Antagonizing a killer: hepatitis C virus-infected cells inhibit natural killer cells

Hepatitis C virus (HCV) infects at least 3% of the global population, 80% of those will develop chronic HCV infection, which can lead to liver scarring and hepatocellular carcinoma. Natural killer (NK) cells provide a rapid defense against viral infections, thus, evasion of NK cell functions may be key for the establishment of viral persistence and chronic infection. Here, we show that HCV-infected cells directly interact with, and dampen NK cell cytokine and cytotoxic functions, independent of cytopathic effects exerted by HCV infection of the human hepatoma cells. We observed no change in expression levels of NK cell activating receptors, NKG2D, NKp46 or CD16 on NK cells exposed to HCV infected cells, nor of human histocompatibility-linked leukocyte antigen (HLA)-E on HCV-infected compared to uninfected cells. However, surface expression of the natural cytotoxicity receptor NKp30 was reduced and infection of Huh-7.5 cells with HCV increased surface binding of an NKp30-lgG1 Fcγ fusion protein, suggesting up-regulation of an antagonistic NKp30 ligand on HCV-infected cells

Natural Killer Cell Function and Dysfunction in Hepatitis C Virus Infection

Viruses must continually adapt against dynamic innate and adaptive responses of the host immune system to establish chronic infection. Only a small minority (∼20%) of those exposed to hepatitis C virus (HCV) spontaneously clear infection, leaving approximately 200 million people worldwide chronically infected with HCV. A number of recent research studies suggest that establishment andmaintenance of chronicHCVinfection involve natural killer (NK) cell dysfunction. This relationship is illustrated in vitro by disruption of typicalNK cell responses including both cell-mediated cytotoxicity and cytokine production. Expression of a number of activating NK cell receptors in vivo is also affected in chronic HCV infection.Thus, direct in vivo and in vitro evidence of compromised NK function in chronic HCV infection in conjunction with significant epidemiological associations between the outcome of HCV infection and certain combinations of NK cell regulatory receptor and class I human histocompatibility linked antigen (HLA) genotypes indicate that NK cells are important in the immune response against HCV infection. In this review, we highlight evidence suggesting that selective impairment of NK cell activity is related to establishment of chronic HCV infection

TIGIT Blockade: A Multipronged Approach to Target the HIV Reservoir

During chronic human immunodeficiency virus type 1 (HIV-1) infection, upregulation of inhibitory molecules contributes to effector cell dysfunction and exhaustion. This, in combination with the ability of HIV-1 to reside dormant in cellular reservoirs and escape immune recognition, makes the pathway to HIV-1 cure particularly challenging. An idealized strategy to achieve HIV-1 cure proposes combined viral and immune activation by “shock”ing HIV-1 out of latency and into an immunologically visible state to be recognized and “kill”ed by immune effector cells. Here we outline the potential for blockade of the inhibitory immune checkpoint T cell immunoreceptor with immunoglobulin and ITIM domains (TIGIT) to overcome natural killer (NK) cell and T cell inhibition associated with HIV-1 infection and invigorate antiviral effector cell responses against HIV-1 reactivated from the latent cellular reservoir

Natural Killer Cells Adapt to Cytomegalovirus Along a Functionally Static Phenotypic Spectrum in Human Immunodeficiency Virus Infection

Events related to HCMV infection drive accumulation of functionally enhanced CD57posNKG2Cpos adapted NK cells. We investigated NK cell adaptation to HCMV along a proposed continuum progressing from acute activation through maturation and memory formation towards functional exhaustion. Acute exposure to conditioned medium collected 24 h after HCMV infection (HCMVsn) increased NK cell cytotoxicity for all HCMV-seronegative and seropositive donors tested, with mean 38 and 29% boosts in natural and antibody-dependent cell-mediated cytotoxicity (ADCC), respectively. Increases in NK cell cytotoxicity were completely abrogated by blocking type I interferon (IFN) receptors and equivalent responses occurred with exposure to IFN-α2 alone at the same concentration present in HCMVsn. To study longer term effects of HCMV infection, we focused on three groups of human immunodeficiency virus (HIV)-infected subjects distinguished as HCMV-seronegative or HCMV-seropositive with either high (>20%) or low (<6%) fractions of their NK cells expressing NKG2C. The NK cells of all three HIV-infected groups responded to HCMVsn and IFN-α2 in a manner similar to the NK cells of either HCMV-seronegative or seropositive controls. Neither HCMV status, nor the extent of phenotypic evidence of adaptation to HCMV infection significantly affected mean levels of ADCC or CD16-mediated NK cell degranulation and IFN-γ production compared between the HIV-infected groups. Levels of IFN-γ production correlated significantly with the fraction of NK cells lacking FcεRIγ (FcRγ), but not with the fraction of NK cells expressing NKG2C. There was negligible expression of exhaustion markers Lag-3 and PD-1 on NK cells in any of the groups and no significant difference between groups in the fraction of NK cells expressing Tim-3. The fraction of NK cells expressing Tim-3 was unaffected by CD16 stimulation. Relative to the total NK cell population, responses of Tim-3-expressing cells to CD16 stimulation were variably compromised in HCMV seronegative and seropositive groups. In general, NK cell function in response to signaling through CD16 was well preserved in HIV infection and although HCMV had a clear effect on NK cell FcRγ and NKG2C expression, there was little evidence that the level of adaptation to HCMV infection affected CD16-dependent NK cell signaling in HIV infection

