Human Immunodeficiency Virus (HIV)-specific Effector CD8 T Cell Activity in Patients with Primary HIV Infection

The Journal of Infectious Diseases. Mar, 2002  |  Pubmed ID: 11920293

The interferon-gamma ELISPOT assay was used to assess and compare the magnitude and breadth of human immunodeficiency virus (HIV)-specific CD8 T cell responses in treatment-naive subjects during the first year of HIV primary infection and during the chronic phase of infection. Twenty-five subjects tested within a year of exposure to HIV resulting in seroconversion and 20 subjects with chronic infection were screened for HIV peptide-specific activity by stimulating peripheral blood mononuclear cells with a panel of 5-21 HLA class I-restricted HIV peptides (mean, 11.2 +/- 3.5 HIV peptides). There was a significant correlation between the magnitude and breadth of HIV-specific effector responses and time elapsed from exposure (r=0.63 for magnitude vs. time and r=0.64 for breadth vs. time; P<.02, paired t test). Maximal breadth of the HIV gene product reactivity was achieved within 2 months of exposure for Nef-specific responses and by 4 months of exposure for responses directed to Env, Gag, and reverse transcriptase.

HIV-1-specific Cytotoxicity is Preferentially Mediated by a Subset of CD8(+) T Cells Producing Both Interferon-gamma and Tumor Necrosis Factor-alpha

Blood. Jul, 2004  |  Pubmed ID: 15059848

CD8(+) T cells play a crucial role in the control of viral infections by direct elimination of infected cells and secretion of a number of soluble factors. Recent data suggest that HIV-1-specific CD8(+) T cell subsets may differ in their ability to exert these effector functions. Here, we directly compared the cytokine secretion patterns and cytotoxic capacity of HIV-1-specific CD8(+) T cells, using a flow-cytometric cytotoxicity assay based on caspase-3 activation in dying target cells. These experiments revealed considerable intraindividual and interindividual differences among epitope-specific T-cell effector functions: while the frequency of HIV-1-specific CD8(+) T cells secreting interferon-gamma but no tumor necrosis factor-alpha (TNF-alpha) following antigenic stimulation was only weakly correlated to their cytotoxic activity (R = 0.05, P =.57), a subset of CD8(+) T cells secreting both inter-feron-gamma and TNF-alpha was substantially more strongly associated with cytotoxicity (R = 0.67, P <.001). This subset of CD8(+) T cells also exhibited stronger intracellular perforin expression and more pronounced direct ex vivo HIV-1-specific cytoxicity than CD8(+) T cells secreting solely interferon-gamma following sorting of these subpopulations according to their cytokine profile. These results suggest that HIV-1-specific cytotoxicity of CD8(+) T cells is preferentially mediated by a subset of CD8(+) T cells secreting both interferon-gamma and TNF-alpha.

Loss of HIV-1-specific CD8+ T Cell Proliferation After Acute HIV-1 Infection and Restoration by Vaccine-induced HIV-1-specific CD4+ T Cells

The Journal of Experimental Medicine. Sep, 2004  |  Pubmed ID: 15381726

Virus-specific CD8(+) T cells are associated with declining viremia in acute human immunodeficiency virus (HIV)1 infection, but do not correlate with control of viremia in chronic infection, suggesting a progressive functional defect not measured by interferon gamma assays presently used. Here, we demonstrate that HIV-1-specific CD8(+) T cells proliferate rapidly upon encounter with cognate antigen in acute infection, but lose this capacity with ongoing viral replication. This functional defect can be induced in vitro by depletion of CD4(+) T cells or addition of interleukin 2-neutralizing antibodies, and can be corrected in chronic infection in vitro by addition of autologous CD4(+) T cells isolated during acute infection and in vivo by vaccine-mediated induction of HIV-1-specific CD4(+) T helper cell responses. These data demonstrate a loss of HIV-1-specific CD8(+) T cell function that not only correlates with progressive infection, but also can be restored in chronic infection by augmentation of HIV-1-specific T helper cell function. This identification of a reversible defect in cell-mediated immunity in chronic HIV-1 infection has important implications for immunotherapeutic interventions.

Increased Natural Killer Cell Activity in Viremic HIV-1 Infection

Journal of Immunology (Baltimore, Md. : 1950). Oct, 2004  |  Pubmed ID: 15470077

NK cells are a subset of granular lymphocytes that are critical in the innate immune response to infection. These cells are capable of killing infected cells and secreting integral cytokines and chemokines. The role that this subset of cytolytic cells plays in HIV infection is not well understood. In this study, we dissected the function of NK cells in viremic and aviremic HIV-1-infected subjects, as well as HIV-1-negative control individuals. Despite reduced NK cell numbers in subjects with ongoing viral replication, these cells were significantly more active in secreting both IFN-gamma and TNF-alpha than NK cells from aviremic subjects or HIV-1-negative controls. In addition, NK cells in subjects with detectable viral loads expressed significantly higher levels of CD107a, a marker of lysosomal granule exocytosis. The expression of CD107a correlated with NK cell-mediated cytokine secretion and cytolytic activity as well as with the level of viral replication, suggesting that CD107a represents a good marker for the functional activity of NK cells. Finally, killer Ig-related receptor+ NK cells were stable or elevated in viremic subjects, while the numbers of CD3-/CD56+/CD94+ and CD3-/CD56+/CD161+ NK cells were reduced. Taken together, these data demonstrate that viremic HIV-1 infection is associated with a reduction in NK cell numbers and a perturbation of NK cell subsets, but increased overall NK cell activity.

Assessment of Longitudinal Changes in HIV-specific Effector Activity in Subjects Undergoing Untreated Primary HIV Infection

AIDS (London, England). Oct, 2004  |  Pubmed ID: 15577619

Despite the failure of HIV-specific cell-mediated immune responses to clear the virus, these cells play a critical role in the control of viral replication throughout HIV infection.

CD107a As a Functional Marker for the Identification of Natural Killer Cell Activity

Journal of Immunological Methods. Nov, 2004  |  Pubmed ID: 15604012

Natural killer (NK) cells are a subset of lymphocytes that play a central role in the innate immune response to tumors and infections. An important limitation in the field of NK research is attributable to the deficit of assays available for the detection of the functional activity of NK cells. Recently, lysosomal-associated membrane protein-1 (LAMP-1 or CD107a) has been described as a marker of CD8+ T-cell degranulation following stimulation. Here we describe CD107a as a marker of NK cell functional activity using multi-parameter flow cytometry. CD107a is significantly upregulated on the surface of NK cells following stimulation with MHC devoid targets. Additionally, CD107a expression correlates with both cytokine secretion and NK cell-mediated lysis of target cells. However, as well as being coordinately expressed on nearly all cytokine secreting cells, CD107a was also expressed on a large subset of NK cells that did not secrete cytokine following stimulation. These data suggest that employing CD107a as a marker of NK cell functional activity may allow for the identification of a large fraction of activated NK cells that may degranulate in the absence of cytokine secretion. Cumulatively, the data presented here demonstrate that CD107a is a sensitive marker of NK cell activity.

Human Immunodeficiency Virus (HIV)-specific Gamma Interferon Secretion Directed Against All Expressed HIV Genes: Relationship to Rate of CD4 Decline

Journal of Virology. Apr, 2005  |  Pubmed ID: 15795276

Immune responses to human immunodeficiency virus (HIV) are detected at all stages of infection and are believed to be responsible for controlling viremia. This study seeks to determine whether gamma interferon (IFN-gamma)-secreting HIV-specific T-cell responses influence disease progression as defined by the rate of CD4 decline. The study population consisted of 31 subjects naive to antiretroviral therapy. All were monitored clinically for a median of 24 months after the time they were tested for HIV-specific responses. The rate of CD4+-T-cell loss was calculated for all participants from monthly CD4 counts. Within this population, 17 subjects were classified as typical progressors, 6 subjects were classified as fast progressors, and 8 subjects were classified as slow progressors. Peripheral blood mononuclear cells were screened for HIV-specific IFN-gamma responses to all expressed HIV genes. Among the detected immune responses, 48% of the recognized peptides were encoded by Gag and 19% were encoded by Nef gene products. Neither the breadth nor the magnitude of HIV-specific responses correlated with the viral load or rate of CD4 decline. The breadth and magnitude of HIV-specific responses did not differ significantly among typical, fast, and slow progressors. These results support the conclusion that although diverse HIV-specific IFN-gamma-secreting responses are mounted during the asymptomatic phase, these responses do not seem to modulate disease progression rates.

