Replication competent molecular clones of HIV-1 expressing Renilla luciferase facilitate the analysis of antibody inhibition in PBMC

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.

HIV-1-Specific IgA Monoclonal Antibodies from an HIV-1 Vaccinee Mediate Galactosylceramide Blocking and Phagocytosis

Vaccine-elicited humoral immune responses comprise an array of antibody forms and specificities, with only a fraction contributing to protective host immunity. Elucidation of antibody effector functions responsible for protective immunity against human immunodeficiency virus type 1 (HIV-1) acquisition is a major goal for the HIV-1 vaccine field. Immunoglobulin A (IgA) is an important part of the host defense against pathogens; however, little is known about the role of vaccine-elicited IgA and its capacity to mediate antiviral functions. To identify the antiviral functions of HIV-1-specific IgA elicited by vaccination, we cloned HIV-1 envelope-specific IgA monoclonal antibodies (MAbs) by memory B cell cultures from peripheral blood mononuclear cells from an RV144 vaccinee and produced two IgA clonal cell lines (HG129 and HG130) producing native, nonrecombinant IgA MAbs. The HG129 and HG130 MAbs mediated phagocytosis by monocytes, and HG129 blocked HIV-1 Env glycoprotein binding to galactosylceramide, an alternative HIV-1 receptor. These findings elucidate potential antiviral functions of vaccine-elicited HIV-1 envelope-specific IgA that may act to block HIV-1 acquisition at the portal of entry by preventing HIV-1 binding to galactosylceramide and mediating antibody Fc receptor-mediated virion phagocytosis. Furthermore, these findings highlight the complex and diverse interactions of vaccine-elicited IgA with pathogens that depend on IgA fine specificity and form (e.g., multimeric or monomeric) in the systemic circulation and mucosal compartments.

IMPORTANCE Host-pathogen interactions in vivo involve numerous immune mechanisms that can lead to pathogen clearance. Understanding the nature of antiviral immune mechanisms can inform the design of efficacious HIV-1 vaccine strategies. Evidence suggests that both neutralizing and nonneutralizing antibodies can mediate some protection against HIV in animal models. Although numerous studies have characterized the functional properties of HIV-1-specific IgG, more studies are needed on the functional attributes of HIV-1-specific IgA, specifically for vaccine-elicited IgA. Characterization of the functional properties of HIV-1 Env-specific IgA monoclonal antibodies from human vaccine clinical trials are critical toward understanding the capacity of the host immune response to block HIV-1 acquisition.

Predominant envelope variable loop 2-specific and gp120-specific antibody-dependent cellular cytotoxicity antibody responses in acutely SIV-infected African green monkeys

Background

The initial envelope (Env)-specific antibody response in acutely HIV-1-infected individuals and simian immunodeficiency virus (SIV)-infected rhesus monkeys (RMs) is dominated by non-neutralizing antibodies targeting Env gp41. In contrast, natural primate SIV hosts, such as African green monkeys (AGMs), develop a predominant Env gp120-specific antibody response to SIV infection. However, the fine-epitope specificity and function of SIV Env-specific plasma IgG, and their potential role on autologous virus co-evolution in SIV-infected AGMs and RMs remain unclear.

Results

Unlike the dominant linear gp41-specific IgG responses in RMs, SIV-infected AGMs demonstrated a unique linear variable loop 2 (V2)-specific plasma IgG response that arose concurrently with high gp120-directed antibody-dependent cellular cytotoxicity (ADCC) activity, and SIVsab-infected cell binding responses during acute infection. Moreover, SIV variants isolated from SIV-infected AGMs exhibited high amino acid mutation frequencies within the Env V1V2 loop compared to those of RMs. Notably, the linear V2-specific IgG epitope in AGMs overlaps with an analogous region of the HIV V2 loop containing the K169 mutation epitope identified in breakthrough viruses from RV144 vaccinees.

Conclusion

Vaccine-elicited Env V2-specific IgG responses have been proposed as an immune correlate of reduced risk in HIV-1/SIV acquisition in humans and RMs. Yet the pathways to elicit these potentially-protective V2-specific IgG responses remain unclear. In this study, we demonstrate that SIV-infected AGMs, which are the natural hosts of SIV, exhibited high plasma linear V2-specific IgG binding responses that arose concurrently with SIV Env gp120-directed ADCC-mediating, and SIV-infected cell plasma IgG binding responses during acute SIV infection, which were not present in acutely SIV-infected RMs. The linear V2-specific antibody response in AGMs targets an overlapping epitope of the proposed site of vaccine-induced immune pressure defined in the moderately protective RV144 HIV-1 vaccine trial. Identifying host factors that control the early elicitation of Env V2-specific IgG and ADCC antibody responses in these natural SIV hosts could inform vaccination strategies aimed at rapidly inducing potentially-protective HIV-1 Env-specific responses in humans.

Electronic supplementary material

The online version of this article (10.1186/s12977-018-0406-5) contains supplementary material, which is available to authorized users.

Neutralizing Activity of Broadly Neutralizing Anti-HIV-1 Antibodies against Clade B Clinical Isolates Produced in Peripheral Blood Mononuclear Cells

Recently discovered broadly neutralizing antibodies (bNAbs) against HIV-1 demonstrate extensive breadth and potency against diverse HIV-1 strains and represent a promising approach for the treatment and prevention of HIV-1 infection. The breadth and potency of these antibodies have primarily been evaluated by using panels of HIV-1 Env-pseudotyped viruses produced in 293T cells expressing molecularly cloned Env proteins. Here we report on the ability of five bNAbs currently in clinical development to neutralize circulating primary HIV-1 isolates derived from peripheral blood mononuclear cells (PBMCs) and compare the results to those obtained with the pseudovirus panels used to characterize the bNAbs. The five bNAbs demonstrated significantly less breadth and potency against clinical isolates produced in PBMCs than against Env-pseudotyped viruses. The magnitude of this difference in neutralizing activity varied, depending on the antibody epitope. Glycan-targeting antibodies showed differences of only 3- to 4-fold, while antibody 10E8, which targets the membrane-proximal external region, showed a nearly 100-fold decrease in activity between published Env-pseudotyped virus panels and PBMC-derived primary isolates. Utilizing clonal PBMC-derived primary isolates and molecular clones, we determined that the observed discrepancy in bNAb performance is due to the increased sensitivity to neutralization exhibited by 293T-produced Env-pseudotyped viruses. We also found that while full-length molecularly cloned viruses produced in 293T cells exhibit greater sensitivity to neutralization than PBMC-derived viruses do, Env-pseudotyped viruses produced in 293T cells generally exhibit even greater sensitivity to neutralization. As the clinical development of bNAbs progresses, it will be critical to determine the relevance of each of these in vitro neutralization assays to in vivo antibody performance.

IMPORTANCE Novel therapeutic and preventive strategies are needed to contain the HIV-1 epidemic. Antibodies with exceptional neutralizing activity against HIV-1 may provide several advantages to traditional HIV drugs, including an improved side-effect profile, a reduced dosing frequency, and immune enhancement. The activity of these antibodies has been established in vitro by utilizing HIV-1 Env-pseudotyped viruses derived from circulating viruses but produced in 293T cells by pairing Env proteins with a backbone vector. We tested PBMC-produced circulating viruses against five anti-HIV-1 antibodies currently in clinical development. We found that the activity of these antibodies against PBMC isolates is significantly less than that against 293T Env-pseudotyped viruses. This decline varied among the antibodies tested, with some demonstrating moderate reductions in activity and others showing an almost 100-fold reduction. As the development of these antibodies progresses, it will be critical to determine how the results of different in vitro tests correspond to performance in the clinic.

Tetraspanin blockage reduces exosome-mediated HIV-1 entry

HIV-1 is one of the most studied retroviruses. The role of exosomes in HIV-1 entry and pathogenesis are beginning to be appreciated. Exosomes can incorporate host proteins that are also contained in viruses (e.g., tetraspanins).

Intradermal HIV-1 DNA Immunization Using Needle-Free Zetajet Injection Followed by HIV-Modified Vaccinia Virus Ankara Vaccination Is Safe and Immunogenic in Mozambican Young Adults: A Phase I Randomized Controlled Trial

We assessed the safety and immunogenicity of HIV-DNA priming using Zetajet™, a needle-free device intradermally followed by intramuscular HIV-MVA boosts, in 24 healthy Mozambicans. Volunteers were randomized to receive three immunizations of 600 μg (n = 10; 2 × 0.1 ml) or 1,200 μg (n = 10; 2 × 0.2 ml) of HIV-DNA (3 mg/ml), followed by two boosts of 10⁸ pfu HIV-MVA. Four subjects received placebo saline injections. Vaccines and injections were safe and well tolerated with no difference between the two priming groups. After three HIV-DNA immunizations, IFN-γ ELISpot responses to Gag were detected in 9/17 (53%) vaccinees, while none responded to Envelope (Env). After the first HIV-MVA, the overall response rate to Gag and/or Env increased to 14/15 (93%); 14/15 (93%) to Gag and 13/15 (87%) to Env. There were no significant differences between the immunization groups in frequency of response to Gag and Env or magnitude of Gag responses. Env responses were significantly higher in the higher dose group (median 420 vs. 157.5 SFC/million peripheral blood mononuclear cell, p = .014). HIV-specific antibodies to subtype C gp140 and subtype B gp160 were elicited in all vaccinees after the second HIV-MVA, without differences in titers between the groups. Neutralizing antibody responses were not detected. Two (13%) of 16 vaccinees, one in each of the priming groups, exhibited antibodies mediating antibody-dependent cellular cytotoxicity to CRF01_AE. In conclusion, HIV-DNA vaccine delivered intradermally in volumes of 0.1-0.2 ml using Zetajet was safe and well tolerated. Priming with the 1,200 μg dose of HIV-DNA generated higher magnitudes of ELISpot responses to Env.

Maternal HIV-1 Env Vaccination for Systemic and Breast Milk Immunity To Prevent Oral SHIV Acquisition in Infant Macaques

Without novel strategies to prevent mother-to-child HIV-1 transmission, more than 5% of HIV-1-exposed infants will continue to acquire HIV-1, most through breastfeeding. This study of rhesus macaque dam-and-infant pairs is the first preclinical study to investigate the protective role of transplacentally transferred HIV-1 vaccine-elicited antibodies and HIV-1 vaccine-elicited breast milk antibody responses in infant oral virus acquisition. It revealed highly variable placental transfer of potentially protective antibodies and emphasized the importance of pregnancy immunization timing to reach peak antibody levels prior to delivery. While there was no discernible impact of maternal immunization on late infant oral virus acquisition, we observed a strong correlation between the percentage of activated CD4⁺ T cells in infant peripheral blood and a reduced number of challenges to infection. This finding highlights an important consideration for future studies evaluating alternative strategies to further reduce the vertical HIV-1 transmission risk.

