R5 clade C SHIV strains with tier 1 or 2 neutralization sensitivity: tools to dissect env evolution and to develop AIDS vaccines in primate models

SHIV-C109p5 NHP induces rapid disease progression in elderly macaques with extensive GI viral replication

CCR5-tropic simian/human immunodeficiency viruses (SHIV) with clade C transmitted/founder envelopes represent a critical tool for the investigation of HIV experimental vaccines and microbicides in nonhuman primates, although many such isolates lead to spontaneous viral control post infection. Here, we generated a high-titer stock of pathogenic SHIV-C109p5 by serial passage in two rhesus macaques (RM) and tested its virulence in aged monkeys. The co-receptor usage was confirmed before infecting five geriatric rhesus macaques (four female and one male). Plasma viral loads were monitored by reverse transcriptase-quantitative PCR (RT-qPCR), cytokines by multiplex analysis, and biomarkers of gastrointestinal damage by enzyme-linked immunosorbent assay. Antibodies and cell-mediated responses were also measured. Viral dissemination into tissues was determined by RNAscope. Intravenous SHIV-C109p5 infection of aged RMs leads to high plasma viremia and rapid disease progression; rapid decrease in CD4+ T cells, CD4+CD8+ T cells, and plasmacytoid dendritic cells; and wasting necessitating euthanasia between 3 and 12 weeks post infection. Virus-specific cellular immune responses were detected only in the two monkeys that survived 4 weeks post infection. These were Gag-specific TNFα+CD8+, MIP1β+CD4+, Env-specific IFN-γ+CD4+, and CD107a+ T cell responses. Four out of five monkeys had elevated intestinal fatty acid binding protein levels at the viral peak, while regenerating islet-derived protein 3α showed marked increases at later time points in the three animals surviving the longest, suggesting gut antimicrobial peptide production in response to microbial translocation post infection. Plasma levels of monocyte chemoattractant protein-1, interleukin-15, and interleukin-12/23 were also elevated. Viral replication in gut and secondary lymphoid tissues was extensive.IMPORTANCESimian/human immunodeficiency viruses (SHIV) are important reagents to study prevention of virus acquisition in nonhuman primate models of HIV infection, especially those representing transmitted/founder (T/F) viruses. However, many R5-tropic SHIV have limited fitness in vivo leading to many monkeys spontaneously controlling the virus post acute infection. Here, we report the generation of a pathogenic SHIV clade C T/F stock by in vivo passage leading to sustained viral load set points, a necessity to study pathogenicity. Unexpectedly, administration of this SHIV to elderly rhesus macaques led to extensive viral replication and fast disease progression, despite maintenance of a strict R5 tropism. Such age-dependent rapid disease progression had previously been reported for simian immunodeficiency virus but not for R5-tropic SHIV infections.

A neutralizing antibody target in early HIV-1 infection was recapitulated in rhesus macaques immunized with the transmitted/founder envelope sequence

Transmitted/founder (T/F) HIV-1 envelope proteins (Envs) from infected individuals that developed neutralization breadth are likely to possess inherent features desirable for vaccine immunogen design. To explore this premise, we conducted an immunization study in rhesus macaques (RM) using T/F Env sequences from two human subjects, one of whom developed potent and broad neutralizing antibodies (Z1800M) while the other developed little to no neutralizing antibody responses (R66M) during HIV-1 infection. Using a DNA/MVA/protein immunization protocol, 10 RM were immunized with each T/F Env. Within each T/F Env group, the protein boosts were administered as either monomeric gp120 or stabilized trimeric gp140 protein. All vaccination regimens elicited high titers of antigen-specific IgG, and two animals that received monomeric Z1800M Env gp120 developed autologous neutralizing activity. Using early Env escape variants isolated from subject Z1800M as guides, the serum neutralizing activity of the two immunized RM was found to be dependent on the gp120 V5 region. Interestingly, the exact same residues of V5 were also targeted by a neutralizing monoclonal antibody (nmAb) isolated from the subject Z1800M early in infection. Glycan profiling and computational modeling of the Z1800M Env gp120 immunogen provided further evidence that the V5 loop is exposed in this T/F Env and was a dominant feature that drove neutralizing antibody targeting during infection and immunization. An expanded B cell clonotype was isolated from one of the neutralization-positive RM and nmAbs corresponding to this group demonstrated V5-dependent neutralization similar to both the RM serum and the human Z1800M nmAb. The results demonstrate that neutralizing antibody responses elicited by the Z1800M T/F Env in RM converged with those in the HIV-1 infected human subject, illustrating the potential of using immunogens based on this or other T/F Envs with well-defined immunogenicity as a starting point to drive breadth.

Development of Neutralization Breadth against Diverse HIV-1 by Increasing Ab-Ag Interface on V2

Understanding maturation pathways of broadly neutralizing antibodies (bnAbs) against HIV-1 can be highly informative for HIV-1 vaccine development. A lineage of J038 bnAbs is now obtained from a long-term SHIV-infected macaque. J038 neutralizes 54% of global circulating HIV-1 strains. Its binding induces a unique "up" conformation for one of the V2 loops in the trimeric envelope glycoprotein and is heavily dependent on glycan, which provides nearly half of the binding surface. Their unmutated common ancestor neutralizes the autologous virus. Continuous maturation enhances neutralization potency and breadth of J038 lineage antibodies via expanding antibody-Env contact areas surrounding the core region contacted by germline-encoded residues. Developmental details and recognition features of J038 lineage antibodies revealed here provide a new pathway for elicitation and maturation of V2-targeting bnAbs.

Cooperation Between Systemic IgG1 and Mucosal Dimeric IgA2 Monoclonal Anti-HIV Env Antibodies: Passive Immunization Protects Indian Rhesus Macaques Against Mucosal SHIV Challenges

Understanding the interplay between systemic and mucosal anti-HIV antibodies can provide important insights to develop new prevention strategies. We used passive immunization via systemic and/or mucosal routes to establish cause-and-effect between well-characterized monoclonal antibodies and protection against intrarectal (i.r.) SHIV challenge. In a pilot study, for which we re-used animals previously exposed to SHIV but completely protected from viremia by different classes of anti-HIV neutralizing monoclonal antibodies (mAbs), we made a surprise finding: low-dose intravenous (i.v.) HGN194-IgG1, a human neutralizing mAb against the conserved V3-loop crown, was ineffective when given alone but protected 100% of animals when combined with i.r. applied HGN194-dIgA2 that by itself had only protected 17% of the animals. Here we sought to confirm the unexpected synergy between systemically administered IgG1 and mucosally applied dIgA HGN194 forms using six groups of naïve macaques (n=6/group). Animals received i.v. HGN194-IgG1 alone or combined with i.r.-administered dIgA forms; controls remained untreated. HGN194-IgG1 i.v. doses were given 24 hours before - and all i.r. dIgA doses 30 min before - i.r. exposure to a single high-dose of SHIV-1157ipEL-p. All controls became viremic. Among passively immunized animals, the combination of IgG1+dIgA2 again protected 100% of the animals. In contrast, single-agent i.v. IgG1 protected only one of six animals (17%) - consistent with our pilot data. IgG1 combined with dIgA1 or dIgA1+dIgA2 protected 83% (5/6) of the animals. The dIgA1+dIgA2 combination without the systemically administered dose of IgG1 protected 67% (4/6) of the macaques. We conclude that combining suboptimal antibody defenses at systemic and mucosal levels can yield synergy and completely prevent virus acquisition.

PET/CT targeted tissue sampling reveals virus specific dIgA can alter the distribution and localization of HIV after rectal exposure

Human immunodeficiency virus (HIV) vaccines have not been successful in clinical trials. Dimeric IgA (dIgA) in the form of secretory IgA is the most abundant antibody class in mucosal tissues, making dIgA a prime candidate for potential HIV vaccines. We coupled Positron Emission Tomography (PET) imaging and fluorescent microscopy of 64Cu-labeled, photoactivatable-GFP HIV (PA-GFP-BaL) and fluorescently labeled dIgA to determine how dIgA antibodies influence virus interaction with mucosal barriers and viral penetration in colorectal tissue. Our results show that HIV virions rapidly disseminate throughout the colon two hours after exposure. The presence of dIgA resulted in an increase in virions and penetration depth in the transverse colon. Moreover, virions were found in the mesenteric lymph nodes two hours after viral exposure, and the presence of dIgA led to an increase in virions in mesenteric lymph nodes. Taken together, these technologies enable in vivo and in situ visualization of antibody-virus interactions and detailed investigations of early events in HIV infection.

