SEA-CD70

This trial will look at a drug called SEA-CD70 with and without azacitidine, to find out if it is safe for patients with myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML). It will study SEA-CD70 to find out what its side effects are and if it works for AML and MDS. A side effect is anything the drug does besides treating cancer. This study will have six groups or "parts." * Part A will find out how much SEA-CD70 should be given to patients. * Part B will use the dose found in Part A to find out how safe SEA-CD70 is and if it works to treat patients with MDS. * Part C will use the dose found in Part A to find out how safe SEA-CD70 is and if it works to treat patients with AML. * Part D will find out how much SEA-CD70 with azacitidine should be given to patients. * Part E will use the dose found in Part D to find out how safe SEA-CD70 with azacitidine is and if it works to treat patients with MDS or MDS/AML that has not been treated. * Part F will use the dose found in Part D to find out how safe SEA-CD70 with azacitidine is and if it works to treat patients with MDS or MDS/AML.