This Phase 1, multicenter, open-label trial will assess the safety and feasibility of IFx-Hu2.0 as adjunctive therapy to pembrolizumab in adult patients (≥18 years) with non-cutaneous Merkel Cell Carcinoma. Nine subjects will receive IFx-Hu2.0 as a visceral lesion injection in a single lesion followed by pembrolizumab.

Inclusion Criteria:

1. At least 18 years of age.

2. Life expectancy equal to or greater than six months.

3. Eastern Cooperative Oncology Group (ECOG) Performance Status < 2.

4. Active disease measurable by CT or MRI, measurable lesions are lesions that can be accurately measured in at least one dimension (longest diameter in the plane of measurement is to be recorded).

5. Must be recurrent and/or unresectable Stage III or Stage IV American Joint Committee on Cancer (AJCC) (8th edition) and have histologically confirmed Merkel cell carcinoma

   a. Must have at least one visceral injectable lesion equal to or greater than 3 mm

6. Subject should be CPI naïve i.e., no prior therapy with CPI including but not limited to Pembrolizumab, avelumab, ipilimumab, nivolumab.

7. Tumor tissue from an archival core biopsy or resected site of disease must be provided for biomarker analyses. If archival tissue is not available, then a new biopsy should be performed.

8. Adequate hematological, hepatic, and renal function according to laboratory ranges and medical criteria defined within the study protocol.

Exclusion Criteria

1. Uncontrolled intercurrent illness including, but not limited to, ongoing or active infection, symptomatic congestive heart failure, unstable angina pectoris, cardiac arrhythmia, or psychiatric illness/social situations that would limit compliance with protocol requirements.
2. Subjects with active brain metastases, with the exception of treated brain metastases that have imaging proving stability at least 4 weeks after treatment, no new metastases, and not requiring steroids.
3. Subjects with recurrent resectable MCC
4. Subjects who have received prior systemic chemotherapy
5. Pregnant or breastfeeding females and females desiring to become pregnant or breastfeed within the timeframe of this study.
6. Active, known, or suspected autoimmune disease. Potential subjects with type I diabetes mellitus, residual hypothyroidism due to autoimmune thyroiditis only requiring hormone replacement, skin disorders (such as vitiligo, psoriasis, or alopecia) not requiring systemic treatment are permitted to enroll. Low grade autoimmune toxicity is NOT an exclusion under this criterion.
7. A condition requiring systemic treatment with either corticosteroids (> 10 mg daily prednisone equivalent) or other immunosuppressive medications within 14 days of IFx-Hu2.0 administration. Inhaled or topical steroids are permitted in the absence of active autoimmune disease.