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

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.

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 ~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.

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.