Modified HPV16 E7 genes as DNA vaccine against E7-containing oncogenic cells

Therapeutic vaccines against tumors associated with human papillomaviruses (HPV) should elicit cellular immune responses against early HPV antigens, p rimarily the oncoproteins E7 and E6. Because of safety concerns, the direct use of an unmodified oncogene is impossible in human DNA vaccination. Ther efore, we introduced three point mutations into the pRb-binding site of HPV 16 E7 oncogene to eliminate its transformation potential. The resultant gen e was denoted E7GGG. The rates of expression and the cellular localization of E7 and E7GGG proteins were comparable. In immunization-challenge experim ents, the efficacy of plasmids containing the E7, E7GGG, or fusion genes of HPV16 E7, viz. L1 Delta CE7(1-50) (M. Muller et al., 1997, Virology 234, 9 3-111), and Sig/E7/LAMP-1 (T. C. Wu et al., 1995, Proc. Natl. Acad. Sci. US A 92, 11671-11675), was compared. While tumors developed in all animals imm unized with the wild-type E7 gene, a significant proportion of mice remaine d tumor-free after vaccination with the E7GGG gene. The fusion gene L1 Delt a CE7(1-50) induced negligible protection, but Sig/E7/LAMP-1 conferred the highest protection. Intradermal immunization by gene gun proved superior to i.m. inoculation. In "therapeutic" experiments, a 1-day delay between inoc ulation of oncogenic cells and the start of DNA immunization resulted in pa rtial therapeutic effect, but a 3-day delay produced a substantially lower immunization effect. A combination of Sig/E7/LAMP-1 and E7GGG genes did not enhance the immune response. These results demonstrate a significant enhan cement of HPV16 E7 immunogenicity after mutagenesis of the pRb-binding site , but the mutated E7 gene did not excel the Sig/E7/LAMP-1 fusion gene. (C) 2001 Academic Press.