After infusion, neutrophil recovery is typically observed within about 10–20 days for marrow or peripheral blood grafts, with longer times for umbilical cord blood (often 21–35 days). MedGen (NCI note on engraftment); Translational Medicine report. Chimerism assays (STR‑PCR or newer NGS/digital PCR methods) quantify donor/recipient hematopoiesis to monitor engraftment and detect mixed chimerism or relapse. Diagnostics review; NGS validation.
Guidelines endorse a calcineurin inhibitor (cyclosporine or tacrolimus) plus an antimetabolite (e.g., methotrexate after myeloablative conditioning; mycophenolate commonly with reduced‑intensity) for matched related or unrelated donor HCT, with antithymocyte globulin used in many unrelated donor settings. EBMT recommendations summary. Randomized BMT CTN 1703 demonstrated superior 1‑year GVHD‑free, relapse‑free survival using post‑transplant cyclophosphamide (PTCy) with tacrolimus and mycophenolate versus tacrolimus/methotrexate in HLA‑matched reduced‑intensity transplants, accelerating adoption across donor types; subsequent reports confirm advantages in older adults and across conditioning intensities. NEJM BMT CTN 1703; PubMed NEJM 1703; Blood Advances 2025 analysis ≥70y. A 2025 randomized trial also found longer GVHD‑free, relapse‑free survival with PTCy plus cyclosporine versus standard prophylaxis after matched related donor HCT. NEJM 2025.
Graft source comparisons
In unrelated donor HCT, a major randomized trial found similar survival with peripheral blood versus marrow grafts; peripheral blood reduced graft failure but increased chronic GVHD, illustrating tradeoffs that guide source selection. NEJM BMT CTN 0201; PMC article.
Complications and supportive care
Acute toxicities include mucositis, cytopenias with bleeding and infection risk, organ injury (e.g., hepatic sinusoidal obstruction), and GVHD in allogeneic recipients. Johns Hopkins Medicine; American Cancer Society. FDA‑approved agents for GVHD include ruxolitinib for steroid‑refractory acute and chronic GVHD, belumosudil for chronic GVHD after at least two prior systemic lines, and axatilimab‑csfr for chronic GVHD after failure of at least two systemic therapies. FDA ruxolitinib aGVHD; FDA ruxolitinib cGVHD; FDA belumosudil; FDA axatilimab‑csfr. Long‑term survivors face late effects such as endocrine dysfunction, infertility, and second solid cancers, with risk influenced by irradiation exposure and GVHD. Blood review; Cancer/ACS review.
Utilization and outcomes
CIBMTR’s 2024 U.S. Summary Slides (updated April 2025) document practice patterns and survival across donor sources, conditioning intensity, and diseases, with three‑year survival continuing to improve in allogeneic and autologous cohorts compared with prior eras. CIBMTR Summary Slides (2024, updated 2025); Transplantation and Cellular Therapy 2025 CIBMTR report. In Europe, EBMT activity reports show 2023 increases in allogeneic HCT, particularly for myeloid malignancies, alongside rising use of CAR‑T and stable autologous HCT volumes. EBMT 2023 activity (Passweg et al.). In the United States, the federal program reports thousands of unrelated donor transplants annually, and coverage policies continue to evolve (e.g., 2024 CMS national coverage for MDS including cord blood). HRSA CWBYCTP; ASH summary of CMS NCD for MDS.
Access and equity
Match likelihood varies by ancestry, reflecting HLA diversity and registry composition; NMDP reports that while only a minority of some groups identify an 8/8 unrelated donor, leveraging 7/8 or 5/8 mismatches, haploidentical related donors, or cord blood plus contemporary GVHD prophylaxis can expand access substantially. NMDP modeling; Blood Advances 2024. Ongoing initiatives emphasize diversifying the registry and optimizing donor selection algorithms. NMDP Donor for All.
