Suppression of a Natural Killer Cell Response by Simian Immunodeficiency Virus Peptides

Studying the Interactions of U24 from HHV-6 in Order to Further Elucidate Its Potential Role in MS

A number of studies have suggested that human herpesvirus 6A (HHV-6A) may play a role in multiple sclerosis (MS). Three possible hypotheses have been investigated: (1) U24 from HHV-6A (U24-6A) mimics myelin basic protein (MBP) through analogous phosphorylation and interaction with Fyn-SH3; (2) U24-6A affects endocytic recycling by binding human neural precursor cell (NPC) expressed developmentally down-regulated protein 4-like WW3* domain (hNedd4L-WW3*); and (3) MS patients who express Killer Cell Immunoglobulin Like Receptor 2DL2 (KIR2DL2) on natural killer (NK) cells are more susceptible to HHV-6 infection. In this contribution, we examined the validity of these propositions by investigating the interactions of U24 from HHV-6B (U24-6B), a variant less commonly linked to MS, with Fyn-SH3 and hNedd4L-WW3* using heteronuclear single quantum coherence (HSQC) nuclear magnetic resonance (NMR) titrations and isothermal titration calorimetry (ITC). In addition, the importance of phosphorylation and the specific role of U24 in NK cell activation in MS patients were examined. Overall, the findings allowed us to shed light into the models linking HHV-6 to MS and the involvement of U24.

SARS-CoV-2 peptides bind to NKG2D and increase NK cell activity

Immune dysregulation is commonly observed in patients with coronavirus disease 2019 (COVID-19). Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) induces severe lung inflammation and innate immune cell dysregulation. However, the precise interaction between SARS-CoV-2 and the innate immune system is currently unknown. To understand the interaction between SARS-CoV-2 and natural killer (NK) cells, several SARS-CoV-2 S protein peptides capable of binding to the NKG2D receptor were screened by in silico analysis. Among them, two peptides, cov1 and cov2, bound to NK cells and NKG2D receptors. These cov peptides increased NK cytotoxicity toward lung cancer cells, stimulated interferon gamma (IFN-γ) production by NK cells, and likely mediated these responses through the phosphorylation of Vav1, a key downstream-signaling molecule of NKG2D and NK activation genes. The direct interaction between SARS-CoV-2 and NK cells is a novel finding, and modulation of this interaction has potential clinical application as a therapeutic target for COVID-19.

Current advances in HIV vaccine preclinical studies using Macaque models

The macaque simian or simian/human immunodeficiency virus (SIV/SHIV) challenge model has been widely used to inform and guide human vaccine trials. Substantial advances have been made recently in the application of repeated-low-dose challenge (RLD) approach to assess SIV/SHIV vaccine efficacies (VE). Some candidate HIV vaccines have shown protective effects in preclinical studies using the macaque SIV/SHIV model but the model's true predictive value for screening potential HIV vaccine candidates needs to be evaluated further. Here, we review key parameters used in the RLD approach and discuss their relevance for evaluating VE to improve preclinical studies of candidate HIV vaccines.

Diversification of Bw4 Specificity and Recognition of a Nonclassical MHC Class I Molecule Implicated in Maternal-Fetal Tolerance by Killer Cell Ig-like Receptors of the Rhesus Macaque

The rhesus macaque is an important animal model for AIDS and other infectious diseases; however, studies to address NK cell function in this species have been limited by the lack of defined ligands for killer cell Ig-like receptors (KIRs). To identify ligands for rhesus macaque KIRs, we adopted a novel approach based on a pair of stable cell lines. NFAT-responsive luciferase reporter cell lines expressing the extracellular domains of macaque KIRs fused to the transmembrane and cytoplasmic domains of CD28 and CD3ζ were incubated with target cells expressing individual MHC class I molecules, and ligand recognition was detected by the MHC class I-dependent upregulation of luciferase. Using this approach, we found that Mamu-KIR3DL01, -KIR3DL06, -KIR3DL08, and -KIR3DSw08 all recognize Mamu-Bw4 molecules but with differing allotype specificity. In contrast, Mamu-KIR3DL05 recognizes Mamu-A and Mamu-A-related molecules, including Mamu-A1*002 and -A3*13, Mamu-B*036, the product of a recombinant Mamu-B allele with α1 and α2 domain sequences derived from a MHC-A gene, and Mamu-AG*01, a nonclassical molecule expressed on placental trophoblasts that originated from an ancestral duplication of a MHC-A gene. These results reveal an expansion of the lineage II KIRs in macaques that recognize Bw4 ligands and identify a nonclassical molecule implicated in placental development and pregnancy as a ligand for Mamu-KIR3DL05. In addition to offering new insights into KIR-MHC class I coevolution, these findings provide an important foundation for investigating the role of NK cells in the rhesus macaque as an animal model for infectious diseases and reproductive biology.

