A Study of AB801 Monotherapy and Combination Therapy in Participants With Advanced Malignancies

Key Inclusion Criteria:

* Monotherapy-specific criteria for dose escalation cohorts:

  * Participants may have cytologically or pathologically confirmed non-small cell lung carcinoma (NSCLC), colorectal carcinoma (CRC), breast, ovarian, renal cell carcinoma (RCC), head and neck squamous cell carcinoma (HNSCC), or bladder (including urothelial malignancies of the renal pelvis and ureter) carcinoma that has progressed or was non-responsive to available therapies with no standard of care (SOC) options, or for whom standard therapy has proven ineffective, intolerable, or considered inappropriate; or for whom a clinical study of an investigational agent is a recognized SOC.
* Disease-specific criteria for dose-expansion (NSCLC):

  * Cytologically or pathologically confirmed locally advanced unresectable or metastatic (Stage IIIB-IV per American Joint Committee on Cancer version 8) non-squamous NSCLC negative for actionable mutations in EGFR, ALK, ROS1, NTRK, C-MET, or RET. Mixed SCLC and squamous NSCLC histology is not permitted.
  * Previously treated in the unresectable locally advanced or metastatic setting with a platinum-containing chemotherapy and PD-(L)-1inhibitor.
* Must have at least 1 measurable lesion per Response Evaluation Criteria in Solid Tumors (RECIST) guidance (Version 1.1) (Section 1.1). The measurable lesion must be outside of a radiation field if the participant received prior radiation unless discussed and approved by the study physician.
* Eastern Cooperative Oncology Group (ECOG) performance status score of 0 or 1.

Key Exclusion Criteria:

* Use of any live vaccines against infectious diseases (eg, influenza, varicella) within 4 weeks (28 days) of initiation of investigational product.
* Underlying medical conditions or adverse events that, in the physician or sponsor's opinion, will make the administration of investigational products hazardous.
* Prolonged QT interval defined as mean corrected QT interval (QTc) ≥ 450 milliseconds (ms).
* Any active or documented history of autoimmune disease, including but not limited to inflammatory bowel disease, celiac disease, Wegner syndrome, Hashimoto syndrome, systemic lupus erythematosus, scleroderma, sarcoidosis, or autoimmune hepatitis, within 3 years of the first dose of study treatment.
* Treatment with systemic immunosuppressive medication (including but not limited to corticosteroids, cyclophosphamide, azathioprine, methotrexate, thalidomide, and antitumor necrosis factor-α agents) administered within 2 weeks prior to initiation of study treatment, or anticipation of need for systemic immunosuppressant medication during study treatment.

Note: Other protocol defined Inclusion/Exclusion criteria may apply.