# Rationale and design of the AlloFIST trial: a phase I/IIa study to evaluate dose escalation of allogeneic adipose-derived stroma/stem cells for the treatment of Crohn's fistula

Etienne Buscail, Cyrielle Gilletta de Saint Joseph, Marine Lebrin, Ines Frument, Fabian Gross, Barbara Bournet, Louis Buscail, Adrian Culetto, Fatima Mokrane, Marie Charlotte Delchier, et al.

► To cite this version:

Etienne Buscail, Cyrielle Gilletta de Saint Joseph, Marine Lebrin, Ines Frument, Fabian Gross, et al. Rationale and design of the AlloFIST trial: a phase I/IIa study to evaluate dose escalation of allogeneic adipose-derived stroma/stem cells for the treatment of Crohn's fistula. BMJ Open, 2025, 15 (12), pp.e104517. 10.1136/bmjopen-2025-104517. hal-05453213

HAL Id: hal-05453213

https://hal.inrae.fr/hal-05453213v1

Submitted on 12 Jan 2026

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_1.png" /></figure>

Distributed under a Creative Commons CC BY 4.0 - Attribution - International License
# BMJ Open Rationale and design of the AlloFIST trial: a phase I/IIa study to evaluate dose escalation of allogeneic adipose-derived stroma/stem cells for the treatment of Crohn's fistula

Etienne Buscail,¹,²,³ Cyrielle Gilletta de Saint Joseph,⁴ Marine Lebrin,³ Ines Frument,³ Fabian Gross,³ Barbara Bournet,⁴ Louis Buscail,⁵ Adrian Culetto,⁴ Fatima Mokrane,⁶ Marie Charlotte Delchier,⁶ Isabelle Quelven,⁷ Charline Daguzan,⁸ Grégory Pugnet,⁹ Jean Pierre Duffas,¹ Laurent Ghouti,¹⁰ Antoine Philis,¹⁰ Nicolas Carrere,¹⁰ Benoit Lepage,¹¹ Guillaume Le Cosquer⁴

**To cite:** Buscail E, Gilletta de Saint Joseph C, Lebrin M, et al. Rationale and design of the AlloFIST trial: a phase I/IIa study to evaluate dose escalation of allogeneic adipose-derived stroma/stem cells for the treatment of Crohn's fistula. *BMJ Open* 2025;15:e104517. doi:10.1136/bmjopen-2025-104517

► Prepublication history and additional supplemental material for this paper are available online. To view these files, please visit the journal online (https://doi.org/10.1136/bmjopen-2025-104517).

EB and CGdSJ contributed equally.
BL and GLC contributed equally.

Received 01 May 2025
Accepted 13 December 2025

## ABSTRACT

**Introduction** Crohn's disease (CD) is a chronic inflammatory disorder of the gastrointestinal tract distinguished by progressive bowel damage with a risk of structuring and penetrating complications. It is characterised by focal or segmental transmural inflammation that disrupts intestinal mucosal integrity and favours the development of abscesses and fistulas. Perianal fistula develops in 13%–39% of patients with CD. Their care is difficult but improves with medical and surgical treatment to preserve anal continence and avoid a maximum proctectomy. Combined treatment with seton placement and concomitant anti-TNF (infliximab, adalimumab) allows wound healing in 40%–70% of cases. The currently available treatments are not curative and fail to provide a long-term resolution. The injection of adipose stromal cells is currently being evaluated in clinical studies for repair-damaged tissues in various diseases (limb ischaemia, osteoarthritis, systemic sclerosis, etc). Immunoregulatory and anti-inflammatory properties of AdMSC (adipose-derived stroma/stem cells) are responsible for accelerating healing and represent an innovative approach for treating perianal fistulas associated with CD.

**Methods and analysis** This phase I/IIa study is designed to assess the treatment of complex perianal fistulas linked with CD after failure of conventional treatment by injection of AdMSC (CellReady) into the fistula. Two doses of associated AdMSC will be tested for a dose escalation (5×10⁷ and 10×10⁷ cells) and injected into the wall of the fistula. Those eligible for inclusion include patients with controlled luminal CD characterised by a Harvey-Bradshaw score below or equal to eight and diagnosed on clinical, endoscopic, histological and/or radiological criteria, a colonoscopy dating back less than 1 year without ulcer in the rectum and presence of complex chronic perianal fistula with a maximum of two internal ports and three external ports. All patients must have social security insurance or equivalent social protection. The aim of this study is to determine the optimal dose corresponding to

## STRENGTHS AND LIMITATIONS OF THIS STUDY

⇒ This fast-track dose-escalation study seeks to provide evidence on the safety and tolerability of two doses of associated AdMSC which will be tested for a dose escalation (5×10⁷ and 10×10⁷ cells).

