Changes in Natural Killer cell activation and function during primary HIV-1 Infection

An early functional adaptive NK cell signature drives optimal CD8 + T-cell activation and predicts sustained HIV-1 viral control

A better understanding of the immune responses associated with future viral control in humans during acute HIV-1 infection (AHI) is critical to inform vaccines and immune-based therapeutics. Natural killer (NK) cells and CD8 + T-cells are pivotal in antiviral defence, yet the dynamics and complementary roles of these effector subsets during AHI with different HIV-1 subtypes remain poorly understood. Access to a unique patient cohort recruited during and post-peak HIV-1 viral load with different HIV-1 subtypes and followed up longitudinally in the absence of antiretroviral therapy up to six years post estimated date of infection (EDI) provided a rare opportunity to fill this knowledge gap. Our data show an early expansion of FcεRγ - CD57 + NK cells with classical adaptive traits concomitant with an enhanced capacity for antibody-dependent cellular cytotoxicity (ADCC) and reactivity against HIV-1 antigens. This distinctive NK cell profile was more abundant in donors with subtype A infection compared to non-subtype A, partially driven by elevated pro-inflammatory cytokine levels and changes in the epigenetic landscape. The accumulation of adaptive NK cells during the first month of infection contributed to the optimal activation of CD8 + T-cells, promoting virus-specific responses. Notably, individuals with higher levels of FcεRγ - CD57 + adaptive NK cells during the first month of infection were more likely to exhibit long-term viral control in the absence of ART. These findings underscore the critical role of early, high-magnitude adaptive NK cell responses in CD8 + T-cell activation and subsequent immune control. This work provides novel insights into the correlates of protective immunity against HIV-1 infection, with implications for preventative or therapeutic vaccine strategies aimed at promoting adaptive NK cell responses.

One Sentence Summary

Early expansion of adaptive NK cells during acute HIV-1 infection promotes long-term viral control.

Clinical and experimental treatment of residual immune activation in people living with HIV

Potent inflammatory responses stemming from innate and T cell activation are initiated during acute human immunodeficiency virus infection. Suppression of the virus replication by antiretroviral therapy reduces but does not normalize immune activation. By now, it is clear that residual immune activation can persist even after years of antiretroviral therapy and associates with increased risks for co-morbidities, thereby raising interest for strategies that can resolve the residual immune activation in people with human immunodeficiency virus on antiretrovirals. This brief review reports the human studies with various drugs with anti-inflammatory properties and their effects on measures of systemic immune activation on people with human immunodeficiency virus. Along with the possible reasons for conflicting outcomes, considerations for ongoing and future approaches are outlined.

The Role of Natural Killer Cells and Their Metabolism in HIV-1 Infection

Natural killer (NK) cells are multifaceted innate effector cells that critically influence antiviral immunity, and several protective NK cell features that modulate HIV-1 acquisition and viral control have been described. Chronic HIV-1 infection leads to NK cell impairment that has been associated with metabolic dysregulations. Therapeutic approaches targeting cellular immune metabolism represent potential novel interventions to reverse defective NK cell function in people living with HIV.

NKG2C and NKG2A coexpression defines a highly functional antiviral NK population in spontaneous HIV control

Elite controllers (ECs), a unique group of people with HIV (PWH), exhibit remarkable control of viral replication in the absence of antiretroviral therapy. In this study, we comprehensively characterized the NK cell repertoire in ECs after long-term viral control. Phenotypic profiling of NK cells revealed profound differences compared with other PWH, but marked similarities to uninfected individuals, with a distinctive prevalence of NKG2C+CD57+ memory-like NK cells. Functional analyses indicated that ECs had limited production of functional molecules upon NK stimulation and consequently reduced natural cytotoxicity against non-HIV target cells. Importantly, ECs showed an exceptional ability to kill primary HIV-infected cells by the antibody-dependent cell cytotoxicity adaptive mechanism, which was achieved by a specific memory-like NK population expressing CD16, NKG2A, NKG2C, CD57, and CXCR3. In-depth single-cell RNA-seq unveiled a unique transcriptional signature in these NK cells linked to increased cell metabolism, migration, chemotaxis, effector functions, cytokine secretion, and antiviral response. Our findings underscore a pivotal role of NK cells in the immune control of HIV and identify specific NK cells as emerging targets for immunotherapies.

Adaptive NK Cells Rapidly Expand during Acute HIV Infection and Persist Despite Early Initiation of Antiretroviral Therapy

HIV is associated with NK cell dysfunction and expansion of adaptive-like NK cells that persist despite antiretroviral therapy (ART). We investigated the timing of NK cell perturbations during acute HIV infection and the impact of early ART initiation. PBMCs and plasma were obtained from people with HIV (PWH; all men who have sex with men; median age, 26.0 y) diagnosed during Fiebig stages I, II, III, or IV/V. Participants initiated ART a median of 3 d after diagnosis, and immunophenotyping was performed at diagnosis and longitudinally after ART. Anti-CMV Abs were assessed by ELISA. Samples from matched HIV-uninfected males were also analyzed. Proportions of adaptive NK cells (A-NKs; defined as Fcε-Receptor-1γ-) were expanded at HIV diagnosis at all Fiebig stages (pooled median 66% versus 25% for controls; p < 0.001) and were not altered by early ART initiation. Abs to CMV immediate early protein were elevated in PWH diagnosed in Fiebig stages III and IV/V (p < 0.03 for both). Proportions of A-NKs defined as either Fcε-Receptor-1γ- or NKG2C+/CD57+ were significantly associated with HIV DNA levels at diagnosis (p = 0.046 and 0.029, respectively) and trended toward an association after 48 wk of ART. Proportions of activated HLA-DR+/CD38+ NK cells remained elevated in PWH despite early ART initiation. NK cell activation and A-NK expansion occur very early after HIV transmission, before T cell activation, and are not altered by ART initiation during acute infection. A-NKs may contribute to HIV control and thus be useful for HIV cure.

Multiplex interrogation of the NK cell signalome reveals global downregulation of CD16 signaling during lentivirus infection through an IL-18/ADAM17-dependent mechanism

Despite their importance, natural killer (NK) cell responses are frequently dysfunctional during human immunodeficiency virus-1 (HIV-1) and simian immunodeficiency virus (SIV) infections, even irrespective of antiretroviral therapies, with poorly understood underlying mechanisms. NK cell surface receptor modulation in lentivirus infection has been extensively studied, but a deeper interrogation of complex cell signaling is mostly absent, largely due to the absence of any comprehensive NK cell signaling assay. To fill this knowledge gap, we developed a novel multiplex signaling analysis to broadly assess NK cell signaling. Using this assay, we elucidated that NK cells exhibit global signaling reduction from CD16 both in people living with HIV-1 (PLWH) and SIV-infected rhesus macaques. Intriguingly, antiretroviral treatment did not fully restore diminished CD16 signaling in NK cells from PLWH. As a putative mechanism, we demonstrated that NK cells increased surface ADAM17 expression via elevated plasma IL-18 levels during HIV-1 infection, which in turn reduced surface CD16 downregulation. We also illustrated that CD16 expression and signaling can be restored by ADAM17 perturbation. In summary, our multiplex NK cell signaling analysis delineated unique NK cell signaling perturbations specific to lentiviral infections, resulting in their dysfunction. Our analysis also provides mechanisms that will inform the restoration of dysregulated NK cell functions, offering potential insights for the development of new NK cell-based immunotherapeutics for HIV-1 disease.