A bone marrow transplant—more precisely, hematopoietic stem cell transplantation—is a medical procedure that replaces or rescues blood‑forming stem cells to reconstitute hematopoiesis and immunity. It is used to treat malignant and non‑malignant disorders, including leukemias, lymphomas, myelodysplastic syndromes, aplastic anemia, thalassemia, and sickle cell disease. Modern practice encompasses autologous, allogeneic, and syngeneic approaches with grafts sourced from peripheral blood, marrow, or umbilical cord blood, with outcomes continually improving through advances in conditioning, donor selection, and graft‑versus‑host disease prophylaxis.
Last updated October 31, 2025
Bone marrow transplant (hematopoietic stem cell transplantation, HSCT) replaces or rescues the recipient’s blood‑forming system using hematopoietic progenitors to restore normal hematopoiesis and immune function after cytotoxic conditioning or marrow failure. According to the National Cancer Institute, HSCT can be autologous (patient’s own cells) or allogeneic (donor cells) and is used in cancers and inherited or acquired marrow failure syndromes. National Cancer Institute.
Terminology and scope
HSCT encompasses autologous, allogeneic, and syngeneic procedures, with grafts obtained from bone marrow, mobilized peripheral blood, or umbilical cord blood; mobilization for peripheral blood collection typically uses granulocyte colony‑stimulating factor. StatPearls; Encyclopaedia Britannica. The procedure is distinct from solid‑organ transplantation in that donor hematolymphoid cells engraft, potentially mediating both graft‑versus‑host disease (GVHD) and graft‑versus‑tumor effects. National Cancer Institute.
Modern HSCT was pioneered by E. Donnall Thomas, whose work—from early twin transplants and canine models to clinical protocols—culminated in the 1990 Nobel Prize in Physiology or Medicine for discoveries enabling therapeutic organ and cell transplantation. Nobel Prize; Fred Hutchinson Cancer Center. Reports of early successful human marrow transplants in the late 1950s informed later clinical implementation. Nobel Prize.
Indications
Allogeneic HSCT is indicated for high‑risk or relapsed acute leukemias, myelodysplastic syndromes, myeloproliferative neoplasms, aplastic anemia, and selected congenital immune or marrow failure states; autologous HSCT is used primarily in lymphomas and multiple myeloma. National Cancer Institute; EBMT 2025 practice recommendations. In sickle cell disease, HSCT remains the only established curative therapy, with formal practice guidelines published by the American Society of Hematology in 2021. NHLBI; ASH Blood Advances guideline.
Donor types include HLA‑matched related donors, matched unrelated donors, haploidentical related donors, and mismatched unrelated donors; umbilical cord blood provides an alternative source with more permissive HLA matching requirements. StatPearls; NMDP donor selection guidance. The U.S. NMDP (formerly Be The Match) connects patients to a worldwide pool exceeding 42 million potential donors and emphasizes the effect of ancestry on 8/8 match likelihood; modeling shows that allowing 7/8 or 5/8 mismatches plus modern prophylaxis greatly expands access. NMDP (organization overview); NMDP modeling; NMDP Donor for All. In FY2024 the U.S. government’s C.W. Bill Young Cell Transplantation Program reported facilitating 7,550 unrelated donor or cord blood transplants (6,457 for U.S. patients). HRSA CWBYCTP.
Conditioning regimens
Conditioning ranges from myeloablative (e.g., high‑dose busulfan‑ or cyclophosphamide‑based, often with total body irradiation) to reduced‑intensity or non‑myeloablative regimens, balancing relapse risk against non‑relapse mortality. StatPearls; J Clin Oncol randomized AML/MDS trial. Systematic reviews suggest similar long‑term survival between regimen intensities in several diseases, with differing profiles of relapse and toxicity. Biol Blood Marrow Transplant systematic review; Meta‑analysis AML/MDS.