Mother-to-child transmission (MTCT) of human immunodeficiency virus type 1 (HIV-1) contributes to an estimated 150,000 new infections annually. Maternal vaccination has proven safe and effective at mitigating the impact of other neonatal pathogens and is one avenue toward generating the potentially protective immune responses necessary to inhibit HIV-1 infection of infants through breastfeeding. In the present study, we tested the efficacy of a maternal vaccine regimen consisting of a modified vaccinia virus Ankara (MVA) 1086.C gp120 prime-combined intramuscular-intranasal gp120 boost administered during pregnancy and postpartum to confer passive protection on infant rhesus macaques against weekly oral exposure to subtype C simian-human immunodeficiency virus 1157ipd3N4 (SHIV1157ipd3N4) starting 6 weeks after birth. Despite eliciting a robust systemic envelope (Env)-specific IgG response, as well as durable milk IgA responses, the maternal vaccine did not have a discernible impact on infant oral SHIV acquisition. This study revealed considerable variation in vaccine-elicited IgG placental transfer and a swift decline of both Env-specific antibodies (Abs) and functional Ab responses in the infants prior to the first challenge, illustrating the importance of pregnancy immunization timing to elicit optimal systemic Ab levels at birth. Interestingly, the strongest correlation to the number of challenges required to infect the infants was the percentage of activated CD4⁺ T cells in the infant peripheral blood at the time of the first challenge. These findings suggest that, in addition to maternal immunization, interventions that limit the activation of target cells that contribute to susceptibility to oral HIV-1 acquisition independently of vaccination may be required to reduce infant HIV-1 acquisition via breastfeeding.

IMPORTANCE Without novel strategies to prevent mother-to-child HIV-1 transmission, more than 5% of HIV-1-exposed infants will continue to acquire HIV-1, most through breastfeeding. This study of rhesus macaque dam-and-infant pairs is the first preclinical study to investigate the protective role of transplacentally transferred HIV-1 vaccine-elicited antibodies and HIV-1 vaccine-elicited breast milk antibody responses in infant oral virus acquisition. It revealed highly variable placental transfer of potentially protective antibodies and emphasized the importance of pregnancy immunization timing to reach peak antibody levels prior to delivery. While there was no discernible impact of maternal immunization on late infant oral virus acquisition, we observed a strong correlation between the percentage of activated CD4⁺ T cells in infant peripheral blood and a reduced number of challenges to infection. This finding highlights an important consideration for future studies evaluating alternative strategies to further reduce the vertical HIV-1 transmission risk.

Astrocytes Resist HIV-1 Fusion but Engulf Infected Macrophage Material

HIV-1 disseminates to diverse tissues and establishes long-lived viral reservoirs. These reservoirs include the CNS, in which macrophage-lineage cells, and as suggested by many studies, astrocytes, may be infected. Here, we have investigated astrocyte infection by HIV-1. We confirm that astrocytes trap and internalize HIV-1 particles for subsequent release but find no evidence that these particles infect the cell. Astrocyte infection was not observed by cell-free or cell-to-cell routes using diverse approaches, including luciferase and GFP reporter viruses, fixed and live-cell fusion assays, multispectral flow cytometry, and super-resolution imaging. By contrast, we observed intimate interactions between HIV-1-infected macrophages and astrocytes leading to signals that might be mistaken for astrocyte infection using less stringent approaches. These results have implications for HIV-1 infection of the CNS, viral reservoir formation, and antiretroviral therapy.

Potent In Vivo NK Cell-Mediated Elimination of HIV-1-Infected Cells Mobilized by a gp120-Bispecific and Hexavalent Broadly Neutralizing Fusion Protein

Antibodies bound to human immunodeficiency virus type 1 (HIV-1) envelope protein expressed by infected cells mobilize antibody-dependent cellular cytotoxicity (ADCC) to eliminate the HIV-1-infected cells and thereby suppress HIV-1 infection and delay disease progression. Studies treating HIV-1-infected individuals with latency reactivation agents to reduce their latent HIV-1 reservoirs indicated that their HIV-1-specific immune responses were insufficient to effectively eliminate the reactivated latent HIV-1-infected T cells. Mobilization of ADCC may facilitate elimination of reactivated latent HIV-1-infected cells to deplete the HIV-1 reservoir and contribute to a functional HIV-1 cure. The most effective antibodies for controlling and eradicating HIV-1 infection would likely have the dual capacities of potently neutralizing a broad range of HIV-1 isolates and effectively mobilizing HIV-1-specific ADCC to eliminate HIV-1-infected cells. For this purpose, we constructed LSEVh-LS-F, a broadly neutralizing, defucosylated hexavalent fusion protein specific for both the CD4 and coreceptor gp120-binding sites. LSEVh-LS-F potently inhibited in vivo HIV-1 and simian-human immunodeficiency virus (SHIV) infection in humanized mouse and macaque models, respectively, including in vivo neutralization of HIV-1 strains resistant to the broadly neutralizing antibodies VRC01 and 3BNC117. We developed a novel humanized mouse model to evaluate in vivo human NK cell-mediated elimination of HIV-1-infected cells by ADCC and utilized it to demonstrate that LSEVh-LS-F rapidly mobilized NK cells to eliminate >80% of HIV-1-infected cells in vivo 1 day after its administration. The capacity of LSEVh-LS-F to eliminate HIV-1-infected cells via ADCC combined with its broad neutralization activity supports its potential use as an immunotherapeutic agent to eliminate reactivated latent cells and deplete the HIV-1 reservoir.IMPORTANCE Mobilization of antibody-dependent cellular cytotoxicity (ADCC) to eliminate reactivated latent HIV-1-infected cells is a strategy which may contribute to depleting the HIV-1 reservoir and achieving a functional HIV-1 cure. To more effectively mobilize ADCC, we designed and constructed LSEVh-LS-F, a broadly neutralizing, defucosylated hexavalent fusion protein specific for both the CD4 and coreceptor gp120-binding sites. LSEVh-LS-F potently inhibited in vivo HIV-1 and SHIV infection in humanized mouse and macaque models, respectively, including in vivo neutralization of an HIV-1 strain resistant to the broadly neutralizing antibodies VRC01 and 3BNC117. Using a novel humanized mouse model, we demonstrated that LSEVh-LS-F rapidly mobilized NK cells to eliminate >80% of HIV-1-infected cells in vivo 1 day after its administration. The capacity of LSEVh-LS-F to eliminate HIV-1-infected cells via ADCC combined with its broad neutralization activity supports its potential use as an immunotherapeutic agent to eliminate reactivated latent cells and deplete the HIV-1 reservoir.

Cooperation between Strain-Specific and Broadly Neutralizing Responses Limited Viral Escape and Prolonged the Exposure of the Broadly Neutralizing Epitope

V3-glycan-targeting broadly neutralizing antibodies (bNAbs) are a focus of HIV-1 vaccine development. Understanding the viral dynamics that stimulate the development of these antibodies can provide insights for immunogen design. We used a deep-sequencing approach, together with neutralization phenotyping, to investigate the rate and complexity of escape from V3-glycan-directed bNAbs compared to overlapping early strain-specific neutralizing antibody (ssNAb) responses to the V3/C3 region in donor CAP177. Escape from the ssNAb response occurred rapidly via an N334-to-N332 glycan switch, which took just 7.5 weeks to reach >50% frequency. In contrast, escape from the bNAbs was mediated via multiple pathways and took longer, with escape first occurring through an increase in V1 loop length, which took 46 weeks to reach 50% frequency, followed by an N332-to-N334 reversion, which took 66 weeks. Importantly, bNAb escape was incomplete, with contemporaneous neutralization observed up to 3 years postinfection. Both the ssNAb response and the bNAb response were modulated by the presence/absence of the N332 glycan, indicating an overlap between the two epitopes. Thus, selective pressure by ssNAbs to maintain the N332 glycan may have constrained the bNAb escape pathway. This slower and incomplete viral escape resulted in prolonged exposure of the bNAb epitope, which may in turn have aided the maturation of the bNAb lineage.IMPORTANCE The development of an HIV-1 vaccine is of paramount importance, and broadly neutralizing antibodies are likely to be a key component of a protective vaccine. The V3-glycan-targeting bNAb responses are among the most promising vaccine targets, as they are commonly elicited during infection. Understanding the interplay between viral evolution and the development of these antibodies provides insights that may guide immunogen design. Our work contrasted the dynamics of the early strain-specific antibodies and the later broadly neutralizing responses to a common Env target (V3C3), showing slower and more complex escape from bNAbs. Constrained bNAb escape, together with evidence of contemporaneous autologous virus neutralization, supports the proposal that prolonged exposure of the bNAb epitope enabled the maturation of the bNAb lineage.

HIV-1 Consensus Envelope-Induced Broadly Binding Antibodies

Antibodies that cross-react with multiple HIV-1 envelopes (Envs) are useful reagents for characterizing Env proteins and for soluble Env capture and purification assays. We previously reported 10 murine monoclonal antibodies induced by group M consensus Env, CON-6 immunization. Each demonstrated broad cross-reactivity to recombinant Envs. Here we characterized the Env epitopes to which they bind. Seven mapped to linear epitopes in gp120, five at the Env N-terminus, and two at the Env C-terminus. One antibody, 13D7, bound at the gp120 N-terminus (aa 30-42), reacted with HIV-1-infected CD4+ T cells, and when expressed in a human IgG1 backbone, mediated antibody-dependent cellular cytotoxicity. Antibody 18F11 bound at the gp120 C-terminus (aa 445-459) and reactivity was glycan dependent. Antibodies 13D7, 3B3, and 16H3 bound to 100 percent of HIV-1 Envs tested in ELISA and sodium dodecyl sulfate/polyacrylamide gel electrophoresis/western blot analysis. These data define the epitopes of monoclonal antibody reagents for characterization of recombinant Envs, one epitope of which is also expressed on the surface of HIV-1-infected CD4+ T cells.

Pentavalent HIV-1 vaccine protects against simian-human immunodeficiency virus challenge

The RV144 Thai trial HIV-1 vaccine of recombinant poxvirus (ALVAC) and recombinant HIV-1 gp120 subtype B/subtype E (B/E) proteins demonstrated 31% vaccine efficacy. Here we design an ALVAC/Pentavalent B/E/E/E/E vaccine to increase the diversity of gp120 motifs in the immunogen to elicit a broader antibody response and enhance protection. We find that immunization of rhesus macaques with the pentavalent vaccine results in protection of 55% of pentavalent-vaccine-immunized macaques from simian–human immunodeficiency virus (SHIV) challenge. Systems serology of the antibody responses identifies plasma antibody binding to HIV-infected cells, peak ADCC antibody titres, NK cell-mediated ADCC and antibody-mediated activation of MIP-1β in NK cells as the four immunological parameters that best predict decreased infection risk that are improved by the pentavalent vaccine. Thus inclusion of additional gp120 immunogens to a pox-prime/protein boost regimen can augment antibody responses and enhance protection from a SHIV challenge in rhesus macaques.

A previous human HIV-1 vaccine clinical trial, boosting with HIV envelope protein from two strains, demonstrated moderate vaccine efficacy. Here, Bradley et al. show that a pentavalent HIV envelope protein boost improves protection from viral challenge in non-human primates and they identify immune correlates of protection.

