Human PDA has not responded to therapy with antagonists of T cell checkpoints (Brahmer et al., 2012, Royal et al., 2010), and the mouse model of this disease is also resistant to antibodies specific for PD-1, PD-L1, and CTLA-4 (Feig et al., 2013, Zhu et al., 2014). Here, CTLA4 is linked to Patent ductus arteriosus.