The Majority of Currently Circulating Human Immunodeficiency Virus Type 1 Clade B Viruses Fail to Prime Cytotoxic T-lymphocyte Responses Against an Otherwise Immunodominant HLA-A2-restricted Epitope: Implications for Vaccine Design

Journal of Virology. Apr, 2005  |  Pubmed ID: 15795285

Human immunodeficiency virus type 1 (HIV-1) mutates to escape immune selection pressure, but there is little evidence of selection mediated through HLA-A2, the dominant class I allele in persons infected with clade B virus. Moreover, HLA-A2-restricted responses are largely absent in the acute phase of infection as the viral load is being reduced, suggesting that circulating viruses may lack immunodominant epitopes targeted through HLA-A2. Here we demonstrate an A2-restricted epitope within Vpr (Vpr59-67) that is targeted by acute-phase HIV-1-specific CD8+ T cells, but only in a subset of persons expressing HLA-A2. Individuals in the acute stage of infection with viruses containing the most common current sequence within this epitope (consensus sequence) were unable to mount epitope-specific T-cell responses, whereas subjects infected with the less frequent I60L variant all developed these responses. The I60L variant epitope was a stronger binder to HLA-A2 and was recognized by epitope-specific T cells at lower peptide concentrations than the consensus sequence epitope. These data demonstrate that HLA-A2 is capable of contributing to the acute-phase cytotoxic T-lymphocyte response in infected subjects, but that most currently circulating viruses lack a dominant immunogenic epitope presented by this allele, and suggest that immunodominant epitopes restricted by common HLA alleles may be lost as the epidemic matures.

Sequential Deregulation of NK Cell Subset Distribution and Function Starting in Acute HIV-1 Infection

Blood. Nov, 2005  |  Pubmed ID: 16002429

Natural killer (NK) cells are critical in the first-line defense against viral infections. Chronic HIV-1 infection leads to a perturbation in the NK cell compartment, yet the kinetics of this deregulation and the functional consequences are unclear. Here, we characterized changes in the NK cell compartment longitudinally by multiparameter flow cytometry, starting in acute HIV-1 infection. Acute HIV-1 infection was associated with elevated NK cell numbers, with an expansion of CD3(neg)CD56(dim)CD16(pos) NK cells and an early depletion of CD3(neg)CD56(bright)CD16(neg) NK cells. Ongoing viral replication resulted in a depletion of CD3(neg)CD56(dim)CD16(pos) NK cells with a paralleled increase in functionally anergic CD3(neg)CD56(neg)CD16(pos) NK cells, accompanied by reduced functional activity, as measured by CD107a expression and cytokine secretion. Taken together, these studies demonstrate a sequential impairment of NK cell function with persistent viral replication resulting from a progressive deregulation of NK cell subsets with distinct functional properties.

High Degree of Inter-clade Cross-reactivity of HIV-1-specific T Cell Responses at the Single Peptide Level

AIDS (London, England). Sep, 2005  |  Pubmed ID: 16135897

To determine HIV-1-specific T cell responses in clade B infected individuals recognizing the clade A, B and C consensus sequences in order to assess the degree of inter-clade cross-reactivity of these immune responses at the single epitope level.

De Novo Generation of Escape Variant-specific CD8+ T-cell Responses Following Cytotoxic T-lymphocyte Escape in Chronic Human Immunodeficiency Virus Type 1 Infection

Journal of Virology. Oct, 2005  |  Pubmed ID: 16188997

Human immunodeficiency virus type 1 (HIV-1) evades CD8(+) T-cell responses through mutations within targeted epitopes, but little is known regarding its ability to generate de novo CD8(+) T-cell responses to such mutants. Here we examined gamma interferon-positive, HIV-1-specific CD8(+) T-cell responses and autologous viral sequences in an HIV-1-infected individual for more than 6 years following acute infection. Fourteen optimal HIV-1 T-cell epitopes were targeted by CD8(+) T cells, four of which underwent mutation associated with dramatic loss of the original CD8(+) response. However, following the G(357)S escape in the HLA-A11-restricted Gag(349-359) epitope and the decline of wild-type-specific CD8(+) T-cell responses, a novel CD8(+) T-cell response equal in magnitude to the original response was generated against the variant epitope. CD8(+) T cells targeting the variant epitope did not exhibit cross-reactivity against the wild-type epitope but rather utilized a distinct T-cell receptor Vbeta repertoire. Additional studies of chronically HIV-1-infected individuals expressing HLA-A11 demonstrated that the majority of the subjects targeted the G(357)S escape variant of the Gag(349-359) epitope, while the wild-type consensus sequence was significantly less frequently recognized. These data demonstrate that de novo responses against escape variants of CD8(+) T-cell epitopes can be generated in chronic HIV-1 infection and provide the rationale for developing vaccines to induce CD8(+) T-cell responses directed against both the wild-type and variant forms of CD8 epitopes to prevent the emergence of cytotoxic T-lymphocyte escape variants.

Consistent Effects of TSG101 Genetic Variability on Multiple Outcomes of Exposure to Human Immunodeficiency Virus Type 1

Journal of Virology. Jul, 2006  |  Pubmed ID: 16809281

Tumor susceptibility gene 101 (TSG101) encodes a host cellular protein that is appropriated by human immunodeficiency virus type 1 (HIV-1) in the budding process of viral particles from infected cells. Variation in the coding or noncoding regions of the gene could potentially affect the degree of TSG101-mediated release of viral particles. While the coding regions of the gene were found to lack nonsynonymous variants, two polymorphic sites in the TSG101 5' area were identified that were associated with the rate of AIDS progression among Caucasians. These single-nucleotide polymorphisms (SNPs), located at positions -183 and +181 relative to the translation start, specify three haplotypes termed A, B, and C, which occur at frequencies of 67%, 21%, and 12%, respectively. Haplotype C is associated with relatively rapid AIDS progression, while haplotype B is associated with slower disease progression. Both effects were dominant over the intermediate haplotype A. The haplotypes also demonstrated parallel effects on the rate of CD4 T-cell depletion and viral load increase over time, as well as a possible influence on HIV-1 infection. The data raise the hypothesis that noncoding variation in TSG101 affects the efficiency of TSG101-mediated release of viral particles from infected cells, thereby altering levels of plasma viral load and subsequent disease progression.

Low Perforin and Elevated SHIP-1 Expression is Associated with Functional Anergy of Natural Killer Cells in Chronic HIV-1 Infection

AIDS (London, England). Jul, 2006  |  Pubmed ID: 16847410

Natural killer (NK) cells are critical for the first-line defense in infection. Treated viremic HIV-1 infection is associated with the expansion of an anergic subset of CD3-CD56-CD16+ NK cells unable to respond to stimulation with MHC-devoid target cells or with mitogens. These CD3-CD56-CD16+ NK cells expressed SHIP-1 and had significantly reduced perforin levels. This observation suggests a mechanism for the reduced functional activity of CD3-CD56-CD16+ NK cells in chronic HIV-1 infection.

