This is the author accepted manuscript (AAM). The final published version (version of record) is available online via AAAS at http://immunology.sciencemag.org/content/2/15/eaal5296. Please refer to any applicable terms of use of the publisher. University of Bristol -Explore Bristol Research General rightsThis document is made available in accordance with publisher policies. Please cite only the published version using the reference above. KIR2DS2, an activating natural killer cell receptor recognizes highly conserved peptides derived from the RNA helicases of pathogenic flaviviruses. AbstractKiller cell immunoglobulin-like receptors (KIR) are rapidly evolving species-specific natural killer cell receptors associated with protection against multiple different human viral infections. We report that the activating receptor KIR2DS2 directly recognizes viral peptides derived from conserved regions of flaviviral superfamily 2 RNA helicases in the context of MHC class I. The peptide LNPSVAATL, from the HCV helicase, binds HLA-C*0102 leading to NK cell activation through engagement of KIR2DS2. Similarly, HLA-C*0102 presents highly conserved peptides from the helicase motif 1b region of related flaviviruses, including dengue, Zika, yellow fever and Japanese encephalitis viruses, to KIR2DS2. These flaviviral peptides all contain an "MCHAT" motif, which is present in 61 out of 63 flaviviruses.LNPSVAATL is also highly conserved across HCV genotypes and mutation of this epitope is poorly tolerated by HCV. KIR2DS2 recognizes endogenously presented helicase peptides and KIR2DS2 is sufficient to inhibit HCV and dengue virus replication in the context of HLA-C*0102. Targeting short, but highly conserved, viral peptides provide non-rearranging innate immune receptors with an efficient mechanism to recognize multiple, highly variable pathogenic RNA viruses.4

The interactions of killer Ig–like receptor 2D (KIR2D) with HLA-C ligands contribute to functional NK cell education and regulate NK cell functions. Although simple alloreactive rules have been established for inhibitory KIR2DL, those governing activating KIR2DS function are still undefined, and those governing the formation of the KIR2D repertoire are still debated. In this study, we investigated the specificity of KIR2DL1/2/3 and KIR2DS1/2, dissected each KIR2D function, and assessed the impact of revisited specificities on the KIR2D NK cell repertoire formation from a large cohort of 159 KIR and HLA genotyped individuals. We report that KIR2DL2+ and KIR2DL3+ NK cells reacted similarly against HLA-C+ target cells, irrespective of C1 or C2 allele expression. In contrast, KIR2DL1+ NK cells specifically reacted against C2 alleles, suggesting a larger spectrum of HLA-C recognition by KIR2DL2 and KIR2DL3 than KIR2DL1. KIR2DS2+ KIR2DL2− NK cell clones were C1-reactive irrespective of their HLA-C environment. However, when KIR2DS2 and KIR2DL2 were coexpressed, NK cell inhibition via KIR2DL2 overrode NK cell activation via KIR2DS2. In contrast, KIR2DL1 and KIR2DS2 had an additive enhancing effect on NK cell responses against C1C1 target cells. KIR2DL2/3/S2 NK cells predominated within the KIR repertoire in KIR2DL2/S2+ individuals. In contrast, the KIR2DL1/S1 NK cell compartment is dominant in C2C2 KIR2DL2/S2− individuals. Moreover, our results suggest that together with KIR2DL2, activating KIR2DS1 and KIR2DS2 expression limits KIR2DL1 acquisition on NK cells. Altogether, our results suggest that the NK cell repertoire is remolded by the activating and inhibitory KIR2D and their cognate ligands.

CMV infection represents a major complication in hematopoietic stem cell transplantation, which compromises graft outcome. Downregulation of HLA class I expression is one mechanism by which CMV evades T cell–mediated immune detection, rendering infected cells vulnerable to killer cell Ig-like receptor (KIR)+ NK cells. In this study, we observed that the amplified NKG2C+ NK cell population observed specifically in CMV seropositive individuals mainly expressed KIR2DL receptors. We have shown that HLA class I expression was downregulated on CMV-infected immature dendritic cells (iDCs), which escape to HLA-A2-pp65–specific T lymphocytes but strongly trigger the degranulation of KIR2D+ NK cells. CMV infection conferred a vulnerability of C2C2+ iDCs to educated KIR2DL1+ and KIR2DL3+ NK cell subsets. Alloreactivity of KIR2DL1+ NK cell subsets against C1C1+ iDCs was maintained independently of CMV infection. Unexpectedly, CMV-infected C1C1+ iDCs did not activate KIR2DL3+ NK cell reactivity, suggesting a potential CMV evasion to KIR2DL3 NK cell recognition. Altogether, the coexpression of KIR and NKG2C on expanded NK cell subsets could be related to a functional contribution of KIR in CMV infection and should be investigated in hematopoietic stem cell transplantation, in which the beneficial impact of CMV infection has been reported on the graft-versus-leukemia effect.