HIV/AIDS Vaccine Candidates Based on Replication-Competent Recombinant Poxvirus NYVAC-C-KC Expressing Trimeric gp140 and Gag-Derived Virus-Like Particles or Lacking the Viral Molecule B19 That Inhibits Type I Interferon Activate Relevant HIV-1-Specific B and T Cell Immune Functions in Nonhuman Primates

The nonreplicating attenuated poxvirus vector NYVAC expressing clade C(CN54) HIV-1 Env(gp120) and Gag-Pol-Nef antigens (NYVAC-C) showed limited immunogenicity in phase I clinical trials. To enhance the capacity of the NYVAC vector to trigger broad humoral responses and a more balanced activation of CD4⁺ and CD8⁺ T cells, here we compared the HIV-1-specific immunogenicity elicited in nonhuman primates immunized with two replicating NYVAC vectors that have been modified by the insertion of the K1L and C7L vaccinia virus host range genes and express the clade C(ZM96) trimeric HIV-1 gp140 protein or a Gag(ZM96)-Pol-Nef(CN54) polyprotein as Gag-derived virus-like particles (termed NYVAC-C-KC). Additionally, one NYVAC-C-KC vector was generated by deleting the viral gene B19R, an inhibitor of the type I interferon response (NYVAC-C-KC-ΔB19R). An immunization protocol mimicking that of the RV144 phase III clinical trial was used. Two groups of macaques received two doses of the corresponding NYVAC-C-KC vectors (weeks 0 and 4) and booster doses with NYVAC-C-KC vectors plus the clade C HIV-1 gp120 protein (weeks 12 and 24). The two replicating NYVAC-C-KC vectors induced enhanced and similar HIV-1-specific CD4⁺ and CD8⁺ T cell responses, similar levels of binding IgG antibodies, low levels of IgA antibodies, and high levels of antibody-dependent cellular cytotoxicity responses and HIV-1-neutralizing antibodies. Small differences within the NYVAC-C-KC-ΔB19R group were seen in the magnitude of CD4⁺ and CD8⁺ T cells, the induction of some cytokines, and the neutralization of some HIV-1 isolates. Thus, replication-competent NYVAC-C-KC vectors acquired relevant immunological properties as vaccine candidates against HIV/AIDS, and the viral B19 molecule exerts some control of immune functions.IMPORTANCE It is of special importance to find a safe and effective HIV/AIDS vaccine that can induce strong and broad T cell and humoral immune responses correlating with HIV-1 protection. Here we developed novel replicating poxvirus NYVAC-based HIV/AIDS vaccine candidates expressing clade C HIV-1 antigens, with one of them lacking the vaccinia virus B19 protein, an inhibitor of the type I interferon response. Immunization of nonhuman primates with these novel NYVAC-C-KC vectors and the protein component gp120 elicited high levels of T cell and humoral immune responses, with the vector containing a deletion in B19R inducing a trend toward a higher magnitude of CD4⁺ and CD8⁺ T cell responses and neutralization of some HIV-1 strains. These poxvirus vectors could be considered HIV/AIDS vaccine candidates based on their activation of potential immune correlates of protection.

Characterization of immune cells and infection by HIV in human ovarian tissues

PROBLEM

New HIV infections in women are predominantly spread through sexual intercourse. Recent non-human primate studies demonstrated that simian immunodeficiency virus (SIV) deposited in the vagina infected immune cells in the ovary. Whether immune cells in the human ovary are susceptible to HIV infection is unknown.

METHOD OF STUDY

Immune cells were isolated from ovaries and characterized by flow cytometry. Cells were exposed to HIV for 2 hours. HIV infection was measured by flow cytometry and p24 secretion following 6 days in culture.

RESULTS

CD4⁺ T cells and CD14⁺ cells are present in the ovary and susceptible to infection by HIV-BaL. Among the CD45⁺ cells present, 30% were CD3⁺ T cells (with similar proportions of CD4⁺ or CD8⁺ T cells), and 7%-10% were CD14⁺ cells. Both CD4⁺ T cells and CD14⁺ cells were productively infected and supported replication.

CONCLUSION

Immune cells in the ovary are potential targets for HIV infection.

T-Cell Receptor (TCR) Clonotype-Specific Differences in Inhibitory Activity of HIV-1 Cytotoxic T-Cell Clones Is Not Mediated by TCR Alone

Functional analysis of T-cell responses in HIV-infected individuals has indicated that virus-specific CD8⁺ T cells with superior antiviral efficacy are well represented in HIV-1 controllers but are rare or absent in HIV-1 progressors. To define the role of individual T-cell receptor (TCR) clonotypes in differential antiviral CD8⁺ T-cell function, we performed detailed functional and mass cytometric cluster analysis of multiple CD8⁺ T-cell clones recognizing the identical HLA-B*2705-restricted HIV-1 epitope KK10 (KRWIILGLNK). Effective and ineffective CD8⁺ T-cell clones segregated based on responses to HIV-1-infected and peptide-loaded target cells. Following cognate peptide stimulation, effective HIV-specific clones displayed significantly more rapid TCR signal propagation, more efficient initial lytic granule release, and more sustained nonlytic cytokine and chemokine secretion than ineffective clones. To evaluate the TCR clonotype contribution to CD8⁺ T-cell function, we cloned the TCR α and β chain genes from one effective and two ineffective CD8⁺ T-cell clones from an elite controller into TCR-expressing lentivectors. We show that Jurkat/MA cells and primary CD8⁺ T cells transduced with lentivirus expressing TCR from one of the ineffective clones exhibited a level of activation by cognate peptide and inhibition of in vitro HIV-1 infection, respectively, that were comparable to those of the effective clonotype. Taken together, these data suggest that the potent antiviral capacity of some HIV-specific CD8⁺ T cells is a consequence of factors in addition to TCR sequence that modulate functionality and contribute to the increased antiviral capacity of HIV-specific CD8⁺ T cells in elite controllers to inhibit HIV infection.IMPORTANCE The greater ex vivo antiviral inhibitory activity of CD8⁺ T cells from elite controllers than from HIV-1 progressors supports the crucial role of effective HIV-specific CD8⁺ T cells in controlling HIV-1 replication. The contribution of TCR clonotype to inhibitory potency was investigated by delineating the responsiveness of effective and ineffective CD8⁺ T-cell clones recognizing the identical HLA-B*2705-restricted HIV-1 Gag-derived peptide, KK10 (KRWIILGLNK). KK10-stimulated "effective" CD8⁺ T-cell clones displayed significantly more rapid TCR signal propagation, more efficient initial lytic granule release, and more sustained cytokine and chemokine secretion than "ineffective" CD8⁺ T-cell clones. However, TCRs cloned from an effective and one of two ineffective clones conferred upon primary CD8⁺ T cells the equivalent potent capacity to inhibit HIV-1 infection. Taken together, these data suggest that other factors aside from intrinsic TCR-peptide-major histocompatibility complex (TCR-peptide-MHC) reactivity can contribute to the potent antiviral capacity of some HIV-specific CD8⁺ T-cell clones.

The transcriptome of HIV-1 infected intestinal CD4+ T cells exposed to enteric bacteria

Global transcriptome studies can help pinpoint key cellular pathways exploited by viruses to replicate and cause pathogenesis. Previous data showed that laboratory-adapted HIV-1 triggers significant gene expression changes in CD4+ T cell lines and mitogen-activated CD4+ T cells from peripheral blood. However, HIV-1 primarily targets mucosal compartments during acute infection in vivo. Moreover, early HIV-1 infection causes extensive depletion of CD4+ T cells in the gastrointestinal tract that herald persistent inflammation due to the translocation of enteric microbes to the systemic circulation. Here, we profiled the transcriptome of primary intestinal CD4+ T cells infected ex vivo with transmitted/founder (TF) HIV-1. Infections were performed in the presence or absence of Prevotella stercorea, a gut microbe enriched in the mucosa of HIV-1-infected individuals that enhanced both TF HIV-1 replication and CD4+ T cell death ex vivo. In the absence of bacteria, HIV-1 triggered a cellular shutdown response involving the downregulation of HIV-1 reactome genes, while perturbing genes linked to OX40, PPAR and FOXO3 signaling. However, in the presence of bacteria, HIV-1 did not perturb these gene sets or pathways. Instead, HIV-1 enhanced granzyme expression and Th17 cell function, inhibited G1/S cell cycle checkpoint genes and triggered downstream cell death pathways in microbe-exposed gut CD4+ T cells. To gain insights on these differential effects, we profiled the gene expression landscape of HIV-1-uninfected gut CD4+ T cells exposed to bacteria. Microbial exposure upregulated genes involved in cellular proliferation, MAPK activation, Th17 cell differentiation and type I interferon signaling. Our findings reveal that microbial exposure influenced how HIV-1 altered the gut CD4+ T cell transcriptome, with potential consequences for HIV-1 susceptibility, cell survival and inflammation. The HIV-1- and microbe-altered pathways unraveled here may serve as a molecular blueprint to gain basic insights in mucosal HIV-1 pathogenesis.

Boosting of HIV envelope CD4 binding site antibodies with long variable heavy third complementarity determining region in the randomized double blind RV305 HIV-1 vaccine trial

The canary pox vector and gp120 vaccine (ALVAC-HIV and AIDSVAX B/E gp120) in the RV144 HIV-1 vaccine trial conferred an estimated 31% vaccine efficacy. Although the vaccine Env AE.A244 gp120 is antigenic for the unmutated common ancestor of V1V2 broadly neutralizing antibody (bnAbs), no plasma bnAb activity was induced. The RV305 (NCT01435135) HIV-1 clinical trial was a placebo-controlled randomized double-blinded study that assessed the safety and efficacy of vaccine boosting on B cell repertoires. HIV-1-uninfected RV144 vaccine recipients were reimmunized 6–8 years later with AIDSVAX B/E gp120 alone, ALVAC-HIV alone, or a combination of ALVAC-HIV and AIDSVAX B/E gp120 in the RV305 trial. Env-specific post-RV144 and RV305 boost memory B cell V_H mutation frequencies increased from 2.9% post-RV144 to 6.7% post-RV305. The vaccine was well tolerated with no adverse events reports. While post-boost plasma did not have bnAb activity, the vaccine boosts expanded a pool of envelope CD4 binding site (bs)-reactive memory B cells with long third heavy chain complementarity determining regions (HCDR3) whose germline precursors and affinity matured B cell clonal lineage members neutralized the HIV-1 CRF01 AE tier 2 (difficult to neutralize) primary isolate, CNE8. Electron microscopy of two of these antibodies bound with near-native gp140 trimers showed that they recognized an open conformation of the Env trimer. Although late boosting of RV144 vaccinees expanded a novel pool of neutralizing B cell clonal lineages, we hypothesize that boosts with stably closed trimers would be necessary to elicit antibodies with greater breadth of tier 2 HIV-1 strains.

Trial Registration: ClinicalTrials.gov NCT01435135

Developing a successful HIV-1 vaccine remains a high global health priority. Several HIV-1 vaccine trials have been performed with only the RV144 vaccine trial showing vaccine efficacy, albeit modest. No broadly neutralizing antibody activity was identified in RV144 and inducing sterilizing immunity against a complex pathogen like HIV-1 remains a major challenge. Here we characterize the B cell responses after RV144 vaccine-recipients received two additional boosts severals years after the conclusion of the RV144 vaccine trial. Delayed and repetitive boosting of RV144 vaccine-recipients was capable of increasing somatic hypermutation of the Env-reactive antibodies and expanding subdominant pools of neutralizing B cell clonal lineages. These data are pertinent to HIV-1 vaccine-regimen design.

