Id1 and PD-1 Combined Blockade Impairs Tumor Growth and Survival of KRAS-mutant Lung Cancer by Stimulating PD-L1 Expression and Tumor Infiltrating CD8+ T Cells

Abstract

The use of PD-1/PD-L1 checkpoint inhibitors in advanced NSCLC is associated with longer survival. However, many patients do not benefit from PD-1/PD-L1 blockade, largely because of immunosuppression. New immunotherapy-based combinations are under investigation in an attempt to improve outcomes. <i>Id1</i> (inhibitor of differentiation 1) is involved in immunosuppression. In this study, we explored the potential synergistic effect of the combination of <i>Id1</i> inhibition and pharmacological PD-L1 blockade in three different syngeneic murine <i>KRAS</i>-mutant lung adenocarcinoma models. TCGA analysis demonstrated a negative and statistically significant correlation between PD-L1 and <i>Id1</i> expression levels. This observation was confirmed in vitro in human and murine <i>KRAS</i>-driven lung cancer cell lines. In vivo experiments in <i>KRAS</i>-mutant syngeneic and metastatic murine lung adenocarcinoma models showed that the combined blockade targeting <i>Id1</i> and PD-1 was more effective than each treatment alone in terms of tumor growth impairment and overall survival improvement. Mechanistically, multiplex quantification of CD3⁺/CD4⁺/CD8⁺ T cells and flow cytometry analysis showed that combined therapy favors tumor infiltration by CD8⁺ T cells, whilst in vivo CD8⁺ T cell depletion led to tumor growth restoration. Co-culture assays using CD8⁺ cells and tumor cells showed that T cells present a higher antitumor effect when tumor cells lack <i>Id1</i> expression. These findings highlight that <i>Id1</i> blockade may contribute to a significant immune enhancement of antitumor efficacy of PD-1 inhibitors by increasing PD-L1 expression and harnessing tumor infiltration of CD8⁺ T lymphocytes.