ADCC develops over time during persistent infection with live-attenuated SIV and is associated with complete protection against SIV(mac)251 challenge

Application of area scaling analysis to identify natural killer cell and monocyte involvement in the GranToxiLux antibody dependent cell-mediated cytotoxicity assay

Several different assay methodologies have been described for the evaluation of HIV or SIV-specific antibody-dependent cell-mediated cytotoxicity (ADCC). Commonly used assays measure ADCC by evaluating effector cell functions, or by detecting elimination of target cells. Signaling through Fc receptors, cellular activation, cytotoxic granule exocytosis, or accumulation of cytolytic and immune signaling factors have been used to evaluate ADCC at the level of the effector cells. Alternatively, assays that measure killing or loss of target cells provide a direct assessment of the specific killing activity of antibodies capable of ADCC. Thus, each of these two distinct types of assays provides information on only one of the critical components of an ADCC event; either the effector cells involved, or the resulting effect on the target cell. We have developed a simple modification of our previously described high-throughput ADCC GranToxiLux (GTL) assay that uses area scaling analysis (ASA) to facilitate simultaneous quantification of ADCC activity at the target cell level, and assessment of the contribution of natural killer cells and monocytes to the total observed ADCC activity when whole human peripheral blood mononuclear cells are used as a source of effector cells. The modified analysis method requires no additional reagents and can, therefore, be easily included in prospective studies. Moreover, ASA can also often be applied to pre-existing ADCC-GTL datasets. Thus, incorporation of ASA to the ADCC-GTL assay provides an ancillary assessment of the ability of natural and vaccine-induced antibodies to recruit natural killer cells as well as monocytes against HIV or SIV; or to any other field of research for which this assay is applied. © 2018 The Authors. Cytometry Part A published by Wiley Periodicals, Inc. on behalf of ISAC.

Antibody Functional Assays as Measures of Fc Receptor-Mediated Immunity to HIV - New Technologies and their Impact on the HIV Vaccine Field

Background:

There is now intense interest in the role of HIV-specific antibodies and the engagement of FcγR functions in the control and prevention of HIV infection. The analyses of the RV144 vaccine trial, natural progression cohorts, and macaque models all point to a role for Fc-dependent effector functions, such as cytotoxicity (ADCC) or phagocytosis (ADCP), in the control of HIV. However, reliable assays that can be reproducibly used across different laboratories to measure Fc-dependent functions, such as antibody dependent cellular cytotoxicity (ADCC) are limited.

Method:

This brief review highlights the importance of Fc properties for immunity to HIV, particular-ly via FcγR diversity and function. We discuss assays used to study FcR mediated functions of HIV-specific Ab, including our recently developed novel cell-free ELISA using homo-dimeric FcγR ecto-domains to detect functionally relevant viral antigen-specific antibodies.

Results:

The binding of these dimeric FcγR ectodomains, to closely spaced pairs of IgG Fc, mimics the engagement and cross-linking of Fc receptors by IgG opsonized virions or infected cells as the es-sential prerequisite to the induction of Ab-dependent effector functions. The dimeric FcγR ELISA reli-ably correlates with ADCC in patient responses to influenza. The assay is amenable to high throughput and could be standardized across laboratories.

Conclusion:

We propose the assay has broader implications for the evaluation of the quality of anti-body responses in viral infections and for the rapid evaluation of responses in vaccine development campaigns for HIV and other viral infections.

Coupling of Single Molecule, Long Read Sequencing with IMGT/HighV-QUEST Analysis Expedites Identification of SIV gp140-Specific Antibodies from scFv Phage Display Libraries

The simian immunodeficiency virus (SIV)/macaque model of human immunodeficiency virus (HIV)/acquired immunodeficiency syndrome pathogenesis is critical for furthering our understanding of the role of antibody responses in the prevention of HIV infection, and will only increase in importance as macaque immunoglobulin (IG) gene databases are expanded. We have previously reported the construction of a phage display library from a SIV-infected rhesus macaque (Macaca mulatta) using oligonucleotide primers based on human IG gene sequences. Our previous screening relied on Sanger sequencing, which was inefficient and generated only a few dozen sequences. Here, we re-analyzed this library using single molecule, real-time (SMRT) sequencing on the Pacific Biosciences (PacBio) platform to generate thousands of highly accurate circular consensus sequencing (CCS) reads corresponding to full length single chain fragment variable. CCS data were then analyzed through the international ImMunoGeneTics information system^® (IMGT^®)/HighV-QUEST (www.imgt.org) to identify variable genes and perform statistical analyses. Overall the library was very diverse, with 2,569 different IMGT clonotypes called for the 5,238 IGHV sequences assigned to an IMGT clonotype. Within the library, SIV-specific antibodies represented a relatively limited number of clones, with only 135 different IMGT clonotypes called from 4,594 IGHV-assigned sequences. Our data did confirm that the IGHV4 and IGHV3 gene usage was the most abundant within the rhesus antibodies screened, and that these genes were even more enriched among SIV gp140-specific antibodies. Although a broad range of VH CDR3 amino acid (AA) lengths was observed in the unpanned library, the vast majority of SIV gp140-specific antibodies demonstrated a more uniform VH CDR3 length (20 AA). This uniformity was far less apparent when VH CDR3 were classified according to their clonotype (range: 9–25 AA), which we believe is more relevant for specific antibody identification. Only 174 IGKV and 588 IGLV clonotypes were identified within the VL sequences associated with SIV gp140-specific VH. Together, these data strongly suggest that the combination of SMRT sequencing with the IMGT/HighV-QUEST querying tool will facilitate and expedite our understanding of polyclonal antibody responses during SIV infection and may serve to rapidly expand the known scope of macaque V genes utilized during these responses.

Monkey Models and HIV Vaccine Research

Since the discovery of acquired immunodeficiency syndrome (AIDS) in 1981, it has been extremely difficult to develop an effective vaccine or a therapeutic cure despite over 36 years of global efforts. One of the major reasons is due to the lack of an immune-competent animal model that supports live human immunodeficiency virus (HIV) infection and disease progression such that vaccine-induced correlates of protection and efficacy can be determined clearly before human trials. Nevertheless, rhesus macaques infected with simian immunodeficiency virus (SIV) and chimeric simian human immunodeficiency virus (SHIV) have served as invaluable models not only for understanding AIDS pathogenesis but also for studying HIV vaccine and cure. In this chapter, therefore, we summarize major scientific evidence generated in these models since the beginning of the AIDS pandemic. Hopefully, the accumulated knowledge and lessons contributed by thousands of scientists will be useful in promoting the search of an ultimate solution to end HIV/AIDS.

Human immunodeficiency virus type-1 (HIV-1) evades antibody-dependent phagocytosis

Fc gamma receptor (FcyR)-mediated antibody functions play a crucial role in preventing HIV infection. One such function, antibody-dependent phagocytosis (ADP), is thought to be involved in controlling other viral infections, but its role in HIV infection is unknown. We measured the ability of HIV-specific polyclonal and monoclonal antibodies (mAbs) to mediate the internalization of HIV-1 virions and HIV-1-decorated cells by phagocytes. To measure ADP of virions, we primarily used a green-fluorescent protein-expressing molecular clone of HIV-1JRFL, an R5, clinical isolate, in combination with polyclonal HIVIG or mAbs known to capture and/or neutralize HIV-1. THP-1 and U937 cells, as well as freshly isolated primary monocytes from healthy individuals, were used as phagocytic effector cells, and uptake of virions was measured by cytometry. We surprisingly found minimal or no ADP of virions with any of the antibodies. However, after coating virions with gp41 or with gp41-derived peptides, gp41- (but not gp120-) specific mAbs efficiently mediated phagocytosis. We estimated that a minimum of a few hundred gp41 molecules were needed for successful phagocytosis, which is similar to the number of envelope spikes on viruses that are readily phagocytosed (e.g. influenza virus). Furthermore, by employing fluorescence correlation spectroscopy, a well-established technique to measure particle sizes and aggregation phenomena, we found a clear association between virus aggregation and ADP. In contrast to virions themselves, virion-decorated cells were targets for ADP or trogocytosis in the presence of HIV-specific antibodies. Our findings indicate that ADP of virions may not play a role in preventing HIV infection, likely due to the paucity of trimers and the consequent inability of virion-bound antibody to cross-link FcyRs on phagocytes. However, ADP or trogocytosis could play a role in clearing HIV-infected cells and cells on the verge of infection.

Novel Concepts for HIV Vaccine Vector Design

The unprecedented challenges of developing effective vaccines against intracellular pathogens such as HIV, malaria, and tuberculosis have resulted in more rational approaches to vaccine development. Apart from the recent advances in the design and selection of improved epitopes and adjuvants, there are also ongoing efforts to optimize delivery platforms.

The unprecedented challenges of developing effective vaccines against intracellular pathogens such as HIV, malaria, and tuberculosis have resulted in more rational approaches to vaccine development. Apart from the recent advances in the design and selection of improved epitopes and adjuvants, there are also ongoing efforts to optimize delivery platforms. Viral vectors are the best-characterized delivery tools because of their intrinsic adjuvant capability, unique cellular tropism, and ability to trigger robust adaptive immune responses. However, a known limitation of viral vectors is preexisting immunity, and ongoing efforts are aimed at developing novel vector platforms with lower seroprevalence. It is also becoming increasingly clear that different vectors, even those derived from phylogenetically similar viruses, can elicit substantially distinct immune responses, in terms of quantity, quality, and location, which can ultimately affect immune protection. This review provides a summary of the status of viral vector development for HIV vaccines, with a particular focus on novel viral vectors and the types of adaptive immune responses that they induce.

eCD4-Ig promotes ADCC activity of sera from HIV-1-infected patients

Antibody-dependent cell-mediated cytotoxity (ADCC) can eliminate HIV-1 infected cells, and may help reduce the reservoir of latent virus in infected patients. Sera of HIV-1 positive individuals include a number of antibodies that recognize epitopes usually occluded on HIV-1 envelope glycoprotein (Env) trimers. We have recently described eCD4-Ig, a potent and exceptionally broad inhibitor of HIV-1 entry that can be used to protect rhesus macaques from multiple high-dose challenges with simian-human immunodeficiency virus AD8 (SHIV-AD8). Here we show that eCD4-Ig bearing an IgG1 Fc domain (eCD4-IgG1) can mediate efficient ADCC activity against HIV-1 isolates with differing tropisms, and that it does so at least 10-fold more efficiently than CD4-Ig, even when more CD4-Ig molecules bound cell surface-expressed Env. An ADCC-inactive IgG2 form of eCD4-Ig (eCD4-IgG2) exposes V3-loop and CD4-induced epitopes on cell-expressed trimers, and renders HIV-1-infected cells susceptible to ADCC mediated by antibodies of these classes. Moreover, eCD4-IgG2, but not IgG2 forms of the broadly neutralizing antibodies VRC01 and 10-1074, enhances the ADCC activities of serum antibodies from patients by 100-fold, and significantly enhanced killing of two latently infected T-cell lines reactivated by vorinostat or TNFα. Thus eCD4-Ig is qualitatively different from CD4-Ig or neutralizing antibodies in its ability to mediate ADCC, and it may be uniquely useful in treating HIV-1 infection or reducing the reservoir of latently infected cells.