CD4 regulatory T cells augment HIV-1 expression of polarized M1 and M2 monocyte derived macrophages

Previous in vitro studies have shown that the HIV-1 virus can alter the cytokine/chemokine profile of polarized macrophages which may lead to their increased susceptibility to viral infection. Here, we found that M2 monocyte derived macrophages (MDM) were significantly more permissive to productive infection by R5-tropic HIV-1 strains, including transmitted founder (T/F) viruses, than M1 MDM. Previous in vitro studies by our lab showed that regulatory T cells (Tregs) suppress HIV-1 infection in non-Treg CD4 T cells. Here, we investigated potential inhibitory effects of Tregs on HIV-1 infection of polarized MDM. We found that Tregs significantly increased HIV-1 infection in M1 and M2 MDM via a mechanism that was cell contact dependent. These findings suggest a potential role for Tregs in HIV-1 infection of tissue resident macrophages of M1 and M2 phenotype, which may contribute to the establishment and pathogenesis of HIV-1 disease.

Visualization of X4- and R5-Tropic HIV-1 Viruses Expressing Fluorescent Proteins in Human Endometrial Cells: Application to Tropism Study

Worldwide most HIV infections occur through heterosexual transmission, involving complex interactions of cell-free and cell-associated particles with cells of the female genital tract mucosa. The ability of HIV-1 to "infect" epithelial cells remains poorly understood. To address this question, replicative-competent chimeric constructs expressing fluorescent proteins and harboring the envelope of X4- or R5-tropic HIV-1 strains were used to "infect" endometrial HEC1-A cells. The virus-cell interactions were visualized using confocal microscopy (CM) at various times post infection. Combined with quantification of viral RNA and total HIV DNA in infected cells, the CM pictures suggest that epithelial cells do not support a complete viral replication cycle: X4-tropic viruses are imported into the nucleus in a non-productive way, whereas R5-tropic viruses transit through the cytoplasm without replication and are preferentially transmitted to susceptible activated peripheral blood mononuclear cells. Within the limit of experiments conducted in vitro on a continued cell line, these results indicate that the epithelial mucosa may participate to the selection of HIV-1 strains at the mucosal level.

Diversity of Antiviral IgG Effector Activities Observed in HIV-Infected and Vaccinated Subjects

Diverse Ab effector functions mediated by the Fc domain have been commonly associated with reduced risk of infection in a growing number of nonhuman primate and human clinical studies. This study evaluated the anti-HIV Ab effector activities in polyclonal serum samples from HIV-infected donors, VAX004 vaccine recipients, and healthy HIV-negative subjects using a variety of primary and cell line-based assays, including Ab-dependent cellular cytotoxicity (ADCC), Ab-dependent cell-mediated viral inhibition, and Ab-dependent cellular phagocytosis. Additional assay characterization was performed with a panel of Fc-engineered variants of mAb b12. The goal of this study was to characterize different effector functions in the study samples and identify assays that might most comprehensively and dependably capture Fc-mediated Ab functions mediated by different effector cell types and against different viral targets. Deployment of such assays may facilitate assessment of functionally unique humoral responses and contribute to identification of correlates of protection with potential mechanistic significance in future HIV vaccine studies. Multivariate and correlative comparisons identified a set of Ab-dependent cell-mediated viral inhibition and phagocytosis assays that captured different Ab activities and were distinct from a group of ADCC assays that showed a more similar response profile across polyclonal serum samples. The activities of a panel of b12 monoclonal Fc variants further identified distinctions among the ADCC assays. These results reveal the natural diversity of Fc-mediated Ab effector responses among vaccine recipients in the VAX004 trial and in HIV-infected subjects, and they point to the potential importance of polyfunctional Ab responses.

Neutralization Takes Precedence Over IgG or IgA Isotype-related Functions in Mucosal HIV-1 Antibody-mediated Protection

HIV-1 infection occurs primarily through mucosal transmission. Application of biologically relevant mucosal models can advance understanding of the functional properties of antibodies that mediate HIV protection, thereby guiding antibody-based vaccine development. Here, we employed a human ex vivo vaginal HIV-1 infection model and a rhesus macaque in vivo intrarectal SHIV challenge model to probe the protective capacity of monoclonal broadly-neutralizing (bnAb) and non-neutralizing Abs (nnAbs) that were functionally modified by isotype switching. For human vaginal explants, we developed a replication-competent, secreted NanoLuc reporter virus system and showed that CD4 binding site bnAbs b12 IgG1 and CH31 IgG1 and IgA2 isoforms potently blocked HIV-1JR-CSF and HIV-1Bal26 infection. However, IgG1 and IgA nnAbs, either alone or together, did not inhibit infection despite the presence of FcR-expressing effector cells in the tissue. In macaques, the CH31 IgG1 and IgA2 isoforms infused before high-dose SHIV challenge were completely to partially protective, respectively, while nnAbs (CH54 IgG1 and CH38 mIgA2) were non-protective. Importantly, in both mucosal models IgG1 isotype bnAbs were more protective than the IgA2 isotypes, attributable in part to greater neutralization activity of the IgG1 variants. These findings underscore the importance of potent bnAb induction as a primary goal of HIV-1 vaccine development.

Fc Receptor-Mediated Activities of Env-Specific Human Monoclonal Antibodies Generated from Volunteers Receiving the DNA Prime-Protein Boost HIV Vaccine DP6-001

HIV-1 is able to elicit broadly potent neutralizing antibodies in a very small subset of individuals only after several years of infection, and therefore, vaccines that elicit these types of antibodies have been difficult to design. The RV144 trial showed that moderate protection is possible and that this protection may correlate with antibody-dependent cellular cytotoxicity (ADCC) activity. Our previous studies demonstrated that in an HIV vaccine phase I trial, the DP6-001 trial, a polyvalent Env DNA prime-protein boost formulation could elicit potent and broadly reactive, gp120-specific antibodies with positive neutralization activities. Here we report on the production and analysis of HIV-1 Env-specific human monoclonal antibodies (hMAbs) isolated from vaccinees in the DP6-001 trial. For this initial report, 13 hMAbs from four vaccinees in the DP6-001 trial showed broad binding to gp120 proteins of diverse subtypes both autologous and heterologous to vaccine immunogens. Equally cross-reactive Fc receptor-mediated functional activities, including ADCC and antibody-dependent cellular phagocytosis (ADCP) activities, were present with both immune sera and isolated MAbs, confirming the induction of nonneutralizing functional hMAbs by the DNA prime-protein boost vaccination. Elicitation of broadly reactive hMAbs by vaccination in healthy human volunteers confirms the value of the polyvalent formulation in this HIV vaccine design.

IMPORTANCE

The roles of Fc receptor-mediated protective antibody responses are gaining more attention due to their potential contribution to the low-level protection against HIV-1 infection that they provided in the RV144 trial. At the same time, information about hMabs from other human HIV vaccine studies is very limited. In the current study, both immune sera and monoclonal antibodies from vaccinated humans showed not only high-level ADCC and ADCP activities but also cross-subtype ADCC and ADCP activities when a polyvalent DNA prime-protein boost vaccine formulation was used.

Characterization of Simian Immunodeficiency Virus Variants Anatomically Compartmentalized in Plasma and Milk in Chronically Infected African Green Monkeys

Unlike human immunodeficiency virus type 1 (HIV-1)-infected humans, African-origin, natural simian immunodeficiency virus (SIV) hosts, such as African green monkeys (AGMs), sustain nonpathogenic SIV infections and rarely vertically transmit SIV to their infants. Interestingly, chronically SIV-infected AGMs have anatomically compartmentalized SIV variants in plasma and milk, whereas humans and SIV-infected rhesus monkeys (RMs), Asian-origin nonnatural SIV hosts, do not exhibit this compartmentalization. Thus, it is possible that AGM SIV populations in milk have unique phenotypic features that contribute to the low postnatal transmission rates observed in this natural host species. In this study, we explored this possibility by characterizing the infectivity, tropism, and neutralization susceptibility of plasma and milk SIVsab env variants isolated from chronically SIVsab92018ivTF-infected AGMs. AGM plasma and milk SIVsab env pseudovirus variants exhibited similar infectivities, neutralization susceptibilities to autologous and heterologous plasma, and chemokine coreceptor usages for cell entry, suggesting similar abilities to initiate infection in a new host. We also assessed the cytokine milieu in SIV-infected AGM milk and compared it to that of SIV-infected RMs. MIP-1β, granulocyte colony-stimulating factor (G-CSF), interleukin-12/23 (IL-12/23), and IL-13 trended significantly higher in SIV-infected AGM milk than in that of RMs, while IL-18 and IL-6 trended significantly higher in SIV-infected RM milk than in that of AGMs. Taken together, our findings imply that nonviral maternal factors, such as the cytokine milieu, rather than unique characteristics of SIV populations in the milk contribute to the low postnatal transmission rates observed in AGMs.

IMPORTANCE

Due to the ongoing global incidence of pediatric HIV-1 infections, including many that occur via breastfeeding, development of effective vaccine strategies capable of preventing vertical HIV transmission through breastfeeding remains an important goal. Unlike HIV-1-infected humans, African green monkeys (AGMs), the natural SIV host species, sustain nonpathogenic SIV infections, rarely transmit the virus postnatally to their infants, and exhibit anatomically compartmentalized SIV populations in milk and plasma. Identifying unique features of the anatomically compartmentalized milk SIV populations could enhance our understanding of how AGMs may have evolved to avoid transmission through breastfeeding. While this study identified limited phenotypic distinctions between AGM plasma and milk SIV populations, potential differences in milk cytokine profiles of natural and nonnatural SIV hosts were observed. These findings imply the potential importance of nonviral factors in natural SIV host species, such as innate SIV/HIV immune factors in milk, as a means of naturally preventing vertical transmission.

Induction of Heterologous Tier 2 HIV-1-Neutralizing and Cross-Reactive V1/V2-Specific Antibodies in Rabbits by Prime-Boost Immunization

Poxvirus prime-protein boost used in the RV144 trial remains the only immunization strategy shown to elicit a modest level of protection against HIV-1 acquisition in humans. Although neutralizing antibodies (NAb) were generated, they were against sensitive viruses, not the more resistant "tier 2" isolates that dominate circulating strains. Instead, risk reduction correlated with antibodies recognizing epitopes in the V1/V2 region of HIV-1 envelope glycoprotein (Env). Here, we examined whether tier 2 virus NAb and V1/V2-specific non-NAb could be elicited by a poxvirus prime-gp120 boost strategy in a rabbit model. We studied two clade B Envs that differ in multiple parameters, including tissue origin, neutralization sensitivity, and presence of the N197 (N7) glycan that was previously shown to modulate the exposure of conserved epitopes on Env. We demonstrate that immunized rabbits generated cross-reactive neutralizing activities against >50% of the tier 2 global HIV-1 isolates tested. Some of these activities were directed against the CD4 binding site (CD4bs). These rabbits also generated antibodies that recognized protein scaffolds bearing V1/V2 sequences from diverse HIV-1 isolates and mediated antibody-dependent cellular cytotoxicity. However, there are subtle differences in the specificities and the response rates of V1/V2-specific antibodies between animals immunized with different Envs, with or without the N7 glycan. These findings demonstrate that antibody responses that have been correlated with protection against HIV-1 acquisition in humans can be elicited in a preclinical model by a poxvirus prime-gp120 boost strategy and that improvements may be achievable by optimizing the nature of the priming and boosting immunogens.

