Studies show that chimeric mRNAs induce neutralizing antibodies that act strongly and broadly against SARS-CoV-2 mutants.

March 10, 2022

In a recent study posted on bioRxiv* Preprint server, researchers have found that messenger ribonucleic acid (mRNA) -based coronavirus can provide safer and broader protection against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants. I sought a strategy to develop a disease 2019 (COVID-19) vaccine Concerns (VOC).

Background

The new SARS-CoV-2VOC threatens public health in the ongoing COVID-19 pandemic. In previous studies, Puranik et al. Shows that the efficacy of existing mRNA vaccines was reduced from about 95% of the original Washington (WA) strain to 76% and 42% against delta VOCs with the mRNA-1273 and BNT162b2 vaccines, respectively. I did.

In addition, there are safety concerns associated with the mRNA vaccines currently in use. First, Peacock et al. As demonstrated in the 2021 study, the mRNA vaccine encodes a multibasic furin cleavage site (FCS) at the junction of the S1 and S2 subunits, affecting the stability of the spike (S) protein. Give and reduce the number of antigens. Epitopes that can be used to induce cell-mediated and humoral immunity.

Ogata et al. In another study by 2022, they detected truncated S1 in the blood of immunized subjects receiving the mRNA vaccine. Therefore, there is concern that this free portion may mimic the full-length S protein and activate angiotensin converting enzyme 2 (ACE2), causing side effects such as myocarditis.

Therefore, there is an urgent need to develop more effective mRNA vaccines, optimize existing vaccines, and combat infections from current and future SARS-CoV-2 VOCs. Coronaviridae family.

About research

In the current study, researchers mutated the FCS of the predominant VOC S protein, identified expression and cleavage defects in furin variants, and evaluated the ability of the resulting mRNA to induce. Neutralizing antibody (NAb) Mice after intramuscular administration.

To this end, they first screened five monovalent mRNA vaccines encoding the S protein and VOCs of the SARS-CoV-2 WA strain. These include alpha (B.1.1.7), beta (B.1.351), gamma (P.1), and delta (B.1.617.2). They constructed two sets of mRNAs encoding the S proteins of all SARS-CoV-2 VOCs described above, one using wild-type (WT) FCS and the other using mutation sites. , We investigated the expression of these VOC mRNAs in 293T cells. ..

Flow cytometric results showed that removal of FCS increased surface expression of VOCS proteins in transfected 293T cells. Western blotting confirmed that all these vaccines have mutations that negate furin-mediated cleavage between the S1 and S2 domains of the S protein.

They prescribed WT or furin variant mRNAs containing lipid nanoparticles (LNPs) and administered each LNP-mRNA intramuscularly to 6-week-old female BALB / c mice twice at 3-week intervals. ..

They performed an enzyme-linked immunosorbent assay (ELISA) on mouse sera collected 14 days after booster immunization (double dose vaccine) to determine the endpoint titer (EPT) of total bound antibody. They then performed a plaque reduction neutralization test (PRNT) and challenged VeroE6 cells with live viruses of 5 VOCs in the absence or presence of diluted serum collected from immunized mice. ..

They also investigated the ability of individual SARS-CoV-2 VOC mRNA vaccines to produce nAbs and profiled their coverage spectra. In vivo Six-week-old female BALB / c mice were immunized with LNP-encapsulated furin mutant VOC mRNA and the performance of individual mRNAs in vaccinated mice was compared.

In previous studies, K18-hACE2 transgenic mice have been widely used to evaluate vaccine efficacy in preclinical studies. Following the proceedings, researchers used these mice to identify a broad spectrum of nAb generated. These mice were immunized twice with 5 μg WA-Furin or Beta-Furinm RNA at 3-week intervals.5 weeks after vaccination, challenge with 1 x 10^Five Up to half the amount of tissue culture infection (TC)_ID50) WA or beta variant.

Finally, researchers also addressed the limitations of Omicron VOC-specific mRNA vaccines. To this end, they have developed a bivalent vaccine with chimeric mRNAs by incorporating one additional receptor-binding domain (RBD) from the delta mutant into intact S. antigen Of Omicron.

Survey results

In vaccinated mice, individual VOC mRNA induced nAb production in a VOC-specific manner, with the exception of gamma mutants.

NAbs produced in mice that received WA-Furin and Beta-FurinmRNA cross-reactive with other VOCs. This indicates that some VOC mRNA vaccines, especially Beta-Furin, have led to the production of antibodies that can bind to the S proteins of multiple VOCs. .. However, neither of these vaccines was able to effectively neutralize Omicron.

ELISA results revealed that mRNA with a furin-cleaving mutation elicited an average EPT of fully bound antibodies higher than its WT version. The PRNT results confirmed that the serum neutralization activity of mice injected with the WA furin mutant was improved.

In live virus challenge experiments, immunization with either WA-Furin or Beta-Furin mRNA almost completely inhibited viral replication in the lung, and virus titers were below the detection limit. None of the mice immunized with the beta or WA-Flynn vaccine showed signs of weight loss, and some animals in these treatment groups gained weight up to 5 days after infection.

Interestingly, boost immunization of mice with the Omicron and WA-Flinn mRNA vaccines provided similar protection against Omicron. The mRNA vaccine encoding Omicron S elicited the strongest defense against Omicron, but did not exhibit broad neutralizing capacity against other VOCs such as Delta.

The chimeric mRNA vaccine induced the strongest, broad-spectrum nAb with significantly higher cross-neutralizing activity against deltas. While maintaining its effectiveness against Omicron.

Conclusion

Together, research data show that while VOC-specific strategies can provide SARS-CoV-2 strain-specific protection, some with relatively enhanced potential are genetically existing SARS-CoV-. Two variants that have been shown to be able to provoke a broader and stronger immune response to different sets. In addition, the in-house designed mRNA vaccine was much safer than existing vaccines.

More importantly, the design of the chimeric vaccine has achieved a balance between efficacy and scope not only for SARS-CoV-2 variants, but also for other viruses. It significantly restored strong defenses against delta infections while maintaining effective immunity to Omicron. This aspect of chimeric mRNA vaccine candidates is also very attractive as SARS-CoV-2 continues to mutate. Effectiveness of Existing mRNA vaccine.

Overall, chimeric mRNA-based vaccines pave the way for developing next-generation COVID-19 vaccine candidates that may target new SARS-CoV-2 variants and several other respiratory pathogens in the future. open.

*Important Notices

bioRxiv publishes unpeer-reviewed preliminary scientific reports and should not be considered definitive, guide clinical / health-related behaviors, or be treated as established information.