Additional Study Information: The purpose of this study is to compare the effects, both good and bad, of magrolimab in combination with azacitidine, to those of azacitidine in combination with placebo, to find out which is better for treating patients with MDS (Myelodysplastic Syndrome). Other purposes of this study include determining the quantity of magrolimab in the blood, aspects of your disease management (e.g. if you can have less frequent blood transfusions), your quality of life and the side effects magrolimab has on the body.