Lactose drives Enterococcus expansion to promote graft-versus-host disease

Disruption of intestinal microbial communities appears to underlie many human illnesses, but the mechanisms that promote this dysbiosis and its adverse consequences are poorly understood. In patients who received allogeneic hematopoietic cell transplantation (allo-HCT), we describe a high incidence of enterococcal expansion, which was associated with graft-versus-host disease (GVHD) and mortality. We found that Enterococcus also expands in the mouse gastrointestinal tract after allo-HCT and exacerbates disease severity in gnotobiotic models. Enterococcus growth is dependent on the disaccharide lactose, and dietary lactose depletion attenuates Enterococcus outgrowth and reduces the severity of GVHD in mice. Allo-HCT patients carrying lactose-nonabsorber genotypes showed compromised clearance of postantibiotic Enterococcus domination. We report lactose as a common nutrient that drives expansion of a commensal bacterium that exacerbates an intestinal and systemic inflammatory disease.

2640. Aerosol vs. Oral Ribavirin for the Treatment of Community-Acquired Respiratory Virus Infections in Lung Transplant Recipients

Background

Community-acquired respiratory virus (CARV) infections are associated with an increased risk of chronic lung allograft dysfunction (CLAD) and graft loss in lung transplant recipients (LTR). Administration of ribavirin by aerosol was the standard of care at Stanford Health Care in the management of CARV infections. Given the sparse evidence of benefit with aerosol ribavirin (AR) and its increasing cost and teratogenic risk for exposed healthcare personnel, AR was restricted to the treatment of respiratory syncytial virus (RSV) in 2016 and was ultimately removed from formulary in 2017. Oral (PO) ribavirin was used at the discretion of the transplant team. The objective of this study was to evaluate the clinical outcomes of AR compared with PO ribavirin in lung transplant recipients.

Methods

We performed a retrospective cohort analysis of adult lung transplant recipients diagnosed with CARV (metapneumovirus, parainfluenza virus, and RSV) infections treated with either AR or PO ribavirin. The analysis included the first treatment course of ribavirin by either route and patients were excluded if they received ribavirin in the prior 12 months. The primary outcome was the development/progression of CLAD, acute organ rejection, and overall mortality.

Results

Of 85 patients, 41 received AR and 44 received PO ribavirin. There was no significant difference in the following clinical outcomes with AR and oral ribavirin, respectively: development or progression of CLAD (30 days: 9.7% vs. 4.5%, P = 0.4227; 90 days: 14.6% vs. 6.8%, P = 0.303; 6 months: 17% vs. 9%, P = 0.3413; 12 months: 24% vs. 15.9%, P = 0.4188), acute organ rejection (90 days: 7.3% vs. 4.5%, P = 0.6689; 6 months: 12.1% vs. 9%, P = 0.7329; 12 months: 19.5% vs. 13.6%, P = 0.5635), and overall mortality (30 days: 0% vs. 4.5%, P = 0.4947; 90 days: 7.3% vs. 4.5%, P = 0.6689; 6 months: 7.3% vs. 9%, P = 1.0; 12 months: 7.3% vs. 13.6%, P = 0.4858). There was no observable difference in reported adverse effects between AR and PO ribavirin.

Conclusion

Lung transplant recipients with CARV infections had similar outcomes when treated with AR or PO ribavirin. Oral ribavirin is a less costly treatment than AR, but the efficacy of ribavirin by any route remains questionable.

Disclosures

All authors: No reported disclosures.

Calculating radiotherapy margins based on Bayesian modelling of patient specific random errors

Collected real-life clinical target volume (CTV) displacement data show that some patients undergoing external beam radiotherapy (EBRT) demonstrate significantly more fraction-to-fraction variability in their displacement ('random error') than others. This contrasts with the common assumption made by historical recipes for margin estimation for EBRT, that the random error is constant across patients. In this work we present statistical models of CTV displacements in which random errors are characterised by an inverse gamma (IG) distribution in order to assess the impact of random error variability on CTV-to-PTV margin widths, for eight real world patient cohorts from four institutions, and for different sites of malignancy. We considered a variety of clinical treatment requirements and penumbral widths. The eight cohorts consisted of a total of 874 patients and 27 391 treatment sessions. Compared to a traditional margin recipe that assumes constant random errors across patients, for a typical 4 mm penumbral width, the IG based margin model mandates that in order to satisfy the common clinical requirement that 90% of patients receive at least 95% of prescribed RT dose to the entire CTV, margins be increased by a median of 10% (range over the eight cohorts -19% to +35%). This substantially reduces the proportion of patients for whom margins are too small to satisfy clinical requirements.