INTRODUCTION
Crohn's disease (CD) is a complex, chronic immune-mediated inflammatory bowel disease affecting the gastrointestinal tract discontinuously from mouth to anus (1). Chronic intestinal inflammation can result in progressive bowel damage and complications including fistulas, strictures, and abscesses (2,3). Fistulizing CD is a severe and complicated form, characterized by fistula formation between the bowel and adjacent organs, with the most common location perianal (fistula-in-ano) (1,3,4).
Approximately one in 4 patients with CD develop perianal fistulas within 20 years of diagnosis (5–7), and those with perianal fistulizing CD (pCD) at diagnosis experience a more severe and disabling clinical course (3,8). As such, patients with pCD have significant disease and treatment burden, and overall poor prognosis (9–11). These patients often experience debilitating symptoms, including considerable pain, persistent perianal discharge, and fecal incontinence, which can significantly impair their quality of life (QoL) (10,12,13).
Despite this, pCD remains underexplored and lacks validated endpoints for clinical research.
The aim of this review was to provide expert opinion on the most appropriate endpoints for pCD clinical trials. We provide an overview of diagnosis and classification and discuss guidance from the European Medicines Agency (EMA) and US Food and Drug Administration (FDA) for clinical trials. To inform discussion of pCD endpoints, a literature review was conducted on May 1, 2024, in PubMed using broad search terms including Crohn's, fistula/fistulizing, perianal and anal fistula, and randomized controlled trial (RCT) and clinical trial filters.
The endpoints used in pivotal phase III and phase IV trials with a primary or main post hoc endpoint for pCD were scored on a Likert scale (strongly agree, agree, neutral, disagree, or strongly disagree) based on criteria considered essential for an optimal pCD endpoint. Specifically, next to being rooted in the biology of the disease, a pCD endpoint should be objective, accurate, and reproducible (measured easily, inexpensively); account for expected effect size and the placebo effect (low background noise and response rate); and show clinically meaningful changes. Separately, the endpoint should be predictive for long-term outcomes of pCD.
Finally, we consider key components of a pCD trial design.
DIAGNOSIS AND CLASSIFICATION OF PERIANAL FISTULAS
Accurate diagnosis and classification of perianal fistulas is vital because these findings affect medical and surgical treatment approaches (14,15). The European Crohn's and Colitis Organisation guidelines recommend pelvic magnetic resonance imaging (MRI), with examination under anesthesia, for the initial assessment of perianal fistulas (15). Pelvic MRI is the examination of choice for the anatomical and complexity classification of fistula, as well as the evaluation of fistula activity and detection of associated complications (13).
Pelvic MRI is increasingly used for assessment of radiologic response and healing after biologic and surgical therapy (16–18). Several MRI-based scoring methods are available to assess fistula activity, severity, and response to treatment (e.g., Van Assche Index [VAI], modified VAI, and Magnetic Resonance Novel Index for Fistula Imaging in Crohn's Disease [MAGNIFI-CD]) and have been reviewed elsewhere (17,19–22). More recently, the pediatric MRI-based perianal CD index was derived specifically for this population (23).
Different approaches exploring the diagnostic use of quantitative MRI sequences have been investigated (16).
Perianal fistulas are classified as simple or complex based on their anatomy and complexity on MRI (Table 1) (4,15,18). Several more detailed classifications have been proposed and applied with varied use, but there is no universal consensus (14,24,25). Recently, the TOpClass Consortium proposed a new classification system for pCD with the aim of standardizing pCD clinical practice and research (26).
Patients are stratified into 4 classes based on disease severity and fistula anatomy; synchronization of patient and clinician goals in decision-making; and identification of indications for curative fistula treatment, diverting ostomy, and proctectomy (26). Patients can cycle through different classes, and treatment strategy recommendations and clinical trial suitability are provided for each class (26).
ASSESSING pCD DISEASE ACTIVITY, CLINICAL RESPONSE, AND SYMPTOMS
Clinical scoring methods addressing pCD disease activity include the Crohn's Disease Activity Index and the Perianal Disease Activity Index (PDAI). The Crohn's Disease Activity Index has limited value in pCD (27); it was primarily developed for luminal disease to assess symptom severity, which often differs from underlying endoscopic disease activity and fistula activity (4). Fistulas are captured under complications, with scores allocated independently of fistula severity.
