PreprintCited by 636SARS-CoV-2 and COVID-19 ResearchCircular RNAs in diseasesAnimal Virus Infections Studies

The DOI matches its Crossref record; 109 of the 109 references it cites were found in a registry or an index; none of the 54 sources its claims cite is checked for support yet.

Circular RNA Vaccines against SARS-CoV-2 and Emerging Variants

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Abstract

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and its emerging variants of concern (VOC), such as Delta (B.1.617.2) and Omicron (B.1.1.529), has continued to drive the worldwide pandemic. Therefore, there is a high demand for vaccines with enhanced efficacy, high thermostability, superior design flexibility, and fast manufacturing speed. Here, we report a circular RNA (circRNA) vaccine that encodes the trimeric RBD of SARS-CoV-2 Spike protein. Without the need of nucleotide modification, 5’-capping or 3’-polyadenylation, circRNA could be rapidly produced via in vitro transcription and is highly thermostable whether stored in naked or lipid-nanoparticle (LNP)-encapsulated format. LNP-encapsulated circRNA RBD elicited potent neutralizing antibodies and T cell responses, providing robust protection against Beta (B.1.351) and native viruses in mice and rhesus macaques, respectively. Notably, circRNA vaccine enabled higher and more durable antigen production than 1mΨ-modified mRNA vaccine, eliciting a higher proportion of neutralizing antibodies and stronger Th1-biased immune responses. Importantly, we found that circRNA RBD-Omicron vaccine induced effective neutralizing antibodies against only Omicron but not Delta variant. By contrast, circRNA RBD-Delta could elicit high level of neutralizing antibodies against both Delta and Omicron. Following two doses of either native- or Delta-specific vaccination, circRNA RBD-Delta , but not Omicron or Beta vaccines, could effectively boost the neutralizing antibodies against both Delta and Omicron variants. These results suggest that circRNA RBD-Delta is a favorable choice for vaccination to provide a broad-spectrum protection against the current variants of concern of SARS-CoV-2.

Overview

AI snapshot

Written from the paper’s full text.

TL;DR

A circular RNA vaccine expressing trimeric SARS-CoV-2 RBD elicited neutralizing antibodies and T cell responses in mice and rhesus macaques, with higher and more durable antigen expression than 1mΨ-modified mRNA. The circRNARBD-Delta vaccine showed broad neutralization against Delta and Omicron and was an effective booster, whereas the Omicron-specific vaccine neutralized Omicron but not Delta.

Key findings

  • LNP-circRNARBD induced RBD-specific IgG endpoint GMTs of ∼1.9 × 10⁴ (10 μg) and ∼5.7 × 10⁵ (50 μg) in mice, with pseudovirus NT50 ∼4.5 × 10³ and authentic SARS-CoV-2 NT50 ∼7.0 × 10⁴.
  • circRNARBD-Delta elicited an NT50 of ∼1.4 × 10⁵ against Delta pseudovirus at 10 μg and maintained Omicron neutralization with NT50 ∼4.7 × 10³; as a third booster after two-dose circRNARBD, it raised Omicron geometric mean NT50 from ∼4 × 10² to ∼3.2 × 10⁴.
  • circRNARBD-Omicron induced Omicron-specific IgG GMTs of ∼4.7 × 10⁴ (5 μg) and ∼2.2 × 10⁵ (10 μg), with Omicron NT50s of ∼2.5 × 10³ and ∼8.6 × 10³, but neutralizing activity was hardly detected against native strain or Delta.
  • In rhesus macaques, circRNARBD IgG GMTs were ∼2.1 × 10⁴ (20 μg), ∼1.6 × 10⁴ (100 μg), and ∼7 × 10³ (500 μg); authentic virus NT50s were ∼80, ∼120, and ∼50, respectively. Vaccinated macaques showed nearly 1,000-fold reduced lung genomic RNA at 100/500 μg and nearly no detectable subgenomic RNA at all doses, with no severe clinical adverse effects.

Methods

  • circRNA vaccines encoded trimeric SARS-CoV-2 RBD with a human tPA signal peptide and T4 fibritin foldon, produced by group I intron autocatalysis or T4 RNA ligase, and encapsulated in LNPs; comparisons used 1mΨ-modified and unmodified mRNA encoding the same RBD sequence.
  • Female BALB/c mice (6–8 weeks) were immunized intramuscularly with varying circRNA doses; 2–4-year-old male rhesus macaques received 20, 100, or 500 μg circRNARBD, circRNACtrl, or PBS on days 0 and 21. Mice were challenged with Beta variant; macaques were challenged with native SARS-CoV-2.
  • Analyses included ELISA endpoint GMTs, pseudovirus and authentic virus NT50 assays, RT-qPCR viral loads, ELISpot and flow cytometry for T cell cytokines, histopathology, and unpaired or paired two-sided Student’s t tests.

