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In response to immune pressure, influenza viruses evolve, producing drifted variants capable of escaping immune recognition. One strategy for inducing a broad-spectrum immune response capable of recognizing multiple antigenically diverse strains is to target conserved proteins or protein domains. To that end, we assessed the efficacy and immunogenicity of mRNA vaccines encoding either the conserved stem domain of a group 1 hemagglutinin (HA), a group 2 nucleoprotein (NP), or a combination of the two antigens in mice, as well as evaluated immunogenicity in naïve and influenza seropositive nonhuman primates (NHPs). HA stem-immunized animals developed a robust anti-stem antibody binding titer, and serum antibodies recognized antigenically distinct group 1 HA proteins. These antibodies showed little to no neutralizing activity in vitro but were active in an assay measuring induction of antibody-dependent cellular cytotoxicity. HA-directed cell-mediated immunity was weak following HA stem mRNA vaccination; however, robust CD4 and CD8 T cell responses were detected in both mice and NHPs after immunization with mRNA vaccines encoding NP. Both HA stem and NP mRNA vaccines partially protected mice from morbidity following lethal influenza virus challenge, and superior efficacy against two different H1N1 strains was observed when the antigens were combined. In vivo T cell depletion suggested that anti-NP cell-mediated immunity contributed to protection in the mouse model. Taken together, these data show that mRNA vaccines encoding conserved influenza antigens, like HA stem and NP in combination, induce broadly reactive humoral responses as well as cell-mediated immunity in mice and NHPs, providing protection against homologous and heterologous influenza infection in mice.

We evaluated novel Chlamydial vaccines, consisting of major outer membrane protein (MOMP) alone or in combination with polymorphic membrane proteins D (PmpD) and G (PmpG) using a C57BL/6 mouse model. Native MOMP (nMOMP) isolated from C. muridarum elementary bodies (EBs) and recombinant PmpD and PmpG proteins were adjuvanted with Monophosphoryl lipid A (MPLA), with either lipid nanoparticles (LNPs) or the cationic lipid dimethyldioctadecylammonium bromide (DDA). Antibody titers to C. muridarum nMOMP, and EBs were evaluated by ELISA, and T-cell responses were analyzed by intracellular cytokine staining (ICS). Protection from challenge was determined by qPCR. Vaccine immunized mice showed significantly higher antibody titers to nMOMP (P C. muridarum EBs (P C. muridarum EBs and PmpG. ICS analysis showed more robust CD4 + T-cell responses (IFN-γ/IL-2/TNF-a) in the DDA and LNP groups compared to the adjuvant alone group. The DDA + MPLA gave robust Th17 responses in comparison to MPLA and LNP group. Mice immunized with Chlamydia antigens also showed protection from C. muridarum challenge, by reduction in bacterial shedding for all groups (P < 0.003) compared to shedding from the adjuvant control. Both vaccine formulations generated robust immunological responses, and both were protective by reducing bacterial shedding after challenge. This data indicates equal protection can be achieved without the induction of Th17 responses.

Respiratory syncytial virus (RSV) infection is a major cause of severe respiratory illness in both young infants and the elderly. While antibodies represent key correlates of protection, the antibody mechanisms remain poorly understood. Emerging data point to additional humoral Fc-mediated mechanisms of action beyond neutralization. Therefore, to map the humoral correlates of immunity against RSV, antibody responses were profiled in a highly controlled non-human primate challenge model. Six different vaccine platforms were tested in African Green Monkeys, which post-challenge, yielded distinct antibody profiles and viral loads in both upper and lower respiratory tracts. Machine learning was then used to determine antibody features associated with protection. Upper respiratory control involved virus specific IgA levels, neutralization, and complement whereas lower respiratory control involved Fc-mediated mechanisms. These data highlight a collaborative Fab and Fc protective signature, induced selectively by distinct vaccine platforms, and provides mechanistic insights for the rational development of vaccines.

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.

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.