Modified Adenovirus Prime-Protein Boost Clade C HIV Vaccine Strategy Results in Reduced Viral DNA in Blood and Tissues Following Tier 2 SHIV Challenge

Designing immunogens and improving delivery methods eliciting protective immunity is a paramount goal of HIV vaccine development. A comparative vaccine challenge study was performed in rhesus macaques using clade C HIV Envelope (Env) and SIV Gag antigens. One group was vaccinated using co-immunization with DNA Gag and Env expression plasmids cloned from a single timepoint and trimeric Env gp140 glycoprotein from one of these clones (DNA+Protein). The other group was a prime-boost regimen composed of two replicating simian (SAd7) adenovirus-vectored vaccines expressing Gag and one Env clone from the same timepoint as the DNA+Protein group paired with the same Env gp140 trimer (SAd7+Protein). The env genes were isolated from a single pre-peak neutralization timepoint approximately 1 year post infection in CAP257, an individual with a high degree of neutralization breadth. Both DNA+Protein and SAd7+Protein vaccine strategies elicited significant Env-specific T cell responses, lesser Gag-specific responses, and moderate frequencies of Env-specific T_FH cells. Both vaccine modalities readily elicited systemic and mucosal Env-specific IgG but not IgA. There was a higher frequency and magnitude of ADCC activity in the SAd7+Protein than the DNA+Protein arm. All macaques developed moderate Tier 1 heterologous neutralizing antibodies, while neutralization of Tier 1B or Tier 2 viruses was sporadic and found primarily in macaques in the SAd7+Protein group. Neither vaccine approach provided significant protection from viral acquisition against repeated titered mucosal challenges with a heterologous Tier 2 clade C SHIV. However, lymphoid and gut tissues collected at necropsy showed that animals in both vaccine groups each had significantly lower copies of viral DNA in individual tissues compared to levels in controls. In the SAd7+Protein-vaccinated macaques, total and peak PBMC viral DNA were significantly lower compared with controls. Taken together, this heterologous Tier 2 SHIV challenge study shows that combination vaccination with SAd7+Protein was superior to combination DNA+Protein in reducing viral seeding in tissues in the absence of protection from infection, thus emphasizing the priming role of replication-competent SAd7 vector. Despite the absence of correlates of protection, because antibody responses were significantly higher in this vaccine group, we hypothesize that vaccine-elicited antibodies contribute to limiting tissue viral seeding.

ALVAC-HIV B/C candidate HIV vaccine efficacy dependent on neutralization profile of challenge virus and adjuvant dose and type

The ALVAC-HIV clade B/AE and equivalent SIV-based/gp120 + Alum vaccines successfully decreased the risk of virus acquisition in humans and macaques. Here, we tested the efficacy of HIV clade B/C ALVAC/gp120 vaccine candidates + MF59 or different doses of Aluminum hydroxide (Alum) against SHIV-Cs of varying neutralization sensitivity in macaques. Low doses of Alum induced higher mucosal V2-specific IgA that increased the risk of Tier 2 SHIV-C acquisition. High Alum dosage, in contrast, elicited serum IgG to V2 that correlated with a decreased risk of Tier 1 SHIV-C acquisition. MF59 induced negligible mucosal antibodies to V2 and an inflammatory profile with blood C-reactive Protein (CRP) levels correlating with neutralizing antibody titers. MF59 decreased the risk of Tier 1 SHIV-C acquisition. The relationship between vaccine efficacy and the neutralization profile of the challenge virus appear to be linked to the different immunological spaces created by MF59 and Alum via CXCL10 and IL-1β, respectively.

Mucosal Antibodies: Defending Epithelial Barriers against HIV-1 Invasion

The power of mucosal anti-HIV-1 envelope immunoglobulins (Igs) to block virus transmission is underappreciated. We used passive immunization, a classical tool to unequivocally prove whether antibodies are protective. We mucosally instilled recombinant neutralizing monoclonal antibodies (nmAbs) of different Ig classes in rhesus macaques (RMs) followed by mucosal simian–human immunodeficiency virus (SHIV) challenge. We gave anti-HIV-1 IgM, IgG, and dimeric IgA (dIgA) versions of the same human nmAb, HGN194 that targets the conserved V3 loop crown. Surprisingly, dIgA1 with its wide-open, flat hinge protected 83% of the RMs against intrarectal R5-tropic SHIV-1157ipEL-p challenge, whereas dIgA2, with its narrow hinge, only protected 17% of the animals—despite identical epitope specificities and in vitro neutralization curves of the two dIgA isotypes (Watkins et al., AIDS 2013 27(9):F13-20). These data imply that factors in addition to neutralization determine in vivo protection. We propose that this underlying protective mechanism is immune exclusion, which involves large nmAb/virion aggregates that prevent virus penetration of mucosal barriers. Future studies need to find biomarkers that predict effective immune exclusion in vivo. Vaccine development strategies against HIV-1 and/or other mucosally transmissible pathogens should include induction of strong mucosal Abs of different Ig classes to defend epithelial barriers against pathogen invasion.

Rational design and in vivo selection of SHIVs encoding transmitted/founder subtype C HIV-1 envelopes

Chimeric Simian-Human Immunodeficiency Viruses (SHIVs) are an important tool for evaluating anti-HIV Env interventions in nonhuman primate (NHP) models. However, most unadapted SHIVs do not replicate well in vivo limiting their utility. Furthermore, adaptation in vivo often negatively impacts fundamental properties of the Env, including neutralization profiles. Transmitted/founder (T/F) viruses are particularly important to study since they represent viruses that initiated primary HIV-1 infections and may have unique attributes. Here we combined in vivo competition and rational design to develop novel subtype C SHIVs containing T/F envelopes. We successfully generated 19 new, infectious subtype C SHIVs, which were tested in multiple combinatorial pools in Indian-origin rhesus macaques. Infected animals attained peak viremia within 5 weeks ranging from 10³ to 10⁷ vRNA copies/mL. Sequence analysis during primary infection revealed 7 different SHIVs replicating in 8 productively infected animals with certain clones prominent in each animal. We then generated 5 variants each of 6 SHIV clones (3 that predominated and 3 undetectable after pooled in vivo inoculations), converting a serine at Env375 to methionine, tyrosine, histidine, tryptophan or phenylalanine. Overall, most Env375 mutants replicated better in vitro and in vivo than wild type with both higher and earlier peak viremia. In 4 of these SHIV clones (with and without Env375 mutations) we also created mutations at position 281 to include serine, alanine, valine, or threonine. Some Env281 mutations imparted in vitro replication dynamics similar to mutations at 375; however, clones with both mutations did not exhibit incremental benefit. Therefore, we identified unique subtype C T/F SHIVs that replicate in rhesus macaques with improved acute phase replication kinetics without altering phenotype. In vivo competition and rational design can produce functional SHIVs with globally relevant HIV-1 Envs to add to the growing number of SHIV clones for HIV-1 research in NHPs.

Nonhuman primates provide useful models for studying HIV transmission, pathogenesis and cure strategies. Due to species-specific antiviral factors, however, HIV cannot replicate in Asian macaques directly. Some chimeric viruses incorporating HIV Envelope genes in simian immunodeficiency virus (SIV) backbone can replicate to sufficient levels in Asian macaques to permit evaluation of anti-HIV interventions. Here we describe the generation of new SHIV clones unique to the field in 4 important ways. First, these clones were generated from the globally relevant HIV-1 subtype C, which is the most prevalent form of HIV globally and is found predominately in sub-Saharan Africa where the pandemic is particularly devastating but is poorly represented among SHIVs studied to date. Second, we utilized Envelope genes from viruses that established primary infection, making these clones particularly useful in transmission studies. Third, these clones were not generated by animal passage, which may alter some of the unique properties of these Envelopes. Finally, we used direct within animal competition studies and two targeted mutations to select highly replicative clones. We provide here both the discovery of new SHIV clones, and also a process to generate additional clones in the future.

Accelerating HIV vaccine development using non-human primate models

INTRODUCTION

The search for a preventative HIV vaccine is ongoing after three decades of research. Contributions of non-human primate (NHP) models to this research are irrefutable, however interpreting data obtained for translation to humans has been problematic. As knowledge concerning NHP models has accumulated, their utility and value in assessing immunogenicity and efficacy of novel vaccines have become apparent. NHP models have become a critical component of vaccine design.

AREAS COVERED

Beginning with early vaccine studies, we trace the development and evolution of NHP models concurrent with changes in HIV vaccine concepts and in response to their ability to predict clinical trial efficacy. The value of NHP studies in guiding vaccine design is highlighted along with their importance in opening new areas of investigation and facilitating movement of promising approaches into the clinic.

