Results of the First Pilot Randomized Controlled Trial of Fecal Microbiota Transplant In Pediatric Ulcerative Colitis: Lessons, Limitations, and Future Prospects

Abstract

The incidence of childhood-onset inflammatory bowel disease (IBD) has increased significantly over the past decade.1Carroll M.W. Kuenzig M.E. Mack D.R. et al.The impact of inflammatory bowel disease in Canada 2018: children and adolescents with IBD.J Can Assoc Gastroenterol. 2019; 2: S49-S67Crossref PubMed Google Scholar Despite advances in therapy families remain concerned about long-term harms of immunosuppressive therapy and their associated costs.2Ledder O. Assa A. Levine A. et al.Vedolizumab in paediatric inflammatory bowel disease: a retrospective multi-centre experience from the Paediatric IBD Porto Group of ESPGHAN.J Crohns Colitis. 2017; 11: 1230-1237Crossref PubMed Scopus (38) Google Scholar The role of the enteric microbiome in IBD is well described and has been implicated in the pathogenesis of ulcerative colitis (UC).3Torres J. Danese S. Colombel J.-F. New therapeutic avenues in ulcerative colitis: thinking out of the box.Gut. 2013; 62: 1642-1652Crossref PubMed Scopus (50) Google Scholar While drug development continues to focus on modifying dysregulated intestinal immune pathways, targeting enteric microbiota has become increasingly attractive. Four randomized controlled trials (RCTs) of fecal microbiota transplant (FMT) in UC have been conducted since 2015. Three demonstrated clinical and endoscopic remission in adult patients with active UC, and a 2017 systematic review reported a pooled rate of clinical and endoscopic remission of 27.9%, with a number needed to treat of 5 (95% confidence interval [CI], 4–10).4Narula N. Kassam Z. Yuan Y. et al.Systematic review and meta-analysis: fecal microbiota transplantation for treatment of active ulcerative colitis.Inflamm Bowel Dis. 2017; 23: 1702-1709Crossref PubMed Scopus (94) Google Scholar Compelling data from adult UC has increased interest for pediatric UC, but no RCTs have been conducted in children. Three uncontrolled case series and case reports have yielded conflicting results with limited follow-up duration. Kunde et al5Kunde S. Pham A. Bonczyk S. et al.Safety, tolerability, and clinical response after fecal transplantation in children and young adults with ulcerative colitis.J Pediatr Gastroenterol Nutr. 2013; 56: 597-601Crossref PubMed Scopus (224) Google Scholar administered serial enemas containing healthy donor stool for 5 days to 9 patients with UC, ages 7 to 21, and 6 patients showed clinical response at the 1-month follow-up. Suskind et al6Suskind D.L. Brittnacher M.J. Wahbeh G. et al.Fecal microbial transplant effect on clinical outcomes and fecal microbiome in active Crohn’s disease.Inflamm Bowel Dis. 2015; 21: 556-563Crossref PubMed Scopus (150) Google Scholar,7Kronman M.P. Nielson H.J. Adler A.L. et al.Fecal microbiota transplantation via nasogastric tube for recurrent Clostridium difficile infection in pediatric patients.J Pediatr Gastroenterol Nutr. 2015; 60: 23-26Crossref PubMed Scopus (49) Google Scholar reported 2 case series of FMT for Crohn’s disease and UC in which a single FMT was administered via nasogastric tube to 4 patients with UC, with no clinical response seen. Kellermayer et al8Kellermayer R. Nagy-Szakal D. Harris R.A. et al.Serial fecal microbiota transplantation alters mucosal gene expression in pediatric ulcerative colitis.Am J Gastroenterol. 2015; 110: 604-606Crossref PubMed Scopus (51) Google Scholar reported 3 pediatric patients with UC who received serial FMT enemas and colonoscopic infusions, and all achieved clinical remission at weeks 2 and 4. Three further case reports reported an 18-month-old, 3-year-old, and 11-year-old with severe, treatment refractory colitis.9Vandenplas Y. Veereman G. van der Werff Ten Bosch J. et al.Fecal microbial transplantation in early-onset colitis: caution advised.J Pediatr Gastroenterol Nutr. 2015; 61: e12-e14Crossref PubMed Scopus (23) Google Scholar, 10Shimizu H. Arai K. Abe J. et al.Repeated fecal microbiota transplantation in a child with ulcerative colitis.Pediatr Int. 2016; 58: 781-785Crossref PubMed Scopus (19) Google Scholar, 11Kumagai H. Yokoyama K. Imagawa T. et al.Failure of fecal microbiota transplantation in a three-year-old child with severe refractory ulcerative colitis.Pediatr Gastroenterol Hepatol Nutr. 2016; 19: 214Crossref PubMed Scopus (11) Google Scholar All received serial FMT infusions over varying frequencies and routes of administration, and 2 showed response.12Wang A.Y. Popov J. Pai N. Fecal microbial transplant for the treatment of pediatric inflammatory bowel disease.World J Gastroenterol. 