Live Vector-based Mucosal Vaccine Delivery Approach against Campylobacter jejuni

Gorain, Chandan (2024) Live Vector-based Mucosal Vaccine Delivery Approach against Campylobacter jejuni. PhD thesis, Indian Institute of Science Education and Research Kolkata.

Text (PhD thesis of Chandan Gorain (17RS059))) 17RS059.pdf - Submitted Version Restricted to Repository staff only Download (9MB)

Abstract

Campylobacter jejuni (C. jejuni) is accountable for more than 400-500 million cases of gastroenteritis each year and is listed as a high-priority gut pathogen by the World Health Organization (WHO). Although the acute infection of C. jejuni (campylobacteriosis) is commonly treated with macrolides and fluoroquinolones, the emergence of antibiotic resistance among C. jejuni warrants an alternative approach to control Campylobacter infection. To this end, vaccines remain a safe, effective, and widely accepted strategy for combating emerging and re-emerging infectious diseases. Successful colonization of the mucosal epithelial cells is the key early step for C. jejuni pathogenesis in humans. A set of Surface Exposed Colonization Proteins (SECPs) are known to play a leading role in bacterial adhesion and subsequent host pathogenesis. Among the major SECPs, the constitutively expressed C. jejuni surface lipoprotein Jejuni lipoprotein A (JlpA) interacts with intestinal heat shock protein 90α (Hsp90α) and contributes to disease progression by triggering pro-inflammatory responses via activation of NF-κB and p38 MAP kinase pathways. In addition to its ability to express on the surface, the high sequence conservation of JlpA protein among different Campylobacter spp. makes it a suitable vaccine target against C. jejuni. Given that chickens are the primary source of C. jejuni transmission to humans and persistent cecal colonization in avian gut significantly contributes to pathogen transmission, we explicitly used chickens as a model to test the immune-protective efficacy of JlpA protein. Since the gastrointestinal tract is the major site for C. jejuni colonization, we chose to use the mucosal (intragastric) route as the mode of JlpA antigen delivery. To deliver JlpA via the mucosal route, we engineered a food-grade lactic acid-producing bacteria (LAB), Lactococcus lactis (L. lactis), to express functionally active JlpA protein on the surface. Finally, we demonstrated its ability to substantially improve the antigen-specific local immune responses in the intestine along with significant immune protection against enteric colonization of C. jejuni in chickens. Since C. jejuni adhesion is a multifactorial process and several factors, including other major SECPs and effector proteins, are essential in active adherence, colonization, and subsequent pathogenesis, we also explored the potential of Haemolysin co-regulated protein (Hcp) of Type VI Secretion System (T6SS) of C. jejuni in imparting immune-protection against C. jejuni. Since the clinical features of human campylobacteriosis are more complicated than the avians, we investigated the vaccine potential of Hcp in a murine host as a more reliable and reproducible in vivo model against C. jejuni. Because C. jejuni primarily utilizes the mucosal route for host pathogenesis, we analyzed the immunogenicity of a mucosally deliverable L. lactis expressing Hcp. Considering the role of Hcp in both structural (membrane-bound) and functional (effector protein) exhibition of C. jejuni T6SS, a head-to-head comparison of two different forms of recombinant LAB vectors (cell wall anchored and secreted form of Hcp) was tested and assessed the immune phenotypes of each system in BALB/c mice. We show that regardless of the Hcp protein localization, mucosal delivery of bioengineered LAB vector expressing Hcp can induce high-level production of antigen-specific neutralizing antibody (sIgA) in the gut and reduce the cecal load of C. jejuni in mice. Together with the non-commensal nature of L. lactis, short gut transit time, and ability to express the heterologous protein, the present study highlights the benefits of bioengineered LAB vectors-based mucosal vaccine modality against C. jejuni without the risk of immunotolerance.

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