⇒ The originality of our study lies first and foremost in the use of the production process.

⇒ Due to its single-arm design, this study does not allow direct outcome comparisons with a respective control group.

maximum efficacy 6 months after injection of cells with a treatment-related adverse event rate of 20%.

**Ethics and dissemination** The EU CT number 2024-511821-75-00 was approved by the following Ethics Committee: CPP (committee for the protection of persons in French: comité de protection des personnes) Ouest 1 – Tours #2024UEMED-18 and ANSM (French Agency for the Safety of Health and Medicinal Products in French: Agence nationale de sécurité du médicament et des produits de santé) #2024-511821-75-00 (Sponsor number RC31/13/7030, protocol V2.1). The results will be disseminated through conventional scientific channels.

**Trial registration number** NCT06636032.
The results will be disseminated through conventional scientific channels.

## INTRODUCTION

Perianal fistulas are at the forefront (42% to 72.4%) of morbid complications of Crohn's disease (CD), affecting nearly one third of patients and complicating abscesses in 35%–48% of cases. The current treatment is based on a combination of drainage (proctologic and surgical) and biologic (anti-TNF) techniques, but the failure rate varies from 30% to 80%.¹ The literature shows that

<figure><img src="image_2.png" /></figure>

Check for updates

© Author(s) (or their employer(s)) 2025. Re-use permitted under CC BY. Published by BMJ Group.

For numbered affiliations see end of article.

**Correspondence to** Dr Etienne Buscail; ebuscail@gmail.com
injection of autologous or allogeneic AdMSCs, after
appropriate surgical and medical preparation, represents
a promising combination strategy for the management of
resistant perianal fistulas.² However, multiple prospects
(and unknowns) exist for the treatment of anoperineal
fistulas in CD by cell therapy. The current problem lies
with standardising trials by selection of the study popu-
lation, route of administration, type (autologous, aloge-
neic or FSV) and number of cells (1 to 12×10⁷), mode
and number of injections, volume injected, associated
surgical procedures, clinical and radiological assessment
criteria and immuno-monitoring. The relative robustness
of allogeneic AdMSC trials in terms of patient numbers
and follow-up opens the door to the use of allogeneic
stem cells in this indication and enables systematic, trace-
able preparation of cells from healthy donors.³

We propose to regulate the injection conditions,
volume, number of cells and evaluation mode (clin-
ical and MRI) in a phase I/IIa study using allogeneic
cells whose expansion and certification process is well-
mastered and standardised.

The originality of our study lies first and foremost
in the use of the production process mastered by Cell-
Easy, a pharmaceutical company, in premises adapted
to the production of Advanced Therapy Medicinal
Products (ATMPs) and well-characterised (CellReady
drug). This production process is both shorter in time
(14 days), therefore reducing the number of passages of
these cells and more efficient in terms of the number of
cells obtained and their quality than that used in other
studies conducted in the same field.⁴,⁵ This reduction in
cell amplification duly preserves the immunomodula-
tory properties of native cells as much as possible while
limiting the drift associated with culture processes. This
experimental drug (CellReady) has been approved as
part of a cell therapy protocol for the healing of digital
ulcers in scleroderma (ADUSE study MTIMSANAT-2023-
07-0016_2019-003906-28). This protocol therefore targets
patients with complex CD-related anoperineal fistula
previously managed with combined treatment (drainage
on setons+anti-TNFα or biotherapies) according to an
identical protocol for all patients, failing to heal after 6
months but with controlled intra-luminal disease. The
rationale for this study is based on the immunoregulatory,
anti-inflammatory and trophic properties of AdMSCs
which could enhance and accelerate healing of fistulous
tracts.⁶,⁷ AdMSCs are injected into the wall of the fistula
tract. We aimed to assess the safety and effectiveness
of AdMSCs for treatment-refractory complex perianal
fistulas in patients with CD.

OBJECTIVES

Primary objective

The primary objective of this study is to determine the
optimal dose of cells to inject, making it possible to obtain
a rate of grade ≥2 treatment-related adverse events (AEs)

below the threshold of 20% with the best clinical effec-
tiveness 6 months after injection.

