Specific memory B cell response and participation of CD4+ central and effector memory T cells in mice immunized with liposome encapsulated recombinant NE protein based Hepatitis E vaccine candidate

Abstract

BackgroundLiposome encapsulated neutralizing epitope protein of Hepatitis E virus (HEV), rNEp, our Hepatitis E vaccine candidate, was shown to be immunogenic and safe in pregnant and non-pregnant mice and yielded sterilizing immunity in rhesus monkeys. MethodsThe current study in Balb/c mice assessed the levels and persistence of anti-HEV IgG antibodies by ELISA, frequencies of B, memory B, T and memory T cells by flow cytometry and HEV-specific IgG secreting memory B cells by ELISPOT till 420days post immunization (PI) with 5μg rNEp encapsulated in liposome based adjuvant (2 doses, 4weeks apart). Mice immunized with a lower dose (1μg) were assessed only for anamnestic response post booster dose. ResultsVaccine candidate immunized mice (5μg dose) elicited strong anti-HEV IgG response that was estimated to persist for lifetime. At day 120 PI, frequency of memory B cells was higher in immunized mice than those receiving adjuvant alone. Anti-HEV IgG titers were lower in mice immunized with 1μg dose. A booster dose yielded a heightened antibody response in mice with both high (>800GMT, 5μg) and low (⩽100GMT, 1μg) anti-HEV IgG titers. At day 6th post booster dose, HEV-specific antibody secreting plasma cells (ASCs) were detected in 100% and 50% of mice with high and low anti-HEV IgG titers, respectively, whereas the frequencies of CD4+ central and effector memory T cells were high in mice with high anti-HEV IgG titers only. ConclusionsTaken together, the vaccine candidate effectively generates persistent and anamnestic antibody response, elicits participation of CD4+ memory T cells and triggers memory B cells to differentiate into ASCs upon boosting. This approach of assessing the immunogenicity of vaccine candidate could be useful to explore the longevity of HEV-specific memory response in future HEV vaccine trials in human.