By contrast, the PDAI quantifies severity in 5 categories affected by fistulas using a 5-point scale, including both patient-reported and physician-assessed outcomes (4). PDAI was evaluated against both physician and patient global assessments (28).
Fistula drainage assessment in clinical trials is often based on a physician's examination (29–38). Fistulas are classified as open (or draining) if pus discharges after digital compression. Clinical response and remission are defined by a >50% reduction in the number of draining fistulas and the absence of draining fistulas, respectively, in 2 consecutive visits.
However, digital compression is inherently prone to bias in clinical trials, and if the 2 visits are close, it represents a cross-sectional assessment, without any guarantee of longevity. There is no evidence supporting its reproducibility or predictive value for long-term outcomes because it has never been formally validated. Moreover, it may not align with objective radiologic assessments of fistula closure (39).
The Inflammatory Bowel Disease Questionnaire (IBDQ) is widely used to assess health-related QoL in patients with CD (40,41). Nevertheless, the IBDQ does not explore fistula-related QoL, as highlighted by the phase III Adipose Derived Mesenchymal stem cells for Induction of REmission in perianal fistulizing Crohn's Disease (ADMIRE-CD) study where the primary objective of fistula response was achieved for darvadstrocel vs placebo, but there was no significant difference in IBDQ (38). There is no universally accepted gold standard patient-reported outcome measure (PROM) for assessing QoL in patients with perianal fistulas (42,43).
Although the EMA recommends PROMs to support definitions of clinical remission/response for trials in CD, specific PROMs for pCD are not recommended (43). The US FDA recommends PROMs to explore symptoms, rather than support efficacy endpoints (44). More recently, a novel PROM was developed for pCD, Crohn's Anal Fistula Quality of Life (CAF-QoL), which comprises 28 questions and can be used in clinical trials and practice after a provisional psychometric validation (42).
The questionnaire consists of 3 domains: A (symptoms from fistula), B (effects of current fistula treatment [medication, operations, or seton]), and C (impact of fistula on QoL over past 6–8 weeks) (42). The total score can range from 0 to 108, with a higher score indicating poorer QoL (42). CAF-QoL has demonstrated good internal consistency (Cronbach alpha 0.88), excellent stability (intraclass correlation 0.98), and good responsiveness and construct validity, with positive correlation with the UK-IBDQ and Hospital Anxiety and Depression Scale (42).
Potential limitations of the CAF-QoL were the lack of access to objective data (e.g., MRI and other anatomic fistula data) for some participants (those recruited through charities), inclusion of patients across the spectrum of pCD (now described classes 1–4), and variability in fistula anatomy and behavior based on patients' longitudinal history of their fistula (42).
In a study conducted in patients with pCD starting on anti-tumor necrosis factor (anti-TNF) therapy, mesenchymal stem cell injection, or hyperbaric oxygen therapy followed by surgical closure (n = 62), CAF-QoL was reported as a reliable and consistently responsive tool that captured meaningful changes in QoL over time regardless of the treatment modality (45). CAF-QoL ≤37 was associated with complete fistula remission and correlated with other QoL measures such as PDAI ≤4 and MAGNIFI-CD = 0. The sensitivity and specificity (95% confidence interval) of CAF-QoL were 80% (58–92) and 56% (39–71), respectively (45).
The low specificity may reflect the known deficiencies in the PDAI and MAGNIFI-CD rather than the CAF-QoL, and both have been identified as inadequate in the recent Core Outcome Measurement Set also undertaken by the TOpClass consortium (manuscript in preparation).
pCD CLINICAL TRIAL CONSIDERATIONS
Surgical interventions
Routine clinical management of pCD involves a combined surgical and medical approach, guided by radiologic and endoscopic diagnostics, which provides improved outcomes compared with surgical or medical treatment alone (12,46). This was demonstrated in the Surgical Closure vs Anti-TNF in the Treatment of Perianal Fistulas in Crohn's Disease (PISA-II) trial, where surgical closure (seton insertion for 6 weeks) combined with short-term anti-TNF therapy-induced fistula healing more frequently than anti-TNF alone (39). Patients with simple perianal fistulas may require surgical treatment (e.g., abscess drainage, fistulotomy, and seton placement) combined with antibiotics (15,47).
Seton placement after surgical treatment of sepsis is recommended for patients with complex fistulas, with the timing of seton removal dependent on subsequent therapy (15).
