Inclusion Criteria:  Dose-escalation cohorts only:  -- Must have an advanced solid tumor who are considered refractory to or intolerant of all existing therapies known to provide a clinical benefit for their condition.  Relapsed Non-Small Cell Lung Cancer (NSCLC) Head and Neck Squamous Cell Carcinoma (HNSCC) dose-expansion cohorts only:  Must have histologically or cytologically confirmed advanced or metastatic NSCLC or HNSCC that has been treated with platinum-based chemotherapy and a programmed cell death (PD)-1 or PD ligand 1 (PD-L1) targeting agent (separately or in combination therapy). Must have failed (or refused) treatment with available therapies known to be active for treatment of their disease. Participants enrolled in dose escalation must have disease that is evaluable or measurable per Response Evaluation Criteria in Solid Tumors (RECIST, version 1.1). Participants enrolled in dose expansion must have measurable disease per RECIST, version 1.1. Eastern Cooperative Oncology Group (ECOG) performance status of ≤ 1. Laboratory values meeting the criteria outlined in the protocol.  Exclusion Criteria:  Relapsed Non-Small Cell Lung Cancer (NSCLC) Head and Neck Squamous Cell Carcinoma (HNSCC) dose-expansion cohorts only:  Non-Small Cell Lung Cancer (NSCLC) participants with known EGFR mutations or ALK gene rearrangements are ineligible.