Abstract LB005: High quality neoantigens are immunoedited in long term survivors of pancreatic cancer

Abstract Cancer immunoediting, a hallmark of cancer, predicts that lymphocytes recognize tumor-specific mutations (neoantigens) to kill immunogenic tumor cells and select less immunogenic clones to survive in immunocompetent hosts. Yet, though proven in mice, whether immunoediting governs how human tumors evolve naturally, and the principles of how the immune system edits tumors remain unclear. Here, we report that T cell rich tumors of rare long-term survivors of human pancreatic ductal adenocarcinoma longitudinally lose immunogenic features predicted by a fitness model based on immune recognition of high quality neoantigens. We find that compared to T cell poor tumors in short-term survivors, long-term survivors evolve less immunogenic recurrent tumors over 10 years with fewer clones, fewer neoantigens, and new neoantigens of markedly lower quality, to indicate that the immune system edits lower fitness clones with high-quality neoantigens. To explore if the immune system more broadly selects against non-self-like changes in host genomes, we define a minimal amino acid substitution distance sufficient for T cell receptors to discriminate self from non-self mutations. We find that both primary and recurrent tumors in long but not short-term survivors are enriched in self-like mutations, to suggest that the immune system depletes non-self-like mutations. Thus, we submit longitudinal evidence that the immune system edits neoantigens to sculpt recurrent human pancreatic ductal adenocarcinomas, a lethal tumor largely considered resistant to endogenous immune attack. Furthermore, we demonstrate that the neoantigen quality fitness model predicts how immune pressure changes tumor cell populations over time, with significant implications for cancer biology and immunotherapy. More broadly, our results argue that cancer immunoediting is a fundamental principle of how human cancers evolve in immunocompetent hosts. Citation Format: Marta Luksza, Zachary Sethna, Luis Rojas, Kevin Soares, Yuval Elhanati, Jayon Lihm, David Hoyos, Rajya Kappagantula, Alvin M. Moore, Erin Patterson, Christine Iacobuzio-Donahue, Benjamin Greenbaum, Vinod P. Balachandran. High quality neoantigens are immunoedited in long term survivors of pancreatic cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr LB005.