In a recent article posted to the bioRxiv* preprint server, investigators studied a linear deoxyribonucleic acid (linDNA) severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccine option in felines.
SARS-CoV-2, the Coronavirus disease 2019 (COVID-19) pandemic’s etiologic agent, has afflicted a broad range of animal species, particularly mammals, globally from its initial discovery in late 2019 in China. The American Veterinary Medical Association noted that in addition to human-to-human transmission, some pets and wild animals, particularly cats, have shown evidence of human-to-animal SARS-CoV-2 spread.
According to several prior studies, cats are receptive to COVID-19 and are vulnerable to airborne infections, which has shown the value of using animal models in the study of infectious illnesses and emphasized that SARS-CoV-2’s intermediate animal source is still unidentified. Finding ways to break the chain of transmission and lessen the threat of spillover to vulnerable species is essential considering the high transmissibility capability of SARS-CoV-2 to many host species, and the close interaction between animals and humans.
About the study
In the current research, the scientists presented findings from a randomized Phase 1/2 clinical trial in domestic cats using a nucleic acid-based COVID-19 vaccine made of polymerase chain reaction (PCR)-based linDNA. They evaluate the immunogenicity and safety of the linDNA vaccine that contained the SARS-CoV-2 receptor-binding domain (RBD). Moreover, the vaccine was delivered utilizing electro-gene transfer (EGT).
The expression sequence harboring the RBD region of the SARS-CoV-2 spike(S) protein found in the pTK1A-TPA-RBD plasmid was amplified using PCR primers. The template for the PCR-centered linDNA amplicon expression vector production was pTK1A-TPARBD, a plasmid DNA that encodes the RBD area of the SARS-CoV-2 S protein. The authors included a tissue plasminogen activator (tPA) leader sequence for stimulating protein production.
By electroporating either linDNA or a plasmid expressing the RBD region of the SARS-CoV-2 S protein across the skeletal muscle of BALB/c mice, the researchers evaluated the in vivo immunogenicity of the linDNA COVID-19 vaccine. The vaccination protocol involved injecting 6-week-old BALB/c mice with 20 μg of plasmid DNA, ie, 10 μg per quadriceps, or an equimolar linDNA dose, ie, 4,3 μg per quadriceps at day 0 as prime and day 28 as boost with a sacrifice at day 38.
Further, the investigators conducted a randomized phase 1/2 clinical investigation comprising 11 domestic cats to evaluate the effectiveness of the linDNA vaccine in an animal species predisposed to SARS-CoV-2 infection. The vaccination protocol involved administering 1 mg of linDNA intramuscularly twice, on days 0 and 28, and then immediately electroporating the co-localized intramuscular region of each rear leg’s tibialis cranilis.
The team used an enzyme-linked immunosorbent assay (ELISA) to measure anti-RBD immunoglobulin G (IgG) titers after the prime and the boost. Thereby analyzed the immunogenicity of the linDNA vaccine towards the RBD region of SARS-CoV-2 S protein among domestic cats. They investigated the cellular immune reaction generated by the linDNA vaccine in 10 of 11 felines immunized with the prime-boost regimen by using an enzyme-linked immunosorbent spot (ELISpot) analysis on PBMCs procured on days 28 and 56.
The authors noted that the preclinical findings have demonstrated that a linDNA vaccine expressing the SARS-CoV-2 RBD region was immunogenic in mice when given in a prime-boost vaccination regimen because it consistently elicits cellular and humoral immune reactions. The linDNA vaccine was safe and lacked any detrimental side effects when given to cats as part of a prime-boost vaccination program.
Notably, the linDNA COVID-19 vaccine option demonstrated immunogenicity by inducing binding and neutralizing antibodies, the latter of which is necessary to safeguard against live viral shortly after priming against the S RBD of the SARS-CoV-2 ancestral strain and three SARS- CoV-2 variants (P.1, B.1.1.7, and B.1526). In addition, compared to those found against the B.1.526 and P.1 variants, neutralizing titers evaluated against the ancestral SARS-CoV-2 and B.1.1.7 strains were drastically elevated. Furthermore, an RBD-specific T cell reaction to comparable humoral immunity was found shortly after the prime.
Collectively, the study data illustrated that immunizing cats with the current linDNA-based COVID-19 vaccine candidate induces an RBD-selective T cell reaction and produces neutralizing antibodies towards SARS-CoV-2 and its variants. Additionally, there were no notable adverse events. These findings promote the establishment of vaccines for avoiding viral transmission in SARS-CoV-2-vulnerable animals, specifically those in close contact with people, and show the immunogenicity and safety of a genetic vaccination delivered to cats towards COVID-19.
The team mentioned that even though the present cat data support further research, more experiments are required to show that the linDNA vaccination effectively shields larger animals against SARS-CoV-2 challenges.
In conclusion, the current study indicated that the SARS-CoV-2 linDNA vaccine provides an excellent vaccination platform triggering protective substantial T cell reactions and neutralizing antibodies among felines and potentially other vulnerable animal species.
bioRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.
- Antonella Conforti, Elisa Sanchez, Erika Salvatore, Lucia Lione, Mirco Compagnone, Eleonora Pinto, Fabio Palombo, Yuhua Sun, Brian Viscount, James Hayward, Clay Shorrock, Diego G. Diel, Joseph A. Impellizeri, Luigi Aurisicchio. (2022). A linear DNA vaccine candidate encoding the SARS-CoV-2 Receptor Binding Domain elicits protective immunity in domestic cats. bioRxiv. doi: https://doi.org/10.1101/2022.07.20.500860 https://www.biorxiv.org/content/10.1101/2022.07.20.500860v1