A P79S ORF2 variant demonstrates reduced RNA copy numbers released in the supernatant and impaired the production of infectious disease particles, investigators said.
The antiviral agent Ribavirin, which many individuals who are chronically infected with the hepatitis E virus (HEV) receive, can increase the formation of random mutations that coexist with virus variants, according to findings from a study led by investigators from the Department for Molecular and Medical Virology at Ruhr-Universität Bochum.1
Investigators analyzed various mutations of the virus and found that these changes could allow the virus to evade the immune system.1
Ribavirin is the only treatment option for HEV, but there are frequent reports of posttreatment relapses or treatment failure, the study results showed.
Evidence has shown that the therapy was associated with an increase in HEV genome heterogeneity and distinct variants.2
Investigators examined 8 capsid protein variants from samples of individuals with chronic HEV who were treated with ribavirin in the laboratory.1
“While 7 of the investigated mutations behaved exactly like the wild-type virus, we found differences in 1 mutant,” Toni Luise Meister from Ruhr-Universität Bochum, said in a statement.1
The parental HEV strain and 7 patient-derived open reading frame 2 (ORF2) variants all had comparable levels of RNA replication. However a P79S ORF2 variant demonstrated reduced RNA copy numbers that were released in the supernatant and impaired the production of infectious disease particles.2
Furthermore, investigators said that the single-nucleotide variants (SNV) caused defective smaller HEV particles with reduced infectiousness.
P79S also showed an altered subcellular distribution of the ORF2 protein, which was able to interfere with antibody-meditated neutralization of HEV that could “trick” the immune system.1,2
The investigators reported that the viruses with this mutation are not assembled correctly and are smaller than the wild-type virus. The capsid protein is does not accumulate in the cell.1
The particles are not infectious but are correctly recognized and bound by antibodies from the immune system, investigators said.1
The results also indicated that the defective variants could be rescued in infected hepatocytes.2
“This could be an advantage for the virus. These defective particles could potentially catch antibodies, so that there are no longer enough to neutralize correctly assembled, infectious virus particles,” Eike Steinmann from Ruhr-Universität Bochum said in the statement.1
Investigators analyzed 581 HEV-3 genomes that had the 8 ORF2 variants, which were found in between 1% and 29% of individuals with HEV. Investigators examined the influence of the variants on the ability to replicate by introducing different SNVs into the Kernow-C1/p6 strain. Then, they performed reverse-transcription quantitative polymerase chain reaction to the viral RNA.2
The investigators described these defects as “immune decoys” that were present both in vitro and in vivo, even though they were noninfectious.2
Investigators think that their findings could help provide insight and understanding that may guide development of antiviral strategies.2
1. How hepatitis E tricks the immune system. News release. Science Daily. August 17, 2022. Accessed August 19, 2022. https://www.sciencedaily.com/releases/2022/08/220817104023.htm
2. Meister TL, Brüggemann Y, Nocke MK, Ulrich RG, et al. A ribavirin-induced ORF2 single-nucleotide variant produces defective hepatitis E virus particles with immune decoy function. PNAS. 2022;119 (34) e2202653119. doi:10.1073/pnas.2202653119