Expression, role and regulation of NK cell immune checkpoints (PD-1, KIRs, NKG2A) in Ovarian Cancer

Outstanding results can be obtained with immune-checkpoints (ICs)/ligands blockade strategies (mainly PD-1/PD-L axis) in immunotherapeutic protocols for aggressive tumors. We previously showed that higher proportions of PD-1+NK cells can be detected in ovarian cancer (OC) patients. Here, we deeply characterized the features of the PD-1+NK cell subset in a large cohort of patients with high-grade serous OC subtype with the aim to dissect the NK/tumor interconnections existing in this TME. We identified two new PD-1+NK subsets occurring only in OC patients, primarily in the peritoneal fluid (PF) compartment, while absent in healthy donors. These subsets show an immature phenotype, characterized by high expression of NKG2A and NKp46, variable expression of KIRs, and low/lack expression of CD57. Functional analyses revealed that PF-PD-1+NK cells are not anergic, but able to degranulate in response to appropriate stimuli. In addition, we found PD-1+NK cells in different tumor tissue compartments, mainly in metastatic niche, suggesting a role for PD-1 in tumor metastatic progression/promotion. However, even if PD-1+NK cells are functional and infiltrate the tumor, they are unable to produce an efficient anti-tumor response towards OC cells, due to NK cells expressing multiple ICs including PD-1,NKG2A,KIRs, and OC cells expressing both PD-Ls and HLA-I, completely impairing the NK activity. Importantly, our data show that by blocking all the ICs pathways, NK cell activity can be restored. This indicates that a proper use of multiple targeted therapies, including a combination of ICs-inhibitors, represents a possible solution to restore NK cell anti-tumor activity in seropapillary OC subtype.