Intranasal recombinant MVA-based vaccines effective against SARS-CoV-2 variants in mice

By Pooja Toshniwal PahariaDec 11 2022Reviewed by Benedette Cuffari, M.Sc.

In a recent study posted to the bioRxiv* preprint server, researchers construct a recombinant host-range restricted vaccinia virus Ankara (rMVAs) expressing the spike (S) proteins of several severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants of concern (VOCs) and evaluate the vaccine immunogenicity when delivered by the intranasal (IN) and intramuscular (IM) routes.

Study: Enhanced Protection from SARS-CoV-2 Variants by MVA-Based Vaccines Expressing Matched or Mismatched S Proteins Administered Intranasally to hACE2 Mice. Image Credit: Lightspring / Shutterstock.com

This news article was a review of a preliminary scientific report that had not undergone peer-review at the time of publication. Since its initial publication, the scientific report has now been peer reviewed and accepted for publication in a Scientific Journal. Links to the preliminary and peer-reviewed reports are available in the Sources section at the bottom of this article. View Sources

The urgent need for new COVID-19 vaccines

The continual emergence of SARS-CoV-2 VOCs has threatened the efficacy of anti-SARS-CoV-2 vaccines and therapeutic agents, thus warranting the need to update current vaccines and develop more effective treatments. MVA is an attenuated vaccinia virus vector vaccine currently being investigated in clinical trials for several infections, including the coronavirus disease 2019 (COVID-19).

The present study's authors previously reported that IN administration of rMVA-W, the rMVA vaccine expressing the ancestral Wuhan-Hu-1 strain S protein, stimulated antigen-specific T lymphocytes, as well as most of the positive pool peptides present in the SARS-CoV-2 VOC S proteins. This route of vaccine administration prevented or more rapidly eliminated CoV-W infections as compared to IM administration.

About the study

In the present study, researchers extend their previous analysis by constructing additional rMVAs and pseudoviruses expressing modified SARS-CoV-2 VOC S proteins. Herein, they compare the ability of these vaccines to bind with SARS-CoV-2 VOC S proteins and protect K18-host angiotensin-converting enzyme 2 (hACE2) mice from SARS-CoV-2 infection.

C57BL/6 mice and K18-hACE2 mice were obtained, and rMVA-Beta VOC (B), rMVA-Delta VOC (D), and rMVA-Omicron VOC (O) viruses were constructed. In addition, Vero E6 cells and Vero E6 transmembrane protease serine 2 (hTMPRSS2) hACE2 cells were used for in vitro experiments, wherein cells were infected with SARS-CoV-2 United States of America (USA)-WA1/2020 strain, Beta VOC, Delta VOC, and Omicron BA.1 VOC. The 50% tissue culture infectious dose (TCID₅₀) values were subsequently calculated.

The rMVAs were injected IM into the mice's hind legs, and vaccine immunogenicity was compared to that following IN injections of matched and mismatched rMVA vaccines. Post-infection, the morbidity and/or mortality status and body weights were monitored for up to two weeks.

Detection of Wuhan S, Omicron S, and S protein receptor-binding domain (RBD) immunoglobulin G (IgG) and IgA antibody titers was performed using enzyme-linked immunosorbent assays (ELISA). In addition, recombinant vesicular stomatitis virus (rVSV)-based pseudoviral neutralization assays were performed to evaluate VOC-neutralizing antibody titers. K18-hACE2 mice lung, brain, and nasal turbinate tissues were examined to quantify infectious SARS-CoV-2 titers.

Additionally, ribonucleic acid (RNA) was extracted from tissues and subjected to digital droplet polymerase chain reaction (ddCR) analysis to quantify SARS-CoV-2 single-stranded guided S protein (sgS), sg nucleoprotein (sgN), and 18S ribosomal RNA (rRNA) levels two days and four days post-infection.

Prior to vaccine efficacy experiments, the infection potential of SARS-CoV-2 VOCs in K18-hACE2 transgenic mice was compared. The team concentrated on the capability of rMVA-W to induce cross-neutralizing antibody titers.

Subsequently, mice were vaccinated with rMVAs-W, -D, and -O. The mismatched and matched SARS-CoV-2 pseudovirus neutralization was comparatively evaluated.  

MVA-based vaccines protect against SARS-CoV-2 VOCs

The USA-WA1/2020 strain, Beta VOC, and Delta VOC were fatal, whereas Omicron VOC showed lesser lethality, and lower Omicron titers were observed in the murine respiratory tracts. However, sgRNAs levels in mice infected with different SARS-CoV-2 VOCs were comparable.

The order of VOC neutralization was highest for the Wuhan-Hu-1 strain, followed by the Delta, Beta, and Omicron VOCs. Repeated rMVA-W vaccinations enhanced Beta VOC and Delta VOC neutralization but were associated with a modest increase in Omicron VOC neutralization. No antibodies approximated that of the Wuhan-Hu-1 strain.

Nevertheless, rMVA-W vaccinations protected transgenic mice against weight loss and mortality and lowered SARS-CoV-2 proliferation for over nine months in the murine respiratory system tracts. Further, no Wuhan-Hu-1 strain replication was observed in mice lungs, and VOC proliferation was significantly lowered compared to control animals.

The rMVA-W vaccination induced scarce neutralizing antibodies against the Omicron VOC. However, significant titers of Omicron S protein-binding antibodies were induced that partially protected mice post-passive antibody transfer.

In every experiment, matched pseudovirus neutralization was greater than mismatched pseudovirus neutralization. Furthermore, the slightest difference was observed between the Wuhan-Hu-1 strain and Delta VOC, whereas the greatest difference was between the Omicron VOC and other strains.

Nevertheless, rMVA-O elicited antibodies that showed significant rVSV-O neutralization. However, antibody titers were less than rMVA-D-elicited anti-Delta titers or rMVA-W-elicited anti-Wuhan-Hu-1 titers.

Comparable cross-neutralizing antibody titers were observed in hACE2 mice sera inoculated with sub-fatal VOC doses. In addition, after two rMVA-W vaccinations, one rMVA-D vaccination or rMVA-B vaccination boosted Wuhan-Hu-1 strain neutralization.

Double rMVA-O immunizations were required to enhance Omicron neutralization in rMVA-W-vaccinated and naïve mice. The sgRNA titers in K18-hACE2 transgenic mice confirmed the greater protection elicited by IN rMVA-W vaccinations compared to when the vaccine was administered by IM, with antigen-targeted IgA titers and more numerous pulmonary clusters of differentiation 8+ (CD8+) T lymphocytes.

Conclusions

Overall, the study findings demonstrated that IN MVA-based vaccinations conferred greater immune protection against SARS-CoV-2 VOCs in mice after vaccinating with mismatched and matched S proteins.

This news article was a review of a preliminary scientific report that had not undergone peer-review at the time of publication. Since its initial publication, the scientific report has now been peer reviewed and accepted for publication in a Scientific Journal. Links to the preliminary and peer-reviewed reports are available in the Sources section at the bottom of this article. View Sources