BACKGROUND: The inoculation of plasmid DNA encoding tumor-associated antigens is a novel and powerful strategy for antitumor vaccination. This study was designed to construct the DNA vaccine of mouse AFP and to observe the specific cellular immunologic responses and the antitumor responses in mice induced by this vaccine.
METHODS: The murine AFP gene was amplified by RT-PCR from total RNA extracted from Hepa1-6 cells and cloned into the vector pcDNA3.1 to construct pmAFP.The DNA vaccine was identified by restriction enzymeanalysis, sequencing and expression. EL-4 (mAFP) was developed by stable transfection of EL-4 cells with pmAFP. The frequency of cells producing IFN-γ in splenocytes harvested from the mice immunized with the DNA vaccine by intramuscular injection was measured by enzyme linked immunospot (ELISPOT).  The mice immunized with the DNA vaccine were inoculated with EL-4 (mAFP) cells in back to observe the inhibitory effect of the immunization on tumor. On the other hand, blood samples were collected from the immunized mice to check the functions of the liver and kidney.
RESULTS: The murine AFP gene was successfully cloned by RT-PCR. Results from restriction enzyme analysis, sequencing and expression showed that the DNA vaccine was successfully constructed. The expression of mAFP mRNA in EL-4 (mAFP) was confirmed by RT-PCR.  The results of ELISPOT showed that the number of IFN-γ- producing  cells of the pmAFP  vaccine group was significantly higher than that of other groups (P<0.01). The tumor volume in the pmAFP vaccine  group （1042.42±123.71 mm3） was significantly smaller than that in other groups (P<0.01). The function of mouse liver and kidney in each group was unchanged.
CONCLUSION: The successfully constructed DNA vaccine of AFP can induce specific cellular immunologic responses and significant antitumor reponses in mouse and has no impact on the function of mouse liver and kindey.