Antibody-dependent Cellular Cytotoxicity Antibodies Research Articles

Cross-Reactive Influenza-Specific Antibody-Dependent Cellular Cytotoxicity Antibodies in the Absence of Neutralizing Antibodies

A better understanding of immunity to influenza virus is needed to generate cross-protective vaccines. Engagement of Ab-dependent cellular cytotoxicity (ADCC) Abs by NK cells leads to killing of virus-infected cells and secretion of antiviral cytokines and chemokines. ADCC Abs may target more conserved influenza virus Ags compared with neutralizing Abs. There has been minimal interest in influenza-specific ADCC in recent decades. In this study, we developed novel assays to assess the specificity and function of influenza-specific ADCC Abs. We found that healthy influenza-seropositive young adults without detectable neutralizing Abs to the hemagglutinin of the 1968 H3N2 influenza strain (A/Aichi/2/1968) almost always had ADCC Abs that triggered NK cell activation and in vitro elimination of influenza-infected human blood and respiratory epithelial cells. Furthermore, we detected ADCC in the absence of neutralization to both the recent H1N1 pandemic strain (A/California/04/2009) as well as the avian H5N1 influenza hemagglutinin (A/Anhui/01/2005). We conclude that there is a remarkable degree of cross-reactivity of influenza-specific ADCC Abs in seropositive humans. Targeting cross-reactive influenza-specific ADCC epitopes by vaccination could lead to improved influenza vaccines.

Influence of Cytokines on HIV-Specific Antibody-Dependent Cellular Cytotoxicity Activation Profile of Natural Killer Cells

There is growing interest in HIV-specific antibody-dependent cellular cytotoxicity (ADCC) as an effective immune response to prevent or control HIV infection. ADCC relies on innate immune effector cells, particularly NK cells, to mediate control of virus-infected cells. The activation of NK cells (i.e., expression of cytokines and/or degranulation) by ADCC antibodies in serum is likely subject to the influence of other factors that are also present. We observed that the HIV-specific ADCC antibodies, within serum samples from a panel of HIV-infected individuals induced divergent activation profiles of NK cells from the same donor. Some serum samples primarily induced NK cell cytokine expression (i.e., IFNγ), some primarily initiated NK cell expression of a degranulation marker (CD107a) and others initiated a similar magnitude of responses across both effector functions. We therefore evaluated a number of HIV-relevant soluble factors for their influence on the activation of NK cells by HIV-specific ADCC antibodies. Key findings were that the cytokines IL-15 and IL-10 consistently enhanced the ability of NK cells to respond to HIV-specific ADCC antibodies. Furthermore, IL-15 was demonstrated to potently activate “educated” KIR3DL1+ NK cells from individuals carrying its HLA-Bw4 ligand. The cytokine was also demonstrated to activate “uneducated” KIR3DL1+ NK cells from HLA-Bw6 homozygotes, but to a lesser extent. Our results show that cytokines influence the ability of NK cells to respond to ADCC antibodies in vitro. Manipulating the immunological environment to enhance the potency of NK cell-mediated HIV-specific ADCC effector functions could be a promising immunotherapy or vaccine strategy.

Activation of NK Cells by ADCC Antibodies and HIV Disease Progression

Antibody-dependent cellular cytotoxicity (ADCC) is of considerable interest as an immune response that may facilitate the control of HIV infection. We studied ADCC responses prospectively in a cohort of 79 HIV-positive subjects followed up for a mean of 2.3 years without antiretroviral therapy. We used a novel assay of the ability of ADCC to activate natural killer (NK) cells, either from the same HIV-positive subject or from a healthy blood donor. We found that ADCC responses to either gp140 Env protein or HIV peptide pools were common in HIV-positive subjects when NK cells from the HIV-positive subject were used but did not correlate with markers of HIV disease progression. In contrast, ADCC responses to whole gp140 Env protein were strongly associated with a slower decline in CD4 T-cell loss when healthy donor NK cells were used as effectors. Our data had implications for induction of the most effective ADCC responses by HIV vaccines.

