Summary
The goal of the proposed study is to better understand the role of antibodies in HEV infection and determine if
antibodies can prevent or cure chronic hepatitis E virus (HEV) infection. HEV infections are usually self-limited,
but the infections frequently persist when the immune system is compromised and if left untreated, can lead to
serious liver disease. HEV exists in two distinct virion forms: naked virions (nHEV) that are shed into feces and
mediate virus transmission between hosts, and quasi-enveloped HEV (eHEV) virions that circulate in the
bloodstream and mediate virus spread between cells. The eHEV particles lack viral antigens on their surface,
thus they are resistant to circulating HEV-specific antibodies. We previously show that eHEV particles enter cells
via a novel entry mechanism that involves lysosomal degradation of the viral envelope. Our recent data show
that HEV-specific IgG, but not IgM, effectively block eHEV-mediated spread in cell culture. Our central
hypothesis is that antibodies neutralize eHEV intracellularly by preventing virus uncoating in the
endosome/lysosome where the viral membrane degrades. Antibodies generated by natural HEV infection and
vaccination with truncated HEV capsid proteins (CP) are highly protective against HEV infection, while anti-HEV
antibody titers are usually low in patients with chronic HEV infection. Thus, antibodies may have the potential to
prevent or treat chronic HEV infection. Despite these encouragements, there are several significant roadblocks.
First, the C terminus of the HEV CP, which is not present in the current vaccine and the fecal virus, is intact in
the eHEV particles. This is important since structural modeling suggests that the presence of the C terminus of
CP significantly alters the surface structure of the virion which likely makes vaccine-induced antibodies less
effective against eHEV. Second, our recent work indicates that HEV produces a capsid decoy that is secreted
from infected cells in a large quantity and interferes with antibody-mediated neutralization. Third, antibody uptake
by hepatocytes is an inefficient process. Here we propose to overcome these obstacles. Aim 1 will test the
hypothesis that antibodies targeting virions with intact CP will block eHEV-mediated spread more efficiently. We
will determine the structure of authentic HEV virions with intact or cleaved CP and assess if antibodies targeting
virions with intact CP neutralize eHEV more efficiently. We will also determine if glycoengineered antibodies with
enhanced lysosomal targeting neutralize eHEV more efficiently. Aim 2 will test the hypothesis that neutralizing
antibodies that do not bind or bind poorly to the decoy will block HEV spread more efficiently. We will also
determine the structure of the CP decoy in complex with antibodies by cryo-EM to gain a better understanding
of the evasion mechanism by the decoy. The completion of the proposed work will provide novel insights into
the role of antibodies in HEV infection and inform strategies to prevent or cure chronic HEV infection.