This study is a single-center, single-arm, prospective, phase II clinical trial designed to evaluate the efficacy and safety of Cidabenamine combined with Azacitidine as maintenance therapy following allogeneic peripheral blood hematopoietic stem cell transplantation in patients with high-risk peripheral T-cell lymphoma.During the screening/baseline period, informed consent will be obtained, and inclusion/exclusion criteria will be verified. The study plans to enroll 40 patients in each group. Enrolled patients will undergo demographic and medical history data collection, along with assessments including vital signs, physical examination, PET-CT, bone marrow aspiration smear, flow cytometry, lymphoid gene rearrangement, and bone marrow pathology.

Inclusion Criteria:

1. Aged 18 to 70 years, male or female.

2. Diagnosis of peripheral T-cell lymphoma (PTCL) according to the 2022 WHO criteria, including pathological subtypes such as PTCL not otherwise specified (PTCL-NOS), anaplastic large cell lymphoma (ALCL), and angioimmunoblastic T-cell lymphoma (AITL), but excluding hepatosplenic T-cell lymphoma; and meeting at least one of the following high-risk criteria:

   ① Stable Disease (SD) at the time of transplantation;

   ② Relapse after autologous hematopoietic stem cell transplantation (any disease status);

   ③ ≥ Partial Response 1 (PR1).

3. Underwent allogeneic peripheral blood hematopoietic stem cell transplantation for PTCL, with no restriction on donor type.

4. Presence of complete donor chimerism in the bone marrow (T-cell chimerism >95%).

5. ECOG performance status of 0 or 1.

6. Hematological function meeting the following requirements:

   ① Absolute neutrophil count (ANC) ≥ 1.0 × 10⁹/L;

   ② Platelet count (PLT) ≥ 50 × 10⁹/L.

7. Patients must have the ability to understand and be willing to participate in the study and must provide signed informed consent.

Exclusion Criteria:

1. Known hypersensitivity to hypomethylating agents or Cidabenamine.
2. Presence of grade II or higher active acute Graft-versus-Host Disease (GVHD).
3. Presence of moderate or more severe chronic GVHD.
4. Any unstable systemic disease, including but not limited to: unstable angina, cerebrovascular accident or transient ischemic attack (within 3 months prior to screening), myocardial infarction (within 3 months prior to screening), congestive heart failure (New York Heart Association [NYHA] Class ≥ III), status post pacemaker implantation, severe arrhythmia requiring pharmacological treatment, hepatic, renal, or metabolic disease, or pulmonary hypertension.
5. Active, uncontrolled infection, evidenced by any of the following: infection-related hemodynamic instability, worsening or new-onset infectious symptoms/signs, radiologic evidence of a new infectious focus, or persistent fever without localizing symptoms/signs where infection cannot be ruled out.
6. Known HIV infection.
7. Active Hepatitis B (HBV) or active Hepatitis C (HCV) requiring antiviral therapy.
8. History of an autoimmune disease.
9. Pregnant or lactating women.
10. Concurrent participation in another interventional clinical trial and receiving other investigational drugs.