Combined anti-S1 and anti-S2 antibodies from hybrid immunity elicit potent cross-variant ADCC against SARS-CoV-2

Antibodies capable of neutralizing SARS-CoV-2 are well studied, but Fc receptor–dependent antibody activities that can also significantly impact the course of infection have not been studied in such depth. Since most SARS-CoV-2 vaccines induce only anti-spike antibodies, here we investigated spike-specific antibody-dependent cellular cytotoxicity (ADCC). Vaccination produced antibodies that weakly induced ADCC; however, antibodies from individuals who were infected prior to vaccination (hybrid immunity) elicited strong anti-spike ADCC. Quantitative and qualitative aspects of humoral immunity contributed to this capability, with infection skewing IgG antibody production toward S2, vaccination skewing toward S1, and hybrid immunity evoking strong responses against both domains. A combination of antibodies targeting both spike domains support strong antibody-dependent NK cell activation, with 3 regions of antibody reactivity outside the receptor-binding domain (RBD) corresponding with potent anti-spike ADCC. Consequently, ADCC induced by hybrid immunity with ancestral antigen was conserved against variants containing neutralization escape mutations in the RBD. Induction of antibodies recognizing a broad range of spike epitopes and eliciting strong and durable ADCC may partially explain why hybrid immunity provides superior protection against infection and disease compared with vaccination alone, and it demonstrates that spike-only subunit vaccines would benefit from strategies that induce combined anti-S1 and anti-S2 antibody responses

Innate adaptation: the influence of human cytomegalovirus on natural killer cells

During their lifetime, over half the world’s population will experience chronic viral infection or cancer, both of which involve evasion of host immunity. We have within us immune cells called natural killer (NK) cells that constantly survey our tissues to detect and eliminate transformed and infected cells. Thus, they have a critical role in preventing cancer and containing virus infection. Although most viruses only disrupt our lives transiently, if at all, some viruses establish life-long persistent infection. Human cytomegalovirus (HCMV) is a common herpesvirus infecting most of the adult population and although relatively innocuous in healthy individuals, HCMV infection or reactivation has an enormous impact on the human immune system, poses serious health risks to the immunocompromised, and is an important cofactor driving ongoing immune activation in people living with HIV (PLWH). One outcome of HCMV infection is emergence of a stable differentiated population of phenotypically and functionally adapted NK cells exhibiting a form of memory. While mechanisms that create adapted NK cells in vivo remain enigmatic, exposure to HCMV is the one common factor underlying their presence. Exploring basic molecular mechanisms governing NK cell-mediated immunity can inform cell-based treatment strategies against virus infection or cancer. As chronic HIV-1 infection amplifies HCMV-driven accumulation of adaptive NK cells, we studied whether NK cell adaptation to HCMV infection functionally impacts their natural and antibody-dependent cytotoxic functions in this setting. Although factors present during HCMV infection augmented NK cell activity, we found no evidence that NK cells acquire superior cytotoxic function or capacity for interferon-γ secretion in response to target cells following adaptation to HCMV infection. However, HCMV-driven NK cell adaptation in HIV-1 infection paralleled increased expression of TIGIT, an inhibitory immune checkpoint receptor, on NK cells. As chronic virus infection contributes to effector cell dysfunction, punctuated by increased expression of inhibitory immune checkpoint receptors, it is important to unravel the mechanisms by which viruses affect regular NK cell functions to either prevent dysfunction or introduce disease-appropriate mediators to invigorate NK cell responses. Understanding basic molecular mechanisms governing NK cell-mediated immunity will inform new strategies to optimize our immune system capacities

