Background/Objectives: The SARS-CoV-2 pandemic challenged patients with inflammatory bowel disease (IBD) under immunosuppressive therapies. We used data from the RisCoin cohort to investigate factors associated with a poor immune response to mRNA vaccination in these patients. Methods: From 4115 RisCoin participants, we matched 110 IBD patients by age and time interval since the second mRNA vaccination with 306 healthcare workers (HCW) without comorbidities (HCW-healthy) and 292 with medical conditions (HCW-plus); all were SARS-CoV-2 infection naïve. Basic questionnaires collected data on medication, COVID-19 vaccinations and side-effects, dietary patterns, lifestyle factors, and self-perceived stress. Main outcomes included anti-spike immunoglobulin levels and antibody-mediated live-virus neutralization immunity (NT) to the Omicron BA.1 variant (threshold NT ≥ 10 defined as IC50 values ≥1:10 serum dilution) after the second (baseline) and third vaccinations. Results: At baseline, IBD patients treated with anti-TNF but not those under vedolizumab or ustekinumab therapy had lower anti-spike levels compared to HCW-healthy and HCW-plus (166 versus 1384 and 1258 BAU/mL, respectively; p < 0.0001). Anti-TNF compared to vedolizumab/ustekinumab-treated patients reached NT titers above threshold in 17% versus 64%, respectively, and HCW-subgroups in 73% and 79% (all p < 0.0001). Current smokers showed a four to five times increased risk for non-neutralizing immunity compared to non-smokers. After the third vaccination, NT titers did not reach threshold in 15% anti-TNF compared to 5% vedolizumab/ustekinumab-treated patients and none of HCW (p < 0.01). Patients with IBD reported fewer clinical symptoms after vaccination. Perceived stress was not increased. Conclusions: Our findings support individualized schedules for mRNA-based vaccines in IBD patients with different immunosuppressive therapies and enforcement of non-smoking.

Pathogenic mutations in Tetratricopeptide repeat domain 7A ( TTC7A ) result in gastrointestinal and immunological disorders of which the pathobiology is not fully understood. Previous case reports indicate that TTC7A plays an important role in preserving intestinal epithelial integrity, but thus far only few variants have been investigated and it is unclear if different variants exert the same effects. Here, we aim to study the effects of different variants on the intestinal epithelium. We present three instances of pediatric inflammatory bowel disease (IBD), displaying varying clinical symptoms and severity levels, and associated with different heterozygous missense mutations in TTC7A . Intestinal organoids derived from patients show dissimilar epithelial phenotypes and exhibit differences in growth, morphology, apicobasal polarity, responses to specific drugs, TTC7A expression, and transcriptional profiles. The findings of our study suggest differences in pathobiology between individuals with different TTC7A mutations. This investigation enhances our comprehension of TTC7A-related conditions and can have implications for developing targeted therapies for TTC7A-associated disorders. ### Competing Interest Statement The authors have declared no competing interest. EU H2020, 801540 Leona M. and Harry B. Helmsley Charitable Trust, https://ror.org/011x6n313 Maag Lever Darm Stichting, CDG-15

Endoscopic healing (EH) is the major long-term treatment target for inflammatory bowel diseases (IBDs), mainly achieved by immune-suppressive therapies. However, the chronic and relapsing nature of the disease indicates a lifelong persistence of unknown tissue-associated IBD residues. Based on longitudinally collected gastrointestinal biopsies (n = 217) from pediatric patients with IBD (N = 32) and pediatric non-IBD controls (N = 5), we describe cellular, molecular, and microbial drivers of IBD that persist under EH in the terminal ileum and sigmoid colon. Whole biopsy transcriptomics in combination with single T cell analysis (72,026 cells) characterizes an inflammatory bowel residual disease (IBrD) signature, connecting stress- and inflammation-related tissue markers (e.g., DUOX2, SAA2, and NOS2) with pathogenic interleukin-17 (IL-17)-producing T helper cells. 16S rRNA gene sequencing reveals individual microbial composition with persistently low diversity, irrespective of disease location and activity. Overall, our study identifies a persisting IBD signature that reflects ongoing mucosal alterations despite EH. These markers may provide targets for future or sequential therapies.