Prestudy/run-in study procedures in clinical trials can influence response to treatment in both intervention and comparator arms. Although they are often needed for patient eligibility, this influence must be carefully considered in the design and analysis of studies. Baseline fistula tract anatomy, including lack of associated collections, should be assessed using an MRI technique that is clearly defined and justified, with blinded image reading, ideally performed centrally (43).
Concomitant medications
Phase III clinical trials evaluating pCD typically include patients taking accepted doses of immunosuppressants, corticosteroids, or antibiotics before enrollment, with stable doses maintained during the study period (Table 2) (30,31,38,48,49). The wash-out period for biologics ranges from 1 to ≥3 months, depending on the pharmacokinetic half-life of the corresponding biologic (Table 2) (29,36,48–51). Biologics and combinations thereof can be useful in pCD studies; however, biologic eligibility depends on its mode of action and potential additive or synergistic toxicities.
A biologic that is not efficacious for perianal disease could be efficacious for luminal disease, but the concomitant use of biologics is complex. Furthermore, concomitant biologics could increase placebo response rates and reduce the effect size. This was highlighted in the ADMIRE-CD study, where combined remission for darvadstrocel vs a surgical comparator arm was 54% vs 21% (effect size 33.1%) in patients not receiving stable-dose anti-TNF-α/immunomodulators and 47% vs 38% (9.7%) in patients receiving stable-dose anti-TNF-α only (37).
EVALUATING pCD TREATMENTS
Along with considerable variation in the management of patients with pCD, available treatment options have limited efficacy; hence, an unmet need exists in this hard-to-treat population (12). The anti-TNF therapies infliximab and adalimumab are the only established pCD therapies, with evidence from RCTs conducted specifically in patients with perianal fistulas (29–31). Other treatment recommendations are largely based on post hoc analyses from RCTs in CD that include some patients with pCD, real-world studies, and expert opinion (9,52–54).
Of note, the interleukin-23 inhibitor guselkumab has previously been evaluated in CD, and a phase III trial specifically in pCD is currently ongoing (55).
The greatest limiting factor for addressing pCD treatment challenges is the paucity of evidence from well-designed RCTs to guide treatment recommendations (15,52). Moreover, before evidence can be generated, there is the limitation of a lack of universal validated endpoints for pCD.
The EMA recommends that pCD clinical trials should reflect therapeutic management goals, with the primary endpoint being fistula closure (evidenced by imaging over >1 year) and maintenance of fistula closure (no new fistulas/abscesses) (43). Depending on the drug's mode of action, early clinical response should be documented at 12–24 weeks (43). These endpoints are consistent with a focus on class 2a patients (those who have symptomatic fistulas and are suitable for combined medical and surgical treatment).
As other classes are increasingly studied, a wider range of endpoints will be needed. The US FDA does not provide guidance regarding pCD endpoints (44).
One difficulty in pCD clinical trials is changing placebo response rates and effect sizes over time due to patient-related, disease-related, and intervention-related factors (56). This includes the use of concomitant medications, changes in surgical technique, natural variations in disease course, enhanced adherence in clinical trials, regression to the mean, disease activity and location, seton placement during the run-in period, and the method of treatment administration (56). For example, in A retrospective chart review study evaluatINg the longer-term effectiveneSs of darvadstrocel in PatiEnts who CompleTed ADMIRE-CD study, increasing placebo rates over time caused a decrease in the effect size for darvadstrocel vs placebo; clinical remission rates were 67.4% vs 52.2% (effect size 15.3%), 53.5% vs 43.5% (10.0%), and 53.5% vs 45.7% (7.8%) at weeks 52, 104, and 156, respectively (57).
In the ADMIRE-CD II trial of darvadstrocel vs placebo, all patients underwent surgical fistula preconditioning 2–3 weeks before treatment and closure of internal fistula opening as part of the intervention, which may have contributed to the high response rate in the comparator arm and the limited treatment effect (58).
HISTORICAL pCD ENDPOINTS
Endpoints in pivotal phase III and phase IV trials and post hoc analyses
Table 2 summarizes key trial characteristics and endpoints used in analyses (primary and post hoc) from pivotal phase III and phase IV RCTs assessing new treatments for perianal fistulas. The main endpoint differed in all 10 analyses and none included PDAI. The timing of primary endpoint assessments ranged between 12 weeks and 2 years.