IMPORTANCE

The only vaccine approach shown to elicit any protective efficacy against HIV-1 acquisition is based on a poxvirus prime-protein boost regimen (RV144 Thai trial). Reduction of risk was associated with nonneutralizing antibodies targeting the V1/V2 loops of the envelope protein gp120. However, the modest efficacy (31.2%) achieved in this trial highlights the need to examine approaches and factors that may improve vaccine-induced responses, including cross-reactive neutralizing activities. We show here that rabbits immunized with a novel recombinant vaccinia virus prime-gp120 protein boost regimen generated antibodies that recognize protein scaffolds bearing V1/V2 sequences from diverse HIV-1 isolates and mediated antibody-dependent cellular cytotoxicity. Importantly, immunized rabbits also showed neutralizing activities against heterologous tier 2 HIV-1 isolates. These findings may inform the design of prime-boost immunization approaches and help improve the protective efficacy of candidate HIV-1 vaccines.

Negative Feedback Regulation of HIV-1 by Gene Editing Strategy

The CRISPR/Cas9 gene editing method is comprised of the guide RNA (gRNA) to target a specific DNA sequence for cleavage and the Cas9 endonuclease for introducing breaks in the double-stranded DNA identified by the gRNA. Co-expression of both a multiplex of HIV-1-specific gRNAs and Cas9 in cells results in the modification and/or excision of the segment of viral DNA, leading to replication-defective virus. In this study, we have personalized the activity of CRISPR/Cas9 by placing the gene encoding Cas9 under the control of a minimal promoter of HIV-1 that is activated by the HIV-1 Tat protein. We demonstrate that functional activation of CRISPR/Cas9 by Tat during the course of viral infection excises the designated segment of the integrated viral DNA and consequently suppresses viral expression. This strategy was also used in a latently infected CD4+ T-cell model after treatment with a variety of HIV-1 stimulating agents including PMA and TSA. Controlled expression of Cas9 by Tat offers a new strategy for safe implementation of the Cas9 technology for ablation of HIV-1 at a very early stage of HIV-1 replication during the course of the acute phase of infection and the reactivation of silent proviral DNA in latently infected cells.

Adenovirus-based HIV-1 vaccine candidates tested in efficacy trials elicit CD8+ T cells with limited breadth of HIV-1 inhibition

OBJECTIVES

The ability of HIV-1 vaccine candidates MRKAd5, VRC DNA/Ad5 and ALVAC/AIDSVAX to elicit CD8 T cells with direct antiviral function was assessed and compared with HIV-1-infected volunteers.

DESIGN

Adenovirus serotype 5 (Ad5)-based regimens MRKAd5 and VRC DNA/Ad5, designed to elicit HIV-1-specific T cells, are immunogenic but failed to prevent infection or impact on viral loads in volunteers infected subsequently. Failure may be due in part to a lack of CD8 T cells with effective antiviral functions.

METHODS

An in-vitro viral inhibition assay tested the ability of bispecific antibody expanded CD8 T cells from peripheral blood mononuclear cells to inhibit replication of a multiclade panel of HIV-1 isolates in autologous CD4 T cells. HIV-1 proteins recognized by CD8 T cells were assessed by IFNγ enzyme-linked immunospot assay.

RESULTS

Ad5-based regimens elicited CD8 T cells that inhibited replication of HIV-1 IIIB isolate with more limited inhibition of other isolates. IIIB isolate Gag and Pol genes have high sequence identities (>96%) to vector HIV-1 gene inserts, and these were the predominant HIV-1 proteins recognized by CD8 T cells. Virus inhibition breadth was greater in antiretroviral naïve HIV-1-infected volunteers naturally controlling viremia (plasma viral load < 10 000/ml). HIV-1-inhibitory CD8 T cells were not elicited by the ALVAC/AIDSVAX regimen.

CONCLUSION

The Ad5-based regimens, although immunogenic, elicited CD8 T cells with limited HIV-1-inhibition breadth. Effective T-cell-based vaccines should presumably elicit broader HIV-1-inhibition profiles. The viral inhibition assay can be used in vaccine design and to prioritize promising candidates with greater inhibition breadth for further clinical trials.

Immunization with an SIV-based IDLV Expressing HIV-1 Env 1086 Clade C Elicits Durable Humoral and Cellular Responses in Rhesus Macaques

The design of an effective HIV-1 vaccine remains a major challenge. Several vaccine strategies based on viral vectors have been evaluated in preclinical and clinical trials, with largely disappointing results. Integrase defective lentiviral vectors (IDLV) represent a promising vaccine candidate given their ability to induce durable and protective immune responses in mice after a single immunization. Here, we evaluated the immunogenicity of a SIV-based IDLV in nonhuman primates. Six rhesus monkeys were primed intramuscularly with IDLV-Env and boosted with the same vector after 1 year. A single immunization with IDLV-Env induced broad humoral and cellular immune responses that waned over time but were still detectable at 1 year postprime. The boost with IDLV-Env performed at 1 year from the prime induced a remarkable increase in both antibodies and T-cell responses. Antibody binding specificity showed a predominant cross-clade gp120-directed response. Monkeys' sera efficiently blocked anti-V2 and anti-CD4 binding site antibodies, neutralized the tier 1 MW965.26 pseudovirus and mediated antibody-dependent cellular cytotoxicity (ADCC). Durable polyfunctional Env-specific T-cell responses were also elicited. Our study demonstrates that an IDLV-Env-based vaccine induces functional, comprehensive, and durable immune responses in Rhesus macaques. These results support further evaluation of IDLV as a new HIV-1 vaccine delivery platform.

Flexible and rapid construction of viral chimeras applied to hepatitis C virus

A novel and broadly applicable strategy combining site-directed mutagenesis and DNA assembly for constructing seamless viral chimeras is described using hepatitis C virus (HCV) as an exemplar. Full-length HCV genomic cloning cassettes, which contained flexibly situated restriction endonuclease sites, were prepared via a single, site-directed mutagenesis reaction and digested to receive PCR-amplified virus envelope genes by In-Fusion cloning. Using this method, we were able to construct gene-shuttle cassettes for generation of cell culture-infectious JFH-1-based chimeras containing genotype 1–3 E1E2 genes. Importantly, using this method we also show that E1E2 clones that were not able to support cell entry in the HCV pseudoparticle assay did confer entry when shuttled into the chimeric cell culture chimera system. This method can be easily applied to other genes of study and other viruses and, as such, will greatly simplify reverse genetics studies of variable viruses.

Boosting with Subtype C CN54rgp140 Protein Adjuvanted with Glucopyranosyl Lipid Adjuvant after Priming with HIV-DNA and HIV-MVA Is Safe and Enhances Immune Responses: A Phase I Trial

Background

A vaccine against HIV is widely considered the most effective and sustainable way of reducing new infections. We evaluated the safety and impact of boosting with subtype C CN54rgp140 envelope protein adjuvanted in glucopyranosyl lipid adjuvant (GLA-AF) in Tanzanian volunteers previously given three immunizations with HIV-DNA followed by two immunizations with recombinant modified vaccinia virus Ankara (HIV-MVA).

Methods

Forty volunteers (35 vaccinees and five placebo recipients) were given two CN54rgp140/GLA-AF immunizations 30–71 weeks after the last HIV-MVA vaccination. These immunizations were delivered intramuscularly four weeks apart.

Results

The vaccine was safe and well tolerated except for one episode of asymptomatic hypoglycaemia that was classified as severe adverse event. Two weeks after the second HIV-MVA vaccination 34 (97%) of the 35 previously vaccinated developed Env-specific binding antibodies, and 79% and 84% displayed IFN-γ ELISpot responses to Gag and Env, respectively. Binding antibodies to subtype C Env (included in HIV-DNA and protein boost), subtype B Env (included only in HIV-DNA) and CRF01_AE Env (included only in HIV-MVA) were significantly boosted by the CN54rgp140/GLA-AF immunizations. Functional antibodies detected using an infectious molecular clone virus/peripheral blood mononuclear cell neutralization assay, a pseudovirus/TZM-bl neutralization assay or by assays for antibody-dependent cellular cytotoxicity (ADCC) were not significantly boosted. In contrast, T-cell proliferative responses to subtype B MN antigen and IFN-γ ELISpot responses to Env peptides were significantly enhanced. Four volunteers not primed with HIV-DNA and HIV-MVA before the CN54rgp140/GLA-AF immunizations mounted an antibody response, while cell-mediated responses were rare. After the two Env subtype C protein immunizations, a trend towards higher median subtype C Env binding antibody titers was found in vaccinees who had received HIV-DNA and HIV-MVA prior to the two Env protein immunizations as compared to unprimed vaccinees (p = 0.07).

Conclusion

We report excellent tolerability, enhanced binding antibody responses and Env-specific cell-mediated immune responses but no ADCC antibody increase after two immunizations with a subtype C rgp140 protein adjuvanted in GLA-AF in healthy volunteers previously immunized with HIV-DNA and HIV-MVA.

Trial Registration

International Clinical Trials Registry PACTR2010050002122368

Combined HIV-1 Envelope Systemic and Mucosal Immunization of Lactating Rhesus Monkeys Induces a Robust Immunoglobulin A Isotype B Cell Response in Breast Milk

Maternal vaccination to induce anti-HIV immune factors in breast milk is a potential intervention to prevent postnatal HIV-1 mother-to-child transmission (MTCT). We previously demonstrated that immunization of lactating rhesus monkeys with a modified vaccinia Ankara (MVA) prime/intramuscular (i.m.) protein boost regimen induced functional IgG responses in milk, while MVA prime/intranasal (i.n.) boost induced robust milk Env-specific IgA responses. Yet, recent studies have suggested that prevention of postnatal MTCT may require both Env-specific IgA and functional IgG responses in milk. Thus, to investigate whether both responses could be elicited by a combined systemic/mucosal immunization strategy, animals previously immunized with the MVA prime/i.n. boost regimen received an i.n./i.m. combined C.1086 gp120 boost. Remarkably, high-magnitude Env-specific IgA responses were observed in milk, surpassing those in plasma. Furthermore, 29% of vaccine-elicited Env-specific B cells isolated from breast milk were IgA isotype, in stark contrast to the overwhelming predominance of IgG isotype Env-specific B cells in breast milk of chronically HIV-infected women. A clonal relationship was identified between Env-specific blood and breast milk B cells, suggesting trafficking of that cell population between the two compartments. Furthermore, IgA and IgG monoclonal antibodies isolated from Env-specific breast milk B cells demonstrated diverse Env epitope specificities and multiple effector functions, including tier 1 neutralization, antibody-dependent cellular cytotoxicity (ADCC), infected cell binding, and inhibition of viral attachment to epithelial cells. Thus, maternal i.n./i.m. combined immunization is a novel strategy to enhance protective Env-specific IgA in milk, which is subsequently transferred to the infant via breastfeeding.

IMPORTANCE

Efforts to increase the availability of antiretroviral therapy to pregnant and breastfeeding women in resource-limited areas have proven remarkably successful at reducing HIV vertical transmission rates. However, more than 200,000 children are infected annually due to failures in therapy implementation, monitoring, and adherence, nearly half by postnatal HIV exposure via maternal breast milk. Intriguingly, in the absence of antiretroviral therapy, only 10% of breastfed infants born to HIV-infected mothers acquire the virus, suggesting the existence of naturally protective immune factors in milk. Enhancement of these protective immune factors through maternal vaccination will be a critical strategy to reduce the global pediatric AIDS epidemic. We have previously demonstrated that a high magnitude of HIV Env-specific IgA in milk correlates with reduced risk of infant HIV acquisition. In this study, we describe a novel HIV vaccine regimen that induces potent IgA responses in milk and therefore could potentially protect against breast milk HIV MTCT.

