16Dynamic regulation of cellular metabolism is important for maintaining homeostasis and can directly 17 influence immune cell function and differentiation including Natural Killer (NK) cell responses. 18Persistent HIV-1 infection leads to a state of chronic activation, subset redistribution and progressive 45 et al., 2015) (Lee et al., 2015). The adaptive reconfiguration of NK cells during HIV-1 infection is further 46 delineated by loss of the transcription factor promyelocytic leukaemia zinc finger protein (PLZF), and 47 downstream signalling molecules such as FcεRI-γ (Peppa et al., 2018), which partly overlap with 48 NKG2C expression. While these attributes are considered important in the functional specialisation of 49 2 these NK cells, the development of these features under conditions of continuous 50 stimulation/persistent inflammation during HIV-1 infection could lead to the establishment of 51 functionally and metabolically exhausted NK cells akin to exhausted CD8 T cells. In keeping with this 52 notion, chronic stimulation of adaptive NK cells through NKG2C ligation was recently found to lead to 53 a molecular programme of exhaustion that is shared between NK cells and CD8 T cells (Merino et al., 54 2019). Exhausted CD8 T cells are characterised by a number of metabolic defects, however, to date it 55 remains unexplored how persistent HIV-1 infection contributes to the metabolic remodelling of NK 56 cell subsets. NK cell exhaustion could influence responses to CD16 engagement linked to vaccine-57 induced protective immunity against HIV-1 infection and phenotypes of viral control (Scully and Alter, 58 2016). Such knowledge represents a critical first step in our understanding of the metabolic machinery 59 of NK cell subsets with distinct immunologic features that can be potentially targeted for developing 60 new or complementary antiviral approaches aimed at enhancing ADCC responses. 61 62 Whereas metabolic regulation of T cell function is well characterised, evidence of the importance of 63 immunometabolism in facilitating robust NK cell functions is gradually emerging. Notably, impaired 64 NK cell cellular metabolism has been implicated in obesity and cancer, providing a new framework for 65 understanding NK cell functionality (Michelet et al., 2018) (Cong et al., 2018). Studies from both 66 human and murine models have demonstrated that NK cells activated through cytokine stimulation 67 exhibit substantial increases in the rates of both glycolysis and oxidative phosphorylation (OXPHOS) 68 pathways (Marcais et al., 2014) (Donnelly et al., 2014) (Keating et al., 2016; O'Brien and Finlay, 2019). 69However, the metabolic requirement of NK cells for optimal effector function, in terms of IFN- 70 production, depends on the specific activation stimuli. In particular, receptor mediated activation 71 through anti-NK1.1 and anti-Ly49D in mice appears to require OXPHOS as an essential second signal 72 for IFN- production and appears more susceptible to metabolic inhibition compared to cytokine 73 stimulation ...

Natural Killer (NK) cells play an important role in antiviral defence and their potent effector function identifies them as key candidates for immunotherapeutic interventions in chronic viral infections. Their remarkable functional agility is achieved by virtue of a wide array of germline encoded inhibitory and activating receptors ensuring a self-tolerant and tunable repertoire. NK cell diversity is generated by a combination of factors including genetic determinants and infections/environmental factors, which together shape the NK cell pool and functional potential. Recently a genetic polymorphism at position −21 of HLA-B, which influences the supply of HLA-E binding peptides and availability of HLA-E for recognition by the inhibitory NK cell receptor NKG2A, was shown to have a marked influence on NK cell functionality in healthy human cytomegalovirus (HCMV) seronegative Caucasian individuals. In this study, −21 methionine (M)-expressing alleles supplying HLA-E binding peptides were largely poor ligands for inhibitory killer immunoglobulin-like receptors (KIRs), and a bias to NKG2A-mediated education of functionally-potent NK cells was observed. Here, we investigated the effect of this polymorphism on the phenotype and functional capacity of NK cells in a cohort of African individuals with human immunodeficiency virus type 1 (HIV-1)/HCMV co-infection. A similarly profound influence of dimorphism at position −21 of HLA-B on NK cells was not evident in these subjects. They predominantly expressed African specific HLA-B and −C alleles that contribute a distinct supply of NKG2A and KIR ligands, and these genetic differences were compounded by the marked effect of HIV/HCMV coinfection on NK cell differentiation. Together, these factors resulted in a lack of correlation of the HLA-B −21 polymorphism with surface abundance of HLA-E and loss of the NK cell functional advantage in subjects with −21M HLA-B alleles. Instead our data suggest that during HIV/HCMV co-infection exposure of NK cells to an environment that displays altered HLA-E ligands drives adaptive NKG2C+ NK cell expansions influencing effector responses. Increased efforts to understand how NK cells are functionally calibrated to self-HLA during chronic viral infections will pave the way to developing targeted therapeutic interventions to overcome the current barriers to enhancing immune-based antiviral control.