The European Commission granted a marketing authorisation valid throughout the European Union for darvadstrocel on 23 March 2018. Darvadstrocel is a medicine that is used to treat complex anal fistulas in adults with Crohn’s disease when a conventional or biological medicine has not worked well enough. Fistulas are abnormal passages between the lower parts of the gut and the skin near the anus. Complex fistulas are those with several abnormal passages and openings, or with passages that go deep inside the body, or where there are other complications such as collection of pus. Darvadstrocel comprises stem cells removed from fat tissue of adult donors. It is a type of advanced therapy medicine called a ‘somatic cell therapy product’. This is a type of medicine that contains cells or tissues that have been modified so that they can be used to cure, diagnose or prevent a disease. Because the number of patients with anal fistula is low, the disease is considered ‘rare’, and darvadstrocel was designated an ‘orphan medicine’ on 8 October 2009. Darvadstrocel is given just once. The patient is given an anaesthetic. After preparing the fistulas for treatment in an operating room, the contents of two vials (each containing 30 million cells) are injected around the internal openings and two further vials through the external openings into the walls of the fistula. Darvadstrocel is made up of ‘mesenchymal stem cells’ from the fat tissue of a donor. To make this medicine, the cells are selected and cultivated in the laboratory to increase their number. When injected into the walls of the fistula, these cells can help to reduce inflammation and support the growth of new tissue. This encourages the fistula to heal and close. One main study, involving 212 patients with Crohn’s disease and complex anal fistulas, found darvadstrocel more effective than placebo 24 weeks after treatment. Treatment with conventional or biological medicines had not worked in these patients. The main measure of effectiveness, called ‘combined remission’, was the closing of abnormal external openings together with lack of fluid collections of more than 2 cm associated with internal passages (since these are likely to re-open the fistula). Of the patients treated with darvadstrocel, combined remission occurred in almost 50% of patients (53 out of 107); this compared with 34% of patients (36 out of 105) receiving placebo. The most common side effects with darvadstrocel (which may affect up to 1 in 10 people) are anal abscess (a swollen area with a collection of pus), proctalgia (anal pain), anal fistula and pain during treatment. Darvadstrocel must not be used in patients with hypersensitivity (allergy) to bovine serum (the clear liquid in blood from cattle) or to any of the ingredients of darvadstrocel.