A Study of KQ-2003 CAR-T Cell Therapy for Patients With Relapsed or Refractory Multiple Myeloma

Inclusion Criteria: * Age ≥18 years old, male or female; * Diagnosis of MM with relapsed or refractory disease; * Eastern Cooperative Oncology Group (ECOG) Performance ≤2 ; * Expected survival of at least 12 weeks; * Participant has measurable disease; * Adequate venous access for the apheresis of peripheral blood mononuclear cell; * Adequate organ function; * Able and willing to comply with the study protocol and follow-up plan, and sign the informed consent form in writing. Exclusion Criteria: * Received any treatment that might influence the activity of CAR-T cells prior to the collection of peripheral blood mononuclear cells; * Have history of vaccination within the 4 weeks preceding the collection of peripheral blood mononuclear cells; * Have active bleeding or venous thromboembolic events requiring anticoagulation; * Have tested positive for cytomegalovirus and/or mycobacterium tuberculosis, or had any uncontrolled active infection within 14 days prior to the collection of peripheral blood mononuclear cells; * Subjects infected with active HBV or HCV, HIV, syphilis; * Subjects with known central nervous system disease or multiple myeloma involving the central nervous system (CNS) or presenting with CNS-related symptoms; * Patients currently experiencing active autoimmune diseases; * Diagnosed with immunodeficiency or receiving any other form of immunosuppressive therapy within 7 days prior to enrollment in this study. * Have following severe diseases: unstable angina, cerebrovascular accident or transient ischemic attack, myocardial infarction , New York Heart Association (NYHA) Class ≥ III, congestive heart failure, poorly controlled severe arrhythmias or other cardiac diseases requiring mechanical support; subjects with known chronic obstructive pulmonary disease (COPD) with a forced expiratory volume in 1 second (FEV1) \< 50% of predicted normal; subjects with known moderate or severe persistent asthma, or a history of asthma within the past 2 years, or currently having any category of uncontrolled asthma; subjects requiring oxygen to maintain adequate oxygen saturation; subjects with hypertension whose blood pressure cannot be lowered to the following range despite treatment with two or more antihypertensive medications;. * Subjects with malignancies other than multiple myeloma; * Have any non-hematologic toxicity resulting from prior treatments that cannot be restored to ≤ grade 1 or baseline, excluding alopecia and grade 2 neuropathy; * History of alcohol abuse, drug addiction, substance abuse, or mental illness within the past year; * Presence of acute graft-versus-host disease (GVHD) or extensive chronic GVHD of Grade ≥ 2 requiring treatment within the 4 weeks before enrollment, or as judged by the investigator to likely require anti-GVHD treatment during the study; Subjects who had previously received BCMA-CD19 dual-target CAR-T cell products or autologous stem cell transplantation within 12 weeks before the collection of peripheral blood mononuclear cells; * Known allergy or hypersensitivity reactions to cyclophosphamide, fludarabine, dimethyl sulfoxide (DMSO), CD19, or BCMA-targeted drugs; * Subjects had participated in other clinical trials and used its investigational drugs within the 3 months prior to the collection of peripheral blood mononuclear cells * Pregnant or lactating women * Any situation that the investigator believes may increase the risk of subjects or interfere with the results of clinical trials