BACKGROUND:Patients with eosinophilic esophagitis (EoE) require long-lasting resolution of inflammation to prevent fibrostenosis and dysphagia. However, the dissociation between symptoms and histologic improvement suggests persistent molecular drivers despite histologic remission. OBJECTIVE:We characterized persisting molecular alterations in pediatric patients with EoE using tissue transcriptomics and proteomics. METHODS:Esophageal biopsy samples (n = 247) collected prospectively during 189 endoscopies from pediatric patients with EoE (n = 36, up to 11 follow-up endoscopies) and pediatric controls (n = 44, single endoscopies) were subjected to bulk transcriptomics (n = 96) and proteomics (n = 151). Intercellular junctions (desmoglein-1/3, desmoplakin, E-cadherin) and epithelial-to-mesenchymal transition (vimentin:E-cadherin ratio) were assessed by immunofluorescence staining. RESULTS:Active EoE (≥15 eosinophils per high-power field [eos/hpf]), inactive EoE (<15 eos/hpf), and deep-remission EoE (0 eos/hpf) were diagnosed in 107 of 185, 78 of 185, and 41 of 185 biopsy samples, respectively. Among the dysregulated genes (up-/downregulated 310/112) and proteins (up-/downregulated 68/16) between active EoE and controls, 17 genes, and 6 proteins remained dysregulated in inactive EoE. Using persistently upregulated genes (n = 9) and proteins (n = 3) only, such as ALOX15, CXCL1, CXCL6, CTSG, CDH26, PRRX1, CLC, EPX, and periostin (POSTN), was sufficient to separate inactive EoE and deep-remission biopsy samples from control tissue. While 32 differentially expressed genes persisted in deep-remission EoE compared to controls, the proteome normalized except for persistently upregulated POSTN. Epithelial-to-mesenchymal transition normalized in inactive EoE, whereas desmosome recovery remained impaired as a result of desmoglein-1 downregulation. CONCLUSION:The analysis of molecular changes shows persistent EoE-associated esophageal dysregulation despite histologic remission. These data expand our understanding of inflammatory processes and possible mechanisms that underlie tissue remodeling in EoE.

OBJECTIVES:European Society for Pediatric Gastroenterology, Hepatology, and Nutrition (ESPGHAN) guidelines recommend first-line serology for suspected celiac disease (CeD), measuring only transglutaminase antibodies (TGA-immunoglobulin A [IgA]) plus total IgA. If TGA-IgA is ≥10 times the normal value, pediatric gastroenterologists (pedGI) may diagnose CeD without biopsies if autoantibodies against endomysial antibodies (EMA-IgA) are positive in a 2nd blood sample. This Quality-of-Care (QoC) project benchmarked diagnostic workup in clinical practice using ESPGHAN CeD guidelines as reference. METHODS:A pseudonymized survey on CeD practices was sent to 141 hospitals within the ESPGHAN QoC-network in 28 countries. RESULTS:Questionnaires were completed by 129/141 (91.5%) hospitals, with 121 (94%) having pedGI staff. As reasons conflicting with good QoC for CeD in their setting, responders assumed knowledge deficits among the public (57%), primary care providers (64%), non-GI physicians (16%), and pedGIs (0%). For initial testing, 66% of physicians ordered only total IgA and TGA-IgA, 7% did not use this combination, and 29% ordered additional serology (TGA-IgG, EMA, antibodies against deaminated gliadin peptide, or native gliadin). Regarding conflicting results for TGA-IgA and histopathology in IgA-sufficient children, 61% incorrectly classified negative TGA-IgA with Marsh 2 and 57% with Marsh 3 lesions as "potential CeD," while 49% excluded CeD in the case of villous atrophy and negative TGA-IgA. Routine practice did not align with the ESPGHAN recommendations regarding performance of duodenal biopsies (27%), EMA-testing (34%), and diagnosis of CeD in IgA-deficient children (32%). CONCLUSIONS:We identified areas for improving QoC regarding both effectiveness and efficacy, in pediatric patients with suspected CeD, and consequently developed easy-to-use tools to improve guideline implementation.

