Soluble ORF2 protein enhances HEV replication and induces long-lasting antibody response and protective immunity in vivo

Background and Aims: The HEV is a small positive-sense RNA virus that encodes a cytoplasmic form of the capsid protein (ORF2c), essential for virion structure, and a secreted glycosylated form (ORF2s) that accumulates at high titer in serum and can mask neutralizing epitopes. We explored the contribution of ORF2s to HEV replication and its role in generating antibodies against ORF2 in a nonhuman primate model. Approach and Results: We used a recombinant HEV genotype 3 variant that does not express ORF2s due to the introduction of stop codons (ORF2s(mut)). Rhesus macaques (RMs) were given intrahepatic injections of infectious wildtype HEV (ORF2s(wt)) RNA or a variant lacking ORF2s expression (ORF2s(mut)). The replication of the ORF2s(mut) virus was delayed by similar to 2 weeks compared with ORF2s(wt), and peak titers were nearly tenfold lower. Reversions of the 3 mutations that blocked ORF2s expression were not detected in the ORF2s(mut) genomes, indicating genetic stability. However, serum antibodies against ORF2 were transiently detected in RMs infected with ORF2s(mut,) whereas they were long-lasting in RMs infected with ORF2s(wt). Moreover, RMs infected with ORF2s(mut) were more susceptible to reinfection, as evidenced by the viral RNA detected in fecal samples and the expansion of HEV-specific CD8(+) T cells. Conclusions: These findings indicate that ORF2s may be dispensable for viral replication in vivo but is required for long-lived antibody-mediated responses that protect against HEV re-exposure.

Automated summary

This study investigates the role of ORF2s in HEV replication and antibody generation. The findings suggest that ORF2s may not be essential for viral replication in vivo but is required for the formation of long-lived antibody responses and protection against HEV re-exposure.