EXPERT COMMENTARY

Due to their close relatedness to humans, NHPs are an excellent choice for immunogenicity studies. The ability of NHP models to predict clinical efficacy has improved with the introduction of low-dose challenge viruses and recognition of confounding variables in study outcomes. Use of NHP models has opened new research areas with outstanding potential for generating vaccine efficacy against HIV and other infectious agents.

Polyclonal HIV envelope-specific breast milk antibodies limit founder SHIV acquisition and cell-associated virus loads in infant rhesus monkeys

Breast milk HIV-1 transmission is currently the predominant contributor to pediatric HIV infections. Yet, only ~10% of breastfeeding infants born to untreated HIV-infected mothers become infected. This study assessed the protective capacity of natural HIV envelope-specific antibodies isolated from the milk of HIV-infected women in an infant rhesus monkey (RM), tier 2 SHIV oral challenge model. To mimic placental and milk maternal antibody transfer, infant RMs were i.v. infused and orally treated at the time of challenge with a single weakly neutralizing milk monoclonal antibody (mAb), a tri-mAb cocktail with weakly neutralizing and ADCC functionalities, or an anti-influenza control mAb. Of these groups, the fewest tri-mAb-treated infants had SHIV detectable in plasma or tissues (2/6, 5/6, and 7/8 animals infected in tri-mAb, single-mAb, and control-mAb groups, respectively). Tri-mAb-treated infants demonstrated significantly fewer plasma transmitted/founder variants and reduced peripheral CD4+ T cell proviral loads at 8 weeks post-challenge compared to control mAb-treated infants. Abortive infection was observed as detectable CD4+ T cell provirus in non-viremic control mAb- and single mAb-, but not in tri-mAb-treated animals. These results suggest that polyfunctional milk antibodies contribute to the natural inefficiency of HIV-1 transmission through breastfeeding and infant vaccinations eliciting non-neutralizing antibody responses could reduce postnatal HIV transmission.

SIV/SHIV-Zika co-infection does not alter disease pathogenesis in adult non-pregnant rhesus macaque model

Due to the large geographical overlap of populations exposed to Zika virus (ZIKV) and human immunodeficiency virus (HIV), understanding the disease pathogenesis of co-infection is urgently needed. This warrants the development of an animal model for HIV-ZIKV co-infection. In this study, we used adult non-pregnant macaques that were chronically infected with simian immunodeficiency virus/chimeric simian human immunodeficiency virus (SIV/SHIV) and then inoculated with ZIKV. Plasma viral loads of both SIV/SHIV and ZIKV co-infected animals revealed no significant changes as compared to animals that were infected with ZIKV alone or as compared to SIV/SHIV infected animals prior to ZIKV inoculation. ZIKV tissue clearance of co-infected animals was similar to animals that were infected with ZIKV alone. Furthermore, in co-infected macaques, there was no statistically significant difference in plasma cytokines/chemokines levels as compared to prior to ZIKV inoculation. Collectively, these findings suggest that co-infection may not alter disease pathogenesis, thus warranting larger HIV-ZIKV epidemiological studies in order to validate these findings.

Anti-HIV IgM protects against mucosal SHIV transmission

OBJECTIVE

Worldwide, most new HIV infections occur through mucosal exposure. Immunoglobulin M (IgM) is the first antibody class generated in response to infectious agents; IgM is present in the systemic circulation and in mucosal fluids as secretory IgM. We sought to investigate for the first time the role of IgM in preventing AIDS virus acquisition in vivo.

DESIGN

Recombinant polymeric monoclonal IgM was generated from the neutralizing monoclonal IgG1 antibody 33C6-IgG1, tested in vitro, and given by passive intrarectal immunization to rhesus macaques 30 min before intrarectal challenge with simian-human immunodeficiency virus (SHIV) that carries an HIV-1 envelope gene.

RESULTS

In vitro, 33C6-IgM captured virions more efficiently and neutralized the challenge SHIV with a 50% inhibitory molar concentration (IC50) that was 1 log lower than that for 33C6-IgG1. The IgM form also exhibited significantly higher affinity and avidity compared with 33C6-IgG1. After intrarectal administration, 33C6-IgM prevented viremia in four out of six rhesus macaques after high-dose intrarectal SHIV challenge. Five out of six rhesus macaques given 33C6-IgG1 were protected at a five times higher molar concentration compared with the IgM form; all untreated controls became highly viremic. Rhesus macaques passively immunized with 33C6-IgM with breakthrough infection had notably early development of autologous neutralizing antibody responses.

CONCLUSION

Our primate model data provide the first proof-of-concept that mucosal IgM can prevent mucosal HIV transmission and have implications for HIV prevention and vaccine development.

Novel Strategy To Adapt Simian-Human Immunodeficiency Virus E1 Carrying env from an RV144 Volunteer to Rhesus Macaques: Coreceptor Switch and Final Recovery of a Pathogenic Virus with Exclusive R5 Tropism

The phase III RV144 human immunodeficiency virus (HIV) vaccine trial conducted in Thailand remains the only study to show efficacy in decreasing the HIV acquisition risk. In Thailand, circulating recombinant forms of HIV clade A/E (CRF01_AE) predominate; in such viruses, env originates from clade E (HIV-E). We constructed a simian-human immunodeficiency virus (SHIV) chimera carrying env isolated from an RV144 placebo recipient in the SHIV-1157ipd3N4 backbone. The latter contains long terminal repeats (LTRs) with duplicated NF-κB sites, thus resembling HIV LTRs. We devised a novel strategy to adapt the parental infectious molecular clone (IMC), R5 SHIV-E1, to rhesus macaques: the simultaneous depletion of B and CD8⁺ cells followed by the intramuscular inoculation of proviral DNA and repeated administrations of cell-free virus. High-level viremia and CD4⁺ T-cell depletion ensued. Passage 3 virus unexpectedly caused acute, irreversible CD4⁺ T-cell loss; the partially adapted SHIV had become dual tropic. Virus and IMCs with exclusive R5 tropism were reisolated from earlier passages, combined, and used to complete adaptation through additional macaques. The final isolate, SHIV-E1p5, remained solely R5 tropic. It had a tier 2 neutralization phenotype, was mucosally transmissible, and was pathogenic. Deep sequencing revealed 99% Env amino acid sequence conservation; X4-only and dual-tropic strains had evolved independently from an early branch of parental SHIV-E1. To conclude, our primate model data reveal that SHIV-E1p5 recapitulates important aspects of HIV transmission and pathobiology in humans.IMPORTANCE Understanding the protective principles that lead to a safe, effective vaccine against HIV in nonhuman primate (NHP) models requires test viruses that allow the evaluation of anti-HIV envelope responses. Reduced HIV acquisition risk in RV144 has been linked to nonneutralizing IgG antibodies with a range of effector activities. Definitive experiments to decipher the mechanisms of the partial protection observed in RV144 require passive-immunization studies in NHPs with a relevant test virus. We have generated such a virus by inserting env from an RV144 placebo recipient into a SHIV backbone with HIV-like LTRs. The final SHIV-E1p5 isolate, grown in rhesus monkey peripheral blood mononuclear cells, was mucosally transmissible and pathogenic. Earlier SHIV-E passages showed a coreceptor switch, again mimicking HIV biology in humans. Thus, our series of SHIV-E strains mirrors HIV transmission and disease progression in humans. SHIV-E1p5 represents a biologically relevant tool to assess prevention strategies.

High throughput generation and characterization of replication-competent clade C transmitter-founder simian human immunodeficiency viruses

Traditional restriction endonuclease-based cloning has been routinely used to generate replication-competent simian-human immunodeficiency viruses (SHIV) and simian tropic HIV (stHIV). This approach requires the existence of suitable restriction sites or the introduction of nucleotide changes to create them. Here, using an In-Fusion cloning technique that involves homologous recombination, we generated SHIVs and stHIVs based on epidemiologically linked clade C transmitted/founder HIV molecular clones from Zambia. Replacing vif from these HIV molecular clones with vif of SIVmac239 resulted in chimeric genomes used to generate infectious stHIV viruses. Likewise, exchanging HIV env genes and introducing N375 mutations to enhance macaque CD4 binding site and cloned into a SHIVAD8-EO backbone. The generated SHIVs and stHIV were infectious in TZMbl and ZB5 cells, as well as macaque PBMCs. Therefore, this method can replace traditional methods and be a valuable tool for the rapid generation and testing of molecular clones of stHIV and SHIV based on primary clinical isolates will be valuable to generate rapid novel challenge viruses for HIV vaccine/cure studies.