Immunological and Virological Impact of Highly Active Antiretroviral Therapy Initiated During Acute HIV-1 Infection

The Journal of Infectious Diseases. Sep, 2006  |  Pubmed ID: 16941338

The immunological and virological impact of short-term treatment initiated during acute human immunodeficiency virus type 1 (HIV-1) infection was assessed prospectively in 20 subjects, 12 of whom initiated highly active antiretroviral therapy (HAART) for 24 weeks and then terminated treatment. Treatment resulted in suppression of viremia, an increase in the CD4+ T cell count, enhanced differentiation of HIV-1-specific CD8(+) T cells from effector memory to effector cells at week 24 of HAART, and significantly higher virus-specific interferon- gamma+ CD8+ T cell responses after viral rebound (at week 48). However, despite these immunological changes, no differences in viremia or in the CD4+ T cell count were found 6 months after HAART was stopped, when treated subjects were compared with untreated subjects.

NK Cell Function in HIV-1 Infection

Current Molecular Medicine. Sep, 2006  |  Pubmed ID: 17022732

NK cells are critical effector cells of the innate immune response to malignancy and infection. These cells have a wide array of direct antiviral activities and have been critically implicated in the regulation and induction of an effective adaptive immune response. Although the pivotal role of this cell subset in the context of a number of viral infections is well established, the role of NK cells in HIV-1 infection is less well understood. Recent data has demonstrated the association between an NK cell receptor, KIR3DS1, and it's ligand, HLA-Bw4 with an isoleucine at position 80, and slower disease progression. This data suggests that NK cells may play an essential role in the control of HIV-1 disease, and has provided the impetus to begin to better understand the role of this cell subset in the context of HIV-1 infection, replication, and pathogenesis. Here we present a review of the literature pertaining to both the effect of HIV-1 infection on NK cell activity and the potential role that this subset of cells may play in controlling HIV-1 disease.

HLA Alleles Associated with Delayed Progression to AIDS Contribute Strongly to the Initial CD8(+) T Cell Response Against HIV-1

PLoS Medicine. Oct, 2006  |  Pubmed ID: 17076553

Very little is known about the immunodominance patterns of HIV-1-specific T cell responses during primary HIV-1 infection and the reasons for human lymphocyte antigen (HLA) modulation of disease progression.

Perspective Natural Killer Cells: Bridging Innate and Adaptive Immunity?

IAVI Report : Newsletter on International AIDS Vaccine Research. May-Jun, 2006  |  Pubmed ID: 20217934

Evolution of Innate and Adaptive Effector Cell Functions During Acute HIV-1 Infection

The Journal of Infectious Diseases. May, 2007  |  Pubmed ID: 17436225

Early events during acute human immunodeficiency virus type 1 (HIV-1) infection are critical in determining the course of disease progression. Cells of the innate and adaptive immune responses are involved in this acute response to infection; however, little is known about the coevolution of innate and adaptive effector cell populations during the initial phase of HIV-1 infection. Here, we have characterized the development of innate natural killer (NK) cell and adaptive HIV-1-specific CD8(+) T cell function during acute HIV-1 infection. Although NK cell populations were significantly expanded during acute infection before HIV-1 seroconversion, HIV-1-specific CD8(+) T cell responses were absent or weak and were inversely correlated with the level of NK cell activity. NK cell activity was directly correlated with the level of viral replication during acute HIV-1 infection and declined rapidly in subjects who initiated highly active antiretroviral therapy, whereas NK cell activity remained elevated in subjects who did not initiate therapy. Yet, reexposure to HIV-1 antigen during treatment discontinuation in chronic infection resulted in a synchronous increase in NK and CD8(+) T cell activity. Overall, these data demonstrate that expansion of the NK cell population precedes the development of adaptive HIV-1-specific CD8(+) T cells during acute infection but that both effector cell subsets respond with similar kinetics during chronic HIV-1 infection.

Recognition of a Defined Region Within P24 Gag by CD8+ T Cells During Primary Human Immunodeficiency Virus Type 1 Infection in Individuals Expressing Protective HLA Class I Alleles

Journal of Virology. Jul, 2007  |  Pubmed ID: 17494064

Human immunodeficiency virus type 1 (HIV-1)-specific immune responses during primary HIV-1 infection appear to play a critical role in determining the ultimate speed of disease progression, but little is known about the specificity of the initial HIV-1-specific CD8(+) T-cell responses in individuals expressing protective HLA class I alleles. Here we compared HIV-1-specific T-cell responses between subjects expressing the protective allele HLA-B27 or -B57 and subjects expressing nonprotective HLA alleles using a cohort of over 290 subjects identified during primary HIV-1 infection. CD8(+) T cells of individuals expressing HLA-B27 or -B57 targeted a defined region within HIV-1 p24 Gag (amino acids 240 to 272) early in infection, and responses against this region contributed over 35% to the total HIV-1-specific T-cell responses in these individuals. In contrast, this region was rarely recognized in individuals expressing HLA-B35, an HLA allele associated with rapid disease progression, or in subjects expressing neither HLA-B57/B27 nor HLA-B35 (P < 0.0001). The identification of this highly conserved region in p24 Gag targeted in primary infection specifically in individuals expressing HLA class I alleles associated with slower HIV-1 disease progression provides a rationale for vaccine design aimed at inducing responses to this region restricted by other, more common HLA class I alleles.

MyD88-dependent Immune Activation Mediated by Human Immunodeficiency Virus Type 1-encoded Toll-like Receptor Ligands

Journal of Virology. Aug, 2007  |  Pubmed ID: 17507480

Immune activation is a major characteristic of human immunodeficiency virus type 1 (HIV-1) infection and a strong prognostic factor for HIV-1 disease progression. The underlying mechanisms leading to immune activation in viremic HIV-1 infection, however, are not fully understood. Here we show that, following the initiation of highly active antiretroviral therapy, the immediate decline of immune activation is closely associated with the reduction of HIV-1 viremia, which suggests a direct contribution of HIV-1 itself to immune activation. To propose a mechanism, we demonstrate that the single-stranded RNA of HIV-1 encodes multiple uridine-rich Toll-like receptor 7/8 (TLR7/8) ligands that induce strong MyD88-dependent plasmacytoid dendritic cell and monocyte activation, as well as accessory cell-dependent T-cell activation. HIV-1-encoded TLR ligands may, therefore, directly contribute to the immune activation observed during viremic HIV-1 infection. These data provide an initial rationale for inhibiting the TLR pathway to directly reduce the chronic immune activation induced by HIV-1 and the associated immune pathogenesis.

Single-stranded RNA Derived from HIV-1 Serves As a Potent Activator of NK Cells

Journal of Immunology (Baltimore, Md. : 1950). Jun, 2007  |  Pubmed ID: 17548602

Persistent immune activation is a hallmark of chronic viremic HIV-1 infection. Activation of cells of the innate immune system, such as NK cells, occurs rapidly upon infection, and is sustained throughout the course of the disease. However, the precise underlying mechanism accounting for the persistent HIV-1-induced activation of NK cells is poorly understood. In this study, we assessed the role of uridine-rich ssRNA derived from the HIV-1 long terminal repeat (ssRNA40) on activation of NK cells via TLR7/8. Although dramatic activation of NK cells was observed following stimulation of PBMC with ssRNA40, negligible activation was observed following stimulation of purified NK cells despite their expression of TLR8 mRNA and protein. The functional activation of NK cells by this HIV-1-encoded TLR7/8 ligand could not be reconstituted with exogenous IL-12, IFN-alpha, or TNF-alpha, but was critically dependent on the direct contact of NK cells with plasmacytoid dendritic cells or CD14(+) monocytes, indicating an important level of NK cell cross-talk and regulation by accessory cells during TLR-mediated activation. Coincubation of monocyte/plasmacytoid dendritic cells, NK cells, and ssRNA40 potentiated NK cell IFN-gamma secretion in response to MHC-devoid target cells. Studies using NK cells derived from individuals with chronic HIV-1 infection demonstrated a reduction of NK cell responsiveness following stimulation with TLR ligands in viremic HIV-1 infection. These data demonstrate that HIV-1-derived TLR ligands can contribute to the immune activation of NK cells and may play an important role in HIV-1-associated immunopathogenesis and NK cell dysfunction observed during acute and chronic viremic HIV-1 infection.

