Study to Investigate the Safety and Clinical Activity of GSK3326595 and Other Agents to Treat Myelodysplastic Syndrome (MDS) and Acute Myeloid Leukemia (AML)

Inclusion Criteria:

Males and females greater than or equal to (>=)18 years of age (at the time consent is obtained).
Diagnosis of MDS, CMML or AML
Eastern Cooperative Oncology Group (ECOG) performance status score of 0 or 1 or 2
Adequate organ function
A woman of childbearing potential (WOCBP) must have a negative highly sensitive serum pregnancy test within 7 days before the first dose of study intervention.

Exclusion Criteria:

History of, or known, central nervous system (CNS) involvement
Prior solid organ transplantation
Known allergies, hypersensitivity, or intolerance to GSK3326595 or 5-Azacitidine or its excipient
Prior therapy with any Protein arginine methyl transferase 5 (PRMT5) inhibitor
History of a second malignancy, excluding non-melanoma skin cell cancer, within the last three years
Active severe or uncontrolled infection
History of optic nerve neuropathy or neuritis.
History of sensitivity to any of the study medications, or components thereof, or a history of drug or other allergy that, in the opinion of the investigator or Medical Monitor, contraindicates their participation.