Senotherapeutics: An emerging approach to the treatment of viral infectious diseases in the elderly

In the context of the global COVID-19 pandemic, the phenomenon that the elderly have higher morbidity and mortality is of great concern. Existing evidence suggests that senescence and viral infection interact with each other. Viral infection can lead to the aggravation of senescence through multiple pathways, while virus-induced senescence combined with existing senescence in the elderly aggravates the severity of viral infections and promotes excessive age-related inflammation and multiple organ damage or dysfunction, ultimately resulting in higher mortality. The underlying mechanisms may involve mitochondrial dysfunction, abnormal activation of the cGAS-STING pathway and NLRP3 inflammasome, the role of pre-activated macrophages and over-recruited immune cells, and accumulation of immune cells with trained immunity. Thus, senescence-targeted drugs were shown to have positive effects on the treatment of viral infectious diseases in the elderly, which has received great attention and extensive research. Therefore, this review focused on the relationship between senescence and viral infection, as well as the significance of senotherapeutics for the treatment of viral infectious diseases.

Human Hematopoietic Stem Cell Engrafted IL-15 Transgenic NSG Mice Support Robust NK Cell Responses and Sustained HIV-1 Infection

Mice reconstituted with human immune systems are instrumental in the investigation of HIV-1 pathogenesis and therapeutics. Natural killer (NK) cells have long been recognized as a key mediator of innate anti-HIV responses. However, established humanized mouse models do not support robust human NK cell development from engrafted human hematopoietic stem cells (HSCs). A major obstacle to human NK cell reconstitution is the lack of human interleukin-15 (IL-15) signaling, as murine IL-15 is a poor stimulator of the human IL-15 receptor. Here, we demonstrate that immunodeficient NOD.Cg-Prkdcscid Il2rgtm1Wjl/SzJ (NSG) mice expressing a transgene encoding human IL-15 (NSG-Tg(IL-15)) have physiological levels of human IL-15 and support long-term engraftment of human NK cells when transplanted with human umbilical-cord-blood-derived HSCs. These Hu-NSG-Tg(IL-15) mice demonstrate robust and long-term reconstitution with human immune cells, but do not develop graft-versus-host disease (GVHD), allowing for long-term studies of human NK cells. Finally, we show that these HSC engrafted mice can sustain HIV-1 infection, resulting in human NK cell responses in HIV-infected mice. We conclude that Hu-NSG-Tg(IL-15) mice are a robust novel model to study NK cell responses to HIV-1.

Natural killer cells during acute HIV-1 infection: clues for HIV-1 prevention and therapy

Despite progress in preexposure prophylaxis, the number of newly diagnosed cases with HIV-1 remains high, highlighting the urgent need for preventive and therapeutic strategies to reduce HIV-1 acquisition and limit disease progression. Early immunological events, occurring during acute infection, are key determinants of the outcome and course of disease. Understanding early immune responses occurring before viral set-point is established, is critical to identify potential targets for prophylactic and therapeutic approaches. Natural killer (NK) cells represent a key cellular component of innate immunity and contribute to the early host defence against HIV-1 infection, modulating the pathogenesis of acute HIV-1 infection (AHI). Emerging studies have identified tools for harnessing NK cell responses and expanding specialized NK subpopulations with adaptive/memory features, paving the way for development of novel HIV-1 therapeutics. This review highlights the knowns and unknowns regarding the role of NK cell subsets in the containment of acute HIV-1 infection, and summarizes recent advances in selectively augmenting NK cell functions through prophylactic and therapeutic interventions.

Mucosal-homing natural killer cells are associated with aging in persons living with HIV

Natural killer (NK) cells are critical modulators of HIV transmission and disease. Recent evidence suggests a loss of NK cell cytotoxicity during aging, yet analysis of NK cell biology and aging in people with HIV (PWH) is lacking. Herein, we perform comprehensive analyses of people aging with and without HIV to determine age-related NK phenotypic changes. Utilizing high-dimensional flow cytometry, we analyze 30 immune-related proteins on peripheral NK cells from healthy donors, PWH with viral suppression, and viremic PWH. NK cell phenotypes are dynamic across aging but change significantly in HIV and on antiretroviral drug therapy (ART). NK cells in healthy aging show increasing ⍺4β7 and decreasing CCR7 expression and a reverse phenomenon in PWH. These HIV-associated trafficking patterns could be due to NK cell recruitment to HIV reservoir formation in lymphoid tissue or failed mucosal signaling in the HIV-infected gut but appear to be tight delineators of age-related NK cell changes.

Mechanisms of immune aging in HIV

Massive CD4+ T-cell depletion as well as sustained immune activation and inflammation are hallmarks of Human Immunodeficiency Virus (HIV)-1 infection. In recent years, an emerging concept draws an intriguing parallel between HIV-1 infection and aging. Indeed, many of the alterations that affect innate and adaptive immune subsets in HIV-infected individuals are reminiscent of the process of immune aging, characteristic of old age. These changes, of which the presumed cause is the systemic immune activation established in patients, likely participate in the immuno-incompetence described with HIV progression. With the success of antiretroviral therapy (ART), HIV-seropositive patients can now live for many years despite chronic viral infection. However, acquired immunodeficiency syndrome (AIDS)-related opportunistic infections have given way to chronic diseases as the leading cause of death since HIV infection. Therefore, the comparison between HIV-1 infected patients and uninfected elderly individuals goes beyond the sole onset of immunosenescence and extends to the deterioration of several physiological functions related to inflammation and systemic aging. In light of this observation, it is interesting to understand the precise link between immune activation and aging in HIV-1 infection to figure out how to best care for people living with HIV (PLWH).

The New Kid on the Block: HLA-C, a Key Regulator of Natural Killer Cells in Viral Immunity

The human leukocyte antigen system (HLA) is a cluster of highly polymorphic genes essential for the proper function of the immune system, and it has been associated with a wide range of diseases. HLA class I molecules present intracellular host- and pathogen-derived peptides to effector cells of the immune system, inducing immune tolerance in healthy conditions or triggering effective immune responses in pathological situations. HLA-C is the most recently evolved HLA class I molecule, only present in humans and great apes. Differentiating from its older siblings, HLA-A and HLA-B, HLA-C exhibits distinctive features in its expression and interaction partners. HLA-C serves as a natural ligand for multiple members of the killer-cell immunoglobulin-like receptor (KIR) family, which are predominately expressed by natural killer (NK) cells. NK cells are crucial for the early control of viral infections and accumulating evidence indicates that interactions between HLA-C and its respective KIR receptors determine the outcome and progression of viral infections. In this review, we focus on the unique role of HLA-C in regulating NK cell functions and its consequences in the setting of viral infections.

ADCC-mediating non-neutralizing antibodies can exert immune pressure in early HIV-1 infection

Despite antibody-dependent cellular cytotoxicity (ADCC) responses being implicated in protection from HIV-1 infection, there is limited evidence that they control virus replication. The high mutability of HIV-1 enables the virus to rapidly adapt, and thus evidence of viral escape is a very sensitive approach to demonstrate the importance of this response. To enable us to deconvolute ADCC escape from neutralizing antibody (nAb) escape, we identified individuals soon after infection with detectable ADCC responses, but no nAb responses. We evaluated the kinetics of ADCC and nAb responses, and viral escape, in five recently HIV-1-infected individuals. In one individual we detected viruses that escaped from ADCC responses but were sensitive to nAbs. In the remaining four participants, we did not find evidence of viral evolution exclusively associated with ADCC-mediating non-neutralizing Abs (nnAbs). However, in all individuals escape from nAbs was rapid, occurred at very low titers, and in three of five cases we found evidence of viral escape before detectable nAb responses. These data show that ADCC-mediating nnAbs can drive immune escape in early infection, but that nAbs were far more effective. This suggests that if ADCC responses have a protective role, their impact is limited after systemic virus dissemination.

Host genetic control of natural killer cell diversity revealed in the Collaborative Cross

Natural killer (NK) cells are innate effectors armed with cytotoxic and cytokine-secreting capacities whose spontaneous antitumor activity is key to numerous immunotherapeutic strategies. However, current mouse models fail to mirror the extensive immune system variation that exists in the human population which may impact on NK cell-based therapies. We performed a comprehensive profiling of NK cells in the Collaborative Cross (CC), a collection of novel recombinant inbred mouse strains whose genetic diversity matches that of humans, thereby providing a unique and highly diverse small animal model for the study of immune variation. We demonstrate that NK cells from CC strains displayed a breadth of phenotypic and functional variation reminiscent of that reported for humans with regards to cell numbers, key marker expression, and functional capacities. We took advantage of the vast genetic diversity of the CC and identified nine genomic loci through quantitative trait locus mapping driving these phenotypic variations. SNP haplotype patterns and variant effect analyses identified candidate genes associated with lung NK cell numbers, frequencies of CD94⁺ NK cells, and expression levels of NKp46. Thus, we demonstrate that the CC represents an outstanding resource to study NK cell diversity and its regulation by host genetics.

