Aerosol delivery of SARS-CoV-2 human monoclonal antibodies in macaques limits viral replication and lung pathology

Passively administered monoclonal antibodies (mAbs) given before or after viral infection can prevent or blunt disease. Here, we examine the efficacy of aerosol mAb delivery to prevent infection and disease in rhesus macaques inoculated with the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Delta variant via intranasal and intratracheal routes. SARS-CoV-2 human mAbs or a human mAb directed to respiratory syncytial virus (RSV) are nebulized and delivered using positive airflow via facemask to sedated macaques pre- and post-infection. Nebulized human mAbs are detectable in nasal, oropharyngeal, and bronchoalveolar lavage (BAL) samples. SARS-CoV-2 mAb treatment significantly reduces levels of SARS-CoV-2 viral RNA and infectious virus in the upper and lower respiratory tracts relative to controls. Reductions in lung and BAL virus levels correspond to reduced BAL inflammatory cytokines and lung pathology. Aerosolized antibody therapy for SARS-CoV-2 could be effective for reducing viral burden and limiting disease severity.

Evidence for the Role of a Second Fc-Binding Receptor in Placental IgG Transfer in Nonhuman Primates

Transplacental transfer of maternal antibodies provides the fetus and newborn with passive protection against infectious diseases. While the role of the highly conserved neonatal Fc receptor (FcRn) in transfer of IgG in mammals is undisputed, recent reports have suggested that a second receptor may contribute to transport in humans. We report poor transfer efficiency of plant-expressed recombinant HIV-specific antibodies, including engineered variants with high FcRn affinity, following subcutaneous infusion into rhesus macaques close to parturition. Unexpectedly, unlike those derived from mammalian tissue culture, plant-derived antibodies were essentially unable to cross macaque placentas. This defect was associated with poor Fcγ receptor binding and altered Fc glycans and was not recapitulated in mice. These results suggest that maternal-fetal transfer of IgG across the three-layer primate placenta may require a second receptor and suggest a means of providing maternal antibody treatments during pregnancy while avoiding fetal harm. IMPORTANCE This study compared the ability of several human HIV envelope-directed monoclonal antibodies produced in plants with the same antibodies produced in mammalian cells for their ability to cross monkey and mouse placentas. We found that the two types of antibodies have comparable transfer efficiencies in mice, but they are differentially transferred across macaque placentas, consistent with a two-receptor IgG transport model in primates. Importantly, plant-produced monoclonal antibodies have excellent binding characteristics for human FcRn receptors, permitting desirable pharmacokinetics in humans. The lack of efficient transfer across the primate placenta suggests that therapeutic plant-based antibody treatments against autoimmune diseases and cancer could be provided to the mother while avoiding transfer and preventing harm to the fetus.

Differential V2-directed antibody responses in non-human primates infected with SHIVs or immunized with diverse HIV vaccines

V2p and V2i antibodies (Abs) that are specific for epitopes in the V1V2 region of the HIV gp120 envelope (Env) do not effectively neutralize HIV but mediate Fc-dependent anti-viral activities that have been correlated with protection from, or control of HIV, SIV and SHIV infections. Here, we describe a novel molecular toolbox that allows the discrimination of antigenically and functionally distinct polyclonal V2 Ab responses. We identify different patterns of V2 Ab induction by SHIV infection and three separate vaccine regimens that aid in fine-tuning an optimized immunization protocol for inducing V2p and V2i Abs. We observe no, or weak and sporadic V2p and V2i Abs in non-vaccinated SHIV-infected NHPs, but strong V2p and/or V2i Ab responses after immunization with a V2-targeting vaccine protocol. The V2-focused vaccination is superior to both natural infection and to immunization with whole Env constructs for inducing functional V2p- and V2i-specific responses. Strikingly, levels of V2-directed Abs correlate inversely with Abs specific for peptides of V3 and C5. These data demonstrate that a V1V2-targeting vaccine has advantages over the imprecise targeting of SIV/SHIV infections and of whole Env-based immunization regimens for inducing a more focused functional V2p- and V2i-specific Ab response.

Here the authors show that an HIV vaccine in non-human primates that focuses antibodies on the V1V2 region of gp120 is superior to infection or immunization with whole envelope vaccines for inducing V1V2 antibodies with anti-viral functions that correlate with protection.

Phagocytosis by an HIV antibody is associated with reduced viremia irrespective of enhanced complement lysis

Increasingly, antibodies are being used to treat and prevent viral infections. In the context of HIV, efficacy is primarily attributed to dose-dependent neutralization potency and to a lesser extent Fc-mediated effector functions. It remains unclear whether augmenting effector functions of broadly neutralizing antibodies (bNAbs) may improve their clinical potential. Here, we use bNAb 10E8v4 targeting the membrane external proximal region (MPER) to examine the role of antibody-mediated effector and complement (C’) activity when administered prophylactically against SHIV challenge in rhesus macaques. With sub-protective dosing, we find a 78–88% reduction in post-acute viremia that is associated with 10E8v4-mediated phagocytosis acting at the time of challenge. Neither plasma nor tissue viremic outcomes in vivo is improved with an Fc-modified variant of 10E8v4 enhanced for C’ functions as determined in vitro. These results suggest that effector functions inherent to unmodified 10E8v4 contribute to efficacy against SHIV_SF162P3 in the absence of plasma neutralizing titers, while C’ functions are dispensable in this setting, informing design of bNAb modifications for improving protective efficacy.

While antibodies neutralize HIV via Fab recognition of viral surface antigens, antibody Fc domains mediate effector functions, including antibody-dependent cellular phagocytosis (ADCP) and cytotoxicity (ADCC), and complement (C') activity. Here, Spencer et al. modify bNAb 10E8v4 to enhance C'-mediated potency in SHIV challenged rhesus macaques to probe its function in protection, showing that in the absence of neutralization, enhancing C' activities in vitro adds no value toward reducing viremia in either blood or tissue.

CD4+ T Cells Are Dispensable for Induction of Broad Heterologous HIV Neutralizing Antibodies in Rhesus Macaques

Induction of broadly neutralizing antibodies (bNAbs) is a major goal for HIV vaccine development. HIV envelope glycoprotein (Env)-specific bNAbs isolated from HIV-infected individuals exhibit substantial somatic hypermutation and correlate with T follicular helper (Tfh) responses. Using the VC10014 DNA-protein co-immunization vaccine platform consisting of gp160 plasmids and gp140 trimeric proteins derived from an HIV-1 infected subject that developed bNAbs, we determined the characteristics of the Env-specific humoral response in vaccinated rhesus macaques in the context of CD4+ T cell depletion. Unexpectedly, both CD4+ depleted and non-depleted animals developed comparable Tier 1 and 2 heterologous HIV-1 neutralizing plasma antibody titers. There was no deficit in protection from SHIV challenge, no diminution of titers of HIV Env-specific cross-clade binding antibodies, antibody dependent cellular phagocytosis, or antibody-dependent complement deposition in the CD4+ depleted animals. These collective results suggest that in the presence of diminished CD4+ T cell help, HIV neutralizing antibodies were still generated, which may have implications for developing effective HIV vaccine strategies.