2016; 22: 10304-10315Crossref PubMed Scopus (17) Google Scholar Current evidence for FMT in UC offers reasons for both optimism and further study. Adult RCTs demonstrate that FMT leads to significant rates of clinical and endoscopic healing. One study suggests FMT may have a particular role in patients with new-onset disease duration. Colonic FMT appears more effective for the treatment of UC than upper-tract delivery, and serial, multidose treatments correlate with greatest efficacy in both adult and pediatric recipients.4Narula N. Kassam Z. Yuan Y. et al.Systematic review and meta-analysis: fecal microbiota transplantation for treatment of active ulcerative colitis.Inflamm Bowel Dis. 2017; 23: 1702-1709Crossref PubMed Scopus (94) Google Scholar,12Wang A.Y. Popov J. Pai N. Fecal microbial transplant for the treatment of pediatric inflammatory bowel disease.World J Gastroenterol. 2016; 22: 10304-10315Crossref PubMed Scopus (17) Google Scholar An RCT of FMT in pediatric patients with UC has never been reported, and there are multiple feasibility questions associated with running a placebo-controlled pediatric FMT trial. In 2015, after publication of the first RCT by adult gastroenterology colleagues from our center and strong interest from families,13Moayyedi P. Surette M.G. Kim P.T. et al.Fecal microbiota transplantation induces remission in patients with active ulcerative colitis in a randomized controlled trial.Gastroenterology. 2015; 149: 102-109.e6Abstract Full Text Full Text PDF PubMed Scopus (796) Google Scholar our team launched the first pilot trial of FMT in pediatric UC. Our pilot feasibility protocol has been reported previously.14Pai N. Popov J. Protocol for a randomised, placebo-controlled pilot study for assessing feasibility and efficacy of faecal microbiota transplantation in a paediatric ulcerative colitis population: PediFETCh trial.BMJ Open. 2017; 7e016698Crossref PubMed Scopus (15) Google Scholar We discuss our findings and experience conducting the Pediatric FEcal microbiota Transplant in ulcerative Colitis (PediFETCh) Trial and important lessons that may support future investigators. During a 36-month study period, 48 patients, aged 4 to 17 years, with active UC were referred by the patients’ primary pediatric gastroenterologists for screening across 3 pediatric IBD centers in Canada (McMaster Children’s Hospital, Hamilton, Ontario; Children’s Hospital at London Health Sciences Centre, London, Ontario; and Centre Hospitalier Universitaire Sainte-Justine, Montreal, Quebec). Of these, 23 patients were excluded: 30.4% (n = 7) had medication changes made by their primary gastroenterologist within 4 weeks of trial entry, 34.8% (n = 8) were unable to fulfill trial requirements of in-hospital FMT treatments, 21.7% (n = 5) withdrew interest for unspecified reasons, and 13.0% (n = 3) were in remission by trial commencement. Ultimately, 52.1% (n = 25) of referred patients entered the trial. Patients were randomized to FMT (n = 13) or placebo (n = 12) arms; 46% of patients in the trial were diagnosed with UC for less than 1 year. At diagnosis, 77% (10 of 13) in the FMT arm had pancolitis vs 58% (7 of 12) in the placebo arm. During the trial, 54% (7 of 13) in the FMT arm received antitumor necrosis factor (TNF) (n = 3) or immunomodulator (IM) (n = 4) therapies vs 17% (2 of 12; 1 anti-TNF, 1 IM) in the placebo arm. Seven patients randomized to the placebo arm crossed over to the open-label arm (Figure 1). We did not reach our primary feasibility outcome of achieving recruitment targets (50 patients over 2 years). We reached our composite clinical end point (improvement in pediatric UC activity index, C-reactive protein, or fecal calprotectin) in 92% (11 of 12) assigned to FMT vs 50% (6 of 12) assigned to placebo at week 6 (risk ratio, 1.8; 95% CI, 1.1–3.7). At 12 months, 75% (9 of 12) had maintained clinical response (Table 