Haemopoietic stem-cell transplantation: recent progress and future promise.

Transplantation of haemopoietic stem cells is an increasingly important approach in the management of malignant haematological disease. Recent developments in our understanding of stem-cell biology have profoundly influenced the practice of both autologous and allogeneic stem cell transplantation. The demonstration that cytokines, such as granulocyte colony-stimulating factor, mobilise large numbers of haemopoietic progenitors has resulted in the peripheral blood rather than the bone marrow becoming the preferred source of haemopoietic stem cells in autologous, and increasingly in allogeneic, stem-cell transplantation. This has substantially reduced the morbidity of autografting, so that disease relapse now represents the most important cause of treatment failure. Current efforts are aimed at reducing this risk, either by employing novel conditioning regimens or by tumour purging. With regard to allogeneic transplantation, there is a growing realisation of the importance of a graft-versus-leukaemia effect, and this has encouraged the use of strategies which optimise an immunologically-mediated antitumour effect. This, coupled with increased understanding of the biology of stem-cell engraftment, has resulted in the development of less toxic conditioning regimens, designed to allow the benefits of allografting to be extended to patients in whom this procedure is contraindicated.