Protection of Newborn Macaques by Plant-Derived HIV Broadly Neutralizing Antibodies: a Model for Passive Immunotherapy during Breastfeeding

Preventing human immunodeficiency virus (HIV) infection in newborns by vertical transmission remains an important unmet medical need in resource-poor areas where antiretroviral therapy (ART) is not available and mothers and infants cannot be treated prepartum or during the breastfeeding period. In the present study, the protective efficacy of the potent HIV-neutralizing antibodies PGT121 and VRC07-523, both produced in plants, were assessed in a multiple-SHIV (simian-human immunodeficiency virus)-challenge breastfeeding macaque model. Newborn macaques received either six weekly subcutaneous injections with PGT121 alone or as a cocktail of PGT121-LS plus VRC07-523-LS injected three times every 2 weeks. Viral challenge with SHIVSF162P3 was twice weekly over 5.5 weeks using 11 exposures. Despite the transient presence of plasma viral RNA either immediately after the first challenge or as single-point blips, the antibodies prevented a productive infection in all babies with no sustained plasma viremia, compared to viral loads ranging from 103 to 5 × 108 virions/ml in four untreated controls. No virus was detected in peripheral blood mononuclear cells (PBMCs), and only 3 of 159 tissue samples were weakly positive in the treated babies. Newborn macaques proved to be immunocompetent, producing transient anti-Env antibodies and anti-drug antibody (ADA), which were maintained in the circulation after passive broadly neutralizing antibody clearance. ADA responses were directed to the IgG1 Fc CH2-CH3 domains, which has not been observed to date in adult monkeys passively treated with PGT121 or VRC01. In addition, high levels of VRC07-523 anti-idiotypic antibodies in the circulation of one newborn was concomitant with the rapid elimination of VRC07. Plant-expressed antibodies show promise as passive immunoprophylaxis in a breastfeeding model in newborns. IMPORTANCE Plant-produced human neutralizing antibody prophylaxis is highly effective in preventing infection in newborn monkeys during repeated oral exposure, modeling virus in breastmilk, and offers advantages in cost of production and safety. These findings raise the possibility that anti-Env antibodies may contribute to the control of viral replication in this newborn model and that the observed immune responsiveness may be driven by the long-lived presence of immune complexes.

A large repertoire of B cell lineages targeting one cluster of epitopes in a vaccinated rhesus macaque

The repertoire of antibodies (Abs) produced upon vaccination against a particular antigenic site is rarely studied due to the complexity of the immunogens. We received such an opportunity when one rhesus macaque was immunized six times at 0, 4, 10, 16, 32, and 143 weeks with C4-447 peptide containing the 8-mer epitope for human monoclonal Ab (mAb) 447-52D specific to the V3 region of gp120 HIV-1. Strong anti-V3 antibody responses reached 50% binding titer in serum of 10^-5 at week 10 that declined to 10^-3 by week 70. After an additional boost of C4-447 peptide at week 143, titers rebounded to 10^-5 at week 146, or 2.7 years after the first immunization. Using the blood sample at week 146, we produced 41 V3-specific recombinant mAbs by single B cell isolation and cloning. Sequence analysis revealed 21B cell lineages, single and clonally related, based on immunoglobulin gene usage and CDR3s. The broad repertoire of Abs directed to a small antigenic site shows the targeting potency of a vaccine-elicited immune response in rhesus macaques.

Improved delivery of broadly neutralizing antibodies by nanocapsules suppresses SHIV infection in the CNS of infant rhesus macaques

Broadly neutralizing antibodies (bNAbs) directed to HIV-1 have shown promise at suppressing viremia in animal models. However, the use of bNAbs for the central nervous system (CNS) infection is confounded by poor penetration of the blood brain barrier (BBB). Typically, antibody concentrations in the CNS are extremely low; with levels in cerebrospinal fluid (CSF) only 0.1% of blood concentrations. Using a novel nanotechnology platform, which we term nanocapsules, we show effective transportation of the human bNAb PGT121 across the BBB in infant rhesus macaques upon systemic administration up to 1.6% of plasma concentration. We demonstrate that a single dose of PGT121 encased in nanocapsules when delivered at 48h post-infection delays early acute infection with SHIV_SF162P3 in infants, with one of four animals demonstrating viral clearance. Importantly, the nanocapsule delivery of PGT121 improves suppression of SHIV infection in the CNS relative to controls.

In patients where HIV-1 is fully suppressed by antiretroviral drugs, HIV-1 still persists in reservoirs. If antiretroviral drugs are stopped, the virus will emerge from these reservoirs and re-seeds systemically. The central nervous system (CNS) is proposed to be a tissue compartment that harbors other HIV-1 reservoirs. A key obstacle that constrains the treatment for the CNS infection is the blood–brain barrier (BBB), a highly restrictive barrier separating the circulating blood from the brain and extracellular fluid in the CNS, which impedes ~98% of the small molecule therapeutics and almost all macromolecules including broadly neutralizing antibodies (bNAbs) directed to HIV-1. Our “nanocapsule” strategy is based on a nanotechnology wherein bNAb molecules are encapsulated within nanocapsules of which the surface contains abundant choline and acetylcholine analogues. This design allows the nanocapsules to effectively cross the BBB to deliver bNAbs into the CNS upon systemic administration and show an impact of bNAb on CNS reservoirs in SHIV infected infant macaques.

Antibody-based CCR5 blockade protects Macaques from mucosal SHIV transmission

In the absence of a prophylactic vaccine, the use of antiretroviral therapy (ART) as pre-exposure prophylaxis (PrEP) to prevent HIV acquisition by uninfected individuals is a promising approach to slowing the epidemic, but its efficacy is hampered by incomplete patient adherence and ART-resistant variants. Here, we report that competitive inhibition of HIV Env-CCR5 binding via the CCR5-specific antibody Leronlimab protects rhesus macaques against infection following repeated intrarectal challenges of CCR5-tropic SHIVSF162P3. Injection of Leronlimab weekly at 10 mg/kg provides significant but partial protection, while biweekly 50 mg/kg provides complete protection from SHIV acquisition. Tissue biopsies from protected macaques post challenge show complete CCR5 receptor occupancy and an absence of viral nucleic acids. After Leronlimab washout, protected macaques remain aviremic, and adoptive transfer of hematologic cells into naïve macaques does not transmit viral infection. These data identify CCR5 blockade with Leronlimab as a promising approach to HIV prophylaxis and support initiation of clinical trials.

Advancing HIV Broadly Neutralizing Antibodies: From Discovery to the Clinic

Despite substantial progress in confronting the global HIV-1 epidemic since its inception in the 1980s, better approaches for both treatment and prevention will be necessary to end the epidemic and remain a top public health priority. Antiretroviral therapy (ART) has been effective in extending lives, but at a cost of lifelong adherence to treatment. Broadly neutralizing antibodies (bNAbs) are directed to conserved regions of the HIV-1 envelope glycoprotein trimer (Env) and can block infection if present at the time of viral exposure. The therapeutic application of bNAbs holds great promise, and progress is being made toward their development for widespread clinical use. Compared to the current standard of care of small molecule-based ART, bNAbs offer: (1) reduced toxicity; (2) the advantages of extended half-lives that would bypass daily dosing requirements; and (3) the potential to incorporate a wider immune response through Fc signaling. Recent advances in discovery technology can enable system-wide mining of the immunoglobulin repertoire and will continue to accelerate isolation of next generation potent bNAbs. Passive transfer studies in pre-clinical models and clinical trials have demonstrated the utility of bNAbs in blocking or limiting transmission and achieving viral suppression. These studies have helped to define the window of opportunity for optimal intervention to achieve viral clearance, either using bNAbs alone or in combination with ART. None of these advances with bNAbs would be possible without technological advancements and expanding the cohorts of donor participation. Together these elements fueled the remarkable growth in bNAb development. Here, we review the development of bNAbs as therapies for HIV-1, exploring advances in discovery, insights from animal models and early clinical trials, and innovations to optimize their clinical potential through efforts to extend half-life, maximize the contribution of Fc effector functions, preclude escape through multiepitope targeting, and the potential for sustained delivery.