NK Cell Function and Antibodies Mediating ADCC in HIV-1-Infected Viremic and Controller Patients

Natural killer (NK) cells have been suggested to play a protective role in HIV disease progression. One potent effector mechanism of NK cells is antibody-dependent cellular cytotoxicity (ADCC) mediated by antiviral antibodies binding to the FcγRIIIa receptor (CD16) on NK cells. We investigated NK cell-mediated ADCC function and the presence of ADCC antibodies in plasma from 20 HIV-1-infected patients and 10 healthy donors. The HIV-positive patients were divided into two groups: six who controlled viremia for at least 8 y without treatment (controllers), and 14 who were persistently viremic and not currently on treatment. Plasma from both patient groups induced NK cell IFN-γ expression and degranulation in response to HIV-1 envelope (Env) gp140-protein-coated cells. Patient antibodies mediating ADCC were largely directed towards the Env V3 loop, as identified by a gp140 protein lacking the V3 loop. Interestingly, in two controllers ADCC-mediating antibodies were more broadly directed to other parts of Env. A high viral load in patients correlated with decreased ADCC-mediated cytolysis of gp140-protein-coated target cells. NK cells from both infected patients and healthy donors degranulated efficiently in the presence of antibody-coated HIV-1-infected Jurkat cells. In conclusion, the character of ADCC-mediating antibodies differed in some controllers compared to viremic patients. NK cell ADCC activity is not compromised in HIV-infected patients.

Immune escape from HIV-specific antibody-dependent cellular cytotoxicity (ADCC) pressure

Effective immunity to HIV is poorly understood. In particular, a role for antibody-dependent cellular cytotoxicity (ADCC) in controlling HIV is controversial. We hypothesized that significant pressure from HIV-specific ADCC would result in immune-escape variants. A series of ADCC epitopes in HIV-infected subjects to specific consensus strain HIV peptides were mapped using a flow cytometric assay for natural killer cell activation. We then compared the ADCC responses to the same peptide epitope derived from the concurrent HIV sequence(s) expressed in circulating virus. In 9 of 13 epitopes studied, ADCC antibodies were unable to recognize the concurrent HIV sequence. Our studies suggest ADCC responses apply significant immune pressure on the virus. This result has implications for the induction of ADCC responses by HIV vaccines.

Activation of NK Cells by ADCC Responses During Early HIV Infection

Partial control of HIV occurs during acute infection, although the mechanisms responsible are poorly understood. We studied the ability of antibody-dependent cellular cytotoxicity (ADCC) antibodies in serum to activate natural killer (NK) cells in longitudinal samples from 8 subjects with well-defined early HIV infection who controlled viremia to low levels. NK cell activation by ADCC antibodies to gp140 Env proteins was detected in half of the subjects at the first time point studied, a mean of 111 d after the estimated time of infection. In contrast, ADCC-mediated NK cell activation in response to linear HIV peptides evolved more slowly, over the first 2 y of infection. Our studies suggest that HIV-specific ADCC responses to conformational epitopes occur early during acute HIV infection, and broaden to include linear epitopes over time. These findings have implications for the immune control of HIV.

Designing Immunity to Hiv: Manipulating Antibody-Dependent Cellular Cytotoxicity Antibodies

The failure of HIV vaccine concepts based upon either simple antibody or T-cell immunity means that newer concepts in immunity to HIV require urgent investigation. Antibody-dependent cellular cytotoxicity (ADCC) responses, utilizing the arms of humoral and innate immunity, have been studied for many years, but their role in controlling or preventing HIV-1 remains controversial. Newer technologies can now be applied to study and map ADCC responses. This permits experiments to purify and isolate HIV-specific ADCC antibodies and directly assess their role in preventing simian–HIV infections in macaques. Analogous to complexities in the quality and specificity of T-cell and neutralizing antibody immunity to HIV, it is likely that some ADCC antibodies will be more efficient than others in controlling HIV infection and limiting viral escape. Rationally defining broadly reactive ADCC antibodies with potent in vivo activity should allow the selection of the most appropriate ADCC-inducing vaccine antigens. This pathway towards manipulating ADCC antibodies, which control HIV infection, will ultimately improve our understanding of ADCC against HIV infection and potentially yield new HIV vaccine candidates.

The Utility of ADCC Responses in HIV Infection

Simple antibodies or vector-induced T cell immunity are unable to provide broad immunity to HIV. Although broadly reactive neutralising antibodies are a goal of vaccination, this remains elusive. There is growing evidence that HIV-specific antibodies that mediate their activity via the Fc-receptor, such as antibody dependent cellular cytotoxicity (ADCC), have an important role in controlling HIV infection. Newer assays are being developed that enable HIV-specific ADCC responses to be finely mapped. In turn, this should allow a more definitive analysis of the effectiveness of HIV-specific ADCC antibodies. However, progressive dysfunction of effector cells that mediate ADCC responses, such as NK cells, combined with immune escape variants that emerge from effective ADCC responses, likely undermine the utility of ADCC responses during chronic HIV infection. Nonetheless the utility of ADCC responses in preventing HIV infection requires urgent consideration.

