The study will determine the recommended Phase 2 dose (RP2D) of livmoniplimab (ABBV-151) administered as monotherapy and in combination with budigalimab (ABBV-181) as well as to assess the safety, tolerability, pharmacokinetics (PK), and preliminary efficacy of livmoniplimab alone and in combination with budigalimab. The study will consist of 2 parts: dose escalation and dose expansion.

Inclusion Criteria:

• For Dose Escalation only: Participants with an advanced solid tumor who are considered refractory to or intolerant of all existing therapy(ies) known to provide a clinical benefit for their condition. Additionally, participants who have been offered standard therapies and refused, or who are considered ineligible for standard therapies, may be eligible for this study on a case-by-case basis, after discussion with and agreement from the sponsor. Participants with pancreatic adenocarcinoma, urothelial cancer (UC), hepatocellular carcinoma (HCC), or head and neck squamous cell carcinoma (HNSCC) who are being considered for the dose escalation cohorts must also meet the histology specific eligibility criteria described below for dose expansion.

• For Dose Expansion only participants must meet criteria specific to the type of cancer:

  • Pancreatic adenocarcinoma and have disease progression during or after 1 systemic therapy (gemcitabine monotherapy or in combination with other agents, FOLFIRINOX [or another regimen including both 5-fluorouracil and oxaliplatin], capecitabine monotherapy or in combination with other agents) administered in the adjuvant, locally advanced, or metastatic setting. If the therapy was used in an adjuvant setting, disease progression must have occurred within 6 months of completing adjuvant therapy.
  • UC of the bladder and urinary tract and must have progressed following treatment with:
  • Cohort 4: A platinum-based regimen (administered in any line of therapy) and a programmed death 1/programmed death ligand 1 (PD1/PDL1) antagonist administered in the recurrent or metastatic setting (progression following a PD1/PDL1 antagonist is defined as unequivocal progression on or within 3 months of the last dose of anti-PD1 or anti-PDL1 therapy).
  • Cohort 11: One or more prior line of therapy in the locally advanced or metastatic setting. Participant must have experienced radiographic progression or relapse during or after a CPI (anti-PD1 or anti-PD-L1) for locally advanced or metastatic disease.
  • HCC and must have disease progression during or after 1 prior line of systemic therapy.
  • HNSCC (arising from the oral cavity, oropharynx, hypopharynx, or larynx) and must have progressed following treatment with platinum-based regimen (administered in any line of therapy) and a PD1/PDL1 antagonist administered in the recurrent or metastatic setting (progression following a PD1/PDL1 antagonist is defined as unequivocal progression on or within 3 months of the last dose of anti-PD1 or anti-PDL1 therapy).
  • Microsatellite stable colorectal cancer (MSS-CRC) [unselected] participants with microsatellite stable or mismatch repair proficient colorectal adenocarcinoma (as determined by polymerase chain reaction (PCR)/Next-Generation sequencing (NGS) or immunohistochemistry (IHC), respectively) who have received 1-2 prior chemotherapy regimens.
  • Non-small cell lung cancer (NSCLC) relapsed/refractory (R/R): Participants with histologically or cytologically confirmed advanced or metastatic NSCLC who have received 1 prior line of chemotherapy and 1 prior anti-PD-(L)1 antibody, administered either concurrently or sequentially in the metastatic setting.
  • MSS-CRC (CMS4 enriched): Participants with microsatellite stable or mismatch repair proficient colorectal adenocarcinoma who have received prior fluorouracil-based combination chemotherapy regimens including oxaliplatin and irinotecan (with or without VEGF and/or EGFR targeted agents) and with a CMS4 subtype as determined by NGS of tumor biopsies. Archival tissue must be submitted for assessment of CMS4 subtype status during prescreening. Participants must have progressed on or refused available standard of care therapies. Additionally, participant who are considered not appropriate or ineligible for available standard of care therapies per investigator assessment will be eligible for this study.
  • Ovarian granulosa (OG) cell tumor: Participants with histologically confirmed advanced nonresectable or metastatic adult granulosa cell tumor of the ovary that is not amenable to curative intent surgery or radiation. Additionally, there is documentation of radiological evidence of relapse after at least 1 line of systemic chemotherapy.

• Participant has an Eastern Cooperative Oncology Group (ECOG) Performance Status of 0 to 1.

• Participant has adequate bone marrow, renal, hepatic, and coagulation function.

• Must have a viral status consistent with the requirements described in the protocol specific to type of cancer and stage of study (Dose Escalation or Dose Expansion).

Exclusion Criteria:

• For Dose Expansion only:

  • Participants with HCC, pancreatic adenocarcinoma, or MSS-CRC having prior exposure to a prior PD-1/PD-L1 antagonist in any line of therapy.
  • Participants (except for participants with urothelial cancer or HNSCC) who have had prior exposure to immunotherapies as listed in the protocol.

• Has received anticancer therapy including chemotherapy, immunotherapy, radiation therapy, biologic, herbal therapy, or any investigational therapy within a period of 5 half-lives or 28 days (whichever is shorter), prior to the first dose of the study drug.

• Participant has unresolved AEs > Grade 1 from prior anticancer therapy except for alopecia.

• Has a history of primary immunodeficiency, bone marrow transplantation, solid organ transplantation, or previous clinical diagnosis of tuberculosis.

• Has a known uncontrolled metastases to the central nervous system (with certain exceptions).

• Current or prior use of immunosuppressive medication within 14 days prior to the first dose of the study drug.

• Has clinically significant uncontrolled condition(s).

• History of inflammatory bowel disease, interstitial lung disease or pneumonitis, myocarditis, Stevens-Johnson syndrome, toxic epidermal necrolysis or drug reaction with eosinophilia and systemic symptoms (DRESS).

• Live vaccine administration <= 28 days prior to the first dose of study drug.