Combination Adenovirus and Protein Vaccines Prevent Infection or Reduce Viral Burden after Heterologous Clade C Simian-Human Immunodeficiency Virus Mucosal Challenge

HIV vaccine development is focused on designing immunogens and delivery methods that elicit protective immunity. We evaluated a combination of adenovirus (Ad) vectors expressing HIV 1086.C (clade C) envelope glycoprotein (Env), SIV Gag p55, and human pegivirus GBV-C E2 glycoprotein. We compared replicating simian (SAd7) with nonreplicating human (Ad4) adenovirus-vectored vaccines paired with recombinant proteins in a novel prime-boost regimen in rhesus macaques, with the goal of eliciting protective immunity against SHIV challenge. In both vaccine groups, plasma and buccal Env-specific IgG, tier 1 heterologous neutralizing antibodies, and antibody-dependent cell-mediated viral inhibition were readily generated. High Env-specific T cell responses elicited in all vaccinees were significantly greater than responses targeting Gag. After three intrarectal exposures to heterologous tier 1 clade C SHIV, all 10 sham-vaccinated controls were infected, whereas 4/10 SAd7- and 3/10 Ad4-vaccinated macaques remained uninfected or maintained tightly controlled plasma viremia. Time to infection was significantly delayed in SAd7-vaccinated macaques compared to the controls. Cell-associated and plasma virus levels were significantly lower in each group of vaccinated macaques compared to controls; the lowest plasma viral burden was found in animals vaccinated with the SAd7 vectors, suggesting superior immunity conferred by the replicating simian vectors. Furthermore, higher V1V2-specific binding antibody titers correlated with viral control in the SAd7 vaccine group. Thus, recombinant Ad plus protein vaccines generated humoral and cellular immunity that was effective in either protecting from SHIV acquisition or significantly reducing viremia in animals that became infected, consequently supporting additional development of replicating Ad vectors as HIV vaccines.IMPORTANCE There is a well-acknowledged need for an effective AIDS vaccine that protects against HIV infection and limits in vivo viral replication and associated pathogenesis. Although replicating virus vectors have been advanced as HIV vaccine platforms, there have not been any direct comparisons of the replicating to the nonreplicating format. The present study directly compared the replicating SAd7 to nonreplicating Ad4 vectors in macaques and demonstrated that in the SAd7 vaccine group, the time to infection was significantly delayed compared to the control group, and V1V2 Env-specific binding antibodies correlated with viral outcomes. Viral control was significantly enhanced in vaccinated macaques compared to controls, and in infected SAd7-vaccinated macaques compared to Ad4-vaccinated macaques, suggesting that this vector may have conferred more effective immunity. Because blocking infection is so difficult with current vaccines, development of a vaccine that can limit viremia if infection occurs would be valuable. These data support further development of replicating adenovirus vectors.

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.

Antibody-mediated immune exclusion of HIV

PURPOSE OF REVIEW

Although approximately 90% of all HIV transmissions in humans occur through mucosal contact, the induction of mucosal anti-HIV immune responses has remained understudied. Here we summarize data demonstrating the powerful protection that is achievable at mucosal frontlines through virus-specific mucosal IgA alone or combined with IgG.

RECENT FINDINGS

Passive immunization with different monoclonal antibody subclasses but identical epitope specificity (the conserved V3-loop crown of HIV gp120) has revealed that the dimeric IgA1 (dIgA1) form with its open hinge can prevent simian-human immunodeficiency virus (SHIV) acquisition in rhesus macaques at a higher rate than dIgA2. Both dIgAs neutralized the challenge SHIV equally well. Protection was linked to better virion capture and inhibition of cell-free virus transcytosis by dIgA1. Synergistic interactions at the mucosal level between the IgG1 and dIgA2 versions of this monoclonal antibody yielded complete protection. Active vaccine strategies designed to induce mucosal IgA and systemic/mucosal IgG have given promising data.

SUMMARY

This review seeks to highlight the importance of mucosal IgAs in preventing virus acquisition. Passive immunization gave proof-of-concept for immune exclusion by mucosally administered monoclonal dIgAs. Unanswered questions remain regarding the interplay between mucosal IgA and other host immune defenses, including their induction with active immunization.

Repertoire comparison of the B-cell receptor-encoding loci in humans and rhesus macaques by next-generation sequencing

Rhesus macaques (RMs) are a widely used model system for the study of vaccines, infectious diseases and microbial pathogenesis. Their value as a model lies in their close evolutionary relationship to humans, which, in theory, allows them to serve as a close approximation of the human immune system. However, despite their prominence as a human surrogate model system, many aspects of the RM immune system remain ill characterized. In particular, B cell-mediated immunity in macaques has not been sufficiently characterized, and the B-cell receptor-encoding loci have not been thoroughly annotated. To address these gaps, we analyzed the circulating heavy- and light-chain repertoires in humans and RMs by next-generation sequencing. By comparing V gene segment usage, J-segment usage and CDR3 lengths between the two species, we identified several important similarities and differences. These differences were especially notable in the IgM(+) B-cell repertoire. However, the class-switched, antigen-educated B-cell populations converged on a set of similar characteristics, implying similarities in how each species responds to antigen. Our study provides the first comprehensive overview of the circulating repertoires of the heavy- and light-chain sequences in RMs, and provides insight into how they may perform as a model system for B cell-mediated immunity in humans.

Envelope residue 375 substitutions in simian-human immunodeficiency viruses enhance CD4 binding and replication in rhesus macaques

Most simian-human immunodeficiency viruses (SHIVs) bearing envelope (Env) glycoproteins from primary HIV-1 strains fail to infect rhesus macaques (RMs). We hypothesized that inefficient Env binding to rhesus CD4 (rhCD4) limits virus entry and replication and could be enhanced by substituting naturally occurring simian immunodeficiency virus Env residues at position 375, which resides at a critical location in the CD4-binding pocket and is under strong positive evolutionary pressure across the broad spectrum of primate lentiviruses. SHIVs containing primary or transmitted/founder HIV-1 subtype A, B, C, or D Envs with genotypic variants at residue 375 were constructed and analyzed in vitro and in vivo. Bulky hydrophobic or basic amino acids substituted for serine-375 enhanced Env affinity for rhCD4, virus entry into cells bearing rhCD4, and virus replication in primary rhCD4 T cells without appreciably affecting antigenicity or antibody-mediated neutralization sensitivity. Twenty-four RMs inoculated with subtype A, B, C, or D SHIVs all became productively infected with different Env375 variants-S, M, Y, H, W, or F-that were differentially selected in different Env backbones. Notably, SHIVs replicated persistently at titers comparable to HIV-1 in humans and elicited autologous neutralizing antibody responses typical of HIV-1. Seven animals succumbed to AIDS. These findings identify Env-rhCD4 binding as a critical determinant for productive SHIV infection in RMs and validate a novel and generalizable strategy for constructing SHIVs with Env glycoproteins of interest, including those that in humans elicit broadly neutralizing antibodies or bind particular Ig germ-line B-cell receptors.

Production of Mucosally Transmissible SHIV Challenge Stocks from HIV-1 Circulating Recombinant Form 01_AE env Sequences

Simian-human immunodeficiency virus (SHIV) challenge stocks are critical for preclinical testing of vaccines, antibodies, and other interventions aimed to prevent HIV-1. A major unmet need for the field has been the lack of a SHIV challenge stock expressing circulating recombinant form 01_AE (CRF01_AE) env sequences. We therefore sought to develop mucosally transmissible SHIV challenge stocks containing HIV-1 CRF01_AE env derived from acutely HIV-1 infected individuals from Thailand. SHIV-AE6, SHIV-AE6RM, and SHIV-AE16 contained env sequences that were >99% identical to the original HIV-1 isolate and did not require in vivo passaging. These viruses exhibited CCR5 tropism and displayed a tier 2 neutralization phenotype. These challenge stocks efficiently infected rhesus monkeys by the intrarectal route, replicated to high levels during acute infection, and established chronic viremia in a subset of animals. SHIV-AE16 was titrated for use in single, high dose as well as repetitive, low dose intrarectal challenge studies. These SHIV challenge stocks should facilitate the preclinical evaluation of vaccines, monoclonal antibodies, and other interventions targeted at preventing HIV-1 CRF01_AE infection.

In this study, we generated and evaluated novel simian-human immunodeficiency virus (SHIV) challenge stocks expressing env sequences from HIV-1 strains from Thailand. The lack of such SHIV challenge stocks has been a major unmet need for the field and has hindered progress to evaluate strategies aimed at preventing HIV-1 infection for this region of the world. The challenge stocks described in this manuscript should prove useful for studying the preclinical efficacy and mechanisms of vaccines, antibodies, and other interventions.

