Immunogenicity of a spike protein subunit-based COVID-19 vaccine with broad protection against various SARS-CoV-2 variants in animal studies
Ming-Chen Yang, Chun-Chung Wang, Wei-Chien Tang, Kuan-Ming Chen, Chu-Ying Chen, Hsiao-Han Lin, Yin-Cheng Hsieh, Nan-Hsuan Wang, Yin-Chieh Kuo, Ping-Tzu Chu, Hsin-Yi Tung, Yi-Chen Wu, Juo-Ling Sun, Sheng-Yu Liu, Wan-Fen Li, Wei-Han Lee, Jiann-Shiun Lai, Michael Chang †, Ming-Tain Lai
Abstract
SARS-CoV-2 pandemic has profound impacts on human life and global economy since the outbreak in 2019. With the new variants continue to emerge with greater immune escaping capability, the protectivity of the available vaccines is compromised. Therefore, development a vaccine that is capable of inducing immunity against variants including omicron strains is in urgent need. In this study, we developed a protein-based vaccine BCVax that is consisted of antigen delta strain spike protein and QS21-based adjuvant AB801 in nanoparticle immune stimulation complex format (AB801-ISCOM). Results from animal studies showed that high level of anti-S protein IgG was induced after two doses of BCVax and the IgG was capable of neutralizing multiple variants of pseudovirus including omicron BA.1 or BA.2 strains.
Introduction
Since the outbreak of SARS-CoV-2 pandemic occurred in Dec. 2019, there are over 757 million confirmed cases and 6.8 million deaths of the world, as of 2023 Feb. The persistence and wide spread of this pandemic greatly impact global economy and public health. Tremendous endeavors have been taken to develop vaccines to control the pandemic. Up to date, as many as 34 vaccines have been authorized as either a primary vaccination or booster [1–4]. However, constantly evolution of the virus renders the emergence of several variants in less than two years such as alpha, beta, gamma, delta, and the current dominant omicron strains [5, 6]. Given that most of the COVID-19 vaccines were developed based on wild type strain, the emerged variants are capable of escaping the induced immune responses, thus compromising the protectivity of the vaccines. Lopez Bernal reported that the effectiveness of vaccine after one dose was notably lower against delta variant compared to alpha variant infection [7].
Material and methods
Delta strain S protein expression and purification
The S protein DS2P employed in this manuscript (sequence ID: GenBank QWK65230.1, SARS-CoV-2 lineage B.1.617.2) were mutated at specific sites for abolishment of cellular furin cleavage [19] and for protein stabilization in culture system to ensure steady production. The mutation sites include T19R, G142D, Δ156–157, R158G, L452R, T478K, D614G, P681R, D950N. DS2P was the fusion of ectodomain of delta SARS-CoV-2 spike protein (amino acid residues 14 to 1219) with 2 proline substitutions (K986P and V987P) [20] and 6x His tag. A human rhinovirus 3C protease (HRV3C) recognition sequence was inserted into the sequences between spike protein and His tag to facilitate the removal of His tag after purification. The sequence scheme is shown in Fig 1A. DNA sequence encoding DS2P was codon optimized for CHO cells and synthesized in-vitro by Genewiz. The DNA was then ligated into pcDNA3.4 expression vector (Thermo Fisher Scientific) using NEBuilder DNA Assembly kit (New England Biolabs).
Results
Characteristics of antigen delta S protein
The design of protein sequence for delta S protein production is shown in Fig 1A. The His-tag sequence was included to facilitate the purification of the protein. In addition, a sequence containing HRV3C cleavage site was inserted into the region between spike protein and His-tag. The cDNA sequence corresponding to delta strain SARS-CoV-2 S protein shown in Fig 1A was cloned into pcDNA3.4 plasmid for transient ExpiCHO cell expression. The secreted S protein was collected through centrifugation followed by purification with Ni-affinity column. The His tag was removed through proteolytic cleavage by HRV3C.
Discussion
COVID-19 delta strain began to emerge in the late 2020 and quickly became the most deadly variant of the virus. It is reported to be less sensitive to convalescent or vaccination induced antibodies [28–31]. With the emergence of omicron strain in late 2021, it quickly became the dominant strain worldwide. Despite the fast spread, most of the omicron cases were found to have mild symptoms, while the delta strain is still the strain poses the highest risk of disease severity [32–34]. Another potential threat of delta strain comes from the possibility of “deltacron” strain to emerge, especially an actual deltacron case was reported in China in Apr 2022 [35]. A study conducted in Israel indicated that the crypt circulation of delta strain during omicron dominant period [36].
Acknowledgments
We thank the National RNAi Core Facility at Academia Sinica in Taiwan for providing pseudovirus neutralization assay services.
Citation: Yang M-C, Wang C-C, Tang W-C, Chen K-M, Chen C-Y, Lin H-H, et al. (2023) Immunogenicity of a spike protein subunit-based COVID-19 vaccine with broad protection against various SARS-CoV-2 variants in animal studies. PLoS ONE 18(3): e0283473.
https://doi.org/10.1371/journal.pone.0283473
Editor: Etsuro Ito, Waseda University: Waseda Daigaku, JAPAN
Received: December 8, 2022; Accepted: March 8, 2023; Published: March 24, 2023
Copyright: © 2023 Yang et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Data Availability: All relevant data are within the paper and its Supporting Information files.
Funding: The author(s) received no specific funding for this work.
Competing interests: The authors have declared that no competing interests exist.
https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0283473#abstract0
