The study design included two stages. The first stage of the trial was to enroll 15 patients on a single arm to be treated with "study treatment" (visilizumab, tacrolimus and methotrexate) to assess for treatment safety and exclude intolerable GVHD. The second stage of the trial was to include a random control group of patients treated with the current "standard treatment" (ATG, tacrolimus, and methotrexate) or "study treatment". The purpose of this comparison was to determine if the "study treatment" visilizumab causes less severe side effects and if it is more potent in reducing graft-versus-host disease symptoms than the "standard treatment".