Assuming a success rate of 40% to achieve mucosal healing at week 8 in the donor FMT arm, a treatment difference of 25% in the autologous FMT arm, a sample size of 49 patients per group is required to obtain a power of 80% and a statistical significance at the 5% level. In addition, considering 10% dropouts, a total of 108 patients will be included. Two interim analysis will be performed after inclusion of respectively 33% and 66% of the sample size (N=108) at week 8.