Impact of HIV-1 Envelope Conformation on ADCC Responses

HIV-1 envelope glycoproteins (Env) represent the only virus-specific antigen exposed at the surface of infected cells. In its unliganded form, Env from primary viruses samples a 'closed' conformation (State 1), which is preferentially recognized by broadly neutralizing antibodies (bNAbs). CD4 engagement drives Env into an intermediate 'partially open' (State 2) and then into the 'open' CD4-bound conformation (State 3). Emerging evidence suggests a link between Env conformation and Ab-dependent cellular cytotoxicity (ADCC). HIV-1-infected cells exposing Env in the CD4-bound conformation are susceptible to ADCC mediated by CD4-induced Abs and HIV+sera. Cells exposing State 1 Env are susceptible to ADCC mediated by bNAbs. Here, we discuss how Env conformation affects ADCC responses and in vitro measurements.

Immunogenicity and efficacy of DNA/MVA HIV vaccines in rhesus macaque models

INTRODUCTION

Despite 30 years of research on HIV, a vaccine to prevent infection and limit disease progression remains elusive. The RV144 trial showed moderate, but significant protection in humans and highlighted the contribution of antibody responses directed against HIV envelope as an important immune correlate for protection. Efforts to further build upon the progress include the use of a heterologous prime-boost regimen using DNA as the priming agent and the attenuated vaccinia virus, Modified Vaccinia Ankara (MVA), as a boosting vector for generating protective HIV-specific immunity. Areas covered: In this review, we summarize the immunogenicity of DNA/MVA vaccines in non-human primate models and describe the efficacy seen in SIV infection models. We discuss immunological correlates of protection determined by these studies and potential approaches for improving the protective immunity. Additionally, we describe the current progress of DNA/MVA vaccines in human trials. Expert commentary: Efforts over the past decade have provided the opportunity to better understand the dynamics of vaccine-induced immune responses and immune correlates of protection against HIV. Based on what we have learned, we outline multiple areas where the field will likely focus on in the next five years.

Natural Killer (NK) Cell Education Differentially Influences HIV Antibody-Dependent NK Cell Activation and Antibody-Dependent Cellular Cytotoxicity

Immunotherapy using broadly neutralizing antibodies (bNAbs) endowed with Fc-mediated effector functions has been shown to be critical for protecting or controlling viral replication in animal models. In human, the RV144 Thai trial was the first trial to demonstrate a significant protection against HIV infection following vaccination. Analysis of the correlates of immune protection in this trial identified an association between the presence of antibody-dependent cellular cytotoxicity (ADCC) mediated by immunoglobulin G (IgG) antibodies (Abs) to HIV envelope (Env) V1/V2 loop structures and protection from infection, provided IgA Abs with competing specificity were not present. Systems serology analyses implicated a broader range of Ab-dependent functions in protection from HIV infection, including but not limited to ADCC and Ab-dependent NK cell activation (ADNKA) for secretion of IFN-γ and CCL4 and expression of the degranulation marker CD107a. The existence of such correlations in the absence of bNAbs in the RV144 trial suggest that NK cells could be instrumental in protecting against HIV infection by limiting viral spread through Fc-mediated functions such as ADCC and the production of antiviral cytokines/chemokines. Beside the engagement of FcγRIIIa or CD16 by the Fc portion of anti-Env IgG1 and IgG3 Abs, natural killer (NK) cells are also able to directly kill infected cells and produce cytokines/chemokines in an Ab-independent manner. Responsiveness of NK cells depends on the integration of activating and inhibitory signals through NK receptors, which is determined by a process during their development known as education. NK cell education requires the engagement of inhibitory NK receptors by their human leukocyte antigen ligands to establish tolerance to self while allowing NK cells to respond to self cells altered by virus infection, transformation, stress, and to allogeneic cells. Here, we review recent findings regarding the impact of inter-individual differences in NK cell education on Ab-dependent functions such as ADCC and ADNKA, including what is known about the HIV Env epitope specificity of ADCC competent Abs and the conformation of HIV Env on target cells used for ADCC assays.

Analysis of SIVmac Envelope-Specific Antibodies Selected Through Phage Display

We have constructed a single chain fragment variable (scFv) phage display library from a simian immunodeficiency virus (SIV)-infected rhesus macaque that developed unusually high-titer neutralizing antibody responses against tier-3, neutralization-resistant SIVmac239. The library was screened using trimeric (gp140) and monomeric (gp120) forms of the SIVmac239 envelope (Env) glycoprotein. We also cloned variable-heavy and variable-light (VH-VL) antibody fragments from seven previously described rhesus macaque B-cell lines (BLCLs) that produce SIV gp120-specific monoclonal antibodies (mAbs). Thirty-two gp140-specific mAbs were selected along with 20 gp120-specific ones. gp120-specific mAbs were only from the VH4 family, while gp41-specific mAbs were primarily from VH1, followed by VH4 and VH3. Rhesus macaque BLCL-derived mAbs belonged primarily to the VH4 family of antibodies followed by VH3 and a smaller number of VH1s. A preferential VH combination with Vλ light chain was observed with phage display-selected SIV Env-specific mAbs (gp120 and gp140), but not with BLCL-derived antibodies or the unpanned library. None of the tested antibodies had detectable neutralizing activity against tier-3 SIVmac239. The majority of gp120-specifc mAbs potently neutralized tier-1 SIVmac316 with 50% inhibitory concentration (IC50) values below 1 μg/ml. For gp140-specific antibodies, which were all specific for the gp41-subunit, 2 out of 11 tested neutralized SIVmac316 (IC50 of 7 and 5 μg/ml, respectively). These data suggest an order of preferential VH segment usage for SIV-specific antibodies in rhesus macaques. These antibodies will be useful in assessing the contribution of non-neutralizing antibodies to inhibition of SIV infection in vitro and in vivo.

Vaccine-induced immune responses against both Gag and Env improve control of simian immunodeficiency virus replication in rectally challenged rhesus macaques

The ability to control lentivirus replication may be determined, in part, by the extent to which individual viral proteins are targeted by the immune system. Consequently, defining the antigens that elicit the most protective immune responses may facilitate the design of effective HIV-1 vaccines. Here we vaccinated four groups of rhesus macaques with a heterologous vector prime/boost/boost/boost (PBBB) regimen expressing the following simian immunodeficiency virus (SIV) genes: env, gag, vif, rev, tat, and nef (Group 1); env, vif, rev, tat, and nef (Group 2); gag, vif, rev, tat, and nef (Group 3); or vif, rev, tat, and nef (Group 4). Following repeated intrarectal challenges with a marginal dose of the neutralization-resistant SIVmac239 clone, vaccinees in Groups 1-3 became infected at similar rates compared to control animals. Unexpectedly, vaccinees in Group 4 became infected at a slower pace than the other animals, although this difference was not statistically significant. Group 1 exhibited the best post-acquisition virologic control of SIV infection, with significant reductions in both peak and chronic phase viremia. Indeed, 5/8 Group 1 vaccinees had viral loads of less than 2,000 vRNA copies/mL of plasma in the chronic phase. Vaccine regimens that did not contain gag (Group 2), env (Group 3), or both of these inserts (Group 4) were largely ineffective at decreasing viremia. Thus, vaccine-induced immune responses against both Gag and Env appeared to maximize control of immunodeficiency virus replication. Collectively, these findings are relevant for HIV-1 vaccine design as they provide additional insights into which of the lentiviral proteins might serve as the best vaccine immunogens.

BST-2 Expression Modulates Small CD4-Mimetic Sensitization of HIV-1-Infected Cells to Antibody-Dependent Cellular Cytotoxicity

Antibodies recognizing conserved CD4-induced (CD4i) epitopes on human immunodeficiency virus type 1 (HIV-1) Env and able to mediate antibody-dependent cellular cytotoxicity (ADCC) have been shown to be present in sera from most HIV-1-infected individuals. These antibodies preferentially recognize Env in its CD4-bound conformation. CD4 downregulation by Nef and Vpu dramatically reduces exposure of CD4i HIV-1 Env epitopes and therefore reduce the susceptibility of HIV-1-infected cells to ADCC mediated by HIV-positive (HIV+) sera. Importantly, this mechanism of immune evasion can be circumvented with small-molecule CD4 mimetics (CD4mc) that are able to transition Env into the CD4-bound conformation and sensitize HIV-1-infected cells to ADCC mediated by HIV+ sera. However, HIV-1 developed additional mechanisms to avoid ADCC, including Vpu-mediated BST-2 antagonism, which decreases the overall amount of Env present at the cell surface. Accordingly, BST-2 upregulation in response to alpha interferon (IFN-α) was shown to increase the susceptibility of HIV-1-infected cells to ADCC despite the activity of Vpu. Here we show that BST-2 upregulation by IFN-β and interleukin-27 (IL-27) also increases the surface expression of Env and thus boosts the ability of CD4mc to sensitize HIV-1-infected cells to ADCC by sera from HIV-1-infected individuals.IMPORTANCE HIV-1 evolved sophisticated strategies to conceal Env epitopes from ADCC-mediating antibodies present in HIV+ sera. Vpu-mediated BST-2 downregulation was shown to decrease ADCC responses by limiting the amount of Env present at the cell surface. This effect of Vpu was shown to be attenuated by IFN-α treatment. Here we show that in addition to IFN-α, IFN-β and IL-27 also affect Vpu-mediated BST-2 downregulation and greatly enhance ADCC responses against HIV-1-infected cells in the presence of CD4mc. These findings may inform strategies aimed at HIV prevention and eradication.

