In vivo expansion of the circulating stem cell pool

Stem cell trafficking between extravascular marrow sites and circulating blood is an essential part of the blood stem cell transplantation technology. Recombinant human G‐CSF (rHuG‐CSF) is widely used for stem cell peripheralization alone or together with chemopriming mobilizing early and pluripotent CD34 + cell subsets. New cytokin/chemokine mobilization regimens are under investigation such as combined rHuG‐CSF and rHu thrombopoietin, rHuG‐CSF and interleukin 3, rHuG‐CSF and rHu stem cell factor, rHuG‐CSF and Flt‐3 ligand, human macrophage inflammatory protein, interleukin 1, and interleukin 8. Modifying the adherence of CD34 + cells to extracellular matrix molecules is a new mechanism by which hematopoietic progenitor cells are released into the circulating blood. Blocking the α 4 β 1 integrin receptor on CD34 + progenitor cells by using monoclonal antibodies specific for the heterodimeric complex α 4 β 1 has been shown to further increase the circulating stem cell concentration when given following rHuG‐CSF priming. The current clinical research is primarily focused on improving stem cell mobilization efficiency in heavily pretreated and poorly mobilizing patients, and to decrease adverse effects of cytokine treatment.