Secondary objective

The secondary objectives are to evaluate:

▶ Effectiveness and safety up to 6 months after injection of the cells.

► Efficacy up to 6 months post-injection of the cells on clinical, biological and radiological criteria:

- Clinical criteria: discharge, general examination, specific quality of life, disease activity, fistula classification, anal incontinence, symptoms and impact of treatment on perineal lesions.

- Biological criteria: blood count, inflammation, liv-
er function, coagulation.

- Radiological criteria: disappearance or persistence of the fistula tract, presence of fibrous sequelae, T2 hypersignal of the tract, enhancement following gadolinium injection into the tract(s) and presence or absence of abscesses.

► The therapeutic effect obtained depends on the quantity of AdMSC injected.

METHOD AND ANALYSIS

Study design

This is a phase I/IIa, single-centre (Toulouse university
hospital), open-label study using a cell therapy drug
injected in situ into the fistula tract.

It is a dose-escalation study testing two different doses of AdMSC: (5×10⁷ and 10×10⁷ cells). Switching to the higher dose will take place after a meeting of the Independent Monitoring Committee (IMC) after 6 months of follow-up. Dose escalation is defined a priori from an ‘up-and-down’ scheme on 3 cohorts of 3 patients, determined using a ‘Bayesian Optimal Interval (BOIN) Design’ approach.⁸

The trial will be organised in line with the phase I
methodology described by Storer⁹ and Zhou *et al*.⁸ The
dose will be assessed 6 months after injection of the last
patient in each group according to an a priori defined
dose escalation scheme (up-and-down type). Escalation
to the higher dose, maintenance at the same dose or
de-escalation will occur after a meeting of the IMC for
each cohort of 3 patients. Prior to each ISC meeting (for
each patient group), the efficacy rate and number of
AEs will be estimated using a continuous reassessment
method.¹⁰

Previous studies by Korean and Spanish teams have
evaluated the feasibility, safety and efficacy of the
cells.⁴,⁵ Here, we are carrying out a phase I/II study aimed
at determining the optimal dose, including both efficacy
and safety criteria. The 6-month assessment allows an
additional 4 months to highlight any AEs attributable
to the treatment. However, it is not considered neces-
sary to extend this period for the analysis of the primary
endpoint, given the low risk of AEs expected after this
6-month follow-up period.
The final dose selected for a subsequent clinical phase will be the one that achieves the best efficacy with a serious AE rate under 20%.

This approach presents certain constraints since success and AE rates need to be recalculated regularly as patients are recruited. The dose escalation scheme is defined a priori. However, calculations of efficacy and AE rates can be executed at successive stages to provide objective quantitative elements for discussion by the IMC, which may or may not decide to continue with the dose escalation scheme as defined a priori.

### Dose escalation procedure—sample size calculation

The optimal dose will be determined 6 months after the injection of the last patient in the last group: after completing the full dose escalation schedule with 9 patients (3 patients per group), we will select the dose for which under 20% of grade ≥2 treatment-related AEs have been reported and for which healing is most complete. The probability of observing AEs at 6 months will be estimated using a continual reassessment method described by Seeger et al.¹⁰ Follow-up visits will take place 1, 3 and 6 months after cell injection.

A total of 9 patients will be included. Each patient will receive the pre-determined dose of stem cells after conventional treatment combining drainage with setons and biotherapy with infliximab or adalimumab. This treatment will be carried out identically for each patient.

The following up-and-down scheme will be applied. It has been defined using the 'BOIN Suite' application, available at https://www.trialdesign.org. The parameters used to define the scheme are as follows:

* Calculation based on a non-informative a priori distribution.

* Doses evaluated (dose h=50 million and dose h+1: 100 million).

* Starting at the lowest dose (h).

* 3 cohorts of 3 patients.

* Probability of target dose limiting toxicity (defined as the proportion of grade ≥2 AEs): 20%.

The decision table (online supplemental table 1) associated with these parameters is as follows (from https://www.trialdesign.org/one-page-shell.html#BOIN):

The flow chart is detailed in the figure below (figure 1).

The study is continued until 9 patients are included, unless the following early stopping rules are applied:

* Cohort 1 (patients 1 to 3): discontinuation if two or 3 patients observed with an AE grade ≥2 related to treatment.

