Aplastic anemia (AA) is a rare bone marrow failure syndrome with an annual incidence of about 0.74/100,000, affecting all ages but more common in the elderly. It's divided into congenital and acquired forms, with the latter being more prevalent. The primary acquired form is linked to T lymphocyte activation and genetic factors. The best treatment is allogeneic hematopoietic stem cell transplantation (allo-HSCT), with a near 90% cure rate. Sibling allo-HSCT is ideal but finding a match is challenging. For those who relapse after immunosuppressive therapy, haploidentical HSCT is a viable option despite risks like graft failure and GVHD. Advances in transplantation have made haplo-HSCT's efficacy comparable to other methods. Recent studies suggest co-transplantation with umbilical cord blood cells can improve outcomes by hastening hematopoietic recovery and prognosis. Our study will evaluate the feasibility and safety of this approach in AA treatment, comparing it to sibling fully matched transplantation, with a focus on infection rates, GVHD incidence, TRM, and EFS, aiming to enhance treatment practices and benefit patients and the medical industry.

Aplastic anemia (aplastic anaemia，AA) is a syndrome of bone marrow hematopoietic dysfunction （bone marrow hematopoietic failure，BMF）with an annual incidence rate of approximately 0.74/100,000 people, affecting all age groups with a higher incidence rate in the elderly, and similar incidence rates between males and females. AA is divided into congenital and acquired types, with acquired AA being more common. The pathogenesis of primary acquired AA is mainly related to the abnormal activation of T lymphocytes, and genetic background may also play a role in the development and progression of AA. Currently, allogeneic hematopoietic stem cell transplantation (allo-HSCT) is the best treatment for AA, with a cure rate close to 90%. Sibling allogeneic hematopoietic stem cell transplantation (HLA-matched HSCT) is the preferred treatment plan, but it is not easy to find a fully matched sibling donor. For patients who relapse after immunosuppressive therapy (IST), haploidentical hematopoietic stem cell transplantation (haplo-HSCT) is a good alternative, despite the risks of engraftment failure, infection, and graft-versus-host disease (GVHD). With the advancement of transplantation technology, the efficacy of haplo-HSCT is not significantly different from that of unrelated donor hematopoietic stem cell transplantation (MUD-HSCT) and HLA-matched sibling donor hematopoietic stem cell transplantation (MSD-HSCT). Studies have shown that haplo-HSCT has a higher survival rate in treating patients with severe aplastic anemia (SAA), and there is no significant difference compared to MSD-HSCT.To address the risk of complications associated with haplo-HSCT, recent research has indicated that co-transplantation with third-party umbilical cord blood cells can shorten the time for hematopoietic reconstitution and improve prognosis. The co-transplantation of third-party umbilical cord blood with bone marrow and peripheral blood hematopoietic stem cells has become a new transplantation option. Studies at home and abroad have shown that combined third-party transplantation can shorten the time for hematopoietic reconstitution and improve long-term survival rates. This study plans to adopt a prospective, open-label, parallel-controlled trial design to conduct a clinical study of non-related umbilical cord blood-assisted haploidentical allogeneic hematopoietic stem cell transplantation for the treatment of AA. The study will compare the umbilical cord blood combined with haploidentical transplantation plan with sibling fully matched transplantation, to assess the feasibility and safety of the umbilical cord blood combined with haploidentical transplantation plan, and to monitor the incidence of patient infections, acute/chronic GVHD incidence, transplant-related mortality (TRM), and event-free survival (EFS), in the hope of providing new practical experience in the field of AA treatment, and bringing dual benefits to patients and the social medical enterprise.

Inclusion Criteria:

• A patient age of 6-75 years
• Patients diagnosed with Severe Aplastic Anemia (SAA) , Transfusion-Dependent Non-Severe Aplastic Anemia (TD-NSAA) or Paroxysmal nocturnal hemoglobinuria (PNH) acquired clonal-aplastic anemia(AA) according to the Chinese Guidelines for the Diagnosis and Treatment of Aplastic Anemia (2022 Edition) and suitable for allo-HSCT
• Subjects (or their legally acceptable representatives) must have signed an informed consent document indicating that they understand the purpose of and procedures required for the study and are willing to participate in the study

Exclusion Criteria:

• Any abnormality in a vital sign (e.g., heart rate, respiratory rate, or blood pressure)
• Patients with any conditions not suitable for the trial (investigators' decision)