To investigate the potential checkpoint inhibitors in this PDA model, we examined the expression of programmed cell death protein 1 (PD-1), cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), and lymphocyte-activation gene 3 (Lag-3) on T cells within the KPC tumor microenvironment. The gene discussed is CTLA4; the disease is Patent ductus arteriosus.