* Cohort 2 (patients 4 to 6): discontinuation if ≥3 patients with an AE grade ≥2 related to treatment are observed among all patients recruited.

* Cohort 3 (patients 7 to 9): discontinuation if ≥4 patients with an AE grade ≥2 related to treatment among all recruited patients are observed.

After 6 months of follow-up has been completed for the last patient in each group, the Independent Supervisory Board meets to decide whether to switch the next group to the higher dose, maintain the dose or de-escalate. Only safety criteria (number of patients with AE grade ≥2) can allow the dose to be increased.

### Experimental design

In this study, patients are followed up over six visits.

The pre-injection/injection period comprises two visits:

* Selection visit (V0).

* Inclusion visit (V1) 2 weeks maximum before injection.

The injection period comprises two visits:

* Visit 2 (V2) fistula preparation visit, including examination under anaesthesia, fistula curettage.

* Visit 3 (V3) injection of AdMSCs.

The follow-up period comprises 3 visits at 1 month, 3 months and 6 months post-injection (V4, V5, V6).

<figure><img src="image_3.png" /><figcaption>**Figure 1** Study flow-chart.</figcaption></figure>
<figure><img src="image_4.png" /><figcaption>**Figure 2** Study Timeline.</figcaption></figure>

Study assessment and study time line are detailed in figure 2 and table figure 3.

## Study population

### Inclusion criteria

* Patients must meet all the following criteria in order to be eligible to participate in the study.

* Patients over 18 years old.

* Patients who signed the informed consent.

* Patient affiliated to a social security system.

* Controlled luminal CD characterised by a Harvey-Bradshaw score below or equal to eight and diagnosed on clinical, endoscopic, histological and/or radiological criteria.

* Colonoscopy dating back less than 1 year without ulcer in the rectum.

* The fistula had to have a maximum of two internal and three external openings.

* Patient treated at least 6 months by advance therapy (anti TNF, anti-integrin, anti-interleukin 12/23, anti-interleukin 23, JAK inhibitors) and drainage with one or more setons, with good drainage confirmed by the absence of residual collection or an undrained tract on MRI.

### Exclusion criteria

Any patient who meets the following criteria is not to be enrolled in this study:

<table><caption>**Figure 3** Study visit. PDAl, perineal disease activity index.</caption><thead><tr><th rowspan="2"></th><th colspan="2">PERIOD 1 Pre-injection</th><th colspan="2">PERIOD 2 Injection period</th><th colspan="3">PERIOD 3 Follow-up period</th></tr><tr><th>selection/Inclusion period</th><th>1</th><th>Injection period</th><th>3</th><th>4</th><th>5</th><th>6</th></tr></thead><tbody><tr><td>Visit</td><td>0</td><td>1</td><td>2</td><td>3</td><td>M1+/- 7D</td><td>M3+/- 7D</td><td>M6+/- 7D</td></tr><tr><td>Day (D)/Month (M)</td><td colspan="7">D-90 to j-16</td></tr><tr><td>Inform consent</td><td colspan="7">*</td></tr><tr><td>Inclusion/exclusion criteria</td><td colspan="7">*</td></tr><tr><td>QuantIFERON</td><td colspan="7">*</td></tr><tr><td>Parks classification</td><td colspan="7">*</td></tr><tr><td>Montréal Classification</td><td colspan="7">*</td></tr><tr><td>Anaesthesia consultation</td><td colspan="7">*</td></tr><tr><td>Blood sampling</td><td colspan="7">*</td></tr><tr><td>Physical exam</td><td colspan="7">*</td></tr><tr><td>Pregnancy test</td><td colspan="7">*</td></tr><tr><td>Stool sampling</td><td colspan="7">*</td></tr><tr><td>Anoscope</td><td colspan="7">*</td></tr><tr><td>MRI</td><td colspan="7">*</td></tr><tr><td>Harvey-Bradshaw index</td><td colspan="7">*</td></tr><tr><td>PDAl</td><td colspan="7">*</td></tr><tr><td>CAPQoL</td><td colspan="7">*</td></tr><tr><td>Cardiff classification</td><td colspan="7">*</td></tr><tr><td>Wexner score</td><td colspan="7">*</td></tr><tr><td>Allan Score</td><td colspan="7">*</td></tr><tr><td>ADMSC Injection</td><td colspan="7">*</td></tr><tr><td>Anti-HLA antibodies</td><td colspan="7">*</td></tr><tr><td>Fistula examination</td><td colspan="7">*</td></tr><tr><td>Other treatments</td><td colspan="7">*</td></tr><tr><td>Adverse events</td><td colspan="7">*</td></tr></tbody></table>

* Refusal of the patient to participate in the study.

