This is a Phase II, single-arm, open-label, multinational, multicenter study of rATG in patients with low or intermediate-1 risk MDS who have either failed 1 prior treatment with growth factor(s), hypomethylating agents (5-azacitidine or decitabine), or the antiangiogenic agents lenalidomide or thalidomide, or who have never been treated for MDS (i.e., treatment-naïve patients).