Phenotypic and Functional Characterization of Monoclonal Antibodies with Specificity for Rhesus Macaque CD200, CD200R and Mincle

Lectin-like molecules and their receptors are cell surface molecules that have been shown to play a role in either facilitating infection or serving as transporters of HIV/SIV in vivo. The role of these lectin-like molecules in the pathogenesis of HIV/SIV infection continues to be defined. In efforts to gain further insight on the potential role of these lectin-like molecules, our laboratory generated monoclonal antibodies (mAb) against the human analogs of rhesus macaque CD200, CD200R and Mincle, since the rhesus macaques are accepted as the most reliable animal model to study human HIV infection. The characterization of the cell lineages from the blood and various tissues of rhesus macaques that express these lectin-like molecules are described herein. Among the mononuclear cells, the cells of the myeloid lineage of rhesus macaques are the predominant cell lineages that express readily detectable levels of CD200, CD200R and Mincle that is similar to the expression of Siglec-1 and Siglec-3 reported by our laboratory earlier. Subset analysis revealed that a higher frequency of the CD14⁺/CD16^- subset from normal rhesus macaques express CD200, CD200R and Mincle. Differences in the frequencies and density of expression of these molecules by the gated population of CD14⁺ cells from various tissues are noted with PBMC and bone marrow expressing the highest and the mononuclear cells isolated from the colon and ileum expressing the lowest levels. While a significant frequency of pDCs and mDCs express Siglec-1/Siglec-3, a much lower frequency expresses CD200, CD200R and Mincle in PBMCs from rhesus macaques. The mAb against CD200 and CD200R but not Mincle appear to inhibit the infection of macrophage tropic SIV/SHIV in vitro. We conclude that these mAbs may have potential to be used as adjunctive therapeutic agents to control/inhibit SIV/HIV infection.

Combined Antiviral Therapy Using Designed Molecular Scaffolds Targeting Two Distinct Viral Functions, HIV-1 Genome Integration and Capsid Assembly

Designed molecular scaffolds have been proposed as alternative therapeutic agents against HIV-1. The ankyrin repeat protein (Ank(GAG)1D4) and the zinc finger protein (2LTRZFP) have recently been characterized as intracellular antivirals, but these molecules, used individually, do not completely block HIV-1 replication and propagation. The capsid-binder Ank(GAG)1D4, which inhibits HIV-1 assembly, does not prevent the genome integration of newly incoming viruses. 2LTRZFP, designed to target the 2-LTR-circle junction of HIV-1 cDNA and block HIV-1 integration, would have no antiviral effect on HIV-1-infected cells. However, simultaneous expression of these two molecules should combine the advantage of preventive and curative treatments. To test this hypothesis, the genes encoding the N-myristoylated Myr(+)Ank(GAG)1D4 protein and the 2LTRZFP were introduced into human T-cells, using a third-generation lentiviral vector. SupT1 cells stably expressing 2LTRZFP alone or with Myr(+)Ank(GAG)1D4 showed a complete resistance to HIV-1 in viral challenge. Administration of the Myr(+)Ank(GAG)1D4 vector to HIV-1-preinfected SupT1 cells resulted in a significant antiviral effect. Resistance to viral infection was also observed in primary human CD4+ T-cells stably expressing Myr(+)Ank(GAG)1D4, and challenged with HIV-1, SIVmac, or SHIV. Our data suggest that our two anti-HIV-1 molecular scaffold prototypes are promising antiviral agents for anti-HIV-1 gene therapy.

Development of SHIVs with circulating, transmitted HIV-1 variants

SHIV/macaque model is critical for pre-clinical HIV-1 research. The ability of this model to predict efficacious intervention(s) in humans depends on how faithfully the model recapitulates key features of HIV-1 transmission and pathogenesis. Here, we provide insights for rationally designing SHIVs with transmitted HIV-1 variants for vaccine and prevention research.

Characterization of protective immune response elicited by a trimeric envelope protein from an Indian clade C HIV-1 isolate in rhesus macaques

BACKGROUND

Recent preclinical studies have demonstrated the use of properly folded trimeric HIV-1 envelope proteins as immunogen for eliciting protecting immune response in macaques.

METHODS

Trimeric gp145 protein of Indian clade C HIV-1 (93IN101) was characterized for antigenicity by evaluating its binding to sCD4, and several monoclonal antibodies to HIV-1 by bio-layer interferometry. Ten macaques were immunized four times with purified gp145 in adjuplex adjuvant, and serum antibodies were characterized for binding to gp145 and neutralization. Immunized macaques were subjected to weekly low-dose vaginal challenge with SHIV1157-ipEL-p for 8 weeks.

RESULTS

Env protein elicited strong antibody response in macaques. Following challenge, seven of ten immunized macaques resisted challenge, while six of eight control animals were infected.

CONCLUSIONS

Env proteins from a clade C Indian isolate can elicit protective immune response and therefore may be a candidate for inclusion in a multiclade-based HIV-1 vaccine.

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.

Generation and evaluation of clade C simian-human immunodeficiency virus challenge stocks

The development of a panel of mucosally transmissible simian-human immunodeficiency virus (SHIV) challenge stocks from multiple virus clades would facilitate preclinical evaluation of candidate HIV-1 vaccines and therapeutics. The majority of SHIV stocks that have been generated to date have been derived from clade B HIV-1 env sequences from viruses isolated during chronic infection and typically required serial animal-to-animal adaptation for establishing mucosal transmissibility and pathogenicity. To capture essential features of mucosal transmission of clade C viruses, we produced a series of SHIVs with early clade C HIV-1 env sequences from acutely HIV-1-infected individuals from South Africa. SHIV-327c and SHIV-327cRM expressed env sequences that were 99.7 to 100% identical to the original HIV-1 isolate and did not require in vivo passaging for mucosal infectivity. These challenge stocks infected rhesus monkeys efficiently by both intrarectal and intravaginal routes, replicated to high levels during acute infection, and established chronic setpoint viremia in 13 of 17 (76%) infected animals. The SHIV-327cRM challenge stock was also titrated for both single, high-dose intrarectal challenges and repetitive, low-dose intrarectal challenges in rhesus monkeys. These SHIV challenge stocks should facilitate the preclinical evaluation of vaccines and other interventions aimed at preventing clade C HIV-1 infection.

IMPORTANCE

We describe the development of two related clade C SHIV challenge stocks. These challenge stocks should prove useful for preclinical testing of vaccines and other interventions aimed at preventing clade C HIV-1 infection.

Natural killer T cell and TLR9 agonists as mucosal adjuvants for sublingual vaccination with clade C HIV-1 envelope protein

The vast majority of HIV-1 infections occur at mucosa during sexual contact. It may therefore be advantageous to provide mucosal barrier protection against this entry by mucosal vaccination. While a number of mucosal routes of vaccination are possible, many like enteric oral vaccines or intranasal vaccines have significant impediments that limit vaccine efficacy or pose safety risks. In contrast, immunogens applied to the sublingual region of the mouth could provide a simple route for mucosal vaccination. While sublingual immunization is appealing, this site does not always drive strong immune responses, particularly when using protein antigens. To address this issue, we have tested the ability of two mucosal adjuvants: alpha-galactosylceramide (αGalCer) that is a potent stimulator of natural killer T cells and CpG-oligodeoxynucleotide (CpG-ODN) a TLR9 agonist for their ability to amplify immune responses against clade C gp140 HIV-1 envelope protein antigen. Immunization with envelope protein alone resulted in a weak T cell and antibody responses. In contrast, CD4(+) and CD8(+) T cells responses in systemic and mucosal tissues were significantly higher in mice immunized with gp140 in the presence of either αGalCer or CpG-ODN and these responses were further augmented when the two adjuvants were used together. While both the adjuvants effectively increased gp140-specific serum IgG and vaginal IgA antibody levels, combining both significantly improved these responses. Memory T cell responses 60 days after immunization revealed αGalCer to be more potent than CpG-ODN and the combination of the αGalCer and CpG-ODN adjuvants was more effective than either alone. Serum and vaginal washes collected 60 days after immunization with gp140 with both αGalCer and CpG-ODN adjuvants had significant neutralization activity against Tier 1 and Tier 2 SHIVs. These data support the utility of the sublingual route for mucosal vaccination particularly in combination with αGalCer and CpG-ODN adjuvants.