OBJECTIVES:Celiac disease (CeD) is a life-long systemic immune-mediated disorder. Data on burden and cost of CeD in children are scarce. We assessed healthcare resource utilization (HCRU) and cost of healthcare services of newly diagnosed children in Germany. METHODS:This retrospective case-control study covered a period from 2014 to 2021, using German Statutory Health Insurance claims data from the "Institute for Applied Health Research Berlin" (InGef). The HCRU (hospitalizations, outpatient contacts, outpatient drug prescriptions) and cost of CeD patients aged <6 (group 1) and 6-11 years (group 2) between 2017 and 2019 were compared with matched non-CeD individuals (1:5 matching by age, sex, Charlson Comorbidity Index, and region) during the time of diagnosis and 2 years thereafter. Case definition required ≥1 diagnosis of CeD (ICD-10-GM K90.0) as inpatient or ≥2 recorded diagnoses as outpatient plus ≥1 CeD-related serological test, and no recorded CeD diagnoses during the 3-year preobservation period. RESULTS:We identified 410 CeD cases resulting in incidence rates of 32.5 and 34.1 per 100,000 individuals in groups 1 and 2, respectively. During time of diagnosis and 2 years thereafter, CeD patients had increased HCRU (median) compared to their controls (two more hospitalizations, almost three-times more outpatient contacts, and 3-4 more prescriptions), resulting in higher total costs (median difference €1677 and €1343 in group 1 and 2, respectively) (all p < 0.001). CONCLUSIONS:These findings underscore the substantial burden of CeD on patients and healthcare systems, highlighting the need for targeted interventions and effective management strategies to mitigate this impact.

Background and aims: We aimed to identify serum metabolites associated with mucosal and transmural inflammation in pediatric Crohn disease (pCD). Methods: Fifty-six pCD patients were included through a pre-planned sub-study of the multicenter, prospective, ImageKids cohort, designed to develop the Pediatric Inflammatory Crohn's MRE Index (PICMI). Children were included throughout their disease course when undergoing ileocolonoscopy and magnetic resonance enterography (MRE) and followed for 18 months when MRE was repeated. Serum metabolites were identified using liquid chromatography/mass spectroscopy. Outcomes included: PICMI, the simple endoscopic score (SES), faecal calprotectin (FCP), and C-reactive protein (CRP), to assess transmural, mucosal, and systemic inflammation, respectively. Random forest models were built by outcome. Maximum relevance minimum redundancy (mRMR) feature selection with a j-fold cross validation scheme identified the best subset of features and hyperparameter settings. Results: Tryptophan and glutarylcarnitine were the top common mRMR metabolites linked to pCD inflammation. Random forest models established that amino acids and amines were among the most influential metabolites for predicting transmural and mucosal inflammation. Predictive models performed well, each with an area under the curve (AUC) > 70%. In addition, serum metabolites linked with pCD inflammation mainly related to perturbations in citrate cycle (TCA cycle), aminoacyl-tRNA biosynthesis, tryptophan metabolism, butanoate metabolism, and tyrosine metabolism. Conclusions: We extend on recent studies, observing differences in serum metabolite between healthy controls and Crohn disease patients, and suggest various associations of serum metabolites with transmural and mucosal inflammation. These metabolites could improve the understanding of pCD pathogenesis and assess disease severity.

OBJECTIVES:Assessment of anthropometric data is essential for paediatric healthcare. We surveyed the implementation of European Society of Paediatric Gastroenterology, Hepatology and Nutrition (ESPGHAN) evidence-based guidelines and practical recommendations on nutritional care, particularly regarding anthropometric measurements. METHODS:Paediatric hospitals from 28 European countries provided pseudonymized data through online questionnaires on hospital characteristics and their standards of nutritional care. Practical tasks assessed an unbiased collection and reporting of anthropometric measurements in random patients' files and discharge letters. RESULTS:Of 114 hospitals (67% academic), 9% have no nutritionist/dietitian available, 18% do not provide standard policy to assess weight and height and 15% lack training for nursing staff for accurate performance. A wall-mounted stadiometer to measure standing height and equipment for sitting weight is unavailable in 9% and 32%, respectively. Infant length is measured by one instead of two healthcare professionals and with a tape instead of a rigid length measuring board in 58% and 15% of hospitals, respectively. The practical tasks reviewed 1414 random patients, thereof 446 younger than 2 years of age. Missing documentation occurred significantly more often for height versus weight and their percentiles in infants ≤2 years versus older children, and in general paediatric versus gastrointestinal patients, with no difference between academic and nonacademic hospitals. Review of documented anthropometric data in discharge letters disclosed that consultants significantly underestimated the deficits in their units compared to documented data. CONCLUSIONS:The survey revealed significant gaps in performance and documentation of anthropometry in the participating hospitals. A resurvey will assess changes in quality of care over time.