1). β-Diversity trended higher from baseline to week 6 in FMT vs placebo arms (Supplementary Figure 1). Several bacterial taxa were associated with achieving the composite clinical outcome after multiple test correction, including Alistipes spp and Escherichia spp (Supplementary Table 1).Table 1Secondary Outcome Measures Comparing Fecal Microbiota Transplant vs Placebo ArmsVariableFMT (n = 12)Placebo (n = 12)RR95% CIComposite clinical outcomeaComposite clinical outcome defined as any improvement from baseline of at least 1 of PUCAI, FC, or CRP; improvements in individual outcomes further described in rows below.11 (91.7)6 (50.0)1.8b9 stool samples from FMT group, 7 stool samples from placebo group.1.1–3.7Clinical response, week 6cClinical response defined as improvement from baseline PUCAI.7 (58.3)4 (33.3)1.80.7–4.6FC response week 6dFC response defined as improvement from baseline FC.8 (88.9)b9 stool samples from FMT group, 7 stool samples from placebo group.3 (42.9)b9 stool samples from FMT group, 7 stool samples from placebo group.2.11.0–5.7CRP response week 6eCRP response defined as improvement from baseline CRP.8 (66.7)2 (18.2)4.01.3–14.8Clinical response week 30cClinical response defined as improvement from baseline PUCAI.6 (50.0)3 (25.0)2.00.7–6.3FC response week 30dFC response defined as improvement from baseline FC.6 (85.7)f7 stool samples from FMT group, 8 stool samples from placebo group.2 (25.0)f7 stool samples from FMT group, 8 stool samples from placebo group.3.41.2–12.2CRP response week 30eCRP response defined as improvement from baseline CRP.5 (41.7)3 (25.0)1.50.5–5.0Clinical remission week 6gClinical remission defined as PUCAI <15.4 (33.3)4 (33.3)1.00.3–3.0Clinical remission week 30gClinical remission defined as PUCAI <15.5 (41.7)4 (33.3)1.30.5–3.5FC <250 μg/g week 305 (71.4)f7 stool samples from FMT group, 8 stool samples from placebo group.4 (50.0)f7 stool samples from FMT group, 8 stool samples from placebo group.1.40.6–3.6FC change week 6hReported as change (+/−) from baseline.−881.1b9 stool samples from FMT group, 7 stool samples from placebo group.−390.4b9 stool samples from FMT group, 7 stool samples from placebo group.……CRP change week 6hReported as change (+/−) from baseline.+0.1+5.7……FC change week 30hReported as change (+/−) from baseline.−1282.9f7 stool samples from FMT group, 8 stool samples from placebo group.−583.2f7 stool samples from FMT group, 8 stool samples from placebo group.……CRP change week 30hReported as change (+/−) from baseline.−1.3+7.1……Patients with serious adverse events5i3 patients developed worsening colitis requiring hospitalization for intravenous methylprednisolone; 2 patients with a past history of Clostridioides difficile colitis were diagnosed with Clostridioides difficile colitis within 2 weeks of discontinuing therapy. (41.7)1j1 patient developed worsening colitis requiring hospitalization for intravenous methylprednisolone. (8.3)5.01.0–30.2NOTE: Categorical data are shown as n (%) and continuous data as mean values. Continuous data were measured using the independent sample t test, and categorical data were measured using Fisher’s exact test. Missing values were excluded. All analyses are modified intention to treat.CI, confidence interval; CRP, C-reactive protein; FC, fecal calprotectin; FMT, fecal microbiota transplant; PUCAI, Pediatric Ulcerative Colitis Activity Index; RR, risk ratio.a Composite clinical outcome defined as any improvement from baseline of at least 1 of PUCAI, FC, or CRP; improvements in individual outcomes further described in rows below.b 9 stool samples from FMT group, 7 stool samples from placebo group.c Clinical response defined as improvement from baseline PUCAI.d FC response defined as improvement from baseline FC.e CRP response defined as improvement from baseline CRP.f 7 stool samples from FMT group, 8 stool samples from placebo group.g Clinical remission defined as PUCAI <15.h Reported as change (+/−) from baseline.i 3 patients developed worsening colitis requiring hospitalization for intravenous methylprednisolone; 2 patients with a past history of Clostridioides difficile colitis were diagnosed with Clostridioides difficile colitis within 2 weeks of discontinuing therapy.j 1 patient developed worsening colitis requiring hospitalization for intravenous