CD4 and Patent ductus arteriosus: Early-stage PDA patients showed increase of CD8+ CD103+ and/or CD69+ TRM that also expressed PD-1 and/or HLA-DR (C6, C8 and C10), and higher CD4+ memory T cells with low level of PD-1 (C6) (Figure 5), suggesting that early-stage PDA contained more activated TRM expressing PD-1.