Immune checkpoint inhibitors can induce clinical responses to a broad range of tumor types by presumably enhancing T cell responses against the tumor. These treatments are also associated with certain side effects that are also thought to be immune mediated (termed immune-related adverse events, or IRAEs). The mechanism by which IRAEs occur, and biomarkers that may predict IRAE development, are unknown. In prior work (Cha et al. Sci Transl Med 2014), we demonstrated that treating metastatic cancer patients with checkpoint inhibitors blocking CTLA-4 can lead to T cell repertoire diversification. However, we found that prolonged survival was not associated with the induction of high frequency clonotypes, but rather the maintenance of a pre-existing T cell response. Here, we examined whether treatment-induced TCR diversification is related to another clinical outcome: the development of IRAEs. We find that IRAEs are specifically associated with a more diverse T cell repertoire and with an increase in the number of T cell clonotypes, including the generation of de novo clones. This broadening of the circulating T cell repertoire occurred early with treatment, preceding the development of IRAEs. While IRAE patients demonstrate markedly greater diversity in their CD4+ T cells, they demonstrate a greater degree of change in clonal frequencies in their CD8+ T cells after ipilimumab, which may have key implications in the pathogenic mechanism of IRAE development. Finally, clinical response to checkpoint blockade is also associated with increased diversity. These results indicate that immune repertoire diversity following immune checkpoint inhibition can be both detrimental and beneficial to patients with metastatic cancer.

Citation Format: David Y. Oh, Jason Cham, Li Zhang, Grant Fong, Mark Klinger, Malek Faham, Lawrence Fong. T cell repertoire diversification is associated with immune related toxicities following immune checkpoint inhibition in metastatic cancer patients. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4362.