Abstract 1124: PTEN loss confers resistance to anti-PD-1 therapy in NSCLC by increasing tumor infiltration of T regulatory cells

Immune checkpoint inhibitors (ICIs) targeting PD-L1/PD-1 have dramatically improved the management of NSCLC patients. Nevertheless, more than 50% patients will present primary resistance or will develop secondary resistance within 12-25 months after treatment initiation. The mechanisms of resistance to ICIs may depend on tumor-intrinsic molecular/genetic alterations that generate an immunosuppressive tumor microenvironment (isTME). Using In silico analyses (TCGA and AACR-GENIE cohorts), and protein expression analysis in our institutional CIMA-CUN cohort, we have shown that >50% LUSC and ~28% LUAD tumors exhibited reduced PTEN mRNA/protein levels. Patients with PTEN-low tumors had higher levels of CXCL10, PD-L1 and PD-L2. In a cohort of stage IV NSCLC patients treated with ICIs, we found that patients with low tumor PTEN levels were significantly associated with worse OS (p=0.021). We have developed and characterized a Pten-null LUSC model using UN680 cells, which was also refractory to anti-PD-1 when implanted in syngeneic mice. Pten loss led to a deregulation of multiple pathways related to immunosuppression, with a positive enrichment in “IL-6/JAK/STAT3” and “TNF-α via NFkB” hallmarks, identified by GSEA. Tumors from the Pten-null LUSC model were highly metastatic and fibrotic, and secreted TGF-β/CXCL10, thus favoring conversion of CD4+ lymphocytes into Tregs. Human/mouse PTEN-low tumors were enriched in Tregs and immunosuppressive genes. Importantly, treatment of mice bearing Pten-null tumors with TLR agonists+anti-TGF-β, aimed to alter this isTME, led to tumor rejection and immunological memory in 100% of mice. Our results demonstrate that lack of PTEN causes immunotherapy resistance in LUSC by establishing an isTME that can be reversed therapeutically. Citation Format: Francisco Exposito, Miriam Redrado, Maeva Houry, Katherine Hastings, Magdalena Molero-Abraham, Teresa Lozano, Jose L. Solorzano, Julian Sanz Ortega, Vera Andradas, Ramon Amat, Esther Redin, Sergio Leon, Naroa Legarra, Javier García, Diego Serrano, Karmele Valencia, Camila Robles-Oteiza, Giorgia Foggetti, Enriqueta Felip, Juan J. Lasarte, Luis Paz-Ares, Jon Zugazagoitia, Katerina Politi, Luis M Montuenga, Alfonso Calvo. PTEN loss confers resistance to anti-PD-1 therapy in NSCLC by increasing tumor infiltration of T regulatory cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orla