Surface NKG2C Identifies Differentiated αβT-Cell Clones Expanded in Peripheral Blood

T cells that express CD56 in peripheral blood of healthy humans represent a heterogeneous and poorly studied subset. In this work, we analyzed this subset for NKG2C expression. In both CD56 and CD56 subsets most of the NKG2C T cells had a phenotype of highly differentiated CD8 TEMRA cells. The CD56 NKG2C T cells also expressed a number of NK cell receptors, such as NKG2D, CD16, KIR2DL2/DL3, and maturation marker CD57 more often than the CD56 NKG2C CD3 cells. TCR β-chain repertoire of the CD3 CD56 NKG2C cell fraction was limited by the prevalence of one or several clonotypes which can be found within the most abundant clonotypes in total or CD8 T cell fraction TCRβ repertoire. Thus, NKG2C expression in highly differentiated CD56 T cells was associated with the most expanded αβ T cell clones. NKG2C T cells produced almost no IFN-γ in response to stimulation with HCMV pp65-derived peptides. This may be partially due to the high content of CD45RA CD57 cells in the fraction. CD3 NKG2C cells showed signs of activation, and the frequency of this T-cell subset in HCMV-positive individuals was positively correlated with the frequency of NKG2C NK cells that may imply a coordinated in a certain extent development of the NKG2C T and NK cell subsets under HCMV infection.