Detection of KIR3DS1 on the Cell Surface of Peripheral Blood NK Cells Facilitates Identification of a Novel Null Allele and Assessment of KIR3DS1 Expression During HIV-1 Infection

Journal of Immunology (Baltimore, Md. : 1950). Aug, 2007  |  Pubmed ID: 17641029

KIR3DL1 is a highly polymorphic killer cell Ig-like receptor gene with at least 23 alleles described, including its activating counterpart, KIR3DS1. Recently, the KIR3DS1 allele has been shown to slow progression to AIDS in individuals expressing HLA-Bw4 with isoleucine at position 80. However, due to the lack of a specific Ab, KIR3DS1 expression and function is not well characterized. In this study, we demonstrate KIR3DS1 expression on a substantial subset of peripheral natural killer cells through its recognition by the mAb Z27. The fidelity of this detection method was confirmed by analysis of KIR3DS1 transfectants and the identification of a novel KIR3DS1 null allele. Interestingly, KIR3DS1 is also expressed by a small proportion of CD56(+) T cells. We show that ligation of KIR3DS1 by Z27 leads to NK cell IFN-gamma production and degranulation as assessed by expression of CD107a. Furthermore, we document the persistence of KIR3DS1(+) NK cells in HIV-1 viremic patients. The high frequency of KIR3DS1 expression, along with its ability to activate NK cells, and its maintenance during HIV-1 viremia are consistent with the epidemiological data suggesting a critical role for this receptor in controlling HIV-1 pathogenesis.

Differential Natural Killer Cell-mediated Inhibition of HIV-1 Replication Based on Distinct KIR/HLA Subtypes

The Journal of Experimental Medicine. Nov, 2007  |  Pubmed ID: 18025129

Decline of peak viremia during acute HIV-1 infection occurs before the development of vigorous adaptive immunity, and the level of decline correlates inversely with the rate of AIDS progression, implicating a potential role for the innate immune response in determining disease outcome. The combined expression of an activating natural killer (NK) cell receptor, the killer immunoglobulin-like receptor (KIR) 3DS1, and its presumed ligand, human leukocyte antigen (HLA)-B Bw4-80I, has been associated in epidemiological studies with a slow progression to AIDS. We examined the functional ability of NK cells to differentially control HIV-1 replication in vitro based on their KIR and HLA types. NK cells expressing KIR3DS1 showed strong, significant dose- and cell contact-dependent inhibition of HIV-1 replication in target cells expressing HLA-B Bw4-80I compared with NK cells that did not express KIR3DS1. Furthermore, KIR3DS1+ NK cells and NKLs were preferentially activated, and lysed HIV-1 infected target cells in an HLA-B Bw4-80I-dependent manner. These data provide the first functional evidence that variation at the KIR locus influences the effectiveness of NK cell activity in the containment of viral replication.

Biology of Plasmacytoid Dendritic Cells and Natural Killer Cells in HIV-1 Infection

Current Opinion in HIV and AIDS. May, 2007  |  Pubmed ID: 19372886

This review summarizes recent literature on the biology of dendritic cells and natural killer cells in HIV-1 infection and the importance of crosstalk between them in the development of strong antiviral immunity.

Rapid Ex Vivo Isolation and Long-term Culture of Human Th17 Cells

Journal of Immunological Methods. Apr, 2008  |  Pubmed ID: 18314131

T helper (Th) 17 cells are a distinct lineage of CD4+ T cells mediating tissue inflammation through the secretion of IL-17. In addition, it has been shown that the expression of the transcriptional factor RORgammat is responsible for the induction and maintenance of this cell line. Th17 cells are believed to be involved in a variety of autoimmune disorders, but may also play an important role in host defense. Here we describe a novel technique to reproducibly isolate viable Th17 cells based on their IL-17 secreting ability. We confirmed Th17 cell enrichment by quantitative PCR analysis and demonstrate that positively selected cells using this technique express significantly increased mRNA levels of RORgammat, IL-23 receptor and CCR4 when compared to negatively selected cells. Furthermore, we show that purified Th17 cells can be maintained in long-term culture and expand in vitro. In conclusion, this technique will allow for the first time the direct, ex vivo analysis of phenotypic and functional properties of Th17 cells.

Upregulation of PD-L1 on Monocytes and Dendritic Cells by HIV-1 Derived TLR Ligands

AIDS (London, England). Mar, 2008  |  Pubmed ID: 18317010

Increased PD-L1 expression has been reported in HIV-1-infected individuals, but the mechanisms leading to PD-L1 upregulation remain to be elucidated. Here we demonstrate that HIV-1-derived Toll-like receptor (TLR)7/8 ligands can induce MyD88-dependent upregulation of PD-L1 on plasmacytoid dendritic cells, myeloidic dendritic cells and monocytes. These data suggest a mechanism through which HIV-1-derived TLR ligands might contribute to the functional impairment of virus-specific PD-1-positive T cells by inducing the upregulation of PD-L1 on antigen-presenting cells.

Novel KIR3DL1 Alleles and Their Expression Levels on NK Cells: Convergent Evolution of KIR3DL1 Phenotype Variation?

Journal of Immunology (Baltimore, Md. : 1950). May, 2008  |  Pubmed ID: 18453594

KIR3DL1 shows extensive polymorphism, and its variation has functional significance in terms of cell-surface expression levels and inhibitory capacity. We characterized nine KIR3DL1 alleles (*022, *028, *029, *033, *035, *051, *052, *053, and *054), four of which were identified for the first time in this study, and compared them to known alleles in phylogenetic analysis. Blood was available from eight individuals with these alleles, and cell-surface expression on NK cells could be determined for six of them using the KIR3DL1-specific Ab DX9. Four of the alleles were expressed at clearly detectable levels, and two others showed exceptionally low levels of expression. Site-directed mutagenesis demonstrated that single amino acid changes can result in either diminished or enhanced DX9 staining compared with the respective related KIR3DL1 allotypes. These results raise the possibility that KIR3DL1 evolution maintains variation in KIR3DL1 cell-surface expression levels, potentially due to the effect of such variation on functional capacity.

Antigen Load and Viral Sequence Diversification Determine the Functional Profile of HIV-1-specific CD8+ T Cells

PLoS Medicine. May, 2008  |  Pubmed ID: 18462013

Virus-specific CD8(+) T lymphocytes play a key role in the initial reduction of peak viremia during acute viral infections, but display signs of increasing dysfunction and exhaustion under conditions of chronic antigen persistence. It has been suggested that virus-specific CD8(+) T cells with a "polyfunctional" profile, defined by the capacity to secrete multiple cytokines or chemokines, are most competent in controlling viral replication in chronic HIV-1 infection. We used HIV-1 infection as a model of chronic persistent viral infection to investigate the process of exhaustion and dysfunction of virus-specific CD8(+) T cell responses on the single-epitope level over time, starting in primary HIV-1 infection.

Ligand-independent Exhaustion of Killer Immunoglobulin-like Receptor-positive CD8+ T Cells in Human Immunodeficiency Virus Type 1 Infection

Journal of Virology. Oct, 2008  |  Pubmed ID: 18579582

Virus-specific CD8(+) T cells play a central role in the control of viral infections, including human immunodeficiency virus type 1 (HIV-1) infection. However, despite the presence of strong and broad HIV-specific CD8(+) T-cell responses in chronic HIV-1 infection, these cells progressively lose critical effector functions and fail to clear the infection. Mounting evidence suggests that the upregulation of several inhibitory regulatory receptors on the surface of CD8(+) T cells during HIV-1 infection may contribute directly to the impairment of T-cell function. Here, we investigated the role of killer immunoglobulin receptors (KIR), which are expressed on NK cells and on CD8(+) T cells, in regulating CD8(+) T-cell function in HIV-1 infection. KIR expression was progressively upregulated on CD8(+) T cells during HIV-1 infection and correlated with the level of viral replication. Expression of KIR was associated with a profound inhibition of cytokine secretion, degranulation, proliferation, and activation by CD8(+) T cells following stimulation with T-cell receptor (TCR)-dependent stimuli. In contrast, KIR(+) CD8(+) T cells responded potently to TCR-independent stimulation, demonstrating that these cells are functionally competent. KIR-associated suppression of CD8(+) T-cell function was independent of ligand engagement, suggesting that these regulatory receptors may constitutively repress TCR activation. This ligand-independent repression of TCR activation of KIR(+) CD8(+) T cells may represent a significant barrier to therapeutic interventions aimed at improving the quality of the HIV-specific CD8(+) T-cell response in infected individuals.

