An atlas of natural killer cell receptor expression on healthy donor T and NK lymphocytes

Human T cells and natural killer (NK) cells exhibit variegated co-expression of germlineencoded receptors, which diversifies their effector functions. CD8+ T cell expression of receptors more typically associated with NK cells has been noted, but a systematic analysis of their distribution has not been described. Here, we comprehensively measured human NK cells and T cells’ expression of NK cell-associated receptors to define their co-expression and patterns associated with donor sex, maturation, and activation.

To assess the activating and inhibitory receptor repertoire of human T cells and NK cells, we developed a 25-colour flow cytometry panel that included channels based on receptor functions. Since NK cell function is known to be driven by interactions with HLA supergroups (KIR ligands), we stratified donors based on KIR-HLA allelic combinations. NK and CD8+ T cell phenotypes and responsiveness were assessed at rest, and in response to the missing self target cell line, K562. We find that NK cells universally express CD45RA, CD161, and the inhibitory receptors TIGIT/TIM3/LAG3. On CD56 ^dim CD16 ^high NK cells (those most aligned with missing self reactivity, CD161, CD45RA, natural cytotoxicity receptors (NCRs), and TIGIT/TIM3/LAG3 were most frequently expressed. Not all educated NK cells respond to missing self-targets; those that did exhibited high expression of NCRs, NKG2C, IL-7R/IL-18Ra, and TIGIT/TIM3/LAG3, and lower expression of DNAM-1 and CCR7, in addition to the KIR molecules that defined their status as educated. We note that up to 50% of NK cells express CD8, and this population co-expressed CD16, NCRs, and KIR, and exhibited greater cytotoxicity than the CD8-NK cell population. Among CD8 ⁺ T cells, acquisition of NK cell-associated receptors was increased as they progressed through differentiation states: effector memory and terminally-differentiated CD8 ⁺ T cells exhibiting higher expression of NKG2A, KIR, and CD16.

Taken together, the variability of receptor expression patterns highlights the diversity of lymphocyte populations and suggests shared features among the cytotoxic lymphocytes.