Generation of SARS-CoV-2 reporter replicon for high-throughput antiviral screening and testing.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) research and antiviral discovery are hampered by the lack of a cell-based virus replication system that can be readily adopted without biosafety level 3 (BSL-3) restrictions. Here, the construction of a noninfectious SARS-CoV-2 reporter replicon and its application in deciphering viral replication mechanisms and evaluating SARS-CoV-2 inhibitors are presented. The replicon genome is replication competent but does not produce progeny virions. Its replication can be inhibited by RdRp mutations or by known SARS-CoV-2 antiviral compounds. Using this system, a high-throughput antiviral assay has also been developed. Significant differences in potencies of several SARS-CoV-2 inhibitors in different cell lines were observed, which highlight the challenges of discovering antivirals capable of inhibiting viral replication in vivo and the importance of testing compounds in multiple cell culture models. The generation of a SARS-CoV-2 replicon provides a powerful platform to expand the global research effort to combat COVID-19.

Potent Bispecific Neutralizing Antibody Targeting Glycoprotein B and the gH/gL/pUL128/130/131 Complex of Human Cytomegalovirus.

Human cytomegalovirus (HCMV) is a ubiquitous pathogen that can cause developmental disorders following congenital infection and life-threatening complications among transplant patients. Potent neutralizing monoclonal antibodies (MAbs) are promising drug candidates against HCMV infection. HCMV can infect a broad range of cell types. Therefore, single neutralizing antibodies targeting one HCMV glycoprotein often lack either potency or broad cell-type coverage. We previously characterized two human-derived HCMV neutralizing MAbs. One was the broadly neutralizing MAb 3-25, which targets the antigenic domain 2 of glycoprotein B (gB). The other was the highly potent MAb 2-18, which specifically recognizes the gH/gL/pUL128/130/131 complex (pentamer). To combine the strengths of gB- and pentamer-targeting MAbs, we developed an IgG-single-chain variable fragment (scFv) bispecific antibody by fusing the 2-18 scFv to the heavy-chain C terminus of MAb 3-25. The resulting bispecific antibody showed high-affinity binding to both gB and pentamer. Functionally, the bispecific antibody demonstrated a combined neutralization breadth and potency of the parental MAbs in multiple cell lines and inhibited postinfection viral spreading. Furthermore, the bispecific antibody was easily produced in CHO cells at a yield above 1 g/liter and showed a single-dose pharmacokinetic profile comparable to that of parental MAb 3-25 in rhesus macaques. Importantly, the bispecific antibody retained broadly and potent neutralizing activity after 21 days in circulation. Taken together, our research provides a proof-of-concept study for developing bispecific neutralizing antibody therapies against HCMV infection.

Identification of adipocyte plasma membrane-associated protein as a novel modulator of human cytomegalovirus infection.

Human cytomegalovirus (HCMV) is a ubiquitous pathogen that can cause disability in newborns and serious clinical diseases in immunocompromised patients. HCMV has a large genome with enormous coding potential; its viral particles are equipped with complicated glycoprotein complexes and can infect a wide range of human cells. Although multiple host cellular receptors interacting with viral glycoproteins have been reported, the mechanism of HCMV infection remains a mystery. Here we report identification of adipocyte plasma membrane-associated protein (APMAP) as a novel modulator active in the early stage of HCMV infection. APMAP is necessary for HCMV infection in both epithelial cells and fibroblasts; knockdown of APMAP expression significantly reduced HCMV infection of these cells. Interestingly, ectopic expression of human APMAP in cells refractory to HCMV infection, such as canine MDCK and murine NIH/3T3 cells, promoted HCMV infection. Furthermore, reduction in viral immediate early (IE) gene transcription at 6 h post infection and delayed nucleus translocation of tegument delivered pp65 at 4 h post infection were detected in APMAP-deficient cells but not in the wildtype cells. These results suggest that APMAP plays a role in the early stage of HCMV infection. Results from biochemical studies of APMAP and HCMV proteins suggest that APMAP could participate in HCMV infection through interaction with gH/gL containing glycoprotein complexes at low pH and mediate nucleus translocation of tegument pp65. Taken together, our results suggest that APMAP functions as a modulator promoting HCMV infection in multiple cell types and is an important player in the complex HCMV infection mechanism.

A Replication-Defective Human Cytomegalovirus Vaccine Elicits Humoral Immune Responses Analogous to Those with Natural Infection.

