Abstract Background Pulmonary injury is a major cause of morbidity and mortality after allogeneic hematopoietic stem cell transplantation (HSCT). The underlying mechanism of tissue injury is widely variable. Neutrophil extracellular traps (NETs) play a role in acute lung injury and are cleared from circulation by DNases. Hypothesis Evaluation of NETs and DNaseI levels in bronchoalveolar lavage fluid (BALF) at the time of respiratory events will be valuable in differentiating the cause of acute pulmonary injury after HSCT. Methods We reviewed medical records of patients who underwent bronchoscopy for acute pulmonary events. We measured circulating double-stranded DNA (ds-DNA) as a surrogate of NETs (Quant-iT PicoGreen P7589) and DNaseI (MBS2515385) in BALF. Pulmonary events were classified in 8 groups (pre-transplant, infection, endothelial injury (EI), diffuse alveolar hemorrhage (DAH), idiopathic pulmonary syndrome (IPS), early bronchiolitis obliterans syndrome (eBOS), established BOS, BOS with infection). Early BOS was defined as BOS developed within 1 year of bronchoscopy. Results There were 124 BALF samples from 100 patients. Pre-transplant BALF had lowest levels of NETs, neutrophils and DNaseI. Patients with infection had a wide range of BALF NETs levels. IPS and DAH patients had low levels of NETs (Fig 1A). Patients with established BOS had lower levels of NETs compared to developing BOS, supporting an inflammatory neutrophilic component of early BOS. Patients with BOS and infection had high levels of NETs. BALF neutrophil percentage was positively correlated with NETs (r = 0.59, p = 0.0001). DAH and established BOS patients had high neutrophil percentages, yet low NETs levels, suggesting neutrophils in lungs do not always NETose (Fig 1B). IPS patients had low levels of NETs and neutrophils. BALF NETs and DNaseI were positively correlated (r = 0.51, p = 0.001) (Fig 3). EI, DAH, and IPS patients had higher levels of DNAseI in BALF compared to patients with eBOS, BOS, and infection (Fig 1C). There was no correlation between plasma neutrophil count, NETs and BALF neutrophil percentage and NETs. Conclusion Our data show high levels of NETs in some subsets of lung injury after HSCT, particularly developing BOS which has been described as a neutrophilic process. Data analysis is challenged by the number of lung injury events that occur after HSCT, demonstrating the value of multi-center cohort studies like TRANSPIRE. These data provide consideration of pharmacological agents to target NETs. Measurement of NETs and DNaseI can be done quickly. Inhaled DNaseI may be an intervention for patients in the early stages of BOS or severe infection. This abstract is funded by: TRANSPIRE
Strecker et al. (Fri,) studied this question.