* Positive QuantiFERON test.

* Patient with transplanted organ.

* History of cancer in the last 5 years or lymphoproliferative disease.

* Persistent bacterial or viral infection.

* Patient with a contraindication to MRI.

* Known allergy to gadolinium.

* Known allergy to albumin.

* End-stage organ failure.

* Pregnant or breastfeeding women.

* Women of childbearing age without effective contraception.

* Patient under judicial protection, under guardianship or curatorship.

## Injection method (surgical procedure)

The selected patients undergo a preliminary examination under anaesthesia to prepare the fistula, with cleaning/curettage of the fistula tract(s). The purpose of this preliminary surgical phase is to confirm effective drainage of the suppuration and to eliminate granulous tissues from the fistula tract(s). The injection of the cells is performed during a second procedure under anaesthesia 2 weeks after the first. Patients are managed by outpatient hospitalisation sessions for both surgical procedures. The AdMSC are thawed and prepared in syringes on the day of injection. The transport conditions and quality of the product are checked in the pharmacy and then in the operating room. The doses will be stored in nitrogen gas at Cell-Easy (-150°C). A few days before a patient's injection, the frozen cell doses will be shipped to the Toulouse hospital pharmacy specialised in ATMPs management in a special dry-shipper container containing liquid nitrogen with continuous temperature monitoring. The thawed cells will be stored at 2-8°C until they are dispensed to the investigator team for injection within a maximum of 10 hours, in accordance with the stability studies conducted on the reconstituted product in the syringe. Transport conditions will comply with Good Transport Practices (in accordance with European Directive 2004/23/EC). Frozen cell doses will be stored at Cell-Easy and then sent to the Toulouse hospital pharmacy specialised in ATMPs on the day of a patient's injection. The thawed product in the syringe will be checked by a pharmacist and then dispensed by authorised personnel. All checks are carried out by the manufacturer before shipment and then by the
hospital pharmacist on receipt and before dispensing. A
single practitioner from the team (EB) performs all the
injections to ensure that the technique is homogeneous
and comparable.

The injection protocol is standardised in line with the ADMIRE CD study³: curettage/cleaning of the tract(s), removal of the seton(s) and then closure of the internal opening(s) with an ‘X’ stitch of absorbable suture or a mucosal or musculo-mucosal advancement flap if the internal opening appears large and/or fibrous.

Four or eight 2.5 mL vials (12.5×10⁶ AdMSC/vial) containing a total of 50 or 100 million AdMSC are then taken up into two 10mL syringes. For 50million cells, there are two 10mL syringes, and for 100million cells, there are four 10mL syringes. The final volume of the cell suspension is 2.5mL (overfilled to 2.7mL) and the medium consists of DMEM containing human albumin and Cryostor CS 10. The content of two of the syringes is injected submucosally into the internal opening(s) and the remaining half is injected into the wall of all fistula tract(s). At the end of the procedure, the skin around the external openings is massaged to promote cell diffusion and the external openings are covered with a dry dressing.

At the end of the surgery, patients are hospitalised for
24 hours for monitoring. At the end of this period, if
notable AEs have occurred, the patient is then allowed to
go home with a simple prescription for analgesics and no
specific requirements for local care.

Evaluation

The patients are followed up during consultations at
1, 3 and 6 months. At the time of inclusion, Montreal
phenotypic classification is used to identify the different
presentations of CD and Parks classification is used to
characterise fistula tracts.

The Cardiff classification is used at the time of inclu-
sion and compared at 1-month, 3-month and 6-month
follow-up visit to evaluate the evolution of the anoperi-
neal disease. Anoperineal disease activity is determined
with the perineal disease activity index (PDAI), anal
continence is assessed by determining Jorge and Wexner
score, luminal disease activity is identified using the
Harvey-Bradshaw index and quality of life is evaluated
with CAF-QoL score.

A control anoperineal MRI scan is performed at the inclusion and 6-month follow-up visits to ascertain the radiological response. MR studies will be evaluated by a single referring radiologist with 15 years of experience in pelvic disease and CD.

Outcomes

Primary endpoint

The optimal dose will be determined by the following
combined criteria at 6 months:

- No AEs of grade ≥2 attributable to the experimental treatment (CellReady).