Objectives To investigate the associations of physical activity (PA) and sedentary behaviour in early childhood with asthma and reduced lung function in later childhood within a large collaborative study.Design Pooling of longitudinal data from collaborating birth cohorts using meta-analysis of separate cohort-specific estimates and analysis of individual participant data of all cohorts combined.Setting Children aged 0-18 years from 26 European birth cohorts.Participants 136 071 individual children from 26 cohorts, with information on PA and/or sedentary behaviour in early childhood and asthma assessment in later childhood.Main outcome measure Questionnaire-based current asthma and lung function measured by spirometry (forced expiratory volume in 1 s (FEV1), FEV1/forced vital capacity) at age 6-18 years.Results Questionnaire-based and accelerometry-based PA and sedentary behaviour at age 3-5 years was not associated with asthma at age 6-18 years (PA in hours/day adjusted OR 1.01, 95% CI 0.98 to 1.04; sedentary behaviour in hours/day adjusted OR 1.03, 95% CI 0.99 to 1.07). PA was not associated with lung function at any age. Analyses of sedentary behaviour and lung function showed inconsistent results.Conclusions Reduced PA and increased sedentary behaviour before 6 years of age were not associated with the presence of asthma later in childhood.

Abstract Issue RisCoin, a prospective monocentric longitudinal observational study, aimed to identify risk factors for COVID-19 vaccine failure. Secondary aim is to monitor symptoms, SARS-CoV-2 infection, vaccination status of 3816 enrolled healthcare workers (HCW) and 180 patients with inflammatory bowel disease (IBD). Since the LMU University Hospital Munich served both as study sponsor and employer of the HCW, a secured approach was required. Description of the solution Participants accessed the study app (CentraXX, KAIROS GmbH, Germany) via pseudonymized Contact-ID with irreversible anonymization after 6 months. Key app features were the serological results report, bidirectional messaging, and weekly survey for self-reported data on vaccinations, infections, and symptoms. Active app use was defined as submitting >1 weekly survey during the study period 10.2021-12.2022. Results Over 15 months, our study team maintained 1964 two-way communications with 958 participants via the app. Of 3979 participants with app access, 3622 (91%) were active users, 2606 (65%) submitted 1 to 11 surveys, 1016 (26%) made ≥12 submissions (P75, “frequent users”). Frequent users were more likely to be IBD patients (p = 0.001), female (p < 0.001), aged 60 or older (p < 0.001). Staff in administration and nurses were more likely to be frequent users compared to physicians (p < 0.001). Main problems included the initial operational system disparities resulting in app crashes and continuous need for app reactivation. Both led to loss of active participants and required substantial staff resources to onboard and support participants during the study. Lessons The study app enabled secure, flexible, bidirectional communication with all participants. Despite technical issues, the majority actively used the app and provided valuable longitudinal data through weekly survey submissions. Key messages • A study-specific app provides a flexible and secure bidirectional anonymous communication for the study team and participants. • Adherence to app-based communication and data collection for pandemic monitoring was particularly high among patients, nurses and administrative staff.

Schlüsselwörter SARS-CoV-2-Infektionen - Chronisch-entzündliche Darmerkrankung - CED - Morbus crohn - Colitis ulcerosa

Season of birth, viral infections, HLA haplogenotypes and non-HLA variants are implicated in the development of celiac disease and celiac disease autoimmunity, suggesting a combined role of genes and environmental exposures. The aim of the study was to further decipher the biological pathways conveying the season of birth effect in celiac disease autoimmunity to gain novel insights into the early pathogenesis of celiac disease. Interactions between season of birth, genetics, and early-life environmental factors on the risk of celiac autoimmunity were investigated in the multicenter TEDDY birth cohort study. Altogether 6523 genetically predisposed children were enrolled to long-term follow-up with prospective sampling and data collection at six research centers in the USA, Germany, Sweden and Finland. Celiac disease autoimmunity was defined as positive tissue transglutaminase antibodies in two consecutive serum samples. There was a significant season of birth effect on the risk of celiac autoimmunity. The effect was dependent on polymorphisms in CD247 gene encoding for CD3 zeta chain of TCR-CD3 complex. In particular, children with major alleles for SNP rs864537A > G, in CD247 (AA genotype) had an excess risk of celiac autoimmunity when born March-August as compared to other months. The interaction of CD247 with season of birth on autoimmunity risk was accompanied by interactions with febrile infections between the ages of 3-6 months. Considering the important role of TCR-CD3 complex in the adaptive immune response and our findings here, CD247 variants and their possible effect of subgroups in autoimmunity development could be of interest in the design of future gene-environment studies of celiac disease.

