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

Abstract

The declaration of the conclusion of the COVID-19 pandemic notwithstanding, coronavirus remains prevalent in circulation, and the potential emergence of novel variants of concern introduces the possibility of new outbreaks. 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 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. 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.

Evaluation of Immune Response to Mucosal Immunization with an Oral Probiotic-Based Vaccine in Mice: Potential for Prime-Boost Immunization against SARS-CoV-2

“…The capability of recombinant probiotics to stimulate T-cell-mediated immune responses, in addition to IgG and sIgA production, broadens their potential and offers new opportunities for protection against viral infections [ 57 , 58 , 59 ], including the current SARS-CoV-2 infection [ 26 ].…”

“…This viral antigen integrated into the structure of bacterial pili was able to evoke both innate and adaptive immune responses in experimental animals. Studies on Syrian hamsters demonstrated that recombinant vaccine strains, derived from the probiotic strain E. faecium L3 and expressing an immunogenic fragment of the S1 protein of the coronavirus, are both safe and capable of effectively suppressing SARS-CoV-2 infection in laboratory hamsters following oral vaccination [ 26 ].…”