Competitive inhibition of IL-2/IL-2R has a dual effect on HSC ex vivo expansion and IL-2R (CD25) content

Interleukin-2 (IL-2) and its receptor play a pivotal role in the regulation of immune response and possess both immune-regulatory and immune-stimulatory functions. As a cytokine of lymphoid cells, the role of IL-2 has been revealed in hematopoietic stem cell (HSC) maintenance and proper hematopoiesis. Here, we investigated that small molecule Ro 26-4550 trifluoroacetate (Ro) mediated competitive inhibition of IL-2 and its receptor alpha subunit (IL-2R alpha) throughout ex vivo culture. Ro treatment induced murine and human ex vivo expansion of hematopoietic stem and progenitor cells (HSPCs). Ro treated HSPCs sustained self-renewal ability and low apoptotic activity. As a competitive inhibitor of IL-2/IL-2R alpha interaction, Ro small molecule induced human HSPCs to entry into cell cycle. The proliferation of bone marrow mesenchymal stem cells (MSC) and fibroblasts were also highly increased post treatment. Besides, Ro treatment enhanced IL-2R alpha (CD25) expression indepen-dent of IL-2 administration in human mPB-derived HSPCs and BM-derived HSPCs. Increased IL-2R alpha (CD25) expression in BM-HSPCs was associated with the increase in the CD4(+)CD25(+) T cell population. Xeno-transplantation of immunodeficient mice with ex vivo expanded human CD34(+) cells after Ro treatment revealed an efficient multi-lineage reconstitution in the recipient. These findings shed light on the role of IL-2/IL-2R alpha interaction in HSC expansion, in vivo and in vitro HSC self-renewal ability and repopulation capacity as well as a possible mean for the induction of CD25 expressing cells in hematopoietic compartments.