Limitations

  • Stated by the paper: small rhesus macaque numbers caused high variation and large error bars; immunogenicity of IVT-produced circRNAs remains a potential concern; safety awaits further NHP and clinical trials; the mRNA comparator encoded trimeric RBD and differed from mRNA-1273 and BNT162b2, which encode full-length spike and use different manufacturing processes.
  • Evident from the text: no human clinical data are reported; protection against Omicron and Delta was assessed mainly by neutralization assays, while mouse challenge used Beta and macaque challenge used native SARS-CoV-2.

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Integrity signals

Registry

Crossref · 10.1101/2021.03.16.435594

Cites

109 of 109 references verified0 citation errors · 0 not checkable

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Verification

Claims the paper makes

77 Own result · 21 Not checked yet · 13 Own method · 12 Own interpretation

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Show all 72 claims

  • It may state two separate claims as one. 41
  • The quote only partly states this claim. 1
  • Probably not a substantial claim. 12
51 of 51
  • The paper relies on this without support.

    Neutralizing antibody titers against a SARS-CoV-2 variant in vitro predict protection against that variant in vivo.

    “Among all three, the circRNARBD-Delta vaccine maintained sufficient neutralizing activity against Omicron (Figure 5A), with an NT50 of ∼4.7 × 103,”
    “the circRNARBD-Delta vaccine protected against both Delta and Omicron”
  • The paper relies on this without support.

    Results in mice and rhesus macaques predict immunogenicity, protection, and safety of circRNA vaccines in humans.

    “In summary, circRNA holds the potential to become an effective and safe platform for vaccination against viral infection—including SARS-CoV-2 emerging variants—as well as possibly becoming a therapeutic platform, owing to its specific properties.”
  • The paper relies on this without support.

    Neutralizing antibody titers are a correlate of protection against SARS-CoV-2 in humans.

    “Our Delta-specific vaccination could cross-protect against all other variants, including Omicron (Figures 2E, 5A, 5B, and 5C), and could also be used as an effective booster following two-dose original SARS-CoV-2 vaccines (Figures 5K and 5L).”
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Metadata

Authors
Qu, L., Yi, Z., Shen, Y., Lin, L., Chen, F., Xu, Y., Wu, Z., Tang, H., Zhang, X., Tian, F., Wang, C., Xiao, X., Dong, X., Guo, L., Lu, S., Yang, C., Tang, C., Yang, Y., Yu, W., Wang, J., Zhou, Y., Huang, Q., Yisimayi, A., Cao, Y., Wang, Y., Zhou, Z., Peng, X., Wang, J., Xie, X. S., & Wei, W.
Affiliations
  • Peking University (CN)
  • Chinese Academy of Medical Sciences & Peking Union Medical College (CN)
  • National Institutes for Food and Drug Control (CN)
Corresponding author
Wei, Wensheng
Venue
Cell
Publisher
openRxiv
Published
2021-03-16
Volume
185
Issue
10
Pages
1728-1744.e16
ISSN
0092-8674 (ISSN-L)
OpenAlex
W4226027283
Cited by
636
References
107
Citations by year
2026: 107 · 2025: 170 · 2024: 151 · 2023: 129 · 2022: 73 · 2021: 4
FWCI
64.04
Type
journal article
Language
en
Open access
Locations
  • Cell (publishedVersion, cc-by)
  • bioRxiv (Cold Spring Harbor Laboratory) (acceptedVersion)
  • PubMed Central (publishedVersion)
  • PubMed (publishedVersion)
Funders
  • National Natural Science Foundation of China (2018ZX10301401, 2020YFA0707800, 31870893, 31930016)
  • Chinese Academy of Sciences
  • Ministry of Science and Technology of the People's Republic of China
  • China Postdoctoral Science Foundation
  • Tsinghua University
  • Peking University
  • Beijing Municipal Science and Technology Commission
  • National Postdoctoral Program for Innovative Talents
  • Institute of Microbiology, Chinese Academy of Sciences
Topics
  • Health Sciences › Medicine › Infectious Diseases › SARS-CoV-2 and COVID-19 Research
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › Circular RNAs in diseases
  • Life Sciences › Agricultural and Biological Sciences › Animal Science and Zoology › Animal Virus Infections Studies
Keywords
SARS-CoV-2, COVID-19 vaccines, SARS-CoV-2 variants of concern, Omicron variant, Delta variant, booster vaccination, vaccine protection
MeSH terms
RNA, Circular, COVID-19, SARS-CoV-2, COVID-19 Vaccines, mRNA Vaccines, Animals, Antibodies, Viral, Humans, Macaca mulatta, Vaccines, Synthetic, Mice, Antibodies, Neutralizing

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