Data from PD-1 Expression on Intratumoral Regulatory T Cells Is Associated with Lack of Benefit from Anti–PD-1 Therapy in Metastatic Clear-Cell Renal Cell Carcinoma Patients

AbstractPurpose:Programmed cell death protein 1 (PD-1) expression on CD8+TIM-3−LAG-3− tumor-infiltrating cells predicts positive response to PD-1 blockade in metastatic clear-cell renal cell carcinoma (mccRCC). Because inhibition of PD-1 signaling in regulatory T cells (Treg) augments their immunosuppressive function, we hypothesized that PD-1 expression on tumor-infiltrating Tregs would predict resistance to PD-1 inhibitors.Experimental Design:PD-1+ Tregs were phenotyped using multiparametric immunofluorescence in ccRCC tissues from the CheckMate-025 trial (nivolumab: n = 91; everolimus: n = 90). Expression of CD8, PD-1, TIM-3, and LAG-3 was previously determined (Ficial and colleagues, 2021). Clinical endpoints included progression-free survival (PFS), overall survival (OS), and objective response rate (ORR).Results:In the nivolumab (but not everolimus) arm, high percentage of PD-1+ Tregs was associated with shorter PFS (3.19 vs. 5.78 months; P = 0.021), shorter OS (18.1 vs. 27.7 months; P = 0.013) and marginally lower ORR (12.5% vs. 31.3%; P = 0.059). An integrated biomarker (PD-1 Treg/CD8 ratio) was developed by calculating the ratio between percentage of PD-1+Tregs (marker of resistance) and percentage of CD8+PD-1+TIM-3−LAG-3− cells (marker of response). In the nivolumab (but not everolimus) arm, patients with high PD-1 Treg/CD8 ratio experienced shorter PFS (3.48 vs. 9.23 months; P P P = 0.009). Compared with the individual biomarkers, the PD-1 Treg/CD8 ratio showed improved ability to predict outcomes to nivolumab versus everolimus.Conclusions:PD-1 expression on Tregs is associated with resistance to PD-1 blockade in mccRCC, suggesting that targeting Tregs may synergize with PD-1 inhibition. A model that integrates PD-1 expression on Tregs and CD8+TIM-3−LAG-3− cells has higher predictive value.