The PROCTO trial is a double-blind randomized, placebo-controlled, 24-week, comparative, exploratory phase II proof of concept trial. The trial will be conducted with 2 treatment groups as a parallel group comparison and will serve to compare a 7500 TSO regimen vs. placebo for achieving clinically meaningful responses in Ulcerative Colitis.

Inclusion Criteria:

1. Signed informed consent
2. Between 18 and 75 years of age
3. Established diagnosis of UC confirmed by endoscopic (sigmoidoscopy) and histological criteria, at least 3 months prior to inclusion
4. Disease extension corresponding to E2 (left side colitis) or E3 (extensive colitis) according to the Montreal Classification, i.e. at least 15 cm from anal verge, confirmed by an index sigmoidoscopy
5. Mayo-score between 6 and 10 and including 6 and 10 corresponding to moderately active disease
6. Calprotectin ≥ 250 µg/g and an endoscopic Mayo score ≥ 2
7. Negative pregnancy test in females of childbearing potential and the use of an acceptable effective method of contraception
8. No treatment or if treated with 5-Aminosalicyl acid (5-ASA): 5-ASA ≥ 8 weeks with a stable dose for at least 4 weeks both oral and rectal use
9. Tapered down from last oral steroid ≥ 4 weeks ago

Exclusion Criteria:

1. Disease extension corresponding only to E1 (proctitis), i.e. less than 15 cm from the anal verge
2. Bowel surgery, except appendectomy and removal of polyps
3. Septic complications
4. Evidence of infectious diarrhea (i.e. pathogenic bacteria or Clostridium difficile toxin in stool)
5. Abscess, perforation, active fistula or perianal lesions
6. Abnormal hepatic function (ALAT or ALP > 2.5 x ULN at screening), liver cirrhosis, or portal hypertension
7. Abnormal renal function (Creatinine > ULN) at screening
8. Any severe concomitant cardiovascular, renal, endocrine, or psychiatric disorder, which in the opinion of the investigator might have an influence on the patient's compliance or the interpretation of the results
9. Any condition associated with significant immunosuppression
10. Treatment with immunosuppressants or anti-cancer drugs, e.g., anti-TNF-α agents, anti-integrin agents, azathioprine or 6-MP, 6-thioguanine, methotrexate, tacrolimus, cyclophosphamide, or cyclosporine within the last 3 months prior to baseline
11. Treatment with systemic broad-spectrum antibiotics (e.g. metronidazole or ciprofloxacin), anti-parasitic medications, or probiotic (e.g. fecal transplantation) medication within the last 4 weeks prior to baseline, except for probiotic lactobacillus or bifidobacteria within 2 week prior to baseline (and minimum 1 week before screening visit (sampling and biopsies)).
12. Treatment with systemic glucocorticosteroid within the last 4 weeks or treatment with topical steroid within the last 2 weeks prior to baseline
13. Application of systemic non-steroidal anti-inflammatory drugs (NSAIDs) within 2 weeks before baseline visit for more than 3 consecutive days, except acetylsalicylic acid ≤ 350 mg/d which is allowed
14. Immunization with live vaccines within 12 weeks prior to baseline or during the trial
15. Travelling to rural districts in countries outside of Europe, USA, Australia or Canada within the last 12 weeks prior to baseline or during trial participation. If patients travel outside of Europe, USA, Australia or Canada they must be tested negative in the standard stool tests (parasites, bacteria and virus) when they return, as at the screening visit.
16. Well-founded doubt about the patient's cooperation, (e.g., addiction to alcohol or drugs).
17. Existing or intended pregnancy or breast-feeding
18. Participation in another clinical trial within the last 60 days, simultaneous participation in another clinical trial

Double-blind