The current multicentre phase III study is proposed to confirm in an add-on therapy design compared to a placebo-control group, the efficacy of adipose-derived stem cells (eASCs) from healthy donors for the treatment of complex anal fistulas in patients with Crohn's disease over a 24-week period and an extended follow-up period up to 104 weeks.

The current multicentre phase III study is proposed to confirm in an add-on therapy design compared to a placebo-control group, the efficacy of adipose-derived stem cells (eASCs) from healthy donors for the treatment of complex anal fistulas in patients with Crohn's disease over a 24-week period and an extended follow-up period up to 104 weeks. Subject with perianal fistulising Crohn's disease will be treated with Cx601, suspension of eASCs, at a dose of 120 million cells administered by intralesional injection. The treatment of complex perianal fistulas by local application of eASCs intends to improve significantly the local conditions with very few inconveniences (ambulatory procedure) and minimal risk of possible complications (anal incontinence). Therefore, this is a new therapeutic resource that is expected to be safe and efficacious as well as is expected to improve the quality of life of the patients in this highly debilitating and chronic condition. This treatment would prevent one of the main causes of anal incontinence, would diminish recurrence of the fistula disease and would reduce drastically the significant disorders provoked by the standard fistula surgery in the patients. Indeed, patients can be discharged according to the "One Day Surgical" procedures (major ambulatory surgery).

Inclusion Criteria:

The reference population will consist of patients with perianal fistulising Crohn´s disease refractory to at least one of the following treatments: antibiotics, immunosuppressants or anti-tumor necrosis factor (TNF). Naïve patients are excluded, and those patients refractory to antibiotics will represent less than 25% of the total recruited patients.

All of them must comply with the following inclusion criteria:

1. Signed informed consent.

2. Patients with Crohn's Disease (CD) diagnosed at least 6 months earlier in accordance with accepted clinical, endoscopic, histological and/or radiologic criteria.

3. Presence of complex perianal fistulas with a maximum of 2 fistulas (internal openings) and a maximum of 3 external openings, assessed by clinical assessment and MRI. Fistula must have been draining for at least 6 weeks prior to the inclusion. A complex perianal fistula is defined as a fistula that met one or more of the following criteria during its evolution:

   • High inter-sphincteric, trans-sphincteric, extra-sphincteric or supra-sphincteric.
   • Presence of ≥ 2 external openings (tracts).
   • Associated collections

4. Non-active or mildly active luminal CD defined by a CDAI ≤ 220.

5. Patients of either sex aged 18 years or older

6. Good general state of health according to clinical history and a physical examination.

7. For women of a childbearing age, they must have negative serum or urine pregnancy test (sensitive to 25 IU human chorionic gonadotropin (hCG)). Both men and women should use appropriate birth control methods defined by the investigator.

Exclusion Criteria:

1. Presence of dominant luminal active Crohn's disease requiring immediate therapy.

2. CDAI >220.

3. Concomitant rectovaginal fistulas

4. Patient naïve to specific treatment for perianal fistulising Crohn's disease including antibiotics

5. Presence of an abscess or collections > 2 cm, unless resolved in the preparation procedure (week -3 to day 0).

6. Presence of > 2 fistular lesions.

7. Presence of > 3 external openings.

8. Rectal and/or anal stenosis and / or active proctitis, if this means a limitation for any surgical procedure.

9. Patient who underwent surgery for the fistula other than drainage or seton placement.

10. Patient with diverting stomas

11. Patient with ongoing steroid treatment or treated with steroids in the last 4 weeks

12. Renal impairment defined by creatinine clearance below 60 ml/min calculated using Cockcroft-Gault formula or by serum creatinine ≥ 1.5 x upper limit of normality (ULN)

13. Hepatic impairment defined by both of the following laboratory ranges:

    • Total bilirubin ≥ 1.5 x ULN
    • Aspartate aminotransferase (AST) and alanine aminotransferase(ALT) ≥ 2.5 x ULN

14. Known history of abuse of alcohol or other addictive substances in the 6 months prior to inclusion.

15. Malignant tumour or patients with a prior history of any malignant tumour, including any type of fistula carcinoma.

16. Current or recent history of abnormal, severe, progressive, uncontrolled hepatic, haematological, gastrointestinal (except CD), endocrine, pulmonary, cardiac, neurological, psychiatric, or cerebral disease.

17. Congenital or acquired immunodeficiencies.

18. Known allergies or hypersensitivity to antibiotics including but not limited to penicillin, streptomycin, gentamicin, aminoglycosides; Human Serum Albumin (HSA); Dulbecco Modified Eagle's Medium (DMEM); materials of bovine origin; local anaesthetics or gadolinium (MRI contrast).

19. Contraindication to MRI scan, (e.g., due to the presence of pacemakers, hip replacements or severe claustrophobia).

20. Major surgery or severe trauma within the previous 6 months.

21. Pregnant or breastfeeding women.

22. Patients who do not wish to or cannot comply with study procedures.

23. Patients currently receiving, or having received within 3 months prior to enrolment into this clinical study, any investigational drug.

24. Patients previously treated with eASCs can not be enrol into this clinical study.

25. Subjects who need surgery in the perianal region for reasons other than fistulas at the time of inclusion in the study, or for whom such surgery is foreseen in this region in the 24 weeks after treatment administration.

26. Contraindication to the anaesthetic procedure.