A Study of MK-6194 (PT101) in Participants With Active Ulcerative Colitis (UC) (MK-6194-002)

Prior treatment

• Prior treatment with recombinant IL-2 or modified IL-2 therapy, including MK-6194 (PT101).
• Previously had surgery for UC, or likely to require surgery for UC during the study period in the opinion of the Investigator.
• Active clinically significant infection, or any infection requiring hospitalization or treatment with intravenous anti-infectives within 8 weeks of randomization, or any infection requiring oral anti-infective therapy within 6 weeks of randomization.
• Currently on any chronic systemic (oral or IV) anti-infective therapy for chronic infection (such as pneumocystis, cytomegalovirus, herpes zoster, or atypical mycobacteria).
• Exposure to advanced therapy within 5 half-lives of the Day 1 visit, or documentation of detectable drug during screening.
• Received a live attenuated vaccine \< 1 month prior to screening or is planning to receive a live attenuated vaccine during the study period or within 12 weeks of the end of participation in the study.
• Any uncontrolled or clinically significant concurrent systemic disease other than UC.

Other illness

• Known history of hypersensitivity to interleukin-2 (IL-2).
• Disease limited to the rectum (i.e., within 15 cm of the anal verge).
• Diagnosis of Crohn's disease, or indeterminant colitis.
• History of abnormal thallium stress test or functional cardiac function test.
• History of significant cardiac, pulmonary, renal, hepatic, or central nervous system (CNS) impairment.
• History of opportunistic infection.
• History of symptomatic herpes zoster within 16 weeks of randomization, or any history of disseminated herpes simplex, disseminated herpes zoster, ophthalmic zoster, or central nervous system (CNS) zoster.
• History of abnormal pulmonary function tests.
• Malignancy within 5 years of screening, with the exception of adequately treated or excised non-metastatic basal cell or squamous cell cancer of the skin.

Lab values

• Currently receiving lymphocyte depleting therapy.

Other

• Known sensitivity to MK-6194 (PT101) or its excipients.
• Diagnosis of toxic megacolon.
• Suspected or known colon stricture or stenosis.
• Has severe colitis as evidenced by:
  • Current hospitalization for the treatment of UC
  • Likely to require a colectomy within 12 weeks of baseline in the opinion of the Investigator
  • At least 4 symptoms of severe colitis as identified at screening or baseline visits.
• Participants with organ or tissue allograft.
• Is pregnant or nursing or is planning to become pregnant during the study.

• Diagnosis of UC at least 3 months prior to screening.
• Mildly to severely active UC.
• Inadequate response, loss of response, or intolerance to at least 1 prior conventional therapy, and no more than 2 prior advanced therapies.
• Participants at risk for colorectal cancer must have a colonoscopy prior to or at screening as follows:
  • Participants \> 50 years of age must have documentation of a colonoscopy within 3 years of the screening visit to exclude adenomatous polyps. Participants whose adenomas have been completely excised at screening are eligible.
  • Participants with extensive colitis for ≥ 8 years, or disease limited to the left side of the colon for ≥ 10 years, must either have had a full colonoscopy to assess for the presence of dysplasia within 1 year before first administration of study drug or a full colonoscopy to assess for the presence of malignancy at the screening visit.
• No evidence of active tuberculosis (TB), latent TB, or inadequately treated TB.
• Women of childbearing potential (WOCBP) and males with female partners of childbearing potential must utilize highly effective contraceptive methods beginning 4 weeks prior to first dose of study drug and continue for 30 days after the last dose of study drug.
• Body mass index (BMI) 18 to 35 kg/m\^2 inclusive and weight ≥ 50 kg.