Evolution and Diversity of Immune Responses during Acute HIV Infection

Understanding the earliest immune responses following HIV infection is critical to inform future vaccines and therapeutics. Here, we review recent prospective human studies in at-risk populations that have provided insight into immune responses during acute infection, including additional relevant data from non-human primate (NHP) studies. We discuss the timing, nature, and function of the diverse immune responses induced, the onset of immune dysfunction, and the effects of early anti-retroviral therapy administration. Treatment at onset of viremia mitigates peripheral T and B cell dysfunction, limits seroconversion, and enhances cellular antiviral immunity despite persistence of infection in lymphoid tissues. We highlight pertinent areas for future investigation, and how application of high-throughput technologies, alongside targeted NHP studies, may elucidate immune response features to target in novel preventions and cures.

TRIGGERED: could refocused cell signaling be key to natural killer cell-based HIV immunotherapeutics?

Natural killer (NK) cells are one of the critical innate immune effector cells that directly kill tumors and virus-infected cells, and modulate other immune cells including dendritic cells, CD4+ and CD8+ T cells. Signals from activating and inhibitory surface receptors orchestrate the regulatory and cytotoxic functions of NK cells. Although a number of surface receptors are involved, multiple signaling molecules are shared so that NK cell responses are synergistically regulated. Many pathogens and tumors evade NK cell responses by targeting NK cell signaling. Particularly in HIV/simian immunodeficiency virus (SIV) infection, the NK cell repertoire is diminished by changes in subsets of NK cells, expression of activating and inhibitory receptors, and intracellular signaling molecules. However, in-depth studies on intracellular signaling in NK cells in HIV/SIV infections remain limited. Checkpoint blockade and chimeric antigen receptor (CAR)-NK cells have demonstrated enhanced NK cell activities against tumors and viral infections. In addition, targeting intracellular signaling molecules by small molecules could also improve NK cell responses towards HIV/SIV infection in vivo. Therefore, further understanding of NK cell signaling including identification of key signaling molecules is crucial to maximize the efficacy of NK cell-based treatments. Herein, we review the current state of the literature and outline potential future avenues where optimized NK cells could be utilized in HIV-1 cure strategies and other immunotherapeutics in PLWH.

Preclinical Development and Clinical-Scale Manufacturing of HIV Gag-Specific, LentivirusModified CD4 T Cells for HIV Functional Cure

Activation, infection, and eventual depletion of human immunodeficiency virus (HIV)-specific cluster of differentiation 4 (CD4) T cells are the crucial pathogenetic events in acquired immunodeficiency syndrome (AIDS). We developed a cell and gene therapy to reconstitute HIV-specific CD4 T cells and prevent their destruction by HIV. Antigen-specific CD4 T cells will provide helper functions to support antiviral cytotoxic T lymphocyte (CTL) function and the production of virus-specific antibodies. However, ex vivo expansion of HIV-specific CD4 T cells is poor and previous gene therapies focused on bulk CD4 T cells without enriching for an antigen-specific subset. We developed a method for manufacturing autologous CD4⁺ T cell products highly enriched with Gag-specific T cells. Rare Gag-specific CD4 T cells in peripheral blood mononuclear cells (PBMCs) were increased nearly 1,000-fold by stimulating PBMC with Gag peptides, followed by depleting nontarget cells and transducing with lentivirus vector AGT103 to protect against HIV-mediated depletion and inhibit HIV release from latently infected cells. The average percentage of HIV-specific CD4 cells in the final products was 15.13%, and the average yield was 7 × 10⁸ cells. The protocol for clinical-scale manufacturing of HIV-specific and HIV-resistant CD4 T cells is an important step toward effective immunotherapy for HIV disease.

FcγRIIIa receptor polymorphism influences NK cell mediated ADCC activity against HIV

BACKGROUND

HIV-specific Antibody Dependent Cell Cytotoxicity (ADCC) has shown to be important in HIV control and resistance. The ADCC is mediated primarily by natural killer cell activated through the binding of FcγRIIIa receptor to the Fc portion of antibody bound to the antigen expressed on the infected cells. However, no data is available on the influence of the polymorphism in FcγRIIIa receptor on HIV-specific ADCC response.

METHODS

The Sanger's method of sequencing was used to sequence the exon of FcγRIIIa receptor while the ADCC activity was determined using NK cell activation assay. The polymorphism in FcγRIIIa receptor was assessed in HIV-infected Indian individuals with or without HIV-specific ADCC antibodies and its influence on the magnitude of HIV-specific ADCC responses was analyzed.

RESULTS

Two polymorphisms: V176F (rs396991) and Y158H (rs396716) were observed. The Y158H polymorphism is reported for the first time in Indian population. Both, V176F (V/V genotype) (p = 0.004) and Y158H (Y/H genotype) (p = 0.032) were found to be significantly associated with higher magnitude of HIV-specific ADCC response.

CONCLUSION

The study underscores the role of polymorphism in the FcγRIIIa receptor on HIV-specific ADCC response and suggests that the screening of the individuals for FcγRIIIa-V176F and Y158H polymorphisms could be useful for prediction of efficient treatment in monoclonal antibody-based therapies aimed at ADCC in HIV infection.

High Activation of γδ T Cells and the γδ2pos T-Cell Subset Is Associated With the Onset of Tuberculosis-Associated Immune Reconstitution Inflammatory Syndrome, ANRS 12153 CAPRI NK

Background: Human Immunodeficiency Virus 1 (HIV-1) and Mycobacterium Tuberculosis (Mtb) co-infected patients are commonly at risk of immune reconstitution inflammatory syndrome (IRIS) when initiating antiretroviral treatment (ART). Evidence indicates that innate immunity plays a role in TB-IRIS. Here, we evaluate the phenotype of Gamma-delta (γδ) T cells and invariant Natural Killer (iNK) T cells in tuberculosis-associated IRIS.

Methods: Forty-eight HIV+/TB+ patients (21 IRIS) and three control groups: HIV–/TB– (HD, n = 11), HIV+/TB– (n = 26), and HIV–/TB+ (n = 22) were studied. Samples were taken at ART initiation (week 2 of anti-tuberculosis treatment) and at the diagnosis of IRIS for HIV+/TB+; before ART for HIV+/TB-, and at week 2 of anti-tuberculosis treatment for HIV–/TB+ patients. γδ T cells and Invariant natural killer T (iNKT) cells were analyzed by flow cytometry.

Results: Before ART, IRIS, and non-IRIS patients showed a similar proportion of γδ^pos T and iNKT cells. HLA-DR on γδ^pos T cells and δ2^posγδ^pos T cells was significantly higher in TB-IRIS vs. non-IRIS patients and controls (p < 0.0001). NKG2D expression on γδ^pos T cells and the δ2^posγδ^pos T cell subset was lower in HIV+/TB+ patients than controls. CD158a expression on γδ^pos T cells was higher in TB-IRIS than non-IRIS (p = 0.02), HIV+/TB–, and HIV–/TB- patients.

Conclusion: The higher activation of γδ^posT cells and the γδ2^posγδ^pos T cell subset suggests that γδ T cells may play a role in the pathogenesis of TB-IRIS.

