Split-Dose Administration Enhances Immune Responses Elicited by a mRNA/Lipid Nanoparticle Vaccine Expressing Respiratory Syncytial Virus F Protein.

mRNA vaccines have recently received significant attention due to their role in combating the SARS-CoV-2 pandemic. As a platform, mRNA vaccines have been shown to elicit strong humoral and cellular immune responses with acceptable safety profiles for prophylactic use. Despite their potential, industrial challenges have limited realization of the vaccine platform on a global scale. Critical among these challenges are supply chain considerations, including mRNA production, cost of goods, and vaccine frozen-chain distribution. Here, we assess the delivery of lipid nanoparticle-encapsulated mRNA (mRNA/LNP) vaccines using a split-dose immunization regimen as an approach to develop mRNA dose-sparing vaccine regimens with potential to mitigate mRNA supply chain challenges. Our data demonstrate that immunization by a mRNA/LNP vaccine encoding respiratory syncytial virus pre-F (RSV pre-F) over a 9 day period elicits comparable or superior magnitude of antibodies when compared to traditional bolus immunization of the vaccine. The split-dose immunization regimens evaluated in our studies were designed to mimic reported drug or antigen release profiles from microneedle patches, highlighting the potential benefit of pairing mRNA vaccines with patch-based delivery technologies to enable sustained release and solid-state stabilization. Overall, our findings provide a proof of concept to support further investigations into the development of sustained delivery approaches for mRNA/LNP vaccines.

Potent neutralizing antibodies elicited by dengue vaccine in rhesus macaque target diverse epitopes.

There is still no safe and effective vaccine against dengue virus infection. Epidemics of dengue virus infection are increasingly a threat to human health around the world. Antibodies generated in response to dengue infection have been shown to impact disease development and effectiveness of dengue vaccine. In this study, we investigated monoclonal antibody responses to an experimental dengue vaccine in rhesus macaques. Variable regions of both heavy chain (VH) and light chain (VL) were cloned from single antibody-secreting B cells. A total of 780 monoclonal antibodies (mAbs) composed of paired VH and VL were characterized. Results show that the vaccination induces mAbs with diverse germline sequences and a wide range of binding affinities. Six potent neutralizing mAbs were identified among 130 dengue envelope protein binders. Critical amino acids for each neutralizing antibody binding to the dengue envelope protein were identified by alanine scanning of mutant libraries. Diverse epitopes were identified, including epitopes on the lateral ridge of DIII, the I-III hinge, the bc loop adjacent to the fusion loop of DII, and the ß-strands and loops of DI. Significantly, one of the neutralizing mAbs has a previously unknown epitope in DII at the interface of the envelope and membrane protein and is capable of neutralizing all four dengue serotypes. Taken together, the results of this study not only provide preclinical validation for the tested experimental vaccine, but also shed light on a potential application of the rhesus macaque model for better dengue vaccine evaluation and design of vaccines and immunization strategies.

Evaluation of luciferase and prefusion-stabilized F protein from respiratory syncytial virus mRNA/LNPs in pre-clinical models using jet delivery compared to needle and syringe.

Described here is the evaluation of a luciferase (luc) and respiratory syncytial virus (RSV) messenger RNA / lipid nanoparticle (mRNA/LNP) vaccine using a Needle-free Injection System, Tropis®, from PharmaJet® (Golden, Colorado USA). Needle-free jet delivery offers an alternative to needle/syringe. To perform this assessment, compatibility studies with Tropis were first performed with a luc mRNA/LNP and compared to needle/syringe. Although minor changes in particle size and encapsulation efficiency were observed when using Tropis on the benchtop, in vitro luciferase activity remained the same. Next, the luc mRNA/LNP was administered to rats intramuscularly using Tropis or needle/syringe and tracking of the injection and distribution was performed. Lastly, an mRNA encoding a prefusion-stabilized F protein from RSV was delivered intramuscularly using both Tropis and needle/syringe at 1 and 5 mcg mRNA. An equivalent IgG response was observed using both Tropis and needle/syringe. The cell mediated immune (CMI) response was also evaluated, and responses to RSV-F were detected from animals immunized with needle/syringe at all dose levels, and from the animals immunized with Tropis in the 5 and 25 ug groups. These results indicated that delivery of mRNA/LNPs with Tropis is a potential means of administration and an alternative to needle/syringe.

