DNA vaccine candidate encoding SARS-CoV-2 spike proteins elicited potent humoral and Th1 cell-mediated immune responses in mice

Abstract

More than 65 million people have been confirmed infection with SARS-CoV-2 and more than 1 million have died from COVID-19 and this pandemic remains critical worldwide. Effective vaccines are one of the most important strategies to limit the pandemic. Here, we report a construction strategy of DNA vaccine candidates expressing full length wild type SARS-CoV-2 spike (S) protein, S1 or S2 region and their immunogenicity in mice. All DNA vaccine constructs of pCMVkan-S, -S1 and -S2 induced high levels of specific binding IgG that showed a balance of IgG1/IgG2a response. However, only the sera from mice vaccinated with pCMKkan-S or -S1 DNA vaccines could inhibit viral RBD and ACE2 interaction. The highest neutralizing antibody (NAb) titer was found in pCMVkan-S group, followed by -S1, while -S2 showed the lowest PRNT50 titers. The geometric mean titers (GMTs) were 2,551, 1,005 and 291 for pCMVkan-S, -S1 and -S2, respectively. pCMVkan-S construct vaccine also induced the highest magnitude and breadth of T cells response. Analysis of IFN-γ positive cells after stimulation with SARS-CoV-2 spike peptide pools were 2,991, 1,376 and 1,885 SFC/106 splenocytes for pCMVkan-S, -S1 and -S2, respectively. Our findings highlighted that full-length S antigen is more potent than the truncated spike (S1 or S2) in inducing of neutralizing antibody and robust T cell responses.

DNA Vaccine Administered by Cationic Lipoplexes or by In Vivo Electroporation Induces Comparable Antibody Responses against SARS-CoV-2 in Mice

“…The details of plasmid DNA construction were described in the previous report [ 21 ]. In brief, the humanized codon of cytoplasmic-deleted SARS-CoV-2 spike protein was synthesized by GeneScript (Piscataway, NJ, USA), then subcloned into pCMVkan expression vector, designated as pCMVkan-S. pCMVkan-S was propagated in E. coli DH5-alpha (Invitrogen, Carlsbad, CA, USA) and purified by Qiagen endotoxin-free giga plasmid kit (Hilden, Germany) following the manufacturer’s protocol.…”

“…We previously reported a SARS-CoV-2 DNA vaccine candidate expressing spike (S) protein delivered by intramuscular electroporation (IM-EP) and showing excellent immune response in mice [ 21 ]. As in vivo electroporation is an expensive technique and requires professional personnel, it might not be adapted to a pandemic situation.…”

Mini-Review: SARS-CoV-2 and COVID-19

“…In contrast, dipeptidyl peptidase (DPP)-4 and aminopeptidase N (APN) receptors of other CoVs are not used by SARS-CoV-2 (Zhou, P et al, 2020). DPP-4 is a particular receptor for MERS-CoV (Prompetchara et al, 2020;Wan et al, 2020) while SARS-CoV-2 and SARS-CoV recognize ACE2. In addition, the spikes, RBDs, and RBM (receptor binding motif) of human MERS-CoV and bat MERS-like Covs have a lower similarity in their sequencing proteins (Wan et al, 2020).…”

“…Additionally, the severity of COVID-19 and patient death associated with those changing levels of the neutrophils and lymphocytes (Prompetchara et al, 2020). Titers of IgG and IgM have recorded an elevated level in the serum of SARS-CoV-2 patients (Zhou,P et al, 2020).…”

“…The ongoing reported common symptoms of COVID-19 are fever, dry cough, throat sore, dyspnea, and fatigue (Cheng et al, 2020;Huang et al, 2020;Wang et al, 2020). The incubation period of the disease ranges from 2 to 14 days, however, 80% of the patients had mild or asymptomatic illness while 15 % and 5% of the patients had exhibited sever and critical cases respectively (Prompetchara et al, 2020;Rokni et al,2020). Asymptomatic persons have a role in spreading SARS-CoV-2, yet they suffer from the symptoms 14 days after the viral infection (Al-Tawfiq, 2020;Rothe et al, 2020).…”