How does bone-marrow transplantation cure leukaemia?

Bone-marrow transplantation from an HLA-identical sibling is effective in eradicating leukaemia in most patients with acute myelogenous leukaemia (AML) in first remission. The efficacy is widely assumed to be related to the high doses of drugs and radiation administered before transplantation. Relapse rates in 31 transplants from monozygotic twins were compared with those in 339 transplants from HLA-identical siblings managed with similar chemoradiotherapy. The actuarial relapse rate in the twins was 59% (95% confidence interval +/- 20%) compared with 18 +/- 4% in the non-twin siblings. The high relapse rate in identical twins may be related to the absence of graft-versus-host disease after transplantation. If success depends substantially on the immunotherapeutic effect of allogeneic bone-marrow, only limited benefit can be expected from autotransplantation and intensification chemotherapy for AML.