Study To Evaluate The Safety, Tolerability And Immunogenicity Of 4 mg Of ITI-3000 In Patients With Polyomavirus-Positive Merkel Cell Carcinoma (MCC)

Inclusion Criteria: * Evidence of Merkel cell polyomavirus (MCPyV) in the tumor at initial presentation (pre-therapy) can be provided by a positive anti-MCPyV oncoprotein antibody AMERK Test. * Eligible participants have to be both be diagnosed and have completed SOC surgical and/or radiation therapy at least 1 year prior to enrollment in the study and have no evidence of active disease (NEAD). * Participants who were previously diagnosed with MCC and had recurrence and also exhibited no evidence of active disease (NEAD) for more than 2 years prior to enrollment in the study. * Age ≥ 18 years. * Karnofsky performance status (PS) ≥ 70 or ECOG PS 0-1. * Participant has a predicted life expectancy ≥ 3 months. * Participant provided signed and dated informed consent prior to initiation of any study procedures. * Participant has adequate renal function (creatinine ≤ 1.5 times the upper limit of normal \[ULN\]) or a glomerular filtration rate (GFR) of ≥ 50 mL/min/1.73 m2). * Participant has adequate hepatic function, as evidenced by a total bilirubin ≤ 1.5 times the ULN, aspartate transaminase (AST), and/or alanine transaminase (ALT) ≤ 3 times the ULN. * Participant has adequate bone marrow function, as evidenced by hemoglobin ≥ 9.0 g/dL in the absence of transfusion within the previous 72 hours, platelet count ≥ 100×109cells/L, and absolute neutrophil count (ANC) ≥ 1.5×109 cells/L. * Participant and his/her partner agree to use adequate contraception after providing written informed consent through 2 months after the last study drug dose, as follows: * For women: Negative pregnancy test during Screening and at Baseline and compliant with two methods of medically-approved contraceptive regimens or abstinence during and for 2 months after the treatment period or documented to be surgically sterile or postmenopausal. * For men: Compliant with two methods of medically approved contraceptive regimens or abstinence during and for 2 months after the treatment period or documented to be surgically sterile * Participant is willing and able to participate in the study and comply with all study requirements. Exclusion Criteria: * Participation in another therapeutic clinical trial. * Participant who received systemic treatment previously (e.g., chemotherapy, PD-1/PD-L1). * Participant is pregnant or breast-feeding. * Negative for an anti-MCPyV oncogene antibody titer or other evidence of no MCPyV involvement at initial presentation using an acceptable and specific assay at the institution. * Known history of AIDS/HIV, other viral diseases or oncologic disorders such as untreated HCV, chronic active HBV or organ transplantation that may have immunologic consequences or require immunosuppression. No testing required. * Participant with CLL-associated MCC. * On-going immunosuppressive therapy for other conditions with the exception of low-dose topical, nasal or inhaled steroids. * Participant has a history of other malignancy treated with curative intent within the previous 3 years with the exception of adequately treated non-melanoma skin cancer or carcinoma in situ of the cervix. Participants with previous invasive cancers are eligible if the treatment was completed more than 3 years prior to initiating current study treatment, and there is no evidence of recurrent disease. * Participant has a significant medical illness or abnormal laboratory finding that, in the Investigator's opinion, would increase the risk of participating in this study. * Participant with otherwise unexplained \>10% weight loss in the last 30 days prior to the screening. * Participant has evidence of serious active infection (i.e., infection requiring treatment with intravenous antibiotics).