Mpox multi-antigen mRNA vaccine candidates by a simplified manufacturing strategy afford efficient protection against lethal orthopoxvirus challenge.

Current unprecedented mpox outbreaks in non-endemic regions represent a global public health concern. Although two live-attenuated vaccinia virus (VACV)-based vaccines have been urgently approved for people at high risk for mpox, a safer and more effective vaccine that can be available for the general public is desperately needed. By utilizing a simplified manufacturing strategy of mixing DNA plasmids before transcription, we developed two multi-antigen mRNA vaccine candidates, which encode four (M1, A29, B6, A35, termed as Rmix4) or six (M1, H3, A29, E8, B6, A35, termed as Rmix6) mpox virus antigens. We demonstrated that those mpox multi-antigen mRNA vaccine candidates elicited similar potent cross-neutralizing immune responses against VACV, and compared to Rmix4, Rmix6 elicited significantly stronger cellular immune responses. Moreover, immunization with both vaccine candidates protected mice from the lethal VACV challenge. Investigation of B-cell receptor (BCR) repertoire elicited by mpox individual antigen demonstrated that the M1 antigen efficiently induced neutralizing antibody responses, and all neutralizing antibodies among the top 20 frequent antibodies appeared to target the same conformational epitope as 7D11, revealing potential vulnerability to viral immune evasion. Our findings suggest that Rmix4 and Rmix6 from a simplified manufacturing process are promising candidates to combat mpox.

Rapid evaluation of heterologous chimeric RBD-dimer mRNA vaccine for currently-epidemic Omicron sub-variants as booster shot after inactivated vaccine

Graphical With continuous mutations of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the severe immune escape of Omicron sub-variants urges the development of next-generation broad-spectrum vaccines, especially as booster jabs after high-level vaccination coverage of inactivated vaccines in China and many other countries. Previously, we developed a coronavirus disease 2019 (COVID-19) protein subunit vaccine ZF2001® based on the tandem homo-prototype receptor-binding domain (RBD)-dimer of the SARS-CoV-2 spike protein. We upgraded the antigen into a hetero-chimeric prototype (PT)-Beta or Delta-BA.1 RBD-dimer to broaden the cross-protection efficacy and prove its efficiency with protein subunit and mRNA vaccine platforms. Herein, we further explored the hetero-chimeric RBD-dimer mRNA vaccines and evaluated their broad-spectrum activities as booster jabs following two doses of inactivated vaccine in mice. Our data demonstrated that the chimeric vaccines significantly boosted neutralizing antibody levels and specific T-cell responses against the variants, and PT-Beta was superior to Delta-BA.1 RBD as a booster in mice, shedding light on the antigen design for the next-generation COVID-19 vaccines.

Rapid evaluation of heterologous chimeric RBD-dimer mRNA vaccine for currently-epidemic Omicron sub-variants as booster shot after inactivated vaccine.

With continuous mutations of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the severe immune escape of Omicron sub-variants urges the development of next-generation broad-spectrum vaccines, especially as booster jabs after high-level vaccination coverage of inactivated vaccines in China and many other countries. Previously, we developed a coronavirus disease 2019 (COVID-19) protein subunit vaccine ZF2001® based on the tandem homo-prototype receptor-binding domain (RBD)-dimer of the SARS-CoV-2 spike protein. We upgraded the antigen into a hetero-chimeric prototype (PT)-Beta or Delta-BA.1 RBD-dimer to broaden the cross-protection efficacy and prove its efficiency with protein subunit and mRNA vaccine platforms. Herein, we further explored the hetero-chimeric RBD-dimer mRNA vaccines and evaluated their broad-spectrum activities as booster jabs following two doses of inactivated vaccine (IV) in mice. Our data demonstrated that the chimeric vaccines significantly boosted neutralizing antibody levels and specific T-cell responses against the variants, and PT-Beta was superior to Delta-BA.1 RBD as a booster in mice, shedding light on the antigen design for the next-generation COVID-19 vaccines.

A combination vaccine against SARS-CoV-2 and H1N1 influenza based on receptor binding domain trimerized by six-helix bundle fusion core.

