Cord blood CD4+CD25+ regulatory T cells fail to inhibit cord blood NK cell functions due to insufficient production and expression of TGF-beta1

• Cord blood Treg cells have diminished inhibitory effects on NK cell functions.
• Cord blood has relatively higher percentage of FOXP3+ cells in CD4+CD25+ Treg cells.
• Cord blood CD4+CD25+ Treg cells have insufficient expression of TGF-beta1.

Although CD4+CD25+ Treg (Treg) cells are known to modulate NK cell functions, the modulation mechanism of these cells in cord blood has not been fully clarified. The purpose of this study was to clarify the mechanism whereby cord blood Treg cells modulate cord NK cells. By performing various cultures of purified NK cells with or without autologous Treg cells, diminished inhibitory effects of cord Treg cells towards cord NK cell functions, including activation, cytokine production, and cytotoxicity, were observed. We also observed lower secretion of sTGF-beta1 and lower expression of mTGF-beta1 by cord Treg cells than by adult Treg cells. These data revealed the capability of adult Treg cells to suppress rhIL-2-stimulated NK cell function by TGF-beta1, both membrane-bound and soluble types. The reduced inhibitory capabilities of cord Treg cells compared with adult Treg cells is thought to be due to insufficient expression of TGF-beta1.