Increased degranulation of immune cells is associated with higher cervical viral load in HIV-infected women

OBJECTIVE

The activation of effector immune cells at the cervicovaginal mucosa (CVM) might influence the cervical HIV load and thus the secondary transmission; however, limited information is available about the innate effector cells at CVM during HIV infection. In this study, we quantified and assessed the activation of the effector immune cells at the CVM of HIV-infected women with different disease outcomes: nonprogressive HIV disease (LTNPs) and chronic HIV-infected (CHI) and their relationship with cervical viral shedding.

METHOD

The phenotype and frequency of cytobrush-derived effector immune cells like natural killer cells, T cells, and dendritic cells and their degranulation status (CD107a expression as a surrogate marker of activation) was determined using flow cytometry in age-matched HIV- infected and uninfected women and their association with cervical HIV load was determined.

RESULT

The frequencies of dendritic cells, CD56, CD56 natural killer cell subsets were similar in both the study groups and also within the HIV-infected women with and without progressive disease. The frequencies of CD56CD16 natural killer cells (P = 0.04) and degranulating CD56 natural killer cells were significantly higher among HIV-infected women (P < 0.05). Among HIV-infected women, LTNP women showed reduced degranulation of natural killer and CD8 T cells than seen in the CHI women, which was also associated with lower cervical viral load (P < 0.05).

CONCLUSION

The present study showed that increased degranulation of natural killer and T cells is associated with higher HIV shedding at the CVM of HIV-infected women. Hence reduction of the local immune activation at CVM could be an effective strategy to reduce the cervical viral load.

A novel ligand on astrocytes interacts with natural cytotoxicity receptor NKp44 regulating immune response mediated by NK cells

NK cells play important role in immunity against pathogens and cancer. NK cell functions are regulated by inhibitory and activating receptors binding corresponding ligands on the surface of target cells. NK cells were shown to be recruited to the CNS following several pathological conditions. NK cells could impact CNS physiology by killing glial cells and by secreting IFN-γ. Astrocytes are intimately involved in immunological and inflammatory events occurring in the CNS and reactive astrogliosis is a key feature in HIV-associated neurocognitive disorders. There is little data on NK-astrocyte interactions and ligands expressed on astrocytes that could impact NK cell function. Natural cytotoxicity receptors (NCRs) play a critical role in the cytolytic function of NK cells. Among the NCRs, NKp44 is unique in expression and signal transduction. NKp44 is expressed only upon activation of NK cells and it can mediate both activating and inhibitory signals to NK cells. Here, we have studied the expression and function of natural cytotoxicity receptor NKp44 upon NK-astrocytes interactions in the presence or absence of an HIV peptide (HIV-3S peptide) shown to induce NK cell killing of CD4+ T cells during HIV–infection. Using a fusion protein consisting of the extracellular domain of NKp44 fused to Fc portion of human IgG, we determined the expression of a novel ligand for NKp44 (NKp44L) on astrocytes. Incubation of astrocytes with HIV-3S peptide downregulated NKp44L expression on astrocytes implicating protection from NK mediated killing. Thus, our study showed that NKp44 have a protective effect on astrocytes from NK cell mediated killing during HIV infection and impact astrocyte role in HAND.

Reduced Expression of Siglec-7, NKG2A, and CD57 on Terminally Differentiated CD56-CD16+ Natural Killer Cell Subset Is Associated with Natural Killer Cell Dysfunction in Chronic HIV-1 Clade C Infection

HIV-1 viremia has been shown to induce several phenotypic and functional abnormalities in natural killer (NK) cells. To assess immune defects associated with HIV viremia, we examined NK cell function, differentiation status, and phenotypic alterations based on expression of inhibitory and activating receptors on NK cells in HIV-1 subtype C chronically infected participants from Durban, South Africa. NK cell phenotypic profiles were characterized by assessing sialic acid-binding immunoglobulin-like lectin-7 (Siglec-7), NKG2A, and NKG2C markers on frozen peripheral blood mononuclear cells from viremic, antiretroviral therapy (ART)-naive HIV-1 chronically infected participants (n = 23), HIV-1 chronically infected participants who had been on combination antiretroviral therapy (cART) for at least 12 months (n = 23) compared with healthy donors (n = 23). NK cell differentiation was assessed by measurement of killer immunoglobulin receptor (KIR) and NKG2A expression; CD57 and CD107a measurements were carried out in HIV viremic and healthy donors. All phenotypic and functional assessments were analyzed by using multicolor flow cytometry. HIV-1-infected participants displayed greater frequencies of the CD56^-CD16⁺ (CD56negative) NK cell subset compared with healthy donors (p < .0001). Downregulation of Siglec-7 and NKG2A and upregulation of NKG2C were more pronounced in the CD56negative NK cell subset of viremic participants. The CD56negative subset demonstrated a differentiated (KIR⁺NKG2A^-) phenotype with reduced CD57 expression and lower degranulation capacity in HIV-1-infected participants compared with healthy donors. HIV-1 infection induces the expansion of the CD56negative NK cell subset marked by altered receptor expression profiles that are indicative of impaired function and may explain the overall NK cell dysfunction observed in chronic HIV-1 infection.

Natural killer cells in HIV-1 infection and therapy

: Natural killer (NK) cells are important effectors of innate immunity playing a key role in the eradication and clearance of viral infections. Over the recent years, several studies have shown that HIV-1 pathologically changes NK cell homeostasis and hampers their antiviral effector functions. Moreover, high levels of chronic HIV-1 viremia markedly impair those NK cell regulatory features that normally regulate the cross talks between innate and adaptive immune responses. These pathogenic events take place early in the infection and are associated with a pathologic redistribution of NK cell subsets that includes the expansion of anergic CD56/CD16 NK cells with an aberrant repertoire of activating and inhibitory receptors. Nevertheless, the presence of specific haplotypes for NK cell receptors and the engagement of NK cell antibody-dependent cell cytotocity have been reported to control HIV-1 infection. This dichotomy can be extremely useful to both predict the clinical outcome of the infection and to develop alternative antiviral pharmacological approaches. Indeed, the administration of antiretroviral therapy in HIV-1-infected patients restores NK cell phenotype and functions to normal levels. Thus, antiretroviral therapy can help to develop NK cell-directed therapeutic strategies that include the use of broadly neutralizing antibodies and toll-like receptor agonists. The present review discusses how our current knowledge of NK cell pathophysiology in HIV-1 infection is being translated both in experimental and clinical trials aimed at controlling the infection and disease.

Assessing immune aging in HIV-infected patients

Many of the alterations that affect innate and adaptive immune cell compartments in HIV-infected patients are reminiscent of the process of immune aging, characteristic of old age. These alterations define the immunological age of individuals and are likely to participate to the decline of immune competence with HIV disease progression. It is therefore important to characterize these changes, which point toward the accumulation of highly differentiated immunocompetent cells, associated with overall telomere length shortening, as well as understanding their etiology, especially related to the impact of chronic immune activation. Particular attention should be given to the exhaustion of primary immune resources, including haematopoietic progenitors and naïve cells, which holds the key for effective hematopoiesis and immune response induction, respectively. The alteration of these compartments during HIV infection certainly represents the foundation of the immune parallel with aging.

Brief Report: Increased Frequency of CD39+ CD56bright Natural Killer Cells in HIV-1 Infection Correlates With Immune Activation and Disease Progression

The expression pattern of the ectonucleotidases CD39 and CD73 on natural killer (NK) cells was examined in peripheral blood mononuclear cell of 61 HIV-1-infected patients. Increased frequencies of CD39CD56 NK cells were detectable in untreated HIV patients, which was associated with high viral load, low CD4 T-cell count, and CD8 T-cell activation. Additionally, levels of CD39 on NK cells were inducible by in vitro stimulation of NK cells, correlating with aryl hydrocarbon receptor and interleukin 10 expression. Here, we provide the first evidence of increased CD39CD56 NK cell frequencies during HIV infection, which might have consequences for NK cell function and HIV pathogenesis.

