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Background. Recurrent Clostridioides difficile infections (rCDI) are a global public health threat. To reduce rCDI, microbiotarestoring therapies are needed, particularly standardized, easy-to-administer formulations. Methods. This phase I open-label trial assessed the safety, efficacy in preventing rCDI recurrence, and intestinal microbiome effects of RBX7455, a room temperature-stable, orally administered investigational live biotherapeutic. Adult participants with 1 or more prior episodes of rCDI received: 4 RBX7455 capsules twice daily for 4 days (group 1); 4 RBX7455 capsules twice daily for 2 days (group 2); or 2 RBX7455 capsules twice daily for 2 days (group 3). For all groups, the first dose was administered in clinic, with remaining doses selfadministered at home. Adverse events were monitored during and for 6 months after treatment. Treatment success was defined as rCDI prevention through 8 weeks after treatment. Participants’ microbiome composition was assessed prior to and for 6 months after treatment. Results. Nine of 10 group 1 patients (90%), 8 of 10 group 2 patients (80%), and 10 of 10 group 3 patients (100%) were recurrencefree at the 8-week endpoint with durability to 6 months. Seventy-five treatment-emergent adverse events were observed in 27 participants with no serious investigational product-related events. Prior to treatment, participants’ microbiomes were dissimilar from the RBX7455 composition with decreased Bacteroidia- and Clostridia-class bacteria, whereas after treatment, responders’ microbiomes showed increased Bacteroidia and Clostridia. Conclusions. Three dosing regimens of RBX7455 were safe and effective at preventing rCDI. Responders’ microbiomes converged toward the composition of RBX7455. These results support its continued clinical evaluation. [ABSTRACT FROM AUTHOR]

Background Fecal microbiota transplantation (FMT) is highly effective for preventing recurrent Clostridioides difficile infection (CDI). Durability (no recurrence despite additional risk factor exposure) of FMT protection is largely unknown. We studied the durability of FMT in patients with recurrent CDI. Methods We conducted a retrospective study of adults undergoing FMT for recurrent CDI. Data collected included demographics, CDI risk factors (comorbidities, healthcare exposure, non-CDI antibiotic use, acid suppressant medications), and future CDI episodes. Durable response to FMT was defined as lack of CDI episodes within 1 year post-FMT despite risk factor exposure. Results Overall, 460 patients were included (median age, 57 years [18–94]; 65.2% female). Comorbidities included chronic liver disease, 12.8% (n = 59); cancer, 11.7% (n = 54); chronic kidney disease, 3.9% (n = 18); and inflammatory bowel disease, 21.9% (n = 101). Overall, 31.3% (n = 144) received antibiotics, 21.7% (n = 100) received acid suppressants, and 76.8% (n = 350) had healthcare exposure after FMT. Of 374 patients with risk factor exposure, 78.1% (95% confidence interval [CI], 72.7%–84.0%) had durable response to FMT at 1 year. On multivariable analysis, antibiotic use was independently associated with decreased durability of FMT (hazard ratio, 0.27; 95% CI,.15–.49; P  < .001). Conclusions The majority of patients had a durable response to FMT despite exposure to CDI risk factors. Antibiotic exposure after FMT independently predicted loss of durability of FMT. Larger studies are needed to define predictors of durable response in patients with and without exposure to antibiotics. [ABSTRACT FROM AUTHOR]

Background Recurrent Clostridioides difficile infection (rCDI) is associated with loss of microbial diversity and microbe-derived secondary bile acids, which inhibit C. difficile germination and growth. SER-109, an investigational microbiome drug of donor-derived, purified spores, reduced recurrence in a dose-ranging, phase (P) 1 study in subjects with multiple rCDIs. Methods In a P2 double-blind trial, subjects with clinical resolution on standard-of-care antibiotics were stratified by age (< or ≥65 years) and randomized 2:1 to single-dose SER-109 or placebo. Subjects were diagnosed at study entry by PCR or toxin testing. Safety, C. difficile–positive diarrhea through week 8, SER-109 engraftment, and bile acid changes were assessed. Results 89 subjects enrolled (67% female; 80.9% diagnosed by PCR). rCDI rates were lower in the SER-109 arm than placebo (44.1% vs 53.3%) but did not meet statistical significance. In a preplanned analysis, rates were reduced among subjects ≥65 years (45.2% vs 80%, respectively; RR, 1.77; 95% CI, 1.11–2.81), while the <65 group showed no benefit. Early engraftment of SER-109 was associated with nonrecurrence (P <.05) and increased secondary bile acid concentrations (P <.0001). Whole-metagenomic sequencing from this study and the P1 study revealed previously unappreciated dose-dependent engraftment kinetics and confirmed an association between early engraftment and nonrecurrence. Engraftment kinetics suggest that P2 dosing was suboptimal. Adverse events were generally mild to moderate in severity. Conclusions Early SER-109 engraftment was associated with reduced CDI recurrence and favorable safety was observed. A higher dose of SER-109 and requirements for toxin testing were implemented in the current P3 trial. Clinical Trials Registration NCT02437487, https://clinicaltrials.gov/ct2/show/NCT02437487?term=SER-109&draw= 2&rank=4. [ABSTRACT FROM AUTHOR]