Immunobiology of allogeneic peripheral blood mononuclear cells mobilized with granulocyte-colony stimulating factor

The use of mobilized peripheral blood (PB) stem cells for autologous transp lantation initially generated much enthusiasm because of enhanced engraftme nt in comparison to marrow stem cells and avoidance of general anesthesia f or the donor. Its application to the allogeneic setting seemed inevitable. For obvious ethical reasons, allogeneic donors are mobilized with cytokines only, mainly granulocyte colony-stimulating factor (G-CSF), Results from p reliminary studies suggest that in comparison to standard bone marrow trans plants, outcomes such as engraftment, host-versus-graft reaction, graft-ver sus-host disease, graft-versus-leukemia and immunological reconstitution ma y be different. Surprisingly, G-CSF, previously recognized as a late acting lineage-specific factor for neutrophil production, not only disrupts homeo stasis bet tr een stem cells and their microenvironment, but also induces s ignificant quantitative and qualitative changes in the accessory cell compa rtment, affecting lymphocytes, monocytes, natural killer, dendritic, and st romal cells. Furthermore, mobilization of huge numbers of non-professional antigen presenting cells (CD34(+) stem cells) amplifies the tolerizing pote ntial of PB stem cell grafts. Thus, G-CSF mobilization provides PB transpla nts with different immunobiologic properties in comparison to standard bone marrow grafts. Whether these immunobiologic differences will lead to bette r transplant outcomes remains to be shown through much awaited results of l arge randomized clinical trials.