Autologous stem cell transplantation as post-remission therapy in adult acute myelogenous leukemia: Does platelet contamination of peripheral blood mobilized stem cell grafts influence the risk of leukemia relapse?

Conventional chemotherapy of acute myelogenous leukemia (AML) results in an overall long-term disease-free survival of less than 50%, but for selected subsets of younger patients the prognosis can be improved by allogeneic st em cell transplantation. The use of autologous stem cell transplantation is now investigated as an alternative to allotransplantation due to its lower risk of serious complications. However, autotransplantation is associated with a relatively high risk of post-transplant AML relapse that can be deri ved from contaminating leukemia cells in the autograft. Peripheral blood mo bilized stem cell (PBSC) grafts usually contain a higher number of platelet s. The degree of platelet contamination is determined by the peripheral blo od platelet count at the time of harvesting, and the platelets become activ ated and release soluble mediators during the ex vivo handling of PBSC graf ts. Many of these platelet-derived mediators can bind to specific receptors expressed by AML blasts, and the platelet contamination may then alter AML blast survival and thereby influence the risk of post-transplant leukemia relapse. Therefore, we conclude that the platelet contamination of autologo us stem cell grafts is possibly of clinical importance, but the effect of t his nonstandardized parameter is difficult to predict in individual patient s because the number of graft-contaminating platelets, the degree of platel et activation, and the effects of platelet-derived mediators on AML blasts differ between patients.