PD-1 Antibody Improve Mixed Chimerism

Inclusion Criteria: 1. EBV-HLH according to the HLH-04 diagnostic criteria. 2. After allo-HCT, have achieved engraftment and reconstitute of hematopoiesis. have achieved full donor chimerism. 3. Withdraw immunosuppressive agent, chimeric rate was 80%-95% 4. Age \>18 years old, gender is not limited. 5. no graft-versus-host disease was observed. 6. No secondary graft failure (ANC \<0.5\*10\^9/l,PLT \<10\*10\^9/l) 7. Before the start of the study, aminopherase (ALT/AST) and total bilirubin were normal. Serum creatinine ≤ 1.5 times the upper limit of Normal (ULN); No thyroid dysfunction. The left ventricular ejection fraction (LVEF) was normal. 8. Informed consent. Exclusion Criteria: 1. Allergic to the test drug ingredients or to a more severe allergic constitution. 2. Chimeric rate continue to decline after 2 weeks of toripalimab Injection used. 3. Serious immunoreaction: myocardial damage, hepatitis, pneumonia. 4. Central nervous system symptoms. 5. Serious mental illness. 6. Active bleeding of the internal organs 7. Uncontrollable infection； 8. Pancreatitis history. Patients unable to comply during the trial and/or follow-up phase; 9. Participate in other clinical research at the same time.