Polyfunctional Tier 2-Neutralizing Antibodies Cloned following HIV-1 Env Macaque Immunization Mirror Native Antibodies in a Human Donor

Vaccine efforts to combat HIV are challenged by the global diversity of viral strains and shielding of neutralization epitopes on the viral envelope glycoprotein trimer. Even so, the isolation of broadly neutralizing Abs from infected individuals suggests the potential for eliciting protective Abs through vaccination. This study reports a panel of 58 mAbs cloned from a rhesus macaque (Macaca mulatta) immunized with envelope glycoprotein immunogens curated from an HIV-1 clade C-infected volunteer. Twenty mAbs showed neutralizing activity, and the strongest neutralizer displayed 92% breadth with a median IC50 of 1.35 μg/ml against a 13-virus panel. Neutralizing mAbs predominantly targeted linear epitopes in the V3 region in the cradle orientation (V3C) with others targeting the V3 ladle orientation (V3L), the CD4 binding site (CD4bs), C1, C4, or gp41. Nonneutralizing mAbs bound C1, C5, or undetermined conformational epitopes. Neutralization potency strongly correlated with the magnitude of binding to infected primary macaque splenocytes and to the level of Ab-dependent cellular cytotoxicity, but did not predict the degree of Ab-dependent cellular phagocytosis. Using an individualized germline gene database, mAbs were traced to 23 of 72 functional IgHV alleles. Neutralizing V3C Abs displayed minimal nucleotide somatic hypermutation in the H chain V region (3.77%), indicating that relatively little affinity maturation was needed to achieve in-clade neutralization breadth. Overall, this study underscores the polyfunctional nature of vaccine-elicited tier 2-neutralizing V3 Abs and demonstrates partial reproduction of the human donor's humoral immune response through nonhuman primate vaccination.

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.

Virus Control in Vaccinated Rhesus Macaques Is Associated with Neutralizing and Capturing Antibodies against the SHIV Challenge Virus but Not with V1V2 Vaccine-Induced Anti-V2 Antibodies Alone

The role of vaccine-induced anti-V2 Abs was tested in three protection experiments in rhesus macaques. In an experiment using immunogens similar to those in the RV144 vaccine trial (Anti-envelope [Env]), nine rhesus macaques were coimmunized with gp160_92TH023 DNA and SIV gag and gp120_A244 and gp120_MN proteins. In two V2-focused experiments (Anti-V2 and Anti-V2 Mucosal), nine macaques in each group were immunized with V1V2_92TH023 DNA, V1V2_A244 and V1V2_CasaeA2 proteins, and cyclic V2_CaseA2 peptide. DNA and protein immunogens, formulated in Adjuplex, were given at 0, 4, 12, and 20 weeks, followed by intrarectal SHIV_BaL.P4 challenges. Peak plasma viral loads (PVL) of 10⁶-10⁷ copies/ml developed in all nine sham controls. Overall, PVL was undetectable in one third of immunized macaques, and two animals tightly controlled the virus with the Anti-V2 Mucosal vaccine strategy. In the Anti-Env study, Abs that captured or neutralized SHIV_BaL.P4 inversely correlated with PVL. Conversely, no correlation with PVL was found in the Anti-V2 experiments with nonneutralizing plasma Abs that only captured virus weakly. Titers of Abs against eight V1V2 scaffolds and cyclic V2 peptides were comparable between controllers and noncontrollers as were Ab-dependent cellular cytotoxicity and Ab-dependent cell-mediated virus inhibition activities against SHIV-infected target cells and phagocytosis of gp120-coated beads. The Anti-Env experiment supports the role of vaccine-elicited neutralizing and nonneutralizing Abs in control of PVL. However, the two V2-focused experiments did not support a role for nonneutralizing V2 Abs alone in controlling PVL, as neither Ab-dependent cellular cytotoxicity, Ab-dependent cell-mediated virus inhibition, nor phagocytosis correlated inversely with heterologous SHIV_BaL.P4 infection.

ACTIVating Resources for the COVID-19 Pandemic: In Vivo Models for Vaccines and Therapeutics

The Preclinical Working Group of Accelerating COVID-19 Therapeutic Interventions and Vaccines (ACTIV), a public-private partnership spearheaded by the National Institutes of Health, has been charged with identifying, prioritizing, and communicating SARS-CoV-2 preclinical resources. Reviewing SARS-CoV-2 animal model data facilitates standardization and harmonization and informs knowledge gaps and prioritization of limited resources. To date, mouse, hamster, ferret, guinea pig, and non-human primates have been investigated. Several species are permissive for SARS-CoV-2 replication, often exhibiting mild disease with resolution, reflecting most human COVID-19 cases. More severe disease develops in a few models, some associated with advanced age, a risk factor for human disease. This review provides a snapshot that recommends the suitability of models for testing vaccines and therapeutics, which may evolve as our understanding of COVID-19 disease biology improves. COVID-19 is a complex disease, and individual models recapitulate certain aspects of disease; therefore, the coordination and assessment of animal models is imperative.

Multimeric Epitope-Scaffold HIV Vaccines Target V1V2 and Differentially Tune Polyfunctional Antibody Responses

The V1V2 region of the HIV-1 envelope is the target of several broadly neutralizing antibodies (bNAbs). Antibodies to V1V2 elicited in the RV144 clinical trial correlated with a reduced risk of HIV infection, but these antibodies were without broad neutralizing activity. Antibodies targeting V1V2 also correlated with a reduced viral load in immunized macaques challenged with simian immunodeficiency virus (SIV) or simian/human immunodeficiency virus (SHIV). To focus immune responses on V1V2, we engrafted the native, glycosylated V1V2 domain onto five different multimeric scaffold proteins and conducted comparative immunogenicity studies in macaques. Vaccinated macaques developed high titers of plasma and mucosal antibodies that targeted structurally distinct V1V2 epitopes. Plasma antibodies displayed limited neutralizing activity but were functionally active for ADCC and phagocytosis, which was detectable 1-2 years after immunizations ended. This study demonstrates that multivalent, glycosylated V1V2-scaffold protein immunogens focus the antibody response on V1V2 and are differentially effective at inducing polyfunctional antibodies with characteristics associated with protection.

Rapid Induction of Multifunctional Antibodies in Rabbits and Macaques by Clade C HIV-1 CAP257 Envelopes Circulating During Epitope-Specific Neutralization Breadth Development

We report here on HIV-1 immunization results in rabbits and macaques co-immunized with clade C gp160 DNA and gp140 trimeric envelope vaccines, a strategy similar to a recent clinical trial that showed improved speed and magnitude of humoral responses. Clade C envelopes were isolated from CAP257, an individual who developed a unique temporal pattern of neutralization breadth development, comprising three separate "Waves" targeting distinct Env epitopes and different HIV clades. We used phylogeny and neutralization criteria to down-select envelope vaccine candidates, and confirmed antigenicity of our antigens by interaction with well-characterized broadly neutralizing monoclonal antibodies. Using these envelopes, we performed rabbit studies that screened for immunogenicity of CAP257 Envs from timepoints preceding peak neutralization breadth in each Wave. Selected CAP257 envelopes from Waves 1 and 2, during the first 2 years of infection that were highly immunogenic in rabbits were then tested in macaques. We found that in rabbits and macaques, co-immunization of DNA, and protein envelope-based vaccines induced maximum binding and neutralizing antibody titers with three immunizations. No further benefit was obtained with additional immunizations. The vaccine strategies recapitulated the Wave-specific epitope targeting observed in the CAP257 participant, and elicited Tier 1A, 1B, and Tier 2 heterologous neutralization. CAP257 envelope immunogens also induced the development of ADCC and T_FH responses in macaques, and these responses positively correlated with heterologous neutralization. Together, the results from two animal models in this study have implications for identifying effective vaccine immunogens. We used a multi-step strategy to (1) select an Env donor with well-characterized neutralization breadth development; (2) study Env phylogeny for potential immunogens circulating near peak breadth timepoints during the first 2 years of infection; (3) test down-selected Envs for antigenicity; (4) screen down-selected Envs in an effective vaccine regimen in rabbits; and (5) advance the most immunogenic Envs to NHP studies. The results were an induction of high titers of HIV-1 envelope-specific antibodies with increasing avidity and cross-clade neutralizing antibodies with effector functions that together may improve the potential for protection in a pre-clinical SHIV model.

