A Study of ABBV-927 and ABBV-181, an Immunotherapy, in Participants With Advanced Solid Tumors

Inclusion Criteria: * Participant has an Eastern Cooperative Oncology Group (ECOG) Performance Status of 0 to 1. * Participants have adequate bone marrow, kidney and liver function. * Participants with a history of chronic heart failure or significant cardiovascular disease must have an echocardiogram or multigated acquisition scan indicating left ventricular ejection fraction greater than or equal to 45% within 28 days prior to the first dose of study drug. * Participants must have creatinine clearance greater than or equal to 50 mL/min as measured by 24-hour urine or estimated by the Cockcroft-Gault formula. * Participants must have total bilirubin less than or equal to 1.5 times the upper limit of normal (ULN), and aspartate aminotransferase and alanine aminotransferase less than or equal to 2.5 times ULN. * Participants in all monotherapy arms must have an advanced solid tumor that has progressed on standard therapies known to provide clinical benefit or the participants are intolerant to such therapies. * Participants in all combination therapy arms must have recurrent or metastatic HNSCC or NSCLC and previously received platinum-based therapy and progressed either during or after anti-programmed death ligand 1 (PDL1)-based therapy. In addition, participants must have received only one prior immunotherapy. * The Sponsor may decide to limit the specific tumor types selected or treatment settings for specific arms based on evidence gathered. Exclusion Criteria: * Partic…