Abstract
BackgroundUmbilical cord blood (UCB) is enriched with transplantable CD34+ cells. In addition to CD34-expressing haematopoietic stem cells (HSC), human UCB contains a rare population of CD34-lineage- cells endowed with the ability to differentiate along the T/NK pathway in response to interleukin (IL)-15 and a stromal cell support. IL-21 is a crucial regulator of NK cell function, whose influence on IL-15-induced differentiation of CD34-lineage- cells has not been investigated previously. The present study was designed and conducted to address whether IL-21 might replace the stromal cell requirements and foster the IL-15-induced NK differentiation of human UCB CD34-lineage- cells.ResultsCD34-lineage- cells were maintained in liquid culture with Flt3-L and SCF, with the addition of IL-15 and IL-21, either alone or in combination. Cultures were established in the absence of feeder cells or serum supplementation. Cytokine-treated cells were used to evaluate cell surface phenotype, expression of molecular determinants of lymphoid/NK cell differentiation, secretion of IFN-γ, GM-CSF, TNF-α and CCL3/MIP-1α, and cytolytic activity against NK-sensitive tumour cell targets. CD34-lineage- cells proliferated vigorously in response to IL-15 and IL-21 but not to IL-21 alone, and up-regulated phosphorylated Stat1 and Stat3 proteins. CD34-lineage- cells expanded by IL-21 in combination with IL-15 acquired lymphoid morphology and killer-cell immunoglobulin-like receptor (KIR)-CD56+CD16-/+ phenotype, consistent with pseudo-mature NK cells. IL-21/IL-15-differentiated cells expressed high levels of mRNA for Bcl-2, GATA-3 and Id2, a master switch required for NK-cell development, and harboured un-rearranged TCRγ genes. From a functional standpoint, IL-21/IL-15-treated cells secreted copious amounts of IFN-γ, GM-CSF and CCL3/MIP-1α, and expressed cell surface CD107a upon contact with NK-sensitive tumour targets, a measure of exocytosis of NK secretory granules.ConclusionThis study underpins a novel role for IL-21 in the differentiation of pseudo-mature lytic NK cells in a synergistic context with IL-15, and identifies a potential strategy to expand functional NK cells for immunotherapy.
Highlights
Umbilical cord blood (UCB) is enriched with transplantable CD34+ cells
This study underpins a novel role for IL-21 in the differentiation of pseudo-mature lytic NK cells in a synergistic context with IL-15, and identifies a potential strategy to expand functional NK cells for immunotherapy
The present study aimed to address whether IL-21 might replace the stromal cell requirements and foster the IL-15induced NK differentiation of human UCB CD34-lineagecells
Summary
In addition to CD34-expressing haematopoietic stem cells (HSC), human UCB contains a rare population of CD34-lineage- cells endowed with the ability to differentiate along the T/NK pathway in response to interleukin (IL)-15 and a stromal cell support. Umbilical cord blood (UCB) is increasingly used as an alternative source of transplantable CD34+ haematopoietic stem cells (HSC) for neoplastic and non-neoplastic diseases [1]. We characterized a rare subpopulation of human UCB CD34-CD133-CD7-lineagecells capable of differentiating both into CD34+CD133+ HSC in response to stem cell factor (SCF), and into NK/ lymphoid progenitors if supported by interleukin (IL)-15 and stromal cells engineered to release human granulocyte colony-stimulating factor (G-CSF) and IL-3 [5]. It should be pointed out that mesenchymal stem cells may activate allogeneic T cells during in vitro HSC expansion [8], suggesting need for feeder cell-free culture systems that may support HSC expansion in the absence of untoward effects on other cell types
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