This is a prospective cohort study enrolling ulcerative colitis patients who initiate tofacitinib therapy. Investigators will collect clinical data, blood and stool samples prior to initiation of tofacitinib and, at minimum, monthly after the start of therapy. They will collect tissue from colonoscopies prior to initiation of therapy and within 6 months on therapy. Clinical characteristics and response to treatment will then be associated with genotype, blood immune profiles, stool microbiota, and cellular and molecular profiles of the biopsies to generate a treatment response model. Using predictors identified in our model, we will then attempt to validate the model and findings with the OCTAVE (Pfizer), SPARC (CCF), and RISK (CCF) data.

Inclusion Criteria:

• Total mayo score between 6 and 12
• Endoscopic subscore of 2 or 3

Exclusion Criteria:

• Recent use of antibiotic therapy (<4 weeks)
• Current extreme diet (parenteral nutrition, specific carbohydrate diet).
• Active infection or malignancy.
• Significant underlying liver or renal disease.

Patients 18-70 with moderate to severe ulcerative colitis defined as a total mayo score between 6 and 12, and an endoscopic subscore of 2 or 3.

All of the individual participant data collected during the trial, after deidentification.

Beginning 3 months and ending 5 years following article publication.

Researchers who provide a methodologically sound proposal.