PDCD1 and Patent ductus arteriosus: In PDA, unique CD8+ or CD4+ T cells phenotypes were enriched that frequently expressed co-inhibitory immune checkpoint PD-1 but were lacking all co-stimulatory immune checkpoint receptors including ICOS, OX40, 4-1BB and GITR (Figures 2F–H, 3F–H and Supplementary Figures 3E, F).