PD-1+ NK cell subsets in high grade serous ovarian cancer: an indicator of disease severity and a target for combined immune-checkpoint blockade

Background: Ovarian cancer (OC) is the fifth leading cause of cancer-related death among women, with High-Grade Serous Ovarian Carcinoma (HGSC) representing the most aggressive and prevalent subtype. Despite promising results in other malignancies, immune checkpoint blockade has shown limited efficacy in HGSC, highlighting the need for alternative immunotherapeutic targets. Methods: We conducted an integrated analysis combining multiparametric flow cytometry, RNA sequencing, multiplex immunohistochemistry, and functional assays to characterize NK cells isolated from peripheral blood, peritoneal fluid, primary tumor tissue, and metastases in 60 HGSC patients. Results: We identified a distinct population of PD-1⁺ NK cells enriched in HGSC tumors and metastatic sites but absent in healthy donors. These cells, characterized by a CD56dimNKG2A⁺KIR⁺/⁻NKp46⁺CD57low phenotype, displayed impaired cytotoxicity against autologous HGSC targets, correlating with poorer prognosis. Crucially, this dysfunction was reversible upon combined blockade of PD-1/PD-L1, NKG2A, and KIRs. Spatial and molecular profiling revealed that these cells localize within PD-L1⁺/HLA-E⁺ tumor niches, suggesting that immune suppression is spatially and molecularly coordinated. Transcriptomic analysis confirmed their altered functional state and highlighted actionable checkpoint targets. Conclusions: Our findings uncover a previously underappreciated population of dysfunctional PD-1⁺ NK cells in HGSC and demonstrate that their suppression is reversible through combinatorial checkpoint inhibition. These insights support the development of spatially-informed, NK-targeted immunotherapies for HGSC patients, particularly those resistant to T cell-based strategies.