Development of Polymeric Carriers Having M Cell Homing Peptide for Targeted Oral Vaccine Delivery

Abstract

Compared to other administrative route, oral delivery of vaccine has been received considerable attraction due to providing patient compliances, easy handling, low cost of production, eliminating the injection pain and infection risks, and exerting both systemic and local immune responses. However, low oral bioavailability, degradation in acidic stomach and by gastric enzymes limit the applications of orally delivered drugs including vaccine and probiotics. Polymeric delivery carriers offer potential benefits to limit afore-mentioned problems by protecting the incorporated bioactive agents from the harsh gastric environments. In the first approach, M cells, the key players of the mucosal immunity induction, are one of the intestinal factors for the efficient delivery of vaccines to mucosal immune tissues. To get M cell targeting, we have developed an efficient oral vaccine carrier that constitutes poly (lactic-co-glycolic acid) (PLGA) microparticle coated with M cell targeting peptide. In this study, a membrane protein B of Brachyspira hyodysenteriae (BmpB) as a model vaccine against swine dysentery was loaded into porous PLGA microparticles (MPs). The PLGA MPs was further coated with the water-soluble chitosan (WSC) conjugated with M cell homing peptide (CKS9) to prepare BmpB-CKS9-WSC-PLGA MPs. Oral immunization of BmpB vaccine with CKS9-WSC-PLGA MPs in mice showed elevated secretory IgA (sIgA) responses in the mucosal tissues and systemic IgG antibody responses, providing an efficient immune response. Specifically, the immunization with these MPs demonstrated to induce both Th1- and Th2-type responses based on elevated IgG1 and IgG2a titers. The elevated immune responses were attributed to the enhanced M cell targeting and transcytosis ability of CKS9-WSC-PLGA MPs to Peyers patch regions. The high binding affinity of CKS9-WSC-PLGA MPs with the M cells to enter into the Peyer's patch regions of mouse small intestine was obtained by closed ileal loop assay and it was further confirmed by confocal laser scanning microscopy. These results suggest that the M cell targeting approach used in this study is a promising tool for targeted oral vaccine delivery. In the second approach, oral administration of live probiotics as antigen delivery vectors was studied as a promising approach in vaccine development. However, the low survival of probiotics in the gastrointestinal tract limits this approach. Therefore, the aim of this study was the encapsulation of probiotic expressing vaccine into alginate/chitosan/alginate (ACA) microcapsules (MCs) for efficient oral vaccine delivery. Here, recombinant Lactobacillus plantarum 25 (LP25) expressing M cell homing peptide fused BmpB protein was used as a model probiotic. The viability of LP25 in ACA MCs was more than 65% in simulated gastric fluid (SGF, pH 2.0) and 75% in simulated small intestinal fluid (SIF, pH 7.2) up to 2 h. Encapsulated LP25 were completely released from ACA MCs in SIF within 12 h. When stored at room temperature (RT) or 4°C, the viability of LP25 in ACA MCs was higher than free LP25. Interestingly, the viability of LP25 in ACA MCs at 4°C for 5 weeks was above 58%, whereas viability of free LP25 stored at RT for 5 weeks was zero. After 4 weeks from the first immunization, LP25-M-BmpB-loaded ACA MCs induced a stronger BmpB-specific IgG and IgA production in mice. Collectively, these findings suggest that encapsulation of probiotic by ACA MCs is a promising delivery system for oral administration of probiotic expressing vaccine.