Factors Associated With the Control of Viral Replication and Virologic Breakthrough in a Recently Infected HIV-1 Controller

HIV-1 controllers are patients who control HIV-1 viral replication without antiretroviral therapy. Control is achieved very early in the course of infection, but the mechanisms through which viral replication is restricted are not fully understood. We describe a patient who presented with acute HIV-1 infection and was found to have an HIV-1 RNA level of < 100 copies/mL. She did not have any known protective HLA alleles, but significant immune activation of CD8 + T cells and natural killer (NK) cells was present, and both cell types inhibited viral replication. Virus cultured from this patient replicated as well in vitro as virus isolated from her partner, a patient with AIDS who was the source of transmission. Virologic breakthrough occurred 9 months after her initial presentation and was associated with an increase in CD4 + T cell activation levels and a significant decrease in NK cell inhibitory capacity. Remarkably, CD8 + T cell inhibitory capacity was preserved and there were no new escape mutations in targeted Gag epitopes. These findings suggest that fully replication-competent virus can be controlled in acute HIV-1 infection in some patients without protective HLA alleles and that NK cell responses may contribute to this early control of viral replication.

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We show that an HIV-1 controller was infected with pathogenic virus yet maintained low viral loads during primary infection.

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She had activated NK cells and CD8+ T cells and both cell types suppressed HIV-1 replication shortly after infection.

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She eventually lost control of viral replication, and this was associated with a reduction in NK cell suppressive activity.

HIV-1 controllers are patients who control the virus without HIV-1 medications. These patients may teach us how to design a vaccine against HIV-1. Little is known about how the virus is controlled in the early phase of infection in these patients. Here we show that a recently infected HIV-1 controller had a strong natural killer cell response to the virus. Interestingly, she lost control of the virus 9 months later and her natural killer cell response to the virus was diminished. Our work suggests that natural killer cells may have contributed to viral control in the early phase of infection.

HIV Maintains an Evolving and Dispersed Population in Multiple Tissues during Suppressive Combined Antiretroviral Therapy in Individuals with Cancer

While combined antiretroviral therapy (cART) can result in undetectable plasma viral loads, it does not eradicate HIV infection. Furthermore, HIV-infected individuals while on cART remain at an increased risk of developing serious comorbidities, such as cancer, neurological disease, and atherosclerosis, suggesting that during cART, tissue-based HIV may contribute to such pathologies. We obtained DNA and RNA env, nef, and pol sequences using single-genome sequencing from postmortem tissues of three HIV(+) cART-treated (cART(+)) individuals with undetectable viral load and metastatic cancer at death and performed time-scaled Bayesian evolutionary analyses. We used a sensitive in situ hybridization technique to visualize HIV gag-pol mRNA transcripts in cerebellum and lymph node tissues from one patient. Tissue-associated virus evolved at similar rates in cART(+) and cART-naive (cART(-)) patients. Phylogenetic trees were characterized by two distinct features: (i) branching patterns consistent with constant viral evolution and dispersal among tissues and (ii) very recently derived clades containing both DNA and RNA sequences from multiple tissues. Rapid expansion of virus near death corresponded to wide-spread metastasis. HIV RNA(+) cells clustered in cerebellum tissue but were dispersed in lymph node tissue, mirroring the evolutionary patterns observed for that patient. Activated, infiltrating macrophages were associated with HIV RNA. Our data provide evidence that tissues serve as a sanctuary for wild-type HIV during cART and suggest the importance of macrophages as an alternative reservoir and mechanism of virus spread.

IMPORTANCE

Combined antiretroviral therapy (cART) reduces plasma HIV to undetectable levels; however, removal of cART results in plasma HIV rebound, thus highlighting its inability to entirely rid the body of infection. Additionally, HIV-infected individuals on cART remain at high risk of serious diseases, which suggests a contribution from residual HIV. In this study, we isolated and sequenced HIV from postmortem tissues from three HIV(+) cART(+) individuals who died with metastatic cancer and had no detectable plasma viral load. Using high-resolution evolutionary analyses, we found that tissue-based HIV continues to replicate, evolve, and migrate among tissues during cART. Furthermore, cancer onset and metastasis coincided with increased HIV expansion, suggesting a linked mechanism. HIV-expressing cells were associated with tissue macrophages, a target of HIV infection. Our results suggest the importance of tissues, and macrophages in particular, as a target for novel anti-HIV therapies.

Elevated levels of invariant natural killer T-cell and natural killer cell activation correlate with disease progression in HIV-1 and HIV-2 infections

Objective:

In this study, we aimed to investigate the frequency and activation of invariant natural killer T (iNKT) cells and natural killer (NK) cells among HIV-1, HIV-2, or dually HIV-1/HIV-2 (HIV-D)-infected individuals, in relation to markers of disease progression.

Design:

Whole blood samples were collected from treatment-naive HIV-1 (n = 23), HIV-2 (n = 34), and HIV-D (n = 11) infected individuals, as well as HIV-seronegative controls (n = 25), belonging to an occupational cohort in Guinea-Bissau.

Methods:

Frequencies and activation levels of iNKT and NK cell subsets were analysed using multicolour flow cytometry, and results were related to HIV-status, CD4⁺ T-cell levels, viral load, and T-cell activation.

Results:

HIV-1, HIV-D, and viremic HIV-2 individuals had lower numbers of CD4⁺ iNKT cells in circulation compared with seronegative controls. Numbers of CD56^bright NK cells were also reduced in HIV-infected individuals as compared with control study participants. Notably, iNKT cell and NK cell activation levels, assessed by CD38 expression, were increased in HIV-1 and HIV-2 single, as well as dual, infections. HIV-2 viremia was associated with elevated activation levels in CD4⁺ iNKT cells, CD56^bright, and CD56^dim NK cells, as compared with aviremic HIV-2 infection. Additionally, disease markers such as CD4⁺ T-cell percentages, viral load, and CD4⁺ T-cell activation were associated with CD38 expression levels of both iNKT and NK cells, which activation levels also correlated with each other.

Conclusion:

Our data indicate that elevated levels of iNKT-cell and NK-cell activation are associated with viremia and disease progression markers in both HIV-1 and HIV-2 infections.

Study of Natural Cytotoxicity Receptors in Patients with HIV/AIDS and Cancer: A Cross-Sectional Study

The NCR receptors play a fundamental role in the cytotoxicity mediated by NK cells against tumor cells. In the current study, we investigated possible HIV/AIDS-related changes in the expression of the NCR receptors comparing healthy donors, HIV/AIDS patients, and HIV/AIDS patients with cancer (HIV/AIDSWC). The NCRs were quantified in NK cells (NK^dim and NK^bright) and T lymphocytes from peripheral blood samples by flow cytometry. We found a significant decrease in the frequency of NK cells expressing NKp46 in HIV/AIDS group (p = 0.0012). There was a decrease in the frequency of NK cells expressing NKp46 in the HIV/AIDSWC group; however, this was not statistically significant. We found a significant decrease in the frequency of NK cells expressing NKp30 in the HIV/AIDS group (p = 0.0144). There was a decrease in the frequency of NK cells expressing NKp30 and in the HIV/AIDSWC group, but this was not statistically significant. There were no changes in the distribution of NK cells and their subtypes in both groups.

Mathematical Modeling Predicts that Increased HSV-2 Shedding in HIV-1 Infected Persons Is Due to Poor Immunologic Control in Ganglia and Genital Mucosa

A signature feature of HIV infection is poor control of herpes virus infections, which reactivate from latency and cause opportunistic infections. While the general mechanism underlying this observation is deficient CD4+T-cell function, it is unknown whether increased severity of herpes virus infections is due primarily to poor immune control in latent or lytic sites of infection, or whether CD4+ immunodeficiency leads to more critical downstream deficits in humoral or cell-mediated immunologic responses. Here we compare genital shedding patterns of herpes simplex virus-2 (HSV-2) in 98 HIV infected and 98 HIV uninfected men matched on length of infection, HSV-1 serostatus and nationality. We demonstrate that high copy HSV-2 shedding is more frequent in HIV positive men, particularly in participants with CD4+ T-cell count <200/μL. Genital shedding is more frequent due to higher rate of shedding episodes, as well as a higher proportion of prolonged shedding episodes. Peak episode viral load was not found to differ between HIV infected and uninfected participants regardless of CD4+ T-cell count. We simulate a mathematical model which recapitulates these findings and identifies that rate of HSV-2 release from neural tissue increases, duration of mucosal cytolytic immune protection decreases, and cell-free viral lifespan increases in HIV infected participants. These results suggest that increased HSV-2 shedding in HIV infected persons may be caused by impaired immune function in both latent and lytic tissue compartments, with deficits in clearance of HSV-2 infected cells and extracellular virus.

