Serum NY-ESO-1 and XAGE1 antibodies as predictive biomarkers in anti-PD-1 therapy for non-small-cell lung cancer.
106 Background: Programmed death-1 (PD-1) inhibitors effectively treat non-small-cell lung cancer (NSCLC) and prolong survival, but the clinical benefits are limited in a small population. However, robust biomarkers for predicting clinical benefits with anti-PD-1 therapy have yet to be identified, therefore, predictive biomarkers are needed to select patients with benefits. On the other hand, NSCLC expresses NY-ESO-1 and XAGE1 cancer-testis antigens, which elicit spontaneous immune responses in NSCLC patients. Methods: We conducted a prospective multicenter study to investigate whether serum antibody against NY-ESO-1 and/or XAGE1 antigens was a predictive biomarker in anti-PD-1 therapy for NSCLC. Serum antibody was serially detected by ELISA, and antibody titers were monitored during anti-PD-1 therapy. Tumor tissues were analyzed by immunohistochemistry and whole exome sequencing. Objective response rate (ORR) and survival were the primary and secondary endpoint, respectively. Results: In the discovery cohort (n = 13), six antibody-positive NSCLC responded to anti-PD-1 therapy (two complete and four partial responses), whereas seven antibody-negative NSCLC did not. Antibody positivity was associated with good response and survival, regardless of tumor PD-ligand1 expression, mutation burden, and CD8 T-cell infiltration. In the independent validation cohort (n = 40), ten antibody-positive NSCLC obtained the significant clinical benefits with anti-PD-1 therapy as compared with 30 negative NSCLC (ORR 50% vs 6.7%, P = 0.006). In the multivariate analysis, only antibody positivity was a significantly better predictive biomarker of progression free survival (HR 0.04, 95% CI 0.0 to 0.3) and overall survival (HR 0.2, 95% CI 0.0 to 0.9) after anti-PD-1 therapy. Antibody titers in responders transiently increased with spikes and gradually decreased with tumor shrinkage after anti-PD-1 therapy, and strongly correlated with tumor reduction rates and tumor burden. Conclusions: Our results suggest that NY-ESO-1 and/or XAGE1 serum antibodies are useful biomarkers for predicting clinical benefits and monitoring tumor burden in anti-PD-1 therapy for NSCLC.