To understand the clinical utility of CX3CR1 as a circulating T-cell biomarker, we analyze longitudinal PB samples from patients with NSCLC undergoing anti-PD-1 therapy and evaluate changes in the frequency of PB CX3CR1+ CD8+ T cells as a correlate of response to anti-PD-1 therapy. Here, CX3CR1 is linked to non-small cell lung carcinoma.