► Efficacy of AdMSC treatment on fistula tract healing as defined by a complete clinical and radiological response. Clinical efficacy corresponds to absence of flow through the inner or external orifice observed on an anoscopy and through the external orifice(s) while radiological efficacy refers to the disappearance of fistula tract or fistula tract present but inactive (on pelvic MRI).

The clinical response will be defined as follows:

- Complete: non-catheterizable closure of all external openings without pressure relief.

- Partial: non-catheterizable closure of ≥ 50% of the external opening pathway without pressure relief from any of the openings.

- Failure: closure of < 50% of the external openings ± persistence of pressure relief from one or all of the external openings ± appearance of a new tract or abscess."

The radiological response will be defined as follows:

- Complete: fibrous sequelae with no T2 hypersignal or enhancement after the injection of gadolinium into the tract(s) and no abscesses.

- Partial: decrease of the inflammatory signal (T2 hypersignal and enhancement after the injection of gadolinium) ± the length ± the largest diameter of the tracts, with no abscesses.

- Failure: absence of radiological modification or occurrence of a new fistula tract±abscesses

Secondary endpoints

The efficacy and adverse effects are assessed at 1 month, 3 months and 6 months post-injection.

Safety is determined through the collection of AEs (related or not) occurring throughout the trial.

The effectiveness criteria will also be evaluated:

- At 1, 3 and 6 months on clinical and biological criteria.

- And at 6 months on radiological criteria (MRI).

Changes will be ascertained between the inclusion visit and follow-up visits.

Clinical criteria

- Treatment effectiveness measured by the absence of flow through the internal orifice visualised during an anoscopy and through the external orifice(s) at V1, V4 (M1), V5 (M3), V5 (M6).

- Evolution of quality of life measured by CAFQoL between V1 and V4 (M1), V5 (M3), V6 (M6). This questionnaire measures quality of life specifically for patients with anal fistula in CD.

- Evolution of the Harvey-Bradshaw disease activity score (abdominal examination) between V1 and V4 (M1), V5 (M3) and V6 (M6).

- Evolution of the fistula on clinical examination and search for abnormal tissue formation at V1 and V4 (M1), V5 (M3) and V6 (M6).

- Evolution of the PDAI between V1 and V4 (M1), V5 (M3) and V6 (M6).
* Evolution of the Cardiff classification between V1 and V4 (M1), V5 (M3) and V6 (M6).

* Evolution of the Wexner anal incontinence score between V1 and V4 (M1), V5 (M3) and V6 (M6).

* Evolution of the Allan Score (patient symptoms and impact of treatment on perineal lesions) between V1 and V4 (M1), V5 (M3) and V6 (M6).

### Radiological criteria (pelvic MRI)

* Efficacy of treatment on MRI: disappearance of fistulous tracts or persistent but inactive fistulous tract between V1 and V6 (M6).

### Biological criteria

* Evolution of biological parameters: CBC, Platelets, CRP, hepatic enzyme profile, PT, APTT, albumin between V1 and V5 (M3) and V6 (M6).

### Description of characteristics at inclusion

Characterisation of anal fistulas using the following two classifications:

* Evaluation of the Parks classification at inclusion.

* Evaluation of the Montreal classification at inclusion.

### Sample size calculation

In this type I/IIa dose-finding study, we aimed to assess two doses (5×10⁷ and 10×10⁷). We plan to include a minimum of 3 patients (in case of early stop at the first dose because of safety) to a maximum of 9 patients, as described in figure 1. Dose escalation, maintenance or de-escalation was defined applying a ‘Bayesian Optimal Interval (BOIN) Design’ for 3 cohorts of 3 patients, with a target toxicity probability of 0.20.⁸

### Data analysis

We will describe the number of included patients, potential loss to follow-up and dose escalation using a flow chart. The rate of grade ≥2 AEs attributable to the treatment and the proportion of complete clinical and radiological efficacy will be estimated using a Bayesian continuous reassessment method¹⁰ by applying a non-informative prior. Details regarding the clinical and radiological response will be described (complete/partial response and failures). The statistical distribution of the secondary criteria will be described for each follow-up visit. AEs will be described using the MedDRA classification by AdMSC dose according to their causality and severity. The study is scheduled to begin in May 2025 and end in November 2026.

### Ethics and safety

This study will be conducted according to the principles of Good Clinical Practice or the ethical principles stated in the most recent version of the Declaration of Helsinki.

