Assessment of Lactobacillus gasseri as a Candidate Oral Vaccine Vector

Abstract

Lactobacillus species are commensal bacteria that have long been recognized as probiotic microbes and are generally regarded as safe (GRAS) for human consumption. We have investigated the use of L. gasseri as a vaccine vector for oral immunization against mucosal pathogens. Recent research has shown that the immune response to different lactobacilli can vary widely depending on the species or subspecies of Lactobacillus being studied. While some lactobacilli seem to induce oral tolerance, others induce an adaptive immune response. This study characterized the systemic and mucosal immune response to wild-type and genetically modified L. gasseri. L. gasseri primarily activates TLR2/6, with additional activation through the TLR2 homodimer. To expand the Toll-like receptor (TLR) activation profile of L. gasseri and the immunogenicity of the vector, a plasmid containing fliC, the gene encoding bacterial flagellin, was introduced which resulted in the strong activation of TLR5. The treatment of human myeloid dendritic cells with recombinant lactobacilli expressing flagellin triggered phenotypic maturation and the release of proinflammatory cytokines. In contrast, bacterial treatment also resulted in a statistically significant increase in IL-10 production. In vivo studies established that treatment with L. gasseri led to a diversification of B-cell populations in the lamina propria of the murine colon. Furthermore, treatment with genetically modified L. gasseri led to a significant decrease in the percentage of FoxP3 ؉ colonic lymphocytes. Taken together, these data clarify the interaction of L. gasseri with the host immune system and support further investigation of the in vivo immunogenicity of L. gasseri expressing both flagellin and candidate vaccine antigens.Several species of lactobacilli have been investigated as antigen delivery vehicles against a spectrum of infectious agents, including Helicobacter pylori, tetanus, enterotoxigenic Escherichia coli, severe acute respiratory syndrome (SARS)-associated coronavirus, rotavirus, Brucella abortis, and human papillomavirus (reviewed in reference 34). Despite the growing evidence that lactobacilli are useful as vaccine vectors (21), it is increasingly clear that different species and even subspecies of lactobacilli interact distinctly with the host immune system (1, 32). Several studies have analyzed the abilities of various Lactobacillus species to induce dendritic cell (DC) maturation and cytokine production, showing a range of outcomes that appear to favor tolerance on one end of the spectrum and immune activation on the other (7, 22). There also are clear differences in the ability of lactobacilli species to survive the hostile environment of the upper gastrointestinal (GI) tract and colonize the lower GI tract. Functional genomic studies have greatly improved our understanding of some of these characteristics, but much less is known about the molecular and genetic basis of host immunomodulation by Lactobacillus species. One strategy to develop lactobacilli as va...

Construction and Immunological Evaluation of Dual Cell Surface Display of HIV-1 Gag and Salmonella enterica Serovar Typhimurium FliC in Lactobacillus acidophilus for Vaccine Delivery

“…Single-cell suspensions of spleen and Peyer's patch cells were prepared by mashing the tissues with the plunger end of syringes and filtering through cell strainers. Lymphocytes from the colon and female reproductive tract were isolated in accordance with the procedure described previously (35). The care and use of experimental animals complied with the guidelines of North Carolina State University.…”

“…Untested human blood buffy coats were obtained from the American Red Cross (Durham, NC). Human myeloid dendritic cells (DCs) were isolated in accordance with the method described previously (35). In brief, lymphocytes were separated from whole blood using Ficoll-Plaque Plus (GE Healthcare) and centrifugation.…”

“…The reporter assay using TLR5-expressing HEK293 cells was described previously (35). Freshly prepared bacteria were added to the culture of TLR5-expressing cells and incubated for 48 h. TLR5 activation was determined by NF-B induction using the secreted embryonic alkaline phosphatase (SEAP) pNiFty reporter plasmid (InvivoGen, San Diego, CA).…”

Development of an integration mutagenesis system inLactobacillus gasseri

“…Specifically, L. gasseri exhibits bile resistance, adhesion to Caco-2 intestinal epithelial cells, antimicrobial activity, the ability to degrade oxalate, and immunomodulatory properties. 1,[9][10][11] Consumption of L. gasseri has been associated with health benefits substantiated by randomized human clinical trials, such as the capacity to reduce severity and duration of symptoms associated with acute diarrhea and upper respiratory viral infections alike, as well as suppression of Helicobacter pylori infection and maintenance of vaginal homeostasis. [12][13][14] Given the considerable potential of L. gasseri for probiotic applications, this species warrants genetic efforts to correlate genotypes with phenotypic traits potentially impacting health and well-being.…”

Directional Activation of Intestinal Dendritic Cells by Oral Targeted Multivalent Vaccine

“…Using L. gasseri, our laboratory has been able to deliver the protective antigen (PA) of Bacillus anthracis to vaccinated mice to resist this potential agent of bioterrorism [2]. Additionally, another group has used L. gasseri for successful delivery of Salmonella antigens [9].…”