COVID-eVax, an electroporated plasmid DNA vaccine candidate encoding the SARS-CoV-2 Receptor Binding Domain, elicits protective immune responses in animal models of COVID-19

Abstract

The COVID-19 pandemic caused by the β-coronavirus SARS-CoV-2 has made the development of safe and effective vaccines a critical global priority. To date, four vaccines have already been approved by European and American authorities for preventing COVID-19 but the development of additional vaccine platforms with improved supply and logistics profiles remains a pressing need. Here we report the preclinical evaluation of a novel COVID-19 vaccine candidate based on the electroporation of engineered, synthetic cDNA encoding a viral antigen in the skeletal muscle, a technology previously utilized for cancer vaccines. We constructed a set of prototype DNA vaccines expressing various forms of the SARS-CoV-2 Spike (S) protein and assessed their immunogenicity in animal models. Among them, COVID-eVax – a DNA plasmid encoding a secreted monomeric form of SARS-CoV-2 S protein RBD – induced the most potent anti-SARS-CoV-2 neutralizing antibody responses (including against the current most common variants of concern) and a robust T cell response. Upon challenge with SARS-CoV-2, immunized K18-hACE2 transgenic mice showed reduced weight loss, improved pulmonary function and significantly lower viral replication in the lungs and brain. COVID-eVax conferred significant protection to ferrets upon SARS-CoV-2 challenge. In summary, this study identifies COVID-eVax as an ideal COVID-19 vaccine candidate suitable for clinical development. Accordingly, a combined phase I-II trial has recently started in Italy.

Enhancing Immune Responses against SARS-CoV-2 Variants in Aged Mice with INDUK: A Chimeric DNA Vaccine Encoding the Spike S1-TM Subunits

“…Future studies aimed at exploring the durability of the cellular immune response elicited by INDUK in aged mice will help to further characterize its immunogenic properties. Another limitation of the present study is that INDUK immunogenicity has been studied only in a mouse model, the C57BL/6 mouse, while further evaluation in other experimental models such as rats and larger animals such as ferrets, which are considered valuable models for SARS-CoV-2 research, 38,39 might be beneficial. Although INDUK includes key mutations from Delta and Alpha SARS-CoV-2 variants that are not anymore circulating, the dominant D614G substitution and N501Y mutation are still present in currently circulating Omicron variants, while residues 484 and 452 are also mutated in some Omicron subvariants.…”

Immunogenicity of COVID-eVax Is Moderately Impacted by Temperature and Molecular Isoforms

“…Briefly, Maxisorp 96-well plates (Nunc) were coated with 1 ug/ml of the anti-RBD antibody 5B7 (generated in Takis) in PBS1X overnight at 4 °C, and after a wash in PBS1X-Tween 0.05% (PBST), they were blocked with 3% BSA-PBST 1 h at RT in agitation. Scalar doses of each supernatant in 1% BSA-PBST were added, and purified RBD [3] was used as the reference standard control. After o/n incubation at 4 °C, plates were washed and the SARS-CoV spike antibody, Rabbit PAb, Antigen Affinity Purified (Sino biological Cat: 40150-T62-COV2 100) was added and incubated for 3 h at RT.…”

“…The ELISA assay was performed as previously reported [3]. Briefly, the plates were functionalized by coating the RBD-6xHis protein and blocked with 3% BSA-0.05% Tween 20-PBS.…”

“…To evaluate the impact of DNA integrity on the immune response induced by electroporation delivery, C57/B6 mice were vaccinated with COVID-eVax DNA treated as reported in Figure 2. This vaccination protocol was published recently with a prime injection followed by a boost at Day 28 [3]. One week after the boost, spike-specific T-cell responses were evaluated in the spleen upon overnight stimulation with the peptide pool covering the entire RBD sequence of the spike protein.…”

“…Recently, we have completed a phase I clinical trial with COVID-eVax (NCT04788459), a naked plasmid DNA expressing the receptor binding domain (RBD) of the SARS-COV-2 spike protein, delivered by electroporation (EP). COVID-eVax has shown potent immunologic efficacy and protection in preclinical models of infections [2,3]. In addition to the DNA-EP delivery [4,5], naked DNA has been historically administered as such [6], by air pressure or complexed with different carriers [7].…”