The protocol plan was a two stage, controlled, phase II study to assess safety and compare the grade of acute graft-versus-host disease (GVHD) with visilizumab, or Anti-thymocyte Globulin (ATG) in combination with tacrolimus + methotrexate in patients at high risk of GVHD after transplant from unrelated donors mismatched for 1-2 alleles of any type at human leukocyte antigen (HLA) A, B, C and DRB1.