Human cytomegalovirus (HCMV) can cause congenital infections, which are a leading cause of childhood disabilities. Since the rate of maternal-fetal transmission is much lower in naturally infected (HCMV-seropositive) women, we hypothesize that a vaccine candidate capable of eliciting immune responses analogous to those of HCMV-seropositive subjects may confer protection against congenital HCMV. We have previously described a replication-defective virus vaccine based on strain AD169 (D. Wang, D. C. Freed, X. He, F. Li, et al., Sci Transl Med 8:362ra145, 2016, https://doi.org/10.1126/scitranslmed.aaf9387). The vaccine, named V160, has been shown to be safe and immunogenic in HCMV-seronegative human subjects, eliciting both humoral and cellular immune responses (S. P. Adler, S. E. Starr, S. A. Plotkin, S. H. Hempfling, et al., J Infect Dis 220:411-419, 2019, https://doi.org/10.1093/infdis/171.1.26). Here, we further showed that sera from V160-immunized HCMV-seronegative subjects have attributes similar in quality to those from seropositive subjects, including high-avidity antibodies to viral antigens, coverage against a panel of genetically distinct clinical isolates, and protection against viral infection in diverse types of human cells in culture. More importantly, vaccination appeared efficient in priming the human immune system, inducing memory B cells in six V160 recipients at frequencies comparable to those of three HCMV-seropositive subjects. Our results demonstrate the ability of V160 to induce robust and durable humoral memory responses to HCMV, justifying further clinical evaluation of the vaccine against congenital HCMV.IMPORTANCEIn utero HCMV infection can lead to miscarriage or childhood disabilities, and an effective vaccine is urgently needed. Since children born to women who are seropositive prior to pregnancy are less likely to be affected by congenital HCMV infection, it has been hypothesized that a vaccine capable of inducing an immune response resembling the responses in HCMV-seropositive women may be effective. We previously described a replication-defective virus vaccine that has been demonstrated safe and immunogenic in HCMV-seronegative subjects. Here, we conducted additional analyses to show that the vaccine can induce antibodies with functional attributes similar to those from HCMV-seropositive subjects. Importantly, vaccination can induce long-lived memory B cells at frequencies comparable to those seen in HCMV-seropositive subjects. We conclude that this vaccine is a promising candidate that warrants further clinical evaluation for prevention of congenital HCMV.

Genetic Stability of Parainfluenza Virus 5-Vectored Human Respiratory Syncytial Virus Vaccine Candidates after In Vitro and In Vivo Passage.

Human respiratory syncytial virus (RSV) is the leading etiologic agent of lower respiratory tract infections in children, but no licensed vaccine exists. Previously, we developed two parainfluenza virus 5 (PIV5)-based RSV vaccine candidates that protect mice against RSV challenge. PIV5 was engineered to express either the RSV fusion protein (F) or the RSV major attachment glycoprotein (G) between the hemagglutinin-neuraminidase (HN) and RNA-dependent RNA polymerase (L) genes of the PIV5 genome [PIV5-RSV-F (HN-L) and PIV5-RSV-G (HN-L), respectively]. To investigate the stability of the vaccine candidates in vitro, they were passaged in Vero cells at high and low multiplicities of infection (MOIs) for 11 generations and the genome sequences, growth kinetics, and protein expression of the resulting viruses were compared with those of the parent viruses. Sporadic mutations were detected in the consensus sequences of the viruses after high-MOI passages, and mutation rates increased under low-MOI-passage conditions. None of the mutations abolished antigen expression. Increased numbers of mutations correlated with increased growth rates in vitro, indicating that the viruses evolved through the course of serial passages. We also examined the in vivo stability of the vaccine candidates after a single passage in African green monkeys. No mutations were detected in the consensus sequences of viruses collected from the bronchoalveolar lavage (BAL) fluid of the animals. In vivo, mutations in RSV G and PIV5 L were found in individual isolates of PIV5-RSV-G (HN-L), but plaque isolates of PIV5-RSV-F (HN-L) had no mutations. To improve upon the PIV5-RSV-F (HN-L) candidate, additional vaccine candidates were generated in which the gene for RSV F was inserted into earlier positions in the PIV5 genome. These insertions did not negatively impact the sequence stability of the vaccine candidates. The results suggest that the RSV F and G gene insertions are stable in the PIV5 genome. However, the function of the foreign gene insertion may need to be considered when designing PIV5-based vaccines.IMPORTANCE The genetic stability of live viral vaccines is important for safety and efficacy. PIV5 is a promising live viral vector and has been used to develop vaccines. In this work, we examined the genetic stability of a PIV5-based RSV vaccine in vitro and in vivo We found that insertions of foreign genes, such as the RSV F and G genes, were stably maintained in the PIV5 genome and there was no mutation that abolished the expression of RSV F or G. Interestingly, the function of the inserted gene may have an impact on PIV5 genome stability.

