From an in vivo to an in vitro relative potency (IVRP) assay to fully characterize a multicomponent O-antigen based vaccine against Shigella

Outer membrane vesicles (OMV) represent an innovative platform for the design of polysaccharide based vaccines. Generalized Modules for Membrane Antigens (GMMA), OMV released from engineered Gram-negative bacteria, have been proposed for the delivery of the O-Antigen, key target for protective immunity against several pathogens including Shigella. altSonflex1-2-3 is a GMMA based vaccine, including S. sonnei and S. flexneri 1b, 2a and 3a O-Antigens, with the aim to elicit broad protection against the most prevalent Shigella serotypes, especially affecting children in low-middle income countries. Here we developed an In Vitro Relative Potency assay, based on recognition of O-Antigen by functional monoclonal antibodies selected to bind the key epitopes of the different O-Antigen active ingredients, directly applied to our Alhydrogel-formulated vaccine. Heat-stressed altSonflex1-2-3 formulations were generated and extensively characterized. The impact of detected biochemical changes in in vivo and in vitro potency assays was assessed. The overall results showed how the in vitro assay can replace the use of animals, overcoming the inherently high variability of in vivo potency studies. The entire panel of physico-chemical methods developed will contribute to detect suboptimal batches and will be valuable to perform stability studies. The work on Shigella vaccine candidate can be easily extended to other O-Antigen based vaccines.

Comparative analysis of outer membrane vesicles from uropathogenic Escherichia coli reveal the role of aromatic amino acids synthesis proteins in motility

Uropathogenic Escherichia coli (UPEC) are causative agent that causes urinary tract infections (UTIs) and the recent emergence of multidrug resistance (MDR) of UPEC increases the burden on the community. Recent studies of bacterial outer membrane vesicles (OMV) identified various factors including proteins, nucleic acids, and small molecules which provided inter-cellular communication within the bacterial population. However, the components of UPEC-specific OMVs and their functional role remain unclear. Here, we systematically determined the proteomes of UPEC-OMVs and identified the specific components that provide functions to the recipient bacteria. Based on the functional network of OMVs' proteomes, a group of signaling peptides was found in all OMVs which provide communication among bacteria. Moreover, we demonstrated that treatment with UPEC-OMVs affected the motility and biofilm formation of the recipient bacteria, and further identified aromatic amino acid (AAA) biosynthesis proteins as the key factors to provide their movement.

Evaluation of a protective effect of in ovo delivered Campylobacter jejuni OMVs

Campylobacter jejuni is the most prevalent cause of a food-borne gastroenteritis in the developed world, with poultry being the main source of infection. Campylobacter jejuni, like other Gram-negative bacteria, constitutively releases outer membrane vesicles (OMVs). OMVs are highly immunogenic, can be taken up by mammalian cells, and are easily modifiable by recombinant engineering. We have tested their usefulness for an oral (in ovo) vaccination of chickens. Four groups of 18-day-old chicken embryos (164 animals) underwent injection of wt C. jejuni OMVs or modified OMVs or PBS into the amniotic fluid. The OMVs modifications relied on overexpression of either a complete wt cjaA gene or the C20A mutant that relocates to the periplasm. Fourteen days post-hatch chicks were orally challenged with live C. jejuni strain. Cecum colonization parameters were analyzed by two-way ANOVA with Tukey post-hoc test. The wtOMVs and OMVs with wtCjaA overexpression were found to confer significant protection of chicken against C. jejuni (p = 0.03 and p = 0.013, respectively) in comparison to PBS controls and are promising candidates for further in ovo vaccine development.