Antigen-specific memory NK cell responses against HIV and influenza use the NKG2/HLA-E axis.

Multiple studies have broadened the roles of natural killer (NK) cells functioning as purely innate lymphocytes by demonstrating that they are capable of putative antigen-specific immunological memory against multiple infectious agents including HIV-1 and influenza. However, the mechanisms underlying antigen specificity remain unknown. Here, we demonstrate that antigen-specific human NK cell memory develops upon exposure to both HIV and influenza, unified by a conserved and epitope-specific targetable mechanism largely dependent on the activating CD94/NKG2C receptor and its ligand HLA-E. We validated the permanent acquisition of antigen specificity by individual memory NK cells by single-cell cloning. We identified elevated expression of KLRG1, α4ß7, and NKG2C as biomarkers of antigen-specific NK cell memory through complex immunophenotyping. Last, we uncovered individual HLA-E-restricted peptides that may constitute the dominant NK cell response in HIV-1- and influenza-infected persons in vivo. Our findings clarify the mechanisms contributing to antigen-specific memory NK cell responses and suggest that they could be potentially targeted therapeutically for vaccines or other therapeutic interventions.

Upregulation of the NKG2D ligand ULBP2 by JC polyomavirus infection promotes immune recognition by natural killer cells.

BACKGROUND: JC polyomavirus(JCPyV) causes progressive multifocal leukoencephalopathy(PML), a potentially fatal complication of severe immune suppression with no effective treatment. Natural killer (NK) cells play critical roles in defense against viral infections, yet NK cell response to JCPyV infection remains unexplored. METHODS: NK and T cell responses against the JCPyV VP1 were compared using intracellular cytokine staining (ICS) upon stimulation with peptide pools. A novel flow cytometry-based assay was developed to determine NK cell killing efficiency of JCPyV-infected astrocyte-derived SVG-A cells. Blocking antibodies were used to identify the specific NK cell receptors in immune recognition of JCPyV-infected cells. RESULTS: In about 40% of healthy donors, we detected robust CD107a upregulation and IFN-γ production by NK cells, extending beyond T cell responses. Next, using the NK cell-mediated killing assay, we showed that co-culture of NK cells and JCPyV-infected SVG-A cells leads to a 60% reduction in infection, on average. JCPyV-infected cells had enhanced expression of ULBP2 - a ligand for the activating NK cell receptor NKG2D and addition of NKG2D blocking antibodies decreased NK cell degranulation. CONCLUSION: NKG2D-mediated activation of NK cells plays a key role in controlling JCPyV replication and may be a promising immunotherapeutic target to boost NK cell anti-JCPyV activity.