Adenosine deaminase-1 enhances germinal center formation and functional antibody responses to HIV-1 Envelope DNA and protein vaccines

Adenosine deaminase-1 (ADA-1) plays both enzymatic and non-enzymatic roles in regulating immune cell function. Mutations in the ADA1 gene account for 15% of heritable severe-combined immunodeficiencies. We determined previously that ADA1 expression defines and is instrumental for the germinal center follicular helper T cell (TFH) phenotype using in vitro human assays. Herein, we tested whether ADA-1 can be used as an adjuvant to improve vaccine efficacy in vivo. In vitro, ADA-1 induced myeloid dendritic cell (mDC) maturation as measured by increased frequencies of CD40-, CD83-, CD86-, and HLA-DR-positive mDCs. ADA-1 treatment also promoted the secretion of the TFH-polarizing cytokine IL-6 from mDCs. In the context of an HIV-1 envelope (env) DNA vaccine, co-immunization with plasmid-encoded ADA-1 (pADA) enhanced humoral immunity. Animals co-immunized with env DNA and pADA had significantly increased frequencies of TFH cells in their draining lymph nodes and increased HIV-binding IgG in serum. Next, mice were co-immunized with subtype C env gp160 DNA and pADA along with simultaneous immunization with matched gp140 trimeric protein. Mice that received env gp160 DNA, pADA, and gp140 glycoprotein had significantly more heterologous HIV-specific binding IgG in their serum. Furthermore, only these mice had detectable neutralizing antibody responses. These studies support the use of ADA-1 as a vaccine adjuvant to qualitatively enhance germinal center responses and represent a novel application of an existing therapeutic agent that can be quickly translated for clinical use.

Human natural killer cells mediate adaptive immunity to viral antigens

Adaptive immune responses are defined as antigen sensitization-dependent and antigen-specific responses leading to establishment of long-lived immunological memory. Although natural killer (NK) cells have traditionally been considered cells of the innate immune system, mounting evidence in mice and nonhuman primates warrants reconsideration of the existing paradigm that B and T cells are the sole mediators of adaptive immunity. However, it is currently unknown whether human NK cells can exhibit adaptive immune responses. We therefore tested whether human NK cells mediate adaptive immunity to virally encoded antigens using humanized mice and human volunteers. We found that human NK cells displayed vaccination-dependent, antigen-specific recall responses in vitro, when isolated from livers of humanized mice previously vaccinated with HIV-encoded envelope protein. Furthermore, we discovered that large numbers of cytotoxic NK cells with a tissue-resident phenotype were recruited to sites of varicella-zoster virus (VZV) skin test antigen challenge in VZV-experienced human volunteers. These NK-mediated recall responses in humans occurred decades after initial VZV exposure, demonstrating that NK memory in humans is long-lived. Our data demonstrate that human NK cells exhibit adaptive immune responses upon vaccination or infection. The existence of human memory NK cells may allow for the development of vaccination-based approaches capable of establishing potent NK-mediated memory functions contributing to host protection.

CD4+ T cells are dispensable for induction of heterologous tier 2 HIV neutralizing antibodies in rhesus macaques

Induction of a sustained and broad neutralizing antibody (Ab) response is a major goal in developing a protective HIV vaccine. Many HIV Envelope (Env)-specific broadly neutralizing antibodies isolated to date exhibit substantial somatic hypermutation, and their development in HIV infected individuals has been correlated with T follicular helper responses. This has bolstered the rational that a robust CD4+ T helper cell response will likely be required for the induction of such HIV broadly neutralizing antibody responses by vaccination. Using the VC10014 DNA-protein co-immunization vaccine platform consisting of gp160 envelope plasmids and gp140 trimeric envelope proteins derived from a clade B HIV-1 infected subject who developed broadly neutralizing serum Abs, and which has been previously shown to induce Tier 2 heterologous neutralizing Abs in rabbits and rhesus macaques, we determined the influence of CD4+ T cell depletion during the vaccination regimen on the characteristics of the Env-specific humoral response in rhesus macaques. Both CD4+ depleted and non-depleted animals developed Tier 2 heterologous neutralizing plasma antibodies, with no inferiority in titers among the CD4+ T cell depleted animals. Similarly, there was no diminishment of titers of HIV Env-specific cross-clade binding antibodies, antibody dependent cellular phagocytosis or antibody dependent complement deposition in the CD4+ depleted animals. These results suggest that HIV neutralizing antibodies can be induced in the absence of robust CD4+ T cell help, which may have implications for developing effective HIV vaccine strategies.

Cloning and functional testing of rhesus macaque (Macaca mulatta) IL-9 and IL-33

BACKGROUND

IL-9 and IL-33 can profoundly influence immune responses. As a necessary first step toward defining their impact in the rhesus macaque model, we confirmed their endogenous expression and sequence identity and generated expression vectors for the recombinant expression of rhesus IL-9 and IL-33.

METHODS

RT-PCR and Sanger sequencing was used to define the expression and sequences for rhesus IL-9 and IL-33. The resulting recombinant cytokines were tested by ELISA and proliferation assays.

RESULTS

Full-length rhesus IL-9 and the mature form of rhesus IL-33 share 78% and 73% nucleotide similarity, respectively, with humans. Both cytokines are expressed in lymphocytes, with IL-9 expression also evident in CD4+ T cells. Recombinantly expressed rhesus IL-9 and IL-33 were each biologically active in vitro, including enhancing the proliferation of a rhesus B cell line.

CONCLUSIONS

The recombinant rhesus IL-9 and IL-33 constructs produce biologically active cytokines that can act upon rhesus B cells.

A Meta-analysis of Passive Immunization Studies Shows that Serum-Neutralizing Antibody Titer Associates with Protection against SHIV Challenge

Passively administered broadly neutralizing antibodies (bNAbs) targeting the HIV-1 envelope glycoprotein (Env) have been shown to protect non-human primates (NHPs) against chimeric simian-human immunodeficiency virus (SHIV) infection. With data from multiple non-human primate SHIV challenge studies that used single bNAbs, we conducted a meta-analysis to examine the relationship between predicted serum 50% neutralization titer (ID50) against the challenge virus and infection outcome. In a logistic model that adjusts for bNAb epitopes and challenge viruses, serum ID50 had a highly significant effect on infection risk (p < 0.001). The estimated ID50 to achieve 50%, 75%, and 95% protection was 91 (95% confidence interval [CI]: 55, 153), 219 (117, 410), and 685 (319, 1471), respectively. This analysis indicates that serum neutralizing titer against the relevant virus is a key parameter of protection and that protection from acquisition by a single bNAb might require substantial levels of neutralization at the time of exposure.

Divergent HIV-1-Directed Immune Responses Generated by Systemic and Mucosal Immunization with Replicating Single-Cycle Adenoviruses in Rhesus Macaques

Most human immunodeficiency virus type 1 (HIV-1) infections begin at mucosal surfaces. Providing a barrier of protection at these may assist in combating the earliest events in infection. Systemic immunization by intramuscular (i.m.) injection can drive mucosal immune responses, but there are data suggesting that mucosal immunization can better educate these mucosal immune responses. To test this, rhesus macaques were immunized with replicating single-cycle adenovirus (SC-Ad) vaccines expressing clade B HIV-1 gp160 by the intranasal (i.n.) and i.m. routes to compare mucosal and systemic routes of vaccination. SC-Ad vaccines generated significant circulating antibody titers against Env after a single i.m. immunization. Switching the route of second immunization with the same SC-Ad serotype allowed a significant boost in these antibody levels. When these animals were boosted with envelope protein, envelope-binding antibodies were amplified 100-fold, but qualitatively different immune responses were generated. Animals immunized by only the i.m. route had high peripheral T follicular helper (pTfh) cell counts in blood but low Tfh cell counts in lymph nodes. Conversely, animals immunized by the i.n. route had high Tfh cell counts in lymph nodes but low pTfh cell counts in the blood. Animals immunized by only the i.m. route had lower antibody-dependent cellular cytotoxicity (ADCC) antibody activity, whereas animals immunized by the mucosal i.n. route had higher ADCC antibody activity. When these Env-immunized animals were challenged rectally with simian-human immunodeficiency virus (SHIV) strain SF162P3 (SHIVSF162P3), they all became infected. However, mucosally SC-Ad-immunized animals had lower viral loads in their gastrointestinal tracts. These data suggest that there may be benefits in educating the immune system at mucosal sites during HIV vaccination.IMPORTANCE HIV-1 infections usually start at a mucosal surface after sexual contact. Creating a barrier of protection at these mucosal sites may be a good strategy for to protect against HIV-1 infections. While HIV-1 enters at mucosa, most vaccines are not delivered here. Most are instead injected into the muscle, a site well distant and functionally different than mucosal tissues. This study tested if delivering HIV vaccines at mucosa or in the muscle makes a difference in the quality, quantity, and location of immune responses against the virus. These data suggest that there are indeed advantages to educating the immune system at mucosal sites with an HIV-1 vaccine.

