MX1+ effector T cells hyperactivation at the maternal-fetal interface in unexplained recurrent pregnancy loss

Immune tolerance breakdown at the maternal-fetal interface is implicated in unexplained recurrent pregnancy loss (URPL), but the interplay between T cell hyperactivation and dendritic cells (DCs)-mediated signaling remains poorly defined. First-trimester decidual tissues from 5 healthy controls and 6 URPL patients underwent single-cell RNA sequencing (scRNA-seq, 10× Genomics). Computational analyses included clustering (Seurat), trajectory inference (scTour), intercellular communication (CellChat) and metabolic pathway enrichment (Gene Ontology and scMetabolism). Flow cytometry was performed from 11 patients and 11 healthy controls. Spatial validation was performed via multiplex immunohistochemistry and immunohistochemistry on 12 additional controls and 12 URPL cases. Statistical significance was assessed using Student’s t-test. URPL decidua exhibited marked CD3+ T cells and MX1+effector T (Tem) cells infiltration and activation. Flow cytometry analysis confirmed a significant decidua-specific upregulation of T cell activation markers CD25 and CD69 specifically on the MX1+Tem subset in URPL patients compared to controls. MX1+Tem cell subset demonstrated interferon hyperactivation, proliferative hyperactivity and lipid-biased immunometabolism. Pseudotemporal analysis positioned MX1+ Tem cells between classical Tem and exhausted T cell states, suggesting progressive differentiation. CellChat identified DCs as key regulators of MX1+ Tem expansion via aberrant ICOSL signaling, validated by spatial co-localization of ICOSL+ DCs and MX1+ Tem cells in URPL tissues. Our findings demonstrate that the aberrant activation and proliferation of MX1+Tem cells as a key immunological feature associated with URPL patients.