Soluble immune-checkpoint factors as a complementary biomarker for PD-1 blockade reflect exhaustion of antitumor immunity

BACKGROUND. Precise stratification of patients with non–small cell lung cancer (NSCLC) is needed for appropriate application of PD-1/PD-L1 blockade therapy. METHODS. We measured soluble (s) forms of the PD-L1, PD-1, and CTLA-4 in plasma of patients with advanced NSCLC before PD-1/PD-L1 blockade. Prospective biomarker finding trial (cohort A), 50 patients with pretreated NSCLC received nivolumab. In cohort B to E, retrospective observational study, soluble immune checkpoint molecules were evaluated for patients with advanced NSCLC treated with any PD-1/PD-L1 blockade (cohort B and C), cytotoxic chemotherapy (D) or targeted therapy (E). Blood samples were obtained from all patients and soluble immune checkpoint molecules were evaluated using a highly sensitive chemiluminescence-based assay. RESULTS. Nonresponsiveness to PD-1/PD-L1 blockade therapy was associated with higher concentrations of these soluble immune factors among patients with immune-reactive (hot) tumors. Such correlation was not observed in patients treated with cytotoxic chemotherapy or targeted therapies. Integrative analysis of tumor size, PD-L1 expression in tumor tissue (tPD-L1), and gene expression in tumor tissue and peripheral CD8+ T cells revealed that high concentrations of the three soluble immune factors were associated with hyper or terminal exhaustion of antitumor immunity. The combination of sPD-L1 and sCTLA-4 efficiently discriminated responsiveness among patients with immune-reactive tumors. CONCLUSION. Combinations of soluble immune factors might be able to identify patients unlikely to respond to PD-1/PD-L1 blockade as a result of terminal exhaustion of antitumor immunity. Our data suggest such a combination might provide a biomarker complementary to tPD-L1 for NSCLC patients. 40 samples, compared with soluble plasma markers measured by HISCL system. The data were analyzed with with median polish summarization and quantile normalization by Affymetrix® Transcriptome Analysis Console Software, and obtained normalized intensity values. Values: SST-RMA and quantile normalized non-log2 signal.