A Single-Dose Recombinant Parainfluenza Virus 5-Vectored Vaccine Expressing Respiratory Syncytial Virus (RSV) F or G Protein Protected Cotton Rats and African Green Monkeys from RSV Challenge.

Human respiratory syncytial virus (RSV) is a common cause of severe respiratory disease among infants, immunocompromised individuals, and the elderly. No licensed vaccine is currently available. In this study, we evaluated two parainfluenza virus 5 (PIV5)-vectored vaccines expressing RSV F (PIV5/F) or G (PIV5/G) protein in the cotton rat and African green monkey models for their replication, immunogenicity, and efficacy of protection against RSV challenge. Following a single intranasal inoculation, both animal species shed the vaccine viruses for a limited time but without noticeable clinical symptoms. In cotton rats, the vaccines elicited RSV F- or G-specific serum antibodies and conferred complete lung protection against RSV challenge at doses as low as 103 PFU. Neither vaccine produced the enhanced lung pathology observed in animals immunized with formalin-inactivated RSV. In African green monkeys, vaccine-induced serum and mucosal antibody responses were readily detected, as well. PIV5/F provided nearly complete protection against RSV infection in the upper and lower respiratory tract at a dose of 106 PFU of vaccine. At the same dose levels, PIV5/G was less efficacious. Both PIV5/F and PIV5/G were also able to boost neutralization titers in RSV-preexposed African green monkeys. Overall, our data indicated that PIV5/F is a promising RSV vaccine candidate.IMPORTANCE A safe and efficacious respiratory syncytial virus (RSV) vaccine remains elusive. We tested the recombinant parainfluenza virus 5 (PIV5) vectors expressing RSV glycoproteins for their immunogenicity and protective efficacy in cotton rats and African green monkeys, which are among the best available animal models to study RSV infection. In both species, a single dose of intranasal immunization with PIV5-vectored vaccines was able to produce systemic and local immunity and to protect animals from RSV challenge. The vaccines could also boost RSV neutralization antibody titers in African green monkeys that had been infected previously. Our data suggest that PIV5-vectored vaccines could potentially protect both the pediatric and elderly populations and support continued development of the vector platform.

Recombinant expression of Chlamydia trachomatis major outer membrane protein in E. Coli outer membrane as a substrate for vaccine research.

BACKGROUND: Chlamydia trachomatis is a human pathogen which causes a number of pathologies, including genital tract infections in women that can result in tubal infertility. Prevention of infection and disease control might be achieved through vaccination; however, a safe, efficacious and cost-effective vaccine against C. trachomatis infection remains an unmet medical need. C. trachomatis major outer membrane protein (MOMP), a ß-barrel integral outer membrane protein, is the most abundant antigen in the outer membrane of the bacterium and has been evaluated as a subunit vaccine candidate. Recombinant MOMP (rMOMP) expressed in E. coli cytoplasm forms inclusion bodies and rMOMP extracted from inclusion bodies results in a reduced level of protection compared to the native MOMP in a mouse challenge model. RESULTS: We sought to target the recombinant expression of MOMP to the E. coli outer membrane (OM). Successful surface expression was achieved with codon harmonization, utilization of low copy number vectors and promoters with moderate strength, suitable leader sequences and optimization of cell culture conditions. rMOMP was extracted from E. coli outer membrane, purified, and characterized biophysically. The OM expressed and purified rMOMP is immunogenic in mice and elicits antibodies that react to the native antigen, Chlamydia elementary body (EB). CONCLUSIONS: C. trachomatis MOMP was functionally expressed on the surface of E. coli outer membrane. The OM expressed and purified rMOMP elicits antibodies that react to the native antigen, Chlamydia EB, in a mouse immunogenicity model. Surface expression of MOMP could provide useful reagents for vaccine research, and the methodology could serve as a platform to produce other outer membrane proteins recombinantly.