IL-33 enhances the kinetics and quality of the antibody response to a DNA and protein-based HIV-1 Env vaccine

Induction of a sustained and broad antibody (Ab) response is a major goal in developing a protective HIV-1 vaccine. DNA priming alone shows reduced levels of immunogenicity; however, when combined with protein boosting is an attractive vaccination strategy for induction of humoral responses. Using the VC10014 DNA and protein-based vaccine consisting of HIV-1 envelope (Env) gp160 plasmids and trimeric gp140 proteins derived from an HIV-1 clade B infected subject who developed broadly neutralizing serum Abs, and which has been previously demonstrated to induce Tier 2 heterologous neutralizing Abs in rhesus macaques, we evaluated whether MPLA and IL-33 when administered during the DNA priming phase enhances the humoral response in mice. The addition of IL-33 during the gp160 DNA priming phase resulted in high titer gp120-specific plasma IgG after the first immunization. The IL-33 treated mice had higher plasma IgG Ab avidity, breadth, and durability after DNA and protein co-immunization with alum adjuvant as compared to MPLA and alum only treated mice. IL-33 was also associated with a significant IgM Env-specific response and expansion of peritoneal and splenic B-1b B cells. These results indicate that DNA priming in the presence of exogenous IL-33 qualitatively alters the HIV-1 Env-specific humoral response, improving the kinetics and breadth of potentially protective Ab.

Increased breadth of HIV-1 neutralization achieved by diverse antibody clones each with limited neutralization breadth

Broadly neutralizing antibodies (bNAbs) are rarely elicited by current human immunodeficiency virus type 1 (HIV-1) vaccine designs, but the presence of bNAbs in naturally infected individuals may be associated with high plasma viral loads, suggesting that the magnitude, duration, and diversity of viral exposure may contribute to the development of bNAbs. Here, we report the isolation and characterization of a panel of human monoclonal antibodies (mAbs) from two subjects who developed broadly neutralizing autologous antibody responses during HIV-1 infection. In both subjects, we identified collections of mAbs that exhibited specificity only to a few autologous envelopes (Envs), with some mAbs exhibiting specificity only to a subset of Envs within the quasispecies of a particular sample at one time point. Neutralizing antibodies (NAbs) isolated from these subjects mapped mostly to epitopes in the Env V3 loop region and the CD4 binding site. None of the individual neutralizing mAbs recovered exhibited the cumulative breadth of neutralization present in the serum of the subjects. Surprisingly, however, the activity of polyclonal mixtures comprising individual mAbs that each possessed limited neutralizing activity, could achieve increased breadth of neutralizing activity against autologous isolates. While a single broadly neutralizing antibody targeting one epitope can mediate neutralization breadth, the findings presented here suggest that a cooperative polyclonal process mediated by diverse antibodies with more limited breadth targeting multiple epitopes also can achieve neutralization breadth against HIV-1.

Passive and active antibody studies in primates to inform HIV vaccines

INTRODUCTION

Prevention of infection remains the ultimate goal for HIV vaccination, and there is compelling evidence that antibodies directed to Envelope are necessary to block infection. Generating antibodies that are sufficiently broad, potent, and sustained to block infection by the diverse HIV-1 strains circulating worldwide remains an area of intense study.

AREAS COVERED

In this review, we have summarized progress from publications listed as PubMed citations in 2016-17 in the areas of passive antibody studies using human neutralizing monoclonal antibodies in nonhuman primates, HIV Envelope vaccine development and active vaccination studies to generate potent neutralizing antibodies.

EXPERT COMMENTARY

Passive transfer studies in nonhuman primates using human neutralizing monoclonal antibodies have informed the potency, specificity, and cooperativity of antibodies needed to prevent infection, leading to clinical studies now testing potent antibodies for prevention of HIV. Progress in understanding the structure of Envelope has led to novel vaccine constructs, including mimetics, scaffolds and native-like proteins. As yet, no single approach ensures protection against the circulating global HIV-1 strains, but there is progress in understanding why, and intense research continues in these and other areas for a solution. We offer perspectives on how this knowledge may shape the design of future HIV vaccines.

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.

Use of broadly neutralizing antibodies for HIV-1 prevention

Antibodies have a long history in antiviral therapy, but until recently, they have not been actively pursued for HIV-1 due to modest potency and breadth of early human monoclonal antibodies (MAbs) and perceived insurmountable technical, financial, and logistical hurdles. Recent advances in the identification and characterization of MAbs with the ability to potently neutralize diverse HIV-1 isolates have reinvigorated discussion and testing of these products in humans, since new broadly neutralizing MAbs (bnMAbs) are more likely to be effective against worldwide strains of HIV-1. In animal models, there is abundant evidence that bnMAbs can block infection in a dose-dependent manner, and the more potent bnMAbs will allow clinical testing at infusion doses that are practically achievable. Moreover, recent advances in antibody engineering are providing further improvements in MAb potency, breadth, and half-life. This review summarizes the current state of the field of bnMAb protection in animal models as well as a review of variables that are critical for antiviral activity. Several bnMAbs are currently in clinical testing, and we offer perspectives on their use as pre-exposure prophylaxis (PrEP), potential benefits beyond sterilizing immunity, and a discussion of future approaches to engineer novel molecules.

V1V2 multivalent scaffolds induce focused antibody responses with functional activity, prolonged durability, and modest neutralization potency

The V1V2 region of HIV-1 gp120 is vulnerable to a group of broadly neutralizing monoclonal antibodies (bnMAbs), and RV144 vaccinees developed strongly binding Abs to this region that correlated with a reduced risk of infection. This region of Env is now recognized as an important vaccine target, notwithstanding its relatively poorly immunogenic epitopes. We hypothesized that presenting V1V2 in multivalent scaffolds could improve immunogenicity and structurally constraining the epitopes could induce a more focused immune response in animal models. We designed of a panel of immunogens engrafting the V1V2 domain into trimeric and pentameric scaffolds. Here, we report results of immunogenicity studies in nonhuman primates (NHP) with 2 different V1V2 trimeric scaffolds. Our experimental approach in NHP consisted of 3 DNA and protein co-immunizations and a single protein boost. The DNA components consisted of 50μg of ZM109 gp120 plasmid delivered by gene gun with a simultaneous intramuscular injection of 100 μg of V1V2 scaffold protein immunogens. NHP immune responses were specific for V1V2 conformational epitopes with cross-reactive binding to heterologous gp120s and were functionally active in phagocytosis assays. Notably, V1V2 binding Ab responses were detectable 2 years after immunizations ceased. Neutralizing Abs developed in vaccinated NHP to Tier 1A and 1B, Clade B and Clade C viruses. The V1V2 structurally constrained scaffolds show promise as novel and highly effective at inducing functional antibody responses specifically targeted to the epitopes presented. Our results advance pre-clinical data in support of developing V1V2 vaccine candidates despite the structural complexity of the region.

