Wiskott-Aldrich syndrome protein-deficient hematopoietic cells can be efficiently mobilized by granulocyte colony-stimulating factor

The Wiskott-Aldrich syndrome protein is an essential cytoskeleton regulator found in cells of the hematopoietic lineage and controls the motility of leukocytes. The impact of WAS gene deficiency on the mobilization of hematopoietic progenitor/stem cells in circulation has remained unexplored but information would be pertinent in the context of autologous gene therapy of Wiskott-Aldrich syndrome. The response to granulocyte-colony stimulating factor mobilization was investigated in a murine WAS knock-out model of the disease, by measuring hematologic parameters, circulation and engraftment of hematopoietic progenitor/stem cells. In the steady-state, adult WAS knock-out mice have B-cell lymphopenia, marked neutrophilia, increased counts of circulating hematopoietic progenitor cells and splenomegaly, presumably caused by the retention of hematopoietic progenitor cells due to high levels of splenic CXCL12. In spite of these anomalies, the administration of granulocyte-colony-stimulating factor mobilizes progenitor/stem cells in WAS knock-out mice to the same level and with the same kinetics as in wild-type control mice. Mobilized peripheral blood cells from WAS knock-out mice can be transduced and are able to engraft into lethally-irradiated hosts reconstituting multiple lineages of cells and providing more effective radio-protection than mobilized cells from wild-type control mice. Surprisingly, the homing and the peripheral blood recovery of B lymphocytes was influenced by the background of the host. Thus, in the absence of Wiskott-Aldrich syndrome protein, effective mobilization is achieved but partial correction may occur as a result of an abnormal hematopoietic environment.