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An assessment was made of the effectiveness of DNA vaccination in prevention of the mammary adenocarcinomas of BALB/c female mice transgenic for the activated rat Her2/neu oncogene. Atypical hyperplasia is evident in their mammary glands when they are 6 weeks old and in situ carcinoma by the 13th week. Palpable invasive carcinomas appear around the 17th week and are always evident in all 10 glands by the 33rd week. Intramuscular vaccinations with 100 µg plasmid DNA encoding the extracellular domain of the Her-2/neu p185 (ECD) performed at the 6th, 12th, 18th and 24th week provided no significant protection, whereas those ECD plasmids in which the DNA coding for the immunomodulatory 163-171 (VQGEESNDK) nonapeptide of human IL 1β (ECD-IL 1βp) had been inserted both delayed carcinogenesis and reduced tumor multiplicity. This reduction was associated with a marked immune-inflammatory reaction and a conspicuous leukocyte infiltrate located in the stroma surrounding the hyperplastic mammary ductulalveolar structures. It was also directly correlated with a high anti-p185[sup neu] antibody production and an immunoglobulin switch to IgG2a and IgA. No anti-p185[sup neu] cytotoxic response was found. No significant protection was obtained when the DNA coding for the non-active peptide 189-197 of IL 1β was inserted. [ABSTRACT FROM AUTHOR]