Multimodality vaccination against clade C SHIV: partial protection against mucosal challenges with a heterologous tier 2 virus

We sought to test whether vaccine-induced immune responses could protect rhesus macaques (RMs) against upfront heterologous challenges with an R5 simian-human immunodeficiency virus, SHIV-2873Nip. This SHIV strain exhibits many properties of transmitted HIV-1, such as tier 2 phenotype (relatively difficult to neutralize), exclusive CCR5 tropism, and gradual disease progression in infected RMs. Since no human AIDS vaccine recipient is likely to encounter an HIV-1 strain that exactly matches the immunogens, we immunized the RMs with recombinant Env proteins heterologous to the challenge virus. For induction of immune responses against Gag, Tat, and Nef, we explored a strategy of immunization with overlapping synthetic peptides (OSP). The immune responses against Gag and Tat were finally boosted with recombinant proteins. The vaccinees and a group of ten control animals were given five low-dose intrarectal (i.r.) challenges with SHIV-2873Nip. All controls and seven out of eight vaccinees became systemically infected; there was no significant difference in viremia levels of vaccinees vs. controls. Prevention of viremia was observed in one vaccinee which showed strong boosting of virus-specific cellular immunity during virus exposures. The protected animal showed no challenge virus-specific neutralizing antibodies in the TZM-bl or A3R5 cell-based assays and had low-level ADCC activity after the virus exposures. Microarray data strongly supported a role for cellular immunity in the protected animal. Our study represents a case of protection against heterologous tier 2 SHIV-C by vaccine-induced, virus-specific cellular immune responses.

The Neonatal Fc receptor (FcRn) enhances human immunodeficiency virus type 1 (HIV-1) transcytosis across epithelial cells

The mechanisms by which human immunodeficiency virus type 1 (HIV-1) crosses mucosal surfaces to establish infection are unknown. Acidic genital secretions of HIV-1-infected women contain HIV-1 likely coated by antibody. We found that the combination of acidic pH and Env-specific IgG, including that from cervicovaginal and seminal fluids of HIV-1-infected individuals, augmented transcytosis across epithelial cells as much as 20-fold compared with Env-specific IgG at neutral pH or non-specific IgG at either pH. Enhanced transcytosis was observed with clinical HIV-1 isolates, including transmitted/founder strains, and was eliminated in Fc neonatal receptor (FcRn)-knockdown epithelial cells. Non-neutralizing antibodies allowed similar or less transcytosis than neutralizing antibodies. However, the ratio of total:infectious virus was higher for neutralizing antibodies, indicating that they allowed transcytosis while blocking infectivity of transcytosed virus. Immunocytochemistry revealed abundant FcRn expression in columnar epithelia lining the human endocervix and penile urethra. Acidity and Env-specific IgG enhance transcytosis of virus across epithelial cells via FcRn and could facilitate translocation of virus to susceptible target cells following sexual exposure.

HIV-1 causes a sexually transmitted disease. However, the mechanisms employed by the virus to cross genital tract tissue and establish infection are uncertain. Since cervicovaginal fluid is acidic and HIV-1 in cervicovaginal fluid is likely coated with antibodies, we explored the effect of low pH and HIV-1-specific antibodies on transcytosis, the movement of HIV-1 across tight-junctioned epithelial cells. We found that the combination of HIV-1-specific antibodies and low pH enhanced transcytosis as much as 20-fold. Virus that underwent transcytosis under these conditions was infectious, and infectivity was highly influenced by whether or not the antibody neutralized the virus. We observed enhanced transcytosis using antibody from cervicovaginal and seminal fluids and using transmitted/founder strains of HIV-1. We also found that the enhanced transcytosis was due to the Fc neonatal receptor (FcRn), which binds immune complexes at acidic pH and releases them at neutral pH. Finally, staining of human tissue revealed abundant FcRn expression on columnar epithelial cells of penile urethra and endocervix. Our findings reveal a novel mechanism wherein HIV-1 may facilitate its own transmission by usurping the antibody response directed against itself. These results have important implications for HIV vaccine development and for understanding the earliest events in HIV transmission.

Protective efficacy of a global HIV-1 mosaic vaccine against heterologous SHIV challenges in rhesus monkeys

The global diversity of HIV-1 represents a critical challenge facing HIV-1 vaccine development. HIV-1 mosaic antigens are bioinformatically optimized immunogens designed for improved coverage of HIV-1 diversity. However, the protective efficacy of such global HIV-1 vaccine antigens has not previously been evaluated. Here, we demonstrate the capacity of bivalent HIV-1 mosaic antigens to protect rhesus monkeys against acquisition of infection following heterologous challenges with the difficult-to-neutralize simian-human immunodeficiency virus SHIV-SF162P3. Adenovirus/poxvirus and adenovirus/adenovirus vector-based vaccines expressing HIV-1 mosaic Env, Gag, and Pol afforded a significant reduction in the per-exposure acquisition risk following repetitive, intrarectal SHIV-SF162P3 challenges. Protection against acquisition of infection correlated with vaccine-elicited binding, neutralizing, and functional nonneutralizing antibodies, suggesting that the coordinated activity of multiple antibody functions may contribute to protection against difficult-to-neutralize viruses. These data demonstrate the protective efficacy of HIV-1 mosaic antigens and suggest a potential strategy for the development of a global HIV-1 vaccine. PAPERCLIP:

Isolate-specific differences in the conformational dynamics and antigenicity of HIV-1 gp120

The HIV-1 envelope glycoprotein (Env) mediates viral entry into host cells and is the sole target of neutralizing antibodies. Much of the sequence diversity in the HIV-1 genome is concentrated within Env, particularly within its gp120 surface subunit. While dramatic functional diversity exists among HIV-1 Env isolates-observable even in the context of monomeric gp120 proteins as differences in antigenicity and immunogenicity-we have little understanding of the structural features that distinguish Env isolates and lead to isolate-specific functional differences, as crystal structures of truncated gp120 "core" proteins from diverse isolates reveal a high level of structural conservation. Because gp120 proteins are used as prospective vaccine immunogens, it is critical to understand the structural factors that influence their reactivity with antibodies. Here, we studied four full-length, glycosylated gp120 monomers from diverse HIV-1 isolates by using small-angle X-ray scattering (SAXS) to probe the overall subunit morphology and hydrogen/deuterium-exchange with mass spectrometry (HDX-MS) to characterize the local structural order of each gp120. We observed that while the overall subunit architecture was similar among isolates by SAXS, dramatic isolate-specific differences in the conformational stability of gp120 were evident by HDX-MS. These differences persisted even with the CD4 receptor bound. Furthermore, surface plasmon resonance (SPR) and enzyme-linked immunosorbance assays (ELISAs) showed that disorder was associated with poorer recognition by antibodies targeting conserved conformational epitopes. These data provide additional insight into the structural determinants of gp120 antigenicity and suggest that conformational dynamics should be considered in the selection and design of optimized Env immunogens.

Impact of antibody quality and anamnestic response on viremia control post-challenge in a combined Tat/Env vaccine regimen in rhesus macaques

Previously, priming rhesus macaques with Adenovirus type 5 host range mutant-recombinants encoding Tat and Env and boosting with Tat and Env protein in MPL-SE controlled chronic viremia by 4 logs following homologous intravenous SHIV89.6P challenge. Here we evaluated Tat, Env, and Tat/Env regimens for immunogenicity and protective efficacy using clade C Env, alum adjuvant, and a heterologous intrarectal SHIV1157ipd3N4 challenge. Despite induction of strong cellular and humoral immunity, Tat/Env group T and B-cell memory responses were not significantly enhanced over Tat- or Env-only groups. Lack of viremia control post-challenge was attributed to lower avidity Env antibodies and no anamnestic ADCC response or SHIV1157ipd3N4 neutralizing antibody development post-challenge. Poor biologic activity of the Tat immunogen may have impaired Tat immunity. In the absence of sterilizing immunity, strong anamnestic responses to heterologous virus can help control viremia. Both antibody breadth and optimal adjuvanticity are needed to elicit high-quality antibody for protective efficacy.

Anti-HIV IgA isotypes: differential virion capture and inhibition of transcytosis are linked to prevention of mucosal R5 SHIV transmission

OBJECTIVE

Although passive immunization with anti-HIV-1 Env IgG1 neutralizing monoclonal antibodies (nmAbs) prevented simian-human immunodeficiency virus (SHIV) infection in rhesus monkeys, IgA nmAbs have not been tested. Here, we sought to determine whether human anti-HIV-1 dimeric (d)IgA1, dIgA2, and IgG1 differ in their ability to prevent mucosal R5 SHIV acquisition in rhesus monkeys.

DESIGN

DIgA1, dIgA2, and IgG1 versions of nmAb HGN194 were applied intrarectally in three rhesus monkey groups 30 min before intrarectal SHIV challenge.

METHODS

After a control pharmacokinetic study confirmed that nmAb concentrations in rectal fluids over time were similar for all HGN194 isotypes, control and nmAb-treated animals were challenged intrarectally with an R5 SHIV, and viral loads were monitored.

