Kim CG, Hong MH, Kim KH, et al. - In this study including patients suffering from recurrent and/or metastatic non-small-cell lung cancer (NSCLC) managed with programmed cell death protein 1 (PD-1) inhibitors (discovery cohort; n = 94), researchers sought to determine if dynamic alterations in PD-1⁺CD8 ⁺ T lymphocytes can predict durable clinical benefit (DCB) as well as survival following PD-1 blockade. In an independent cohort (validation cohort; n = 54) of a prospective trial with a PD-1 inhibitor, experts sought to validate the predictive values of dynamic alterations in circulating PD-1 ⁺CD8 ⁺ T lymphocytes during the first cycle. A higher likelihood of DCB as well as superior survival outcomes in the discovery cohort were noted in relation to decrease in the frequency of PD-1 ⁺ cells among CD8 ⁺ T lymphocytes following one cycle of treatment. Experts found comparable outcomes in the analysis of tumor antigen NY-ESO-1-specific CD8 ⁺ T lymphocytes and the validation cohort. Overall, dynamic alterations in circulating PD-1 ⁺CD8 ⁺ T lymphocytes were concluded to be predictive of clinical and survival benefit from PD-1 blockade treatment in NSCLC, offering a beneficial instrument to detect patient subgroups who will optimally benefit from PD-1 inhibitors.