Rapid Loss of Dendritic Cell and Monocyte Responses to TLR Ligands Following Venipuncture

Journal of Immunological Methods. Dec, 2008  |  Pubmed ID: 18848564

Blood samples from multiple sites are collected in multicenter trials, and frequently shipped to centralized laboratories for processing and comparable experimental evaluation. It is therefore of crucial interest to assess the preservation of immune cell functions after overnight shipment of whole blood. Here we evaluated the ability of pDCs, mDCs and monocytes to respond to TLR ligands at multiple timepoints following venipuncture as compared to immediate processing. Our results demonstrate a profound impairment of APC function, in particular of IFN-alpha production of pDCs, if whole blood was processed later than 6 h after venipuncture. Overnight shipment or extended rest of whole blood before processing therefore severely compromises the ability of APCs to respond to TLR ligands, and this has to be taken into consideration when designing multicenter trials.

Type 2 Bias of T Cells Expanded from the Blood of Melanoma Patients Switched to Type 1 by IL-12p70 MRNA-transfected Dendritic Cells

Cancer Research. Nov, 2008  |  Pubmed ID: 19010919

Melanoma patients may exhibit a T(H)2-skewed cytokine profile within blood and tumor-infiltrating lymphocytes. Therapies that induce beneficial T(H)1-type tumor-specific immune responses, therefore, are highly desirable. Dendritic cells (DC) are widely used as immune adjuvants for cancer. Before their administration, DC are generally induced to mature with a cocktail of recombinant cytokines [interleukin (IL)-1beta, tumor necrosis factor alpha, and IL-6] and prostaglandin E(2) (PGE(2)), which is added to preserve the ability of DC to migrate to draining lymph nodes. However, PGE(2) suppresses the production of IL-12p70, a cytokine essential for differentiation of T(H)1 responses. In this study, human DC were transfected with IL-12p70 mRNA and tested for their ability to alter the T(H)2 type bias manifested by blood T cells of patients with melanoma. Transfected DC secreted high levels of bioactive IL-12p70, as indicated by their capacity to enhance natural killer cell activity, skew T(H)1 responses in allogeneic mixed lymphocyte reactions through reduction of IL-4 and IL-5, and prime CD8(+) T cells to the melanoma-associated antigen Melan A/MART-1. Furthermore, T-cell lines primed in vitro from the blood of melanoma patients showed strong type 2 skewing that was dramatically reversed by IL-12p70 transfection of autologous DC. Thus, IL-12p70 transfection of clinical DC preparations may enhance type 1 antitumor responses and may thereby contribute to effective immune-based therapy.

Protective HLA Class I Alleles That Restrict Acute-phase CD8+ T-cell Responses Are Associated with Viral Escape Mutations Located in Highly Conserved Regions of Human Immunodeficiency Virus Type 1

Journal of Virology. Feb, 2009  |  Pubmed ID: 19036810

The control of human immunodeficiency virus type 1 (HIV-1) associated with particular HLA class I alleles suggests that some CD8(+) T-cell responses may be more effective than others at containing HIV-1. Unfortunately, substantial diversities in the breadth, magnitude, and function of these responses have impaired our ability to identify responses most critical to this control. It has been proposed that CD8 responses targeting conserved regions of the virus may be particularly effective, since the development of cytotoxic T-lymphocyte (CTL) escape mutations in these regions may significantly impair viral replication. To address this hypothesis at the population level, we derived near-full-length viral genomes from 98 chronically infected individuals and identified a total of 76 HLA class I-associated mutations across the genome, reflective of CD8 responses capable of selecting for sequence evolution. The majority of HLA-associated mutations were found in p24 Gag, Pol, and Nef. Reversion of HLA-associated mutations in the absence of the selecting HLA allele was also commonly observed, suggesting an impact of most CTL escape mutations on viral replication. Although no correlations were observed between the number or location of HLA-associated mutations and protective HLA alleles, limiting the analysis to mutations selected by acute-phase immunodominant responses revealed a strong positive correlation between mutations at conserved residues and protective HLA alleles. These data suggest that control of HIV-1 may be associated with acute-phase CD8 responses capable of selecting for viral escape mutations in highly conserved regions of the virus, supporting the inclusion of these regions in the design of an effective vaccine.

Report on the AIDS Vaccine 2008 Conference

Human Vaccines. Mar, 2009  |  Pubmed ID: 19202348

The "AIDS Vaccine 2008" Conference was held in Cape Town, South Africa (October 13 to 16, 2008) and organized, under the aegis of the Global HIV Vaccine Enterprise, by Dr. Lynn Morris (Chair of the Conference) National Institute of Communicable Diseases; Dr. Koleka Mlisana from CAPRISA, University KwaZulu-Natal, Durban, Dr. Glenda Gray from Perinatal HIV Research Unit, University Witwatersrand, Johannesburg and Dr. Carolyn Williamson from Institute of Infectious Diseses. and Molecular Medicine, UCT, Cape Town (Co-Chairs of the Conference). Since the first AIDS Vaccine conference, organized in Paris in 2000, this was the first time it was held outside of the U.S. and Europe, and involved nearly 1,000 participants. Besides three Plenary Sessions with ten state-of-the-art plenary lectures and one Keynote Lecture given by Dr. A.S. Fauci (Director of NIAID, NIH, USA), the Conference was organized in nine oral sessions, four poster discussion groups covering a wide spectrum of scientific information relating to HIV vaccine research and development. Moreover three Symposia, two Special Sessions, one Roundtable as well as two Debates were held, the latter focusing on current controversial topics. The conference opening was memorable for a number of reasons: among these was the presence of South Africa's new Minister of Health, Barbara Hogan who, in her first speech in a major forum as a senior member of the SA Government, affirmed that HIV causes AIDS, and that the search for a vaccine is of paramount importance to SA and the rest of the world. A scientific summary of the Conference is reported in the present article, divided into four major topics: (1) vaccine concepts and design; (2) T-cell immunology and innate immunity; (3) B-cell immunology, neutralizing antibodies and mucosal immunology; and (4) clinical trials.

HLA Class I Subtype-dependent Expansion of KIR3DS1+ and KIR3DL1+ NK Cells During Acute Human Immunodeficiency Virus Type 1 Infection

Journal of Virology. Jul, 2009  |  Pubmed ID: 19386717

NK cells are critical in the early containment of viral infections. Epidemiological and functional studies have shown an important role of NK cells expressing specific killer immunoglobulin-like receptors (KIRs) in the control of human immunodeficiency virus type 1 (HIV-1) infection, but little is known about the mechanisms that determine the expansion of these antiviral NK cell populations during acute HIV-1 infection. Here we demonstrate that NK cells expressing the activating receptor KIR3DS1(+) and, to a lesser extent, the inhibitory receptor KIR3DL1(+) specifically expand in acute HIV-1 infection in the presence of HLA-B Bw480I, the putative HLA class I ligand for KIR3DL1/3DS1. These data demonstrate for the first time the HLA class I subtype-dependent expansion of specific KIR(+) NK cells during an acute viral infection in humans.

