Human influenza-specific adaptive NK cells mediate potent HLA-E-restricted responses against antigenically distinct influenza strains

Abstract

Novel influenza vaccine approaches to achieve cross-protection against a broad range of antigenically distinct strains are needed. Beyond their ability to eliminate infected cells without the need for prior sensitization, natural killer (NK) cells have been shown to mediate virus-specific recall responses. Notably, exposure to influenza antigens induces protective influenza-specific memory NK cells in mice, but evidence of influenza-specific memory NK cells in humans is still lacking. Using intracellular cytokine staining, we found that NK cells from 45% of adults can robustly respond to nucleoprotein (NP) from at least 2 heterosubtypic influenza strains completely independent of T cell help. To further determine if a subset of NK cells can specifically react to NP peptide pools from distinct strains, we clonally expanded individual NK cells (NKCL) and measured H1N1, H2N2 and H3N2 NP-specific killing by 33 NKCL from 6 donors. 63% of NKCL showed positive responses against the 2009 H1N1 pandemic strain (2%–57% specific lysis). Strikingly, half of H1N1 NP-specific NKCL also displayed cytotoxicity against either H2N2 or H3N2 (9%–100% specific lysis) or against both H2N2 and H3N2 strains (5%–11% specific lysis). Potent killing by NKCLs was associated with high cell surface expression of the activating NKG2C receptor, a ligand for HLA-E. Accordingly, we identified an HLA-E-restricted NP epitope that triggers activation of influenza-specific NK cells. Collectively, these data provide the first mechanistic evidence of influenza-specific memory NK cells in humans and suggest influenza-specific responses mediated by NK cells may have the potential to be harnessed to enhance influenza vaccine-induced cross-protection.

CXCR2-mediated recruitment of adaptive NK cells with NKG2C/HLA-E dependent antigen-specific memory enhances tumor killing in ovarian cancer

“…Our hypothesis suggests that these molecules play a pivotal role in discerning between self and non-self-peptides. On the other hand, we found that HLA-E and NKG2C are important for the recall responses in aNK cells, which has been earlier reported by us and others in defense against viruses ( 12, 47 ). Moreover, we found e.g., a greater TNFα secretion by aNK cells following a secondary stimulation with specific tumor cells, which facilitates the activation of the transcription factor AP-1 that is activated both in antigen specific T cells and clonal expanded NK cells ( 46, 48 ).…”

Harnessing immune cells to eliminate HIV reservoirs

“…Indeed, earlier work by Reeves et al showed that memory NK cell responses were observed in Ad26/SIV-vaccinated NHPs [42]. With the recent study by Jost and colleagues confirming that HIV antigen-specific NK cells are found in PLWH, it is plausible that both CTL and NK cell responses could be targeted against more conserved (or potentially ‘networked’), viral peptides on HLA-E [44 ▪▪ ]. Methods to enhance IL-15 signaling during the time of vaccination may be required to ensure proper development of effective HLA-E-restricted CTL responses and boost NK cell activity.…”

“…This could be supplemented with a STAT5 agonist, HODHBt, which synergizes with IL-15 to enhance activation of HIV-specific T cells [61 ▪ ]. Separately, as the antigen-specific NK cells are KLRG1 + [44 ▪▪ ], blocking this pathway during chronic infection may be a method to further enhnace the expansion and antiviral activity of this NK cell population [21 ▪▪ ], but how this would affect the antigen-specific CTL populations is unknown. Finally, the evaluation of these strategies should consider whether HIV nef would adapt to elicit stronger HLA-E downregulation (as is seen with primary strains of HIV [62]) in response to CTL/NK selective pressure.…”

“…A potential mechanism of the apparent anitgen specificity is via a conserved Gag epitope, which, when presented on HLA-E, is thought to block the interaction between HLA-E and the inhibitory receptor, NKG2A, resulting in increased NK-mediated killing [43]. Recently, an exciting study by Jost and colleagues observed the presence of HIV antigen-specific NK cells in PLWH, driven by the CD94/NKG2C receptor and viral peptides that stabilize HLA-E surface expression [44 ▪▪ ]. Mechanisms of recognition and function were confirmed in assays with clonal memory-like NK cells, which showed high expression of KLRG1, NKG2C, and α4β7.…”

Harnessing natural killer cells to target HIV-1 persistence

“…In CMV infection, NKG2Cþ NK cells differentially recognized distinct viral strains, and NKG2C represented a marker of NK cell "memory" [121][122][123]. Chronic HIV-1 infection is associated with higher NKG2C expression on NK cells, indicating that the development of such a pool of adaptive NK cells is possible, and can potentially be exploited for enabling faster and stronger recall responses [13,124,125]. In rhesus macaques, blocking NKG2C signalling diminished HIV-1-specific NK cytolytic activity, while tissuespecific vaccination induced HIV-1-specific recall responses in spite of lower NKG2C expression [15,120].…”