Abstract 1579: Evaluation of Adeno-associated virus like particles (AAVLP) coupled with HER-2 mimotopes as novel carrier system for anti-tumor vaccines

Abstract

Background & Aims: Cancer is a major public health problems in western societies, leading to every 4th case of death. To date, passive immunotherapy with monoclonal antibodies (mAbs) is a well-established option in clinical oncology. In contrast, anti-cancer vaccines are less advanced. The development of therapeutic vaccines is still a great challenge mostly due to the self-nature of tumor antigens. Mimotopes, small peptides from 6-38 amino acids, resembling B-cell epitopes do not need consensus sequence with the natural antigen, because molecular mimicry via e.g. amino acid charges is sufficient to shape an electron cloud specifically recognized by the immune system. As they are similar, but not identical to the original tumor antigen, vaccination with mimotopes may overcome tumor tolerance. Adeno-associated virus like particles (AAVLP) could serve as novel vectors for displaying mimotopes to the immune system. We suggest that cancer vaccines will especially open up new treatment options in minimal residual disease and early stage disease. Methods & Results: Adeno-associated viruses (AAV) are ssDNA viruses being replication defective in the absence of Adenovirus. Their surface consists of 60 capsomers, which can be exploited for display of recombinant peptides. AAV-like particles (AAVLP) can be generated via assembling recombinant AAV-2 capsid fusion proteins. In this study different HER-2 derived linear B-cell epitopes, generated in a biopanning with the clinically used anti-HER-2 antibody trastuzumab, were inserted into AAV-2. Mimotope candidates were screened for trastuzumab binding in ELISA. Appropriate candidates, preliminary as AAVs, were employed for immunization of BALB/c mice. Immune response was monitored measuring circulating levels of Abs reactive to recombinant HER-2. Molecular mimicry was also proved in immunofluorescence on human HER-2 overexpressing murine mammary carcinoma D2F2-E2 cells. Sera of mice displaying highest HER-2 specific antibody levels were exploited for Ab purification and purified antibodies were tested for their tumoristatic properties in a tetrazolium based cell viability assay. In this assay HER-2 overexpressing human mammary carcinoma cells mBT474 showed significant growth reduction even after 24h of antibody incubation with purified antibodies of clone DMD1. This effect increased at consecutive measurements after 48 and 72h. Conclusion: In this study we could demonstrate that AAV and probably AAVLP are suitable vectors for mimotope based cancer vaccines. In our system mimotope immunized BALBc mice developed anti-HER-2 antibodies with similar biological properties to the clinically used mAb trastuzumab. Due to their easy application and economic advantages, cancer vaccines might become important supplementary therapy options in cancer treatment, especially in the minimal residual disease setting. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1579. doi:1538-7445.AM2012-1579