Graft-versus-host disease (GVHD) is an important complication after transplantation, with an incidence of 40-60%, which can increase non-relapse mortality if poorly controlled. At present, the standard prophylaxis for GVHD is cyclosporine combined with methotrexate. However, calcineurin inhibitors (CNI) can cause some vital side effects, which are not tolerated by some patients. Therefore, this study aims to explore the safety and efficacy of Sirolimus in combination with Abatacept and Mycophenolate Mofetil for the prophylaxis of GVHD in patients with haplo-HSCT who are intolerant to calcineurin inhibitors.

Inclusion criteria:

1. Primary disease: hematological malignancies (including acute leukemia, myelodysplastic syndromes), nonmalignant disorders (including severe aplastic anaemia)

2. Contraindication or intolerance to CNI

   1. Glomerular filtration rate (GFR) 60-89 ml/min/1.73m2 before transplantation or allergy to CNI
   2. Intolerance to CNI during conditioning or within +45 days post transplantation, such as CNI nephrotoxicity (creatinine higher than the upper limit of normal), uncontrolled hypertension, neurological toxicity, or other conditions deemed by physician to be inappropriate for CNI

3. Receiving haplo-HSCT for the first time

Exclusion Criteria:

1. Allergy or intolerance to study drugs
2. Active infection
3. Active GVHD
4. Transplantation-associated thrombotic microangiopathy
5. Key organ dysfunction: liver injury (total bilirubin more than 2 upper limit of normal) or heart injury (symptomatic heart failure or ejection fraction<50%)
6. Eastern Cooperative Oncology Group (ECOG) score >2
7. Expected survival time <30 days
8. Patients could not cooperate