The number of Toll-like receptor 9-agonist motifs in the adenovirus genome correlates with induction of dendritic cell maturation by adenovirus immune complexes.

Adenovirus serotype 5 (Ad5) vectors and specific neutralizing antibodies (NAbs) generate immune complexes (ICs) which are potent inducers of dendritic cell (DC) maturation. Here we show that ICs generated with rare Ad vector serotypes, such as Ad26 and Ad35, which are lead candidates in HIV vaccine development, are poor inducers of DC maturation and that their potency in inducing DC maturation strongly correlated with the number of Toll-like receptor 9 (TLR9)-agonist motifs present in the Ad vector's genome. In addition, we showed that antihexon but not antifiber antibodies are responsible for the induction of Ad IC-mediated DC maturation.

Low-dose penile SIVmac251 exposure of rhesus macaques infected with adenovirus type 5 (Ad5) and then immunized with a replication-defective Ad5-based SIV gag/pol/nef vaccine recapitulates the results of the phase IIb step trial of a similar HIV-1 vaccine.

The Step Trial showed that the MRKAd5 HIV-1 subtype B Gag/Pol/Nef vaccine did not protect men from HIV infection or reduce setpoint plasma viral RNA (vRNA) levels but, unexpectedly, it did modestly enhance susceptibility to HIV infection in adenovirus type 5 (Ad5)-seropositive, uncircumcised men. As part of the process to understand the results of the Step Trial, we designed a study to determine whether rhesus macaques chronically infected with a host-range mutant Ad5 (Ad5hr) and then immunized with a replication defective Ad5 SIVmac239 Gag/Pol/Nef vaccine were more resistant or susceptible to SIV infection than unimmunized rhesus macaques challenged with a series of escalating dose penile exposures to SIVmac 251. The Ad5 SIV vaccine induced CD8(+) T cell responses in 70% of the monkeys, which is similar to the proportion of humans that responded to the vaccine in the Step Trial. However, the vaccine did not protect vaccinated animals from penile SIV challenge. At the lowest SIV exposure dose (10(3) 50% tissue culture infective doses), 2 of 9 Ad5-seropositive animals immunized with the Ad5 SIV vaccine became infected compared to 0 of 34 animals infected in the other animal groups (naive animals, Ad5-seropositive animals immunized with the empty Ad5 vector, Ad5-seronegative animals immunized with the Ad5 SIV vaccine, and Ad5-seronegative animals immunized with the empty Ad5 vector). Penile exposure to more concentrated virus inocula produced similar rates of infection in all animal groups. Although setpoint viral loads were unaffected in Step vaccinees, the Ad5 SIV-immunized animals had significantly lower acute-phase plasma vRNA levels compared to unimmunized animals. Thus, the results of the nonhuman primate (NHP) study described here recapitulate the lack of protection against HIV acquisition seen in the Step Trial and suggest a greater risk of infection in the Ad5-seropositive animals immunized with the Ad5 SIV vaccine. Further studies are necessary to confirm the enhancement of virus acquisition and to discern associated mechanisms.

Evaluation of a stabilized RSV pre-fusion F mRNA vaccine: Preclinical studies and Phase 1 clinical testing in healthy adults.

Human respiratory syncytial virus (RSV) causes a substantial proportion of respiratory tract infections worldwide. Although RSV reinfections occur throughout life, older adults, particularly those with underlying comorbidities, are at risk for severe complications from RSV. There is no RSV vaccine available to date, and treatment of RSV in adults is largely supportive. A correlate of protection for RSV has not yet been established, but antibodies targeting the pre-fusion conformation of the RSV F glycoprotein play an important role in RSV neutralization. We previously reported a Phase 1 study of an mRNA-based vaccine (V171) expressing a pre-fusion-stabilized RSV F protein (mDS-Cav1) in healthy adults. Here, we evaluated an mRNA-based vaccine (V172) expressing a further stabilized RSV pre-fusion F protein (mVRC1). mVRC1 is a single chain version of RSV F with interprotomer disulfides in addition to the stabilizing mutations present in the mDS-Cav1 antigen. The immunogenicity of the two mRNA-based vaccines encoding mVRC1 (V172) or a sequence-optimized version of mDS-Cav1 to improve transcriptional fidelity (V171.2) were compared in RSV-naïve and RSV-experienced African green monkeys (AGMs). V172 induced higher neutralizing antibody titers than V171.2 and demonstrated protection in the AGM challenge model. We conducted a Phase 1, randomized, placebo-controlled, clinical trial of 25 µg, 100 µg, 200 µg, or 300 µg of V172 in healthy older adults (60-79 years old; N = 112) and 100 µg, 200 µg, or 300 µg of V172 in healthy younger adults (18-49 years old; N = 48). The primary clinical objectives were to evaluate the safety and tolerability of V172, and the secondary objective was to evaluate RSV serum neutralization titers. The most commonly reported solicited adverse events were injection-site pain, injection-site swelling, headache, and tiredness. V172 was generally well tolerated in older and younger adults and increased serum neutralizing antibody titers, pre-fusion F-specific competing antibody titers, and RSV F-specific T-cell responses.