Funding: P01AI100151-03

Pre-existing neutralizing antibody mitigates B cell dysregulation and enhances the Env-specific antibody response in SHIV-infected rhesus macaques

Our central hypothesis is that protection against HIV infection will be powerfully influenced by the magnitude and quality of the B cell response. Although sterilizing immunity, mediated by pre-formed abundant and potent antibodies is the ultimate goal for B cell-targeted HIV vaccine strategies, scenarios that fall short of this may still confer beneficial defenses against viremia and disease progression. We evaluated the impact of sub-sterilizing pre-existing neutralizing antibody on the B cell response to SHIV infection. Adult male rhesus macaques received passive transfer of a sub-sterilizing amount of polyclonal neutralizing immunoglobulin (Ig) purified from previously infected animals (SHIVIG) or control Ig prior to intra-rectal challenge with SHIVSF162P4 and extensive longitudinal sampling was performed. SHIVIG treated animals exhibited significantly reduced viral load and increased de novo Env-specific plasma antibody. Dysregulation of the B cell profile was grossly apparent soon after infection in untreated animals; exemplified by a ≈50% decrease in total B cells in the blood evident 2-3 weeks post-infection which was not apparent in SHIVIG treated animals. IgD+CD5+CD21+ B cells phenotypically similar to marginal zone-like B cells were highly sensitive to SHIV infection, becoming significantly decreased as early as 3 days post-infection in control animals, while being maintained in SHIVIG treated animals, and were highly correlated with the induction of Env-specific plasma antibody. These results suggest that B cell dysregulation during the early stages of infection likely contributes to suboptimal Env-specific B cell and antibody responses, and strategies that limit this dysregulation may enhance the host's ability to eliminate HIV.

Differential induction of anti-V3 crown antibodies with cradle- and ladle-binding modes in response to HIV-1 envelope vaccination

The V3 loop in the HIV envelope gp120 is one of the immunogenic sites targeted by Abs. The V3 crown in particular has conserved structural elements recognized by cross-reactive neutralizing Abs, indicating its potential contribution in protection against HIV. Crystallographic analyses of anti-V3 crown mAbs in complex with the V3 peptides have revealed that these mAbs recognize the conserved sites on the V3 crown via two distinct strategies: a cradle-binding mode (V3C) and a ladle-binding (V3L) mode. However, almost all of the anti-V3 crown mAbs studied in the past were isolated from chronically HIV-infected individuals. The extents to which the two types of anti-V3 crown Abs are generated by vaccination are unknown. This study analyzed the prevalence of V3C-type and V3L-type Ab responses in HIV-infected individuals and in HIV envelope-immunized humans and animals using peptide mimotopes that distinguish the two Ab types. The results show that both V3L-type and V3C-type Abs were generated by the vast majority of chronically HIV-infected humans, although the V3L-type were more prevalent. In contrast, only one of the two V3 Ab types was elicited in vaccinated humans or animal models, irrespective of HIV-1 envelope clades, envelope constructs (oligomeric or monomeric), and protocols (DNA plus protein or protein alone) used for vaccinations. The V3C-type Abs were produced by vaccinated humans, macaques, and rabbits, whereas the V3L-type Abs were made by mice. The V3C-type and V3L-type Abs generated by the vaccinations were able to mediate virus neutralization. These data indicate the restricted repertoires and the species-specific differences in the functional V3-specific Ab responses induced by the HIV envelope vaccines. The study implies the need for improving immunogen designs and vaccination strategies to broaden the diversity of Abs in order to target the different conserved epitopes in the V3 loop and, by extension, in the entire HIV envelope.

E2 multimeric scaffold for vaccine formulation: immune response by intranasal delivery and transcriptome profile of E2-pulsed dendritic cells

BACKGROUND

The E2 multimeric scaffold represents a powerful delivery system able to elicit robust humoral and cellular immune responses upon systemic administrations. Here recombinant E2 scaffold displaying the third variable loop of HIV-1 Envelope gp120 glycoprotein was administered via mucosa, and the mucosal and systemic immune responses were analysed. To gain further insights into the molecular mechanisms that orchestrate the immune response upon E2 vaccination, we analysed the transcriptome profile of dendritic cells (DCs) exposed to the E2 scaffold with the aim to define a specific gene expression signature for E2-primed immune responses.

RESULTS

The in vivo immunogenicity and the potential of E2 scaffold as a mucosal vaccine candidate were investigated in BALB/c mice vaccinated via the intranasal route. Fecal and systemic antigen-specific IgA antibodies, cytokine-producing CD4(+) and CD8(+) cells were induced assessing the immunogenicity of E2 particles via intranasal administration. The cytokine analysis identified a mixed T-helper cell response, while the systemic antibody response showed a prevalence of IgG1 isotype indicative of a polarized Th2-type immune response. RNA-Sequencing analysis revealed that E2 scaffold up-regulates in DCs transcriptional regulators of the Th2-polarizing cell response, defining a type 2 DC transcriptomic signature.

CONCLUSIONS

The current study provides experimental evidence to the possible application of E2 scaffold as antigen delivery system for mucosal immunization and taking advantages of genome-wide approach dissects the type of response induced by E2 particles.

Early prophylaxis impact for newborns at risk for HIV-1 transmission at birth: viral clearance and attenuation with neutralizing monoclonal antibodies in infant rhesus macaques

Our pre-clinical infant macaque model addresses translational implications for early intervention in mother-to-child transmission (MTCT). This model has shown that neutralizing monoclonal antibody (NmAb) therapy given 1 day after SHIVSF162P3 virus exposure intercepts the earliest stages of infection in lymphoid and mucosal tissues. Serial sacrifices revealed that within 2 weeks early viral foci in tissues were eradicated. All animals followed for up to 28 weeks were completely clear of virus infection with no viral rebound after CD8-depletion. Here, twelve 1-month-old rhesus macaques, negative for MHC class I alleles Mamu B*08, B*17 and A*01, were inoculated orally with SHIVSF162P3. Cocktails of NmAbs PGT121 and VRC07-523 were delivered subcutaneously at days 1, 4, 7, and 10 after SHIV exposure. Control groups did not receive NmAbs. Plasma, PBMC, and multiple tissues at necropsy were monitored for viral RNA and DNA. ICS was used to detect Gag and Vif T cell responses. We report that lowering NmAb dosing from 10 to 5 mg/kg given 24 h after virus exposure resulted in only one animal infected, with viremia persisting at about 1 log10 below controls. NmAb treatment at 10 mg/kg delayed for 48 h after oral SHIVSF162P3 exposure resulted in ablated virus infection in 3 of 6 macaques. CD8-depletion resulted in no evidence of virus rebound, indicating the absence of viral latency. In 2 macaques, NmAbs attenuated set-point viremia by 1 – 2 log10, compared to viremia in control animals. These results show that antibodies can have powerful and durable effects on viremia and disease in newborns, but timing and dose are critical. Moreover, post-exposure viral clearance from infected tissue marks a significant advance in pre-clinical platforms to prevent MTCT.

Induction of neutralizing antibodies in rhesus macaques using V3 mimotope peptides

RV144 vaccinees with low HIV-1 Envelope-specific IgA antibodies (Abs) also had Abs directed to the hypervariable region 3 (V3) that inversely correlated with infection risk. Thus, anti-V3 HIV-1 Abs may contribute to protection from HIV-1 infection. The V3 region contains two dominant clusters of epitopes; one is preferentially recognized by mAbs encoded by VH5-51 and VL lambda genes, while the second one is recognized by mAbs encoded by other VH genes. We designed a study in rhesus macaques to induce anti-V3 Abs specific to each of these two dominant clusters of V3 epitopes to test whether the usage of the VH5-51 gene results in different characteristics of antibodies. The two C4-V3 immunogens used for immunization were each comprised of a fusion of the C4 peptide containing the T cell epitope and a V3 mimotope peptide mimicking the V3 epitope. The C4-447 peptide was designed to target B cells with several VH1-VH4 genes, the C4-VH5-51 peptide was designed to specifically target B cells with the VH5-51 gene. Six animals in two groups were immunized five times with these two immunogens, and screening of 10 sequential plasma samples post immunization demonstrated that C4-447 induced higher titers of plasma anti-V3 Abs and significantly more potent neutralizing activities against tier 1 and some tier 2 pseudoviruses than C4-VH5-51. Levels of anti-V3 Abs in buccal secretions were significantly higher in sequential samples derived from C4-447- than from C4-VH5-51-immunized animals. The titers of anti-V3 Abs in plasma strongly correlated with their levels in mucosal secretions. The results show that high titers of vaccine-induced anti-V3 Abs in plasma determine the potency and breadth of neutralization, as well as the rate of transduction of Abs to mucosal tissues, where they can play a role in preventing HIV-1 infection.