Respiratory syncytial virus (RSV) is the most common viral cause of bronchiolitis and pneumonia in children twelve months of age or younger and a significant cause of lower respiratory disease in older adults. As various clinical and preclinical candidates advance, cotton rats (Sigmodon hispidus) and non-human primates (NHP) continue to play a valuable role in RSV vaccine development, since both animals are semi-permissive to human RSV (HRSV). However, appropriate utilization of the models is critical to avoid mis-interpretation of the preclinical findings. Using a multimodality imaging approach; a fluorescence based optical imaging technique for the cotton rat and a nuclear medicine based positron emission tomography (PET) imaging technique for monkeys, we demonstrate that many common practices for intranasal immunization in both species result in inoculum delivery to the lower respiratory tract, which can result in poor translation of outcomes from the preclinical to the clinical setting. Using these technologies we define a method to limit the distribution of intranasally administered vaccines solely to the upper airway of each species, which includes volume restrictions in combination with injectable anesthesia. We show using our newly defined methods for strict intranasal immunization that these methods impact the immune responses and efficacy observed when compared to vaccination methods resulting in distribution to both the upper and lower respiratory tracts. These data emphasize the importance of well-characterized immunization methods in the preclinical assessment of intranasally delivered vaccine candidates.

Respiratory Syncytial Virus (RSV) infection is the leading cause of lower respiratory tract infection in both young children and older adults. Currently, there is no licensed vaccine available, and therapeutic options are limited. The infectious RSV particle is decorated with a type I viral fusion (F) glycoprotein that structurally rearranges from a metastable prefusion form to a highly stable postfusion form. In people naturally infected with RSV, the neutralizing antibodies primarily recognize the prefusion conformation. Therefore, engineered RSV F protein stabilized in its prefusion conformation has been an attractive strategy for developing RSV F vaccine antigens. Long-term stability at 4 °C or higher is a desirable attribute for a RSV F subunit vaccine antigen. We have previously shown that a prefusion stabilized RSV F construct, DS-Cav1, undergoes conformational changes and forms intermediate structures upon long-term storage at 4 °C. Structure-based design was performed to improve the stability of the RSV F subunit vaccine. We identified additional mutations that further stabilize RSV F protein in its prefusion conformation by using binding to a previously described antigenic site I antibody 4D7 as the screening tool. In addition, we designed and identified variants with increased expression levels, which is another desirable attribute for a subunit vaccine. Our data suggested that an RSV F variant F111 is properly folded, and has improved heat stability as well as stability upon long-term storage at 4 °C. A mouse immunogenicity study demonstrated that no compromise in immunogenicity (both binding and neutralizing antibody levels) was observed with the introduction of these additional mutations.

Respiratory syncytial virus (RSV) is a leading cause of serious lower respiratory tract disease in young children and older adults throughout the world. Prevention of severe RSV disease through active immunization is optimal but no RSV vaccine has been licensed so far. Immune mechanisms of protection against RSV infection in humans have not been fully established, thus a comprehensive characterization of virus-specific immune responses in a relevant animal model will be beneficial in defining correlates of protection. In this study, we infected juvenile naive AGMs with RSV A2 strain and longitudinally assessed virus-specific humoral and cellular immune responses in both peripheral blood and the respiratory tract. RSV viral loads at nasopharyngeal surfaces and in the lung peaked at around day 5 following infection, and then largely resolved by day 10. Low levels of neutralizing antibody titers were detected in serum, with similar kinetics as RSV fusion (F) protein-binding IgG antibodies. RSV infection induced CD8+, but very little CD4+, T lymphocyte responses in peripheral blood. Virus-specific CD8+ T cell frequencies were ~10 fold higher in bronchoaveolar lavage (BAL) compared to peripheral blood and exhibited effector memory (CD95+CD28-) / tissue resident memory (CD69+CD103+) T (TRM) cell phenotypes. The kinetics of virus-specific CD8+ T cells emerging in peripheral blood and BAL correlated with declining viral titers, suggesting that virus-specific cellular responses contribute to the clearance of RSV infection. RSV-experienced AGMs were protected from subsequent exposure to RSV infection. Additional studies are underway to understand protective correlates in these seropositive monkeys.