Killer-cell Immunoglobulin-like Receptor (KIR) gene profiles modify HIV disease course, not HIV acquisition in South African women

BACKGROUND

Killer-cell Immunoglobulin-like Receptors (KIR) interact with Human Leukocyte Antigen (HLA) to modify natural killer- and T-cell function. KIR are implicated in HIV acquisition by small studies that have not been widely replicated. A role for KIR in HIV disease progression is more widely replicated and supported by functional studies.

METHODS

To assess the role of KIR and KIR ligands in HIV acquisition and disease course, we studied at-risk women in South Africa between 2004-2010. Logistic regression was used for nested case-control analysis of 154 women who acquired vs. 155 who did not acquire HIV, despite high exposure. Linear mixed-effects models were used for cohort analysis of 139 women followed prospectively for a median of 54 months (IQR 31-69) until 2014.

RESULTS

Neither KIR repertoires nor HLA alleles were associated with HIV acquisition. However, KIR haplotype BB was associated with lower viral loads (-0.44 log10 copies/ml; SE = 0.18; p = 0.03) and higher CD4+ T-cell counts (+80 cells/μl; SE = 42; p = 0.04). This was largely explained by the protective effect of KIR2DL2/KIR2DS2 on the B haplotype and reciprocal detrimental effect of KIR2DL3 on the A haplotype.

CONCLUSIONS

Although neither KIR nor HLA appear to have a role in HIV acquisition, our data are consistent with involvement of KIR2DL2 in HIV control. Additional studies to replicate these findings are indicated.

Modulation of apoptosis and viral latency - an axis to be well understood for successful cure of human immunodeficiency virus

Human immunodeficiency virus (HIV) is the causative agent of the deadly disease AIDS, which is characterized by the progressive decline of CD4(+)T-cells. HIV-1-encoded proteins such as envelope gp120 (glycoprotein gp120), Tat (trans-activator of transcription), Nef (negative regulatory factor), Vpr (viral protein R), Vpu (viral protein unique) and protease are known to be effective in modulating host cell signalling pathways that lead to an alteration in apoptosis of both HIV-infected and uninfected bystander cells. Depending on the stage of the virus life cycle and host cell type, these viral proteins act as mediators of pro- or anti-apoptotic signals. HIV latency in viral reservoirs is a persistent phenomenon that has remained beyond the control of the human immune system. To cure HIV infections completely, it is crucial to reactivate latent HIV from cellular pools and to drive these apoptosis-resistant cells towards death. Several previous studies have reported the role of HIV-encoded proteins in apoptosis modulation, but the molecular basis for apoptosis evasion of some chronically HIV-infected cells and reactivated latently HIV-infected cells still needs to be elucidated. The current review summarizes our present understanding of apoptosis modulation in HIV-infected cells, uninfected bystander cells and latently infected cells, with a focus on highlighting strategies to activate the apoptotic pathway to kill latently infected cells.

Targeting the gastrointestinal tract to develop novel therapies for HIV

Despite the use of antiretroviral therapy (ART), which delays and/or prevents AIDS pathogenesis, human immunodeficiency virus (HIV)-infected individuals continue to face increased morbidities and mortality rates compared with uninfected individuals. Gastrointestinal (GI) mucosal dysfunction is a key feature of HIV infection, and is associated with mortality. In this study, we review current knowledge about mucosal dysfunction in HIV infection, and describe potential avenues for therapeutic targets to enhance mucosal function and decrease morbidities and mortalities in HIV-infected individuals.

Higher Frequency of NK and CD4+ T-Cells in Mucosa and Potent Cytotoxic Response in HIV Controllers

HIV infection induces immune alterations, mainly in gut mucosa, where the main target cells reside. However, the evolution of the infection is variable among infected individuals, as evidenced by HIV controllers who exhibit low or undetectable viral load in the absence of treatment. The aim of this study was to evaluate the frequency, phenotype and activity of T and NK cells in peripheral blood and gut mucosa in a cohort of Colombian HIV controllers. Blood and gut biopsies were included. The frequency and the activation status of T and NK cells were performed by flow cytometry. In addition, Gag-stimulated CD8⁺ T-cells and cytokine-stimulated NK cells were tested for cytotoxic activity. Finally, microbial translocation was measured by plasma lipopolysaccharide quantification. Compared with HIV-progressors, HIV controllers exhibited higher frequency of CD4⁺ T and NK cells, and lower expression of activation molecules in blood and mucosal immune cells, as well as lower microbial translocation. An increased production of molecules associated with cytotoxic activity of CD8⁺ T-cells in blood and mucosa and a higher percentage of polyfunctional CD8⁺ T cells in blood were also observed in HIV controllers. In addition, an increased activity of NK cells was observed in blood. These findings suggest that HIV controllers have a potent immune response, mainly mediated by cytotoxic cells that control HIV replication, which contribute to reducing alterations at the gut mucosa.

In Vivo Activation of Human NK Cells by Treatment with an Interleukin-15 Superagonist Potently Inhibits Acute In Vivo HIV-1 Infection in Humanized Mice

Natural killer (NK) cells with anti-HIV-1 activity may inhibit HIV-1 replication and dissemination during acute HIV-1 infection. We hypothesized that the capacity of NK cells to suppress acute in vivo HIV-1 infection would be augmented by activating them via treatment with an interleukin-15 (IL-15) superagonist, IL-15 bound to soluble IL-15Rα, an approach that potentiates human NK cell-mediated killing of tumor cells. In vitro stimulation of human NK cells with a recombinant IL-15 superagonist significantly induced their expression of the cytotoxic effector molecules granzyme B and perforin; their degranulation upon exposure to K562 cells, as indicated by cell surface expression of CD107a; and their capacity to lyse K562 cells and HIV-1-infected T cells. The impact of IL-15 superagonist-induced activation of human NK cells on acute in vivo HIV-1 infection was investigated by using hu-spl-PBMC-NSG mice, NOD-SCID-IL2rγ(-/-) (NSG) mice intrasplenically injected with human peripheral blood mononuclear cells (PBMCs) which develop productive in vivo infection after intrasplenic inoculation with HIV-1. IL-15 superagonist treatment potently inhibited acute HIV-1 infection in hu-spl-PBMC-NSG mice even when delayed until 3 days after intrasplenic HIV-1 inoculation. Removal of NK cells from human PBMCs prior to intrasplenic injection into NSG mice completely abrogated IL-15 superagonist-mediated suppression of in vivo HIV-1 infection. Thus, the in vivo activation of NK cells, integral mediators of the innate immune response, by treatment with an IL-15 superagonist increases their anti-HIV activity and enables them to potently suppress acute in vivo HIV-1 infection. These results indicate that in vivo activation of NK cells may represent a new immunotherapeutic approach to suppress acute HIV-1 infection.

IMPORTANCE

Epidemiological studies have indicated that NK cells contribute to the control of HIV-1 infection, and in vitro studies have demonstrated that NK cells can selectively kill HIV-1-infected cells. We demonstrated that in vivo activation of NK cells by treatment with an IL-15 superagonist that potently stimulates the antitumor activity of NK cells markedly inhibited acute HIV-1 infection in humanized mice, even when activation of NK cells by IL-15 superagonist treatment is delayed until 3 days after HIV-1 inoculation. NK cell depletion from PBMCs prior to their intrasplenic injection abrogated the suppression of in vivo HIV-1 infection observed in humanized mice treated with the IL-15 superagonist, demonstrating that activated human NK cells were mediating IL-15 superagonist-induced inhibition of acute HIV-1 infection. Thus, in vivo immunostimulation of NK cells, a promising therapeutic approach for cancer therapy, may represent a new treatment modality for HIV-1-infected individuals, particularly in the earliest stages of infection.

