Immature neutrophils are elevated in human PGD and linked to G-CSF-driven injury in a murine model of lung ischemia–reperfusion

BACKGROUND: Primary Graft Dysfunction (PGD) is an early post-lung transplant (LTx) inflammatory condition primarily driven by lung ischemia-reperfusion injury (LIRI). Neutrophils are key mediators of LIRI, but their phenotypic diversity and maturation state remain poorly characterized. In other inflammatory settings, early expansion of immature neutrophils has been linked to increased tissue injury and worse clinical outcomes. Whether immature neutrophils increase following LTx and contribute to PGD severity remains unclear. METHODS: Circulating neutrophil heterogeneity was analyzed by flow cytometry in 20 LTx candidates with advanced lung disease and 30 LTx recipients. Matched plasma samples were used for cytokine profiling. The role of immature neutrophils in LIRI was studied using a murine left pulmonary hilar clamp model with or without anti-G-CSF treatment. The differentiation and effector functions of immature neutrophils derived from murine hematopoietic progenitors were studied in vitro. RESULTS: LTx recipients exhibited an early rise in circulating immature neutrophils, correlated with higher G-CSF levels and PGD severity. In mice, LIRI was linked to increased G-CSF levels, significant mobilization, and lung infiltration of immature neutrophils with an activated, ROS-producing phenotype. These cells showed prolonged survival, strong ROS activity, but impaired phagocytosis. Preoperative anti-G-CSF treatment decreased lung injury while reducing immature neutrophil mobilization and recruitment to the lung. CONCLUSIONS: Our findings underscore the clinical significance of neutrophil heterogeneity in the early perioperative setting following LTx. Targeting the G-CSF-immature neutrophil axis may offer a novel strategy to improve early lung allograft outcomes.