Only 1 of the 4 pCD RCTs identified used combined clinical (closure of all treated external openings that were draining at baseline on gentle compression) and radiologic (absence of collections >2 cm in 2 dimensions) response (29–31,37,38). None of the 6 post hoc analyses used a combined clinical and radiologic primary endpoint (32–36,49–51,59,60). The heterogeneity in endpoints highlights the difficulty clinical researchers face when deciding how best to evaluate efficacy in pCD clinical trials.
The phase II Study to Evaluate the Efficacy and Safety of Filgotinib in the Treatment of Perianal Fistulizing Crohn's Disease (DIVERGENCE 2) highlighted a potential disconnect between clinical and MRI-based fistula healing (61). Fistula response was evaluated using a combined endpoint of reduction from baseline of ≥1 draining external opening, determined by investigator assessment, and no fluid collections >1 cm in 2 dimensions on pelvic MRI (62). Additional MRI measurements included VAI and modified VAI.
Interestingly, clinical fistula healing, but not MRI-based fistula healing, was associated with a high placebo response rate (Dr. Reinisch and Dr. Rimola, personal communication).
Other studies confirmed that MRI-based fistula healing is associated with positive long-term outcomes and MRI-based assessment may identify fistulas with apparent external closure that retain an internal fistula tract (18). This suggests that MRI-associated fistula healing is a more robust endpoint for pCD than clinical fistula healing (18). However, there are some limitations to the use of MRI such as the limited availability of MRI machines, long waiting times, relatively high costs, and lack of expertise to assess the specifics of perianal CD (63).
Furthermore, demonstration of fistula resolution on MRI may lag behind clinical healing (63).
Expert evaluation of pCD endpoints
We individually scored the 12 endpoints listed in Table 2 on how they fulfill the following criteria: objective and accurate, reproducible, shows and effect size, low background placebo noise, low placebo response rate, and ability to measure clinically meaningful change. Scores were highly variable across all criteria for each endpoint (Figure 1, see Supplementary Figure S1, http://links.lww.com/AJG/D849).
We did not agree with more than 1 criteria for any endpoint, and there was no strong agreement for any criteria across the endpoints. No endpoints were agreed/strongly agreed to be reproducible, show an effect size, or provide low placebo background noise or response rates. Five endpoints evaluating fistula closure/healing, clinical remission, and PROMs were agreed to reflect clinically meaningful changes for patients, although the value of PROMs as determinants of clinical utility and predictors of outcome is lacking.
Endpoints were perceived differently due to slight differences in wording, highlighting the need for universality across the literature.
The high variability in our scoring might be due to the lack of stringent definitions, face validity, clinical validity, and clinical utility. Other factors include the lack of clear classification in many of the trials used to generate this endpoint list, and a historic lack of high-quality tools for confirming fistula healing or impact on QoL.
UNMET NEEDS FOR CONSISTENTLY DEFINED CLINICAL AND RADIOLOGICAL pCD ENDPOINTS
Our assessment reinforces the need to define optimal endpoints. The purpose of clinical trials was to generate robust evidence of adequate validity and generalizability to guide decision-making in clinical practice and by policymakers. In this regard, RCTs represent the gold standard for generating evidence (64).
The strengths and limitations of clinical trial endpoints are critical to their interpretation and influence (64). Primary endpoints for pCD have evolved significantly over the past 25 years (65), since the trial by Present et al (1999) that used clinical response (31) to the ADMIRE study (2018) that combined clinical and radiologic remission (38). However, universal definitions to assess clinical fistula response and fistula remission are lacking.
Definitions of fistula healing range from reduction in the number of draining fistulas to the lack of inflammatory activity assessed by MRI (53).
The MRI index MAGNIFI-CD assesses perianal fistulas based on 6 items, including the number of fistula tracts, fistula length, and inflammatory mass (66). The primary endpoint in the PISA-II trial of surgery and anti-TNF was radiological healing, defined as a MAGNIFI-CD score of 0 or a completely fibrotic tract on MRI (39). Radiological healing was associated with improved long-term outcomes and QoL compared with the secondary endpoint of clinical closure (evaluation of discharge on palpation) (39).
Unplanned surgical intervention was also evaluated as a secondary endpoint and identified as a key clinician-reported outcome domain in the core outcome set for pCD that is currently under development (39,67).
