BTLA and Patent ductus arteriosus: Interestingly, we also found a small population of TRM enriched in primary PDA expressing both co-stimulatory, ICOS and 41-BB, and co-inhibitory, PD-1, TIGIT, Tim-3 and BTLA, immune checkpoint receptors, as well as CD95 (Fas) that leads to apoptotic cell death (C9, Supplementary Figures 8I, J).