Functional analysis of human cytomegalovirus UL/b' region using SCID-hu mouse model.

Human cytomegalovirus (HCMV) attenuated strains, Towne, and AD169, differ from prototypic pathogenic strains, such as Toledo, in that they are missing a ∼15-kb segment in the UL/b' region. In contrast to the attenuated strains, Toledo can replicate in human tissue implants in SCID (SCID-hu) mice. Thus, this model provides a unique in vivo system to study the mechanism of viral pathogenesis. Twenty-two ORFs have been annotated in the UL/b' region, including tissue-tropic genes encoded in a pentameric gH/gl complex. To differentiate the role of the pentameric gH/gl complex versus the functions of other ORFs in the 15-kb region in supporting viral growth in vivo, a series of recombinant viral strains were constructed and their ability to replicate in SCID-hu mice was tested. The mutations in the Towne and AD169 strains were repaired to restore their pentameric gH/gl complex and it was found that these changes did not rescue their inability to replicate in the SCID-hu mice. Subsequently four deletion viruses (D1, D2, D3, and D4) in the 15-kb region from the Toledo strain were created. It was demonstrated that D2 and D3 were able to grow in SCID-hu mice, while D1 and D4 were not viable. Interestingly, co-infection of the implant with the D1 and D4 viruses could compensate their respective growth defect in vivo. The results demonstrated that rescuing viral epithelial tropism is not sufficient to revert the attenuation phenotype of AD169 or Towne, and pathogenic genes are located in the segments missing in D1 and D4 viruses. J. Med. Virol. 88:1417-1426, 2016. © 2016 Wiley Periodicals, Inc.

Pentameric complex of viral glycoprotein H is the primary target for potent neutralization by a human cytomegalovirus vaccine.

Human cytomegalovirus (HCMV) can cause serious morbidity/mortality in transplant patients, and congenital HCMV infection can lead to birth defects. Developing an effective HCMV vaccine is a high medical priority. One of the challenges to the efforts has been our limited understanding of the viral antigens important for protective antibodies. Receptor-mediated viral entry to endothelial/epithelial cells requires a glycoprotein H (gH) complex comprising five viral proteins (gH, gL, UL128, UL130, and UL131). This gH complex is notably missing from HCMV laboratory strains as well as HCMV vaccines previously evaluated in the clinic. To support a unique vaccine concept based on the pentameric gH complex, we established a panel of 45 monoclonal antibodies (mAbs) from a rabbit immunized with an experimental vaccine virus in which the expression of the pentameric gH complex was restored. Over one-half (25 of 45) of the mAbs have neutralizing activity. Interestingly, affinity for an antibody to bind virions was not correlated with its ability to neutralize the virus. Genetic analysis of the 45 mAbs based on their heavy- and light-chain sequences identified at least 26 B-cell linage groups characterized by distinct binding or neutralizing properties. Moreover, neutralizing antibodies possessed longer complementarity-determining region 3 for both heavy and light chains than those with no neutralizing activity. Importantly, potent neutralizing mAbs reacted to the pentameric gH complex but not to gB. Thus, the pentameric gH complex is the primary target for antiviral antibodies by vaccination.

A Novel Rotavirus Reverse Genetics Platform Supports Flexible Insertion of Exogenous Genes and Enables Rapid Development of a High-Throughput Neutralization Assay.

Despite the success of rotavirus vaccines, rotaviruses remain one of the leading causes of diarrheal diseases, resulting in significant childhood morbidity and mortality, especially in low- and middle-income countries. The reverse genetics system enables the manipulation of the rotavirus genome and opens the possibility of using rotavirus as an expression vector for heterologous proteins, such as vaccine antigens and therapeutic payloads. Here, we demonstrate that three positions in rotavirus genome-the C terminus of NSP1, NSP3 and NSP5-can tolerate the insertion of reporter genes. By using rotavirus expressing GFP, we develop a high-throughput neutralization assay and reveal the pre-existing immunity against rotavirus in humans and other animal species. Our work shows the plasticity of the rotavirus genome and establishes a high-throughput assay for interrogating humoral immune responses, benefiting the design of next-generation rotavirus vaccines and the development of rotavirus-based expression platforms.

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.

Characterization of humoral and cell-mediated immunity induced by mRNA vaccines expressing influenza hemagglutinin stem and nucleoprotein in mice and nonhuman primates.

