Immune-awakening revealed by peripheral T cell dynamics after one cycle of immunotherapy

BACKGROUND: Our understanding of T cell evolution under checkpoint inhibitors (CPI) is still incomplete, restraining the achievement of full benefit from CPI.OBJECTIVES: We studied peripheral T cell turnover and evolution and their prognostic value after 3weeks on treatment with CPI (one cycle) analysing T cell receptor-β (TCR) sequences in plasma cell-free DNA (cfDNA) and PBMC, and performing a phenotypic analysis of peripheral T cell subsets.RESULTS: Peripheral T cell turnover and TCR repertoire dynamics correlated with response. Additionally, the cfDNA TCR repertoire reorganisation fingerprint correlated with the expansion of an immune-effector subset of peripheral T cells that predicted treatment response and identified the patients with longer overall survival.CONCLUSIONS: Here we show that prognostic changes in peripheral T cells occur within 3 weeks of commencing CPI treatment. This dynamic immune-awakening informs on the immune-system reorganization can be monitored using minimally invasive liquid biopsies.EGA study EGAS00001004043