Overexpression of programmed death ligand 1 enhances immunosuppressive capacity of human umbilical cord mesenchymal stromal cells against T cells

• PD-L1 overexpression in human umbilical cord mesenchymal stromal cells significantly enhances their ability to suppress CD4+ T cell proliferation. • PD-L1 expression decreases with increasing passage number in hUC-MSCs, indicating a need for optimization of culture conditions. • Single-cell RNA sequencing reveals three functional subgroups of PD-L1-overexpressing hUC-MSCs, with subgroup 1 showing high PD-L1 and SETDB1 expression linked to enhanced immunosuppression. • The study provides a theoretical basis for using PD-L1-modified hUC-MSCs as a potential therapeutic strategy for autoimmune diseases.