Matrix Metalloprotease Inhibitors Restore Impaired NK Cell-mediated Antibody-dependent Cellular Cytotoxicity in Human Immunodeficiency Virus Type 1 Infection

Journal of Virology. Sep, 2009  |  Pubmed ID: 19553339

Increasing evidence suggests that NK cells not only are critical in the initial host defense against pathogens but also may contribute to continued protection from human immunodeficiency virus type 1 (HIV-1) disease progression. NK cell cytolysis can be induced directly through diverse receptor families or can be induced indirectly through Fc receptors by antibodies mediating antibody-dependent cellular cytotoxicity (ADCC). ADCC has been implicated in both protection from simian immunodeficiency virus infection and slower progression of HIV-1 disease. ADCC activity declines with advancing infection, and yet the underlying mechanism for this dysfunction has not been defined, nor has it been determined whether the activity can be reconstituted. Here we demonstrate that NK cell-mediated ADCC is severely compromised in chronic HIV infection. The potency of ADCC function was directly correlated with baseline Fc gammaRIIIa receptor (CD16) expression on NK cells. CD16 expression was negatively influenced by elevated expression of a group of enzymes, the matrix metalloproteinases (MMPs), normally involved in tissue/receptor remodeling. Inhibition of MMPs resulted in increased CD16 expression and augmented ADCC activity in response to antibody-coated target cells. These data suggest that MMP inhibitors may improve NK cell-mediated ADCC, which may provide subjects with an opportunity to harness the cytolytic power of NK cells through naturally occurring nonneutralizing HIV-specific antibodies.

Sex Differences in the Toll-like Receptor-mediated Response of Plasmacytoid Dendritic Cells to HIV-1

Nature Medicine. Aug, 2009  |  Pubmed ID: 19597505

Manifestations of viral infections can differ between women and men, and marked sex differences have been described in the course of HIV-1 disease. HIV-1-infected women tend to have lower viral loads early in HIV-1 infection but progress faster to AIDS for a given viral load than men. Here we show substantial sex differences in the response of plasmacytoid dendritic cells (pDCs) to HIV-1. pDCs derived from women produce markedly more interferon-alpha (IFN-alpha) in response to HIV-1-encoded Toll-like receptor 7 (TLR7) ligands than pDCs derived from men, resulting in stronger secondary activation of CD8(+) T cells. In line with these in vitro studies, treatment-naive women chronically infected with HIV-1 had considerably higher levels of CD8(+) T cell activation than men after adjusting for viral load. These data show that sex differences in TLR-mediated activation of pDCs may account for higher immune activation in women compared to men at a given HIV-1 viral load and provide a mechanism by which the same level of viral replication might result in faster HIV-1 disease progression in women compared to men. Modulation of the TLR7 pathway in pDCs may therefore represent a new approach to reduce HIV-1-associated pathology.

Challenges Facing Young Investigators

IAVI Report : Newsletter on International AIDS Vaccine Research. Jan-Feb, 2009  |  Pubmed ID: 20214278

Alterations in Natural Killer Cell Receptor Profiles During HIV Type 1 Disease Progression Among Chronically Infected South African Adults

AIDS Research and Human Retroviruses. Apr, 2010  |  Pubmed ID: 20380481

Recent studies suggest that innate immune responses by natural killer (NK) cells play a significant role in restricting human immunodeficiency virus type-1 (HIV-1) pathogenesis. Our aim was to characterize changes in NK cells associated with HIV-1 clade C disease progression. Here we used multiparametric flow cytometry (LSRII) to quantify phenotype and function of NK cells in a cross-sectional analysis of cryopreserved blood samples from a cohort of 41 chronically HIV-1-infected, treatment-naive adult South Africans. These individuals ranged in disease severity from early (CD4 count >500) to advanced HIV-1 disease (CD4 count <50). We found that the frequency of NK cells expressing KIR2DL1, an inhibitory receptor, and/or KIR2DS1, an activating receptor, tended to decrease with increasing HIV-1 viral load. We also discovered a significant increase (p < 0.05) in overall NK cell degranulation with disease progression. We found that acutely activated NK cells (CD69(pos)) were deficient in NKp46 expression ex vivo. In conclusion, we observed that with viremia and advanced HIV-1 disease, activated NK cells lack NKp46 expression, and KIR2DS1(pos) and/ or KIR2DL1(pos) NK cells are reduced in frequency. These findings suggest that modulation of receptor expression on NK cells may play a role in HIV-1 pathogenesis, and provide new insights on immunological changes in advanced HIV-1 disease.

IL-10 Induces Aberrant Deletion of Dendritic Cells by Natural Killer Cells in the Context of HIV Infection

The Journal of Clinical Investigation. Jun, 2010  |  Pubmed ID: 20440075

Persistent levels of IL-10 play a central role in progressive immune dysfunction associated with chronic viral infections such as HIV, but the underlying mechanisms are poorly understood. Because IL-10 affects the phenotypic and functional properties of DCs, which are responsible for initiating adaptive immune responses, we investigated whether IL-10 induces changes in DC phenotype and function in the context of HIV infection. Here, we show that IL-10 treatment of immature and mature human DCs in culture induced contrasting phenotypic changes in these populations: immature DCs exhibited aberrant resistance to NK cell-mediated elimination, whereas mature DCs exhibited increased susceptibility to NKG2D-dependent NK elimination. Treatment of immature and mature DCs with HIV resulted in potent IL-10 secretion and the same phenotypic and functional changes observed in the IL-10-treated cells. Consistent with these in vitro data, LNs isolated from individuals infected with HIV exhibited aberrant accumulation of a partially "immature" DC population. Together, these data suggest that the progressive immune dysfunction observed in chronic viral infections might be caused in part by IL-10-induced reversal of DC susceptibility to NK cell-mediated elimination, resulting in the accumulation of poorly immunogenic DCs in LNs, the sites of adaptive immune response induction.

MHC Class I Chain-related Protein A Shedding in Chronic HIV-1 Infection is Associated with Profound NK Cell Dysfunction

Virology. Oct, 2010  |  Pubmed ID: 20667578

Natural killer (NK) cells play a critical role in host defense against viral infections. However chronic HIV-1 infection is associated with an accumulation of dysfunctional NK cells, that poorly control viral replication. The underlying mechanisms for this NK cell mediated dysfunction are not understood. Certain tumors evade NK cell mediated detection by dampening NK cell activity through the downregulation of NKG2D, via the release of soluble NKG2D-ligands, resulting in a potent suppression of NK cell function. Here we show that chronic HIV-1 infection is associated with a specific defect in NKG2D-mediated NK cell activation, due to reduced expression and transcription of NKG2D. Reduced NKG2D expression was associated with elevated levels of the soluble form of the NKG2D-ligand, MICA, in patient sera, likely released by HIV+CD4+ T cells. Thus, like tumors, HIV-1 may indirectly suppress NK cell recognition of HIV-1-infected CD4+ T cells by enhancing NKG2D-ligand secretion into the serum resulting in a profound impairment of NK cell function.

The Humoral Response to HIV-1: New Insights, Renewed Focus

The Journal of Infectious Diseases. Oct, 2010  |  Pubmed ID: 20846039

During the past 2 decades, significant advances in our understanding of the humoral immune response to human immunodeficiency virus type 1 (HIV-1) infection have been made, yet a tremendous amount of work lies ahead. Despite these advances, strategies to reliably induce antibodies that can control HIV-1 infection are still critically needed. However, recent advances in our understanding of the kinetics, specificity, and function of early humoral responses offer alternative new approaches to attain this goal. These results, along with the new broadly neutralizing antibody specificities, the role for other antibody functions, the increased understanding of HIV-1-induced changes to B cell biology, and results from the RV144 "Thai" trial showing potential modest sterilizing protection by nonneutralizing antibody responses, have renewed focus on the humoral system. In this review, recent advances in our understanding of the earliest humoral responses are discussed, highlighting presentations from the meeting on the Biology of Acute HIV Infection.