Procedure and peri‑transplant course
Work‑up includes disease assessment, performance status, organ function, infectious disease screening, and donor/HLA selection. Cells are collected by apheresis for peripheral blood or harvested from marrow under anesthesia; filgrastim is used to mobilize peripheral blood stem cells in donors. National Cancer Institute; Mayo Clinic; Encyclopaedia Britannica. After infusion, neutrophil recovery is typically observed within about 10–20 days for marrow or peripheral blood grafts, with longer times for umbilical cord blood (often 21–35 days). MedGen (NCI note on engraftment); Translational Medicine report. Chimerism assays (STR‑PCR or newer NGS/digital PCR methods) quantify donor/recipient hematopoiesis to monitor engraftment and detect mixed chimerism or relapse. Diagnostics review; NGS validation.
Guidelines endorse a calcineurin inhibitor (cyclosporine or tacrolimus) plus an antimetabolite (e.g., methotrexate after myeloablative conditioning; mycophenolate commonly with reduced‑intensity) for matched related or unrelated donor HCT, with antithymocyte globulin used in many unrelated donor settings. EBMT recommendations summary. Randomized BMT CTN 1703 demonstrated superior 1‑year GVHD‑free, relapse‑free survival using post‑transplant cyclophosphamide (PTCy) with tacrolimus and mycophenolate versus tacrolimus/methotrexate in HLA‑matched reduced‑intensity transplants, accelerating adoption across donor types; subsequent reports confirm advantages in older adults and across conditioning intensities. NEJM BMT CTN 1703; PubMed NEJM 1703; Blood Advances 2025 analysis ≥70y. A 2025 randomized trial also found longer GVHD‑free, relapse‑free survival with PTCy plus cyclosporine versus standard prophylaxis after matched related donor HCT. NEJM 2025.
Graft source comparisons
In unrelated donor HCT, a major randomized trial found similar survival with peripheral blood versus marrow grafts; peripheral blood reduced graft failure but increased chronic GVHD, illustrating tradeoffs that guide source selection. NEJM BMT CTN 0201; PMC article.
Complications and supportive care
Acute toxicities include mucositis, cytopenias with bleeding and infection risk, organ injury (e.g., hepatic sinusoidal obstruction), and GVHD in allogeneic recipients. Johns Hopkins Medicine; American Cancer Society. FDA‑approved agents for GVHD include ruxolitinib for steroid‑refractory acute and chronic GVHD, belumosudil for chronic GVHD after at least two prior systemic lines, and axatilimab‑csfr for chronic GVHD after failure of at least two systemic therapies. FDA ruxolitinib aGVHD; FDA ruxolitinib cGVHD; FDA belumosudil; FDA axatilimab‑csfr. Long‑term survivors face late effects such as endocrine dysfunction, infertility, and second solid cancers, with risk influenced by irradiation exposure and GVHD. Blood review; Cancer/ACS review.
Utilization and outcomes
CIBMTR’s 2024 U.S. Summary Slides (updated April 2025) document practice patterns and survival across donor sources, conditioning intensity, and diseases, with three‑year survival continuing to improve in allogeneic and autologous cohorts compared with prior eras. CIBMTR Summary Slides (2024, updated 2025); Transplantation and Cellular Therapy 2025 CIBMTR report. In Europe, EBMT activity reports show 2023 increases in allogeneic HCT, particularly for myeloid malignancies, alongside rising use of CAR‑T and stable autologous HCT volumes. EBMT 2023 activity (Passweg et al.). In the United States, the federal program reports thousands of unrelated donor transplants annually, and coverage policies continue to evolve (e.g., 2024 CMS national coverage for MDS including cord blood). HRSA CWBYCTP; ASH summary of CMS NCD for MDS.
Access and equity
Match likelihood varies by ancestry, reflecting HLA diversity and registry composition; NMDP reports that while only a minority of some groups identify an 8/8 unrelated donor, leveraging 7/8 or 5/8 mismatches, haploidentical related donors, or cord blood plus contemporary GVHD prophylaxis can expand access substantially. NMDP modeling; Blood Advances 2024. Ongoing initiatives emphasize diversifying the registry and optimizing donor selection algorithms. NMDP Donor for All.