Robust, vaccine-induced CD8(+) T lymphocyte response against an out-of-frame epitope.

Rational vaccines designed to engender T cell responses require intimate knowledge of how epitopes are generated and presented. Recently, we vaccinated 8 Mamu-A*02(+) rhesus macaques with every SIV protein except Envelope (Env). Surprisingly, one of the strongest T cell responses engendered was against the Env protein, the Mamu-A*02-restricted epitope, Env(788-795)RY8. In this paper, we show that translation from an alternate reading frame of both the Rev-encoding DNA plasmid and the rAd5 vector engendered Env(788-795)RY8-specific CD8(+) T cells of greater magnitude than "normal" SIV infection. Our data demonstrate both that the pathway from vaccination to immune response is not well understood and that products of alternate reading frames may be rich and untapped sources of T cell epitopes.

Upper and lower respiratory tract correlates of protection against respiratory syncytial virus following vaccination of nonhuman primates.

Respiratory syncytial virus (RSV) infection is a major cause of respiratory illness in infants and the elderly. Although several vaccines have been developed, none have succeeded in part due to our incomplete understanding of the correlates of immune protection. While both T cells and antibodies play a role, emerging data suggest that antibody-mediated mechanisms alone may be sufficient to provide protection. Therefore, to map the humoral correlates of immunity against RSV, antibody responses across six different vaccines were profiled in a highly controlled nonhuman primate-challenge model. Viral loads were monitored in both the upper and lower respiratory tracts, and machine learning was used to determine the vaccine platform-agnostic antibody features associated with protection. Upper respiratory control was associated with virus-specific IgA levels, neutralization, and complement activity, whereas lower respiratory control was associated with Fc-mediated effector mechanisms. These findings provide critical compartment-specific insights toward the rational development of future vaccines.

Profiling of hMPV F-specific antibodies isolated from human memory B cells.

Human metapneumovirus (hMPV) belongs to the Pneumoviridae family and is closely related to respiratory syncytial virus (RSV). The surface fusion (F) glycoprotein mediates viral fusion and is the primary target of neutralizing antibodies against hMPV. Here we report 113 hMPV-F specific monoclonal antibodies (mAbs) isolated from memory B cells of human donors. We characterize the antibodies' germline usage, epitopes, neutralization potencies, and binding specificities. We find that unlike RSV-F specific mAbs, antibody responses to hMPV F are less dominant against the apex of the antigen, and the majority of the potent neutralizing mAbs recognize epitopes on the side of hMPV F. Furthermore, neutralizing epitopes that differ from previously defined antigenic sites on RSV F are identified, and multiple binding modes of site V and II mAbs are discovered. Interestingly, mAbs that bind preferentially to the unprocessed prefusion F show poor neutralization potency. These results elucidate the immune recognition of hMPV infection and provide novel insights for future hMPV antibody and vaccine development.

Preclinical immunogenicity and efficacy of a candidate COVID-19 vaccine based on a vesicular stomatitis virus-SARS-CoV-2 chimera.