HIV-specific ADCC improves after antiretroviral therapy and correlates with normalization of the NK cell phenotype

BACKGROUND

Natural killer (NK) cell phenotype and function have recently gained much attention as playing crucial roles in antibody-dependent cellular cytotoxicity (ADCC). We investigated NK cell function, as measured by ADCC, in HIV-1-positive individuals before and 6 months after highly active antiretroviral therapy (HAART) initiation.

METHOD

The ability of antibodies and NK cells to mediate ADCC was investigated separately and in combination in an autologous model. The NK cell subset distribution and NK cell phenotype (ie, expression of maturation and activation markers within NK cell subsets) were analyzed.

RESULTS

The ability of NK cells to mediate ADCC was significantly increased after only 6 months of HAART and was not explained by a normalization of NK cell subsets (CD56 CD16 and CD56 CD16 NK cells) but rather by normalization in the frequency of NK cells expressing CCR7 and CD27. For individuals with no increase in ADCC after 6 months of HAART, the frequency of NK cells expressing NKp46 was downregulated. The ability of antibodies to mediate ADCC alone and in combination in an autologous model was not improved.

CONCLUSIONS

HAART improves the ability of NK cells to mediate ADCC after 6 months. This improvement does not correlate with general immune restoration, as measured by CD4 T-cell counts, but rather to a decrease in the frequency of NK cells expressing CCR7 and CD27.

Short communication: Longitudinal changes in peripheral blood NK cells during the first year of HIV-1 Infection in CD4Low and CD4High patient groups

Natural killer (NK) cells may modulate the pathogenesis of primary HIV-1 infection. However, the relationship between the number and function of NK cells during an acute HIV-1 infection and HIV-1 disease progression remains to be elucidated. In this study, we enrolled two distinct patient groups. One group progressed to where their CD4 cell counts fell below 200 cells/μl within 2 years (CD4Low group), while the CD4 cell counts of the other group remained above 500 cells/μl for over 2 years (CD4High group). We compared the number and function of NK cells during the first year of HIV-1 infection between the two distinct groups. We found that the number of total NK cells and the number of cells in the CD56(dim)CD16(pos) subset rapidly decreased in both groups during early HIV-1 infection. The absolute number of total NK cells and CD56(dim)CD16(pos) NK cells was significantly higher in the CD4High group when compared to the CD4Low group during the first month of infection. No significant difference between the numbers of CD56(bright)CD16(neg) NK cells of the two groups was observed. However, more CD56(neg)CD16(pos) NK cells were found in the CD4Low group than in the CD4High group. We also found that NK cell function increased within the first 3 months of HIV-1 infection in the CD4High group and then exhibited a decreasing trend. However, in the CD4Low group, NK cell function did not increase significantly within the first 3 months of HIV-1 infection but then gradually increased. We concluded, therefore, that robust NK functioning cells that are present during an acute HIV-1 infection might be beneficial in controlling HIV-1 disease progression.

Progression to AIDS in SIV-Infected Rhesus Macaques is Associated with Distinct KIR and MHC class I Polymorphisms and NK Cell Dysfunction

Killer cell immunoglobulin-like receptors (KIR) regulate the activity of natural killer (NK) cells and have been shown to be associated with susceptibility to a number of human infectious diseases. Here, we analyzed NK cell function and genetic associations in a cohort of 52 rhesus macaques experimentally infected with SIVmac and subsequently stratified into high viral load (HVL) and low viral load (LVL) plasma viral loads at set point. This stratification coincided with fast (HVL) and slow (LVL) disease progression indicated by the disease course and critical clinical parameters including CD4+ T cell counts. HVL animals revealed sustained proliferation of NK cells but distinct loss of peripheral blood NK cell numbers and lytic function. Genetic analyses revealed that KIR genes 3DL05, 3DS05, and 3DL10 as well as 3DSW08, 3DLW03, and 3DSW09 are correlated, most likely due to underlying haplotypes. SIV-infection outcome associated with presence of transcripts for two inhibitory KIR genes (KIR3DL02, KIR3DL10) and three activating KIR genes (KIR3DSW08, KIR3DS02, KIR3DS05). Presence of KIR3DL02 and KIR3DSW08 was associated with LVL outcome, whereas presence of KIR3DS02 was associated with HVL outcome. Furthermore, we identified epistasis between KIR and MHC class I alleles as the transcript presence of the correlated genes KIR3DL05, KIR3DS05, and KIR3DL10 increased HVL risk when Mamu-B*012 transcripts were also present or when Mamu-A1*001 transcripts were absent. These genetic associations were mirrored by changes in the numbers, the level of proliferation, and lytic capabilities of NK cells as well as overall survival time and gastro-intestinal tissue viral load.

Immunogenetics of small ruminant lentiviral infections

The small ruminant lentiviruses (SRLV) include the caprine arthritis encephalitis virus (CAEV) and the Maedi-Visna virus (MVV). Both of these viruses limit production and can be a major source of economic loss to producers. Little is known about how the immune system recognizes and responds to SRLVs, but due to similarities with the human immunodeficiency virus (HIV), HIV research can shed light on the possible immune mechanisms that control or lead to disease progression. This review will focus on the host immune response to HIV-1 and SRLV, and will discuss the possibility of breeding for enhanced SRLV disease resistance.

Increased frequency and function of KIR2DL1-3⁺ NK cells in primary HIV-1 infection are determined by HLA-C group haplotypes

The acquisition and maintenance of NK-cell function is mediated by inhibitory killer-cell immunoglobulin-like receptors (KIRs) through their interaction with HLA class I molecules. Recently, HLA-C expression levels were shown to be correlated with protection against multiple outcomes of HIV-1 infection; however, the underlying mechanisms are poorly understood. As HLA-C is the natural ligand for the inhibitory receptors KIR2DL1 and KIR2DL2/3, we sought to determine whether HLA-C group haplotypes affect NK-cell responses during primary HIV-1 infection. The phenotypes and functional capacity of NK cells derived from HIV-1-positive and HIV-1-negative individuals were assessed (N = 42 and N = 40, respectively). HIV-1 infection was associated with an increased frequency of KIR2DL1-3(+) NK cells. Further analysis showed that KIR2DL1(+) NK cells were selectively increased in individuals homozygous for HLA-C2, while HLA-C1-homozygous individuals displayed increased proportions of KIR2DL2/3(+) NK cells. KIR2DL1-3(+) NK cells were furthermore more polyfunctional during primary HIV-1 infection in individuals also encoding for their cognate HLA-C group haplotypes, as measured by degranulation and IFN-γ and TNF-α production. These results identify a novel relationship between HLA-C and KIR2DL(+) NK-cell subsets and demonstrate that HLA-C-mediated licensing modulates NK-cell responses to primary HIV-1 infection.

Impaired natural killer cell responses are associated with loss of the highly activated NKG2A(+)CD57(+)CD56(dim) subset in HIV-1 subtype D infection in Uganda

Objective:

Of the predominant HIV-1 subtypes in Uganda, subtype D infection confers a worse prognosis. HIV-1 infection causes perturbations to natural killer (NK) cells, and yet these cells can exert immune pressure on the virus and influence clinical outcome. Here, we studied NK cell activation and function in Ugandans with chronic untreated HIV-1 subtype D infection in comparison to uninfected community matched controls.

Methods:

Cryopreserved peripheral blood mononuclear cells (PBMCs) from 42 HIV-infected individuals and 28 HIV-negative controls were analysed using eight-colour flow cytometry. NK cell surface expression of CD16, CD56, CD57, HLA-DR and NKG2A were used to investigate activation, maturation and differentiation status. NK cell function was evaluated by measuring interferon-gamma (IFNγ) production in response to K562 cells, or interleukin (IL)-12 and IL-18.