RESULTS

Unexpectedly, dIgA1 provided the best protection in vivo--although all nmAbs showed similar neutralizing activity in vitro. Five out of the six dIgA1-treated rhesus monkeys remained virus-free compared to only one out of six animals given dIgA2 (P=0.045 by log-rank test) and two out of six rhesus monkeys treated with IgG1 forms of the nmAb (P=0.12). Protection correlated significantly with virion capture activity by a given nmAb form, as well as inhibition of transcytosis of cell-free virus across an epithelial cell layer in vitro.

CONCLUSIONS

Our data imply that dIgA1-mediated capturing of virions in mucosal secretions and inhibition of transcytosis can provide significant prevention of lentiviral acquisition--over and above direct virus neutralization. Vaccine strategies that induce mucosal IgA, especially IgA1, should be developed as a first line of defense against HIV-1, a virus predominantly transmitted mucosally.

Animal models in virus research: their utility and limitations

Viral diseases are important threats to public health worldwide. With the number of emerging viral diseases increasing the last decades, there is a growing need for appropriate animal models for virus studies. The relevance of animal models can be limited in terms of mimicking human pathophysiology. In this review, we discuss the utility of animal models for studies of influenza A viruses, HIV and SARS-CoV in light of viral emergence, assessment of infection and transmission risks, and regulatory decision making. We address their relevance and limitations. The susceptibility, immune responses, pathogenesis, and pharmacokinetics may differ between the various animal models. These complexities may thwart translating results from animal experiments to the humans. Within these constraints, animal models are very informative for studying virus immunopathology and transmission modes and for translation of virus research into clinical benefit. Insight in the limitations of the various models may facilitate further improvements of the models.

Identification and characterization of a broadly cross-reactive HIV-1 human monoclonal antibody that binds to both gp120 and gp41

Identification of broadly cross-reactive HIV-1-neutralizing antibodies (bnAbs) may assist vaccine immunogen design. Here we report a novel human monoclonal antibody (mAb), designated m43, which co-targets the gp120 and gp41 subunits of the HIV-1 envelope glycoprotein (Env). M43 bound to recombinant gp140 s from various primary isolates, to membrane-associated Envs on transfected cells and HIV-1 infected cells, as well as to recombinant gp120 s and gp41 fusion intermediate structures containing N-trimer structure, but did not bind to denatured recombinant gp140 s and the CD4 binding site (CD4bs) mutant, gp120 D368R, suggesting that the m43 epitope is conformational and overlaps the CD4bs on gp120 and the N-trimer structure on gp41. M43 neutralized 34% of the HIV-1 primary isolates from different clades and all the SHIVs tested in assays based on infection of peripheral blood mononuclear cells (PBMCs) by replication-competent virus, but was less potent in cell line-based pseudovirus assays. In contrast to CD4, m43 did not induce Env conformational changes upon binding leading to exposure of the coreceptor binding site, enhanced binding of mAbs 2F5 and 4E10 specific for the membrane proximal external region (MPER) of gp41 Envs, or increased gp120 shedding. The overall modest neutralization activity of m43 is likely due to the limited binding of m43 to functional Envs which could be increased by antibody engineering if needed. M43 may represent a new class of bnAbs targeting conformational epitopes overlapping structures on both gp120 and gp41. Its novel epitope and possibly new mechanism(s) of neutralization could helpdesign improved vaccine immunogens and candidate therapeutics.

No acquisition: a new ambition for HIV vaccine development?

Development of a safe and effective prophylactic HIV-1 vaccine presents unique challenges. The pessimism following the failure of two HIV-1 vaccine concepts in clinical trials, HIV-1 gp120 and an adenovirus-based approach to induce only cellular immune responses, has been replaced by cautious optimism engendered by the RV144 trial outcome, the isolation of several new broadly reactive neutralizing monoclonal antibodies, and recent primate model data indicating prevention of viral acquisition by active or passive immunization. Intense efforts are underway to optimize immunogen design, adjuvants, and the tools for preclinical evaluation of candidate vaccines in primates, where correlates of protection can be examined in detail - as proof-of-concept for clinical trials.

Isolation of monoclonal antibodies with predetermined conformational epitope specificity

Existing technologies allow isolating antigen-specific monoclonal antibodies (mAbs) from B cells. We devised a direct approach to isolate mAbs with predetermined conformational epitope specificity, using epitope mimetics (mimotopes) that reflect the three-dimensional structure of given antigen subdomains. We performed differential biopanning using bacteriophages encoding random peptide libraries and polyclonal antibodies (Abs) that had been affinity-purified with either native or denatured antigen. This strategy yielded conformational mimotopes. We then generated mimotope-fluorescent protein fusions, which were used as baits to isolate single memory B cells from rhesus monkeys (RMs). To amplify RM immunoglobulin variable regions, we developed RM-specific PCR primers and generated chimeric simian-human mAbs with predicted epitope specificity. We established proof-of-concept of our strategy by isolating mAbs targeting the conformational V3 loop crown of HIV Env; the new mAbs cross-neutralized viruses of different clades. The novel technology allows isolating mAbs from RMs or other hosts given experimental immunogens or infectious agents.

Inclusion of a CRF01_AE HIV envelope protein boost with a DNA/MVA prime-boost vaccine: Impact on humoral and cellular immunogenicity and viral load reduction after SHIV-E challenge

The current study assessed the immunogenicity and protective efficacy of various prime-boost vaccine regimens in rhesus macaques using combinations of recombinant DNA (rDNA), recombinant MVA (rMVA), and subunit gp140 protein. The rDNA and rMVA vectors were constructed to express Env from HIV-1 subtype CRF01_AE and Gag-Pol from CRF01_AE or SIVmac 239. One of the rMVAs, MVA/CMDR, has been recently tested in humans. Immunizations were administered at months 0 and 1 (prime) and months 3 and 6 (boost). After priming, HIV env-specific serum IgG was detected in monkeys receiving gp140 alone or rMVA but not in those receiving rDNA. Titers were enhanced in these groups after boosting either with gp140 alone or with rMVA plus gp140. The groups that received the rDNA prime developed env-specific IgG after boosting with rMVA with or without gp140. HIV Env-specific serum IgG binding antibodies were elicited more frequently and of higher titer, and breadth of neutralizing antibodies was increased with the inclusion of the subunit Env boost. T cell responses were measured by tetramer binding to Gag p11c in Mamu-A*01 macaques, and by IFN-γ ELISPOT assay to SIV-Gag. T cell responses were induced after vaccination with the highest responses seen in macaques immunized with rDNA and rMVA. Macaques were challenged intravenously with a novel SHIV-E virus (SIVmac239 Gag-Pol with an HIV-1 subtype E-Env CAR402). Post challenge with SHIV-E, antibody titers were boosted in all groups and peaked at 4 weeks. Robust T cell responses were seen in all groups post challenge and in macaques immunized with rDNA and rMVA a clear boosting of responses was seen. A greater than two-log drop in RNA copies/ml at peak viremia and earlier set point was achieved in macaques primed with rDNA, and boosted with rMVA/SHIV-AE plus gp140. Post challenge viremia in macaques immunized with other regimens was not significantly different to that of controls. These results demonstrate that a gp140 subunit and inclusion of SIV Gag-Pol may be critical for control of SHIV post challenge.

High-level, lasting antiviral immunity induced by a bimodal AIDS vaccine and boosted by live-virus exposure: prevention of viremia

OBJECTIVE

To characterize the correlates of protection from systemic infection in a vaccinated rhesus macaque, RAt-9, which had been challenged sequentially with two related clade C simian/human immunodeficiency viruses (SHIV-Cs) yet remained aviremic for more than 5 years despite indirect evidence of cryptic infection.

DESIGN

To measure long-term anti-SHIV-C immunity, host genetics and gene-expression patterns for protective correlates.

METHODS

Long-term immune reactivity was evaluated and identification of virus in RAt-9 was attempted by RT-PCR analysis of concentrated plasma and blood transfer to CD8(+) cell-depleted infant macaques. Full MHC genotyping of RAt-9, TRIM5α and KIR3DL allelic expression analysis of PBMC, and microarray gene expression analysis were performed.

