A Simplified SARS-CoV-2 Mouse Model Demonstrates Protection by an Oral Replicon-Based mRNA Vaccine

Abstract

A mouse model of SARS-CoV-2 that can be developed in any molecular biology lab with standard facilities will be valuable in evaluating drugs and vaccines. Here we present a simplified SARS-CoV-2 mouse model exploiting the rapid adenoviral purification method. Mice that are sensitive to SARS-CoV-2 infection were generated by transducing human angiotensin-converting enzyme 2 (hACE2) by an adenovirus. The expression kinetics of the hACE2 in transduced mice were assessed by immunohistochemistry, RT-PCR, and qPCR. Further, the ability of the hACE2 to support viral replication was determined in vitro and in vivo. The hACE2 expression in the lungs of mice was observed for at least nine days after transduction. The murine macrophages expressing hACE2 supported viral replication with detection of high viral titers. Next, in vivo studies were carried out to determine viral replication and lung disease following SARS-CoV-2 challenge. The model supported viral replication, and the challenged mouse developed lung disease characteristic of moderate interstitial pneumonia. Further, we illustrated the utility of the system by demonstrating protection using an oral mRNA vaccine. The multicistronic vaccine design enabled by the viral self-cleaving peptides targets receptor binding domain (RBD), heptad repeat domain (HR), membrane glycoprotein (M) and epitopes of nsp13 of parental SARS-CoV-2. Further, Salmonella and Semliki Forest virus replicon were exploited, respectively, for gene delivery and mRNA expression. We recorded potent cross-protective neutralizing antibodies in immunized mice against the SARS-CoV-2 delta variant. The vaccine protected the mice against viral replication and SARS-CoV-2-induced weight loss and lung pathology. The findings support the suitability of the model for preclinical evaluation of anti-SARS-CoV-2 therapies and vaccines. In addition, the findings provide novel insights into mRNA vaccine design against infectious diseases not limiting to SARS-CoV-2.

Oral mRNA Vaccines Against Infectious Diseases- A Bacterial Perspective [Invited]

“…Our proof-of-principle studies using SARS-CoV-2 ( 25 , 81 , 82 ) provide evidence for the development of oral replicon-based mRNA vaccines against infectious diseases. Salmonella is an ideal bacterial vector owing to its unique ability to target GALT upon oral administration, resulting in both systemic and mucosal immune responses in vaccinated individuals.…”

“…Thus, asd serves as a powerful antibiotic-independent selection maker for bacterial delivery. This DNA-launched-mRNA vector design was exploited for the Salmonella- enabled oral delivery of a replicon-based mRNA vaccine against SARS-CoV-2 ( 25 , 81 , 82 ). The detailed mechanism of vector delivery, transgene amplification, and the generation of an immune response upon oral administration of Salmonella carrying the SFV replicon vector encoding vaccine immunogens is furnished in Figure 2 .…”

“…Most importantly, the vaccine protected hamsters against live SARS-CoV-2, and complete protection was elicited by oral immunization against viral replication and lung disease ( 82 ). Moreover, a robust cross-protection against the B.1.617.2 delta variant was evidenced following oral immunization in hamsters ( 82 ) and mice ( 81 ). The fact that an intranasal vaccine durably protected against SARS-CoV-2 variants ( 97 , 98 ) and dimeric IgA had superior neutralizing activity ( 99 ) underscore the efficacy of the mucosal response exerted by oral vaccines in protection against rapidly replicating variants.…”

Targeting primary and metastatic tumor growth in an aggressive breast cancer by engineered tryptophan auxotrophic Salmonella Typhimurium

“…Formalin-fixed paraffin-embedded (FFPE) tumor sections were deparaffinized by immersing in two changes of xylene, followed by one immersion in xylene-alcohol (1:1 ratio) for 3 min each. 49 The sections were rehydrated by immersing in a series of alcohol gradients of 100%, 95%, 75%, and 50% for 3 min each. The sections were washed in tap water and incubated in 3% H 2 O 2 in methanol for 10 min to block endogenous peroxidase activity.…”

Salmonella-mediated oral delivery of multiple-target vaccine constructs with conserved and variable regions of SARS-CoV-2 protect against the Delta and Omicron variants in hamster

“…We previously studied the combination of different targets by designing a multiple-target vaccine consisting of the receptor binding domain (RBD), heptad repeat domain (HR), membrane protein (M) and epitopes of nsp14 of SARS-CoV-2 (V-P2A) using Salmonella delivery system which induced immune response as well as protection efficacy in animal models [ 13 , 15 , 16 ]. Thus, to further explore the different SARS-CoV-2 proteins for potential inclusion in a multiple-target vaccine, we have designed and compared two Salmonella -enabled oral mRNA vaccines targeting the variable and conserved regions of SARS-CoV-2, particularly the RBD, N-terminal domain (NTD), Heptad Repeat (HR), Nucleocapsid (N) protein and selected epitopes of nsp12 (RdRp) in their ability to induce an immune response and protection in the hamster animal model against the Delta and Omicron variants.…”