Abstract PR02: A personalized neoantigen vaccine in patients with high risk melanoma

Abstract Neoantigens arise from somatic tumor mutations and can encode amino acid changes, generating peptides with the potential to bind to HLA molecules. Since these neoepitopes provide exquisite tumor specificity and are expected to be highly immunogenic as they are not subject to central tolerance, they were long-envisioned as highly valuable tumor antigens. Growing evidence has supported tumor neoepitopes as key antigens triggering immune-mediated tumor killing in vivo across settings of effective cancer immunotherapy, including checkpoint blockade and adoptive transfer with tumor-infiltrating lymphocytes. Vaccination is a potentially effective approach for inducing tumor-specific immune responses, but has been limited by the lack of a sufficiently potent vaccine immunogen. By leveraging next-generation sequencing technologies and new analytical pipelines to systematically identify personal tumor neoantigens, in a phase 1 trial we tested the feasibility, safety, and immunogenicity of a multi-epitope cancer vaccine targeting personal tumor neoantigens in patients with high-risk melanoma. Mutations were identified by DNA and RNA sequencing; epitopes were selected based on class I HLA binding prediction algorithms. The vaccines, comprised of up to 20 long peptides spanning mutated tumor epitopes and admixed with the Toll-Like Receptor 3 agonist poly-ICLC, were administered using a prime-boost approach. Of 12 patients enrolled, the initial 6 patients who received the full set of priming and booster vaccinations experienced only minimal adverse events, consisting of mild and transient injection site reaction, flu-like symptoms, and rash. We identified strong, polyfunctional CD4+ and CD8+ T cell responses against multiple neoepitopes in all dosed patients. Processing and presentation of neoantigens on autologous tumors was confirmed by mass spectrometry and recognition of autologous tumor by vaccine-induced neoantigen-specific T cells was verified. These studies show that a personalized neoantigen vaccine is safe, feasible, and strongly immunogenic in cancer patients. The data should reinvigorate the field of cancer vaccines, providing a rational path for the building of combinatorial approaches to extend their efficacy. Citation Format: Patrick A. Ott, Zhuting Hu, Derin B. Keskin, Sachet A. Shukla, Jing Sun, Ed Fritsch, Nir Hacohen, Catherine J. Wu. A personalized neoantigen vaccine in patients with high risk melanoma [abstract]. In: Proceedings of the Second CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; 2016 Sept 25-28; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(11 Suppl):Abstract nr PR02.