BACKGROUND: Increasing severe morbidity and mortality by simultaneous or sequential infections with SARS-CoV-2 and influenza A viruses (IAV), especially in the elderly and obese patients, highlight the urgency of developing a combination vaccine against COVID-19 and influenza. METHODS: Self-assembling SARS-CoV-2 RBD-trimer and Influenza H1N1 HA1-trimer antigens were constructed, upon the stable fusion core in post-fusion conformation. Immunogenicity of SARS-CoV-2 RBD-trimer vaccine and H1N1 HA1-trimer antigens candidates were evaluated in mice. Protection efficacy of a combination vaccine candidate against SARS-CoV-2 and IAV challenge was identified using the K18-hACE2 mouse model. FINDINGS: Both the resultant RBD-trimer for SARS-CoV-2 and HA1-trimer for H1N1 influenza fully exposed receptor-binding motifs (RBM) or receptor-binding site (RBS). Two-dose RBD-trimer induced significantly higher binding and neutralizing antibody titers, and also a strong Th1/Th2 balanced cellular immune response in mice. Similarly, the HA1-trimer vaccine was confirmed to exhibit potent immunogenicity in mice. A combination vaccine candidate, composed of RBD-trimer and HA1-trimer, afforded high protection efficacy in mouse models against stringent lethal SARS-CoV-2 and homogenous H1N1 influenza co-infection, characterized by 100% survival rate. INTERPRETATION: Our results represent a proof of concept for a combined vaccine candidate based on trimerized receptor binding domain against co-epidemics of COVID-19 and influenza. FUNDING: This project was funded by the Strategic Priority Research Program of CAS (XDB29040201), the National Natural Science Foundation of China (81830050, 81901680, and 32070569) and China Postdoctoral Science Foundation (2021M703450).

Structure-based neutralizing mechanisms for SARS-CoV-2 antibodies.

The devastating economic and public health consequences caused by the COVID-19 pandemic have prompted outstanding efforts from the scientific community and pharmaceutical companies to develop antibody-based therapeutics against SARS-CoV-2. Those efforts are encouraging and fruitful. An unprecedentedly large number of monoclonal antibodies (mAbs) targeting a large spectrum of epitopes on the spike protein has been developed in the last two years. The development of structural biology, especially the cryo-EM technology, provides structural insights into the molecular neutralizing mechanisms of those mAbs. Moreover, neutralizing antibodies are essential in protecting host from infection. Therefore, understanding the antibody neutralizing mechanism is critical for optimizing effective antibody-based therapeutics and developing next-generation pan-coronavirus vaccines. This review summarizes the latest understanding of antibody neutralizing mechanisms against SARS-CoV-2 at the molecular and structural levels.

COVID-19 mRNA vaccines.

The ongoing COVID-19 pandemic and its unprecedented global societal and economic disruptive impact highlight the urgent need for safe and effective vaccines. Taking substantial advantages of versatility and rapid development, two mRNA vaccines against COVID-19 have completed late-stage clinical assessment at an unprecedented speed and reported positive results. In this review, we outline keynotes in mRNA vaccine development, discuss recently published data on COVID-19 mRNA vaccine candidates, focusing on those in clinical trials and analyze future potential challenges.

A single-dose mRNA vaccine provides a long-term protection for hACE2 transgenic mice from SARS-CoV-2.

The rapid expansion of the COVID-19 pandemic has made the development of a SARS-CoV-2 vaccine a global health and economic priority. Taking advantage of versatility and rapid development, three SARS-CoV-2 mRNA vaccine candidates have entered clinical trials with a two-dose immunization regimen. However, the waning antibody response in convalescent patients after SARS-CoV-2 infection and the emergence of human re-infection have raised widespread concerns about a possible short duration of SARS-CoV-2 vaccine protection. Here, we developed a nucleoside-modified mRNA vaccine in lipid-encapsulated form that encoded the SARS-CoV-2 RBD, termed as mRNA-RBD. A single immunization of mRNA-RBD elicited both robust neutralizing antibody and cellular responses, and conferred a near-complete protection against wild SARS-CoV-2 infection in the lungs of hACE2 transgenic mice. Noticeably, the high levels of neutralizing antibodies in BALB/c mice induced by mRNA-RBD vaccination were maintained for at least 6.5 months and conferred a long-term notable protection for hACE2 transgenic mice against SARS-CoV-2 infection in a sera transfer study. These data demonstrated that a single dose of mRNA-RBD provided long-term protection against SARS-CoV-2 challenge.

SARS-CoV-2 virus: vaccines in development

The ongoing COVID-19 pandemic, caused by SARS-CoV-2, is an unprecedented challenge to humanity. Global herd immunity may be necessary before resumption of normal economic and societal activities. Since the beginning of the outbreak, the development of COVID-19 vaccines has proceeded at record speed using nearly all available platforms or strategies to maximize vaccine success. A total of 42 vaccine candidates have now entered clinical trials and encouraging data from several vaccine candidates in phase 1 or 2 clinical trials have been reported. In this review, we examine current COVID-19 vaccine candidates, discuss their strengths and weaknesses, summarize published clinical data and analyze future challenges.