methylprednisolone. Open table in a new tab NOTE: Categorical data are shown as n (%) and continuous data as mean values. Continuous data were measured using the independent sample t test, and categorical data were measured using Fisher’s exact test. Missing values were excluded. All analyses are modified intention to treat. CI, confidence interval; CRP, C-reactive protein; FC, fecal calprotectin; FMT, fecal microbiota transplant; PUCAI, Pediatric Ulcerative Colitis Activity Index; RR, risk ratio. There was a numeric increase in at least 1 adverse event occurring in the FMT (83.3% [10 of 12]) vs placebo group (41.7% [5 of 12]) during the 6-week intervention period (P = 0.68; Table 1). Worsening colitis developed in 4 patients (3 FMT, 1 placebo) and required hospitalization for intravenous methylprednisolone, and 2 FMT patients with a prior history of Clostridioides difficile (C difficile) colitis were diagnosed with C difficile colitis within 2 weeks of trial withdrawal due to lack of improvement. Aliquots of FMT donor stools were retested in these patients and confirmed the absence of C difficile in donor samples. Low sample sizes prevented subgroup analyses of potential risk factors for adverse events, such as concurrent medications. Secondary outcomes compared all recipients of FMT (randomized plus open-label placebo crossover arms) vs placebo (Supplementary Table 2). In this cohort, the composite clinical end point was reached in 84% (16 of 19) assigned to FMT vs 50% (6 of 12) assigned to placebo at week 6 (risk ratio, 1.7; 95% CI, 1.0–3.4). Among eligible patients, 34.8% (n = 8) declined participation due to requirements to attend 12 biweekly in-hospital visits for rectal enema treatments. A further 21.7% (n = 5) declined enrolment for unspecified reasons after learning more about the trial protocol from study personnel. Our study attempted to maximize potential benefit through an intensive administration protocol, but this also compromised recruitment. We conducted qualitative follow-up interviews with participants, and intensive administration protocols were reported as a barrier.15Popov J, Hartung E, Hill L, et al. Pediatric patient and parent perceptions of fecal microbiota transplantation for the treatment of ulcerative colitis. J Pediatr Gastroenterol Nutr. Published online November 20, 2020. https://doi.org/10.1097/MPG.0000000000002995Google Scholar Future studies could reduce the number of rectal enema infusions or use home-based interventions, such as offering self-administered FMT enemas or lyophilized, oral FMT capsules. Our recruitment target was based on 1 of 2 RCTs reported at the time of our study’s conception. Our results may support more precise power calculations to establish sample size in future trials. Current data suggest that FMT trials should be powered assuming a 20% response in the FMT arm and 5% response in the control arm, provided a stringent definition of remission is used as a primary end point. Our eligibility criteria also limited recruitment. These criteria required patients to have active disease but also be clinically stable, defined as <4 weeks between medication changes. In several instances where patients and families were permissive of ongoing, active symptoms before trial entry, primary providers encouraged the initiation of evidence-based treatments such as biologic therapies. This had several impacts: patients enrolled in our study either had mild or severe disease that had failed multiple biologics. Patients were also frequently withdrawn from the trial by the primary clinician before meeting formal study end points, if they did not show immediate signs of improvement. Placebo-controlled clinical trials in pediatrics can be ethically challenging for investigators and primary providers.15Popov J, Hartung E, Hill L, et al. Pediatric patient and parent perceptions of fecal microbiota transplantation for the treatment of ulcerative colitis. J Pediatr Gastroenterol Nutr. Published online November 20, 2020. https://doi.org/10.1097/MPG.0000000000002995Google Scholar When our study began in 2015, limited data were available to share with prospective families. As further safety and efficacy data were published, interest significantly increased. Early optimism from studies like ours may encourage greater confidence from primary providers and patients of pediatric FMT trials in the future. Our study was also impacted by high withdrawal rates from patients in our control group, limiting opportunities for better placebo comparisons. Clearer expectations of participants in RCTs and stringent withdrawal criteria may improve analyses in future trials.16Kahn S.A. Rubin D.T. When subjects violate the research covenant: lessons learned from a failed clinical trial of fecal microbiota transplantation.Am J Gastroenterol. 