Study of AMG531 (Romiplostim) in Patients With Aplastic Anemia

Inclusion Criteria: 1. Voluntary signed informed consent to participate in the study; 2. A diagnosis of AA confirmed by blood and bone-marrow examinations, etc.; 3. Considered to require new treatment with immunosuppressive therapy provided that NSAA must be platelet or erythrocyte transfusion-dependent. 4. An Eastern Cooperative Oncology Group (ECOG) performance status (PS) score of 0 to 1at screening; Exclusion Criteria: 1. Previously treated with Anti-human thymocyte immunoglobulin (ATG), CsA, or Alemtuzumab; 2. Diagnosed as having congenital AA (Fanconi anemia, congenital dyskeratosis, etc.); 3. Diagnosed as having acute myelocytic leukemia (AML) or chronic myelomonocytic leukemia; 4. Concurrent thrombocytopenia of other etiologies (e.g., myelodysplastic syndrome (MDS), idiopathic thrombocytopenic purpura (ITP), cirrhosis); 5. Concurrent active infection not adequately responding to appropriate therapy; 6. Concurrent clinically significant illness(es) items which are deemed by the Investigator to be likely to affect the study conduct and assessments. 7. Having active malignancies, or having a history of treatment of malignancies within 5 years prior to informed consent. 8. Concurrent paroxysmal nocturnal hemoglobinuria (PNH) 9. Having Grade 2 or higher bone marrow reticulin based on Bone Marrow Pathology (2nd edition) ; 10. History of chromosome aberrations discovered in bone marrow cells. 11. Having blast cells \> 2% in bone marrow; 12. Positive for anti-human immunodeficiency virus (HIV) antibody; 13. Receiving prophylactic or therapeutic treatment for hepatitis type B 14. Having hepatitis C virus (HCV) infection confirmed by HCV-RNA or other tests at screening. 15. Planned hematopoietic stem cell transplantation during the study; 16. Systemic treatment with any of the following medication for the treatment of AA within 4 weeks before Day 1: * Anabolic steroids * Corticosteroids; 17. Pregnant or breastfeeding women, or women willing to become pregnant; 18. Other conditions unsuitable for participation in the study in the opinion of the Investigator.