Monoclonal Antibodies Specific for the V2, V3, CD4-Binding Site, and gp41 of HIV-1 Mediate Phagocytosis in a Dose-Dependent Manner

In light of the weak or absent neutralizing activity mediated by anti-V2 monoclonal antibodies (MAbs), we tested whether they can mediate Ab-dependent cellular phagocytosis (ADCP), which is an important element of anti-HIV-1 immunity. We tested six anti-V2 MAbs and compared them with 21 MAbs specific for V3, the CD4-binding site (CD4bs), and gp41 derived from chronically HIV-1-infected individuals and produced by hybridoma cells. ADCP activity was measured by flow cytometry using uptake by THP-1 monocytic cells of fluorescent beads coated with gp120, gp41, BG505 SOSIP.664, or BG505 DS-SOSIP.664 complexed with MAbs. The measurement of ADCP activity by the area under the curve showed significantly higher activity of anti-gp41 MAbs than of the members of the three other groups of MAbs tested using beads coated with monomeric gp41 or gp120; anti-V2 MAbs were dominant compared to anti-V3 and anti-CD4bs MAbs against clade C gp120_ZM109 ADCP activity mediated by V2 and V3 MAbs was positive against stabilized DS-SOSIP.664 trimer but negligible against SOSIP.664 targets, suggesting that a closed envelope conformation better exposes the variable loops. Two IgG3 MAbs against the V2 and V3 regions displayed dominant ADCP activity compared to a panel of IgG1 MAbs. This superior ADCP activity was confirmed when two of three recombinant IgG3 anti-V2 MAbs were compared to their IgG1 counterparts. The study demonstrated dominant ADCP activity of anti-gp41 against monomers but not trimers, with some higher activity of anti-V2 MAbs than of anti-V3 and anti-CD4bs MAbs. The ability to mediate ADCP suggests a mechanism by which anti-HIV-1 envelope Abs can contribute to protective efficacy.IMPORTANCE Anti-V2 antibodies (Abs) correlated with reduced risk of HIV-1 infection in recipients of the RV144 vaccine, suggesting that they play a protective role, but a mechanism providing such protection remains to be determined. The rare and weak neutralizing activities of anti-V2 MAbs prompted us to study Fc-mediated activities. We compared anti-V2 MAbs with other MAbs specific for V3, CD4bs, and gp41 for Ab-dependent cellular phagocytosis (ADCP) activity, implicated in protective immunity. The anti-V2 MAbs displayed stronger activity than other anti-gp120 MAbs in screening against one of two gp120s and against DS-SOSIP, which mimics the native trimer. The activity of anti-gp41 MAbs was superior in targeting monomeric gp41 but was comparable to that seen against trimers, which may not adequately expose gp41 epitopes. While anti-envelope MAbs in general mediated ADCP activity, anti-V2 MAbs displayed some dominance compared to other MAbs. Our demonstration that anti-V2 MAbs mediate ADCP activity suggests a functional mechanism for their contribution to protective efficacy.

Lack of ADCC Breadth of Human Nonneutralizing Anti-HIV-1 Antibodies

Anti-human immunodeficiency virus type 1 (HIV-1) nonneutralizing antibodies (nnAbs) capable of antibody-dependent cellular cytotoxicity (ADCC) have been identified as a protective immune correlate in the RV144 vaccine efficacy trial. Broadly neutralizing antibodies (bNAbs) also mediate ADCC in cell culture and rely on their Fc region for optimal efficacy in animal models. Here, we selected 9 monoclonal nnAbs and 5 potent bNAbs targeting various epitopes and conformations of the gp120/41 complex and analyzed the potency of the two types of antibodies to bind and eliminate HIV-1-infected cells in culture. Regardless of their neutralizing activity, most of the selected antibodies recognized and killed cells infected with two laboratory-adapted HIV-1 strains. Some nnAbs also bound bystander cells that may have captured viral proteins. However, in contrast to the bNAbs, the nnAbs bound poorly to reactivated infected cells from 8 HIV-positive individuals and did not mediate effective ADCC against these cells. The nnAbs also inefficiently recognize cells infected with 8 different transmitted-founder (T/F) isolates. The addition of a synthetic CD4 mimetic enhanced the binding and killing efficacy of some of the nnAbs in an epitope-dependent manner without reaching the levels achieved by the most potent bNAbs. Overall, our data reveal important qualitative and quantitative differences between nnAbs and bNAbs in their ADCC capacity and strongly suggest that the breadth of recognition of HIV-1 by nnAbs is narrow.IMPORTANCE Most of the anti-HIV antibodies generated by infected individuals do not display potent neutralizing activities. These nonneutralizing antibodies (nnAbs) with antibody-dependent cellular cytotoxicity (ADCC) have been identified as a protective immune correlate in the RV144 vaccine efficacy trial. However, in primate models, the nnAbs do not protect against simian-human immunodeficiency virus (SHIV) acquisition. Thus, the role of nnAbs with ADCC activity in protection from infection remains debatable. In contrast, broadly neutralizing antibodies (bNAbs) neutralize a large array of viral strains and mediate ADCC in cell culture. We analyzed the capacities of 9 nnAbs and 5 bNAbs to eliminate infected cells. We selected 18 HIV-1 strains, including virus reactivated from the reservoir of HIV-positive individuals and transmitted-founder isolates. We report that the nnAbs bind poorly to cells infected with primary HIV-1 strains and do not mediate potent ADCC. Overall, our data show that the breadth of recognition of HIV-1 by nnAbs is narrow.

Influence of the Envelope gp120 Phe 43 Cavity on HIV-1 Sensitivity to Antibody-Dependent Cell-Mediated Cytotoxicity Responses

HIV-1-infected cells presenting envelope glycoproteins (Env) in the CD4-bound conformation on their surface are preferentially targeted by antibody-dependent cellular-mediated cytotoxicity (ADCC). HIV-1 has evolved sophisticated mechanisms to avoid the exposure of Env ADCC epitopes by downregulating CD4 and by limiting the overall amount of Env on the cell surface. In HIV-1, substitution of large residues such as histidine or tryptophan for serine 375 (S375H/W) in the gp120 Phe 43 cavity, where Phe 43 of CD4 contacts gp120, results in the spontaneous sampling of an Env conformation closer to the CD4-bound state. While residue S375 is well conserved in the majority of group M HIV-1 isolates, CRF01_AE strains have a naturally occurring histidine at this position (H375). Interestingly, CRF01_AE is the predominant circulating strain in Thailand, where the RV144 trial took place. In this trial, which resulted in a modest degree of protection, ADCC responses were identified as being part of the correlate of protection. Here we investigate the influence of the Phe 43 cavity on ADCC responses. Filling this cavity with a histidine or tryptophan residue in Env with a natural serine residue at this position (S375H/W) increased the susceptibility of HIV-1-infected cells to ADCC. Conversely, the replacement of His 375 by a serine residue (H375S) within HIV-1 CRF01_AE decreased the efficiency of the ADCC response. Our results raise the intriguing possibility that the presence of His 375 in the circulating strain where the RV144 trial was held contributed to the observed vaccine efficacy.IMPORTANCE HIV-1-infected cells presenting Env in the CD4-bound conformation on their surface are preferentially targeted by ADCC mediated by HIV-positive (HIV⁺) sera. Here we show that the gp120 Phe 43 cavity modulates the propensity of Env to sample this conformation and therefore affects the susceptibility of infected cells to ADCC. CRF01_AE HIV-1 strains have an unusual Phe 43 cavity-filling His 375 residue, which increases the propensity of Env to sample the CD4-bound conformation, thereby increasing susceptibility to ADCC.

Modulation of innate and adaptive cellular immunity relevant to HIV-1 vaccine design by seminal plasma

OBJECTIVES

Mucosal exposure to HIV-1 infection generally occurs in the presence of semen. Immunomodulation by seminal plasma is well described in the reproductive biology literature. Little is known, however, about the impact of seminal plasma on innate and adaptive anti-HIV-1 cellular immunity.

DESIGN

The study investigated the effects of seminal plasma on immune responses considered important for prophylactic HIV-1 vaccine development, namely innate and adaptive cellular immunity mediated by natural killer (NK) cells and T cells, respectively.

METHODS

The ability of seminal plasma to modulate direct, antibody-dependent and cytokine-stimulated NK cell activation was assessed utilizing intracellular cytokine staining. Direct and antibody-dependent cellular cytotoxicity was assessed using lactate dehydrogenase release assays. The effects of seminal plasma on T-cell activation upon stimulation with staphylococcus enterotoxin B or HIV-1 Gag peptides were assessed by intracellular cytokine staining. The impact of seminal plasma on redirected cytolysis mediated by T cells was measured using lactate dehydrogenase release assays.

RESULTS

Both direct and antibody-dependent NK cell activation were dramatically impaired by the presence of either HIV-1-uninfected or HIV-1-infected seminal plasma in a dose-dependent manner. Additionally, seminal plasma suppressed both direct and antibody-dependent NK cell-mediated cytolysis, including anti-HIV-1 antibody-dependent cytolysis of gp120-pulsed CEM.NKr-CCR5 cells. Finally, seminal plasma attenuated both HIV-1 Gag-specific and staphylococcus enterotoxin B-induced CTL activation.

CONCLUSIONS

Semen contains potent immunosuppressors of both NK cell and CD8 T-cell-mediated anti-HIV-1 immune responses. This could impede attempts to provide vaccine-induced immunity to HIV-1.