BACKGROUND: To investigate a vaccine technology with potential to protect against coronavirus disease 2019 (COVID-19) and reduce transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) with a single vaccine dose, we developed a SARS-CoV-2 candidate vaccine using the live vesicular stomatitis virus (VSV) chimeric virus approach previously used to develop a licensed Ebola virus vaccine. METHODS: We generated a replication-competent chimeric VSV-SARS-CoV-2 vaccine candidate by replacing the VSV glycoprotein (G) gene with coding sequence for the SARS-CoV-2 Spike glycoprotein (S). Immunogenicity of the lead vaccine candidate (VSV∆G-SARS-CoV-2) was evaluated in cotton rats and golden Syrian hamsters, and protection from SARS-CoV-2 infection also was assessed in hamsters. FINDINGS: VSV∆G-SARS-CoV-2 delivered with a single intramuscular (IM) injection was immunogenic in cotton rats and hamsters and protected hamsters from weight loss following SARS-CoV-2 challenge. When mucosal vaccination was evaluated, cotton rats did not respond to the vaccine, whereas mucosal administration of VSV∆G-SARS-CoV-2 was found to be more immunogenic than IM injection in hamsters and induced immunity that significantly reduced SARS-CoV-2 challenge virus loads in both lung and nasal tissues. INTERPRETATION: VSV∆G-SARS-CoV-2 delivered by IM injection or mucosal administration was immunogenic in golden Syrian hamsters, and both vaccination methods effectively protected the lung from SARS-CoV-2 infection. Hamsters vaccinated by mucosal application of VSV∆G-SARS-CoV-2 also developed immunity that controlled SARS-CoV-2 replication in nasal tissue. FUNDING: The study was funded by Merck Sharp & Dohme, Corp., a subsidiary of Merck & Co., Inc., Rahway, NJ, USA, and The International AIDS Vaccine Initiative, Inc. (IAVI), New York, USA. Parts of this research was supported by the Biomedical Advanced Research and Development Authority (BARDA) and the Defense Threat Reduction Agency (DTRA) of the US Department of Defense.

Efficacy of multivalent adenovirus-based vaccine against simian immunodeficiency virus challenge.

The prophylactic efficacies of several multivalent replication-incompetent adenovirus serotype 5 (Ad5) vaccines were examined in rhesus macaques using an intrarectal high-dose simian immunodeficiency virus SIVmac239 challenge model. Cohorts of Mamu-A*01(+)/B*17(-) Indian rhesus macaques were immunized with one of several combinations of Ad5 vectors expressing Gag, Pol, Nef, and Env gp140; for comparison, a Mamu-A*01(+) cohort was immunized using the Ad5 vector alone. There was no sign of immunological interference between antigens in the immunized animals. In general, expansion of the antigen breadth resulted in more favorable virological outcomes. In particular, the order of efficacy trended as follows: Gag/Pol/Nef/Env approximately Gag/Pol > Gag approximately Gag/Pol/Nef > Nef. However, the precision in ranking the vaccines based on the study results may be limited by the cohort size, and as such, may warrant additional testing. The implications of these results in light of the recent discouraging results of the phase IIb study of the trivalent Ad5 HIV-1 vaccine are discussed.

Synthesis and immunological activities of novel Toll-like receptor 7 and 8 agonists.

Single-stranded oligoribonucleotides (ORNs) stimulate innate immune responses through TLR7 and TLR8. Specific linkages and chemical modifications incorporated into synthetic ORN can greatly enhance nuclease stability, selectivity, and potency. In the present study, we have synthesized 15 ORN containing different sequence compositions and chemical modifications and studied their TLR7- and TLR8-mediated immune response profiles in HEK293 cells expressing human TLR7 or TLR8, human PBMCs, mDCs and pDCs, non-human primate (NHP) PBMCs, and in vivo in mice and NHPs. Based on the results obtained, eight of the ORNs containing specific chemical modifications induced immune responses through both TLR7 and TLR8, including activation of NF-κB in TLR7- and TLR8-transfected cell lines; induction of IFN-α, IL-6, TNF-α, IL-12, and IP-10 in human PBMCs; IFN-α induction in human pDCs; CD80 upregulation in human pDCs and mDCs; IL-12 induction following acute administration in mice; IFN-α, IP-10, IL-6, and IL-12 induction in NHP PBMCs; and IFN-α, IP-10, and IL-6 induction following acute administration in NHPs. Seven of the ORNs show selectivity for TLR8-induced responses; they specifically activate only TLR8-transfected cell lines, induce cytokines other than IFN-α in human and NHP PBMCs, activate mDCs more than pDCs, and do not induce IL-12 acutely in mice, consistent with the lack of functional TLR8 in mice. The novel TLR8-selective ORNs also induce cytokines other than IFN-α acutely in NHPs. In conclusion, we have designed and synthesized novel ORNs with varying sequence compositions and chemical modifications, which selectively act as agonists of TLR8 or dual agonists of TLR7 and TLR8.