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.

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.

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.

Host cell factors in HIV replication: meta-analysis of genome-wide studies.

We have analyzed host cell genes linked to HIV replication that were identified in nine genome-wide studies, including three independent siRNA screens. Overlaps among the siRNA screens were very modest (<7% for any pairwise combination), and similarly, only modest overlaps were seen in pairwise comparisons with other types of genome-wide studies. Combining all genes from the genome-wide studies together with genes reported in the literature to affect HIV yields 2,410 protein-coding genes, or fully 9.5% of all human genes (though of course some of these are false positive calls). Here we report an "encyclopedia" of all overlaps between studies (available at http://www.hostpathogen.org), which yielded a more extensively corroborated set of host factors assisting HIV replication. We used these genes to calculate refined networks that specify cellular subsystems recruited by HIV to assist in replication, and present additional analysis specifying host cell genes that are attractive as potential therapeutic targets.

Transplacental Antibody Transfer of Respiratory Syncytial Virus Specific IgG in Non-Human Primate Mother-Infant Pairs.

One approach to protect new-borns against respiratory syncytial virus (RSV) is to vaccinate pregnant women in the last trimester of pregnancy. The boosting of circulating antibodies which can be transferred to the foetus would offer immune protection against the virus and ultimately the disease. Since non-human primates (NHPs) have similar reproductive anatomy, physiology, and antibody architecture and kinetics to humans, we utilized this preclinical species to evaluate maternal immunization (MI) using an RSV F subunit vaccine. Three species of NHPs known for their ability to be infected with human RSV in experimental challenge studies were tested for RSV-specific antibodies. African green monkeys had the highest overall antibody levels of the old-world monkeys evaluated and they gave birth to offspring with anti-RSV titers that were proportional to their mother. These higher overall antibody levels are associated with greater durability found in their offspring. Immunization of RSV seropositive AGMs during late pregnancy boosts RSV titers, which consequentially results in significantly higher titers in the vaccinated new-borns compared to the new-borns of unvaccinated mothers. These findings, accomplished in small treatment group sizes, demonstrate a model that provides an efficient, resource sparing and translatable preclinical in vivo system for evaluating vaccine candidates for maternal immunization.

Novel adjuvants enhance immune responses elicited by a replication-defective human cytomegalovirus vaccine in nonhuman primates.

Adjuvants have long been explored to enhance vaccine efficacy. Current adjuvants approved for human vaccines are mostly studied for their ability to improve antibody responses. There remains a need for development of novel adjuvants, especially those able to enhance cell-mediated immunity (CMI). In this preclinical study we assessed the effect of two novel adjuvants, a delta inulin microparticle Advax formulated with or without a toll-like receptor 9 (TLR9) agonist CpG oligonucleotide, and a Merck & Co., Inc., Kenilworth, NJ, USA proprietary lipid nanoparticle (LNP), on immune responses elicited by V160, an experimental replication-defective human cytomegalovirus vaccine. Adult rhesus macaques were immunized with a low dose of V160 (10 units) either alone or in combination with the adjuvants as compared to those immunized with a high dose of V160 alone (100 units). While neither adjuvant conferred a significant benefit to vaccine-elicited humoral immune responses at the dose tested, both enhanced cellular immune responses to V160, where Advax promoted both CD4+ and CD8+ T cells and LNP predominantly impacted the CD4+ T cell response. Transcriptome analyses of peripheral blood samples demonstrated different modes of action for these adjuvants. One day post vaccination, LNP induced upregulation of a large number of genes involved in the innate immune response similar to those triggered by viral infection. In contrast, Advax did not activate any known inflammatory pathways and did not significantly impact gene expression pattern until day 7 post administration, suggesting a unique, non-inflammatory mechanism. These data warrant further exploration of Advax and LNP as adjuvants in clinical trials for vaccines desiring to elicit both humoral and T cell responses.

A phase 1, randomized, placebo-controlled study to evaluate the safety and immunogenicity of an mRNA-based RSV prefusion F protein vaccine in healthy younger and older adults.

