Researchers at the National Institute of Virology in India recently published in the Virology Journal that their experimental vaccine against hepatitis E virus (HEV) infection yielded encouraging results in terms of safety and efficacy in pregnant mice. The study is entitled “Enhanced humoral response in pregnant mice immunized with liposome encapsulated recombinant neutralizing epitope protein of Hepatitis-E virus.”

Hepatitis E is a liver disease caused by the HEV that usually leads to an acute and self-limiting infection that resolves within 4 to 6 weeks, although occasionally, a fulminant form can develop (acute liver failure) leading to death. HEV is mainly transmitted through contaminated drinking water and it is estimated that there are approximately 20 million incidents of hepatitis E infections every year. Pregnant women and liver transplant recipients who receive immunosuppressors are considered to be at higher risk for HEV infection. The virus has been reported to cause a high mortality (around 20%) among pregnant women, especially in the later trimesters.

Currently, candidate vaccines against HEV have not been assessed during pregnancy. Researchers have now analyzed one experimental vaccine developed by the team, the recombinant Neutralizing Epitope protein (rNEp) vaccine candidate, in pregnant mice. Researchers intramuscularly injected a single dose (10 μg) of the vaccine on day 7 of pregnancy and assessed the levels of anti-HEV antibodies and cytokines. The spleen, liver, brain, kidneys and muscle of the animals were analyzed through histopathology.

Researchers found that the vaccine was well-tolerated during pregnancy, without adverse side effects, abnormal biochemical parameters or tissue pathology. Antibodies against HEV were found to be significantly higher in two different pregnant mice strains in comparison to non-pregnant animals. This was an encouraging result for use of the vaccine specifically in pregnant women.

The team also reported a differential activation of immune cells during pregnancy, where an increased number of CD19+ and CD4+ splenocytes (immune cells in the spleen) was found in the pregnant mice. Interestingly, these numbers correlated with higher levels of anti-HEV antibodies. Researchers also found that vertically transferred anti-HEV antibodies could be detected in the pups up to 9 weeks after birth.

The research team concluded that a single dose of the rNEp vaccine candidate was safe, highly immunogenic and capable of inducing high anti-HEV antibody levels during pregnancy in mouse models. Researchers suggest that further in-depth studies should be conducted to better understand the immunological mechanism behind this response, and that the results should be confirmed in higher animals.