Comparative analysis of immune responses induced by vaccination with SIV antigens by recombinant Ad5 vector or plasmid DNA in rhesus macaques.

DNA vaccines have undergone important enhancements in their design, formulation, and delivery process. Past literature supports that DNA vaccines are not as immunogenic in nonhuman primates as live vector systems. The most potent recombinant vector system for induction of cellular immune responses in macaques and humans is adenovirus serotype 5 (Ad5), an important benchmark for new vaccine development. Here, we performed a head-to-head evaluation of the Merck Ad5 SIV vaccine and an optimized electroporation (EP) delivered SIV DNA vaccine in macaques. Animals receiving the Ad5 vaccine were immunized three times, whereas the DNA-vaccinated animals were immunized up to four times based on optimized protocols. We observed significant differences in the quantity of IFNgamma responses by enzyme-linked immunosorbent spot (ELISpot), greater proliferative capacity of CD8(+) T cells, and increased polyfunctionality of both CD4(+) and CD8(+) T cells in the DNA-vaccinated group. Importantly, Ad5 immunizations failed to boost following the first immunization, whereas DNA responses were continually boosted with all four immunizations demonstrating a major advantage of these improved DNA vaccines. These optimized DNA vaccines induce very different immune phenotypes than traditional Ad5 vaccines, suggesting that they could play an important role in vaccine research and development.

Vaccine-induced cellular responses control simian immunodeficiency virus replication after heterologous challenge.

All human immunodeficiency virus (HIV) vaccine efficacy trials to date have ended in failure. Structural features of the Env glycoprotein and its enormous variability have frustrated efforts to induce broadly reactive neutralizing antibodies. To explore the extent to which vaccine-induced cellular immune responses, in the absence of neutralizing antibodies, can control replication of a heterologous, mucosal viral challenge, we vaccinated eight macaques with a DNA/Ad5 regimen expressing all of the proteins of SIVmac239 except Env. Vaccinees mounted high-frequency T-cell responses against 11 to 34 epitopes. We challenged the vaccinees and eight naïve animals with the heterologous biological isolate SIVsmE660, using a regimen intended to mimic typical HIV exposures resulting in infection. Viral loads in the vaccinees were significantly less at both the peak (1.9-log reduction; P < 0.03) and at the set point (2.6-log reduction; P < 0.006) than those in control naïve animals. Five of eight vaccinated macaques controlled acute peak viral replication to less than 80,000 viral RNA (vRNA) copy eq/ml and to less than 100 vRNA copy eq/ml in the chronic phase. Our results demonstrate that broad vaccine-induced cellular immune responses can effectively control replication of a pathogenic, heterologous AIDS virus, suggesting that T-cell-based vaccines may have greater potential than previously appreciated.

Synthesis and immunological activities of novel agonists of toll-like receptor 9.

Novel agonists of TLR9 with two 5'-ends and synthetic immune stimulatory motifs, referred to as immune modulatory oligonucleotides (IMOs) are potent agonists of TLR9. In the present study, we have designed and synthesized 15 novel IMOs by incorporating specific chemical modifications and studied their immune response profiles both in vitro and in vivo. Analysis of the immunostimulatory profiles of these IMOs in human and NHP cell-based assays suggest that changes in the number of synthetic immunostimulatory motifs gave only a subtle change in immune stimulation of pDCs as indicated by IFN-alpha production and pDC maturation while the addition of self-complementary sequences produced more dramatic changes in both pDC and B cell stimulation. All IMOs induced cytokine production in vivo immediately after administration in mice. Representative compounds were also compared for the ability to stimulate cytokine production in vivo (IFN-alpha and IP-10) in rhesus macaques after intra-muscular administration.

Modified mRNA/lipid nanoparticle-based vaccines expressing respiratory syncytial virus F protein variants are immunogenic and protective in rodent models of RSV infection.