Determinants of Protection Among HIV‐exposed Seronegative Persons: an Overview

The Journal of Infectious Diseases. Nov, 2010  |  Pubmed ID: 20887220

Both clinical experience and a growing medical literature indicate that some persons who have been exposed to human immunodeficiency virus (HIV) infection remain uninfected. Although in some instances this may represent good fortune, cohorts of uninfected persons have been reported who are considered at high risk for infection. In these cohorts a variety of characteristics have been proposed as mediating protection, but to date only the 32–base pair deletion in the chemokine (C‐C motif) receptor 5 gene, which results in complete failure of cell surface expression of this coreceptor, has been associated with high‐level protection from HIV infection. With this in mind, there are probably many other factors that may individually or in combination provide some level of protection from acquisition of HIV infection. Because some of these factors are probably incompletely protective or inconsistently active, identifying them with confidence will be difficult. Nonetheless, clarifying the determinants of protection against HIV infection is a high priority that will require careful selection of high‐risk uninfected cohorts, who should undergo targeted studies of plausible mediators and broad screening for unexpected determinants of protection.

Comprehensive Analysis of Virus-specific T-cells Provides Clues for the Failure of Therapeutic Immunization with ALVAC-HIV Vaccine

AIDS (London, England). Jan, 2011  |  Pubmed ID: 21076273

HIV-specific T-cell-based vaccines have been extensively studied in both prevention and therapeutic settings, with most studies failing to show benefit, and some suggesting harm. We previously performed a multicenter, double-blind, placebo-controlled phase II clinical trial in which 65 antiretroviral-treated patients were randomized to receive an HIV-1 recombinant canarypox vaccine (vCP1452) or placebo, followed by analytical treatment interruption. Patients exposed to vaccine had higher levels of viral replication and more rapid time to treatment resumption.

Reduced Frequencies of NKp30+NKp46+, CD161+, and NKG2D+ NK Cells in Acute HCV Infection May Predict Viral Clearance

Journal of Hepatology. Aug, 2011  |  Pubmed ID: 21168454

While the majority of HCV-infected patients progress to chronic hepatitis, a small fraction of individuals are able to clear the virus. Resolution of infection occurs within the first few weeks to months of infection, suggesting that innate immune functions may be critical for early control. Epidemiologic data support a role for particular NK cell receptor bearing populations in this control, yet the mechanism by which NK cells respond to HCV early in infection is unknown.

A Robust, High-throughput Assay to Determine the Phagocytic Activity of Clinical Antibody Samples

Journal of Immunological Methods. Mar, 2011  |  Pubmed ID: 21192942

Phagocytosis can be induced via the engagement of Fcγ receptors by antibody-opsonized material. Furthermore, the efficiency of antibody-induced effector functions has been shown to be dramatically modulated by changes in antibody glycosylation. Because infection can modulate antibody glycans, which in turn modulate antibody functions, assays capable of determining the induction of effector functions rather than neutralization or titer provide a valuable opportunity to more fully characterize the quality of the adaptive immune response. Here we describe a robust and high-throughput flow cytometric assay to define the phagocytic activity of antigen-specific antibodies from clinical samples. This assay employs a monocytic cell line that expresses numerous Fc receptors: including inhibitory and activating, and high and low affinity receptors--allowing complex phenotypes to be studied. We demonstrate the adaptability of this high-throughput, flow-based assay to measure antigen-specific antibody-mediated phagocytosis against an array of viruses, including influenza, HIV, and dengue. The phagocytosis assay format further allows for simultaneous analysis of cytokine release, as well as determination of the role of specific Fcγ-receptor subtypes, making it a highly useful system for parsing differences in the ability of clinical and vaccine induced antibody samples to recruit this critical effector function.

Expansion of 2B4+ Natural Killer (NK) Cells and Decrease in NKp46+ NK Cells in Response to Influenza

Immunology. Apr, 2011  |  Pubmed ID: 21214542

Several studies have highlighted the importance of murine natural killer (NK) cells in the control of influenza virus infection, notably through the natural cytotoxicity receptor NKp46. However, little is known about the involvement of NK cells in human influenza infection. Here, we show that upon in vitro exposure to influenza, NKp46 expression on NK cells decreases, whereas expression of 2B4, an activating receptor that can enhance natural cytotoxicity in synergy with NKp46, is up-regulated. Consistent with these observations, NKp46(dull) and 2B4(bright) NK cells had a higher functional activity in response to influenza than NK cells expressing high levels of NKp46 or low levels of 2B4, respectively. Importantly, we assessed whether the expression of these receptors was also modified in vivo in response to influenza antigens and showed that an increase in 2B4-expressing NK cells and a decrease in NKp46(+) NK cells occurred following intramuscular influenza vaccination. Altogether, our results further suggest that NKp46 may play an important role in the innate immune response to human influenza and reveal that exposure to influenza antigens is associated with a previously unrecognized increase in 2B4 expression that can impact NK cell activity against the virus.

Characteristics of the Earliest Cross-neutralizing Antibody Response to HIV-1

PLoS Pathogens. 2011  |  Pubmed ID: 21249232

Recent cross-sectional analyses of HIV-1+ plasmas have indicated that broadly cross-reactive neutralizing antibody responses are developed by 10%-30% of HIV-1+ subjects. The timing of the initial development of such anti-viral responses is unknown. It is also unknown whether the emergence of these responses coincides with the appearance of antibody specificities to a single or multiple regions of the viral envelope glycoprotein (Env). Here we analyzed the cross-neutralizing antibody responses in longitudinal plasmas collected soon after and up to seven years after HIV-1 infection. We find that anti-HIV-1 cross-neutralizing antibody responses first become evident on average at 2.5 years and, in rare cases, as early as 1 year following infection. If cross-neutralizing antibody responses do not develop during the first 2-3 years of infection, they most likely will not do so subsequently. Our results indicate a potential link between the development of cross-neutralizing antibody responses and specific activation markers on T cells, and with plasma viremia levels. The earliest cross-neutralizing antibody response targets a limited number of Env regions, primarily the CD4-binding site and epitopes that are not present on monomeric Env, but on the virion-associated trimeric Env form. In contrast, the neutralizing activities of plasmas from subjects that did not develop cross-neutralizing antibody responses target epitopes on monomeric gp120 other than the CD4-BS. Our study provides information that is not only relevant to better understanding the interaction of the human immune system with HIV but may guide the development of effective immunization protocols. Since antibodies to complex epitopes that are present on the virion-associated envelope spike appear to be key components of earliest cross-neutralizing activities of HIV-1+ plasmas, then emphasis should be made to elicit similar antibodies by vaccination.

Natural Killer Cells in Spontaneous Control of HIV Infection

Current Opinion in HIV and AIDS. May, 2011  |  Pubmed ID: 21399495

Over the last decade our understanding of the role of natural killer cells in HIV infection has changed dramatically due to strong epidemiological, phenotypic, and functional data providing evidence for their involvement in antiviral control. Here we review the current literature on natural killer cells in the control of HIV infection, with a specific focus on their role in HIV controllers, individuals that spontaneously control HIV replication in the absence of antiretroviral therapy.

Mutiny or Scrutiny: NK Cell Modulation of DC Function in HIV-1 Infection

Trends in Immunology. May, 2011  |  Pubmed ID: 21411368

Accumulating data suggest that natural killer (NK) cells are involved not only in the innate antiviral response following infection, but also in shaping the quality of the adaptive immune response by modulating the functional properties of myeloid dendritic cells (DC) during the acute immune response to infection. In this role, NK cells ensure that only fully mature, immunogenic DCs gain access to inductive sites, where they might prime effective antiviral adaptive immune responses. However, increasing evidence now suggests that several aspects of this cross-talk between NK cells and DCs are compromised during HIV infection, potentially contributing to immune dysfunction.

