Inclusion Criteria:

          1. Male and female subjects 18 years and older

          2. Histologically or cytologically confirmed diagnosis of HNSCC associated with HPV by a
             p16 immunohistochemistry (IHC) assay or HPV-16 or HPV-18 positive by nucleic acid
             testing.

          3. Recurrent or metastatic disease that has been treated with at least one
             platinum-containing regimen and lacking a curative treatment option.

          4. Patients who are platinum ineligible may be enrolled if they have received and failed
             an approved treatment and lack a treatment option with curative potential.

        Exclusion criteria:

          1. Any concurrent chemotherapy, immune-mediated therapy or biologic or hormonal therapy
             for cancer treatment Active or prior documented autoimmune disease with some
             exceptions.

          2. Current or prior use of immunosuppressive medication within 14 days prior to first
             study dose, with the exception of intranasal and inhaled corticosteroids or systemic
             corticosteroids at doses not to exceed 10 mg/day of prednisone or equivalent. Steroids
             as premedication for hypersensitivity reactions due to radiographic contrast agents
             are allowed.

          3. No prior exposure to immune-mediated therapy defined as prior exposure to T-cell and
             natural killer cell directed therapy (e.g., anti-PD-1, anti-PD-L1, anti-CD137, and
             anti-CTLA4, etc).