- Subjects who became refractory to Anti-thymocyte globulin (ATG)-based Immunosuppressive therapy (IST), who have relapsed after ATG-based IST, or who are ineligible for ATG-based IST. Note: Refractory or relapsed subjects to whom re-treatment with ATG is indicated should not be enrolled in the study. Subjects who have a sibling donor with matched human leukocyte antigen (HLA) should not be enrolled in the study. However, such subjects may be enrolled if the disease relapsed after hematopoietic stem cell transplantation (HSCT), if HSCT is not indicated, or the subject does not want to undergo HSCT.