Allogeneic Hematopoietic Stem Cell Transplantation (Allo-HSCT)

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is a treatment in which blood-forming stem cells from a healthy donor are given to a patient to rebuild the blood and immune systems.

Before transplantation, patients usually receive conditioning therapy with chemotherapy and sometimes radiation to reduce or eliminate abnormal cells and prepare the body for the donor stem cells. After transplantation, donor immune cells may also recognize and attack remaining cancer cells, producing a graft-versus-tumor effect.

Allo-HSCT is mainly used to treat blood cancers such as leukemia, myelodysplastic syndromes (MDS), and certain lymphomas. It is also used for some noncancerous blood disorders, including aplastic anemia.

Whether allo-HSCT is appropriate depends on the type and risk of the disease, response to previous treatment, treatment history, age, overall health, and other clinical factors.

In acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL), transplantation may be considered for selected patients with high-risk disease, an inadequate treatment response, or relapse. For patients with MDS, the timing of transplantation depends largely on disease risk. Allo-HSCT may also be considered for selected patients with relapsed or refractory lymphoma and other high-risk blood cancers.

A suitable stem cell donor is also needed. Donors may include HLA-matched siblings, unrelated donors, or haploidentical family members. Donor selection is individualized by the transplant team.

Allo-HSCT generally involves pre-transplant evaluation, donor selection and HLA matching, conditioning therapy, stem cell infusion, and post-transplant recovery and follow-up.

After conditioning, donor stem cells are infused intravenously. The cells travel to the bone marrow and gradually begin producing new blood cells, a process known as engraftment. While waiting for engraftment, blood cell counts are often very low, requiring close monitoring and prevention or treatment of infection and bleeding.

Engraftment does not mark the end of treatment. Long-term follow-up is needed to monitor blood count recovery, donor chimerism, the underlying disease, infections, and graft-versus-host disease (GVHD). Immunosuppressive medications are also used when needed.

Allo-HSCT is a complex treatment, and the risk of complications depends on factors such as the underlying disease, age and overall health, conditioning regimen, donor type, and immune status after transplantation.

Important complications include infection, bleeding, graft-versus-host disease (GVHD), graft failure or poor graft function, and complications involving organs such as the liver, lungs, and kidneys. Some patients may also develop transplant-associated thrombotic microangiopathy and other transplant-related complications.

Relapse of the underlying disease remains an important concern after transplantation. For this reason, allo-HSCT requires care from an experienced transplant team as well as ongoing disease monitoring and long-term follow-up.