Abstract 716: A novel virus-like particle vaccine presenting HER-2 extracellular domain elicits strong immune responses against mammary carcinoma

Abstract

Abstract Overexpression of human epidermal growth factor receptor-2 (HER-2) occurs in about 20% of invasive breast cancers. Anti-HER-2 monoclonal antibody therapy is effective, but its utility is limited by high costs, side effects and development of resistance, thus underlining the need of new therapeutic approaches. A novel anti-HER-2 vaccine made of virus-like particles (VLPs) displaying the extracellular domain (ECD) of the human oncogene/antigen HER-2 induced protective immune responses against transgenic mouse mammary carcinomas expressing human HER-2. We have developed a versatile antigen display platform that, unlike existing technologies, effectively facilitates directional covalent attachment of large antigens at high density on the surface of VLPs (J. Nanobiotechnology 14: 30, 2016). The system uses a tag/catcher conjugation system that was developed by splitting the CnaB2 domain from the fibronectin-binding protein FbaB of Streptococcus pyogenes into a highly reactive peptide (SpyTag) and a protein (SpyCatcher) binding partner. Interaction between SpyTag and SpyCatcher results in the spontaneous formation of an isopeptide bond, occurring at high efficiency in a wide variety of protein contexts and buffer conditions. Here, we genetically fused with SpyCatcher the full extracellular domain (subdomains I-IV) of human HER-2, and bound the fusion antigen (SpyCatcher-HER2) to the surface of VLPs (derived from the AP205 phage), each presenting 360 SpyTag peptides. The vaccine, referred to as HER2-VLP, effectively overcame immune tolerance and induced Th1 cytokines and high-titer, high affinity, therapeutically potent anti-HER-2 antibodies which inhibited tumor growth in wild-type FVB mice implanted with transgenic mammary carcinomas expressing human HER-2. Furthermore, vaccination with HER2-VLP prevented spontaneous development of human HER2-positive mammary carcinomas in tolerant transgenic mice. Vaccination with a control preparation of untagged VLP and HER-2 ECD did not induce protective immune responses. Polyclonal IgG antibodies elicited by HER2-VLP vaccination had an affinity for human HER-2 comparable to trastuzumab and inhibited the 3D growth in vitro of both trastuzumab-sensitive and trastuzumab-resistant BT-474 human breast cancer cells. In conclusion, the HER2-VLP vaccine has the potential to become a tool in the fight against HER-2-positive human cancer. The results also provide strong proof-of-concept for the use of the versatile VLP platform to develop a variety of vaccines against other tumor antigens. Supported by grants from the Italian Association for Cancer Research (AIRC), the University of Bologna, the Danish Research Council, the Eurostars program and the European Research Council (ERC). Citation Format: Arianna Palladini, Susan Thrane, Christoph M. Janitzek, Jessica Pihl, Stine B. Clemmensen, Wilhelm A. de Jongh, Thomas M. Clausen, Giordano Nicoletti, Lorena Landuzzi, Manuel L. Penichet, Tania Balboni, Marianna L. Ianzano, Veronica Giusti, Thor H. Theander, Morten A. Nielsen, Ali Salanti, Pier-Luigi Lollini, Patrizia Nanni, Adam F. Sander. A novel virus-like particle vaccine presenting HER-2 extracellular domain elicits strong immune responses against mammary carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 716.