Targeting HIV-1 Env gp140 to LOX-1 Elicits Immune Responses in Rhesus Macaques

Improved antigenicity against HIV-1 envelope (Env) protein is needed to elicit vaccine-induced protective immunity in humans. Here we describe the first tests in non-human primates (NHPs) of Env gp140 protein fused to a humanized anti-LOX-1 recombinant antibody for delivering Env directly to LOX-1-bearing antigen presenting cells, especially dendritic cells (DC). LOX-1, or 1ectin-like oxidized low-density lipoprotein (LDL) receptor-1, is expressed on various antigen presenting cells and endothelial cells, and is involved in promoting humoral immune responses. The anti-LOX-1 Env gp140 fusion protein was tested for priming immune responses and boosting responses in animals primed with replication competent NYVAC-KC Env gp140 vaccinia virus. Anti-LOX-1 Env gp140 vaccination elicited robust cellular and humoral responses when used for either priming or boosting immunity. Co-administration with Poly ICLC, a TLR3 agonist, was superior to GLA, a TLR4 agonist. Both CD4+ and CD8+ Env-specific T cell responses were elicited by anti-LOX-1 Env gp140, but in particular the CD4+ T cells were multifunctional and directed to multiple epitopes. Serum IgG and IgA antibody responses induced by anti-LOX-1 Env gp140 against various gp140 domains were cross-reactive across HIV-1 clades; however, the sera neutralized only HIV-1 bearing sequences most similar to the clade C 96ZM651 Env gp140 carried by the anti-LOX-1 vehicle. These data, as well as the safety of this protein vaccine, justify further exploration of this DC-targeting vaccine approach for protective immunity against HIV-1.

A novel dual luciferase assay for the simultaneous monitoring of HIV infection and cell viability

Human immunodeficiency virus type 1 (HIV-1) reporter cell lines are critical tools for drug development. However, one disadvantage of HIV-1 reporter cell lines is that reductions in reporter gene activity need to be normalized to cytotoxicity, i.e., live cell numbers. Here, we developed a dual luciferase assay based on a R. reniformis luciferase (hRLuc)-expressing R5-type HIV-1 (NLAD8-hRLuc) and a CEM cell line expressing CCR5 and firefly luciferase (R5CEM-FiLuc). The NLAD8-hRLuc reporter virus was replication competent in peripheral blood mononuclear cells. The level of hRLuc was correlated with p24 antigen levels (p<0.001, R=0.862). The target cell line, R5CEM-FiLuc, stably expressed the firefly luciferase (FiLuc) reporter gene and allowed the simultaneous monitoring of compound cytotoxicity. The dual reporter assay combining a NLAD8-hRLuc virus with R5CEM-FiLuc cells permitted the accurate determination of drug susceptibility for entry, reverse transcriptase, integrase, and protease inhibitors at different multiplicities of infection. This dual reporter assay provides a rapid and direct method for the simultaneous monitoring of HIV infection and cell viability.

High-Throughput Humanized Mouse Models for Evaluation of HIV-1 Therapeutics and Pathogenesis

Mice cannot be used as a model to evaluate HIV-1 therapeutics because they do not become infected by HIV-1 due to structural differences between several human and mouse proteins required for HIV-1 replication. This has limited their use for in vivo assessment of anti-HIV-1 therapeutics and the mechanism by which cofactors, such as illicit drug use accelerate HIV-1 replication and disease course in substance abusers. Here, we describe the development and application of two in vivo humanized mouse models that are highly sensitive and useful models for the in vivo evaluation of candidate anti-HIV therapeutics. The first model, hu-spl-PBMC-NSG mice, uses NOD-SCID IL2rγ(-/-) (NSG) mice intrasplenically injected with human peripheral blood mononuclear cells (PBMC) which develop productive splenic HIV-1 infection after intrasplenic inoculation with a replication-competent HIV-1 expressing Renilla reniformis luciferase (HIV-LucR) and enables investigators to use bioluminescence to visualize and quantitate the temporal effects of therapeutics on HIV-1 infection. The second model, hCD4/R5/cT1 mice, consists of transgenic mice carrying human CD4, CCR5 and cyclin T1 genes, which enables murine CD4-expressing cells to support HIV-1 entry, Tat-mediated LTR transcription and consequently develop productive infection. The hCD4/R5/cT1 mice develop disseminated infection of tissues including the spleen, small intestine, lymph nodes and lungs after intravenous injection with HIV-1-LucR. Because these mice can be infected with HIV-LucR expressing transmitted/founder and clade A/E and C Envs, these mouse models can also be used to evaluate the in vivo efficacy of broadly neutralizing antibodies and antibodies induced by candidate HIV-1 vaccines. Furthermore, because hCD4/R5/cT1 mice can be infected by vaginal inoculation with replication-competent HIV-1 expressing NanoLuc (HIV-nLucR)-, this mouse model can be used to evaluate the mechanisms by which substance abuse and other factors enhance mucosal transmission of HIV-1.

Optimized Replicating Renilla Luciferase Reporter HIV-1 Utilizing Novel Internal Ribosome Entry Site Elements for Native Nef Expression and Function

We previously developed replication-competent reporter HIV-1 (referred to herein as LucR.T2A reporter viruses), utilizing a "ribosome skipping" T2A peptide strategy to link Renilla luciferase (LucR) with Nef expression. The demonstrated utility for HIV-1 vaccine and transmission study applications included measurement of neutralizing antibody (NAb) activity in vaccine sera, improved cell-mediated virus inhibition assays, such as T cell-mediated virus inhibition and antibody-dependent cell-mediated cytotoxicity (ADCC) assays, and humanized mouse models. Herein, we extend our prior work and introduce reporter virus technology for applications that require fully functional Nef. We demonstrate that in CD4(+) T cells productively infected with LucR.T2A reporter viruses, T2A peptide-driven Nef expression and function, such as down-regulation of surface CD4 and MHC-I, were impaired. We overcame this limitation of LucR.T2A reporter viruses and achieved physiological Nef expression and function by engineering novel LucR reporter HIV-1 comprising 11 different internal ribosome entry site (IRES) elements chosen for size and relative activity. A range of Nef expression was observed in 293T cells transfected with the different LucR.IRES reporter virus constructs. Iteratively, we identified IRES reporter genomes that expressed Nef closest to physiological levels and produced virus with infectivity, titers, and replication kinetics similar to nonreporter viruses. Our results demonstrated that LucR reporter activity was stable over multiple replication cycles in peripheral blood mononuclear cells (PBMCs). Furthermore, we analyzed Nef functionality, i.e., down-modulation of MHC-I and CD4, following infection of T cell lines and PBMCs. Unlike LucR.T2A reporter virus, one of the redesigned LucR.IRES reporter viruses [containing the modified encephalomyocarditis virus (EMCV) 6ATR IRES element, "6ATRi"] demonstrated Nef expression and function similar to parental "nonreporter" virus. In a previously validated (nef-independent) T cell-based NAb neutralization assay, LucR.6ATRi reporter virus performed indistinguishably from LucR.T2A reporter virus. In summary, reporter viruses comprising the "6ATRi" element promise to augment HIV-1 vaccine and transmission research approaches requiring a sensitive reporter readout combined with wild-type Nef function.

Association of HIV-1 Envelope-Specific Breast Milk IgA Responses with Reduced Risk of Postnatal Mother-to-Child Transmission of HIV-1

Infants born to HIV-1-infected mothers in resource-limited areas where replacement feeding is unsafe and impractical are repeatedly exposed to HIV-1 throughout breastfeeding. Despite this, the majority of infants do not contract HIV-1 postnatally, even in the absence of maternal antiretroviral therapy. This suggests that immune factors in breast milk of HIV-1-infected mothers help to limit vertical transmission. We compared the HIV-1 envelope-specific breast milk and plasma antibody responses of clade C HIV-1-infected postnatally transmitting and nontransmitting mothers in the control arm of the Malawi-based Breastfeeding Antiretrovirals and Nutrition Study using multivariable logistic regression modeling. We found no association between milk or plasma neutralization activity, antibody-dependent cell-mediated cytotoxicity, or HIV-1 envelope-specific IgG responses and postnatal transmission risk. While the envelope-specific breast milk and plasma IgA responses also did not reach significance in predicting postnatal transmission risk in the primary model after correction for multiple comparisons, subsequent exploratory analysis using two distinct assay methodologies demonstrated that the magnitudes of breast milk total and secretory IgA responses against a consensus HIV-1 envelope gp140 (B.con env03) were associated with reduced postnatal transmission risk. These results suggest a protective role for mucosal HIV-1 envelope-specific IgA responses in the context of postnatal virus transmission. This finding supports further investigations into the mechanisms by which mucosal IgA reduces risk of HIV-1 transmission via breast milk and into immune interventions aimed at enhancing this response.

IMPORTANCE

Infants born to HIV-1-infected mothers are repeatedly exposed to the virus in breast milk. Remarkably, the transmission rate is low, suggesting that immune factors in the breast milk of HIV-1-infected mothers help to limit transmission. We compared the antibody responses in plasma and breast milk of HIV-1-transmitting and -nontransmitting mothers to identify responses that correlated with reduced risk of postnatal HIV-1 transmission. We found that neither plasma nor breast milk IgG antibody responses were associated with risk of HIV-1 transmission. In contrast, the magnitudes of the breast milk IgA and secretory IgA responses against HIV-1 envelope proteins were associated with reduced risk of postnatal HIV-1 transmission. The results of this study support further investigations of the mechanisms by which mucosal IgA may reduce the risk of HIV-1 transmission via breastfeeding and the development of strategies to enhance milk envelope-specific IgA responses to reduce mother-to-child HIV transmission and promote an HIV-free generation.

Dual-Affinity Re-Targeting proteins direct T cell-mediated cytolysis of latently HIV-infected cells

Enhancement of HIV-specific immunity is likely required to eliminate latent HIV infection. Here, we have developed an immunotherapeutic modality aimed to improve T cell-mediated clearance of HIV-1-infected cells. Specifically, we employed Dual-Affinity Re-Targeting (DART) proteins, which are bispecific, antibody-based molecules that can bind 2 distinct cell-surface molecules simultaneously. We designed DARTs with a monovalent HIV-1 envelope-binding (Env-binding) arm that was derived from broadly binding, antibody-dependent cellular cytotoxicity-mediating antibodies known to bind to HIV-infected target cells coupled to a monovalent CD3 binding arm designed to engage cytolytic effector T cells (referred to as HIVxCD3 DARTs). Thus, these DARTs redirected polyclonal T cells to specifically engage with and kill Env-expressing cells, including CD4+ T cells infected with different HIV-1 subtypes, thereby obviating the requirement for HIV-specific immunity. Using lymphocytes from patients on suppressive antiretroviral therapy (ART), we demonstrated that DARTs mediate CD8+ T cell clearance of CD4+ T cells that are superinfected with the HIV-1 strain JR-CSF or infected with autologous reservoir viruses isolated from HIV-infected-patient resting CD4+ T cells. Moreover, DARTs mediated CD8+ T cell clearance of HIV from resting CD4+ T cell cultures following induction of latent virus expression. Combined with HIV latency reversing agents, HIVxCD3 DARTs have the potential to be effective immunotherapeutic agents to clear latent HIV-1 reservoirs in HIV-infected individuals.

