The roles of mesoporous silica and carbon nanoparticles in antigen stability and intensity of immune response against recombinant subunit B of cholera toxin in a rabbit animal model.

Vaccines are the front line in the fight against diseases. However, setbacks with existing cholera vaccines have ignited a considerable effort to develop more suitable vaccine formulations. In this study, we aim to investigate the effect of antigen stability and controlled release in inducing an immune response. Therefore, two types of silica and carbon mesoporous nanoparticles of the same size and shape but different pore architectures were synthesized and loaded with recombinant cholera toxin subunit B to serve as a model for antigen stability and controlled release of antigenic CTB. In order to evaluate immune response efficacy for these model formulations, IgG and IgA responses and fluid accumulation (FA) index were measured in immunized rabbits, which were challenged with wild-type Vibrio cholerae. Our result suggests that mesoporous silica nanoparticles have greater efficacy in inducing mucosal immune responses, and it proved more proficiency in overall immune responses in challenge experiments and FA index (p < 0.05). These findings indicate that mesoporous nanoparticles and, in particular, mesoporous silica nanoparticles, could be used in oral vaccine formulation against cholera.

Mechanisms Underlying the Immune Response Generated by an Oral Vibrio cholerae Vaccine.

Mechanistic details underlying the resulting protective immune response generated by mucosal vaccines remain largely unknown. We investigated the involvement of Toll-like receptor signaling in the induction of humoral immune responses following oral immunization with Dukoral, comparing wild type mice with TLR-2-, TLR-4-, MyD88- and Trif-deficient mice. Although all groups generated similar levels of IgG antibodies, the proliferation of CD4+ T-cells in response to V. cholerae was shown to be mediated via MyD88/TLR signaling, and independently of Trif signaling. The results demonstrate differential requirements for generation of immune responses. These results also suggest that TLR pathways may be modulators of the quality of immune response elicited by the Dukoral vaccine. Determining the critical signaling pathways involved in the induction of immune response to this vaccine would be beneficial, and could contribute to more precisely-designed versions of other oral vaccines in the future.

Cutting edge: the mucosal adjuvant cholera toxin redirects vaccine proteins into olfactory tissues.

We tested the notion that the mucosal adjuvant cholera toxin (CT) could target, in addition to nasal-associated lymphoreticular tissues, the olfactory nerves/epithelium (ON/E) and olfactory bulbs (OBs) when given intranasally. Radiolabeled CT ((125)I-CT) or CT-B subunit ((125)I-CT-B), when given intranasally to mice, entered the ON/E and OB and persisted for 6 days; however, neither molecule was present in nasal-associated lymphoreticular tissues beyond 24 h. This uptake into olfactory regions was monosialoganglioside (GM1) dependent. Intranasal vaccination with (125)I-tetanus toxoid together with unlabeled CT as adjuvant resulted in uptake into the ON/E but not the OB, whereas (125)I-tetanus toxoid alone did not penetrate into the CNS. We conclude that GM1-binding molecules like CT target the ON/E and are retrograde transported to the OB and may promote uptake of vaccine proteins into olfactory neurons. This raises concerns about the role of GM1-binding molecules that target neuronal tissues in mucosal immunity.

[Preparation of oral microspheres carrying V. cholera vaccine and its target's distribution].

To prepare oral biodegradable microspheres carrying V. cholera vaccine, the major outer membrane protein (OMP, MW = 41 kd) as a common antigen of cholera Vibriae was obtained from the classical strain Inaba 569 B, and the OMP was encapsulated in the biodegradable delivery system comprising Poly (DL-Lactide)-Co-Poly(ethylene glycol)microspheres. The average size of the microspheres was less than 5 microns, the amount of OMP encapsulated in microspheres was 15.3%. It was found that microspheres were taken up in Peyer's patches and then distributed in spleen, liver and mesenteric lymph nodes after oral administration.

Live oral vaccines against cholera: an update.

One hundred years elapsed between the first (live, parenteral) cholera vaccine that entered clinical trials in 1885 and the field trials of two oral inactivated cholera vaccines undertaken in Bangladesh in the mid-1980s. The oral inactivated vaccines advanced the art by establishing, convincingly, that oral vaccines could protect (although multiple doses were required) and that (at least in adults) protection could last 3 years. Attenuated Vibrio cholerae O1 strain CVD 103-HgR (deleted of the cholera toxin A subunit gene and harbouring a gene encoding resistance to Hg++) constitutes another significant advance. This live oral vaccine is well tolerated and highly immunogenic in adults and children and highly protective (in adult volunteer challenge studies) following ingestion of of a single dose.