Immunogenicity and protective efficacy in rhesus monkeys of a recombinant ORF2 protein from hepatitis E virus genotype 4.

Several antigens derived from hepatitis E virus (HEV) genotype 1 strains have shown immunogenicity and efficacy against hepatitis E in primates and humans. However, the protective effect of a vaccine derived from HEV genotype 4 has not been studied. This study aimed to evaluate the immunogenicity and protective efficacy of the T1-ORF2 (56 kDa) capsid protein derived from HEV strain T1 (genotype 4) in rhesus monkeys. Two doses (40 microg) of alum-absorbed T1-ORF2 capsid protein were administered 4 weeks apart. Seroconversion occurred in all immunized monkeys 1-2 weeks after the first dose. The peak levels of anti-HEV IgG appeared at 2-3 weeks after the second dose and ranged from 5.7 to 196.0 U/ml. All monkeys showed an anamnestic antibody response to the second dose. Control monkeys immunized with saline remained negative for HEV antibodies throughout the pre-challenge period. The immunized monkeys were challenged intravenously with HEV genotypes 1 and 4. Monkeys immunized with T1-ORF2 were protected from infection and hepatitis after challenge with 5 x 10(4) genome equivalents of HEV, regardless of the genotype. After challenge with 5 x 10(5) genome equivalents of HEV genotype 4, the monkeys immunized with T1-ORF2 had a shorter period of raised alanine aminotransferase levels and a shorter duration of fecal shedding compared to control monkeys immunized with saline. In conclusion, these results suggest that, in rhesus monkeys, the T1-ORF2 capsid protein of HEV genotype 4 has similar cross-protective effects to other candidate vaccines derived from HEV genotype 1.