Transfer of FRozen Encapsulated Multidonor Stool Filtrate for Active Ulcerative COlitis

Inclusion Criteria: * Age between 18 and 75 years * Prior endoscopic confirmation of UC of at least 6 months AND with a minimum disease extent of 15 cm from the anal verge. * Having active disease, defined with a Mayo Score between 4-10 and Mayo endoscopic subscore \>1 * Failure of conventional therapy or treatment with biologicals and / or small molecules. * previous medical therapy: * oral 5-ASA compounds (5-ASA); stable dosing for 4 weeks before randomization; * Azathioprine, 6-Mercaptopurine (6-MP) or Methotrexate (MTX); stable dosing for 8 weeks before randomization; * Oral corticosteroid therapy (prednisone ≤ 20 mg/day or budesonide ≤ 9 mg/day); stable dosing for 2 weeks before randomization; * Topical therapy (foams, clysms) with mesalazine or budesonide: stable dosing for 2 weeks before randomization. * previous vaccination against SARS-CoV-2 or previous SARS-CoV-2 infection or positive serology * Ability to understand and willingness to sign informed consent document in patients whom the investigator believes can and will comply with the requirements of the protocol. * Potentially childbearing patient: negative pregnancy test and use of a highly effective contraceptive method Exclusion Criteria: * Crohn's disease or indeterminate colitis or proctitis ulcerosa alone * Acute abdomen or other clinical emergencies (e.g. toxic megacolon, fulminant gastrointestinal hemorrhage, ileus, perforation, etc.) * Previous operations on the colon: colectomy, partial colon resections * current gastrointestinal infections * Congenital or acquired immunodeficiency * severe comorbidity (e.g. insulin-dependent diabetes mellitus, decompensated liver cirrhosis, primary sclerosing cholangitis, renal impairment \> grade 2) * diagnosis of a malignoma in the last 3 years * refusal of endoscopies with video documentation * No specific therapy for ulcerative colitis to date * Lack of immunity to SARS-CoV-2 * Previous treatment with TNF-, IL12/IL23-, IL23- or integrin-antibodies within the last 8 weeks before randomisation * Treatment with calcineurin inhibitors within the last 4 weeks before randomization * Treatment with JAK inhibitors (e.g., tofacitinib, filgotinib, or upadacitinib) within the last 4 weeks prior to randomization * Treatment with S1P receptor modulators (e.g. ozanimod, etrasimod) within the last 4 weeks before randomization * Systemic antibiotic treatment within the last 8 weeks prior to randomization. * Known intolerance of metronidazole or vancomycin * Previous FMT or FMFT, previous participation in this study (screening allowed) * Participation in a clinical trial within the last 3 months * Use of probiotics in tablet, capsule, or powder form, or appropriate drinking yogurts (or similar) within 2 weeks prior to randomization * Failure to ensure frozen storage of investigational products * Addictive or other medical conditions or circumstances that do not allow the subject to appreciate the nature, significance, scope, and possible consequences of the clinical trial * Indications that the patient would be unlikely to comply with the protocol (e.g., unwillingness to cooperate - compliance questionable)