A Study of ABBV-428, an Immunotherapy, in Subjects With Advanced Solid Tumors

Inclusion Criteria:

* Participants 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 have adequate bone marrow, renal, hepatic and coagulation function.
* For all dose expansion arms, participants must have measurable disease per Response Evaluation Criteria in Solid Tumors (RECIST) Version 1.1
* Participants in combination therapy cohorts must have an advanced solid tumor where the use of nivolumab is standard therapy.

Exclusion Criteria:

* Active or prior documented autoimmune disease in the last 2 years. Participants with childhood atopy or asthma, vitiligo, alopecia, Hashimoto syndrome, Grave's disease, or psoriasis not requiring systemic treatment (within the past 2 years) are not excluded.
* Current or prior use of immunosuppressive medication within 14 days prior to the first dose (with certain exceptions).
* History of primary immunodeficiency, bone marrow transplantation, chronic lymphocytic leukemia, solid organ transplantation, or previous clinical diagnosis of tuberculosis.
* Confirmed positive test results for human immunodeficiency virus (HIV), or participants with chronic or active hepatitis B or C. Participants who have a history of hepatitis B or C who have undetectable HBV DNA or HCV RNA after anti-viral therapy may be enrolled.
* Prior grade greater than or equal to 3 immune-mediated neurotoxicity or pneumonitis (or any other unresolved or symptomatic adverse event in the last 3 months) while receiving immunotherapy.
* Male participants who are considering fathering a child or donating sperm during the study or for at least 3 or 5 months (for monotherapy and combination therapy participants, respectively) after the last dose of study drug.