Inclusion Criteria:

          -  Histologically proven, recurrent or metastatic squamous cell carcinoma of the head and
             neck (SCCHN) not curable by local therapy

          -  No prior systemic therapy for SCCHN in the recurrent or metastatic setting (with the
             exception of systemic therapy completed > 6 months prior if given as part of
             multimodal treatment for locally advanced disease)

          -  Primary tumor locations of oropharynx, oral cavity, hypopharynx, or larynx. Patients
             may not have a primary tumor site of upper esophagus, salivary gland, or nasopharynx
             (any histology)

          -  Availability of formalin-fixed, paraffin embedded tumor specimen or contemporary
             biopsy for immunohistochemical evaluation of pharmacodynamic markers of interest

          -  Willing to consent for baseline and on-treatment biopsy.

          -  Performance status 0 or 1

          -  Life expectancy of 6 months or more

          -  Adequate end organ function

          -  At least one radiographically measurable lesion

          -  PD-L1 expression level that is either

               1. Positive (combined positive score [CPS] ≥ 1) for the retifanlimab cohort, or

               2. Negative (CPS < 1) for the tebotelimab cohort

          -  Results available from human papilloma virus p16 status for oropharyngeal cancer

          -  Acceptable laboratory results

        Exclusion Criteria:

          -  Disease suitable for local therapy administered with curative intent

          -  Progressive disease within 6 months of completion of curatively intended systemic
             treatment for locoregionally advanced SCCHN

          -  Radiation or other non-systemic therapy within 2 weeks prior to the first dose of
             study drug

          -  Prior therapy with an anti-B7-H3, anti-PD-1, anti-PD-L1, or anti-LAG-3 agent