Additional Study Information: You are being asked to participate in this study because you have Acute Myeloid Leukemia (AML) or Myelodysplastic Syndrome (MDS) and we are testing the study drugs, SEA-CD70, to find out what its side effects are and to see if the study drug is safe for people with these types of cancer are testing to see if SEA-CD70 is safe for people, and its side effects. SEA-CD70 is a type of drug called an antibody. Antibodies are part of your immune system. Usually, they help protect you from getting sick. The purpose of this study is to use study drug SEA-CD70, and while using another antibody drug called azacitidine, designed to find and stick to the AML or MDS cancer cells in your body. SEA-CD70 may also stick to some non-cancer cells in your body. This is the first time SEA-CD70 has been used in people. We don't yet know if SEA-CD70 or with azacitidine is better or worse than other treatments for people with AML or MDS. There are two parts to this study: one being to test the study drug alone and the second in combination with the drug azacitidine for better understanding of the study. The drug azacitidine is FDA-approved.