Modulation of the strength and character of HIV-specific CD8+ T cell responses with heteroclitic peptides

Abstract Chronic infection with human immunodeficiency virus (HIV) causes HIV-specific CD8+ T cell dysfunction and exhaustion. The strong association between non-progression and maintenance of HIV-specific CD8+ T cell cytokine production and proliferative capacities suggests that invigorating CD8+ T cell immune responses would reduce viremia and slow disease progression. A series of studies have demonstrated that sequence variants of native immunogenic peptides can generate more robust CD8+ T cell responses and that stimulation with these ‘heteroclitic’ peptides can steer responses away from the phenotypic and functional attributes of exhaustion acquired during chronic HIV infection. Incorporation of heteroclitic peptide stimulation within therapeutic vaccines could favour induction of more effective cellular antiviral responses, and in combination with ‘shock and kill’ strategies, contribute towards HIV cure

Cytomegalovirus-Driven Adaption of Natural Killer Cells in NKG2Cnull Human Immunodeficiency Virus-Infected Individuals

Expansion of natural killer (NK) cells expressing NKG2C occurs following human cytomegalovirus (HCMV) infection and is amplified by human immunodeficiency virus (HIV) co-infection. These NKG2C-expressing NK cells demonstrate enhanced CD16-dependent cytokine production and downregulate Fc&epsilon;RI&gamma; and promyelocytic leukemia zinc finger protein (PLZF). Lacking NKG2C diminishes resistance to HIV infection, but whether this affects NK cell acquisition of superior antibody-dependent function is unclear. Therefore, our objective was to investigate whether HCMV-driven NK cell differentiation is impaired in NKG2Cnull HIV-infected individuals. Phenotypic (CD2, CD16, CD57, NKG2A, Fc&epsilon;RI&gamma;, and PLZF expression) and functional (cytokine induction and cytotoxicity) properties were compared between HIV&ndash;infected NKG2Cnull and NKG2C-expressing groups. Cytokine production was compared following stimulation through natural cytotoxicity receptors or through CD16. Cytotoxicity was measured by anti-CD16-redirected lysis and by classical antibody-dependent cell-mediated cytotoxicity (ADCC) against anti-class I human leukocyte antigen (HLA) antibody-coated cells. Our data indicate highly similar HCMV-driven NK cell differentiation in HIV infection with or without NKG2C. While the fraction of mature (CD57pos) NK cells expressing CD2 (p = 0.009) or co-expressing CD2 and CD16 (p = 0.03) was significantly higher in NKG2Cnull HIV-infected individuals, there were no significant differences in NKG2A, Fc&epsilon;RI&gamma;, or PLZF expression. The general phenotypic and functional equivalency observed suggests NKG2C-independent routes of HCMV-driven NK cell differentiation, which may involve increased CD2 expression

Cellular Immune Responses to SARS-CoV-2 in Exposed Seronegative Individuals

Some SARS-CoV-2-exposed individuals develop immunity without overt infection. We identified 11 individuals who were negative by nucleic acid testing during prolonged close contact and with no serological diagnosis of infection. As this could reflect natural immunity, cross-reactive immunity from previous coronavirus exposure, abortive infection due to de novo immune responses, or other factors, our objective was to characterize immunity against SARS-CoV-2 in these individuals. Blood was processed into plasma and peripheral blood mononuclear cells (PBMC) and screened for IgG, IgA, and IgM antibodies (Ab) against SARS-CoV-2 and common β-coronaviruses OC43 and HKU1. Receptor blocking activity and interferon-alpha (IFN-α) in plasma were also measured. Circulating T cells against SARS-CoV-2 were enumerated and CD4+ and CD8+ T cell responses discriminated after in vitro stimulation. Exposed uninfected individuals were seronegative against SARS-CoV-2 spike (S) and selectively reactive against OC43 nucleocapsid protein (N), suggesting common β-coronavirus exposure induced Ab cross-reactive against SARS-CoV-2 N. There was no evidence of protection from circulating angiotensin-converting enzyme (ACE2) or IFN-α. Six individuals had T cell responses against SARS-CoV-2, with four involving CD4+ and CD8+ T cells. We found no evidence of protection from SARS-CoV-2 through innate immunity or immunity induced by common β-coronaviruses. Cellular immune responses against SARS-CoV-2 were associated with time since exposure, suggesting that rapid cellular responses may contain SARS-CoV-2 infection below the thresholds required for a humoral response