Abstract

Significance Therapies that harness the immune system have recently been approved for cancer treatment. Identification of biomarkers to monitor or predict patients’ responses to immunotherapies would help guide treatment decisions. Herein we analyzed changes in peripheral blood T cells from lung cancer patients receiving immunotherapy blocking the PD-1 inhibitory pathway. We detected CD8 T-cell responses following treatment in most patients. In addition, our data suggest that an increase in proliferation of PD-1+ CD8 T cells in the blood within 4 wk of treatment initiation may be associated with positive clinical outcome. Our analysis provides valuable insights into cancer patients’ responses to PD-1–targeted therapies and warrant further studies on peripheral blood biomarkers.