Background In response to immune pressure, influenza virus evolves, producing drifted variants capable of escaping immune recognition. One strategy for inducing a broad-spectrum immune response that can recognize multiple antigenically diverse strains is to target conserved proteins or protein domains. To that end, we assessed the immunogenicity of mRNA vaccines encoding the stem domain of hemagglutinin (HA) or nucleoprotein (NP) in nonhuman primates (NHPs). Methods Rhesus macaques were immunized three times intramuscularly, at 28 day intervals, with lipid nanoparticle-encapsulated mRNA encoding either HA stem (Yassine et al, 2015) or NP. Serum and PBMCs were collected up to 14 or 24 weeks, respectively, after the last vaccination. The magnitude and durability of humoral and cell-mediated immunity were evaluated. ELISA, competition ELISA, an in vitro antibody-dependent cell-mediated cytotoxicity (ADCC) reporter bioassay, and microneutralization assays were used to characterize serum immune responses. Intracellular cytokine staining (IFN-gamma and IL-2) was used to assess antigen-specific T-cell responses. Results HA stem-immunized NHPs developed a robust anti-stem binding titer after a single vaccine dose, and after two doses, serum antibodies recognized several antigenically distinct Group 1 HA proteins. This broad antibody response persisted for at least 14 weeks post-dose 3 (PD3). Serum antibodies showed ADCC activity and competed with a well-characterized broadly neutralizing antibody, CR9114, for binding to HA stem; however, the polyclonal serum had only minimal activity against a panel of H1N1 viruses in a microneutralization assay. HA-specific CD4+ T-cell responses were detectable PD3. A robust antibody binding response was also detected in NP-vaccinated NHPs, and titers remained high for at least 14 weeks PD3. Additionally, these animals developed robust NP-specific T-cell responses that persisted for at least 24 weeks PD3. On average, 0.5% of CD4+ and 4% of CD8+ T cells produced IFN-gamma in response to NP peptide stimulation at the peak of the response, 2 weeks after the last vaccine dose was administered. Conclusion Lipid nanoparticle-encapsulated mRNA vaccines encoding conserved influenza antigens induce a robust and durable immune response in NHPs. Disclosures All authors: No reported disclosures.

Next generation NNRTIs are sought which possess both broad spectrum antiviral activity against key mutant strains and a high genetic barrier to the selection of new mutant viral strains. Pyridones were evaluated as an acyclic conformational constraint to replace the aryl ether core of MK-4965 (1) and the more rigid indazole constraint of MK-6186 (2). The resulting pyridone compounds are potent inhibitors of HIV RT and have antiviral activity in cell culture that is superior to other next generation NNRTI's.

A series of HIV-1 protease inhibitors containing an epsilon substituted lysinol backbone was synthesized. Two novel synthetic routes using N-boc-L-glutamic acid alpha-benzyl ester and 2,6-diaminopimelic acid were developed. Incorporation of this epsilon substituent enabled access to the S2 pocket of the enzyme, affording high potency inhibitors. Modeling studies and synthetic efforts suggest the potency increase is due to both conformational bias and van der Waals interactions with the S2 pocket.

Biaryl ethers were recently reported as potent NNRTIs. Herein, we disclose a detailed effort to modify the previously reported compound 1. We have designed and synthesized a series of novel pyrazole derivatives as a surrogate for pyrazolopyridine motif that were potent inhibitors of HIV-1 RT with nanomolar intrinsic activity on the WT and key mutant enzymes and potent antiviral activity in infected cells.

Biaryl ethers were recently reported as potent NNRTIs. Herein we disclose a detailed SAR study that led to the biaryl ether 6. This compound possessed excellent potency against WT RT and key clinically observed RT mutants and had an excellent pharmacokinetic profile in rats, dogs, and rhesus macaques. The compound also exhibited a clean safety profile in preclinical safety studies.

Non-nucleoside reverse transcriptase inhibitors (NNRTIs) are key elements of multidrug regimens, called HAART (Highly Active Antiretroviral Therapy), that are used to treat HIV-1 infections. Elucidation of the structure-activity relationships of the thiocarbamate moiety of the previous published lead compound 2 provided a series of novel tetrahydroquinoline derivatives as potent inhibitors of HIV-1 RT with nanomolar intrinsic activity on the WT and key mutant enzymes and potent antiviral activity in infected cells. The SAR optimization, mutation profiles, preparation of compounds, and pharmacokinetic profile of compounds are described.