Your body makes blood cells in the bone marrow. This is the soft inner part of your bones. You make blood cells in a controlled way, as your body needs them. All blood cells start as the same type of cell, called a stem cell.Stem cells then develop into one of four different types, which in turn become red blood cells, platelets, or different types of white blood cells. In acute myeloid leukaemia, the bone marrow makes too many white cells called monocytes or granulocytes.ll blood cells start as the same type of cell, called a stem cell. Stem cells then develop into one of four different types, which in turn become red blood cells, platelets, or different types of white blood cells. In acute myeloid leukaemia, the bone marrow makes too many white cells called monocytes or granulocytes.