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

Inclusion Criteria:

• 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 priorconventional therapy, and no more than 2 prior advanced therapies.

• Participants at risk for colorectal cancer must have a colonoscopy prior to or atscreening as follows:

• Participants > 50 years of age must have documentation of a colonoscopy within 3 years of the screening visit to exclude adenomatous polyps. Participantswhose adenomas have been completely excised at screening are eligible.

• Participants with extensive colitis for ≥ 8 years, or disease limited to theleft side of the colon for ≥ 10 years, must either have had a full colonoscopyto assess for the presence of dysplasia within 1 year before firstadministration of study drug or a full colonoscopy to assess for the presenceof 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 ofchildbearing potential must utilize highly effective contraceptive methods beginning 4 weeks prior to first dose of study drug and continue for 30 days after the lastdose of study drug.

• Body mass index (BMI) 18 to 35 kg/m^2 inclusive and weight ≥ 50 kg.

Exclusion Criteria:

• Prior treatment with recombinant IL-2 or modified IL-2 therapy, including MK-6194 (PT101).

• Known sensitivity to MK-6194 (PT101) or its excipients.

• 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 toxic megacolon.

• Suspected or known colon stricture or stenosis.

• Diagnosis of Crohn's disease, or indeterminant colitis.

• 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 theInvestigator

• At least 4 symptoms of severe colitis as identified at screening or baselinevisits.

• Previously had surgery for UC, or likely to require surgery for UC during the studyperiod in the opinion of the Investigator.

• History of abnormal thallium stress test or functional cardiac function test.

• History of significant cardiac, pulmonary, renal, hepatic, or central nervous system (CNS) impairment.

• Active clinically significant infection, or any infection requiring hospitalizationor treatment with intravenous anti-infectives within 8 weeks of randomization, orany infection requiring oral anti-infective therapy within 6 weeks of randomization.

• History of opportunistic infection.

• History of symptomatic herpes zoster within 16 weeks of randomization, or anyhistory of disseminated herpes simplex, disseminated herpes zoster, ophthalmiczoster, or central nervous system (CNS) zoster.

• Currently on any chronic systemic (oral or IV) anti-infective therapy for chronicinfection (such as pneumocystis, cytomegalovirus, herpes zoster, or atypicalmycobacteria).

• Currently receiving lymphocyte depleting therapy.

• History of abnormal pulmonary function tests.

• Participants with organ or tissue allograft.

• Malignancy within 5 years of screening, with the exception of adequately treated orexcised non-metastatic basal cell or squamous cell cancer of the skin.

• Exposure to advanced therapy within 5 half-lives of the Day 1 visit, ordocumentation of detectable drug during screening.

• Received a live attenuated vaccine < 1 month prior to screening or is planning toreceive a live attenuated vaccine during the study period or within 12 weeks of theend of participation in the study.

• Is pregnant or nursing or is planning to become pregnant during the study.

• Any uncontrolled or clinically significant concurrent systemic disease other thanUC.