Inclusion Criteria:

   - Histologically or cytologically confirmed recurrent or metastatic SCCHN Stage III/IV
   and not amenable to local therapy with curative intent (surgery or radiation therapy
   with or without chemotherapy). The eligible primary tumor locations are oropharynx,
   oral cavity, hypopharynx, and larynx. Patients may not have a primary tumor site of
   nasopharynx (any histology).

   - Documented treatment failure of no more than one approved PD-1/L1 inhibitor either
   administered alone or in combination.

Patients must have measurable disease.

   - Age ≥ 18 years

   - Adequate renal function

   - Adequate liver function

   - Adequate hematological function

   - Have an Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1.

Exclusion Criteria:

   - Patients must not have a history of ≥ Grade 3 allergic reactions to mAb therapy as
   well as known or suspected allergy or intolerance to any agent given during this
   study.

   - Patients must not have known human immunodeficiency virus (HIV) infection, active
   hepatitis B and/or hepatitis C.

   - Patients must not be women who are pregnant or breast feeding.