Results:

CD56^dim NK cells from HIV-infected individuals produced less IFNγ in response to IL-12 and IL-18 than did CD56^dim NK cells from uninfected controls. Infected individuals had lower levels of CD56^dim NK cells coexpressing the differentiation markers NKG2A and CD57 than controls. In addition, their NKG2A⁺CD57⁺ CD56^dim NK cells displayed elevated activation levels as assessed by HLA-DR expression. Cytokine-induced IFNγ production correlated directly with coexpression of CD57 and NKG2A on CD56^dim NK cells.

Conclusion:

HIV-1 subtype D infection is associated with impaired NK cell responsiveness to cytokines, decline of the NKG2A⁺CD57⁺ CD56^dim NK cell subset, as well as elevated activation in this subset. These alterations within the NK cell compartment may contribute to immunopathogenesis of HIV-1 subtype D infection in Ugandans.

Higher Expression of Activating Receptors on Cytotoxic NK Cells is Associated with Early Control on HIV-1C Multiplication

Natural killer (NK) cells may be important in modulating HIV replication in early course of HIV infection. The effector function of NK cells is finely tuned by a balance between signals delivered by activating and inhibitory receptors. However, the influence of expression of these receptors on the early course of HIV replication and subsequent disease progression is not explored in the context of HIV-1C infection. The expression pattern of activating (NKp46, NKp44, NKp30, NKG2D, and NKG2C) and inhibitory (CD158b, NKG2A, and ILT2) receptors was determined in 20 patients with recent HIV-1C infection within 3–7 months of acquiring HIV infection and was compared with the expression pattern in individuals with progressive (N = 12), non-progressive HIV-1C infection (LTNPs, N = 12) and healthy seronegative individuals (N = 20). The association of the expression of these receptors on the rate of disease progression was assessed using viral load set point of recently infected individuals as a marker of disease progression. The study showed that higher cytotoxic potency of NK cells was associated with low viral load set point in recent HIV infection (r = −0.701; p = 0.0006) and higher CD4 counts (r = 0.720; p = 0.001). The expression of activating receptors (NKp46, NKp30, and NKG2D) on cytotoxic NK cells but not on regulatory NK cells was also significantly associated with low viral set point (p < 0.01) and viral load in LTNPs and progressors (p < 0.01). The study also indicated that cytotoxic NK cells might show the ability to specifically lyse HIV infected CD4 cells. This data collectively showed that early and sustained higher expression of activating receptors on cytotoxic NK cells could be responsible for increased cytotoxicity, reduced viral burden, and thus delaying the disease progression. The study to identify the molecular mechanism of the expression of these receptors in HIV infection will be helpful in further understanding of NK cell mediated control in early HIV infection.

Innate immunity cell activation in virologically suppressed HIV-infected maraviroc-treated patients

This is a cross-sectional, case-control study analyzing the effect of antiretroviral therapy (ART) including or not maraviroc, on circulating monocytes and natural killer cells. Sixty-eight HIV-positive patients virologically suppressed receiving ART at least 6 months were subdivided as receiving (group 1) or not (group 2) maraviroc in their ART. Frequency of monocytes and natural killer cells, as well as their activation markers, were studied. Modulation of innate immune cells may be differently affected by combined ART.

Antiretroviral therapy partly reverses the systemic and mucosal distribution of NK cell subsets that is altered by SIVmac₂₅₁ infection of macaques

We characterized three subsets of NK cells in blood, and two subsets in mucosal tissues. SIVmac251 infection increased total and CD16(+) NK cells in the blood. In the rectum, we observed a significant increase in total and NKG2A(+) NK cells during SIV infection. In contrast, the NKp44(+) subset significantly depleted in acute infection and continued to decline in frequency during chronic phase. During SIV infection, blood CD16 and mucosal NKG2A(+) subsets had increased cytotoxic potential. Intriguingly, the NKp44(+) NK cell subtype that likely mediates mucosal homeostasis via the production of cytokines, acquired cytotoxicity. Antiretroviral therapy significantly increased the frequency of mucosal NKG2A(+) NK cells and peripheral CD16(+) NK cells. However, it failed to restore the normal frequency of NKp44(+) NK cells in the rectum. Thus, SIVmac251 infection causes changes in the distribution and function of NK cells and antiretroviral therapy during chronic infection only partially restores NK homeostasis and function.

Activation of NK cells is associated with HIV-1 disease progression

The main predictor of HIV-1 disease progression is CD8(+) T cell activation, characterized by elevated expression of CD38 and HLA-DR. NK cells are also activated in viremic HIV-1-infected individuals. However, the relationship between NK cell activation and HIV-1 disease progression remains undefined. We characterized NK cell activation and its association with disease progression in treatment of naive HIV-1-infected individuals, who naturally maintained low/undetectable viremia (elite and viremic controllers), compared with progressors and AIDS subjects, and treated individuals. Our results show that CD38 expression on NK cells, predominantly in the cytotoxic CD56(dim)CD16(+) subset, is associated with HIV-1 disease progression (CD4(+) T cell count and pVL), T cell activation (percentage of CD38(+)HLA-DR(+) T cells), sCD14, inflammation, and innate immune activation. Moreover, NK cell activation is increased in HIV-1-infected subjects progressing to AIDS but not in elite and viremic controllers. ART partially reduces the proportion of activated NK cells. Furthermore, our results show that individuals, who naturally control viremia, maintain low levels of innate immune activation similar to those of uninfected controls.

Neonatal natural killer cell function: relevance to antiviral immune defense

Neonates are particularly susceptible to various pathogens compared to adults, which is attributed in part to their immature innate and adaptive immunity. Natural killer cells provide first-line innate immune reactions against virus-infected cells without prior sensitization. This review updates phenotypic and functional deficiencies of neonatal cells compared to their adult counterparts and their clinical implications.

In vivo administration of a JAK3 inhibitor to chronically siv infected rhesus macaques leads to NK cell depletion associated with transient modest increase in viral loads

Innate immune responses are reasoned to play an important role during both acute and chronic SIV infection and play a deterministic role during the acute stages on the rate of infection and disease progression. NK cells are an integral part of the innate immune system but their role in influencing the course of SIV infection has been a subject of debate. As a means to delineate the effect of NK cells on SIV infection, use was made of a Janus kinase 3 (JAK3) inhibitor that has previously been shown to be effective in the depletion of NK cells in vivo in nonhuman primates (NHP). Extensive safety and in vitro/in vivo PK studies were conducted and an optimal dose that depletes NK cells and NK cell function in vivo identified. Six chronically SIV infected rhesus macaques, 3 with undetectable/low plasma viral loads and 3 with high plasma viral loads were administered a daily oral dose of 10 mg/kg for 35 days. Data obtained showed that, at the dose tested, the major cell lineage affected both in the blood and the GI tissues were the NK cells. Such depletion appeared to be associated with a transient increase in plasma and GI tissue viral loads. Whereas the number of NK cells returned to baseline values in the blood, the GI tissues remained depleted of NK cells for a prolonged period of time. Recent findings show that the JAK3 inhibitor utilized in the studies reported herein has a broader activity than previously reported with dose dependent effects on both JAK2 and JAK1 suggests that it is likely that multiple pathways are affected with the administration of this drug that needs to be taken into account. The findings reported herein are the first studies on the use of a JAK3 inhibitor in lentivirus infected NHP.

Cytometry, immunology, and HIV infection: three decades of strong interactions

Flow cytometry (FCM) has been extensively used to investigate immunological changes that occur from infection with the human immunodeficiency virus (HIV). This review describes some of the most relevant cellular and molecular changes in the immune system that can be detected by FCM during HIV infection. Finally, it will be discussed how this technology has facilitated the understanding not only of the biology of the virus but also of the mechanisms that the immune system activates to fight HIV and is allowing to monitor the efficacy of antiretroviral therapy.