Cloning, expression, and proliferation of the S2 Gene of SARS-CoV-2 in Lactococcus lactis for recombinant vaccine design

The widespread and persistent COVID-19 pandemic, caused by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), remains a serious global health threat and continues to place a heavy burden on humanity. Currently, several intramuscular vaccines have been successfully developed, and mass vaccination programs have progressed in many countries. There is growing evidence supporting the use of recombinant probiotics, particularly lactic acid bacteria (LAB), as vaccine carriers. Given the crucial role of the SARS-CoV-2 spike (S) glycoprotein in viral attachment, entry, and induction of neutralizing antibodies, the S protein has been widely targeted for vaccine development. This study aimed to clone and express the S2 subunit gene of the spike protein in Lactococcus lactis.

In this study, the S2 gene, which had been previously amplified and cloned into the pWPI plasmid, was used. The gene was amplified by PCR and subsequently isolated and cloned into the pJET-1.2/blunt plasmid as an intermediate step, then transferred to E. coli DH5α for improved preservation. The S2 gene was then excised from pJET-1.2/blunt, cloned into the pNZ8149 plasmid, and transferred to Lactococcus lactis NZ39000 for gene amplification and expression.

The results demonstrated that the S2 gene (1432 bp) was successfully amplified, isolated, and cloned into the pNZ8149 plasmid. Following its transfer to L. lactis NZ39000, the S2 protein was expressed and detected as a 51 kDa band on SDS-PAGE.

The findings suggest that transferring pathogenic viral genes into beneficial gut bacteria (LAB) may provide a promising strategy for developing oral vaccine candidates.