Study to Evaluate Adverse Events and Movement of Intravenously (IV) Infused ABBV-787 in Adult Participants With Relapsed/Refractory (R/R) Acute Myeloid Leukemia (AML)

Inclusion Criteria:

• Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1.

• Laboratory Criteria matching those outlined in the protocol.

• QT interval corrected for heart rate (QTc) <= 470 msec using Fridericia'scorrection, and no other clinically significant cardiac abnormalities.

• Documented diagnosis of non-promyelocytic acute myeloid leukemia (AML), per 2022European Leukemia Net (ELN) criteria.

• Participants with relapsed/refractory (R/R) acute myeloid leukemia (AML) who havebeen treated with up to 3 prior lines of therapy and are refractory to or intolerantof all established AML therapies that are known to clearly provide clinical benefitat the judgement of the investigator.

• Must have a white blood cell (WBC) count < 25 × 10^9 /L prior to initiation of studydrug (Note: Hydroxyurea or leukapheresis is permitted to meet this criterion and foruse through Cycle 3 to control for hyperleukocytosis.).

Exclusion Criteria:

• Have received a CD33-targeting therapy within 3 months prior to the first dose ofABBV-787.

• Stem cell transplant within 3 months prior to first dose of study drug.

• Have received anticancer therapy including chemotherapy, radiation therapy,immunotherapy, biologic, or any investigational therapy within 14 days or 5half-lives of the drug (whichever is shorter) prior to the first dose of ABBV-787.

• History of documented pneumonitis that required treatment with systemic steroidswithin the last 6 months, nor any evidence of active pneumonitis.

• Unresolved toxicity of Grade >= 2 from prior anticancer therapy, or to levelsdictated in the eligibility criteria, with the exception of alopecia.

• Known active severe or poorly controlled acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection.