Immune checkpoint profiling in unexplained female infertility: a prospective study

To explore the serum levels of soluble PD-1 (sPD-1), soluble OX40 ligand (sOX40L), soluble CD40 ligand (sCD40L), soluble CD25 (sCD25) and soluble B7H3 (sB7H3) during the early to mid-secretory phase (days 15–19 of the menstrual cycle) in women with unexplained infertility (UI) and to evaluate their feasibility as non-invasive biomarkers. This retrospective study included 50 patients with UI (defined as infertility without identifiable causes after comprehensive evaluation) and 45 healthy women as controls, recruited from the First Affiliated Hospital of Soochow University between January 2022 and January 2023. On days 15–19 of the menstrual cycle (early to mid-secretory phase), cubital venous blood was collected from fasting participants by needle in both groups. Serum levels of the soluble molecules were measured using an enzyme-linked immunosorbent assay. Associations with UI were analyzed using multivariate logistic regression and receiver operating characteristic (ROC) curve analysis. Serum levels of sPD-1, sCD40L, sOX40L and sCD25 were significantly elevated in patients with UI compared with the controls, whereas sB7H3 was significantly decreased. In multivariate analysis, sOX40L and sCD25 were identified as factors independently associated with UI. The combination of sOX40L and sCD25 was associated with an area under the ROC curve of 0.826, a sensitivity of 78.0%, and a specificity of 80.0% in this cohort. Elevated serum levels of sOX40L and sCD25 are significantly associated with UI. The combination of these markers showed an association with UI in our analysis, suggesting their potential for further investigation as non-invasive biomarkers. These findings support the hypothesis that immune dysregulation may contribute to UI and highlight the need for further validation in larger cohorts.