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Background & Aims: The COVID-19 pandemic continues to pose unprecedented challenges to worldwide health. While vaccines are effective, additional strategies to mitigate the spread/severity of COVID-19 continue to be needed. Emerging evidence suggests susceptibility to respiratory tract infections in healthy subjects can be reduced by probiotic interventions; thus, probiotics may be a low-risk, low-cost, and easily implementable modality to reduce risk of COVID-19., Methods: In this initial study, we conducted a randomized, double-blind, placebo-controlled trial across the United States testing probiotic Lacticaseibacillus rhamnosus GG (LGG) as postexposure prophylaxis for COVID-19 in 182 participants who had household exposure to someone with confirmed COVID-19 diagnosed within ≤7 days. Participants were randomized to receive oral LGG or placebo for 28 days. The primary outcome was development of illness symptoms within 28 days of COVID-19 exposure. Stool was collected to evaluate microbiome changes., Results: Intention-to-treat analysis showed LGG treatment led to a lower likelihood of developing illness symptoms versus placebo (26.4 % vs. 42.9 %, p = 0.02). Further, LGG was associated with a statistically significant reduction in COVID-19 diagnosis (log rank, p = 0.049) via time-to-event analysis. Overall incidence of COVID-19 diagnosis did not significantly differ between LGG and placebo groups (8.8 % vs. 15.4 %, p = 0.17)., Conclusions: This data suggests LGG is associated with prolonged time to COVID-19 infection, reduced incidence of illness symptoms, and gut microbiome changes when used as prophylaxis ≤7 days post-COVID-19 exposure, but not overall incidence. This initial work may inform future COVID-19 prevention studies worldwide, particularly in developing nations where Lacticaseibacillus probiotics have previously been utilized to reduce other non-COVID infectious-morbidity., Trial Registration: ClinicalTrials.gov, NCT04399252, Date: 22/05/2020. https://clinicaltrials.gov/ct2/show/NCT04399252., Competing Interests: Conflict of interest P.E.W. has received unrestricted gift funding from DSM/iHealth and has an investigator-initiated research grant from Abbott Inc. related to work focused on microbiome and probiotic research. P.E.W. has presented CME lectures for DSM on probiotic research. All other authors declare no competing interests. A.D.S has grants from Merck Sharpe & Dohme, consulting for Targazyme, and receipt of supplies from Clasado., (Copyright © 2023 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

We previously described clinically relevant reductions in fecal microbiota diversity in patients undergoing allogeneic hematopoietic cell transplantation (allo-HCT). Recipients of high-dose chemotherapy and autologous HCT (auto-HCT) incur similar antibiotic exposures and nutritional alterations. To characterize the fecal microbiota in the auto-HCT population, we analyzed 1161 fecal samples collected from 534 adult recipients of auto-HCT for lymphoma, myeloma, and amyloidosis in an observational study conducted at 2 transplantation centers in the United States. By using 16S ribosomal gene sequencing, we assessed fecal microbiota composition and diversity, as measured by the inverse Simpson index. At both centers, the diversity of early pretransplant fecal microbiota was lower in patients than in healthy controls and decreased further during the course of transplantation. Loss of diversity and domination by specific bacterial taxa occurred during auto-HCT in patterns similar to those with allo-HCT. Above-median fecal intestinal diversity in the periengraftment period was associated with decreased risk of death or progression (progression-free survival hazard ratio, 0.46; 95% confidence interval, 0.26-0.82; P = .008), adjusting for disease and disease status. This suggests that further investigation into the health of the intestinal microbiota in auto-HCT patients and posttransplant outcomes should be undertaken., (© 2021 by The American Society of Hematology.)

Studies of the relationship between the gastrointestinal microbiota and outcomes in allogeneic hematopoietic stem cell transplantation (allo-HCT) have thus far largely focused on early complications, predominantly infection and acute graft-versus-host disease (GVHD). We examined the potential relationship of the microbiome with chronic GVHD (cGVHD) by analyzing stool and plasma samples collected late after allo-HCT using a case-control study design. We found lower circulating concentrations of the microbe-derived short-chain fatty acids (SCFAs) propionate and butyrate in day 100 plasma samples from patients who developed cGVHD, compared with those who remained free of this complication, in the initial case-control cohort of transplant patients and in a further cross-sectional cohort from an independent transplant center. An additional cross-sectional patient cohort from a third transplant center was analyzed; however, serum (rather than plasma) was available, and the differences in SCFAs observed in the plasma samples were not recapitulated. In sum, our findings from the primary case-control cohort and 1 of 2 cross-sectional cohorts explored suggest that the gastrointestinal microbiome may exert immunomodulatory effects in allo-HCT patients at least in part due to control of systemic concentrations of microbe-derived SCFAs., (© 2020 by The American Society of Hematology.)