A Study of Siremadlin Alone and in Combination With Donor Lymphocyte Infusion in Acute Myeloid Leukemia Post-allogeneic Stem Cell Transplant

Inclusion Criteria:

Participants with AML diagnosis, who underwent one allo-SCT to treat AML and are currently at ≥ Day 60 but no later than Day 120 (≤ Day 120) post allo-SCT.

Pre-allo-SCT - Participants must have any of the following risk factors that put them at high risk for relapse:

• AML in first CR (CR1) prior to allo-SCT with one of the following:

1. Adverse risk genetic abnormalities per 2017 ELN risk stratification. Patients with TP53 mutant AML at diagnosis are eligible if they meet eligibility criteria.
2. Therapy-related AML (t-AML).

Secondary AML (sAML) [AML secondary to antecedent myelodysplastic syndrome (MDS) or AML secondary to myeloproliferative neoplasm (MPN)].

• AML in second or greater CR (≥CR2) prior to allo-SCT.

Allo-SCT must have the following characteristics:

1. Unmanipulated/T cell-replete bone marrow or peripheral blood stem cells as a graft source.
2. Matched related (family) donor (MFD) or matched unrelated donor (MUD): Human Leukocyte Antigen (HLA) matching of donor and recipient should be at a minimum of 8/8 antigen or allele matched at HLA-A, -B, -C, -DRB1 loci.
3. Any conditioning regimen intensity is permitted, the use of anti-thymocyte globulin (ATG) or alemtuzumab or post-transplant cyclophosphamide as a part of conditioning is allowed.
4. Donor lymphocytes are collected, cryopreserved and available for infusion (DLI), or obtaining donor lymphocytes for DLI is feasible (applicable only for part 2)
5. Post-allo-SCT, participants must have achieved CR or CRi with no current evidence of hematologic relapse
6. Eastern Cooperative Oncology Group (ECOG ) performance status 0, 1 or 2.
7. Laboratory test results indicating adequate liver and kidney function laboratory test results
8. Evidence of adequate engraftment: Absolute Neutrophil Count (ANC) ≥ 1.0x109/L, Platelets (PLT) ≥ 75x109/L, Hemoglobin (Hgb) ≥ 8 g/dL (within 14 days prior to start of study treatment)

Exclusion criteria:

1. Prior exposure to MDM-inhibitor
2. Active acute GvHD (aGvHD) of any grade (per Harris et al 2016) and/or active chronic GvHD (cGvHD ) of any grade (per NIH criteria (Jagasia et al 2015)) requiring systemic therapy at time of study treatment initiation
3. Past history of grade III or IV aGvHD and/or past history of moderate or severe cGvHD. History of lower grades of GvHD is permitted if GvHD resolved to grade 0 for at least 4 weeks prior to start of study treatment.
4. Recipient of allo-SCT from MUD with ≥1 antigen or allele mismatch at HLA-A, -B, -C, -DRB1 locus (HLA matching < 8/8 antigens)
5. Recipient of allo-SCT from a haploidentical family donor; and recipients of cord blood transplant as a graft source
6. Prior systemic AML-directed treatments given at any time after allo-SCT (including DLI)
7. Prior systemic cancer-directed treatments or investigational modalities ≤ 5 half-lives or 4 weeks prior to starting study, whichever is longer
8. GI disorders that may prevent the intake and absorption of oral siremadlin (eg, diarrhea, uncontrolled nausea/vomiting, GI bleeding, etc).
9. Any concurrent severe and/or active uncontrolled bacterial, viral or fungal infection requiring parenteral antibacterial, antiviral or antifungal therapy. Prophylactic antimicrobial use (oral or parenteral) is allowed.
10. Participants who require treatment with moderate or strong CYP3A inducers within 14 days prior to starting study treatment, or are expected to receive moderate or strong CYP3A inducers during the entire study
11. Cardiac or cardiac repolarization abnormality, that are clinically significant

Other protocol defined inclusion/exclusion criteria may apply.