Radiologic assessment using scoring systems currently has several limitations, for example, a lack of validated cutoffs that are associated with response/remission/healing and long-term effects on disease outcome, as well as slow internal fistula healing. In addition, pelvic MRIs are not ubiquitously readily available and require specific radiologist expertise, which contribute to long patient waiting times. As such, potential surrogates are needed and could include changes in fistula volume and the fistula's dominant component (fibrotic/active, dark T2 component, etc), as well as adaptations to current radiological scoring systems.
The TOpClass Consortium's pCD patient classification system considers specific goals for each patient class that can guide endpoint selection (26). For example, the primary goal for class 2b patients, who have chronic fistula symptoms and are unsuitable for surgery (including seton removal), is symptom control, which is best evaluated based on QoL (26). Despite this, it is very doubtful that regulatory agencies will accept patient-assessed primary endpoints.
Class 2a patients have a goal of fistula closure and are more suitable for assessments based on the traditional endpoints described above (26). Patients in other classes require a different approach. For example, class 2b patients undergoing biological or anatomical rationalization of their fistula would be best served by an endpoint of downstaging to class 2a, whereas those wishing for stable disease and improved QoL would want to avoid progression to class 2c (and defunctioning stoma formation).
The narrow focus on fistula healing both historically and in many contemporary discussions of pCD endpoints misses most of the patients with pCD, including those with the most severe disease.
CONCLUSION
Robust data from adequately sized, well-designed clinical trials are needed to guide consistent management in clinical practice in this hard-to-treat patient population. Clearly defined, objective and standardized endpoints are required that pave the way for direct comparisons among treatment options and ultimately reduce challenges with treatment decisions. Efforts are underway to develop a core outcome measurement set for pCD that will address these issues.
Conceptually, we believe that an optimal endpoint for pCD should reflect a patient's subjective disease load as well as the inflammatory, anatomical, and destructive characteristics of the disease. Based on our evaluation, future trials for class 2a patients should use coprimary clinical and radiologic assessments to capture both how the patient feels and an objective measure of disease activity. Currently, the most appropriate clinical assessment is fistula drainage, but in the future, a PROM may be more suitable.
Although there is some evidence that evaluating radiological healing alone may be sufficient, further work is needed to address the limitations with MRI. MAGNIFI-CD is currently the best validated MRI-based scoring method, although others should still be considered and a recent consensus definition from the TOpClass Consortium, based on the PISA-II definition, may provide a simple, universal, and clear alternative. A hypothetical clinical trial design is shown in Figure 2.
CONFLICTS OF INTEREST
Guarantor of the article: Walter Reinisch, MD.
Specific author contributions: W.R.: planning the study, collecting and interpreting data, reviewing draft. R.A.: planning the study, collecting and interpreting data, reviewing draft. F.R.: planning the study, collecting and interpreting data, reviewing draft.
V.J.: planning the study, collecting and interpreting data, reviewing draft. J.R.: planning the study, collecting and interpreting data, reviewing draft. L.P.B.: collecting and interpreting data, reviewing draft.
P.T.: collecting and interpreting data, reviewing draft. C.J.B.: collecting and interpreting data, reviewing draft. A.H.: planning the study, collecting and interpreting data, reviewing draft.
All authors approved the final draft submitted.
Financial support: This study was funded by Boehringer Ingelheim. The authors met criteria for authorship as recommended by the International Committee of Medical Journal Editors (ICMJE). The authors did not receive payment related to the development of this manuscript.
Boehringer Ingelheim was given the opportunity to review the manuscript for medical and scientific accuracy as well as intellectual property considerations.
Potential competing interests: W.R. has served as a speaker for AbbVie, Celltrion, Ferring, Janssen, Galapagos, MSD, Roche, Pfizer, Sobi, and Takeda; as a consultant for AbbVie, Agomab, Alfa Sigma, Amgen, Anaptys Bio, AOP Orphan, Boehringer Ingelheim, Bristol Myers Squibb, Calyx, Celltrion, Eli Lilly, Galapagos, Gilead, Index Pharma, Janssen, Medahead, Merck, Microbiotica, Pfizer, Teva, and Takeda; as an advisory board member for AbbVie, Amgen, Boehringer Ingelheim, Bristol Myers Squibb, Celltrion, Galapagos, Janssen, Pfizer, and Teva; and has received research funding from AbbVie, Janssen, Sandoz, Sanofi, and Takeda. R.A. has served as a speaker, consultant, or received research grants from AbbVie, Abivax, AstraZeneca, Biogen, Boehringer Ingelheim, Bristol Myers Squibb, Celgene, Celltrion Healthcare, Dr. Falk Pharma, Galapagos, Gilead, InDex Pharmaceuticals, Johnson & Johnson, Lilly, Merck Sharp & Dohme, Pfizer, Roche Pharma, and Takeda.
