Abstract 7456: PCSK1 and PCSK7 orchestrate immune checkpoints to amplify anti-tumor immunity

Abstract Background: Immune-checkpoint receptors (ICPs) such as PD-1, CTLA-4, and TIGIT restrain T-cell activation and enable tumor immune evasion. Although ICP-targeting antibodies have transformed cancer therapy, many patients exhibit incomplete or transient responses, underscoring the need to identify upstream regulators that control ICP expression and function. Proprotein convertases (PCSKs) have recently emerged as modulators of immunity, but their roles in T-cell checkpoint regulation remain poorly defined. Methods: We investigated the functions of Furin and PCSK7 using CRISPR/Cas9-mediated gene deletion, antisense oligonucleotides (ASOs), overexpression systems, mouse knockout models, patient-derived tumor samples, paired PBMCs, and ex vivo T-cell activation assays. Immune-checkpoint expression and trafficking were assessed using flow cytometry, transcriptomic profiling, and imaging. Functional consequences were evaluated through cytokine secretion, proliferation assays, cytotoxicity measurements, chemotaxis analyses, and tumor-organoid co-culture systems. Results: Furin and PCSK7 emerged as complementary and essential regulators of ICP biology in T cells. Furin controls ICP expression at the transcriptional level, reducing mRNA abundance of PD-1, CTLA-4, and TIGIT upon deletion. In contrast, PCSK7 functions as a non-enzymatic chaperone, stabilizing newly synthesized ICPs and directing them to the cell surface. Loss of either convertase significantly diminished surface checkpoint levels and reduced the fraction of T cells co-expressing multiple inhibitory receptors. In human tumors and corresponding PBMC-derived T cells, decreased Furin or PCSK7 expression correlated with enhanced T-cell proliferation, cytokine release, and cytotoxic function. Organoid models, ex vivo patient tumor assays, and tumor-bearing mouse models demonstrated that targeting Furin and PCSK7 enhances the efficacy of chemotherapy and immunotherapy. Conclusions: Furin and PCSK7 constitute key upstream regulators of immune checkpoints, controlling both transcriptional abundance and cell-surface availability through distinct mechanisms. Their inhibition enhances T-cell activation and anti-tumor function, representing a promising therapeutic strategy to potentiate immune responses and overcome resistance to current checkpoint-blocking therapies. Citation Format: Marta Martín-Bórnez, Chloé Porcheron, Geraldine Siegfried, Serge Evrard, John Creemers, Nabil Seidah, Simon Pernot, Abdel-Majid Khatib. PCSK1 and PCSK7 orchestrate immune checkpoints to amplify anti-tumor immunity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 7456.