Allo-hematopoietic stem cell transplantation(HSCT) is the only way to cure β-thalassemia major at present. To expand donor pool，we developed a haplo-identical HSCT (Hi-HSCT) platform. But in prior Hi-HSCT using high dose post-transplant Cyclophosphamide in patients with leukemia, cytopenia post-transplant often developed, which was considered as a symptom of GVHD. Therefore, the investigators add unrelated umbilical cord blood (UCB) to the Hi-HSCT. It has reported that, as third-party cells, UCB will reduce GVHD.The purpose of this study is to determine whether unrelated UCB following Hi-HSCT can improve outcomes of Hi-HSCT in patients with β-thalassemia major.

Inclusion Criteria:

• β-thalassemia major
• < 18 year old
• Unrelated umbilical cord blood following Haplo-identical HSCT

Exclusion Criteria:

• ≥ 18 year old
• HLA- matched related donors
• Unrelated donor transplants
• Unrelated umbilical cord blood transplants
• Severe iron overload in heart by T2*