Natural Killer Cell Interactions with Classical and Non-Classical Human Leukocyte Antigen Class I in HIV-1 Infection

Natural killer (NK) cells are effector lymphocytes of the innate immune system that are able to mount a multifaceted antiviral response within hours following infection. This is achieved through an array of cell surface receptors surveilling host cells for alterations in human leukocyte antigen class I (HLA-I) expression and other ligands as signs of viral infection, malignant transformation, and cellular stress. This interaction between HLA-I ligands and NK-cell receptor is not only important for recognition of diseased cells but also mediates tuning of NK-cell-effector functions. HIV-1 alters the expression of HLA-I ligands on infected cells, rendering them susceptible to NK cell-mediated killing. However, over the past years, various HIV-1 evasion strategies have been discovered to target NK-cell-receptor ligands and allow the virus to escape from NK cell-mediated immunity. While studies have been mainly focusing on the role of polymorphic HLA-A, -B, and -C molecules, less is known about how HIV-1 affects the more conserved, non-classical HLA-I molecules HLA-E, -G, and -F. In this review, we will focus on the recent progress in understanding the role of non-classical HLA-I ligands in NK cell-mediated recognition of HIV-1-infected cells.

Specificity of inhibitory KIRs enables NK cells to detect changes in an altered peptide environment

The activity of natural killer (NK) cells is tightly regulated by inhibitory and activating receptors. Inhibitory killer immunoglobulin-like receptors (iKIRs) survey the surface of target cells by monitoring the expression of human leukocyte antigen (HLA) class I. The binding of iKIRs has been shown to be sensitive to the peptides presented by HLA class I, implying that iKIRs have the ability to detect the changes in the repertoire of peptide-HLA class I complexes (pHLA), a process occurring during viral infection and in tumor cells. To study how the pHLA repertoire changes upon infection, and whether an iKIR is able to detect these changes, we study peptides eluted from cells prior and after infection with measles virus (MV). Remarkably, most changes in the repertoire of potential iKIR ligands are predicted to be caused by the altered expression of self-peptides. We show that an iKIR can detect these changes in the presented peptides only if it is sufficiently specific, e.g., if iKIRs can distinguish between different amino acids in the contact residues (e.g., position 7 and 8). Our analysis further indicates that one single iKIR per host is not sufficient to detect changes in the peptide repertoire, suggesting that a multigene family encoding for different iKIRs is required for successful peptide recognition.

KIR3DL01 upregulation on gut natural killer cells in response to SIV infection of KIR- and MHC class I-defined rhesus macaques

Natural killer cells provide an important early defense against viral pathogens and are regulated in part by interactions between highly polymorphic killer-cell immunoglobulin-like receptors (KIRs) on NK cells and their MHC class I ligands on target cells. We previously identified MHC class I ligands for two rhesus macaque KIRs: KIR3DL01 recognizes Mamu-Bw4 molecules and KIR3DL05 recognizes Mamu-A1*002. To determine how these interactions influence NK cell responses, we infected KIR3DL01+ and KIR3DL05+ macaques with and without defined ligands for these receptors with SIVmac239, and monitored NK cell responses in peripheral blood and lymphoid tissues. NK cell responses in blood were broadly stimulated, as indicated by rapid increases in the CD16+ population during acute infection and sustained increases in the CD16+ and CD16-CD56- populations during chronic infection. Markers of proliferation (Ki-67), activation (CD69 & HLA-DR) and antiviral activity (CD107a & TNFα) were also widely expressed, but began to diverge during chronic infection, as reflected by sustained CD107a and TNFα upregulation by KIR3DL01+, but not by KIR3DL05+ NK cells. Significant increases in the frequency of KIR3DL01+ (but not KIR3DL05+) NK cells were also observed in tissues, particularly in the gut-associated lymphoid tissues, where this receptor was preferentially upregulated on CD56+ and CD16-CD56- subsets. These results reveal broad NK cell activation and dynamic changes in the phenotypic properties of NK cells in response to SIV infection, including the enrichment of KIR3DL01+ NK cells in tissues that support high levels of virus replication.

Analysis of Simian Immunodeficiency Virus-specific CD8+ T-cells in Rhesus Macaques by Peptide-MHC-I Tetramer Staining