Persistent Low-Level Replication of SIVΔnef Drives Maturation of Antibody and CD8 T Cell Responses to Induce Protective Immunity against Vaginal SIV Infection

Defining the correlates of immune protection conferred by SIVΔnef, the most effective vaccine against SIV challenge, could enable the design of a protective vaccine against HIV infection. Here we provide a comprehensive assessment of immune responses that protect against SIV infection through detailed analyses of cellular and humoral immune responses in the blood and tissues of rhesus macaques vaccinated with SIVΔnef and then vaginally challenged with wild-type SIV. Despite the presence of robust cellular immune responses, animals at 5 weeks after vaccination displayed only transient viral suppression of challenge virus, whereas all macaques challenged at weeks 20 and 40 post-SIVΔnef vaccination were protected, as defined by either apparent sterile protection or significant suppression of viremia in infected animals. Multiple parameters of CD8 T cell function temporally correlated with maturation of protection, including polyfunctionality, phenotypic differentiation, and redistribution to gut and lymphoid tissues. Importantly, we also demonstrate the induction of a tissue-resident memory population of SIV-specific CD8 T cells in the vaginal mucosa, which was dependent on ongoing low-level antigenic stimulation. Moreover, we show that vaginal and serum antibody titers inversely correlated with post-challenge peak viral load, and we correlate the accumulation and affinity maturation of the antibody response to the duration of the vaccination period as well as to the SIVΔnef antigenic load. In conclusion, maturation of SIVΔnef-induced CD8 T cell and antibody responses, both propelled by viral persistence in the gut mucosa and secondary lymphoid tissues, results in protective immune responses that are able to interrupt viral transmission at mucosal portals of entry as well as potential sites of viral dissemination.

Rationally Designed Vaccines Targeting the V2 Region of HIV-1 gp120 Induce a Focused, Cross-Clade-Reactive, Biologically Functional Antibody Response

Strong antibody (Ab) responses against V1V2 epitopes of the human immunodeficiency virus type 1 (HIV-1) gp120 envelope (Env) correlated with reduced infection rates in studies of HIV, simian-human immunodeficiency virus (SHIV), and simian immunodeficiency virus (SIV). In order to focus the Ab response on V1V2, we used six V1V2 sequences and nine scaffold proteins to construct immunogens which were tested using various immunization regimens for their ability to induce cross-reactive and biologically active V2 Abs in rabbits. A prime/boost immunization strategy was employed using gp120 DNA and various V1V2-scaffold proteins. The rabbit polyclonal Ab responses (i) were successfully focused on the V1V2 region, with weak or only transient responses to other Env epitopes, (ii) displayed broad cross-reactive binding activity with gp120s and the V1V2 regions of diverse strains from clades B, C, and E, (iii) included V2 Abs with specificities similar to those found in HIV-infected individuals, and (iv) remained detectable ≥1 year after the last boosting dose. Importantly, sera from rabbits receiving V1V2-scaffold immunogens displayed Ab-dependent cellular phagocytosis whereas sera from rabbits receiving only gp120 did not. The results represent the first fully successful example of reverse vaccinology in the HIV vaccine field with rationally designed epitope scaffold immunogens inducing Abs that recapitulate the epitope specificity and biologic activity of the human monoclonal Abs from which the immunogens were designed. Moreover, this is the first immunogenicity study using epitope-targeting, rationally designed vaccine constructs that induced an Fc-mediated activity associated with protection from infection with HIV, SIV, and SHIV.

IMPORTANCE

Novel immunogens were designed to focus the antibody response of rabbits on the V1V2 epitopes of HIV-1 gp120 since such antibodies were associated with reduced infection rates of HIV, SIV, and SHIV. The vaccine-induced antibodies were broadly cross-reactive with the V1V2 regions of HIV subtypes B, C and E and, importantly, facilitated Fc-mediated phagocytosis, an activity not induced upon immunization of rabbits with gp120. This is the first immunogenicity study of vaccine constructs that focuses the antibody response on V1V2 and induces V2-specific antibodies with the ability to mediate phagocytosis, an activity that has been associated with protection from infection with HIV, SIV, and SHIV.

Development of novel replication-defective lymphocytic choriomeningitis virus vectors expressing SIV antigens

An important focus in vaccine research is the design of vaccine vectors with low seroprevalence and high immunogenicity. Replication-incompetent lymphocytic choriomeningitis virus (rLCMV) vectors do not elicit vector-neutralizing antibody responses, and homologous prime-boost regimens with rLCMV vectors induce boostable and protective T cell responses to model antigens in mice. However, cellular and humoral immune responses following homologous rLCMV vaccine regimens have not been rigorously evaluated in non-human primates (NHPs). To test whether rLCMV vectors constitute an effective vaccine platform in NHPs, we developed rLCMV vectors expressing SIVmac239 Env and Gag antigens and assessed their immunogenicity in mice and cynomolgus macaques. Immunization with rLCMV vaccine vectors expressing SIV Env and Gag was effective at generating SIV-specific T cell and antibody responses in both mice and NHPs. Epitope mapping using SIV Env in C57BL/6 mice demonstrated that rLCMV vectors induced sustained poly-functional responses to both dominant and subdominant epitopes. Our results suggest the potential of rLCMV vectors as vaccine candidates. Future SIV challenge experiments in rhesus macaques will be needed to assess immune protection by these vaccine vectors.

Tetherin Antagonism by HIV-1 Group M Nef Proteins

Although Nef is the viral gene product used by most simian immunodeficiency viruses to overcome restriction by tetherin, this activity was acquired by the Vpu protein of HIV-1 group M due to the absence of sequences in human tetherin that confer susceptibility to Nef. Thus, it is widely accepted that HIV-1 group M uses Vpu instead of Nef to counteract tetherin. Challenging this paradigm, we identified Nef alleles of HIV-1 group M isolates with significant activity against human tetherin. These Nef proteins promoted virus release and tetherin downmodulation from the cell surface and, in the context of vpu-deleted HIV-1 recombinants, enhanced virus replication and resistance to antibody-dependent cell-mediated cytotoxicity (ADCC). Further analysis revealed that the Vpu proteins from several of these viruses lack antitetherin activity, suggesting that under certain circumstances, HIV-1 group M Nef may acquire the ability to counteract tetherin to compensate for the loss of this function by Vpu. These observations illustrate the remarkable plasticity of HIV-1 in overcoming restriction by tetherin and challenge the prevailing view that all HIV-1 group M isolates use Vpu to counteract tetherin. IMPORTANCE Most viruses of HIV-1 group M, the main group of HIV-1 responsible for the global AIDS pandemic, use their Vpu proteins to overcome restriction by tetherin (BST-2 or CD317), which is a transmembrane protein that inhibits virus release from infected cells. Here we show that the Nef proteins of certain HIV-1 group M isolates can acquire the ability to counteract tetherin. These results challenge the current paradigm that HIV-1 group M exclusively uses Vpu to counteract tetherin and underscore the importance of tetherin antagonism for efficient viral replication.

HIV-specific CD4-induced Antibodies Mediate Broad and Potent Antibody-dependent Cellular Cytotoxicity Activity and Are Commonly Detected in Plasma From HIV-infected humans

HIV-specific antibodies (Abs) can reduce viral burden by blocking new rounds of infection or by destroying infected cells via activation of effector cells through Fc–FcR interaction. This latter process, referred to as antibody-dependent cellular cytotoxicity (ADCC), has been associated with viral control and improved clinical outcome following both HIV and SIV infections. Here we describe an HIV viral-like particle (VLP)-based sorting strategy that led to identification of HIV-specificmemory B cells encoding Abs that mediate ADCC froma subtype A-infected Kenyan woman at 914 days post-infection. Using this strategy, 12 HIV-envelope-specific monoclonal antibodies (mAbs) were isolated and three mediated potent ADCC activitywhen compared to well-characterized ADCC mAbs. The ADCC-mediating Abs also mediated antibody-dependent cell-mediated virus inhibition (ADCVI), which provides a net measure of Fc receptor-triggered effects against replicating virus. Two of the three ADCC-mediating Abs targeted a CD4-induced (CD4i) epitope also bound by the mAb C11; the third antibody targeted the N-terminus of V3. Both CD4i Abs identified here demonstrated strong cross-clade breadth with activity against 10 of 11 envelopes tested, including those from clades A, B, C, A/D and C/D, whereas the V3-specific antibody showed more limited breadth. Variants of these CD4i, C11-like mAbs engineered to interrupt binding to FcγRs inhibited a measurable percentage of the donor's ADCC activity starting as early as 189 days post-infection. C11-like antibodies also accounted for between 18–78% of ADCC activity in 9 chronically infected individuals from the same cohort study. Further, the two CD4i Abs originated from unique B cells, suggesting that antibodies targeting this epitope can be commonly produced. Taken together, these data provide strong evidence that CD4i, C11-like antibodies develop within the first 6 months of infection and they can arise fromunique B-cell lineages in the same individual. Further, thesemAbsmediate potent plasma IgG-specificADCC breadth and potency and contribute to ADCC activity in other HIV-infected individuals.

Co-receptor Binding Site Antibodies Enable CD4-Mimetics to Expose Conserved Anti-cluster A ADCC Epitopes on HIV-1 Envelope Glycoproteins

Human immunodeficiency virus type 1 (HIV-1) has evolved a sophisticated strategy to conceal conserved epitopes of its envelope glycoproteins (Env) recognized by antibody-dependent cellular cytotoxicity (ADCC)-mediating antibodies. These antibodies, which are present in the sera of most HIV-1-infected individuals, preferentially recognize Env in its CD4-bound conformation. Accordingly, recent studies showed that small CD4-mimetics (CD4mc) able to “push” Env into this conformation sensitize HIV-1-infected cells to ADCC mediated by HIV + sera. Here we test whether CD4mc also expose epitopes recognized by anti-cluster A monoclonal antibodies such as A32, thought to be responsible for the majority of ADCC activity present in HIV + sera and linked to decreased HIV-1 transmission in the RV144 trial. We made the surprising observation that CD4mc are unable to enhance recognition of HIV-1-infected cells by this family of antibodies in the absence of antibodies such as 17b, which binds a highly conserved CD4-induced epitope overlapping the co-receptor binding site (CoRBS). Our results indicate that CD4mc initially open the trimeric Env enough to allow the binding of CoRBS antibodies but not anti-cluster A antibodies. CoRBS antibody binding further opens the trimeric Env, allowing anti-cluster A antibody interaction and sensitization of infected cells to ADCC. Therefore, ADCC responses mediated by cluster A antibodies in HIV-positive sera involve a sequential opening of the Env trimer on the surface of HIV-1-infected cells. The understanding of the conformational changes required to expose these vulnerable Env epitopes might be important in the design of new strategies aimed at fighting HIV-1.

