ABSTRACT: Pulmonary complications (PCs) cause significant morbidity and mortality after allogeneic hematopoietic stem cell transplantation (HCT). Shifts in gut microbiota have been linked to HCT outcomes; however, their effect on PCs is unknown.To investigate whether changes in gut microbiota are associated with PCs after HCT.A single-center observational study was performed on 94 patients who underwent HCT from 2009 to 2011 and who were previously enrolled in a protocol for 16S ribosomal RNA sequencing of fecal microbiota. The primary endpoint, PC, was defined by new abnormal parenchymal findings on chest imaging in the setting of respiratory signs and/or symptoms. Outcomes were collected up to 40 months after transplant. Clinical and microbiota risk factors for PCs and mortality were evaluated using survival analysis.One hundred twelve PCs occurred in 66 (70.2%) subjects. A high comorbidity index (hazard ratio [HR], 2.30; 95% confidence interval [CI], 1.30-4.00; P?=?0.004), fluoroquinolones (HR, 2.29, 95% CI, 1.32-3.98; P?=?0.003), low baseline diversity (HR, 2.63; 95% CI, 1.22-5.32; P?=?0.015), and ?-proteobacteria domination of fecal microbiota (HR, 2.64; 95% CI, 1.10-5.65; P?=?0.031), which included common respiratory pathogens, predicted PCs. In separate analyses, low baseline diversity was associated with PCs that occurred preengraftment (HR, 6.30; 95% CI, 1.42-31.80; P?=?0.016), whereas ?-proteobacteria domination predicted PCs postengraftment (HR, 3.68; 95% CI, 1.49-8.21; P?=?0.006) and overall mortality (HR, 3.52; 95% CI, 1.28-9.21; P?=?0.016). Postengraftment PCs were also independent predictors of death (HR, 2.50; 95% CI, 1.25-5.22; P?=?0.009).This is the first study to demonstrate prospective changes in gut microbiota associated with PCs after HCT. Postengraftment PCs and ?-proteobacteria domination were predictive of mortality. This suggests an adverse relationship between the graft and lung, which is perhaps mediated by bacterial composition in the gut. Further study is warranted.