Peptide-major histocompatibility complex class I (pMHC-I) tetramers have been an invaluable tool to study CD8⁺ T-cell responses. Because these reagents directly bind to T-cell receptors on the surface of CD8⁺ T-lymphocytes, fluorochrome-labeled pMHC-I tetramers enable the accurate detection of antigen (Ag)-specific CD8⁺ T-cells without the need for in vitro re-stimulation. Moreover, when combined with multi-color flow cytometry, pMHC-I tetramer staining can reveal key aspects of Ag-specific CD8⁺ T-cells, including differentiation stage, memory phenotype, and activation status. These types of analyses have been especially useful in the field of HIV immunology where CD8⁺ T-cells can affect progression to AIDS. Experimental infection of rhesus macaques with simian immunodeficiency virus (SIV) provides an invaluable tool to study cellular immunity against the AIDS virus. As a result, considerable progress has been made in defining and characterizing T-cell responses in this animal model. Here we present an optimized protocol for enumerating SIV-specific CD8+ T-cells in rhesus macaques by pMHC-I tetramer staining. Our assay permits the simultaneous quantification and memory phenotyping of two pMHC-I tetramer+ CD8⁺ T-cell populations per test, which might be useful for tracking SIV-specific CD8⁺ T-cell responses generated by vaccination or SIV infection. Considering the relevance of nonhuman primates in biomedical research, this methodology is applicable for studying CD8⁺ T-cell responses in multiple disease settings.

Diversification of both KIR and NKG2 natural killer cell receptor genes in macaques - implications for highly complex MHC-dependent regulation of natural killer cells

The killer immunoglobulin-like receptors (KIR) as well as their MHC class I ligands display enormous genetic diversity and polymorphism in macaque species. Signals resulting from interaction between KIR or CD94/NKG2 receptors and their cognate MHC class I proteins essentially regulate the activity of natural killer (NK) cells. Macaque and human KIR share many features, such as clonal expression patterns, gene copy number variations, specificity for particular MHC class I allotypes, or epistasis between KIR and MHC class I genes that influence susceptibility and resistance to immunodeficiency virus infection. In this review article we also annotated publicly available rhesus macaque BAC clone sequences and provide the first description of the CD94-NKG2 genomic region. Besides the presence of genes that are orthologous to human NKG2A and NKG2F, this region contains three NKG2C paralogues. Hence, the genome of rhesus macaques contains moderately expanded and diversified NKG2 genes in addition to highly diversified KIR genes. The presence of two diversified NK cell receptor families in one species has not been described before and is expected to require a complex MHC-dependent regulation of NK cells.

OMIP-035: Functional analysis of natural killer cell subsets in macaques

This panel was developed to measure the functional capability of natural killer (NK) cell subsets in rhesus macaques (Macaca mulatta). It includes markers to determine the frequency of cytokine secreting and cytotoxic NK cell subpopulations in peripheral blood mononuclear cell (PBMC) samples stimulated in vitro with human 721.221 cells. NK cell subsets were defined by the expression of killer cell immunoglobulin-like receptors (KIRs) Mamu-KIR3DL01 and Mamu-KIR3DL05, and differentiation antigens CD16 and CD56. The panel can be used to assess the functional capability of NK cells in a range of normal and pathologic conditions of captive bred rhesus macaques of Indian origin. © 2016 International Society for Advancement of Cytometry.

Animal models to achieve an HIV cure

PURPOSE OF REVIEW

The introduction of effective antiretroviral therapy (ART) has transformed HIV infection from a deadly to a chronic infection. Despite its successes in reducing mortality, ART fails to cure HIV allowing HIV to persist in vivo. HIV persistence under ART is thought to be mediated by a combination of latent infection of long-lived cells, homeostatic proliferation of latently infected cells, anatomic sanctuaries, and low-level virus replication. To understand the contribution of specific cell types and anatomic sites to virus persistence in vivo animal models are necessary.

RECENT FINDINGS

The advancements in ART and our understanding of animal models have facilitated the development of models of HIV persistence in nonhuman primates and mice. Simian immunodeficiency virus (SIV) or simian/HIV infection (SHIV) of rhesus and pigtail macaques followed by effective ART represents the most faithful animal model of HIV persistence. HIV infection of humanized mice also provides a useful model for answering specific questions regarding virus persistence in a uniquely mutable system.

SUMMARY

In this review, we describe the most recent findings using animal models of HIV persistence. We will first describe the important aspects of HIV infection that SIV/SHIV infection of nonhuman primates are able to recapitulate, then we will discuss some recent studies that have used these models to understand viral persistence.

Roles of natural killer cells in antiviral immunity

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NK cells can kill virus-infected cells and protect against severe infections.

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Long-lived memory NK cells may develop after vaccination or infection.

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NK cells are potent regulatory of antiviral T and B cell responses.

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The role of NK cells in human infection is complex and context-dependent.

Natural killer (NK) cells are important in immune defense against virus infections. This is predominantly considered a function of rapid, innate NK-cell killing of virus-infected cells. However, NK cells also prime other immune cells through the release of interferon gamma (IFN-γ) and other cytokines. Additionally, NK cells share features with long-lived adaptive immune cells and can impact disease pathogenesis through the inhibition of adaptive immune responses by virus-specific T and B cells. The relative contributions of these diverse and conflicting functions of NK cells in humans are poorly defined and likely context-dependent, thereby complicating the development of therapeutic interventions. Here we focus on the contributions of NK cells to disease in diverse virus infections germane to human health.