Oral immunization with a <italic>Lactobacillus casei</italic>‐based anti‐porcine epidemic diarrhoea virus (PEDV) vaccine expressing microfold cell‐targeting peptide Co1 fused with the COE antigen of PEDV.

Abstract: Aims: The aims of this study were to develop an effective M cell‐targeting oral vaccine, involving <italic>Lactobacillus casei</italic> to deliver the porcine epidemic diarrhoea virus (PEDV) core neutralizing epitope (COE) antigen conjugated with M cell‐targeting peptide Co1 as an adjuvant, against PEDV infection. Methods and Results: Genetically engineered <italic>L. casei</italic> 393 (L393) strains expressing PEDV COE antigen only (pPG‐COE/L393) or fused‐expressing COE and M cell‐targeting peptide Co1 (pPG‐COE‐Co1/L393) were constructed, and the immunogenicity upon administration as an oral vaccine was evaluated. The results showed that higher anti‐PEDV serum IgG and mucosal SIgA antibody responses were induced in mice orally immunized with strain pPG‐COE‐Co1/L393 as compared to the mice immunized with strain L393 expressing COE alone or carrying the empty plasmid. In addition, the use of the Co1 ligand elicited a splenocyte proliferative response more effectively in comparison with the COE antigen alone and supported a skewed T helper 2 type of immune response against PEDV. Conclusions: pPG‐COE‐Co1/L393 can effectively induce mucosal, humoural and Th2‐type cellular immune responses against PEDV infection via oral administration. Furthermore, M cell‐targeting peptide ligand Co1 is a good mucosal adjuvant. Significance and Impact of the Study: <italic>Lactobacillus casei</italic> delivering the COE antigen of PEDV conjugated with a M cell‐targeting peptide Co1 as an immune adjuvant is a promising oral vaccine candidate for PEDV. [ABSTRACT FROM AUTHOR]