In this study, the term "severe VOD" is defined as those patients who meet the Baltimore diagnostic criteria for VOD (total bilirubin >/= 2.0 mg/dL plus two of the following: ascites, >/=5% weight gain and hepatomegaly), who also have multi-organ failure (i.e., pulmonary and/or renal dysfunction). This represents a group of patients in whom mortality at Day+100 has been estimated to be >80%.