2016; 111: 1508-1510Crossref PubMed Scopus (8) Google Scholar An important consideration for performing FMT is the selection of appropriate donors. The microbiome of children and adults demonstrate considerable variation in composition and function. The pediatric intestinal microbiome is age-dependent and characterized by decreased diversity, increased representation of Bacteroides and glycan synthesis, and predominance of catabolic pathways. The adult microbiota has higher abundance of Blautia, greater carbohydrate degradation, and a shift to anabolic pathways. These differences may support cell division and growth during childhood.17Radjabzadeh D. Boer C.G. Beth S.A. et al.Diversity, compositional and functional differences between gut microbiota of children and adults.Sci Rep. 2020; 10: 1040Crossref PubMed Scopus (31) Google Scholar While evidence for the impact of inoculating children with adult stool is lacking, the long-term effects of such alterations to commensal microbiota on growth and metabolism will be an important outcome in future FMT trials. Our analysis of donor effect was affected by our use of multiple donors during the intervention phase. While samples from multiple donors were never pooled for any single treatment, samples from different donors were given to the same patient at different time points in the study. This approach was influenced by the desire to minimize potential “donor effect,” whereby samples from 1 donor may confer disproportionate benefits. We collaborated with an experienced third-party microbiome company to optimize safety and logistics.18Rebiotix Inc. Microbiota Restoration Therapy.http://www.rebiotix.com/Google Scholar Donor samples were prescreened, approved by federal regulatory bodies, and banked for retesting. This was useful as testing requirements for multidrug-resistant organisms evolved throughout our trial.19U.S. Food and Drug AdministrationImportant Safety Alert Regarding Use of Fecal Microbiota for Transplantation and Risk of Serious Adverse Reactions Due to Transmission of Multi-Drug Resistant Organisms. June 13, 2019.https://www.fda.gov/vaccines-blood-biologics/safety-availability-biologics/important-safety-alert-regarding-use-fecal-microbiota-transplantation-and-risk-serious-adverseGoogle Scholar However, there are also theoretical safety concerns with this approach. If 1 donor harbors a yet unidentified pathogen, there is potential to cause wider harm than if a single donor were used for a single recipient. There are also questions of which control to use in FMT trials. Some trials have used autologous stool as a placebo so that the person administering the product can be appropriately masked.4Narula N. Kassam Z. Yuan Y. et al.Systematic review and meta-analysis: fecal microbiota transplantation for treatment of active ulcerative colitis.Inflamm Bowel Dis. 2017; 23: 1702-1709Crossref PubMed Scopus (94) Google Scholar However, microbial shifts occur when autologous stool is administered, and this could have an unknown impact on UC (therapeutic, neutral, or harmful), making results difficult to interpret. We used normal saline as a placebo in our trial. Appropriate double blinding can be preserved with this approach while giving an inert product as a placebo. The optimal sample volume or bacterial load per inoculum is unclear across FMT UC trials, as is frequency of dosing.20Yalchin M. Segal J.P. Mullish B.H. et al.Gaps in knowledge and future directions for the use of faecal microbiota transplant in the treatment of inflammatory bowel disease.Therap Adv Gastroenterol. 