OBJECTIVEThe goal of this study was to construct a eukaryotic expression plasmid containing the gene encoding herpes simplex virus type I glycoprotein D (HSV-1, gD) and evaluate its utility for DNA immunization in mice.

METHODSThe gD gene was amplified from viral DNA using PCR with EcoR I and BamH I restriction sites encoded on 5' and 3' ends, respectively. The PCR fragment was inserted into the transfer vector pGEM-T Easy. gD was then cut from this vector and inserted into the EcoR I and BamH I sites in the pcDNA3.1 at the multiple cloning sites (MCS). The recombinant plasmid, pcDNA3.1-gD1, was transfected into COS-7 cells using Lipofectamine according to the manufacture's instructions. The expression of the glycoprotein D was analyzed by immunoblotting of the cell lysates. 4-6 weeks old BALB/C mice were given two injections at tibia anterialis muscle, each containing 100 micrograms of plasmid DNA, on days 0 and 15. pcDNA3.1 was used as negative control. Blood samples were taken from all mice at weeks 0, 2, 4, and 6 after the first inoculation. Standard indirect ELISA was employed to evaluate the levels of specific total Ig in serum.

RESULTSThe recombinant plasmid was confirmed with restriction digestion and sequencing to contain target gene segment and expressed in COS-7 cells in vitro shown by Western blotting. The pcDNA3.1-gD1 immunized group induced specific antibody response as compared to the negative control, and the titer was about 1:2000.

CONCLUSIONSThe recombinant plasmid pcDNA3.1-gD1 is potential to be used as a candidate vaccine, for the treatment of HSV-1 infection.