Oral Immunization with aSalmonella typhimuriumVaccine Vector Expressing Recombinant EnterotoxigenicEscherichia coliK99 Fimbriae Elicits Elevated Antibody Titers for Protective Immunity

Abstract

Bovine enterotoxigenic Escherichia coli (ETEC) continues to cause mortality in piglets and newborn calves. In an effort to develop a safe and effective vaccine for the prevention of F5+ ETEC infections, a balanced lethalasd + plasmid carrying the complete K99 operon was constructed and designated pMAK99-asd +. Introduction of this plasmid into an attenuated Salmonella typhimurium Δaro Δasd strain, H683, resulted in strain AP112, which stably expresses E. coli K99 fimbriae. A single oral immunization of BALB/c and CD-1 mice with strain AP112 elicited significant mucosal immunoglobulin A (IgA) titers that remained elevated for >11 weeks. IgA and IgG responses in serum specific for K99 fimbriae were also induced, with a prominent IgG1, as well as IgG2a and IgG2b, titer. To assess the derivation of these antibodies, a K99 isotype-specific B-cell ELISPOT analysis was conducted by using mononuclear cells from the lamina propria of the small intestines (LP), Peyer’s patches (PP), and spleens of vaccinated and control BALB/c mice. This analysis revealed elevated numbers of K99 fimbria-specific IgA-producing cells in the LP, PP, and spleen, whereas elevated K99 fimbria-specific IgG-producing cells were detected only in the PP and spleen. These antibodies were important for protective immunity. One-day-old neonates from dams orally immunized with AP112 were provided passive protection against oral challenge with wild-type ETEC, in contrast to challenged neonates from unvaccinated dams or from dams vaccinated with a control Salmonella vector. These results confirm that oral Salmonella vaccine vectors effectively deliver K99 fimbriae to mucosal inductive sites for sustained elevation of IgA and IgG antibodies and for eliciting protective immunity.

Enhanced immune responses to viral epitopes by combining macrophage-inducible expression with multimeric display on a Salmonella vector

“…It has been shown recently that fimbriae expressed by Salmonella vaccine strains stimulate a mixed T helper cell response [20,50,51]. Interestingly, a comparison of the anti-987P IgG1/IgG2a ratios of the animals immunized with strains x4550/pCS165 or x4550/pCS173 with the ratios of the animals immunized with strains x4550/ pCS154 or x4550/pCS176 suggests that the former groups developed a biased Th1 response, while the latter groups developed a predominant Th2 response [50 -53].…”

Platform technology to deliver prophylactic molecules orally: An example using the Class A select agent Yersinia pestis

“…Over the past decade, there has been increasing interest in the use of bacteria as mucosal delivery vehicles for vaccine antigens. There are a number of reports of oral vaccine candidates established from genetically modified pathogenic bacteria, such as Salmonella and Listeria [2], [3], [4], [5], [6] or commensal bacteria such as Lactococcus lactis and Lactobacillus species [7], [8], [9], [10]. While both pathogenic and commensal bacteria have advantages and disadvantages as mucosal delivery vehicles, lactic acid bacteria are preferable in terms of safety control and greater public acceptance [8], [11].…”

Immune Response to Lactobacillus plantarum Expressing Borrelia burgdorferi OspA Is Modulated by the Lipid Modification of the Antigen

“…Over the past decade there has been increasing interest in the use of lactic acid bacteria (LAB) as mucosal delivery vehicles for vaccine antigens, microbicides and therapeutics [1]. A number of studies of oral vaccines generated from genetically engineered pathogenic or commensal bacteria have been reported [2], [3], [4], [5], [6], [7], [8], [9], [10], [11]. In humans, Lactobacillus plantarum belongs to the natural flora of the vagina and the gastrointestinal tract.…”