The capability of DNA to elicit anti-tumour immunity was studied using human papillomavirus type 16 (HPV16)-transformed Syrian hamster cells denoted K3/II. These cells had been derived after cotransfection of primary kidney cell cultures with p16HHMo plasmid containing E6/E7 oncogenes of HPV16 and pEJ6.6 plasmid containing the activated human H-ras oncogene; they express both the HPV16 and activated H-ras genes. As a DNA vaccine, the p16HHMo plasmid was used. Three doses of the plasmid (either 100 microg or 10-15 microg per dose) were administered intramuscularly at 3-week intervals. The animals were challenged with four different doses (10(3)-10(6) per animal) of K3/II cells 10 days after the last plasmid injection. In one experiment the lower dose of plasmid DNA was also given in a mixture with the cationic lipid DOTAP. In another experiment, the pEJ6.6 plasmid (100 microg per dose) was used either alone or in combination with p16HHMo. In all experiments animals inoculated with the same doses of pBR322 plasmid served as controls. A moderate protective effect was observed in animals inoculated with the 100-microg doses of p16HHMo, but not in those inoculated with 10-15 microg of the same plasmid, whether given with or without DOTAP. A protective effect was also observed after administration of the pEJ6. 6 plasmid. At the time of challenge a portion of the p16HHMo-immunized, but not the pBR322-treated, animals possessed antibodies reactive in ELISA with peptides derived from the N-terminal portion of HPV16 E7 protein and with one peptide derived from E6 protein, while two other E6 peptides exhibited non-specific reactivity.

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