F.R. has attended advisory boards and/or received consultancy fees from AbbVie, Adnovate, Agomab, Allergan, Arena, Boehringer Ingelheim, Celgene, Bristol Myers Squibb, CDISC, Cowen, Ferring, Galapagos, Galmed, Genentech, Gilead, Gossamer, Guidepoint, Helmsley, Horizon Therapeutics, Image Analysis Limited, Index Pharma, Jannsen, Koutif, Mestag, Metacrine, Morphic, Organovo, Origo, Pfizer, Pliant, Prometheus Biosciences, Receptos, Redx, Roche, Samsung, Surmodics, Surrozen, Takeda, Techlab, Theravance, Thetis, Tr1X, UCB, Ysios, and 89Bio. V.J. has received consulting/advisory board fees from AbbVie, Alimentiv, Arena Pharmaceuticals, Asahi Kasei Pharma, Asieris, AstraZeneca, Avoro Capital, Bristol Myers Squibb, Celltrion, Eli Lilly, Endpoint Health, Enthera, Ferring, Flagship Pioneering, Fresenius Kabi, Galapagos, Gilde Healthcare, GlaxoSmithKline, Genentech, Gilead, Innomar, JAMP, Janssen, Merck, Metacrine, Mylan, MRM Health, Pandion, Pendopharm, Pfizer, Protagonist, Prometheus Biosciences, Reistone Biopharma, Roche, Roivant, Sandoz, Second Genome, Sorriso, Synedgen, Takeda, TD Securities, Teva, Topivert, Ventyx, and Vividion; as well as speaker's fees from AbbVie, Bristol Myers Squibb, Ferring, Fresenius Kabi, Galapagos, Janssen, Pfizer, Shire, and Takeda. J.R. has received consulting and/or advisory board fees and speaker fees from Alimentiv Inc, Boehringer Ingelheim, Ferring, Janssen, Lument, Origo, Agomab, and Takeda.
L.P.B. has received consulting fees from Abbvie, Abivax, Adacyte, Alimentiv, Alfasigma, Amgen, Apini, Banook, BMS, Celltrion, Enthera, Ferring, Fresenius Kabi, Galapagos, Genentech, Gilead, Iterative Health, Janssen, Lilly, LifeMine, Medac, Morphic, MSD, Nordic Pharma, Novartis, Oncodesign Precision Medicine, ONO Pharma, OSE Immunotherapeuthics, Par' Immune, Pfizer, Prometheus, Roche, Roivant, Samsung, Sandoz, Sanofi, Sorriso, Spyre, Takeda, Teva, ThirtyfiveBio, Tillots, Vectivbio, Vedanta, and Ventyx and consulting fees from Abbvie, Alfasigma, Amgen, Biogen, Celltrion, Ferring, Galapagos, Genentech, Gilead, Iterative Health, Janssen, Lilly, Medac, MSD, Nordic Pharma, Pfizer, Sandoz, Takeda, and Tillots. P.T. has received speaker fees from Takeda, Ferring, and Falk; and has sat on advisory boards for Takeda, including the Inspire steering group, funded by but scientifically independent from Takeda. C.J.B. has received consultancy fees and/or speaker's honoraria from Janssen, Roche, Takeda, and Tillotts; and is part of Takeda's advisory board.
A.H. has attended advisory boards and/or received consultancy fees from AbbVie, Arena, Atlantic, Bristol Myers Squibb, Celgene, Celltrion, Falk, Galapagos, Janssen, Lilly, Merck Sharp & Dohme, Napp Pharmaceuticals, Pfizer, Pharmacosmos, Roche, Genentech, Shire, and Takeda.
Ethics statement: The trials reporting data in humans were carried out in accordance with several ethical standards, including the Declaration of Helsinki, the International Council for Harmonisation Good Clinical Practice guidelines, European Union Regulation No. 536/2014, and applicable local regulations.
Supplementary Material