RESULTS

All attempts to detect/isolate virus, including blood transfer to CD8(+) cell-depleted infant rhesus macaques, were negative, and the animal maintained normal levels of memory CD4(+) T cells in both peripheral blood and gut tissues. However, RAt-9 maintained high levels of anti-SHIV-C humoral and cellular immunity, including reactivity to nonvaccine neoantigens (Nef and Rev), up to 63 months postinitial challenge, suggesting chronic sub-threshold infection. RAt-9 expressed the Mamu A*001 allele negative for B*008 and B*017, had a B13 serotype, and had increased expression of killer-cell immunoglobulin-like receptors (KIRs) previously linked to favorable outcomes of lentiviral infection. Elements of the gene expression profiling coincided with genotyping results. RAt-9 also displayed CD8 cell noncytotoxic antiviral response (CNAR) activity.

CONCLUSION

Monkey RAt-9 is the first example of a virus-exposed, persistently aviremic animal that has maintained long-term, high-level cellular and humoral antiviral immunity in the absence of an identifiable cryptic reservoir.

Efficiency of neutralizing antibodies targeting the CD4-binding site: influence of conformational masking by the V2 loop in R5-tropic clade C simian-human immunodeficiency virus

In R5-tropic clade C simian-human immunodeficiency viruses (SHIV-Cs), we identified a 3-asparagine (3N) deletion mutation in the V2 loop stem of gp120 as the major determinant of neutralization escape of the anti-CD4-binding site (anti-CD4-bs) neutralizing monoclonal antibody (nMAb) b12. However, the more potent anti-CD4-bs nMAbs VRC01 and VRC03 were not sensitive to this mutation. Using isogenic tier 1 or tier 2 proviruses differing only in the 3N mutation, we showed that this mutation might result in selective conformational b12 epitope masking. Therefore, human immunodeficiency virus (HIV) Env immunogens targeting the CD4-bs and designed to neutralize tier 2 viruses should take conformational masking by the V2 loop into account.

High antibody and cellular responses induced to HIV-1 clade C envelope following DNA vaccines delivered by electroporation

BACKGROUND

Clade C is the predominant HIV-1 strain infecting people in sub-Saharan Africa, India, and China and there is a critical need for a vaccine targeted to these areas. In this study we tested a DNA based vaccine that encodes the SIVgag, SIVpol and HIV-1 envelope clade C.

METHODS

Rhesus macaques were immunized by electroporation with the DNA plasmid encoding optimized SIVgag, SIVpol and an HIV-1 env clade C with or without the adjuvant RANTES. Animals were monitored for immune responses and challenged following the final immunization with 25 animal infectious doses (AID) of SHIV-1157ipd3N4.

RESULTS

We found that the vaccine induced high levels of antigen specific IFN-γ producing effector cells and the capacity for CD4+ and CD8+ to proliferate upon antigen stimulation. Importantly, we found that the vaccine induced antibody titers as high as 1/4000. These antibodies were capable of neutralizing tier 1 HIV-1 viruses. Finally, when macaques were challenged with SHIV, viral loads were controlled in vaccinated groups.

CONCLUSION

We conclude that immunization with a simian/human immunodeficiency virus DNA-based vaccine delivered by electroporation can induce cellular and humoral immune responses that are able to control viral replication.

Vaccination against heterologous R5 clade C SHIV: prevention of infection and correlates of protection

A safe, efficacious vaccine is required to stop the AIDS pandemic. Disappointing results from the STEP trial implied a need to include humoral anti-HIV-1 responses, a notion supported by RV144 trial data even though correlates of protection are unknown. We vaccinated rhesus macaques with recombinant simian immunodeficiency virus (SIV) Gag-Pol particles, HIV-1 Tat and trimeric clade C (HIV-C) gp160, which induced cross-neutralizing antibodies (nAbs) and robust cellular immune responses. After five low-dose mucosal challenges with a simian-human immunodeficiency virus (SHIV) that encoded a heterologous R5 HIV-C envelope (22.1% divergence from the gp160 immunogen), 94% of controls became viremic, whereas one third of vaccinees remained virus-free. Upon high-dose SHIV rechallenge, all controls became infected, whereas some vaccinees remained aviremic. Peak viremia was inversely correlated with both cellular immunity (p<0.001) and cross-nAb titers (p<0.001). These data simultaneously linked cellular as well as humoral immune responses with the degree of protection for the first time.

Prime-boost vaccination with heterologous live vectors encoding SIV gag and multimeric HIV-1 gp160 protein: efficacy against repeated mucosal R5 clade C SHIV challenges

We sought to induce primate immunodeficiency virus-specific cellular and neutralizing antibody (nAb) responses in rhesus macaques (RM) through a bimodal vaccine approach. RM were immunized intragastrically (i.g.) with the live-attenuated Listeria monocytogenes (Lm) vector Lmdd-BdopSIVgag encoding SIVmac239 gag. SIV Gag-specific cellular responses were boosted by intranasal and intratracheal administration of replication-competent adenovirus (Ad5hr-SIVgag) encoding the same gag. To broaden antiviral immunity, the RM were immunized with multimeric HIV clade C (HIV-C) gp160 and HIV Tat. SIV Gag-specific cellular immune responses and HIV-1 nAb developed in some RM. The animals were challenged intrarectally with five low doses of R5 SHIV-1157ipEL-p, encoding a heterologous HIV-C Env (22.1% divergent to the Env immunogen). All five controls became viremic. One out of ten vaccinees was completely protected and another had low peak viremia. Sera from the completely and partially protected RM neutralized the challenge virus > 90%; these RM also had strong SIV Gag-specific proliferation of CD8⁺ T cells. Peak and area under the curve of plasma viremia (during acute phase) among vaccinees was lower than for controls, but did not attain significance. The completely protected RM showed persistently low numbers of the α4β7-expressing CD4⁺ T cells; the latter have been implicated as preferential virus targets in vivo. Thus, vaccine-induced immune responses and relatively lower numbers of potential target cells were associated with protection.

An anti-HIV-1 V3 loop antibody fully protects cross-clade and elicits T-cell immunity in macaques mucosally challenged with an R5 clade C SHIV

Neutralizing antibodies have been shown to protect macaques against SHIV challenge. However, genetically diverse HIV-1 clades have evolved, and a key question left unanswered is whether neutralizing antibodies can confer cross-clade protection in vivo. The novel human monoclonal antibody HGN194 was isolated from an individual infected with an HIV-1 clade AG recombinant circulating recombinant form (CRF). HGN194 targets an epitope in the third hypervariable loop (V3) of HIV-1 gp120 and neutralizes a range of relatively neutralization-sensitive and resistant viruses. We evaluated the potential of HGN194 to protect infant rhesus monkeys against a SHIV encoding a primary CCR5-tropic HIV-1 clade C envelope. After high-dose mucosal challenge, all untreated controls became highly viremic while all HGN194-treated animals (50 mg/kg) were completely protected. When HGN194 was given at 1 mg/kg, one out of two monkeys remained aviremic, whereas the other had delayed, lower peak viremia. Interestingly, all protected monkeys given high-dose HGN194 developed Gag-specific proliferative responses of both CD4+ and CD8+ T cells. To test whether generation of the latter involved cryptic infection, we ablated CD8+ cells after HGN194 clearance. No viremia was detected in any protected monkeys, thus ruling out virus reservoirs. Thus, induction of CD8 T-cell immunity may have resulted from transient "Hit and Run" infection or cross priming via Ag-Ab-mediated cross-presentation. Together, our data identified the HGN194 epitope as protective and provide proof-of-concept that this anti-V3 loop mAb can prevent infection with sterilizing immunity after challenge with virus of a different clade, implying that V3 is a potential vaccine target.

Development of a tier 1 R5 clade C simian-human immunodeficiency virus as a tool to test neutralizing antibody-based immunoprophylaxis

BACKGROUND

While some recently transmitted HIV clade C (HIV-C) strains exhibited tier 1 neutralization phenotypes, most were tier 2 strains (J Virol 2010; 84:1439). Because induction of neutralizing antibodies (nAbs) through vaccination against tier 2 viruses has proven difficult, we have generated a tier 1, clade C simian-human immunodeficiency virus (SHIV-C) to permit efficacy testing of candidate AIDS vaccines against tier 1 viruses.

METHODS

SHIV-1157ipEL was created by swapping env of a late-stage virus with that of a tier 1, early form.

RESULTS

After adaptation to rhesus macaques (RM), passaged SHIV-1157ipEL-p replicated vigorously in vitro and in vivo while maintaining R5 tropism. The virus was reproducibly transmissible intrarectally. Phylogenetically, SHIV-1157ipEL-p Env clustered with HIV-C sequences. All RM chronically infected with SHIV-1157ipEL-p developed high nAb titers against autologous as well as heterologous tier 1 strains.

CONCLUSIONS

SHIV-1157ipEL-p was reproducibly transmitted in RM, induced cross-clade nAbs, and represents a tool to evaluate anti-HIV-C nAb responses in primates.