The study was approved by the French Ethics Committee (Comité de Protection des Personnes CPP Ouest 1 – Tours #2024UEMED-18) and European Medicines Agency with the EudraCT number 2024-511821-75-00. The study is registered on the website clinicalTrials.gov under the

number NCT06636032. The informed consent document (online supplemental file 2) with study information will be used to explain to patients in simple terms what participation in the study means for them. All patients will be asked to sign a written informed consent form received by the principal investigator.

### Patient and public involvement

Patients and/or the public were not involved in the development of this study except for the informed consent validated by a patient association.

## DATA COLLECTION/MANAGEMENT

### Clinical data

All the information required by the protocol must be entered in an electronic data capture system. The investigator will ensure the accuracy, completeness and timeliness of the reported data. A complete audit trail on all data changes will be maintained. The investigator or designee will cooperate with the monitor and the data manager for the periodic review of data in order to ensure the accuracy and completeness of the electronic data capture system at each scheduled monitoring visit and before any submission of results. The data are collected on an electronic case report form. All the information will be contained in the original documents, or in the authenticated copies of said documents; and relating to clinical examinations, observations or other activities conducted as part of a research study and necessary for the reconstitution and evaluation of the research. The documents in which the source data are saved are called the source documents.

## QUALITY CONTROL

A clinical researcher appointed by the Sponsor will regularly visit each investigating centre during the implementation of the research one or several times during the research phase according to the frequency of the inclusions and at the end of the research phase. During these visits and in line with the risk-based monitoring plan (participant, logistics, impact, resources), the following will be reviewed:

* Informed consent.

* Compliance with the research protocol and the procedures defined therein.

* Quality of the data collected in the electronic data capture system: accuracy, missing data, consistency of the data with source documents (medical records, appointment books, originals of laboratory results and so on).

* Management of the ATMP.

All visits will be the subject of a written monitoring report.
## ETHICS AND DISSEMINATION

Study information will be publicly available at www.clinicaltrials.gov (NCT06636032). The results of this trial will be submitted for publication in relevant peer-reviewed publications and the key findings presented at national and international conferences. Dissemination will be done under the responsibility of the study's Coordinating Investigator with the agreement of the Principal Investigators. The co-authors of the report and publications will be the investigators and clinicians involved on a pro rata basis of their contribution to the study as well as the statistician and methodologist.

Sharing of data generated by this project is an essential part of our proposed activities and will be carried out in several different ways. We would wish to make our results available to the community of scientists interested in colorectal disease to avoid unintentional duplication of research and improve the current standard of care. The EU CT number 2024-511821-75-00 was approved by the following Ethics Committee: CPP (committee for the protection of persons in French: comité de protection des personnes) Ouest 1 – Tours #2024UEMED-18 and ANSM (French Agency for the Safety of Health and Medicinal Products in French: Agence nationale de sécurité du médicament et des produits de santé) #2024-511821-75-00 (Sponsor number RC31/13/7030, protocol V2.1).

## PATIENT AND PUBLIC INVOLVEMENT

### Author affiliations

**Acknowledgements** CELL-EASY and Association François-Aupetit.

**Contributors** EB, GLC, CGSJ, FG, ML, IF, BB, LB and BL: conception; EB, ML, IF and BL: manuscript writing; BL: statistical and methodology features; EB, ML, IF, BB, LB, JPD, LG, NC, AP, FM, MCD, CD, GP, IQ, AC and BL: design, final approval of the manuscript. All authors have read and approved the manuscript. EB is the guarantor.

**Funding** This project is funded by DGOS through the grant PHRCi 2013 #13-075. PHRC Régional and with the support of AFA (association François Aupetit), CHU of Toulouse and INSERM. Toulouse University Hospital is in charge of the regulatory

submissions. Address: Toulouse University Hospital, Hotel Dieu-Saint Jacques, 2, rue Viguerie, 31059 Toulouse.

**Competing interests** None declared.

**Patient and public involvement** Patients and/or the public were not involved in the design, or conduct, or reporting, or dissemination plans of this research.