The RSV Fusion (F) protein is a target for neutralizing antibody responses and is a focus for vaccine discovery; however, the process of RSV entry requires F to adopt a metastable prefusion form and transition to a more stable postfusion form, which displays less potent neutralizing epitopes. mRNA vaccines encode antigens that are translated by host cells following vaccination, which may allow conformational transitions similar to those observed during natural infection to occur. Here we evaluate a panel of chemically modified mRNA vaccines expressing different forms of the RSV F protein, including secreted, membrane associated, prefusion-stabilized, and non-stabilized structures, for conformation, immunogenicity, protection, and safety in rodent models. Vaccination with mRNA encoding native RSV F elicited antibody responses to both prefusion- and postfusion-specific epitopes, suggesting that this antigen may adopt both conformations in vivo. Incorporating prefusion stabilizing mutations further shifts the immune response toward prefusion-specific epitopes, but does not impact neutralizing antibody titer. mRNA vaccine candidates expressing either prefusion stabilized or native forms of RSV F protein elicit robust neutralizing antibody responses in both mice and cotton rats, similar to levels observed with a comparable dose of adjuvanted prefusion stabilized RSV F protein. In contrast to the protein subunit vaccine, mRNA-based vaccines elicited robust CD4+ and CD8+ T-cell responses in mice, highlighting a potential advantage of the technology for vaccines requiring a cellular immune response for efficacy.

Development and application of a higher throughput RSV plaque assay by immunofluorescent imaging.

Viral plaque assays are important tools in the development and evaluation of new antiviral drugs or vaccines in both preclinical and clinical research. While plaque assays are the standard tools to measure infectious virus, the methodology is time-consuming and requires experience in recognizing plaques. The assays are also prone to variation among analysts due to plaque recognition and manual counting errors. Here we describe the development of two simplified plaque assays for measuring RSV virus titers and anti-RSV antibody neutralization titers using 96 well plate formats. First, we evaluated multiple parameters to build up a quantitative plaque assay to measure infectious RSV. We then optimized the assay conditions to assess the fundamental changes from the traditional plaque assay, which were elimination of overnight pre-seeding host cells and addition of a centrifugation step after viral infection of the cells. We designed DoE to refine four key parameters within one experiment for host cell density, host cell volume, viral inoculum volume, host cell and viral mixture incubation time to make this assay more robust. We have also adapted these conditions into a second assay, which was an automated plaque reduction neutralization assay (PRNT) to determine neutralization titers of anti-RSV antibodies. Both assays utilize immune fluorescence staining to detect viral plaques. The images of the immuno-stained wells are captured by the PerkinElmer EnSight instrument and show clear visualization of plaques harvesting on day 3. Software algorithm was specifically designed for automatic counting of these fluorescent "objects". The quantitative plaque assay provided titers of RSV similar to those obtained from the traditional plaque assay. The method has been successfully utilized to screen multiple vaccine candidates in viral shedding efficacy studies. The automated PRNT assay provided antibody neutralizing titers that matched with published data. This automated 96 well plaque assay has made it possible to screen RSV samples in a higher throughput manner, and can be extended to other infectious organisms that form plaques for vaccine or drug evaluation.

Immunogenicity and safety of an investigational tetravalent recombinant subunit vaccine for dengue: results of a Phase I randomized clinical trial in flavivirus-naïve adults.

There is an unmet medical need for vaccines to prevent dengue. V180 is an investigational recombinant subunit vaccine that consists of truncated dengue envelope proteins (DEN-80E) for all 4 serotypes. Three dosage levels of the tetravalent DEN-80E antigens were assessed in a randomized, placebo-controlled, Phase I dose-escalation, first-in-human proof-of-principle trial in healthy, flavivirus-naïve adults in Australia (NCT01477580). The 9 V180 formulations that were assessed included either ISCOMATRIX™ adjuvant (2 dosage levels), aluminum-hydroxide adjuvant, or were unadjuvanted, and were compared to phosphate-buffered saline placebo. Volunteers received 3 injections of assigned product on a 0, 1, 2 month schedule, and were followed for safety through 1 year after the last injection. Antibody levels were assessed at 6 time-points: enrollment, 28 days after each injection, and 6 and 12 months Postdose 3 (PD3). Of the 98 randomized participants, 90 (92%) received all 3 injections; 83 (85%) completed 1-year follow-up. Immunogenicity was measured by a qualified Focus Reduction Neutralization Test with a 50% neutralization cutoff (FRNT50). All 6 V180 formulations with ISCOMATRIX™ adjuvant showed robust immunogenicity, while the 1 aluminum-adjuvanted and 2 unadjuvanted formulations were poorly immunogenic. Geometric mean antibody titers generally declined at 6 months and 1 year PD3. All 9 V180 formulations were generally well tolerated. Formulations with ISCOMATRIX™ adjuvant were associated with more adverse events than aluminum-adjuvanted or unadjuvanted formulations.