•

CD4-mimetics fail to enhance recognition of infected cells by anti-cluster A antibodies (Abs).

•

Co-receptor binding site Abs in conjunction with CD4-mimetics allow binding of Env by anti-cluster A Abs.

•

Co-receptor binding site Abs help CD4-mimetics sensitize HIV-1-infected cells to ADCC.

HIV-1 developed sophisticated strategies to conceal vulnerable epitopes of its envelope glycoproteins (Env) recognized by antibody-dependent cellular cytotoxicity (ADCC)-mediating antibodies. CD4-mimetics (CD4mc) were shown to sensitize HIV-1-infected cells to ADCC induced by HIV + sera. Here we show that this response requires a sequential opening of Env at the surface of HIV-1-infected cells. Co-receptor binding site antibodies, also present in HIV + sera, are required to expose ADCC-mediating epitopes recognized by anti-cluster A antibodies upon CD4mc addition. The understanding of the conformational changes required to expose anti-cluster A epitopes might be important in the design of new strategies aimed at fighting HIV-1.

PolyICLC Exerts Pro- and Anti-HIV Effects on the DC-T Cell Milieu In Vitro and In Vivo

Myeloid dendritic cells (mDCs) contribute to both HIV pathogenesis and elicitation of antiviral immunity. Understanding how mDC responses to stimuli shape HIV infection outcomes will inform HIV prevention and treatment strategies. The long double-stranded RNA (dsRNA) viral mimic, polyinosinic polycytidylic acid (polyIC, PIC) potently stimulates DCs to focus Th1 responses, triggers direct antiviral activity in vitro, and boosts anti-HIV responses in vivo. Stabilized polyICLC (PICLC) is being developed for vaccine adjuvant applications in humans, making it critical to understand how mDC sensing of PICLC influences HIV infection. Using the monocyte-derived DC (moDC) model, we sought to describe how PICLC (vs. other dsRNAs) impacts HIV infection within DCs and DC-T cell mixtures. We extended this work to in vivo macaque rectal transmission studies by administering PICLC with or before rectal SIVmac239 (SIVwt) or SIVmac239ΔNef (SIVΔNef) challenge. Like PIC, PICLC activated DCs and T cells, increased expression of α4β7 and CD169, and induced type I IFN responses in vitro. The type of dsRNA and timing of dsRNA exposure differentially impacted in vitro DC-driven HIV infection. Rectal PICLC treatment similarly induced DC and T cell activation and pro- and anti-HIV factors locally and systemically. Importantly, this did not enhance SIV transmission in vivo. Instead, SIV acquisition was marginally reduced after a single high dose challenge. Interestingly, in the PICLC-treated, SIVΔNef-infected animals, SIVΔNef viremia was higher, in line with the importance of DC and T cell activation in SIVΔNef replication. In the right combination anti-HIV strategy, PICLC has the potential to limit HIV infection and boost HIV immunity.

Boosting of ALVAC-SIV Vaccine-Primed Macaques with the CD4-SIVgp120 Fusion Protein Elicits Antibodies to V2 Associated with a Decreased Risk of SIVmac251 Acquisition

The recombinant ALVAC vaccine coupled with the monomeric gp120/alum protein have decreased the risk of HIV and SIV acquisition. Ab responses to the V1/V2 regions have correlated with a decreased risk of virus acquisition in both humans and macaques. We hypothesized that the breadth and functional profile of Abs induced by an ALVAC/envelope protein regimen could be improved by substituting the monomeric gp120 boost, with the full-length single-chain (FLSC) protein. FLSC is a CD4-gp120 fusion immunogen that exposes cryptic gp120 epitopes to the immune system. We compared the immunogenicity and relative efficiency of an ALVAC-SIV vaccine boosted either with bivalent FLSC proteins or with monomeric gp120 in alum. FLSC was superior to monomeric gp120 in directing Abs to the C3 α2 helix, the V5 loop, and the V3 region that contains the putative CCR5 binding site. In addition, FLSC boosting elicited significantly higher binding Abs to V2 and increased both the Ab-dependent cellular cytotoxicity activity and the breadth of neutralizing Abs. However, the FLSC vaccine regimen demonstrated only a trend in vaccine efficacy, whereas the monomeric gp120 regimen significantly decreased the risk of SIVmac251 acquisition. In both vaccine regimens, anti-V2 Abs correlated with a decreased risk of virus acquisition but differed with regard to systemic or mucosal origin. In the FLSC regimen, serum Abs to V2 correlated, whereas in the monomeric gp120 regimen, V2 Abs in rectal secretions, the site of viral challenge, were associated with efficacy.

HIV-1-Specific Antibody Response and Function after DNA Prime and Recombinant Adenovirus 5 Boost HIV Vaccine in HIV-Infected Subjects

Little is known about the humoral immune response against DNA prime-recombinant adenovirus 5 (rAd5) boost HIV vaccine among HIV-infected patients on long-term suppressive antiretroviral therapy (ART). Previous studies emphasized cellular immune responses; however, current research suggests both cellular and humoral responses are likely required for a successful therapeutic vaccine. Thus, we aimed to understand antibody response and function induced by vaccination of ART-treated HIV-1-infected patients with immune recovery. All subjects participated in EraMune 02, an open-label randomized clinical trial of ART intensification followed by a six plasmid DNA prime (envA, envB, envC, gagB, polB, nefB) and rAd5 boost HIV vaccine with matching inserts. Antibody binding levels were determined with a recently developed microarray approach. We also analyzed neutralization efficiency and antibody-dependent cellular cytotoxicity (ADCC). We found that the DNA prime-rAd5 boost vaccine induced a significant cross-clade HIV-specific antibody response, which correlated with antibody neutralization efficiency. However, despite the increase in antibody binding levels, the vaccine did not significantly stimulate neutralization or ADCC responses. This finding was also reflected by a lack of change in total CD4+ cell associated HIV DNA in those who received the vaccine. Our results have important implications for further therapeutic vaccine design and administration, especially in HIV-1 infected patients, as boosting of preexisting antibody responses are unlikely to lead to clearance of latent proviruses in the HIV reservoir.

Comparison of Antibody-Dependent Cell-Mediated Cytotoxicity and Virus Neutralization by HIV-1 Env-Specific Monoclonal Antibodies

Although antibodies to the human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein have been studied extensively for their ability to block viral infectivity, little data are currently available on nonneutralizing functions of these antibodies, such as their ability to eliminate virus-infected cells by antibody-dependent cell-mediated cytotoxicity (ADCC). HIV-1 Env-specific antibodies of diverse specificities, including potent broadly neutralizing and nonneutralizing antibodies, were therefore tested for ADCC against cells infected with a lab-adapted HIV-1 isolate (HIV-1NL4-3), a primary HIV-1 isolate (HIV-1JR-FL), and a simian-human immunodeficiency virus (SHIV) adapted for pathogenic infection of rhesus macaques (SHIVAD8-EO). In accordance with the sensitivity of these viruses to neutralization, HIV-1NL4-3-infected cells were considerably more sensitive to ADCC, both in terms of the number of antibodies and magnitude of responses, than cells infected with HIV-1JR-FL or SHIVAD8-EO ADCC activity generally correlated with antibody binding to Env on the surfaces of virus-infected cells and with viral neutralization; however, neutralization was not always predictive of ADCC, as instances of ADCC in the absence of detectable neutralization, and vice versa, were observed. These results reveal incomplete overlap in the specificities of antibodies that mediate these antiviral activities and provide insights into the relationship between ADCC and neutralization important for the development of antibody-based vaccines and therapies for combating HIV-1 infection.

IMPORTANCE

This study provides fundamental insights into the relationship between antibody-dependent cell-mediated cytotoxicity (ADCC) and virus neutralization that may help to guide the development of antibody-based vaccines and immunotherapies for the prevention and treatment of HIV-1 infection.

Brief Report: Seminal Plasma Anti-HIV Antibodies Trigger Antibody-dependent Cellular Cytotoxicity: Implications for HIV Transmission

Recent evidence from HIV vaccine trials in humans and non-human primates suggests that nonneutralizing antibody functions, such as antibody-dependent cellular cytotoxicity (ADCC), are an important component of vaccine-mediated protection. Whether anti-HIV ADCC antibodies are present in seminal fluid, however, is not known. We assessed whether anti-HIV antibodies within seminal plasma mediate ADCC and activate natural killer (NK) cells. Using matched blood and seminal plasma samples, we detected anti-HIV IgG within samples from all 11 HIV-infected donors. Furthermore, anti-HIV antibodies within the seminal plasma triggered detectable ADCC in 9 of 11 donors and activated NK cells in 6 of 11 donors. The ability of seminal plasma-derived IgG to activate NK cells in an anti-HIV antibody-dependent manner was enhanced when IgG were enriched and other seminal plasma components were removed. These observations have relevance for understanding natural immunity to HIV infection and provide assistance with HIV vaccine design.

Increases in NKG2C Expression on T Cells and Higher Levels of Circulating CD8+ B Cells Are Associated with Sterilizing Immunity Provided by a Live Attenuated SIV Vaccine

Vaccines based on live attenuated viruses are highly effective immunogens in the simian immunodeficiency virus (SIV)/rhesus macaque animal model and offer the possibility of studying correlates of protection against infection with virulent virus. We utilized a tether system for studying, in naive macaques and animals vaccinated with a live-attenuated vaccine, the acute events after challenge with pathogenic SIV. This approach allowed for the frequent sampling of small blood volumes without sedation or restraining of the animals, thus reducing the confounding effect of sampling stress. Before challenge, vaccinated animals presented significantly higher levels of proliferating and activated B cells than naive macaques, which were manifested by high expression of CD8 on B cells. After SIV challenge, the only changes observed in protected vaccinated macaques were significant increases in expression of the NK marker NKG2C on CD4 and CD8 T cells. We also identified that infection of naive macaques with SIV resulted in a transient peak of expression of CD20 on CD8 T cells and a constant rise in the number of B cells expressing CD8. Finally, analysis of a larger cohort of vaccinated animals identified that, even when circulating levels of vaccine virus are below the limit of detection, live attenuated vaccines induce systemic increases of IP-10 and perforin. These studies indicate that components of both the innate and adaptive immune systems of animals inoculated with a live-attenuated SIV vaccine respond to and control infection with virulent virus. Persistence of the vaccine virus in tissues may explain the elevated cytokine and B-cell activation levels. In addition, our report underpins the utility of the tether system for the intensive study of acute immune responses to viral infections.