2019; 12 (175628481989103)Crossref PubMed Scopus (6) Google Scholar We administered a consistent volume of 150 mL/FMT (50 g stool, 107 colony forming units/mL) over 12 infusions to all patients. This approach was akin to mesalamine treatments and influenced by a previous adult trial performed at our center.13Moayyedi P. Surette M.G. Kim P.T. et al.Fecal microbiota transplantation induces remission in patients with active ulcerative colitis in a randomized controlled trial.Gastroenterology. 2015; 149: 102-109.e6Abstract Full Text Full Text PDF PubMed Scopus (796) Google Scholar There is uncertainty regarding optimal frequency and duration to give FMT. We administered FMT twice per week, but in retrospect, this may have been too frequent. Most trials administered FMT less frequently, while showing similar efficacy to a trial that administered FMT 5 times per week.4Narula N. Kassam Z. Yuan Y. et al.Systematic review and meta-analysis: fecal microbiota transplantation for treatment of active ulcerative colitis.Inflamm Bowel Dis. 2017; 23: 1702-1709Crossref PubMed Scopus (94) Google Scholar Weekly therapy is likely sufficient and most trials have evaluated end points at 8 weeks. In our trial, we chose to use noninvasive fecal calprotectin testing as a proxy measure of mucosal healing. However, our lack of endoscopic outcomes was a limitation and was impacted by institutional resources and participant willingness to undergo invasive procedures for research purposes. Adult RCTs assessing the efficacy of biologics have used endoscopic outcomes, although pediatric biologic trials have described similar challenges.21Hyams J. Damaraju L. Blank M. et al.Induction and maintenance therapy with infliximab for children with moderate to severe ulcerative colitis.Clin Gastroenterol Hepatol. 2012; 10: 391-399.e1Abstract Full Text Full Text PDF PubMed Scopus (169) Google Scholar,22Sands B.E. Sandborn W.J. Panaccione R. et al.Ustekinumab as induction and maintenance therapy for ulcerative colitis.N Engl J Med. 2019; 381: 1201-1214Crossref PubMed Scopus (250) Google Scholar To compare efficacy of pediatric FMT for UC against biologics, future trials will need to incorporate endoscopic outcomes into assessment. Pediatric UC FMT trials involving adolescents may tolerate flexible sigmoidoscopy with conscious sedation.23Gilger M.A. Anesthesia for pediatric endoscopy.Gastrointest Endosc. 1995; 42: 596Abstract Full Text Full Text PDF PubMed Scopus (2) Google Scholar FMT for pediatric C difficile treatment has shown low rates of adverse events.24Davidovics Z.H. Michail S. Nicholson M.R. et al.Fecal microbiota transplantation for recurrent Clostridium difficile infection and other conditions in children.J Pediatr Gastroenterol Nutr. 2019; 68: 130-143Crossref PubMed Scopus (43) Google Scholar The safety of FMT in pediatric IBD or in pediatric C difficile with concomitant IBD is less reported.25Cho S. Spencer E. Hirten R. et al.Fecal microbiota transplant for recurrent Clostridium difficile infection in pediatric inflammatory bowel disease.J Pediatr Gastroenterol Nutr. 2019; 68: 343-347Crossref PubMed Scopus (8) Google Scholar In our study, we found a higher proportion of serious adverse events (SAEs) in patients receiving active (FMT) treatment, which has not been demonstrated across other trials.4Narula N. Kassam Z. Yuan Y. et al.Systematic review and meta-analysis: fecal microbiota transplantation for treatment of active ulcerative colitis.Inflamm Bowel Dis. 2017; 23: 1702-1709Crossref PubMed Scopus (94) Google Scholar Our rates may have been impacted by our chosen case definitions. Patient hospitalization was classified as a SAE, including if patients were hospitalized to initiate intravenous steroid treatments, even if this was necessary solely as treatment of active colitis. Development of C difficile was also classified as a SAE, despite being unable to differentiate a recurrent infectious episode from an inflammatory UC flare. Higher asymptomatic C difficile colonization rates have been described in children with IBD.25Cho S. Spencer E. Hirten R. et al.Fecal microbiota transplant for recurrent Clostridium difficile infection in pediatric inflammatory bowel disease.J Pediatr Gastroenterol Nutr. 2019; 68: 343-347Crossref PubMed Scopus (8) Google Scholar Our 2 patients who developed C difficile had a prior history of C difficile infection. Patients in the FMT arm also showed greater baseline disease severity (pancolitis, 77% vs 58%; anti-TNF or IM