CAR-T Cell Therapy Combined With Allogeneic Hematopoietic Stem Cell Transplantation for Relapsed or Refractory Multiple Myeloma

1. Study Title CAR-T Cell Therapy Combined with Allogeneic Hematopoietic Stem Cell Transplantation for Relapsed or Refractory Multiple Myeloma 2. Study Objective This study aims to evaluate the safety and efficacy of CAR-T cell therapy followed by allogeneic hematopoietic stem cell transplantation (allo-HSCT) in patients with relapsed or refractory multiple myeloma. The goal is to explore a novel treatment strategy for this high-risk patient population. 3. Study Design This is a single-center, open-label, single-arm clinical study. A total of 30 patients with relapsed or refractory multiple myeloma will be enrolled. All participants will receive standardized CAR-T cell therapy followed by allo-HSCT and will undergo systematic observation and follow-up to assess therapeutic efficacy and safety. 4. Sample Size A total of 30 patients will be enrolled in this study. 5. Eligibility Criteria (1) Inclusion Criteria Age between 18 and 70 years; Estimated life expectancy of more than 12 weeks; Diagnosis of multiple myeloma confirmed by physical examination, pathology, laboratory tests, and imaging studies; Patients with refractory multiple myeloma; Patients with relapsed multiple myeloma; ALT and AST \< 3 times the upper limit of normal; Total bilirubin \< 2.0 mg/dL; Karnofsky Performance Status (KPS) \> 50%; No severe dysfunction of major organs such as liver, kidney, or heart; Prior failure of autologous or allogeneic hematopoietic stem cell transplantation; Ineligible for stem cell transplantation or patients who declined transplantation due to other constraints; Voluntarily willing to receive CAR-T cell therapy for B cell-derived hematologic malignancies; Suitable for peripheral venous blood collection with no contraindications to leukapheresis; Able to understand and sign a written informed consent form.

(2) Exclusion Criteria Pregnant or lactating women, or women planning pregnancy within 6 months; Presence of infectious diseases (e.g., HIV infection, active tuberculosis); Active hepatitis B or C virus infection; Pre-screening indicates peripheral blood T-cell transduction efficiency \< 10% or expansion fold \< 5× under CD3/CD28 co-stimulation; Abnormal vital signs or inability to cooperate with treatment procedures; Presence of psychiatric or psychological disorders that affect treatment compliance or outcome assessment; History of severe allergy or hypersensitivity, particularly to interleukin-2 (IL-2); Systemic or localized severe infections requiring anti-infective therapy; Significant dysfunction of critical organs such as heart, lung, brain, or kidney; Patients with severe autoimmune diseases; Any other conditions deemed unsuitable for enrollment by the investigator.

6\. Treatment Protocol All enrolled patients will first receive CAR-T cell therapy. Patients who achieve complete remission (CR) following CAR-T infusion will subsequently undergo allogeneic hematopoietic stem cell transplantation (allo-HSCT) based on clinical assessment. The entire treatment process will be standardized and closely monitored, with follow-up evaluations focusing on adverse events, engraftment success, relapse risk, and overall survival.