Objectives: To identify infants with biliary atresia (BA), European Society of Paediatric Gastroenteroloy and Nutrition (ESPGHAN)/North American Society of Pediatric Gastroenteroloy and Nutrition (NASPGHAN) guidelines recommend measurement of conjugated/direct bilirubin in infants with prolonged jaundice and using a stool colour card (SCC). The 'Quality of Care' Task Force of ESPGHAN performed two surveys to assess current case finding for BA and age at Kasai portoenterostomy (KPE). Methods: The first survey approached 26 European hepatology centres to report age at referral and age at KPE of all infants diagnosed with BA from 2015 to 2019. The second survey targeted paediatricians in France to assess awareness and compliance with the recently introduced SCC. Results: Data from 785 patients with BA from 18 centres in 15 countries revealed a mean age at referral to tertiary centre of 55 days (median 53, IQR 48-60) (n = 636). The mean age at KPE was 61 days (median 60; IQR 54-67) (n = 772). For 6% of patients, cirrhosis was too advanced for surgery. Of 392 paediatricians answering the second survey, 53% felt familiar with the target diseases, 80% correctly identified cholestasis and 59% always inquired about the infant's stool colour. If abnormal, 93% would order blood tests and 85% call for advice. The SCC screening was considered helpful for case finding and improving knowledge of cholestatic diseases by 62% and 45% paediatricians, respectively. Conclusions: Referral of infants for KPE remains late, indicating low adherence to search for cholestasis in icteric infants by age 2-3 weeks. Knowledge and structures need improvement to allow earlier guideline conform case finding, diagnosis and therapy.

Purpose To explore occupational and non-occupational risk and protective factors for the coronavirus disease 2019 (COVID-19) in healthcare workers (HCWs). Methods Serum specimens and questionnaire data were obtained between October 7 and December 16, 2021 from COVID-19-vaccinated HCWs at a quaternary care hospital in Munich, Germany, and were analyzed in the RisCoin Study. Results Of 3,696 participants evaluated, 6.6% have had COVID-19 at least once. Multivariate logistic regression analysis identified working in patient care occupations (7.3% had COVID-19, 95% CI 6.4–8.3, P r = 0.0002), especially as nurses, to be a potential occupation-related COVID-19 risk factor. Non-occupational factors significantly associated with high rates of the disease were contacts to COVID-19 cases in the community (12.8% had COVID-19, 95% CI 10.3–15.8, P r < 0.0001), being obese (9.9% had COVID-19, 95% CI 7.1–13.5, P r = 0.0014), and frequent traveling abroad (9.4% had COVID-19, 95% CI 7.1–12.3, P r = 0.0088). On the contrary, receiving the basic COVID-19 immunization early during the pandemic (5.9% had COVID-19, 95% CI 5.1–6.8, P r < 0.0001), regular smoking (3.6% had COVID-19, 95% CI 2.1–6.0, P r = 0.0088), living with the elderly (3.0% had COVID-19, 95% CI 1.0–8.0, P r = 0.0475), and frequent consumption of ready-to-eat meals (2.6% had COVID-19, 95% CI 1.1–5.4, P r = 0.0045) were non-occupational factors potentially protecting study participants against COVID-19. Conclusion The newly discovered associations between the living situation, traveling as well as dietary habits and altered COVID-19 risk can potentially help refine containment measures and, furthermore, contribute to new mechanistic insights that may aid the protection of risk groups and vulnerable individuals.

