Graft-vs-Tumor Effect

In allogeneic stem cell transplantation, the infusion of donor marrow into the patient’s body allows cells from two immune systems the opportunity to interact. Conditioning regimens for patients receiving allogeneic transplants allow the donor stem cells to engraft in the patient by suppressing the immune system. Once the donor’s infection-fighting cells are established in the patient’s body, they may recognize the patient’s tissue and cells, including any residual cancer cells, as being different or foreign. The immune system may then cause damage to certain organs such the liver, gastrointestinal tract or skin; this effect is known as graft-vs-host disease (GvHD).
 
In other ways, the donor’s immune cells may recognize residual leukemia, lymphoma or cancer cells as being different and destroy them. Retrospective studies have demonstrated that patients in whom acute or chronic GvHD develops have lower disease recurrence rates than patients who do not develop GvHD. This finding is an indirect indication of a graft-vs-tumor effect.

Infusion of certain types of the donor’s blood cells such T-lymphocytes can also stimulate a graft-vs-leukemia effect. This effect has been best observed in patients with chronic myeloid leukemia (CML). In CML, 75 percent of patients relapsing after transplant re-enter remission. For other disorders such as acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS), the effect is less pronounced; AML and MDS in approximately 20 percent of patients enter remission. For patients with acute lymphoblastic leukemia (ALL), the presence of graft-vs-leukemia effect is unclear, although small numbers of patients have reportedly benefited, at least transiently, from the effect.