Respiratory Syncytial Virus (RSV) causes lower respiratory tract infections that can be severe and sometimes fatal. The risk for severe RSV infection is highest in infants and older adults. A safe and effective RSV vaccine for older adults represents a serious unmet medical need due to higher morbidity and mortality in this age group. In this randomized, partially double-blind, placebo-controlled, phase 1 dose-escalation study, we evaluated the safety, tolerability and immunogenicity of an investigational messenger ribonucleic acid (mRNA) vaccine encoding the RSV fusion protein (F) stabilized in the prefusion conformation. The study was conducted in healthy younger adults (ages ≥18 and ≤49 years) and healthy older adults (ages ≥60 and ≤79 years). Participants received mRNA-1777 (V171) or placebo as a single intramuscular dose. For each dose level, three sentinel participants were administered open-label mRNA-1777 (V171). Seventy-two younger adults were randomized and administered 25, 100, or 200 µg mRNA-1777 (V171) or placebo, and 107 older adults were randomized and administered 25, 100, 200 or 300 µg mRNA-1777 (V171) or placebo. Primary objectives were safety and tolerability and secondary objectives included humoral and cell-mediated immunogenicity. All dose levels of mRNA-1777 (V171) were generally well tolerated and no serious adverse events related to the vaccine were reported. Immunization with mRNA-1777 (V171) elicited a humoral immune response as measured by increases in RSV neutralizing antibody titers, serum antibody titers to RSV prefusion F protein, D25 competing antibody titers to RSV prefusion F protein, and cell-mediated immune responses to RSV-F peptides.

Forward and reverse translational approaches to predict efficacy of neutralizing respiratory syncytial virus (RSV) antibody prophylaxis.

BACKGROUND: Neutralizing mAbs can prevent communicable viral diseases. MK-1654 is a respiratory syncytial virus (RSV) F glycoprotein neutralizing monoclonal antibody (mAb) under development to prevent RSV infection in infants. Development and validation of methods to predict efficacious doses of neutralizing antibodies across patient populations exposed to a time-varying force of infection (i.e., seasonal variation) are necessary. METHODS: Five decades of clinical trial literature were leveraged to build a model-based meta-analysis (MBMA) describing the relationship between RSV serum neutralizing activity (SNA) and clinical endpoints. The MBMA was validated by backward translation to animal challenge experiments and forward translation to predict results of a recent RSV mAb trial. MBMA predictions were evaluated against a human trial of 70 participants who received either placebo or one of four dose-levels of MK-1654 and were challenged with RSV [NCT04086472]. The MBMA was used to perform clinical trial simulations and predict efficacy of MK-1654 in the infant target population. FINDINGS: The MBMA established a quantitative relationship between RSV SNA and clinical endpoints. This relationship was quantitatively consistent with animal model challenge experiments and results of a recently published clinical trial. Additionally, SNA elicited by increasing doses of MK-1654 in humans reduced RSV symptomatic infection rates with a quantitative relationship that approximated the MBMA. The MBMA indicated a high probability that a single dose of ≥ 75 mg of MK-1654 will result in prophylactic efficacy (> 75% for 5 months) in infants. INTERPRETATION: An MBMA approach can predict efficacy of neutralizing antibodies against RSV and potentially other respiratory pathogens.

A limited group of class I histone deacetylases acts to repress human immunodeficiency virus type 1 expression.

Silencing of the integrated human immunodeficiency virus type 1 (HIV-1) genome in resting CD4(+) T cells is a significant contributor to the persistence of infection, allowing the virus to evade both immune detection and pharmaceutical attack. Nonselective histone deacetylase (HDAC) inhibitors are capable of inducing expression of quiescent HIV-1 in latently infected cells. However, potent global HDAC inhibition can induce host toxicity. To determine the specific HDACs that regulate HIV-1 transcription, we evaluated HDAC1 to HDAC11 RNA expression and protein expression and compartmentalization in the resting CD4(+) T cells of HIV-1-positive, aviremic patients. HDAC1, -3, and -7 had the highest mRNA expression levels in these cells. Although all HDACs were detected in resting CD4(+) T cells by Western blot analysis, HDAC5, -8, and -11 were primarily sequestered in the cytoplasm. Using chromatin immunoprecipitation assays, we detected HDAC1, -2, and -3 at the HIV-1 promoter in Jurkat J89GFP cells. Targeted inhibition of HDACs by small interfering RNA demonstrated that HDAC2 and HDAC3 contribute to repression of HIV-1 long terminal repeat expression in the HeLa P4/R5 cell line model of latency. Together, these results suggest that HDAC inhibitors specific for a limited number of class I HDACs may offer a targeted approach to the disruption of persistent HIV-1 infection.