AN EXPERIMENTAL MUCOSAL VACCINE FOR HEPATITIS E VIRUS

MÜLLER, MELISA FLORENCIA; SACUR, JACINTO ALFREDO; VERA, MARÍA DANIELA; MATIAS BRANCHER, JULIA RAFAELA; ARCE, LORENA PAOLA; VILLENA, JULIO; VIZOSO PINTO, MARÍA GUADALUPE

Mendoza, Argentina

Congreso; Congreso SAIB 2022; 2022

The Hepatitis E virus (HEV) causes hepatitis; its principal port of entry is the gastrointestinalmucosa. Nowadays, there are no vaccines globally available. Our group has been working on aplatform to display antigens on the surface of so-called Bacterium-like-particles (BLP), whichare non-live immunomodulatory bacteria with adjuvant and carrier properties. The main targetfor an HEV vaccine is ORF2, the capsid protein. We cloned ORF2 most immunogenic domain(O2P2) fused to a LysM domain, which in nature mediates attachment of enzymes to bacterialpeptidoglycan, as anchor to expose the antigen on the surface of the BLPs. To evaluate theexperimental vaccines, we immunized mice (n=5) as follows: three oral immunizations with a)the chimeric protein LysM 5 O2P2, b) the chimeric protein displayed on the surface of BLPs(LysM 5 O2P2-BLP) or c) BLP. In a second schedule, we administered the first dosesubcutaneously followed by two oral boosting of d) LysM 5 O2P2 or e) LysM 5 O2P2-BLP. Theimmunizations were performed every 14 days and blood samples were taken each time. Tendays after the last dose, mice were euthanized, and blood and gut fluid were collected toevaluate the humoral response by ELISA. Spleen and Peyer’s patches (PP) were taken to isolatemononuclear cells for an ex vivo stimulation with the capsid antigen, after which, cytokineswere measured by a commercial ELISA on the culture supernatant.Both groups that received oral immunizations produced specific IgG 2 weeks after the firstimmunization, but then, the antibodies were no longer detectable. In contrast, the levels ofspecific anti-HEV IgG in mice receiving one subcutaneous dose followed by oral immunizationsincreased after each dose. Specific IgA was detectable in every group, but it was higher in themice that received oral doses. In every case, the co-administration of the chimeric protein andBLP induced a stronger humoral response. Regarding the cellular response, we measuredhigher amounts of INF-ɤ, TNF-ɑ, IL-4 and IL-17 in the groups that received LysM 5 O2P2-BLPorally or under the mixed schedule. We conclude that the oral schedule induced a knownphenomenon called immune tolerance. This was avoided by giving the first immunizationsubcutaneously. Comparing all groups, the highest humoral response was found in thosegroups which received LysM 5 O2P2-BLP under a mixed schedule. The groups that receivedLysM 5 O2P2-BLP orally or combining subcutaneous and oral administration reached higherlevels of every cytokine measured in comparison with those that received just LysM 5 O2P2,proving the adjuvant effect of BLPs. Here with, we present a promising experimental vaccinethat stimulates systemic as well as mucosal humoral and cellular response against the mainHEV antigen.