This study is for adults, aged 18 to 70, with certain blood cancers: acute myeloid leukemia (AML) and myelodysplastic syndromes (MDS). These are dangerous illnesses where the bone marrow makes abnormal blood cells. The study looks at a new treatment using special cells called VOR33, which are modified stem cells without a protein called CD33. This is to help prevent relapse, using a medicine called Mylotarg without harming the good cells.

Participants will need to undergo a bone marrow transplant first, using healthy stem cells from a matching donor. After this, they will receive up to four treatments of Mylotarg. The main goal is to see if the new treatment is safe and to find the best dose of Mylotarg in two parts of the study.

• The study involves multiple visits and treatments over several weeks.
• Participants must have an HLA-matched donor and good organ function.
• Patients previously treated with Mylotarg or with certain genetic conditions cannot join.