• Written informed consent

• Age ≥ 18 years

• Participants must be able to understand and comply with the purpose and procedures that are involved in the trial

• An established diagnosis of colonic inflammatory bowel disease, with willingness to participate in an annual colonoscopic surveillance program, as per routine standard of care

• An established clinical diagnosis of large duct PSC, with compatible features as assessed by magnetic resonance cholangiopancreatography (MRCP) or endoscopic retrograde cholangiopancreatography (ERCP)

• A persistent ALP value above normal (at least 2 readings at this value over 6 months before screening)

• Evidence of early to moderate stage liver fibrosis, as suspected by any of the following:

∙ Median VCTE score of ≤14.4kPa, with an interquartile range ≤30%

‣ Previous liver biopsy indicating at an absence of established cirrhosis, Ishak fibrosis stage \<IV (or equivalent) in the last 24 months

‣ Serum enhanced liver fibrosis score (ELF) ≤9.8

• A colonoscopy showing no evidence of dysplasia/neoplasia within 24 months before screening

• No evidence of active colitis, as evidenced by a Partial Mayo Score of ≤4, with a score of \<2 on the rectal bleeding domain at screening

⁃ Individuals with IBD who are receiving treatment with biologics, immunosuppression or corticosteroids must be taking a stable dose for at least twelve weeks prior to screening, and be expected to remain on the same medication/same dose for the duration of the trial

⁃ Individuals with PSC having overlapping features of autoimmune hepatitis may be included, provided:

• The dosage of immunosuppression has remained stable for at least twelve weeks prior to screening, and be expected to remain on the same medication/same dose for the duration of the trial; and

∙ There is evidence of concomitant colitis