SARS-CoV-2 Spike Protein-Expressing Enterococcus for Oral Vaccination: Immunogenicity and Protection

Abstract

The COVID-19 pandemic was declared in March 2020 and is still ongoing. The course of the epidemic remains uncertain, and mutations in the coronavirus, as well as the emergence of new variants of concern, make it possible that there will be periodic surges in the number of cases. Moreover, it is not clear how quickly and to what extent the effectiveness of vaccination will decline as the virus continues to mutate.
 One possible solution to combat the rapidly mutating coronavirus is the development of pan-coronavirus vaccines that stimulate the production of antibodies against conserved elements of the virus. Another approach could be the creation of safe vaccine platforms that can be rapidly adapted to deliver new, specific antigens in response to viral mutations.
 Recombinant probiotic microorganisms that can produce viral antigens by inserting specific viral DNA fragments into their genome show promise as a platform and vector for mucosal vaccine antigen delivery. With a well-established safety profile and the ability to transform into vaccine candidates, probiotic bacteria have significant research potential.
 The authors of this study have developed a convenient and universal technique for inserting the DNA sequences of pathogenic bacteria and viruses into the gene that encodes the pili protein of the probiotic strain E. faecium L3. The paper presents data on the immunogenic properties of two E. faecium L3 vaccine strains, which produce two different fragments of the coronavirus S1 protein, and provides an assessment of the protective efficacy of these oral vaccines against coronavirus infection in Syrian hamsters.