GSK‐3β inhibition promotes early engraftment of <i>ex vivo‐</i>expanded haematopoietic stem cells

<jats:title>Abstract</jats:title><jats:sec><jats:title>Objectives</jats:title><jats:p>Umbilical cord blood (<jats:styled-content style="fixed-case">UCB</jats:styled-content>) is a source of stem cells used for allogeneic transplantation, in addition to bone marrow and peripheral blood. Limited numbers of stem cells in a single <jats:styled-content style="fixed-case">UCB</jats:styled-content> unit is associated with slow haematopoietic recovery and high risk of graft failure, particularly in adult patients. <jats:styled-content style="fixed-case">UCB</jats:styled-content> stem cells can be expanded <jats:italic>ex vivo</jats:italic>; however, rapid differentiation reduces their regenerative potential. We have recently shown that Wnt/β‐catenin signalling is down‐regulated in <jats:italic>ex vivo</jats:italic>‐expanded stem cells; therefore, we propose that re‐activation of Wnt signalling using <jats:styled-content style="fixed-case">GSK</jats:styled-content>‐3β inhibition may act to improve regenerative potential of these <jats:italic>ex vivo</jats:italic>‐expanded stem cells.</jats:p></jats:sec><jats:sec><jats:title>Materials and methods</jats:title><jats:p>Immunocompromised mice were employed in transplantation studies to determine stem‐cell engraftment. Flow cytometry was used to phenotype the engrafted human cells. Retroviral gene transfer was used to examine the role of <jats:italic>Myc</jats:italic> gene up‐regulated by <jats:styled-content style="fixed-case">GSK</jats:styled-content>‐3β inhibition, in <jats:italic>ex vivo</jats:italic>‐expanded stem cells.</jats:p></jats:sec><jats:sec><jats:title>Results</jats:title><jats:p>Treatment with <jats:styled-content style="fixed-case">GSK</jats:styled-content>‐3β inhibitor, 6‐bromoindirubin 3′‐oxime (<jats:styled-content style="fixed-case">BIO</jats:styled-content>) improved early human cell engraftment in the mice and elevated the numbers of myeloid progenitor cells in cytokine‐stimulated culture. <jats:styled-content style="fixed-case">BIO</jats:styled-content> up‐regulated β‐catenin and c‐myc in <jats:italic>ex vivo</jats:italic>‐expanded stem cells. Ectopic expression of <jats:italic>Myc</jats:italic> acted to increase clonogenic potential and to delay differentiation of haematopoietic progenitor cells, suggesting the potential mechanism to improve regenerative potential of <jats:italic>ex vivo</jats:italic>‐expanded grafts.</jats:p></jats:sec><jats:sec><jats:title>Conclusions</jats:title><jats:p>Pharmacological inhibition of <jats:styled-content style="fixed-case">GSK</jats:styled-content>‐3β provided a novel approach to improve early engraftment of <jats:italic>ex vivo</jats:italic>‐expanded haematopoietic progenitor cells.</jats:p></jats:sec>