The Significance of a Common Idiotype (1F7) on Antibodies against Human Immune Deficiency Virus Type 1 and Hepatitis C Virus

In this review, we trace the concept and potential functional role of regulatory idiotypes in the immune response to human immunodeficiency virus type 1 (HIV-1), simian immunodeficiency virus, and hepatitis C virus (HCV). A major idiotype involved in these viral infections is recognized and defined by a murine monoclonal antibody (1F7). Antibodies expressing the idiotype defined by 1F7 are dominant in HIV-1 infection and are also found on many broadly neutralizing antibodies against HIV-1. This regulatory idiotypic axis offers opportunities for exploitation in vaccine development for HIV-1, HCV, and other chronic viral infections.

Nef Proteins from HIV-1 Elite Controllers Are Inefficient at Preventing Antibody-Dependent Cellular Cytotoxicity

Impairment of Nef function, including reduced CD4 downregulation, was described in a subset of HIV-1-infected individuals that control viral replication without antiretroviral treatment (elite controllers [EC]). Elimination of HIV-1-infected cells by antibody-dependent cellular cytotoxicity (ADCC) requires the presence of envelope glycoproteins (Env) in the CD4-bound conformation, raising the possibility that accumulating CD4 at the surface of virus-infected cells in EC could interact with Env and thereby sensitize these cells to ADCC. We observed a significant increase in the exposure of Env epitopes targeted by ADCC-mediating antibodies at the surface of cells expressing Nef isolates from EC; this correlated with enhanced susceptibility to ADCC. Altogether, our results suggest that enhanced susceptibility of HIV-1-infected cells to ADCC may contribute to the EC phenotype.

IMPORTANCE

Nef clones derived from elite controllers (EC) have been shown to be attenuated for CD4 downregulation; how this contributes to the nonprogressor phenotype of these infected individuals remains uncertain. Increasing evidence supports a role for HIV-specific antibody-dependent cellular cytotoxicity (ADCC) in controlling viral infection and replication. Here, we show that residual CD4 left at the surface of cells expressing Nef proteins isolated from ECs are sufficient to allow Env-CD4 interaction, leading to increased exposure of Env CD4-induced epitopes and increased susceptibility of infected cells to ADCC. Our results suggest that ADCC might be an active immune mechanism in EC that helps to maintain durable suppression of viral replication and low plasma viremia level in this rare subset of infected individuals. Therefore, targeting Nef's ability to downregulate CD4 could render HIV-1-infected cells susceptible to ADCC and thus have therapeutic utility.

Antigen-specific NK cell memory in rhesus macaques

Natural killer (NK) cells have traditionally been considered nonspecific components of innate immunity, but recent studies have shown features of antigen-specific memory in mouse NK cells. However, it has remained unclear whether this phenomenon also exists in primates. We found that splenic and hepatic NK cells from SHIV(SF162P3)-infected and SIV(mac251)-infected macaques specifically lysed Gag- and Env-pulsed dendritic cells in an NKG2-dependent fashion, in contrast to NK cells from uninfected macaques. Moreover, splenic and hepatic NK cells from Ad26-vaccinated macaques efficiently lysed antigen-matched but not antigen-mismatched targets 5 years after vaccination. These data demonstrate that robust, durable, antigen-specific NK cell memory can be induced in primates after both infection and vaccination, and this finding could be important for the development of vaccines against HIV-1 and other pathogens.

Cocrystal Structures of Antibody N60-i3 and Antibody JR4 in Complex with gp120 Define More Cluster A Epitopes Involved in Effective Antibody-Dependent Effector Function against HIV-1

Accumulating evidence indicates a role for Fc receptor (FcR)-mediated effector functions of antibodies, including antibody-dependent cell-mediated cytotoxicity (ADCC), in prevention of human immunodeficiency virus type 1 (HIV-1) acquisition and in postinfection control of viremia. Consequently, an understanding of the molecular basis for Env epitopes that constitute effective ADCC targets is of fundamental interest for humoral anti-HIV-1 immunity and for HIV-1 vaccine design. A substantial portion of FcR effector function of potentially protective anti-HIV-1 antibodies is directed toward nonneutralizing, transitional, CD4-inducible (CD4i) epitopes associated with the gp41-reactive region of gp120 (cluster A epitopes). Our previous studies defined the A32-like epitope within the cluster A region and mapped it to the highly conserved and mobile layers 1 and 2 of the gp120 inner domain within the C1-C2 regions of gp120. Here, we elucidate additional cluster A epitope structures, including an A32-like epitope, recognized by human monoclonal antibody (MAb) N60-i3, and a hybrid A32-C11-like epitope, recognized by rhesus macaque MAb JR4. These studies define for the first time a hybrid A32-C11-like epitope and map it to elements of both the A32-like subregion and the seven-layered β-sheet of the gp41-interactive region of gp120. These studies provide additional evidence that effective antibody-dependent effector function in the cluster A region depends on precise epitope targeting--a combination of epitope footprint and mode of antibody attachment. All together these findings help further an understanding of how cluster A epitopes are targeted by humoral responses.

IMPORTANCE

HIV/AIDS has claimed the lives of over 30 million people. Although antiretroviral drugs can control viral replication, no vaccine has yet been developed to prevent the spread of the disease. Studies of natural HIV-1 infection, simian immunodeficiency virus (SIV)- or simian-human immunodeficiency virus (SHIV)-infected nonhuman primates (NHPs), and HIV-1-infected humanized mouse models, passive transfer studies in infants born to HIV-infected mothers, and the RV144 clinical trial have linked FcR-mediated effector functions of anti-HIV-1 antibodies with postinfection control of viremia and/or blocking viral acquisition. With this report we provide additional definition of the molecular determinants for Env antigen engagement which lead to effective antibody-dependent effector function directed to the nonneutralizing CD4-dependent epitopes in the gp41-reactive region of gp120. These findings have important implications for the development of an effective HIV-1 vaccine.

Envelope Glycoprotein Internalization Protects Human and Simian Immunodeficiency Virus-Infected Cells from Antibody-Dependent Cell-Mediated Cytotoxicity

The cytoplasmic tails of human and simian immunodeficiency virus (HIV and SIV, respectively) envelope glycoproteins contain a highly conserved, membrane-proximal endocytosis motif that prevents the accumulation of Env on the surface of infected cells prior to virus assembly. Using an assay designed to measure the killing of virus-infected cells by antibody-dependent cell-mediated cytotoxicity (ADCC), we show that substitutions in this motif increase the susceptibility of HIV-1- and SIV-infected cells to ADCC in a manner that directly correlates with elevated Env levels on the surface of virus-infected cells. In the case of HIV-1, this effect is additive with a deletion in vpu recently shown to enhance the susceptibility of HIV-1-infected cells to ADCC as a result of tetherin-mediated retention of budding virions on the cell surface. These results reveal a previously unappreciated role for the membrane-proximal endocytosis motif of gp41 in protecting HIV-1- and SIV-infected cells from antibody responses by regulating the amount of Env present on the cell surface.

IMPORTANCE

This study reveals an unappreciated role for the membrane-proximal endocytosis motif of gp41 in protecting HIV-1- and SIV-infected cells from elimination by Env-specific antibodies. Thus, strategies designed to interfere with this mechanism of Env internalization may improve the efficacy of antibody-based vaccines and antiretroviral therapies designed to enhance the immunological control of HIV-1 replication in chronically infected individuals.

Imaging of Cell-Cell Communication in a Vertical Orientation Reveals High-Resolution Structure of Immunological Synapse and Novel PD-1 Dynamics

The immunological synapse (IS) is one of the most pivotal communication strategies in immune cells. Understanding the molecular basis of the IS provides critical information regarding how immune cells mount an effective immune response. Fluorescence microscopy provides a fundamental tool to study the IS. However, current imaging techniques for studying the IS cannot sufficiently achieve high resolution in real cell-cell conjugates. In this study, we present a new device that allows for high-resolution imaging of the IS with conventional confocal microscopy in a high-throughput manner. Combining micropits and single-cell trap arrays, we have developed a new microfluidic platform that allows visualization of the IS in vertically "stacked" cells. Using this vertical cell pairing (VCP) system, we investigated the dynamics of the inhibitory synapse mediated by an inhibitory receptor, programed death protein-1, and the cytotoxic synapse at the single-cell level. In addition to the technique innovation, we have demonstrated novel biological findings by this VCP device, including novel distribution of F-actin and cytolytic granules at the IS, programed death protein-1 microclusters at the NK IS, and kinetics of cytotoxicity. We propose that this high-throughput, cost-effective, easy-to-use VCP system, along with conventional imaging techniques, can be used to address a number of significant biological questions in a variety of disciplines.

AAV-Delivered Antibody Mediates Significant Protective Effects against SIVmac239 Challenge in the Absence of Neutralizing Activity

Long-term delivery of potent broadly-neutralizing antibodies is a promising approach for the prevention of HIV-1 infection. We used AAV vector intramuscularly to deliver anti-SIV monoclonal antibodies (mAbs) in IgG1 form to rhesus monkeys. Persisting levels of delivered mAb as high as 270 μg/ml were achieved. However, host antibody responses to the delivered antibody were observed in 9 of the 12 monkeys and these appeared to limit the concentration of delivered antibody that could be achieved. This is reflected in the wide range of delivered mAb concentrations that were achieved: 1-270 μg/ml. Following repeated, marginal dose, intravenous challenge with the difficult-to-neutralize SIVmac239, the six monkeys in the AAV-5L7 IgG1 mAb group showed clear protective effects despite the absence of detectable neutralizing activity against the challenge virus. The protective effects included: lowering of viral load at peak height; lowering of viral load at set point; delay in the time to peak viral load from the time of the infectious virus exposure. All of these effects were statistically significant. In addition, the monkey with the highest level of delivered 5L7 mAb completely resisted six successive SIVmac239 i.v. challenges, including a final challenge with a dose of 10 i.v. infectious units. Our results demonstrate the continued promise of this approach for the prevention of HIV-1 infection in people. However, the problem of anti-antibody responses will need to be understood and overcome for the promise of this approach to be effectively realized.