Human Non-neutralizing HIV-1 Envelope Monoclonal Antibodies Limit the Number of Founder Viruses during SHIV Mucosal Infection in Rhesus Macaques

HIV-1 mucosal transmission begins with virus or virus-infected cells moving through mucus across mucosal epithelium to infect CD4+ T cells. Although broadly neutralizing antibodies (bnAbs) are the type of HIV-1 antibodies that are most likely protective, they are not induced with current vaccine candidates. In contrast, antibodies that do not neutralize primary HIV-1 strains in the TZM-bl infection assay are readily induced by current vaccine candidates and have also been implicated as secondary correlates of decreased HIV-1 risk in the RV144 vaccine efficacy trial. Here, we have studied the capacity of anti-Env monoclonal antibodies (mAbs) against either the immunodominant region of gp41 (7B2 IgG1), the first constant region of gp120 (A32 IgG1), or the third variable loop (V3) of gp120 (CH22 IgG1) to modulate in vivo rectal mucosal transmission of a high-dose simian-human immunodeficiency virus (SHIV-BaL) in rhesus macaques. 7B2 IgG1 or A32 IgG1, each containing mutations to enhance Fc function, was administered passively to rhesus macaques but afforded no protection against productive clinical infection while the positive control antibody CH22 IgG1 prevented infection in 4 of 6 animals. Enumeration of transmitted/founder (T/F) viruses revealed that passive infusion of each of the three antibodies significantly reduced the number of T/F genomes. Thus, some antibodies that bind HIV-1 Env but fail to neutralize virus in traditional neutralization assays may limit the number of T/F viruses involved in transmission without leading to enhancement of viral infection. For one of these mAbs, gp41 mAb 7B2, we provide the first co-crystal structure in complex with a common cyclical loop motif demonstrated to be critical for infection by other retroviruses.

The Vaginal Acquisition and Dissemination of HIV-1 Infection in a Novel Transgenic Mouse Model Is Facilitated by Coinfection with Herpes Simplex Virus 2 and Is Inhibited by Microbicide Treatment

Epidemiological studies have demonstrated that herpes simplex virus 2 (HSV-2) infection significantly increases the risk of HIV-1 acquisition, thereby contributing to the expanding HIV-1 epidemic. To investigate whether HSV-2 infection directly facilitates mucosal HIV-1 acquisition, we used our transgenic hCD4/R5/cT1 mouse model which circumvents major entry and transcription blocks preventing murine HIV-1 infection by targeting transgenic expression of human CD4, CCR5, and cyclin T1 genes to CD4(+) T cells and myeloid-committed cells. Productive infection of mucosal leukocytes, predominantly CD4(+) T cells, was detected in all hCD4/R5/cT1 mice intravaginally challenged with an HIV-1 infectious molecular clone, HIV-Du151.2env-NLuc, which expresses an env gene (C.Du151.2) cloned from an acute heterosexually infected woman and a NanoLuc luciferase reporter gene. Lower genital tract HIV-1 infection after HIV-Du151.2env-NLuc intravaginal challenge was increased ~4-fold in hCD4/R5/cT1 mice coinfected with HSV-2. Furthermore, HIV-1 dissemination to draining lymph nodes was detected only in HSV-2-coinfected mice. HSV-2 infection stimulated local infiltration and activation of CD4(+) T cells and dendritic cells, likely contributing to the enhanced HIV-1 infection and dissemination in HSV-2-coinfected mice. We then used this model to demonstrate that a novel gel containing tenofovir disoproxil fumarate (TDF), the more potent prodrug of tenofovir (TFV), but not the TFV microbicide gel utilized in the recent CAPRISA 004, VOICE (Vaginal and Oral Interventions to Control the Epidemic), and FACTS 001 clinical trials, was effective as preexposure prophylaxis (PrEP) to completely prevent vaginal HIV-1 infection in almost half of HSV-2-coinfected mice. These results also support utilization of hCD4/R5/cT1 mice as a highly reproducible immunocompetent preclinical model to evaluate HIV-1 acquisition across the female genital tract.

IMPORTANCE

Multiple epidemiological studies have reported that genital herpes simplex virus 2 (HSV-2) infection increases the risk of HIV-1 sexual acquisition by severalfold. Understanding the underlying mechanisms by which HSV-2 facilitates HIV-1 infection and optimizing the efficacy of therapies to inhibit HIV-1 infection during HSV-2 coinfection should contribute to reducing HIV-1 transmission. Using our novel transgenic hCD4/R5/cT1 mouse model infectible with HIV-1, we demonstrated that HSV-2 infection enhances vaginal transmission and dissemination of HIV-1 infection while stimulating recruitment and activation of CD4(+) T cells and dendritic cells in the lower genital tract. HIV acquisition by hCD4/R5/cT1 mice vaginally coinfected with HSV-2 could be completely prevented in almost half the mice by preexposure prophylaxis (PrEP) with a novel gel containing tenofovir disoproxil fumarate (TDF), the tenofovir prodrug, but not with the tenofovir microbicide gel utilized in CAPRISA-004, VOICE, and FACTS-001 clinical trials. The hCD4/R5/cT1 mice represent a new preclinical mouse model to evaluate vaginal HIV-1 acquisition.

An Enhanced Synthetic Multiclade DNA Prime Induces Improved Cross-Clade-Reactive Functional Antibodies when Combined with an Adjuvanted Protein Boost in Nonhuman Primates

The search for an efficacious human immunodeficiency virus type 1 (HIV-1) vaccine remains a pressing need. The moderate success of the RV144 Thai clinical vaccine trial suggested that vaccine-induced HIV-1-specific antibodies can reduce the risk of HIV-1 infection. We have made several improvements to the DNA platform and have previously shown that improved DNA vaccines alone are capable of inducing both binding and neutralizing antibodies in small-animal models. In this study, we explored how an improved DNA prime and recombinant protein boost would impact HIV-specific vaccine immunogenicity in rhesus macaques (RhM). After DNA immunization with either a single HIV Env consensus sequence or multiple constructs expressing HIV subtype-specific Env consensus sequences, we detected both CD4(+) and CD8(+) T-cell responses to all vaccine immunogens. These T-cell responses were further increased after protein boosting to levels exceeding those of DNA-only or protein-only immunization. In addition, we observed antibodies that exhibited robust cross-clade binding and neutralizing and antibody-dependent cellular cytotoxicity (ADCC) activity after immunization with the DNA prime-protein boost regimen, with the multiple-Env formulation inducing a more robust and broader response than the single-Env formulation. The magnitude and functionality of these responses emphasize the strong priming effect improved DNA immunogens can induce, which are further expanded upon protein boost. These results support further study of an improved synthetic DNA prime together with a protein boost for enhancing anti-HIV immune responses.

IMPORTANCE

Even with effective antiretroviral drugs, HIV remains an enormous global health burden. Vaccine development has been problematic in part due to the high degree of diversity and poor immunogenicity of the HIV Env protein. Studies suggest that a relevant HIV vaccine will likely need to induce broad cellular and humoral responses from a simple vaccine regimen due to the resource-limited setting in which the HIV pandemic is most rampant. DNA vaccination lends itself well to increasing the amount of diversity included in a vaccine due to the ease of manufacturing multiple plasmids and formulating them as a single immunization. By increasing the number of Envs within a formulation, we were able to show an increased breadth of responses as well as improved functionality induced in a nonhuman primate model. This increased breadth could be built upon, leading to better coverage against circulating strains with broader vaccine-induced protection.

Head-to-Head Comparison of Poxvirus NYVAC and ALVAC Vectors Expressing Identical HIV-1 Clade C Immunogens in Prime-Boost Combination with Env Protein in Nonhuman Primates

We compared the HIV-1-specific cellular and humoral immune responses elicited in rhesus macaques immunized with two poxvirus vectors (NYVAC and ALVAC) expressing the same HIV-1 antigens from clade C, Env gp140 as a trimeric cell-released protein and a Gag-Pol-Nef polyprotein as Gag-induced virus-like particles (VLPs) (referred to as NYVAC-C and ALVAC-C). The immunization protocol consisted of two doses of the corresponding poxvirus vector plus two doses of a combination of the poxvirus vector and a purified HIV-1 gp120 protein from clade C. This immunogenicity profile was also compared to that elicited by vaccine regimens consisting of two doses of the ALVAC vector expressing HIV-1 antigens from clades B/E (ALVAC-vCP1521) plus two doses of a combination of ALVAC-vCP1521 and HIV-1 gp120 protein from clades B/E (similar to the RV144 trial regimen) or clade C. The results showed that immunization of macaques with NYVAC-C stimulated at different times more potent HIV-1-specific CD4(+) T-cell responses and induced a trend toward higher-magnitude HIV-1-specific CD8(+) T-cell immune responses than did ALVAC-C. Furthermore, NYVAC-C induced a trend toward higher levels of binding IgG antibodies against clade C HIV-1 gp140, gp120, or murine leukemia virus (MuLV) gp70-scaffolded V1/V2 and toward best cross-clade-binding IgG responses against HIV-1 gp140 from clades A, B, and group M consensus, than did ALVAC-C. Of the linear binding IgG responses, most were directed against the V3 loop in all immunization groups. Additionally, NYVAC-C and ALVAC-C also induced similar levels of HIV-1-neutralizing antibodies and antibody-dependent cellular cytotoxicity (ADCC) responses. Interestingly, binding IgA antibody levels against HIV-1 gp120 or MuLV gp70-scaffolded V1/V2 were absent or very low in all immunization groups. Overall, these results provide a comprehensive survey of the immunogenicity of NYVAC versus ALVAC expressing HIV-1 antigens in nonhuman primates and indicate that NYVAC may represent an alternative candidate to ALVAC in the development of a future HIV-1 vaccine.

IMPORTANCE

The finding of a safe and effective HIV/AIDS vaccine immunogen is one of the main research priorities. Here, we generated two poxvirus-based HIV vaccine candidates (NYVAC and ALVAC vectors) expressing the same clade C HIV-1 antigens in separate vectors, and we analyzed in nonhuman primates their immunogenicity profiles. The results showed that immunization with NYVAC-C induced a trend toward higher HIV-1-specific cellular and humoral immune responses than did ALVAC-C, indicating that this new NYVAC vector could be a novel optimized HIV/AIDS vaccine candidate for human clinical trials.

