Inclusion Criteria:

          -  ≥ 18 years of age

          -  Diagnosis of MDS according to WHO 2016 criteria

          -  ECOG performance status of 0 or 1

          -  Intermediate-2 or high-risk disease per IPSS

          -  Fewer than 20% blasts in the bone marrow or peripheral blood

          -  Disease that is refractory to or relapsed from either a hypomethylating agent (e.g.
             decitabine or azacitidine) or a standard AML-type intensive regimen

          -  Adequate organ function

          -  Prior allogeneic transplant performed ≥ 3 months prior to first dose of AMV564 is
             allowed provided there is no evidence of active graft-versus-host disease (GVHD) and
             the patient has been off immunosuppressive therapy for ≥ 4 weeks.

        Exclusion Criteria:

          -  History of, or known, central nervous system (CNS) disease involvement, or prior
             history of National Cancer Institute (NCI) Common Toxicity Criteria for Adverse Events
             (CTCAE) Grade ≥ 3 drug-related CNS toxicity

          -  Prior allogeneic transplant if performed < 3 months prior to first dose of AMV564, if
             patient has active GVHD, or if patient has not been off immunosuppressive

          -  Prior treatment with a therapeutic agent targeting CD33 (e.g. gemtuzumab ozogamicin,
             SGN-CD33A or AMG 330).