Gas-filled microbubbles: Novel mucosal antigen-delivery system for induction of anti-pathogen's immune responses in the gut

Abstract

Despite important success in protecting individuals against many pathogenic infections, parenteral vaccination is not optimal to induce immunity at the site of pathogen entry, i.e. mucosal surfaces. Moreover, designing adequate delivery systems and safe adjuvants to overcome the inherent tolerogenic environment of the mucosal tissue is challenging, in particular in the gastrointestinal tract prone to antigen degradation. We recently demonstrated that intranasal administration of a Salmonella-derived antigen associated with gas-filled microbubbles induced specific Ab and T cell responses in the gut and was associated with a reduction in local and systemic bacterial load after oral Salmonella infection. Building on these promising data, the adequate choice of antigen(s) to be administered and how to make it suitable for possible human application are discussed. We additionally present novel data dealing with oral administration of microbubbles and describe research strategies to direct them to mucosal sampling/inductive sites.

Keywords: enteropathogen infections; gut immune responses; microparticles; mucosal vaccine; nasal administration; oral administration.

Figure 1.

Gut immune responses induced by intranasal administration of SseB-MBs. Female Balb/c mice (8–10 weeks of age) were intranasally immunized for 3 consecutive days a week for 4 weeks with the indicated SseB formulations, corresponding to a total of 3 μg SseB administered per week. The prototypic murine mucosal adjuvant cholera toxin (CT; 2 μg per administration) was used as control. (A) Cytokine production measured by ELISA in the culture supernatant of PP cell suspensions restimulated in vitro for 72 h with 10 μg/ml SseB. (B) SseB-specific Ab responses measured by ELISA in feces. n = 6 mice per group. The unpaired, nonparametric Kruskal-Wallis test, corrected with Dunn's test for multiple comparisons, was applied to compare the indicated experimental groups. ns, non-significant; *, p < 0.05; **, p < 0.01; ***, p < 0.001.

Figure 2.

MBs cross the intestinal epithelium and are taken up by PP DCs. Plain or fluorescent MBs (1 × 10⁸) were injected in mouse ligated intestinal loops (8–10 weeks old female Balb/c mice). After 1h, PPs included in the loops were processed to cell suspensions, stained with the DC-specific marker CD11c and analyzed by flow cytometry (n = 3 mice). One representative image is depicted.

Figure 3.

Gut immune responses induced by oral administration of SseB-MBs. Female Balb/c mice (8–10 weeks of age) were immunized intragastrically once a week for 4 weeks with the indicated SseB formulations corresponding to a total of 6 μg SseB administered per week. The SseB + cholera toxin group (CT; 2 μg per administration) was used as control. (A) Cytokine production measured by ELISA in the culture supernatant of PP cell suspensions restimulated in vitro for 72 h with 10 μg/ml SseB. (B) T cell proliferative responses in mesenteric LNs (CFSE-based assay; restimulation of cells with 10 μg/ml SseB for 4 days) and cytokine production measured by ELISA in the culture supernatant of mesenteric LN cell suspensions restimulated in vitro for 72 h with 10 μg/ml SseB. (C) Ab responses measured by ELISA in feces. n = 3 mice per group.