Protection of tree shrews by pVAX-PS DNA vaccine against HBV infection.

The immunological protection of pVAX-PS, a DNA vaccine, was assessed in the tree shrews model. pVAX-PS was constructed by inserting the gene encoding the middle (pre-S2 plus S) envelope protein of HBV into a plasmid vector pVAX1. Tree shrews (Tupaia belangeri chinenesis) were experimentally infected with human HBV by inoculation with human serum positive for HBV markers. DNA vaccination-induced seroconversion and antibody to HBV surface antigen (anti-HBs) were analyzed by ELISA, and protective effects elicited by pVAX-PS vaccination against subsequent HBV challenge were evaluated by detection of HBV seromarkers and observation of hepatic lesions in HBV-infected tree shrews. The results shown that anti-HBs were detectable in serum at week 2 after pVAX-PS vaccination and peaked at week 4, and immunization with pVAX-PS decreased the positive conversion rate of HBV seromarkers and relieved hepatic lesions in tree shrews challenged with HBV. These results indicated that pVAX-PS immunization could induce remarkable humoral immune response and prevent the experimental tree shrews from infection of HBV.