A perianal fistula is an abnormal passageway that develops between the rectum and the skin near the anus. The fistula is considered complex if it branches into several openings or an abscess is also present. The main aim of this study is to learn if complex perianal fistulas in children and teenagers close after treatment with darvadstrocel. 2 to 3 weeks before treatment with darvadstrocel, each participant will have surgery to clean the fistula and to drain any abscesses. On the day of treatment, each participant will have the fistula cleaned and will receive an injection of darvadstrocel near the fistula, under anesthetic. For up to 1 year after treatment, participants will regularly visit the clinic for follow-up. The fistula will be examined and any side effects from the treatment will be recorded. Participants will have an MRI at one clinic visit (about 24 weeks after treatment).

The drug being tested in this study is called darvadstrocel (Cx601, cell suspension containing 120 million cells of allogeneic expanded adipose-derived mesenchymal stem cells \[eASCs\]). Darvadstrocel is being tested to treat complex perianal fistula in pediatric participants who have Crohn's disease (CD). This study will look at the safety and efficacy of darvadstrocel in the treatment of complex perianal fistula in CD. The study will enroll at least 20 patients who will receive a single dose of darvadstrocel. This multi-center trial will be conducted worldwide. The overall time to participate in this study is 52 weeks. Participants will make multiple visits to the clinic. In unavoidable circumstances, such as the coronavirus disease 2019 pandemic, exceptions may be granted for alternative methods for conducting participant visits with approval by the medical monitor and/or sponsor.