KIR Polymorphisms Modulate Peptide-dependent Binding to an MHC Class I Ligand with a Bw6 Motif

PLoS Pathogens. Mar, 2011  |  Pubmed ID: 21423672

Molecular interactions between killer immunoglobulin-like receptors (KIRs) and their MHC class I ligands play a central role in the regulation of natural killer (NK) cell responses to viral pathogens and tumors. Here we identify Mamu-A1*00201 (Mamu-A*02), a common MHC class I molecule in the rhesus macaque with a canonical Bw6 motif, as a ligand for Mamu-KIR3DL05. Mamu-A1*00201 tetramers folded with certain SIV peptides, but not others, directly stained primary NK cells and Jurkat cells expressing multiple allotypes of Mamu-KIR3DL05. Differences in binding avidity were associated with polymorphisms in the D0 and D1 domains of Mamu-KIR3DL05, whereas differences in peptide-selectivity mapped to the D1 domain. The reciprocal exchange of the third predicted MHC class I-contact loop of the D1 domain switched the specificity of two Mamu-KIR3DL05 allotypes for different Mamu-A1*00201-peptide complexes. Consistent with the function of an inhibitory KIR, incubation of lymphocytes from Mamu-KIR3DL05(+) macaques with target cells expressing Mamu-A1*00201 suppressed the degranulation of tetramer-positive NK cells. These observations reveal a previously unappreciated role for D1 polymorphisms in determining the selectivity of KIRs for MHC class I-bound peptides, and identify the first functional KIR-MHC class I interaction in the rhesus macaque. The modulation of KIR-MHC class I interactions by viral peptides has important implications to pathogenesis, since it suggests that the immunodeficiency viruses, and potentially other types of viruses and tumors, may acquire changes in epitopes that increase the affinity of certain MHC class I ligands for inhibitory KIRs to prevent the activation of specific NK cell subsets.

Decreased Fc Receptor Expression on Innate Immune Cells is Associated with Impaired Antibody-mediated Cellular Phagocytic Activity in Chronically HIV-1 Infected Individuals

Virology. Jul, 2011  |  Pubmed ID: 21565376

In addition to neutralization, antibodies mediate other antiviral activities including antibody-dependent cellular phagocytosis (ADCP), antibody-dependent cellular cytotoxicity (ADCC), as well as complement deposition. While it is established that progressive HIV infection is associated with reduced ADCC and ADCP, the underlying mechanism for this loss of function is unknown. Here we report considerable changes in FcR expression over the course of HIV infection on both mDCs and monocytes, including elevated FcγRI expression in acute HIV infection and reduced expression of FcγRII and FcγRIIIa in chronic HIV infection. Furthermore, selective blockade of FcγRII alone was associated with a loss in ADCP activity, suggesting that FcγRII plays a central role in modulating ADCP. Overall, HIV infection is associated with a number of changes in FcR expression on phagocytic cells that are associated with changes in their ability to respond to antibody-opsonized targets, potentially contributing to a failure in viral clearance in progressive HIV-1 infection.

Early Viral Replication in Lymph Nodes Provides HIV with a Means by Which to Escape NK-cell-mediated Control

European Journal of Immunology. Sep, 2011  |  Pubmed ID: 21630248

Acute HIV infection is marked by dramatic viral replication associated with preferential replication within secondary lymphoid tissues, such as lymph nodes (LNs), that is rapidly but incompletely contained to a viral setpoint. Accumulating evidence supports a role for natural killer (NK) cells in the early control of HIV infection; however, little is known about the location of their antiviral control. Given that HIV replicates profusely in LNs during early infection, we sought to define whether changes occurred in the NK cell infiltrate within these sites during the first year of HIV infection. Surprisingly, NK cell numbers and distribution were unaltered during early HIV infection. LN NK cells expressed decreased inhibitory receptors, were more highly activated, and expressed elevated TRAIL, potentially conferring a superior capacity for NK cells to become activated and control infection. Most noticeably, KIR(+) NK cells were rarely detected in the LN during HIV infection, associated with diminished migratory capacity in the setting of reduced expression of CX3CR1 and CXCR1. Thus, incomplete control of HIV viral replication during early disease may be due to the inefficient recruitment of KIR(+) NK cells to this vulnerable site, providing HIV a niche where it can replicate unabated by early NK-cell-mediated innate pressure.

HIV-1 Adaptation to NK-cell-mediated Immune Pressure

Nature. Aug, 2011  |  Pubmed ID: 21814282

Natural killer (NK) cells have an important role in the control of viral infections, recognizing virally infected cells through a variety of activating and inhibitory receptors. Epidemiological and functional studies have recently suggested that NK cells can also contribute to the control of HIV-1 infection through recognition of virally infected cells by both activating and inhibitory killer immunoglobulin-like receptors (KIRs). However, it remains unknown whether NK cells can directly mediate antiviral immune pressure in vivo in humans. Here we describe KIR-associated amino-acid polymorphisms in the HIV-1 sequence of chronically infected individuals, on a population level. We show that these KIR-associated HIV-1 sequence polymorphisms can enhance the binding of inhibitory KIRs to HIV-1-infected CD4(+) T cells, and reduce the antiviral activity of KIR-positive NK cells. These data demonstrate that KIR-positive NK cells can place immunological pressure on HIV-1, and that the virus can evade such NK-cell-mediated immune pressure by selecting for sequence polymorphisms, as was previously described for virus-specific T cells and neutralizing antibodies. NK cells might therefore have a previously underappreciated role in contributing to viral evolution.

KIR/HLA: Genetic Clues for a Role of NK Cells in the Control of HIV

Advances in Experimental Medicine and Biology. 2011  |  Pubmed ID: 21842362

Early events following HIV infections determine the course of disease progression. Mounting evidence suggests that antiviral immune responses induced soon after infection, prior to the induction of adaptive immune responses, are key to early control of viral infection. Among the early innate immune effector cells, natural killer (NK) cells represent a unique subset of lymphoctyes that do not express an antigen specific receptor. Rather, these cells integrate signals from an arsenal of non-specific inhibitory and activating receptors that are expressed on their cell surface. As such, these cells are classified as cells of the innate immune system, and they are able to lyse certain tumor targets and infected cells without the need for prior antigen sensitization. Over the past decade, accumulating evidence suggests that these innate lymphocytes may not be as innate as once believed, but that individual NK cell clones may show some target cell specificity, and play a critical early role following infection with HIV.

Copy Number Variation of KIR Genes Influences HIV-1 Control

PLoS Biology. Nov, 2011  |  Pubmed ID: 22140359

A genome-wide screen for large structural variants showed that a copy number variant (CNV) in the region encoding killer cell immunoglobulin-like receptors (KIR) associates with HIV-1 control as measured by plasma viral load at set point in individuals of European ancestry. This CNV encompasses the KIR3DL1-KIR3DS1 locus, encoding receptors that interact with specific HLA-Bw4 molecules to regulate the activation of lymphocyte subsets including natural killer (NK) cells. We quantified the number of copies of KIR3DS1 and KIR3DL1 in a large HIV-1 positive cohort, and showed that an increase in KIR3DS1 count associates with a lower viral set point if its putative ligand is present (p = 0.00028), as does an increase in KIR3DL1 count in the presence of KIR3DS1 and appropriate ligands for both receptors (p = 0.0015). We further provide functional data that demonstrate that NK cells from individuals with multiple copies of KIR3DL1, in the presence of KIR3DS1 and the appropriate ligands, inhibit HIV-1 replication more robustly, and associated with a significant expansion in the frequency of KIR3DS1+, but not KIR3DL1+, NK cells in their peripheral blood. Our results suggest that the relative amounts of these activating and inhibitory KIR play a role in regulating the peripheral expansion of highly antiviral KIR3DS1+ NK cells, which may determine differences in HIV-1 control following infection.

Emerging Concepts on the Role of Innate Immunity in the Prevention and Control of HIV Infection

Annual Review of Medicine. Feb, 2012  |  Pubmed ID: 22077718

While neutralizing antibodies can provide sterilizing protection from HIV infection via their variable domains, the antibody constant domain provides a functional link between innate and adaptive immunity and offers a means to harness the potent antiviral properties of a wide spectrum of innate immune effector cells. There has been a growing appreciation of the role of these effector mechanisms across fields from cancer immunotherapy to autoimmunity and infectious disease, as well as speculation that this mechanism may be responsible for the protection observed in the RV144 HIV vaccine trial. This review summarizes these extraneutralizing humoral immune activities, progress in defining the importance of these effector mechanisms during progression in HIV infection, and the potential impact that such vaccine-induced immune responses may have on protection from infection.