The Efficacy and Safety of Combining Probiotic VSL#3 With Vedolizumab for the Treatment of Moderate Ulcerative Colitis

Inclusion Criteria:

• Subject must be a man or woman aged 18-85 years, inclusive.

• Diagnosed with ulcerative colitis (UC) at least 90 days prior to baseline, supportedby comprehensive colonoscopy findings and histopathological evidence obtained withinthe past year. Participants must provide full colonoscopy or sigmoidoscopy reportsalong with pathology results conducted within the last 3 months, as well as bloodindicators (within 1 week) at baseline screening. Individuals currently experiencinginfection, dysplasia, or malignancy will be excluded from participation.

• Subject has moderate active UC and had a Mayo score of 6-10 at screening.

• Planned treatment with Vedolizumab as initial therapy or reinduction, withreinduction defined as no vedolizumab treatment within 1 year.

• Confirmed by the investigator that despite receiving at least one of the followingtreatments, the subject has shown an inadequate response, loss of response, orintolerance:

1. Oral aminosalicylates (e.g., mesalamine, sulfasalazine, olsalazine,balsalazide), where the subject exhibits ongoing signs and symptoms of activedisease during at least 4 weeks of treatment with mesalamine 2.4 g/day,sulfasalazine 4 g/day, olsalazine 1 g/day, or balsalazide 6.75 g/day.

2. Immunosuppressants: failure to respond after receiving at least 42 consecutivedays of treatment with azathioprine, 6-mercaptopurine, or methotrexate (MTX)injections prior to baseline (Week 0), with minimum doses of azathioprine ≥ 0.75 mg/kg/day or 6-MP ≥ 0.5 mg/kg/day (rounded to the nearest tablet dose) orMTX ≥ 15 mg/week (SC/IM), or the highest tolerated dose due to adverse effectssuch as leukopenia, elevated liver enzymes, or nausea.

• No increase in dose of oral 5-ASA and Immunosuppressants could be allowed if it ismaintained stable at least 2 weeks before screening.

• Subject must be willing and able to adhere to the prohibitions and restrictionsspecified in this protocol.

• Willing and able to complete the required Subject Diary.

• Willing and able to meet all study requirements, including attending all assessmentvisits and phone calls.

Exclusion criteria:

• Diagnosis of Crohn's disease, undetermined IBD or other colitis.

• UC disease limited to the rectum (<15 cm from the anal verge)

• Steroid therapy initiation within 2 weeks before screening visit.

• Used antibiotics for intestinal or other infections within 2 weeks of the screening

• Use of other probiotics preparations within the last 2 weeks before study entry (screening)

• Used rectal 5-ASA within the past week before study entry (screening)

• Adjustment of oral 5-ASA and immunosuppressant dosages due to disease progressionafter colonoscopy screening until enrollment.

• Within 1 week prior to screening, the participant has taken nonsteroidalanti-inflammatory drugs (NSAIDs) or anti-diarrheal medications for 5 consecutivedays.

• Positive Clostridioides difficile detection toxin results within the past monthprior to screening.

• Pregnancy and breastfeeding women

• Other biologics/advanced therapies are used as concomitant therapy and Previous useof other biologics

• History of allergy to maltose and/or cornstarch and/or silica

• Subjects with severe primary heart, liver, lung, kidney, hematologic, or seriousdiseases that affect their survival, such as cancer, AIDS, asthma, kidney stones,renal dysfunction; urine protein >+, microscopic hematuria, ALT >2N (N is the upperlimit of normal), Cr > normal upper limit, platelet count <50x10^9/L, white bloodcell count <3.0x10^9/L.