Evaluation of protection induced by a dengue virus serotype 2 envelope domain III protein scaffold/DNA vaccine in non-human primates

We describe the preclinical development of a dengue virus vaccine targeting the dengue virus serotype 2 (DENV2) envelope domain III (EDIII). This study provides proof-of-principle that a dengue EDIII protein scaffold/DNA vaccine can protect against dengue challenge. The dengue vaccine (EDIII-E2) is composed of both a protein particle and a DNA expression plasmid delivered simultaneously via intramuscular injection (protein) and gene gun (DNA) into rhesus macaques. The protein component can contain a maximum of 60 copies of EDIII presented on a multimeric scaffold of Geobacillus stearothermophilus E2 proteins. The DNA component is composed of the EDIII portion of the envelope gene cloned into an expression plasmid. The EDIII-E2 vaccine elicited robust antibody responses to DENV2, with neutralizing antibody responses detectable following the first boost and reaching titers of greater than 1:100,000 following the second and final boost. Vaccinated and naïve groups of macaques were challenged with DENV2. All vaccinated macaques were protected from detectable viremia by infectious assay, while naïve animals had detectable viremia for 2-7 days post-challenge. All naïve macaques had detectable viral RNA from day 2-10 post-challenge. In the EDIII-E2 group, three macaques were negative for viral RNA and three were found to have detectable viral RNA post challenge. Viremia onset was delayed and the duration was shortened relative to naïve controls. The presence of viral RNA post-challenge corresponded to a 10-30-fold boost in neutralization titers 28 days post challenge, whereas no boost was observed in the fully protected animals. Based on these results, we determine that pre-challenge 50% neutralization titers of >1:6000 correlated with sterilizing protection against DENV2 challenge in EDIII-E2 vaccinated macaques. Identification of the critical correlate of protection for the EDIII-E2 platform in the robust non-human primate model lays the groundwork for further development of a tetravalent EDIII-E2 dengue vaccine.

Achieving Potent Autologous Neutralizing Antibody Responses against Tier 2 HIV-1 Viruses by Strategic Selection of Envelope Immunogens

Advancement in immunogen selection and vaccine design that will rapidly elicit a protective Ab response is considered critical for HIV vaccine protective efficacy. Vaccine-elicited Ab responses must therefore have the capacity to prevent infection by neutralization-resistant phenotypes of transmitted/founder (T/F) viruses that establish infection in humans. Most vaccine candidates to date have been ineffective at generating Abs that neutralize T/F or early variants. In this study, we report that coimmunizing rhesus macaques with HIV-1 gp160 DNA and gp140 trimeric protein selected from native envelope gene sequences (envs) induced neutralizing Abs against Tier 2 autologous viruses expressing cognate envelope (Env). The Env immunogens were selected from envs emerging during the earliest stages of neutralization breadth developing within the first 2 years of infection in two clade B-infected human subjects. Moreover, the IgG responses in macaques emulated the targeting to specific regions of Env known to be associated with autologous and heterologous neutralizing Abs developed within the human subjects. Furthermore, we measured increasing affinity of macaque polyclonal IgG responses over the course of the immunization regimen that correlated with Tier 1 neutralization. In addition, we report firm correlations between Tier 2 autologous neutralization and Tier 1 heterologous neutralization, as well as overall TZM-bl breadth scores. Additionally, the activation of Env-specific follicular helper CD4 T cells in lymphocytes isolated from inguinal lymph nodes of vaccinated macaques correlated with Tier 2 autologous neutralization. These results demonstrate the potential for native Env derived from subjects at the time of neutralization broadening as effective HIV vaccine elements.

Functional and Molecular Characteristics of Novel and Conserved Cross-Clade HIV Envelope Specific Human Monoclonal Antibodies

To define features of the B cell response to HIV that may be translated to vaccine development, we have isolated a panel of monoclonal antibodies (MAbs) from HIV-infected patients. These MAbs are all highly reactive to HIV envelope (Env) from multiple clades, and include gp120 and gp41 specificities. Three of the MAbs exhibit substantial homology to previously described VH1-69, VH3-30, and VH4-59 HIV broadly neutralizing antibody lineages. An inherently autoreactive VH4-34 encoded MAb was reactive to diverse Env despite its minimal mutation from germline. Its isolation is consistent with our previous observation of increased VH4-34+antibodies in HIV-infected patients. These results suggest that conserved developmental processes contribute to immunoglobulin repertoire usage and maturation in response to HIV Env and that intrinsically autoreactive VH genes, despite the absence of mutation, could serve as effective templates for maturation and development of protective antibodies. These results also bear significant implications for the development of immunogens.

Multimeric scaffolds displaying the HIV-1 envelope MPER induce MPER-specific antibodies and cross-neutralizing antibodies when co-immunized with gp160 DNA

Developing a vaccine that overcomes the diversity of HIV-1 is likely to require a strategy that directs antibody (Ab) responses toward conserved regions of the viral Envelope (Env). However, the generation of neutralizing Abs (NAbs) targeting these regions through vaccination has proven to be difficult. One conserved region of particular interest is the membrane proximal external region (MPER) of Env located within the gp41 ectodomain. In order to direct the immune response to this region, the MPER and gp41 ectodomain were expressed separately as N-terminal fusions to the E2 protein of Geobacillus stearothermophilus. The E2 protein acts as a scaffold by self-assembling into 60-mer particles, displaying up to 60 copies of the fused target on the surface. Rabbits were immunized with E2 particles displaying MPER and/or the gp41 ectodomain in conjunction with DNA encoding full-length gp160. Only vaccines including E2 particles displaying MPER elicited MPER-specific Ab responses. NAbs were elicited after two immunizations that largely targeted the V3 loop. To overcome V3 immunodominance in the DNA component, E2 particles displaying MPER were used in conjunction with gp160 DNA lacking hypervariable regions V2, V3, or combined V1V2V3. All rabbits had HIV binding Ab responses and NAbs following the second vaccination. Using HIV-2/HIV-1 MPER chimeric viruses as targets, NAbs were detected in 12/16 rabbits after three immunizations. Low levels of NAbs specific for Tier 1 and 2 viruses were observed in all groups. This study provides evidence that co-immunizing E2 particles displaying MPER and gp160 DNA can focus Ab responses toward conserved regions of Env.

Vaccine delivery to the oral cavity using coated microneedles induces systemic and mucosal immunity

PURPOSE

The objective of this study is to evaluate the feasibility of using coated microneedles to deliver vaccines into the oral cavity to induce systemic and mucosal immune responses.

METHOD

Microneedles were coated with sulforhodamine, ovalbumin and two HIV antigens. Coated microneedles were inserted into the inner lower lip and dorsal surface of the tongue of rabbits. Histology was used to confirm microneedle insertion, and systemic and mucosal immune responses were characterized by measuring antigen-specific immunoglobulin G (IgG) in serum and immunoglobulin A (IgA) in saliva, respectively.

RESULTS

Histological evaluation of tissues shows that coated microneedles can penetrate the lip and tongue to deliver coatings. Using ovalbumin as a model antigen it was found that the lip and the tongue are equally immunogenic sites for vaccination. Importantly, both sites also induced a significant (p < 0.05) secretory IgA in saliva compared to pre-immune saliva. Microneedle-based oral cavity vaccination was also compared to the intramuscular route using two HIV antigens, a virus-like particle and a DNA vaccine. Microneedle-based delivery to the oral cavity and the intramuscular route exhibited similar (p > 0.05) yet significant (p < 0.05) levels of antigen-specific IgG in serum. However, only the microneedle-based oral cavity vaccination group stimulated a significantly higher (p < 0.05) antigen-specific IgA response in saliva, but not intramuscular injection.