Enhanced binding affinity for FcγRIIIa of fucose-negative antibody is sufficient to induce maximal antibody-dependent cellular cytotoxicity

Antibody-dependent cellular cytotoxicity (ADCC) is considered to be an important therapeutic function for clinical efficacy of monoclonal antibodies. Recent studies have revealed two methods to increase binding affinity for FcγRIIIa and enhance ADCC more efficiently for antibodies: (i) fucose removal from antibody N-linked complex oligosaccharides and (ii) amino acid mutations in the antibody Fc region. In this study, we compare the biological activities of the methods of generating high ADCC antibodies. We used a fucose-negative antibody and two antibodies with sets of mutations, demonstrated previously to optimally enhance ADCC using the chimeric anti-CD20 antibody, rituximab, as the model. Both amino acid mutant antibodies showed a significantly higher affinity for recombinant FcγRIIIa than fucose-negative antibody when compared using biosensor analysis. The removal of fucose from the antibodies bearing amino acid mutations exhibited a further enhancement of binding to recombinant FcγRIIIa and significantly increased binding to natural killer (NK) cells. Despite the differences manifested in binding for the FcγR, ADCCs were indistinguishable between methods and even when the methods were combined. These results indicate that the affinity of binding to FcγRIIIa does not predict ADCC beyond a certain threshold and that each method alone is sufficient to induce maximal ADCC of the antibody.

The role of infant immune responses and genetic factors in preventing HIV-1 acquisition and disease progression.

Mother-to-child HIV-1 transmission accounts for more than 700 000 new paediatric HIV-1 infections in developing countries each year [1]. This comprises less than one-third of the infants born to human immunodeficiency virus type 1 (HIV-1) infected mothers, the majority of whom remain uninfected despite recurrent risk for contact with the virus in utero, during delivery and through breastfeeding. A comprehensive approach to studying infant immunity against HIV-1 may provide insight into the determinants of HIV-1 acquisition, promote an understanding of resistance to infection in the setting of repeated exposure to the virus and contribute to the development of therapeutic interventions or vaccines against HIV-1 transmission. Several unique features of mother-to-child HIV-1 transmission provide advantages in determining correlates of HIV-1 acquisition and viral immunity when compared to sexual HIV-1 transmission models. Both HIV-1 infected mothers and their exposed infants can be evaluated for viral and immunological factors associated with transmission. HIV-1 exposure can be characterized by quantifying maternal HIV-1 viral load in plasma, breast milk and genital tract secretions, and infant immune responses can be defined simultaneously or near the time of exposure. Timing of transmission can be estimated using HIV-1 polymerase chain reaction (PCR) at birth and at regular intervals after exposure during delivery and breastfeeding. Vertical HIV-1 transmission risk is also higher than sexual transmission risk. Per sexual act, it is estimated that the risk of heterosexual transmission is approximately 0·1% in an antiretroviral naive population [2]. The risk of HIV-1 acquisition during delivery ranges from 10 to 20%, more than 100-fold higher than heterosexual transmission rates. Disparities between heterosexual and vertical HIV-1 transmission rates persist in the setting of antiretroviral therapy. This enables mother–child transmission studies to provide robust epidemiological data regarding specific immune mechanisms and combinations of immune responses that may constitute protective immunity against HIV-1. This review examines the spectrum of innate, humoral and cellular immune responses and genetic factors that have been studied in infants who are HIV-1 infected or HIV-1 exposed and uninfected (Fig. 1). Fig. 1 Immune responses and genetic factors associated with mother-to-child HIV-1 transmission and paediatric HIV-1 disease progression. *May be maternally acquired in utero or via breast milk. †Alloimmunity is dependent on degree of maternal–infant ... INNATE IMMUNITY Innate immune responses are generated rapidly and are important in preventing and containing infections with a variety of viral pathogens. Broad innate immunity may also be capable of protecting against immune-escape viruses generated by more narrow adaptive immune responses. In HIV-1 transmission and disease progression, relevant innate mechanisms of immunity include the activity of natural killer (NK) cells and antiviral proteins such as the CC chemokines, CD8+ antiviral factor (CAF) and secretory leucocyte protease inhibitor (SLPI). Natural killer (NK) cell activity Natural killer (NK) cells induce inflammation and lyse infected cells without prior sensitization and in a non-HLA restricted manner. NK cells from HIV-1 infected individuals release the CC chemokines MIP-1α, MIP-1β and RANTES, three factors that have been shown to inhibit HIV-1 independently in vitro by blocking the CCR5 HIV-1 coreceptor [3,4]. NK cells also act by lysing HIV-1 infected cells via antibody-dependent cellular cytotoxicity (ADCC). This is initiated by binding of NK cell Fc receptors (CD16) to target cells coated with HIV-specific antibodies of the subclass IgG1 [5–7]. HIV-specific ADCC antibodies are directed against the viral envelope glycoproteins gp120 and gp41 and are distinct from virus-neutralizing antibodies [8]. There is conflicting evidence regarding the role of NK cells in containing HIV-1 in chronically infected children and in preventing vertical HIV-1 transmission. Several studies have evaluated HIV-specific ADCC antibody titres in sera of infants born to HIV-1 infected mothers and found that these antibodies are transferred efficiently across the placenta from mother to fetus [9,10]. However, there was no significant correlation between antibody titres at birth and either HIV-1 disease progression during 2 years of follow-up or mother-to-child HIV-1 transmission [9,10]. Active production of HIV-specific ADCC antibodies was observed in the majority of HIV-infected infants only after 12 months of age [10] and effector cells from HIV-1 infected children appear unable to generate NK cell-mediated cytotoxicity [11]. Thus, an immature immune system may account for the absence of ADCC-mediated NK protection against HIV-1 infection in neonates and young infants, despite adequate levels of passively transferred ADCC antibodies. This may contribute to rapid HIV-1 progression in children infected with HIV-1 early in life [10,11].

