Assessment of the PD-1/PD-L1/PD-L2 Immune Checkpoints Pathway in Endometrial Cancer and Its Clinical Significance

<b>Background</b>: Endometrial cancer is one of the most common female genital cancers and poses a significant clinical problem due to its increasing incidence and variable prognosis depending on the stage of the disease. The development of EC is largely dependent on interactions with the immune system, including immune checkpoints (ICPs) such as PD-1, PD-L1, and PD-L2. The aim of our study was to evaluate the PD-1/PD-L1/PD-L2 pathway in EC and its clinical significance. <b>Methods</b>: The analysis was performed by flow cytometry on myeloid and plasmacytoid dendritic cells and monocytes (MO) in peripheral blood (PB). The concentration of sPD-1, sPD-L1, and sPD-L2 in plasma was determined by ELISA. Additionally, <i>PD-L1</i> and <i>PD-L2</i> gene expression levels in tumor tissue (TT) were assessed using real-time polymerase chain reaction (qPCR). The obtained results were correlated with clinical data of EC patients. <b>Results</b>: Patients with EC had lower percentages of PD-L1-positive MO and pDCs, as well as PD-L2-positive MO and mDCs, compared with the control group. We observed accumulation of sPD-1 and lower levels of sPD-L1 and sPD-L2 in EC patients compared to the control group, with sPD-L2 correlating with <i>PD-L2</i> gene expression level in the TT. <b>Conclusions</b>: The study results indicate a difference in the distribution of mDCs, pDCs, and MO with PD-L1/PD-L2 expression in EC patients. Reduced percentages of MO and DCs expressing PD-L1 and PD-L2, altered concentrations of soluble forms of these IPCs, and correlations with gene expression in TT suggest that dysregulation of this pathway may influence disease progression. Furthermore, the relationships between immunological parameters and clinical features such as BMI and FIGO stages suggest the potential use of these factors as diagnostic and prognostic biomarkers and the possibility of incorporating them into future therapeutic strategies. However, further studies are necessary to validate this hypothesis.