Patient description: The patient is a 55-year-old man diagnosed with HCV 2 years ago and the recent coinfection with HBV. His past medical history is non-significant. He is on IFN, RBV and direct antiviral drugs for the past 6 months. The patient takes no other medications. His medical records show previous positive HCV RNA tests and a positive enzyme immunoassay for anti-HCV-antibodies. The recent biopsy was negative for hepatocellular carcinoma and was only remarkable for chronic inflammation compatible with a chronic viral hepatitis. There is no evidence of alcoholic liver disease, bleeding from esophageal varices, hemochromatosis, autoimmune hepatitis, or metabolic liver disease. He is an alert male with no acute distress. His BP: 130/75, HR: 90/min and BMI: 27. His abdomen is soft with no ascites or tenderness. The lower extremities are normal with no edema.

Clinical trial eligibility criteria: eligible ages (years): 18.0-999.0,  MSI Positive Colorectal Cancer MSI Negative Colorectal Cancer MSI Positive Non-Colorectal Cancers Cohort A only: Patients with microsatellite instability (MSI) positive colorectal cancer Cohort B only: Patients with MSI negative colorectal cancer Cohort C only: Patients with MSI positive non-colorectal cancer - Have measurable disease Eastern Cooperative Oncology Group (ECOG) Performance Status of 0 to 1 Adequate organ function as defined by study-specified laboratory tests Must use acceptable form of birth control through the study and for 28 days after final dose of study drug Signed informed consent form Willing and able to comply with study procedures Agree to have a biopsy of participants' cancer  Patients with uncontrolled intercurrent illness, including but not limited to ongoing or active infection, systematic congestive heart failure, unstable angina pectoris, cardiac arrhythmia or psychiatric condition that would limit compliance with study requirements Patients who have had chemotherapy or biological cancer therapy within 2 weeks prior to the first dose of study drug Patients who have had radiation within 2 weeks prior to the first dose of study drug Patients who have undergone major surgery within 4 weeks of dosing of investigational agent Patients who have received another investigational product or investigational device within 4 weeks prior to receiving study drug Patients who have received any of the following concomitant therapy: Interleukin-2 (IL-2), interferon, or other non-study immunotherapy regimens, immunosuppressive agents, other investigational therapies or chronic use of systemic corticosteroids within one week prior to first dose of study drug Patients who have received a live vaccine within 4 weeks prior to or after any dose of MK-3475 (exception: inactivated flu vaccines) Patients who have received growth factors, including but not limited to granulocyte-colony stimulating factor (G-CSF), granulocyte macrophage-colony stimulating factor (GM-CSF), erythropoietin, etc. within 2 weeks of study drug administration Patient who have had prior treatment with anti-PD-1 (anti-programmed cell death protein 1), anti-PD-L1, anti-PD-L2, anti-CD137, anti-OX-40, anti-CD40, or anti-CTLA-4 antibodies Patients with history of any autoimmune disease:inflammatory bowel disease, (including ulcerative colitis and Crohn's Disease), rheumatoid arthritis, systemic progressive sclerosis (scleroderma), systemic lupus erythematosus (SLE) autoimmune vasculitis, central nervous system (CNS) or motor neuropathy considered to be of autoimmune origin