• Bianca Harris, Sejal M Morjaria, Eric R Littmann, Alexander I Geyer, Diane E Stover, Juliet N Barker, Sergio A Giralt, Ying Taur, and Eric G Pamer.
• 1 Pulmonary Service.
• Am. J. Respir. Crit. Care Med. 2016 Aug 15; 194 (4): 450463450-63.

RationalePulmonary 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.ObjectivesTo investigate whether changes in gut microbiota are associated with PCs after HCT.MethodsA 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.Measurements And Main ResultsOne 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 γ-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 γ-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).ConclusionsThis is the first study to demonstrate prospective changes in gut microbiota associated with PCs after HCT. Postengraftment PCs and γ-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.

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