**Patient consent for publication** Consent obtained directly from patient(s).

**Provenance and peer review** Not commissioned; externally peer reviewed.

**Supplemental material** This content has been supplied by the author(s). It has not been vetted by BMJ Publishing Group Limited (BMJ) and may not have been peer-reviewed. Any opinions or recommendations discussed are solely those of the author(s) and are not endorsed by BMJ. BMJ disclaims all liability and responsibility arising from any reliance placed on the content. Where the content includes any translated material, BMJ does not warrant the accuracy and reliability of the translations (including but not limited to local regulations, clinical guidelines, terminology, drug names and drug dosages), and is not responsible for any error and/or omissions arising from translation and adaptation or otherwise.

**Open access** This is an open access article distributed in accordance with the Creative Commons Attribution 4.0 Unported (CC BY 4.0) license, which permits others to copy, redistribute, remix, transform and build upon this work for any purpose, provided the original work is properly cited, a link to the licence is given, and indication of whether changes were made. See: https://creativecommons.org/licenses/by/4.0/.

## ORCID iD

Etienne Buscail https://orcid.org/0000-0003-2040-3045

## REFERENCES

1 Schwartz DA, Loftus EV Jr, Tremaine WJ, et al. The natural history of fistulizing Crohn's disease in Olmsted County, Minnesota. *Gastroenterology* 2002;122:875-80.

2 Buscail E, Le Cosquer G, Gross F, et al. Adipose-Derived Stem Cells in the Treatment of Perianal Fistulas in Crohn's Disease: Rationale, Clinical Results and Perspectives. *Int J Mol Sci* 2021;22:9967.

3 Panés J, García-Olmo D, Van Assche G, et al. Expanded allogeneic adipose-derived mesenchymal stem cells (Cx601) for complex perianal fistulas in Crohn's disease: a phase 3 randomised, double-blind controlled trial. *Lancet* 2016;388:1281-90.

4 Guadalajara H, Herreros D, De-La-Quintana P, et al. Long-term follow-up of patients undergoing adipose-derived adult stem cell administration to treat complex perianal fistulas. *Int J Colorectal Dis* 2012;27:595-600.

5 Lee WY, Park KJ, Cho YB, et al. Autologous adipose tissue-derived stem cells treatment demonstrated favorable and sustainable therapeutic effect for Crohn's fistula. *Stem Cells* 2013;31:2575-81.

6 Grégoire C, Lechanteur C, Briquet A, et al. Review article: mesenchymal stromal cell therapy for inflammatory bowel diseases. *Aliment Pharmacol Ther* 2017;45:205-21.

7 Bourin P, Bunnell BA, Casteilla L, et al. Stromal cells from the adipose tissue-derived stromal vascular fraction and culture expanded adipose tissue-derived stromal/stem cells: a joint statement of the International Federation for Adipose Therapeutics and Science (IFATS) and the International Society for Cellular Therapy (ISCT). *Cytotherapy* 2013;15:641-8.

8 Zhou Y, Li R, Yan F, et al. A comparative study of Bayesian optimal interval (BOIN) design with interval 3+3 (i3+3) design for phase I oncology dose-finding trials. *Stat Biopharm Res* 2021;13:147-55.

9 Storer BE. An evaluation of phase I clinical trial designs in the continuous dose-response setting. *Stat Med* 2001;20:2399-408.

10 Seegers V, Chevret S, Resche-Rigon M. Dose-finding design driven by efficacy in onco-hematology phase I/II trials. *Stat Med* 2011;30:1574-83.

<footnote n="1">¹Colorectal Surgery, University Hospital Centre Toulouse, Toulouse, France</footnote>

<footnote n="2">²Digestive Health Research Institute, Toulouse, Occitanie, France</footnote>

<footnote n="3">³Centre d'investigation clinique de Toulouse, Toulouse, Occitanie, France</footnote>

<footnote n="4">⁴Gastroenterology, University Hospital Centre Toulouse, Toulouse, France</footnote>

<footnote n="5">⁵Gastroenterology, CHU Toulouse, Toulouse, France</footnote>

<footnote n="6">⁶Radiology, University Hospital Centre Toulouse, Toulouse, France</footnote>

<footnote n="7">⁷Pharmacy, University Hospital Centre Toulouse, Toulouse, France</footnote>

<footnote n="8">⁸DRCI, University Hospital Centre Toulouse, Toulouse, France</footnote>

<footnote n="9">⁹CHU Toulouse, Toulouse, France</footnote>

<footnote n="10">¹⁰University Hospital Centre Toulouse, Toulouse, France</footnote>

<footnote n="11">¹¹Epidemiology, University Hospital Centre Toulouse, Toulouse, France</footnote>