Characterization of potent RSV neutralizing antibodies isolated from human memory B cells and identification of diverse RSV/hMPV cross-neutralizing epitopes.

Respiratory syncytial virus (RSV) is a leading cause of lower respiratory tract infection in young children and older adults. Currently, no licensed vaccine is available, and therapeutic options are limited. The primary target of neutralizing antibodies to RSV is the surface fusion (F) glycoprotein. Understanding the recognition of antibodies with high neutralization potencies to RSV F antigen will provide critical insights in developing efficacious RSV antibodies and vaccines. In this study, we isolated and characterized a panel of monoclonal antibodies (mAbs) with high binding affinity to RSV prefusion F trimer and neutralization potency to RSV viruses. The mAbs were mapped to previously defined antigenic sites, and some that mapped to the same antigenic sites showed remarkable diversity in specificity, binding, and neutralization potencies. We found that the isolated site III mAbs shared highly conserved germline V-gene usage, but had different cross-reactivities to human metapneumovirus (hMPV), possibly due to the distinct modes/angles of interaction with RSV and hMPV F proteins. Furthermore, we identified a subset of potent RSV/hMPV cross-neutralizing mAbs that target antigenic site IV and the recently defined antigenic site V, while the majority of the mAbs targeting these two sites only neutralize RSV. Additionally, the isolated mAbs targeting site Ø were mono-specific for RSV and showed a wide range of neutralizing potencies on different RSV subtypes. Our data exemplify the diversity of anti-RSV mAbs and provide new insights into the immune recognition of respiratory viruses in the Pneumoviridae family.

Immune response and reactogenicity of an unadjuvanted intradermally delivered human papillomavirus vaccine using a first generation Nanopatch™ in rhesus macaques: An exploratory, pre-clinical feasibility assessment.

The human papillomavirus (HPV) 9-valent, recombinant vaccine (Gardasil™9) helps protect young adults (males and females) against anogenital cancers and genital warts caused by certain HPV genotypes (ref. Gardasil™9 insert). This vaccine is administered intramuscularly (IM). The aim of this study was to determine preclinically whether intradermal (ID) vaccination with an unadjuvanted 9-valent recombinant HPV vaccine using a first-generation ID delivery device, the Nanopatch™, could enhance vaccine immunogenicity compared with the traditional ID route (Mantoux technique). IM injection of HPV VLPs formulated with Merck & Co., Inc., Kenilworth, NJ, USA Alum Adjuvant (MAA) were included in the rhesus study for comparison. The Nanopatch™ prototype contains a high-density array comprised of 10,000 microprojections/cm2, each 250 µm long. It was hypothesized the higher density array with shallower ID delivery may be superior to the Mantoux technique. To test this hypothesis, HPV VLPs without adjuvant were coated on the Nanopatch™, stability of the Nanopatch™ with unadjuvanted HPV VLPs were evaluated under accelerated conditions, skin delivery was verified using radiolabelled VLPs or FluoSpheres®, and the immune response and skin site reaction with the Nanopatch™ was evaluated in rhesus macaques. The immune response induced by Nanopatch™ administration, measured as HPV-specific binding antibodies, was similar to that induced using the Mantoux technique. It was also observed that a lower dose of unadjuvanted HPV VLPs delivered with the first-generation Nanopatch™ and applicator or Mantoux technique resulted in an immune response that was significantly lower compared to a higher-dose of alum adjuvanted HPV VLPs delivered IM in rhesus macaques. The study also indicated unadjuvanted HPV VLPs could be delivered with the first-generation Nanopatch™ and applicator to the skin in 15 s with a transfer efficiency of approximately 20%. This study is the first demonstration of patch administration in non-human primates with a vaccine composed of HPV VLPs.