Abstract IA19: Human melanoma neoantigens: Identification and vaccination

Abstract Cancer medicine is in the midst of a dramatic shift towards new therapeutics directed by alterations in the cancer genome. Melanoma genomes harbor somatic mutations that are caused by exposure to mutagens such as ultraviolet light. Tumor missense mutations (MM), translated into amino acid substitutions (AAS), may provide a form of non-self that elicits tumor specific T cell immunity. Indeed, T cell immunity directed against tumor encoded AAS has been reported in humans with cutaneous melanoma, thus implicating MM as a source of patient specific (private) neoantigens. However, a systematic evaluation of these putative neoantigens as validated targets is lacking and it is unknown whether the immune response directed against tumor encoded AAS can be augmented by vaccination. We show that vaccination against melanoma AAS-encoding peptides augments naturally occurring T cell immunity and reveals new HLA class I restricted private neoantigens in patients with advanced melanoma. Neoantigen specific T cells recognized naturally processed and presented antigen but failed to recognize wild type (non-mutated) antigen. The presentation of neoantigens by HLA-A*02:01 in human melanoma was confirmed by mass spectrometry. As determined by TCR beta CDR3 DNA sequencing, vaccination promotes a repertoire of neoantigen-specific T cells that is highly diverse in terms of both TCR beta usage and clonal composition. No evidence of autoimmunity was apparent after vaccination. Our results demonstrate that tumor MM can be targeted as neoantigens and vaccination directed at tumor AAS somatic mutations broadens the antigenic breadth and clonal diversity of anti-tumor immunity. Personalized cancer immunotherapies targeting private somatic tumor alterations may become feasible in the near future. Citation Format: Gerald P. Linette. Human melanoma neoantigens: Identification and vaccination. [abstract]. In: Proceedings of the AACR Precision Medicine Series: Integrating Clinical Genomics and Cancer Therapy; Jun 13-16, 2015; Salt Lake City, UT. Philadelphia (PA): AACR; Clin Cancer Res 2016;22(1_Suppl):Abstract nr IA19.