Abstract Background Endoscopic healing (EH) is the major long-term treatment target for inflammatory bowel diseases (IBD) in adults and paediatric patients. However, EH may not represent disease clearance. Hence, risk of relapse remains high and treatment discontinuation after reaching EH often results in disease exacerbation. We aimed to identify persistent cellular, molecular and microbial drivers of IBD under EH and longitudinally collected endoscopic biopsies from paediatric patients for analysis of single T-cell and bulk transcriptomics as well as mucosa-associated microbiota. Methods We followed disease trajectories of paediatric IBD patients treated according to international guidelines and collected mucosal biopsies from the terminal ileum (TI) and sigmoid colon (SC) at baseline (T1) and after approximately 3-12 months (T2) to assess EH. Non-IBD controls showed no macroscopic or histologic signs of inflammation. Host RNA and bacterial DNA were simultaneously extracted from single biopsies for bulk RNA-seq, and 16S rRNA seq. A second biopsy was used for isolation of lamina propria mononuclear cells (LPMCs), followed by CD45+, CD3+ cell sorting and single T-cell analysis (10X Genomics). Data were quality controlled and integrated. Results 217 biopsies (135 simultaneous extraction of host RNA and bacterial DNA; 82 single T-cell analysis) from 32 paediatric IBD patients (mean age 13 ± 3.5 years, 21 Crohn’s disease [CD], 11 ulcerative colitis [UC]; T1 = 32, T2 = 32, T > 2 = 6) and 5 non-IBD controls were analysed. Time between T1 and T2 averages 40 ± 22 weeks. At baseline, 15 patients (14 CD, 1 UC) were newly diagnosed and 31/32 patients had active mucosal inflammation. Twenty-two patients (71%) achieved EH at T2 (SES-CED ≤2 and absence of ulcerations), mostly on anti-TNF therapy. One patient (EH at T1) experienced relapsing disease within 10 weeks after discontinuing medication. In the bulk RNA-seq, we identified 299 differential expressed genes (DEGs; corrected p-value <0.05, FC >2.0), such as DUOX2, SAA2-SAA4, FCGR3B and NOS2, that are associated with active IBD and remained upregulated in EH in contrast to non-IBD controls. In addition single cell analysis revealed an IBD-specific pathogenic Th17 cluster that continued to exist in EH and showed high correlation with top DEGs after data integration. 16S rRNA gene seq highlighted highly individual mucosa-associated bacterial profiles and a reduced α-diversity in active and EH compared to non-IBD controls. Conclusion A persisting IBD signature in EH reflects ongoing cellular, molecular and microbial activity in comparison to non-IBD controls despite EH and mucosal regeneration. These markers may provide targets for future or sequential therapies.

Key word therapy - diagnostics - eradication - resistance - antibiotics

Abstract Background DEVELOP is a multi-center, global, prospective, observational, longitudinal registry of long-term safety of infliximab (and other treatments) in paediatric patients (pts) with inflammatory bowel disease (IBD) <18 years (yrs) at diagnosis. Over the course of follow-up, many pts required changes in therapy. Ustekinumab (UST) is approved for treatment of Crohn’s disease (CD) in adults and is currently being evaluated for safety/efficacy in paediatric pts. This report focuses on assessment of safety of UST in paediatric pts with CD from DEVELOP. Methods Data included paediatric pts treated with UST from 31 May 2007 through 30 June 2022; data are collected every 6 months. The analyzed population included: all paediatric pts (all pts), pts weighing <40kg (<40kg group), and pts weighing ≥40kg (≥40kg group). Assessments included medical and treatment history, UST exposure, adverse events (AEs), serious AEs (SAEs), CD-related SAEs leading to hospitalization, IBD surgeries, serious and opportunistic infections, malignancies, and deaths. Results A total of 150 pts received UST (49.3% females); 31 in the <40kg group and 119 in the ≥40kg group (Table 1). Most treated pts (92.0%) were 12-17yrs. The majority (91%) of pts were initially dosed with UST every 8 weeks (q8w); at the last known dose, 64% received UST q8w and 22% q4w. Mean (SD) age of initial UST exposure was 15yrs (2.19). Prior IBD surgery was reported in 65.3% pts. The majority of pts (98%) had prior biologic therapy and 72% received ≥2 biologics prior to UST. Overall, 37/150 (24.7%) of pts discontinued UST during follow-up, with a mean (SD) time to discontinuation of 16.7 (17.00) months; 84/150 (56.0%) were exposed to UST for ≥24 months. Rates (events/100 pt-yrs) of AEs were higher in the ≥40kg group (177.62) than in the <40kg group (101.27). Rates of SAEs were slightly lower among the ≥40kg group (25.42) vs <40kg (32.67). There were no SAEs related to infusion or injection site reactions. Rates of serious infections and CD-related hospitalizations were low and similar between groups, and rates of IBD-related surgeries were similar between groups (Figure 1). One malignancy (malignant carcinoid tumor) was reported in a female (18yrs) in the ≥40kg group with a history of prior therapy with vedolizumab, methotrexate, and 6-MP. No deaths or opportunistic infections were reported. Conclusion The safety profile observed for this off-label use of UST in paediatric CD pts in DEVELOP was similar to that of the treated adult population, despite most paediatric pts having prior biologic exposure. No new safety signals are identified in this paediatric population.