A Phase II Study of Vibecotamab (XmAb14045) for MRD- Positive AML and MDS After Hypomethylating Agent Failure

Primary Objectives: * AML MRD cohort: To determine the MRD negativity rate after 4 cycles of vibecotamab in patients with AML with MRD * MDS post-HMA cohort: To determine the response rate (defined as CR + marrow CR \[mCR\] + partial remission \[PR\] + hematologic improvement \[HI\]) after 4 cycles of vibecotamab in patients with MDS after HMA failure Secondary Objectives: * To assess other efficacy endpoints, including remission duration, duration of MRD response (AML MRD arm only), CR rate (MDS arm only), relapse-free survival, overall survival * To assess the safety of vibecotamab in patients with AML with MRD and in patients with MDS post-HMA failure Exploratory Objectives: * To correlate clinical outcomes with CD123 expression * To determine the CD123 expression in patients who relapse after vibecotamab therapy