Study Evaluating Efficacy and Safety of Amiselimod (MT-1303) in Mild to Moderate Ulcerative Colitis

Inclusion Criteria:

• Subjects will be eligible if they are male or female aged between 18 to 75 years attime of consent (inclusive) with normal vital signs and a diagnosis of active mildulcerative colitis (UC) (modified Mayo Score of 3 or 4) or moderate UC (modifiedMayo Score of 5 to 8) confirmed at least 12 weeks prior to randomization by clinicaland endoscopic evidence and corroborated by a histopathology report.

• Subjects must have an endoscopic subscore of ≥2 from and evidence of active UCextending ≥15 cm from the anal verge confirmed by a screening colonoscopy.

• If subjects are receiving oral or rectal 5-aminosalicylates (5-ASAs) or oralcorticosteroids (≤20 mg prednisolone equivalent) for treatment of their UC, theymust be on a stable dose for at least 28 days prior to randomization.

• Subjects who complete the Double-Blind Period of the study who, in the opinion ofthe Investigator, would benefit from continued treatment, may participate in theOpen Label Extension (OLE) Period.

Exclusion Criteria:

• Any of the following: a diagnosis of Crohn's disease, indeterminate colitis, colitis (pseudomembranous, microscopic, or ischemic) or coeliac disease, current or recent (within 12 weeks prior to randomization) evidence of fulminant colitis, proctitis (defined as a rectal inflammation within 15 cm from the anal verge), abdominalabscess, toxic megacolon, bowel obstruction, or bowel perforation; a history orevidence of any colonic resection or subtotal or total colectomy, ileostomy,colostomy, known fixed symptomatic stenosis of the intestine, unresected adenomatouscolonic polyps, or colonic mucosal dysplasia.

• Clinically significant infections (e.g., pneumonia, pyelonephritis, or septicemia)within 4 weeks prior to randomization or previous clinically significant infectionsrequiring hospitalization within 6 months prior to randomization, active or latenttuberculosis, infections of hepatitis B, hepatitis C, human immunodeficiency virus (HIV), or previous shingles outbreak.

• Active SARS-CoV-2 infection or complications related to COVID-19.

• A history of, or currently active, primary or secondary immunodeficiency, presenceof progressive multifocal leukoencephalopathy (PML), or presence of demyelinatingdiseases.

• A history or evidence of two or more failures with biologic treatment for UC.

• Currently taking any medication for treatment of UC other than oral or rectal 5-ASAs (5-aminosalicylic acids) or oral corticosteroids (≤20 mg prednisolone equivalent)

• Been taking enemas or suppositories (other than stable dose of 5-ASA) for treatmentof UC within 2 weeks prior to the Screening Visit.

• Been taking an unstable dose of probiotics or antidiarrheals 2 weeks prior to theScreening Visit.

• Had recent myocardial infarction, unstable angina, stroke, transient ischemicattack, decompensated heart failure with hospitalization, Class III/IV heartfailure, Mobitz Type II 2nd degree or 3rd degree atrioventricular (AV) block, sicksinus syndrome, prolonged QT interval, Wolff Parkinson White or other conductionabnormalities, low heart rate, ongoing treatment with Class I or Class IIIanti-arrhythmic drugs, heart-rate-lowering calcium-channel blockers, β blockers orwith any other drugs which can reduce the heart rate, have known high risk forQT/QTc prolongation, or have clinically significant abnormal findings in 12-lead ECGthat the Investigator considers may jeopardize the subject's health.

• Forced expiratory volume in one second (FEV1) or forced expiratory vital capacity (FVC) <70% of predicted values at screening. For sites where DLCO (diffusingcapacity of the lungs for carbon monoxide) will be assessed, the value (mL/min/mmHg)is < 80% of the predicted normal value for age, height, and gender.

• Macular oedema as assessed by OCT (Optical Coherence Tomography).

• History of non-response or treatment failure with MT-1303 or other sphingosine 1phosphate (S1P) receptor modulators.

• Fecal microbiota transplantation (FMT) within 12 months prior to the ScreeningVisit.

• Any of the following laboratory abnormalities:

• Hemoglobin (Hb) <9.0 g/dL.

• White blood cell (WBC) count <3.50 × 109/L (<3,500/µL).

• Neutrophil count <1.50 × 109/L (<1,500/µL).

• Lymphocyte count <0.80 × 109/L (<800/µL).

• Aspartate aminotransferase (AST) or alanine aminotransferase (ALT) >2 × theupper limit of normal (ULN).

• Bilirubin >1.5 x the ULN; subjects with Gilbert's syndrome may be enrolled withtotal bilirubin up to 5.0 mg/dl.

• Positive stool tests for enteric pathogens, pathogenic ova or parasites, orClostridium difficile (C. difficile) during the Screening Period. If subject has ahistory of recent C. difficile infection (within 60 days prior to Screening Visit),they should not be considered for study enrollment until subject has been treatedfor C. difficile and is symptom free for at least 14 days prior to the ScreeningVisit.

• Any physical or mental conditions which would interfere with the studyparticipation, collection of data, or study completion as determined by theInvestigator.