Together with the observation in the current study that the level of PD-L1 on circulating CD4+ and CD8+ T-cells is of importance for the outcome of anti-PD-1 treatment, these findings suggest that PD-L1 expression in the lymphocyte compartment might be an important blood biomarker in cancer patients receiving PD-1 blockade. The gene discussed is PDCD1; the disease is cancer.