Objective: To develop a recombinant vaccinia virus vaccine expressing HPV58 E7 and to determine its immuno-protective activity in mice bearing HPV58 E7+ tumor.
Methods: E7 DNA was amplified and cloned from a plasmid containing HPV58 E7 genome by PCR. To abolish its transforming activity, the nucleotides coding for amino acid residues at positions 24 and 92 were modified by site-directed mutagenesis so that cysteine was substituted by glycine. Balb/c 3T3 cells were transfected with mE7. The expression of E7 protein by the mE7-transfected Balb/c cells was confirmed by immunofluorescence staining. The transfected cells were observed in vitro for anchorage-independent growth and tumorigenesis in nude mice. Recombinant E7 vaccinia virus vaccine was constructed by homologous recombination of HPV58 E7 vaccinia expression plasmid and vaccinia virus (Tiantan stain). The immuno-protective activity of the vaccines was determined by tumor growth inhibition and cytotoxic T lymphocytes (CTL) induction in vaccine-immunized syngeneic mice.
Results: Substitution of cysteine by glycine at both positions 24 and 92 of HPV58 E7 abolished its transforming activity. Growth of HPV E7+ tumor in mice immunized with the recombinant vaccinia virus expressing HPV58 E7 was inhibited, and the surviving time of the immunized mice was prolonged. CTL activity was induced as revealed by in vitro cytotoxicity assay using E7+ tumor cells as target cells.
Conclusions: HPV58 E7, with its transforming potential abolished, may be used as vaccine for immunotherapy of patients with HPV 58 related cancers.