Accumulating evidence has shown that MPE/MA induces PD-L1 expression on both tumor cells and immune cells, and simultaneously exacerbates PD-L1-mediated T-cell dysfunction.18,20,21 To investigate PD-L1 expression in malignant effusions, firstly, cells from human ovarian cancer ascites were analyzed, using public single-cell RNA-sequencing (scRNA-seq) data set (GSE146026) downloaded from Gene Expression Omnibus (GEO). The gene discussed is CD274; the disease is ovarian carcinoma.