This phase I trial studies the side effects and best dose of anti-cluster of differentiation (CD)47 monoclonal antibody Hu5F9-G4 in treating patients with haematological malignancies including acute myeloid leukemia that has returned after a period of improvement (relapsed) or has not responded to previous treatment (refractory), or high risk myelodysplastic syndrome. Monoclonal antibodies, such as anti-CD47 monoclonal antibody Hu5F9-G4, block cancer growth in different ways by targeting certain cells.

Key Inclusion Criteria:

• Pathologically confirmed relapsed or refractory (primary refractory and relapsed refractory) Acute Myeloid Leukemia (AML) (defined by World Health Organization (WHO) criteria) for which no further conventional therapy is suitable for the patient, or confirmed myelodysplastic syndrome defined according to WHO classification, with an International Prognostic Scoring System (IPSS) risk category of intermediate-2 or high risk, that is relapsed, refractory or intolerant to conventional therapy within 3 weeks of registration.
• Male or female, Age ≥ 18 years.
• Eastern Cooperative Oncology Group (ECOG) performance score of 0-1
• Willing to undergo blood transfusions as deemed clinically necessary.
• Adequate hematological, liver, and kidney function

Key Exclusion Criteria:

• Females: Pregnant or breast-feeding women, or women of childbearing potential unless effective method of contraception is used during and for 3 months after the trial. Males: unless an effective method of contraception is used during and for 3 months after the trial.
• Any prior exposure to Hu5F9-G4 or other CD47 targeting agents.
• Treatment with any other investigational agent within 28 days prior to enrolment.
• Previous allogeneic stem cell transplant within 6 months prior to enrolment, active graft vs host disease (GVHD), or requiring transplant-related immunosuppression
• Evidence for active CNS involvement by leukaemia
• Clinical evidence or known history of cardiopulmonary disease