Reduced Intensity Conditioning Regimens

Reduced intensity conditioning refers to a conditioning regimen that uses less chemotherapy and radiation than the standard myeloablative conditioning regimen. Myeloablation is the result of an intensive conditioning regimen in which the bone marrow cells are destroyed. The goal of using a reduced intensity conditioning regimen is to decrease the transplant-related complications, toxicity and mortality. However, since myeloablation may not be achieved with this approach, the risk of rejecting the transplant may be higher compared to a full-intensity (myeloablative) conditioning regimen.

We offer two different reduced-intensity conditioning regimens. One uses busulfan, Fludarabine and anti-thymocyte globulin (ATG), which is an antibody made in rabbits and used to increase the likelihood of engraftment in bone marrow transplant recipients and to treat graft-versus-host disease (GvHD). This regimen is offered to patients with bone marrow failure syndromes, myelodysplastic syndrome, acute and chronic myeloid leukemias or metabolic disorders. The advantage of this conditioning is that it reduces the incidence of disease and eliminates mortality during conditioning regimen. The disadvantage is that the rate of transplant rejection may be higher than with a myeloablative regimen.

The other reduced intensity conditioning regimen uses Fludarabine, Melphalan, rabbit ATG and additional donor lymphocyte infusions post transplant. This regimen is offered to patients with acute leukemias who sustained organ damage from previous therapies. The advantage of this conditioning regimen is that it is safer than the myeloablative conditioning. We are currently investigating if donor lymphocyte infusions can reduce the risk of relapse after reduced intensity conditioning.


These regimes are used for patients with:

  • Immune deficiencies or bone marrow failure defects, such as congenital neutropenia, thrombocytopenia and aplastic anemia
  • Pre-leukemia syndromes, such as myelodysplastic syndrome and monosomy 7
  • Acute myeloid leukemia (AML) in first remission or chronic myeloid leukemia (CML) in the chronic phase
  • Metabolic disorders, such as Hurler's disease, metachromatic leukodystrophy and adrenal leukodystrophy
  • Acute leukemia and dysfunction of the lung, heart or kidney or previous life-threatening infections or treatment complications

Currently, the non-myeloablative protocol is open to children who have the following:

  • A related or unrelated donor including umbilical cord blood
  • High-risk for a transplant-related toxic complication
  • Leukemia or a non-malignant bone marrow disorder
  • High risk leukemia and the inability to withstand a standard transplant using high-dose chemotherapy

Eventually, we hope to be able to offer this potentially safer approach to all bone marrow transplant patients.


Reviewed by health care specialists at UCSF Benioff Children's Hospital.

Related Information

UCSF Clinics & Centers

Blood & Marrow Transplant

Blood and Marrow Transplant Program
1975 Fourth St., Sixth Floor
San Francisco, CA 94158
Phone: (415) 476-2188
Fax: (415) 502-4867

Medical Genetics

Patient Experiences

Our Experts

Morton J. Cowan
Dr. Morton J. Cowan,
pediatric immunologst and bone marrow transplant specialist
Christopher Dvorak
Dr. Christopher Dvorak,
pediatric hematologist and oncologist
Robert E. Goldsby
Dr. Robert E. Goldsby,
pediatric hematologist and oncologist
James Huang
Dr. James Huang,
pediatric hematologist