Umbilical cord blood T cells express multiple natural cytotoxicity receptors after IL-15 stimulation, but only NKp30 is functional

The natural cytotoxicity receptors (NCRs) NKp30, NKp44, and NKp46 are thought to be NK lineage restricted. Herein we show that IL-15 induces NCR expression on umbilical cord blood (UCB) T cells. NCRs were mainly on CD8 ⁺ and CD56⁺ UCB T cells. Only NKp30 was functional as demonstrated by degranulation, IFN-γ release, redirected killing, and apoptosis. Since NCRs require adaptor proteins for function, the expressions of these adaptors were determined. The adaptors used by NKp30 and NKp46, FcεR1γ and CD3ζ, were detected in UCB T cells. There was a near absence of DAP12, the adaptor for NKp44, consistent with a hypofunctional state. NKp46 was on significantly fewer UCB T cells, possibly accounting for its lack of function. Adult peripheral blood (PB) T cells showed minimal NCR acquisition after culture with IL-15. Since UCB contains a high frequency of naive T cells, purified naive T cells from adult PB were tested. Although NKp30 was expressed on a small fraction of naive PB T cells, it was nonfunctional. In contrast to UCB, PB T cells lacked FcεR1γ expression. These results demonstrate differences between UCB and PB T cells regarding NCR expression and function. Such findings challenge the concept that NCRs are NK cell specific.