Evidence for a correlation between antibody-dependent cellular cytotoxicity-mediating anti-HIV-1 antibodies and prognostic predictors of HIV infection.

Using our gp120/41-expressing, NK cell activity-resistant CEM.NKR cell clones as targets in HIV-1-specific antibody-dependent cellular cytotoxicity (ADCC) assays, we demonstrate here that the serum titers of anti-HIV-1 ADCC antibodies bear a significant (P < 0.05) positive correlation with the peripheral blood CD4+ T cell counts and a negative one with the number of copies of HIV-1 RNA in the plasma of HIV-infected individuals. These findings underscore the importance of these antibodies as a protective immune parameter in these infections.

Delayed generation of antibodies mediating human immunodeficiency virus type 1-specific antibody-dependent cellular cytotoxicity in vertically infected infants. WITS Study Group. Women and Infants Transmission Study.

Human immunodeficiency virus type 1 (HIV-1)-specific antibody-dependent cellular cytotoxicity (ADCC) antibody titers were serially measured from birth to 24 months in the plasma of 14 intrapartum-infected and 10 uninfected infants born to HIV-1-infected women. The mean ADCC antibody titers measured at birth in infected and uninfected infants were similar (10(-3.9) and 10(-4.0), respectively), suggesting that ADCC antibodies did not protect infants from the intrapartum transmission of HIV-1. In infected infants, ADCC titers at birth did not predict subsequent clinical disease course. The active production of HIV-1-specific ADCC antibodies was detected in most infected infants only after 12 months of age, well after the loss of passively acquired maternal ADCC antibody. The delayed production of ADCC antibodies in infancy may account, in part, for the less efficient control of viral replication and more rapid disease progression following vertical infection compared with that in adults.

Association between Anti-Human Immunodeficiency Virus Type 1 (HIV-I) Antibody-Dependent Cellular Cytotoxicity Antibody Titers at Birth and Vertical Transmission of HIV-I

Because vertical transmission of human immunodeficiency virus type 1 (HIV-1) from mother to infant occurs in only 15%-35% of possible opportunities, natural immune defenses of the mother, fetus, or neonate may be protective against infection. The relation between antibody-dependent cellular cytotoxicity (ADCC) antibodies and HIV-1 infection was explored in 78 neonates born to HIV-infected women. More than 90% of sera had measurable ADCC titers against HIV-1IIIB. Infant titers were closely correlated with maternal titers but were independent of total IgG and total antibody reactive to the same strain in whole virus ELISA. At birth, mean ADCC antibody levels of infants or their mothers were the same for infants who were infected and those who ultimately seroreverted and remained healthy. ADCC antibody titers against HIV-1SF2 were weakly correlated with anti-HIV-1IIIB titers and did not predict protection from HIV-1 infection. High levels of anti-HIV-1 ADCC antibody at birth are not protective against vertical transmission of HIV-1.

