Evaluation and Immunogenicity of Combined Liposome-Based Vaccine Candidates against Hepatitis E and B Viruses in Rhesus Monkeys.

The administration of vaccines using a combination approach ensures better coverage and reduces the number of injections and cost. The present study assessed liposome-complexed DNA-corresponding proteins of hepatitis E and B viruses (HEV and HBV) as combined vaccine candidates in rhesus monkeys. The HEV and HBV components consisted of 450 bps, neutralizing the epitope/s (NE) region, and 685 bps small (S) envelope gene-corresponding proteins, respectively. Three groups (n = 2 monkeys/group) were intramuscularly immunized with a total of three doses of NE Protein (Lipo-NE-P), NE DNA + Protein (Lipo-NE-DP), and each of NE and S DNA + Protein (Lipo-NES-DP), respectively, given one month apart. All immunized monkeys were challenged with 10,000 fifty percent monkey infectious dose of homologous HEV strain. Post-immunization anti-HEV antibody levels in monkeys were 59.4 and 148.4 IU/mL (Lipo-NE-P), 177.0 and 240.8 IU/mL (Lipo-NE-DP), and 240.7 and 164.9 IU/mL (Lipo-NES-DP). Anti-HBV antibody levels in Lipo-NES-DP immunized monkeys were 58,786 and 6213 mIU/mL. None of the challenged monkeys showed viremia and elevation in serum alanine amino transferase levels. Monkeys immunized with Lipo-NE-DP and Lipo-NES-DP exhibited a sterilizing immunity, indicating complete protection, whereas monkeys immunized with Lipo-NE-P showed limited viral replication. In conclusion, the liposome-complexed DNA-corresponding proteins of HEV and HBV induced protective humoral immune responses to both components in monkeys and are worth exploring further.

Serum immunoglobulin G subclass responses in different phases of hepatitis E virus infection.

To investigate the specific immunoglobulin (Ig) G subclass responses in patients with hepatitis E virus (HEV) infection, an open reading frame 2 (ORF2) protein based enzyme-linked immunosorbant assay was used to measure antibody levels in sera obtained at different phases of infection. Sera were collected at 2-31 days and at 6 months after the onset of symptoms corresponding to the acute (n = 48, 100% IgM-positive) and convalescent (n = 17/48, 53% IgM-positive) phases of infection, respectively. IgM-negative sera from 61 individuals infected at least ≥6 months ago (prior exposure) were also tested. IgG1, IgG2, IgG3, and IgG4 antibodies were detected in 100%, 6%, 56%, and 4% of acute phase sera, respectively, and in 100%, 0%, 0%, and 65% of convalescent phase sera, respectively. IgG1 antibody levels were significantly higher than those of the other detectable subclasses of IgG in the acute and convalescent sera (P < 0.05). The IgG3 antibodies in six acute phase patients were replaced by IgG4 antibodies in the convalescent phase of infection. Patients with prior exposure to HEV had low total IgG antibody titers and decreased IgG1 seropositivity compared with those in the acute and convalescent phases. IgG1 was the only major subclass of antibody to be detected in all the three phases of infection. Other than IgG1 antibodies, the subclass antibody response was restricted to IgG3 and IgG4 antibodies in the acute and convalescent phases of infection, respectively.