Natural killer cell education does not affect the magnitude of granzyme B delivery to target cells by antibody-dependent cellular cytotoxicity

OBJECTIVE

Interest in the role of antibody-dependent cellular cytotoxicity (ADCC) in protection from HIV infection has grown since analyses of the RV144 HIV vaccine trial results found ADCC correlated with protection. Natural killer (NK) cells are among the effector cells that mediate ADCC. The level of antibody-induced NK cell activation depends on NK cell education through inhibitory NK cell receptor human leukocyte antigen (HLA) ligand interactions. Here, we investigated the impact of NK cell education on the delivery of Granzyme B (GzB) to target cells.

DESIGN

Lymphocytes from 50 HIV-uninfected [30 Bw4 (Bw4) and 20 Bw4 (Bw6)] KIR3DL1 homozygote persons were used as effectors and cocultured with gp120-coated target cells in the presence of a single source of anti-HIV gp120 antibody to ascertain whether NK cell education status influenced the level of GzB delivered to target cells.

METHODS

The GTL assay assessed the frequency of GzB-positive (%GzB) CEM.NKr.CCR5 target cells generated by effectors from each individual. The frequency of CD107a, interferon (IFN)-γ and CCL4 NK cells was assessed as a measure of antibody-induced NK cell activation.

RESULTS

KIR3DL1 NK cells from the Bw4 group were more functional than KIR3DL1 NK cells. Despite this, the %GzB target cells generated in the GTL assay did not differ according to the KIR3DL1-HLA-B genotype of the effector cells. The %GzB cells positively correlated with the frequency of CD16KIR3DL1 NK cells in the effector population.

CONCLUSION

ADCC potency does not depend on NK cell education.

Development of IgG Mediated Antibody Dependent Cell-mediated Cytotoxicity (ADCC) in the Serum and Genital Mucosa of HIV Seroconverters

Background

We measured antibody-dependent cell mediated cytotoxicity (ADCC) activity in serum and genital fluids of heterosexually exposed women during HIV seroconversion.

Methods

Plasma and cervico-vaginal lavage (CVL) fluid from 11 seroconverters (SC) were analyzed biannually from one year pre- to 6 year post-seroconversion using a ⁵¹Cr-release assay to measure HIV-1 gp120 specific ADCC.

Results

No SC had significant HIV specific CVL ADCC activity before seroconversion or until 1.5 yr after seroconversion. One individual had a %Specific Release (SR) of 25.4 at 2 years, 26.7 at 3 years and 21.0 at 4 years after seroconversion in CVL. Another sample had 4.7% SR at 2 years, 5.3 at 3 years, 10.9 at 4 years, and 8.4 at 5 years after seroconversion in CVL. A third had no activity until 17% SR 5 years after seroconversion in CVL. A fourth showed activity of 36.5% SR at 6.5 years after seroconversion. Seven women had no ADCC activity in their CVL. Paired serum samples showed HIV specific ADCC activity prior to the appearance of CVL ADCC activity.

Conclusions

HIV specific ADCC activity in CVL rose 2 years after seroconversion; ADCC was present in the serum prior to this time. These data suggest that genital tract ADCC activity is not present until well after acute infection.

Imaging of Cell-Cell Communication in a Vertical Orientation Reveals High-Resolution Structure of Immunological Synapse and Novel PD-1 Dynamics

The immunological synapse (IS) is one of the most pivotal communication strategies in immune cells. Understanding the molecular basis of the IS provides critical information regarding how immune cells mount an effective immune response. Fluorescence microscopy provides a fundamental tool to study the IS. However, current imaging techniques for studying the IS cannot sufficiently achieve high resolution in real cell-cell conjugates. In this study, we present a new device that allows for high-resolution imaging of the IS with conventional confocal microscopy in a high-throughput manner. Combining micropits and single-cell trap arrays, we have developed a new microfluidic platform that allows visualization of the IS in vertically "stacked" cells. Using this vertical cell pairing (VCP) system, we investigated the dynamics of the inhibitory synapse mediated by an inhibitory receptor, programed death protein-1, and the cytotoxic synapse at the single-cell level. In addition to the technique innovation, we have demonstrated novel biological findings by this VCP device, including novel distribution of F-actin and cytolytic granules at the IS, programed death protein-1 microclusters at the NK IS, and kinetics of cytotoxicity. We propose that this high-throughput, cost-effective, easy-to-use VCP system, along with conventional imaging techniques, can be used to address a number of significant biological questions in a variety of disciplines.

Phenotypical and functional profiles of natural killer cells exhibiting matrix metalloproteinase-mediated CD16 cleavage after anti-HIV antibody-dependent activation

Natural killer (NK) cell-mediated antibody-dependent cellular cytotoxicity (ADCC) has been linked to protection from HIV infection and slower progression towards AIDS. However, antibody-dependent activation of NK cells results in phenotypical alterations similar to those observed on NK cells from individuals with progressive HIV infection. Activation of NK cells induces matrix metalloproteinase (MMP)-mediated cleavage of cell surface CD16. In the present study we assessed the phenotype and functional profile of NK cells exhibiting post-activation MMP-mediated CD16 cleavage. We found that NK cells achieving the highest levels of activation during stimulation exhibit the most profound decreases in CD16 expression. Further, we observed that educated KIR3DL1(+) NK cells from human leucocyte antigen (HLA)-Bw4-carrying donors exhibit larger decreases in CD16 expression post-activation than the KIR3DL1(-) NK cell subset containing cells educated via other inhibitory receptor/ligand combinations and non-educated NK cells. Lastly, we assessed the ex-vivo expression of CD16 on educated KIR3DL1(+) NK cells and the KIR3DL1(-) NK cell subset from HLA-Bw4-carrying HIV-uninfected and HIV-infected donors. Suggestive of in-vivo activation of KIR3DL1(+) NK cells during HIV infection, CD16 expression was higher on KIR3DL1(+) than KIR3DL1(-) NK cells in uninfected donors but similar on both subsets in HIV-infected donors. These results are discussed in the context of how they may assist with understanding HIV disease progression and the design of immunotherapies that utilize antibody-dependent NK cell responses.

CD4 mimetics sensitize HIV-1-infected cells to ADCC

HIV-1-infected cells presenting envelope glycoproteins (Env) in the CD4-bound conformation on their surface are preferentially targeted by antibody-dependent cell-mediated cytotoxicity (ADCC). HIV-1 has evolved a sophisticated mechanism to avoid exposure of ADCC-mediating Env epitopes by down-regulating CD4 and by limiting the overall amount of Env at the cell surface. Here we report that small-molecule CD4-mimetic compounds induce the CD4-bound conformation of Env, and thereby sensitize cells infected with primary HIV-1 isolates to ADCC mediated by antibodies present in sera, cervicovaginal lavages, and breast milk from HIV-1-infected individuals. Importantly, we identified one CD4 mimetic with the capacity to sensitize endogenously infected ex vivo-amplified primary CD4 T cells to ADCC killing mediated by autologous sera and effector cells. Thus, CD4 mimetics hold the promise of therapeutic utility in preventing and controlling HIV-1 infection.

Potent functional antibody responses elicited by HIV-I DNA priming and boosting with heterologous HIV-1 recombinant MVA in healthy Tanzanian adults

Vaccine-induced HIV antibodies were evaluated in serum samples collected from healthy Tanzanian volunteers participating in a phase I/II placebo-controlled double blind trial using multi-clade, multigene HIV-DNA priming and recombinant modified vaccinia Ankara (HIV-MVA) virus boosting (HIVIS03). The HIV-DNA vaccine contained plasmids expressing HIV-1 gp160 subtypes A, B, C, Rev B, Gag A, B and RTmut B, and the recombinant HIV-MVA boost expressed CRF01_AE HIV-1 Env subtype E and Gag-Pol subtype A. While no neutralizing antibodies were detected using pseudoviruses in the TZM-bl cell assay, this prime-boost vaccination induced neutralizing antibodies in 83% of HIVIS03 vaccinees when a peripheral blood mononuclear cell (PBMC) assay using luciferase reporter-infectious molecular clones (LucR-IMC) was employed. The serum neutralizing activity was significantly (but not completely) reduced upon depletion of natural killer (NK) cells from PBMC (p=0.006), indicating a role for antibody-mediated Fcγ-receptor function. High levels of antibody-dependent cellular cytotoxicity (ADCC)-mediating antibodies against CRF01_AE and/or subtype B were subsequently demonstrated in 97% of the sera of vaccinees. The magnitude of ADCC-mediating antibodies against CM235 CRF01_AE IMC-infected cells correlated with neutralizing antibodies against CM235 in the IMC/PBMC assay. In conclusion, HIV-DNA priming, followed by two HIV-MVA boosts elicited potent ADCC responses in a high proportion of Tanzanian vaccinees. Our findings highlight the potential of HIV-DNA prime HIV-MVA boost vaccines for induction of functional antibody responses and suggest this vaccine regimen and ADCC studies as potentially important new avenues in HIV vaccine development.

A novel non-integrative single-cycle chimeric HIV lentivector DNA vaccine

Novel HIV vaccine vectors and strategies are needed to control HIV/AIDS epidemic in humans and eradicate the infection. DNA vaccines alone failed to induce immune responses robust enough to control HIV-1. Development of lentivirus-based DNA vaccines deficient for integration and with a limited replication capacity is an innovative and promising approach. This type of vaccine mimics the early stages of virus infection/replication like the live-attenuated viruses but lacks the inconvenient integration and persistence associated with disease. We developed a novel lentivector DNA vaccine "CAL-SHIV-IN(-)" that undergoes a single round of replication in the absence of integration resulting in augmented expression of vaccine antigens in vivo. Vaccine gene expression is under control of the LTRs of a naturally attenuated lentivirus, Caprine arthritis encephalitis virus (CAEV) the natural goat lentivirus. The safety of this vaccine prototype was increased by the removal of the integrase coding sequences from the pol gene. We examined the functional properties of this lentivector DNA in cell culture and the immunogenicity in mouse models. Viral proteins were expressed in transfected cells, assembled into viral particles that were able to transduce once target permissive cells. Unlike the parental replication-competent SHIV-KU2 that was detected in DNA samples from any of the serial passage infected cells, CAL-SHIV-IN(-) DNA was detected only in target cells of the first round of infection, hence demonstrating the single cycle replication of the vaccine. A single dose DNA immunization of humanized NOD/SCID/β2 mice showed a substantial increase of IFN-γ-ELISPOT in splenocytes compared to the former replication and integration defective Δ4SHIV-KU2 DNA vaccine.

