Hepatitis E virus: neutralizing sites, diagnosis, and protective immunity

There have been increased attentions on HEV and its associated diseases in recent years as a result of an increased number of reports on autochthonous patients from many developed countries. Vaccine development and better disease management are expected from protective immunity with increased knowledge on the pathogenesis and virology of HEV. This review summarizes the current understanding of the HEV virology, the key neutralization sites (epitopes) on the surface of the viral capsid, the host humoral immune responses for HEV infection, and the protective immunity conferred by natural infection and vaccination. Recombinant VLPs were prepared to mimic the protective and neutralizing epitopes on the virion surface, thus being capable of eliciting protective immunity when injected to nonhuman primates or human volunteers during preclinical tests and clinical trials. Four markers-viral RNA, anti-HEV IgM, anti-HEV IgG, and low avidity of anti-HEV IgG-are important in the diagnosis of HEV infection, particularly for patients presenting with acute hepatitis symptoms. This toolbox of genomic and immunological assays is valuable in furthering our understanding of the time course of HEV infection and the subsequent hepatitis during preclinical and clinical development of an efficacious vaccine. Two vaccine candidates had shown good tolerability, high immunogenicity, and high efficacy against symptomatic and/or asymptomatic HEV infection. One of them has been licensed in China recently. However, many issues need to be resolved before new technological progresses can benefit the people who need them most.