Inhibitory Effect of Individual or Combinations of Broadly Neutralizing Antibodies and Antiviral Reagents against Cell-Free and Cell-to-Cell HIV-1 Transmission

To date, most therapeutic and vaccine candidates for human immunodeficiency virus type 1 (HIV-1) are evaluated preclinically for efficacy against cell-free viral challenges. However, cell-associated HIV-1 is suggested to be a major contributor to sexual transmission by mucosal routes. To determine if neutralizing antibodies or inhibitors block cell-free and cell-associated virus transmission of diverse HIV-1 strains with different efficiencies, we tested 12 different antibodies and five inhibitors against four green fluorescent protein (GFP)-labeled HIV-1 envelope (Env) variants from transmitted/founder (T/F) or chronic infection isolates. We evaluated antibody/inhibitor-mediated virus neutralization using either TZM-bl target cells, in which infectivity was determined by virus-driven luciferase expression, or A3R5 lymphoblastoid target cells, in which infectivity was evaluated by GFP expression. In both the TZM-bl and A3R5 assays, cell-free virus or infected CD4+ lymphocytes were used as targets for neutralization. We further hypothesized that the combined use of specific neutralizing antibodies targeting HIV-1 Env would more effectively prevent cell-associated virus transmission than the use of individual antibodies. The tested antibody combinations included two gp120-directed antibodies, VRC01 and PG9, or VRC01 with the gp41-directed antibody 10E8. Our results demonstrated that cell-associated virus was less sensitive to neutralizing antibodies and inhibitors, particularly using the A3R5 neutralization assay, and the potencies of these neutralizing agents differed among Env variants. A combination of different neutralizing antibodies that target specific sites on gp120 led to a significant reduction in cell-associated virus transmission. These assays will help identify ideal combinations of broadly neutralizing antibodies to use for passive preventive antibody administration and further characterize targets for the most effective neutralizing antibodies/inhibitors.

IMPORTANCE

Prevention of the transmission of human immunodeficiency virus type 1 (HIV-1) remains a prominent goal of HIV research. The relative contribution of HIV-1 within an infected cell versus cell-free HIV-1 to virus transmission remains debated. It has been suggested that cell-associated virus is more efficient at transmitting HIV-1 and more difficult to neutralize than cell-free virus. Several broadly neutralizing antibodies and retroviral inhibitors are currently being studied as potential therapies against HIV-1 transmission. The present study demonstrates a decrease in neutralizing antibody and inhibitor efficiencies against cell-associated compared to cell-free HIV-1 transmission among different strains of HIV-1. We also observed a significant reduction in virus transmission using a combination of two different neutralizing antibodies that target specific sites on the outermost region of HIV-1, the virus envelope. Therefore, our findings support the use of antibody combinations against both cell-free and cell-associated virus in future candidate therapy regimens.

Comparable Antigenicity and Immunogenicity of Oligomeric Forms of a Novel, Acute HIV-1 Subtype C gp145 Envelope for Use in Preclinical and Clinical Vaccine Research

Eliciting broadly reactive functional antibodies remains a challenge in human immunodeficiency virus type 1 (HIV-1) vaccine development that is complicated by variations in envelope (Env) subtype and structure. The majority of new global HIV-1 infections are subtype C, and novel antigenic properties have been described for subtype C Env proteins. Thus, an HIV-1 subtype C Env protein (CO6980v0c22) from an infected person in the acute phase (Fiebig stage I/II) was developed as a research reagent and candidate immunogen. The gp145 envelope is a novel immunogen with a fully intact membrane-proximal external region (MPER), extended by a polylysine tail. Soluble gp145 was enriched for trimers that yielded the expected "fan blade" motifs when visualized by cryoelectron microscopy. CO6980v0c22 gp145 reacts with the 4E10, PG9, PG16, and VRC01 HIV-1 neutralizing monoclonal antibodies (MAbs), as well as the V1/V2-specific PGT121, 697, 2158, and 2297 MAbs. Different gp145 oligomers were tested for immunogenicity in rabbits, and purified dimers, trimers, and larger multimers elicited similar levels of cross-subtype binding and neutralizing antibodies to tier 1 and some tier 2 viruses. Immunized rabbit sera did not neutralize the highly resistant CO6980v0c22 pseudovirus but did inhibit the homologous infectious molecular clone in a peripheral blood mononuclear cell (PBMC) assay. This Env is currently in good manufacturing practice (GMP) production to be made available for use as a clinical research tool and further evaluation as a candidate vaccine.

IMPORTANCE

At present, the product pipeline for HIV vaccines is insufficient and is limited by inadequate capacity to produce large quantities of vaccine to standards required for human clinical trials. Such products are required to evaluate critical questions of vaccine formulation, route, dosing, and schedule, as well as to establish vaccine efficacy. The gp145 Env protein presented in this study forms physical trimers, binds to many of the well-characterized broad neutralizing MAbs that target conserved Env epitopes, and induce cross-subtype neutralizing antibodies as measured in both cell line and primary cell assays. This subtype C Env gp145 protein is currently undergoing good manufacturing practice production for use as a reagent for preclinical studies and for human clinical research. This product will serve as a reagent for comparative studies and may represent a next-generation candidate HIV immunogen.

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.

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

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

IMPORTANCE

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

Antiviral gene expression in psoriasis

BACKGROUND

Psoriasis patients have relatively infrequent cutaneous viral infections compared to atopic dermatitis patients. Increased expression of four antiviral proteins (MX1, BST2, ISG15 and OAS2) has been reported in psoriatic skin and genetic studies of psoriasis have identified susceptibility genes in antiviral pathways.

OBJECTIVE

To determine if psoriasis is associated with pervasive expression of antiviral genes in skin and blood.

METHODS

We performed RNA sequencing on skin samples of 18 subjects with chronic plaque psoriasis and 16 healthy controls. We examined the expression of a predefined set of 42 antiviral genes, each of which has been shown in previous studies to inhibit viral replication. In parallel, we examined antiviral gene expression in atopic dermatitis, non-lesional psoriatic skin and psoriatic blood. We performed HIV-1 infectivity assays in CD4+ peripheral blood T cells from psoriatic and healthy individuals.

RESULTS

We observed significant overexpression of 16 antiviral genes in lesional psoriatic skin, with a greater than two-fold increase in ISG15, RSAD2, IRF7, MX2 and TRIM22 (P < 1E-07). None of these genes was overexpressed in atopic dermatitis skin (P < 0.0001) or non-lesional psoriatic skin. In contrast to the skin compartment, no differences in antiviral gene expression were detected in the peripheral blood of psoriasis cases compared to healthy controls. CD4+ T cells from both psoriatic and healthy patients supported HIV-1 infection at a similar rate.

CONCLUSION

Our findings highlight psoriasis as an inflammatory disease with cutaneous but not systemic immune activation against viral pathogens.

Defense-in-depth by mucosally administered anti-HIV dimeric IgA2 and systemic IgG1 mAbs: complete protection of rhesus monkeys from mucosal SHIV challenge

Although IgA is the most abundantly produced immunoglobulin in humans, its role in preventing HIV-1 acquisition, which occurs mostly via mucosal routes, remains unclear. In our passive mucosal immunizations of rhesus macaques (RMs), the anti-HIV-1 neutralizing monoclonal antibody (nmAb) HGN194, given either as dimeric IgA1 (dIgA1) or dIgA2 intrarectally (i.r.), protected 83% or 17% of the RMs against i.r. simian-human immunodeficiency virus (SHIV) challenge, respectively. Data from the RV144 trial implied that vaccine-induced plasma IgA counteracted the protective effector mechanisms of IgG1 with the same epitope specificity. We thus hypothesized that mucosal dIgA2 might diminish the protection provided by IgG1 mAbs targeting the same epitope. To test our hypothesis, we administered HGN194 IgG1 intravenously (i.v.) either alone or combined with i.r. HGN194 dIgA2. We enrolled SHIV-exposed, persistently aviremic RMs protected by previously administered nmAbs; RM anti-human IgG responses were undetectable. However, low-level SIV Gag-specific proliferative T-cell responses were found. These animals resemble HIV-exposed, uninfected humans, in which local and systemic cellular immune responses have been observed. HGN194 IgG1 and dIgA2 used alone and the combination of the two neutralized the challenge virus equally well in vitro. All RMs given only i.v. HGN194 IgG1 became infected. In contrast, all RMs given HGN194 IgG1+dIgA2 were completely protected against high-dose i.r. SHIV-1157ipEL-p challenge. These data imply that combining suboptimal defenses at the mucosal and systemic levels can completely prevent virus acquisition. Consequently, active vaccination should focus on defense-in-depth, a strategy that seeks to build up defensive fall-back positions well behind the fortified frontline.

Synergy in monoclonal antibody neutralization of HIV-1 pseudoviruses and infectious molecular clones

Background

Early events in HIV infection are still poorly understood; virus derived from acute infections, the transmitted/founders IMCs, could provide more reliable information as they represent strains that established HIV infection in vivo, and therefore are investigated to elucidate potentially shared biological features.

Methods

This study examined synergy in neutralization by six monoclonal antibodies targeting different domains in gp120 and gp41 and assayed in pairwise combination against 11 HIV-1 clade B strains, either Env pseudoviruses (PV, n = 5) or transmitted/founder infectious molecular clones (T/F IMCs, n = 6). Three of the early-infection env tested as PV were juxtaposed with T/F viruses derived from the same three patients, respectively.

Results

All antibodies reaching IC50 were assayed pairwise (n = 50). T/F IMCs showed overall lower sensitivity to neutralization by single antibodies than PV, including within the three patient-matched pairs. Remarkably, combination index (CI) calculated using the Chow and Talalay method indicated synergy (CI < 0.9) in 42 data sets, and occurred in T/F IMC at similar proportions (15 of 17 antibody-T/F IMC combinations tested) as in pseudoviruses (27 of 33). CI values indicative of additivity and low-level antagonism were seen in 5 and 3 cases, respectively. Most pairs showed comparable synergic neutralizing effects on both virus groups, with the 4E10 + PG16 pair achieving the best synergic effects. Variability in neutralization was mostly observed on pseudovirus isolates, suggesting that factors other than virus isolation technology, such as env conformation, epitope accessibility and antibody concentration, are likely to affect polyclonal neutralization.

Conclusions

The findings from this study suggest that inhibitory activity of bNAbs can be further augmented through appropriate combination, even against viruses representing circulating strains, which are likely to exhibit a less sensitive Tier 2 neutralization phenotype. This notion has important implications for the design and development of anti-Env bNAb-inducing vaccines and polyclonal sera for passive immunization.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-014-0346-3) contains supplementary material, which is available to authorized users.

Comparison of neutralizing antibody responses elicited from highly diverse polyvalent heterotrimeric HIV-1 gp140 cocktail immunogens versus a monovalent counterpart in rhesus macaques

Eliciting neutralizing antibodies capable of inactivating a broad spectrum of HIV-1 strains is a major goal of HIV-1 vaccine design. The challenge is that envelopes (Envs) of circulating viruses are almost certainly different from any Env used in a vaccine. A novel immunogen composed of a highly diverse set of gp140 Envs including subtypes A, B, C, D and F was developed to stimulate a more cross-neutralizing antibody response. Env heterotrimers composed of up to 54 different gp140s were produced with the aim of focusing the response to the conserved regions of Env while reducing the dominance of any individual hypervariable region. Heterotrimeric gp140 Envs of inter- and intra-subtype combinations were shown to bind CD4 and a panel of neutralizing monoclonal antibodies with similar affinity to monovalent UG37 gp140. Macaques immunized with six groups of heterotrimer mixtures showed slightly more potent neutralizing antibody responses in TZM-BL tier 1 and A3R5 tier 2 pseudovirus assays than macaques immunized with monovalent Env gp140, and exhibited a marginally greater focus on the CD4-binding site. Carbopol enhanced neutralization when used as an adjuvant instead of RIBI in combination with UG37 gp140. These data indicate that cross-subtype heterotrimeric gp140 Envs may elicit some improvement of the neutralizing antibody response in macaques compared to monovalent gp140 Env.