The coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has led to substantial damage to all aspects of our society. Vaccination is the most effective strategy to prevent infectious diseases. Since the pandemic, several vaccine platforms, including inactivated, mRNA, viral vector-based, and protein subunit vaccines have been developed. While these vaccines have been highly effective in reducing severe disease and mortality, they still have several limitations, such as the inability to prevent virus infection and transmission, particularly against emerging variants of concern (VoCs), short duration of protection, failure to induce mucosal IgA antibodies and resident memory T cells in the respiratory tract, and high cost of production or distribution. Therefore, there is an urgent need to develop the next generation of intranasal COVID-19 vaccines that induce durable and broadly protective immunity, both in the airways and systemically.
The combined MMR (measles/mumps/rubella) vaccine has been available in the United States since 1971 and is one of the safest and most effective human vaccines. The MMR vaccine contains attenuated strains of measles virus (MeV), mumps virus (MuV), and rubella virus and confers lifelong protection against these three viruses. Both MeV and MuV have been used as delivery platforms for experimental vaccines against highly pathogenic viruses. In this study, we have developed a highly efficacious, intranasally delivered, trivalent measles-mumps-SARS-CoV-2 spike (S) protein (MMS) vaccine candidate that induces robust systemic and mucosal immunity with broad protection. MMS vaccine candidate is based on three components of the MMR vaccine, a measles virus Edmonston, and the two mumps virus strains [Jeryl Lynn 1 (JL1) and JL2], which are known for their high safety and long-lasting immunity. The six proline-stabilized prefusion S protein (preS-6P) genes for ancestral SARS-CoV-2 WA1 and two important SARS-CoV-2 VoCs (Delta and Omicron BA.1.) were each inserted into one of these three viruses which were then combined into a trivalent “MMS” candidate vaccine. Intranasal immunization of MMS vaccine in IFNAR1-/- mice induced a strong SARS-CoV-2-specific serum IgG response, cross-variant neutralizing antibodies, mucosal IgA, and systemic and lung-resident memory T cells. Immunization of golden Syrian hamsters with the MMS vaccine induced similarly high levels of antibodies that efficiently neutralized SARS-CoV-2 VoCs and provided broad and complete protection against challenge with any of these VoCs. This MMS vaccine is an efficacious, broadly protective next-generation COVID-19 vaccine candidate that is readily adaptable to new variants, built on a platform with a 50-year safety record that also protects against measles and mumps.
SARS-CoV-2 live attenuated vaccine (LAV) is one of the three approaches supported by WHO and BARDA for the development of next-generation COVID-19 vaccines but remains underexplored. Unlike other vaccine types that use only S protein as an antigen, LAVs mimic natural infections, which can elicit systemic and mucosal immune responses and both B and T cell responses targeting various viral protein components. In this study, we developed a novel yeast-based reverse genetic system for SARS-CoV-2 Omicron JN.1. Using this system, we rationally designed several SARS-CoV-2 JN.1 LAV vaccine candidates by introducing D130A mutation in the KDKE motif in the nsp16 protein to inhibit mRNA cap ribose 2’-O methyltransferase, deleting the furin cleavage site (FCS) in the spike to block virus transmission, and/or deleting accessory proteins ORF6, ORF7, and ORF8 for additional attenuation strategy, and/or modifying the transcription regulatory sequence (TRS) of SARS-CoV-2 genome to prevent recombination between SARS-CoV-2 LAVs with the circulating wild-type SARS-CoV-2. The resultant LAVs rJN.1-D130A, rJN.1-D130A-dFCS, and rJN.1-D130A-dFCS-dORF6-8, rJN.1-mTRS-D130A-dFCS were significantly attenuated in cell culture, ex vivo primary human bronchial epithelial (HBE) cultures, and golden Syrian hamsters.
While SARS-CoV-2 vaccine has been a primary focus, development of mucosal vaccines for other respiratory viruses, such as human respiratory syncytial virus (RSV), a major cause of respiratory illness in infants, children, and older adults, is also urgently needed. Toward this goal, we aimed to develop SARS-CoV-2 as a vector to deliver other respiratory virus vaccines. The fusion (F) protein of RSV is the main target for inducing neutralizing antibodies against RSV infection. The stabilized prefusion F gene is more immunogenic than the native F protein. Thus, the stabilized prefusion F gene of RSV (RSVF) was inserted into the attenuated SARS-CoV-2 JN.1 vectors by fusing RSVF to the upstream of SARS-CoV-2 nucleocapsid (N) gene or replacing ORF7a with RSVF, and recombinant JN.1 carrying RSVF were recovered. We found that the RSV F protein was highly expressed by SARS-CoV-2 JN.1 vector. One of the bivalent vaccine candidates, rJN.1-D130A-dFCS-RSVF, is not only highly attenuated in cell culture, ex vivo HBE cultures and hamsters but also highly immunogenic, eliciting high levels of SARS-CoV-2- and RSV-specific neutralizing antibodies and mucosal IgA antibodies, and providing complete protection against challenge with SARS-CoV-2 and RSV. Collectively, we found that combination of several arrays of attenuating mutations led to SARS-CoV-2 LAVs with enhanced safety profile and that SARS-CoV-2 LAV is an effective vector to deliver bivalent vaccine against SARS-CoV-2 and RSV.
Overall, we have rationally designed intranasal (1) MeV-MuV-vectored multivalent SARS-CoV-2 vaccines, (2) live attenuated SARS-CoV-2 vaccines, and (3) SARS-CoV-2-vectored bivalent RSV vaccines, which induce strong immune responses at both systemic and mucosal levels and provide complete protection. These efforts pave a new way for developing next-generation intranasal vaccines that could provide broad protection against multiple respiratory pathogens in a single immunization.