Abstract 470: Electrovaccination of domestic cats with a hybrid heterologous Her2 DNA vaccine overcomes immune tolerance to self Her2.

About 20% of non-castrated female domestic cats develop malignant mammary tumors with similar histopathology and disease progression as human breast cancer. Her2 over-expression is reported in 40-85% of feline mammary carcinomas, indicating this disease is particularly suited for testing Her2 DNA vaccination. To corroborate these findings, expression of Her2 was evaluated in 4 feline mammary tumors resected from three feline patients. Immunohistochemistry analysis with anti-human Her2 mAb showed regions of intense membrane staining in all four tumor samples, indicating high frequency of Her2 expression among feline mammary tumors and immune cross-reactivity of human and feline Her2. Feline mammary tumor lines K248 (Minke, et. al. 1991) and K12 (Modiano, et. al. 1991) both express Her2 as measured by flow cytometry, further demonstrating Her2 as a common antigen in feline mammary tumors. Feline Her2 cDNAs cloned from K248 and K12 (GenBank Accession JN990983) are identical to each other and show 93% sequence identity with human Her2. To test the feasibility of conducting DNA electrovaccination in cats, 3 pathogen-free domestic short hair cats between 1-2 years of age were injected i.m. in the biceps femoris of the hind legs or triceps of the front legs with vaccine DNA. Each cat received admix of 1.5mg of pE2Neu encoding a hybrid human Her2 and rat neu fusion protein and 1.5mg of feline pGM-CSF. Each injection site was subjected to electroporation with a NEPA21 electroporator, consisting of three 50msec 100V degenerating bipolar pulses. The vaccination was repeated at 3 week intervals and blood was drawn 2 weeks after each vaccination. Anti-human Her2 antibody was detected in the immune serum after 2 vaccinations, as demonstrated by binding to SKOV3 cells that over-express human Her2. After 4 vaccinations, anti-human Her2 antibody titers ranged from 50,000 to 200,000. Therefore, DNA electrovaccination is an effective means to induce immune response in cats. To test if immunization with heterologous pE2Neu induced cross-reactive antibody to self feline Her2, immune serum was incubated with 3T3/fHer2 cells that express feline Her2. Specific binding to 3T3/fHer2 was observed after 3 vaccinations at 1:100 serum dilutions. These results provide the first evidence that immune tolerance in cats to self Her2 is overcome by a hybrid DNA vaccine encoding a fusion protein of two heterologous genes: human Her2 and rat neu. This vaccine regimen is a candidate veterinary therapeutic agent and the insight gained from cat vaccination provides strong support for human vaccine trials. Citation Format: Heather M. Gibson, Richard Jones, Marie Piechocki, Joyce Reyes, Michele Sauerbrey, Ulka Vaishampayan, Wei-Zen Wei. Electrovaccination of domestic cats with a hybrid heterologous Her2 DNA vaccine overcomes immune tolerance to self Her2. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 470. doi:10.1158/1538-7445.AM2013-470