HIV-1 gp120/160 expressing transfected cell clones to evaluate the Antibody-Dependent Cellular Cytotoxicity (ADCC) during the course of HIV-1 infection

Transfection by electroporation of the CEM.NK R cell line with a plasmid containing the H1VNL43 gp160 gene resulted in the establishment of HIV-1 gp120/160 expressing CEM.NK R cell clones. The cell-surface expression of the recombinant viral envelope is stable and does not lead to syncytium formation among a substantial number of cells expressing envelope glycoprotein, suggesting that these cells are suitable as targets to monitor HIV-specific ADCC activities with the stage or the progression of HIV-1 disease. By using these cells, the ability of sera from HIV-1 seropositive individuals to mediate ADCC against HIV-1 gp120/160 transfected cells in an antigen-specific manner was established. Approximately 63% of the HIV-infected individuals representing all stages of infection have virus-specific ADCC antibodies. Moreover, sera from healthy seropositive (CDC class II) subjects mediated substantially higher levels of ADCC activity (25.7 ± 11.5%) than did sera from individuals in CDC class III (10.3 ± 8.9%) or IVC1 (6.4 ± 8.1%). The mean ADCC activity for the sera from the seronegative volunteers was 2 ± 1.3%. The correlation between the ADCC level and CD4 cell depletion remains uncertain. Therefore, the established transfected cell line may be used to probe the role of gp120/160-specific ADCC activity in the development of AIDS and may also prove useful in screening human and murine monoclonal antibodies with potential ADCC activity. Such monoclonals may be useful for future immunotherapeutic agents in conjunction with antiviral chemotherapy.

Role of Antibody-Dependent Cellular Cytotoxicity and Lymphokine-Activated Killer Cells in AIDS and Related Diseases

This overview summarizes current knowledge on the overall efficacy and potential contribution of antibody-dependent cellular cytotoxicity (ADCC) and lymphokine-activated killer cell (LAK) activities in evoking non-major histocompatibility complex (non-MHC) cytolytic responses to human immunodeficiency virus-1 (HIV-1)-infected targets. High titers of ADCC antibodies to the HIV-1 virion are present in HIV-1-seropositive populations at all stages of disease. These antibodies are broadly reactive with a large number of HIV-1 strains and are predominantly directed against envelope determinants spanning both gp120 and gp41. However, the relative ability of natural killer (NK) effectors, derived from HIV-seropositive individuals, to evoke ADCC responses becomes increasingly impaired with disease progression. HIV-1-seropositive individuals also show marked decreases in both production of and responsiveness to interleukin-2 (IL-2). HIV-1-seropositive individuals generally have the ability to generate ex vivo propagated LAK cells; however, these cytolytic effectors are less effective than their counterparts derived from healthy controls. Increased understanding and control of non-MHC-restricted cytotoxic-responses to HIV, and their induction by lymphokines, may lead to improved treatment strategies for the management of AIDS and related diseases.

Biological significance of the antibody response to HIV antigens expressed on the cell surface.

Human antibodies to HIV antigens expressed on the surface of infected cells may inhibit cell fusion with uninfected CD 4-positive cells and mediate killing of the infected cells by effector cells bearing the Fc receptor. Sequential sera from ten HIV-antibody seroconverted men, of which five progressed to ARC or AIDS (CDC stage IV) during the follow-up period of two years, were tested for the ability to inhibit CD 4-dependent cell fusion, (CFI) and to mediate antibody-dependent cellular cytotoxicity (ADCC). Nine patients developed HIV-specific ADCC and seven CFI-antibodies using the HIV strain HTLV-IIIB as target antigen. These antibodies appeared approximately at the same time 2-12 months after primary infection, defined as antibody seroconversion or antigenaemia. ADCC antibodies were detectable at higher titers as compared to CFI-antibodies. All sera of asymptomatic individuals (CDC stage II and III) were CFI antibody positive and had a higher mean ADCC titer as compared to sera from patients progressing to AIDS or ARC. ADCC and CFI antibodies coincided in some cases in the complete absence of core antibodies. Because the relationship between ADCC and CFI was not exclusive it is concluded that distinct domains of the HIV envelope induce natural antibodies mediating ADCC and CFI.