therapy, 54% vs 17%) than patients in the placebo arm. We were unable to adjust for disease distribution, history of C difficile infection, or concomitant medication use in our trial, but baseline differences between study arms likely impacted our SAE rates. As more pediatric centers are performing FMT for the treatment of C difficile colitis, we must now share our experience of FMT in pediatric IBD to increase confidence among patients and primary providers to support future trials. This may be further enhanced by collaboration with adult gastroenterology centers to share the enormous upfront costs of developing FMT programs, expertise, and obtaining institutional and federal regulatory approvals. Combined adult/pediatric trials with discrete pediatric study arms could mitigate many of these obstacles. This first pilot RCT suggests that recruitment remains the most significant challenge. A larger number of centers are likely required to achieve sufficient recruitment, but pediatric FMT studies are also affected by the complexity of the intervention and regulatory approvals needed to conduct these trials. Studies involving potentially biologically hazardous materials in vulnerable populations require safe transport, storage, and safety screening. Early-stage trials also require careful ongoing observation for the emergence of pediatric-specific adverse effects. Despite the many challenges underlying this work, our trial offers the first pilot RCT evidence that FMT may have an important role in improving symptoms and inflammatory indices in pediatric UC. Limited data suggest response may be sustained for up to 24 weeks after the final FMT infusion, and distinct microbial changes may predict improvements in clinical response and mucosal inflammation associated with FMT. We did not reach our primary feasibility outcome of achieving recruitment targets. These findings are preliminary, and additional data on efficacy and adverse events are needed. Lessons learned from this first placebo-controlled trial will support future pediatric investigators’ work in this novel, cost-effective, targeted approach to pediatric IBD treatment. We believe future trials assessing FMT for pediatric UC should (1) select age-appropriate donors, (2) incorporate endoscopic assessment to better identify mucosal healing, (3) assess microbiome functional data, and (4) perform follow-on mechanistic studies to develop further understanding of the role of FMT in UC management. McMaster Pediatric Fecal Microbiota Transplant Research Collaboration: Michael Surette,1 Christine Lee,2 David Godin,3 J.C. Szamosi,4 Waliul I. Khan,5 Michelle Shah,6 Laura Rossi,6 Lehana Thabane,7 Michal Moshkovich,8 and Melanie Figueiredo,8 from the 1Farncombe Family Digestive Health Research Institute, Department of Medicine, Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, Canada; 2Department of Pathology and Laboratory Medicine, University of British Columbia, Vancouver, British Columbia, Canada; 3Département de Pédiatrie, Division de Gastroentérologie, Hépatologie & Nutrition, Université de Montréal, Montreal, Canada; 4Farncombe Family Digestive Health Research Institute, Department of Medicine, McMaster University, Hamilton, Canada; 5Division of Clinical Pathology, Department of Pathology and Molecular Medicine, McMaster University, Hamilton, Canada; 6Farncombe Family Digestive Health Research Institute, Department of Medicine, McMaster University, Hamilton, Canada; 7Department of Health Research Methods, Evidence and Impact, McMaster University, Hamilton, Ontario, Canada; and 8Department of Pediatrics, McMaster University, Hamilton, Ontario, Canada. N.P., J.P., and P.M. contributed to study concept and design. N.P. and J.P. were responsible for recruitment and screening of all patients, with support provided by E.H. and L.H. K.G. was responsible for recruitment and screening of patients at Centre hospitalier universitaire Sainte-Justine. Fecal microbiota transplants were administered by N.P., J.P., L.H. and K.G. P.M. provided technical support and study supervision. N.P. wrote the initial draft of the manuscript, with assistance from P.M. N.P., J.P., L.H., E.H. and K.G. provided critical review and approval of the final version of the manuscript. The authors disclose no conflicts.