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Despite more than two decades of research and development on nucleic acid vaccines, there is still no commercial product for human use. Taking advantage of the recent innovations in systemic delivery of short interfering RNA (siRNA) using lipid nanoparticles (LNPs), we developed a self-amplifying RNA vaccine. Here we show that nonviral delivery of a 9-kb self-amplifying RNA encapsulated within an LNP substantially increased immunogenicity compared with delivery of unformulated RNA. This unique vaccine technology was found to elicit broad, potent, and protective immune responses, that were comparable to a viral delivery technology, but without the inherent limitations of viral vectors. Given the many positive attributes of nucleic acid vaccines, our results suggest that a comprehensive evaluation of nonviral technologies to deliver self-amplifying RNA vaccines is warranted.vaccine platform | SAM vaccine | respiratory syncytial virus | HIV

Nucleic acid-based vaccines such as viral vectors, plasmid DNA, and mRNA are being developed as a means to address a number of unmet medical needs that current vaccine technologies have been unable to address. Here, we describe a cationic nanoemulsion (CNE) delivery system developed to deliver a self-amplifying mRNA vaccine. This nonviral delivery system is based on Novartis's proprietary adjuvant MF59, which has an established clinical safety profile and is well tolerated in children, adults, and the elderly. We show that nonviral delivery of a 9 kb self-amplifying mRNA elicits potent immune responses in mice, rats, rabbits, and nonhuman primates comparable to a viral delivery technology, and demonstrate that, relatively low doses (75 µg) induce antibody and T-cell responses in primates. We also show the CNE-delivered self-amplifying mRNA enhances the local immune environment through recruitment of immune cells similar to an MF59 adjuvanted subunit vaccine. Lastly, we show that the site of protein expression within the muscle and magnitude of protein expression is similar to a viral vector. Given the demonstration that self-amplifying mRNA delivered using a CNE is well tolerated and immunogenic in a variety of animal models, we are optimistic about the prospects for this technology.

Respiratory syncytial virus (RSV), the main cause of infant bronchiolitis, remains a major unmet vaccine need despite more than 40 years of vaccine research. Vaccine candidates based on a chief RSV neutralization antigen, the fusion (F) glycoprotein, have foundered due to problems with stability, purity, reproducibility, and potency. Crystal structures of related parainfluenza F glycoproteins have revealed a large conformational change between the prefusion and postfusion states, suggesting that postfusion F antigens might not efficiently elicit neutralizing antibodies. We have generated a homogeneous, stable, and reproducible postfusion RSV F immunogen that elicits high titers of neutralizing antibodies in immunized animals. The 3.2-Å X-ray crystal structure of this substantially complete RSV F reveals important differences from homology-based structural models. Specifically, the RSV F crystal structure demonstrates the exposure of key neutralizing antibody binding sites on the surface of the postfusion RSV F trimer. This unanticipated structural feature explains the engineered RSV F antigen's efficiency as an immunogen. This work illustrates how structural-based antigen design can guide the rational optimization of candidate vaccine antigens.subunit | epitope

39A SARS-CoV-2 vaccine is needed to control the global COVID-19 public health crisis. Atomic-40 level structures directed the application of prefusion-stabilizing mutations that improved 41 expression and immunogenicity of betacoronavirus spike proteins. Using this established 42 immunogen design, the release of SARS-CoV-2 sequences triggered immediate rapid 43 manufacturing of an mRNA vaccine expressing the prefusion-stabilized SARS-CoV-2 spike 44 trimer (mRNA-1273). Here, we show that mRNA-1273 induces both potent neutralizing antibody 45 and CD8 T cell responses and protects against SARS-CoV-2 infection in lungs and noses of 46 mice without evidence of immunopathology. mRNA-1273 is currently in a Phase 2 clinical trial 47 sequences (then known as "2019-nCoV") on January 10 th , the 2P mutations were substituted 98 into S positions aa986 and 987 to produce prefusion-stabilized SARS-CoV-2 S (S-2P) protein 99 for structural analysis 22 and serological assay development 23,24 in silico without additional 100 experimental validation. Within 5 days of sequence release, current Good Manufacturing 101

A cytomegalovirus (CMV) vaccine that is effective at preventing congenital infection and reducing CMV disease in transplant patients remains a high priority as no approved vaccines exist. While the precise correlates of protection are unknown, neutralizing antibodies and antigen-specific T cells have been implicated in controlling infection. We demonstrate that the immunization of mice and nonhuman primates (NHPs) with lipid nanoparticles (LNP) encapsulating modified mRNA encoding CMV glycoproteins gB and pentameric complex (PC) elicit potent and durable neutralizing antibody titers. Since the protective correlates in pregnant women and transplant recipients may differ, we developed an additional mRNA vaccine expressing the immunodominant CMV T cell antigen pp65. Administration of pp65 vaccine with PC and gB elicited robust multi-antigenic T cell responses in mice. Our data demonstrate that mRNA/LNP is a versatile platform that enables the development of vaccination strategies that could prevent CMV infection and consequent disease in different target populations.

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, prefusionstabilized, 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) 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.