CONCLUSION

In conclusion, this study provides a novel method using microneedles to induce systemic IgG and secretory IgA in saliva, and could offer a versatile technique for oral mucosal vaccination.

Improvement of antibody responses by HIV envelope DNA and protein co-immunization

BACKGROUND

Developing HIV envelope (Env) vaccine components that elicit durable and protective antibody responses is an urgent priority, given the results from the RV144 trial. Optimization of both the immunogens and vaccination strategies will be needed to generate potent, durable antibodies. Due to the diversity of HIV, an effective Env-based vaccine will most likely require an extensive coverage of antigenic variants. A vaccine co-delivering Env immunogens as DNA and protein components could provide such coverage. Here, we examine a DNA and protein co-immunization strategy by characterizing the antibody responses and evaluating the relative contribution of each vaccine component.

METHOD

We co-immunized rabbits with representative subtype A or B HIV gp160 plasmid DNA plus Env gp140 trimeric glycoprotein and compared the responses to those obtained with either glycoprotein alone or glycoprotein in combination with empty vector.

RESULTS

DNA and glycoprotein co-immunization was superior to immunization with glycoprotein alone by enhancing antibody kinetics, magnitude, avidity, and neutralizing potency. Importantly, the empty DNA vector did not contribute to these responses. Humoral responses elicited by mismatched DNA and protein components were comparable or higher than the responses produced by the matched vaccines.

CONCLUSION

Our data show that co-delivering DNA and protein can augment antibodies to Env. The rate and magnitude of immune responses suggest that this approach has the potential to streamline vaccine regimens by inducing higher antibody responses using fewer vaccinations, an advantage for a successful HIV vaccine design.

SIV infection of rhesus macaques of Chinese origin: a suitable model for HIV infection in humans

Simian immunodeficiency virus (SIV) infection of Indian-origin rhesus macaques (RM) has been widely used as a well-established nonhuman primate (NHP) model for HIV/AIDS research. However, there have been a growing number of studies using Chinese RM to evaluate immunopathogenesis of SIV infection. In this paper, we have for the first time reviewed and discussed the major publications related to SIV or SHIV infection of Chinese RM in the past decades. We have compared the differences in the pathogenesis of SIV infection between Chinese RM and Indian RM with regard to viral infection, immunological response, and host genetic background. Given AIDS is a disease that affects humans of diverse origins, it is of importance to study animals with different geographical background. Therefore, to examine and compare results obtained from RM models of Indian and Chinese origins should lead to further validation and improvement of these animal models for HIV/AIDS research.

Lessons in nonhuman primate models for AIDS vaccine research: from minefields to milestones

Nonhuman primate (NHP) disease models for AIDS have made important contributions to the search for effective vaccines for AIDS. Viral diversity, persistence, capacity for immune evasion, and safety considerations have limited development of conventional approaches using killed or attenuated vaccines, necessitating the development of novel approaches. Here we highlight the knowledge gained and lessons learned in testing vaccine concepts in different virus/NHP host combinations.

Motif-optimized subtype A HIV envelope-based DNA vaccines rapidly elicit neutralizing antibodies when delivered sequentially

HIV-1 infection results in the development of a diverging quasispecies unique to each infected individual. Envelope (Env)-specific neutralizing antibodies (NAbs) typically develop over months to years after infection and initially are limited to the infecting virus. In some subjects, antibody responses develop that neutralize heterologous isolates (HNAbs), a phenomenon termed broadening of the NAb response. Studies of co-crystalized antibodies and proteins have facilitated the identification of some targets of broadly neutralizing monoclonal antibodies (NmAbs) capable of neutralizing many or most heterologous viruses; however, the ontogeny of these antibodies in vivo remains elusive. We hypothesize that Env protein escape variants stimulate broad NAb development in vivo and could generate such NAbs when used as immunogens. Here we test this hypothesis in rabbits using HIV Env vaccines featuring: (1) use of individual quasispecies env variants derived from an HIV-1 subtype A-infected subject exhibiting high levels of NAbs within the first year of infection that increased and broadened with time; (2) motif optimization of envs to enhance in vivo expression of DNA formulated as vaccines; and (3) a combined DNA plus protein boosting regimen. Vaccines consisted of multiple env variants delivered sequentially and a simpler regimen that utilized only the least and most divergent clones. The simpler regimen was as effective as the more complex approach in generating modest HNAbs and was more efficient when modified, motif-optimized DNA was used in combination with trimeric gp140 protein. This is a rationally designed strategy that facilitates future vaccine design by addressing the difficult problem of generating HNAbs to HIV by empirically testing the immunogenicity of naturally occurring quasispecies env variants.

Neutralizing antibodies and control of HIV: moves and countermoves

It is now evident that powerful antibodies directed to conserved regions of HIV-1 envelope protein develop during chronic infection in some individuals and that these antibodies can neutralize a broad array of diverse isolates in vitro, so termed broadly neutralizing antibodies (bNAbs). A great deal of effort is directed internationally at understanding the ontogeny of NAbs during infection as well as in designing and testing immunogens that can elicit bNAbs in animal models and in humans. Given the parrying tactics of Env, multiple approaches, along with high-resolution structural studies, will be needed to reach a degree of understanding sufficient to design an effective vaccine. We discuss and note here some of the most important recent advances in our knowledge of how neutralizing antibodies develop in vivo, the recent discovery of extremely powerful neutralizing monoclonal antibodies isolated from natural infection, enhanced methodologies that have accelerated discoveries on both fronts, and the progress made in eliciting potent NAbs with limited breadth by vaccination.

Co-immunization with multimeric scaffolds and DNA rapidly induces potent autologous HIV-1 neutralizing antibodies and CD8+ T cells

To obtain proof of concept for HIV vaccines, we generated recombinant multimeric particles displaying the HIV-1 Envelope (Env) third hypervariable region (V3) as an N-terminal fusion protein on the E2 subunit of the pyruvate dehydrogenase complex of Geobacillus stearothermophilus. The E2 scaffold self-assembles into a 60-mer core that is 24 nm in diameter, with a molecular weight of 1.5 MDa, similar to a virus like particle with up to 60 copies of a heterologous protein accessible on the surface. Env(V3)-E2 multimers were tested alone and in combination with Env(gp160) DNA in mice and rabbits. Following two or more co-immunizations with Env(V3)-E2 and Env gp160 DNA, all 18 rabbits developed potent autologous neutralizing antibodies specific for V3 in six weeks. These neutralizing antibodies were sustained for 16 weeks without boosting, and comparable responses were obtained when lipopolysaccharide, a contaminant from expression in E. coli, was removed. Co-immunizations of Env(V3)-E2 and DNA expressing gp160 elicited moderate CD8-specific responses and Env-specific antibodies in mice. Co-immunization with DNA and E2 was superior to individual or sequential vaccination with these components in eliciting both neutralizing antibodies in rabbits and CD8(+) T cell responses in mice. Co-immunization with DNA and multimeric E2 scaffolds appears to offer a highly effective means of eliciting rapid, specific, and sustained immune responses that may be a useful approach for other vaccine targets.

Delivery strategies for novel vaccine formulations

A major challenge in vaccine design is to identify antigen presentation and delivery systems capable of rapidly stimulating both the humoral and cellular components of the immune system to elicit a strong and sustained immunity against different viral isolates. Approaches to achieve this end involve live attenuated and inactivated virions, viral vectors, DNA, and protein subunits. This review reports the state of current antigen delivery, and focuses on two innovative systems recently established at our labs. These systems are the filamentous bacteriophage fd and an icosahedral scaffold formed by the acyltransferase component (E2 protein) of the pyruvate dehydrogenase complex of Bacillus stearothermophilus.