Antigenic properties of the human immunodeficiency virus envelope glycoprotein gp120 on virions bound to target cells

The HIV-1 envelope glycoprotein, gp120, undergoes multiple molecular interactions and structural rearrangements during the course of host cell attachment and viral entry, which are being increasingly defined at the atomic level using isolated proteins. In comparison, antigenic markers of these dynamic changes are essentially unknown for single HIV-1 particles bound to target cells. Such markers should indicate how neutralizing and/or non-neutralizing antibodies might interdict infection by either blocking infection or sensitizing host cells for elimination by Fc-mediated effector function. Here we address this deficit by imaging fluorescently labeled CCR5-tropic HIV-1 pseudoviruses using confocal and superresolution microscopy to track the exposure of neutralizing and non-neutralizing epitopes as they appear on single HIV-1 particles bound to target cells. Epitope exposure was followed under conditions permissive or non-permissive for viral entry to delimit changes associated with virion binding from those associated with post-attachment events. We find that a previously unexpected array of gp120 epitopes is exposed rapidly upon target cell binding. This array comprises both neutralizing and non-neutralizing epitopes, the latter being hidden on free virions yet capable of serving as potent targets for Fc-mediated effector function. Under non-permissive conditions for viral entry, both neutralizing and non-neutralizing epitope exposures were relatively static over time for the majority of bound virions. Under entry-permissive conditions, epitope exposure patterns changed over time on subsets of virions that exhibited concurrent variations in virion contents. These studies reveal that bound virions are distinguished by a broad array of both neutralizing and non-neutralizing gp120 epitopes that potentially sensitize a freshly engaged target cell for destruction by Fc-mediated effector function and/or for direct neutralization at a post-binding step. The elucidation of these epitope exposure patterns during viral entry will help clarify antibody-mediated inhibition of HIV-1 as it is measured in vitro and in vivo.

A major strategy for blocking HIV-1 infection is to target antiviral antibodies or drugs to sites of vulnerability on the surface proteins of the virus. It is a relatively straightforward matter to explore these sites on the surfaces of free HIV-1 particles or on isolated viral envelope antigens. However, one difficulty presented by HIV-1 is that its surface proteins are flexible and change shape once the virus has attached to its host cell. To date, it has been difficult to predict how cell-bound HIV-1 exposes its sites of vulnerability. Yet the antiviral activities of certain antibodies indirectly suggest that there must be unique sites on cell-bound HIV-1 that are not found on free virus. Here, we use new techniques and tools to determine how HIV-1 exposes unique sites of vulnerability after attaching to host cells. We find that the virus exposes a remarkable array of these sites, including ones previously believed hidden. These exposure patterns explain the antiviral activities of various anti-HIV-1 antibodies and provide a new view of how HIV-1 might interact with the immune system. Our study also provides insights for how to target HIV-1 with antiviral antibodies, vaccines, or antiviral agents.

Primate immune responses to HIV-1 Env formulated in the saponin-based adjuvant AbISCO-100 in the presence or absence of TLR9 co-stimulation

Protein-based vaccines require adjuvants to achieve optimal responses. Toll-like receptor (TLR) 9 agonists were previously shown to improve responses to protein-based vaccines, such as the Hepatitis B virus vaccine formulated in alum. Here, we used CpG-C together with the clinically relevant saponin-based adjuvant AbISCO-100/Matrix-M (AbISCO), to assess if TLR9 co-stimulation would quantitatively or qualitatively modulate HIV-1 envelope glycoprotein (Env)-specific B and T cell responses in rhesus macaques. The macaques were inoculated with soluble Env trimers in AbISCO, with or without the addition of CpG-C, using an interval similar to the Hepatitis B virus vaccine. Following a comprehensive evaluation of antigen-specific responses in multiple immune compartments, we show that the Env-specific circulating IgG, memory B cells and plasma cells displayed similar kinetics and magnitude in the presence or absence of CpG-C and that there was no apparent difference between the two groups in the elicited HIV-1 neutralizing antibody titers or antigen-specific CD4+ T cell responses. Importantly, the control of SHIV viremia was significantly improved in animals from both Env-immunized groups relative to adjuvant alone controls, demonstrating the potential of AbISCO to act as a stand-alone adjuvant for Env-based vaccines.

AAV-expressed eCD4-Ig provides durable protection from multiple SHIV challenges

Long-term in vivo expression of a broad and potent entry inhibitor could circumvent the need for a conventional vaccine for HIV-1. Adeno-associated virus (AAV) vectors can stably express HIV-1 broadly neutralizing antibodies (bNAbs). However, even the best bNAbs neutralize 10-50% of HIV-1 isolates inefficiently (80% inhibitory concentration (IC80) > 5 μg ml(-1)), suggesting that high concentrations of these antibodies would be necessary to achieve general protection. Here we show that eCD4-Ig, a fusion of CD4-Ig with a small CCR5-mimetic sulfopeptide, binds avidly and cooperatively to the HIV-1 envelope glycoprotein (Env) and is more potent than the best bNAbs (geometric mean half-maximum inhibitory concentration (IC50) < 0.05 μg ml(-1)). Because eCD4-Ig binds only conserved regions of Env, it is also much broader than any bNAb. For example, eCD4-Ig efficiently neutralized 100% of a diverse panel of neutralization-resistant HIV-1, HIV-2 and simian immunodeficiency virus isolates, including a comprehensive set of isolates resistant to the CD4-binding site bNAbs VRC01, NIH45-46 and 3BNC117. Rhesus macaques inoculated with an AAV vector stably expressed 17-77 μg ml(-1) of fully functional rhesus eCD4-Ig for more than 40 weeks, and these macaques were protected from several infectious challenges with SHIV-AD8. Rhesus eCD4-Ig was also markedly less immunogenic than rhesus forms of four well-characterized bNAbs. Our data suggest that AAV-delivered eCD4-Ig can function like an effective HIV-1 vaccine.

Molecular mechanisms of functional natural killer deficiency in patients with partial DiGeorge syndrome

BACKGROUND

DiGeorge syndrome affects more than 3.5 million persons worldwide. Partial DiGeorge syndrome (pDGS), which is characterized by a number of gene deletions in chromosome 22, including the chicken tumor virus number 10 regulator of kinase (Crk)-like (CrkL) gene, is one of the most common genetic disorders in human subjects. To date, the role of natural killer (NK) cells in patients with pDGS remains unclear.

OBJECTIVE

We sought to define the effect of pDGS-related Crk haploinsufficiency on NK cell activation and cytotoxic immunological synapse (IS) structure and function.

METHODS

Inducible CrkL-silenced NK cells were used to recapitulate the pDGS, CrkL-haploinsufficient phenotype. Findings were validated by using NK cells from patients with actual pDGS. Ultimately, deficits in the function of NK cells from patients with pDGS were restored by lentiviral transduction of CrkL.

RESULTS

Silencing of CrkL expression inhibits NK cell function. Specifically, pDGS haploinsufficiency of CrkL inhibits accumulation of activating receptors, polarization of cytolytic machinery and key signaling molecules, and activation of β2-integrin at the IS. Reintroduction of CrkL protein restores NK cell cytotoxicity.

CONCLUSION

CrkL haploinsufficiency causes functional NK deficits in patients with pDGS by disrupting both β2-integrin activation and activating receptor accumulation at the IS. Our results suggest that NK cell IS quality can directly affect immune status, providing a potential target for diagnosis and therapeutic manipulation in patients with pDGS and in other patients with functional NK cell deficiencies.

CD8 T cell response maturation defined by anentropic specificity and repertoire depth correlates with SIVΔnef-induced protection

The live attenuated simian immunodeficiency virus (LASIV) vaccine SIVΔnef is one of the most effective vaccines in inducing protection against wild-type lentiviral challenge, yet little is known about the mechanisms underlying its remarkable protective efficacy. Here, we exploit deep sequencing technology and comprehensive CD8 T cell epitope mapping to deconstruct the CD8 T cell response, to identify the regions of immune pressure and viral escape, and to delineate the effect of epitope escape on the evolution of the CD8 T cell response in SIVΔnef-vaccinated animals. We demonstrate that the initial CD8 T cell response in the acute phase of SIVΔnef infection is mounted predominantly against more variable epitopes, followed by widespread sequence evolution and viral escape. Furthermore, we show that epitope escape expands the CD8 T cell repertoire that targets highly conserved epitopes, defined as anentropic specificity, and generates de novo responses to the escaped epitope variants during the vaccination period. These results correlate SIVΔnef-induced protection with expanded anentropic specificity and increased response depth. Importantly, these findings render SIVΔnef, long the gold standard in HIV/SIV vaccine research, as a proof-of-concept vaccine that highlights the significance of the twin principles of anentropic specificity and repertoire depth in successful vaccine design.

The role of HIV-specific antibody-dependent cellular cytotoxicity in HIV prevention and the influence of the HIV-1 Vpu protein

There is growing interest in the role of anti-HIV antibody-dependent cellular cytotoxicity (ADCC) antibodies in the prevention and control of HIV infection. Passive transfer studies in macaques support a role for the Fc region of antibodies in assisting in the prevention of simian-human immunodeficiency virus (SHIV) infection. The Thai RV144 HIV-1 vaccine trial induced anti-HIV ADCC antibodies that may have played a role in the partial protection observed. Several observational studies support a role for ADCC antibodies in slowing HIV disease progression. However, HIV evolves to escape ADCC antibodies and chronic HIV infections causes dysfunction of effector cells such as natural killer (NK) cells that mediate the ADCC functions. Further, four recent studies show that the HIV-1 Vpu protein, by promoting release of virions, reduces the capacity of ADCC antibodies to recognize HIV-infected cells. The review dissects some of the recent research on HIV-specific ADCC antibodies and discusses mechanisms to further harness ADCC antibodies in the prevention and control of HIV infection.