Evaluate the Safety and Efficacy of Tafasitamab Combined With Lenalidomide in Patients With Relapsed or Refractory DLBCL

Inclusion Criteria: 1. Age \>18 years. 2. Histologically confirmed diagnosis of DLBCL not otherwise specified (NOS); T cell/histiocyte rich large B-cell lymphoma (THRLBCL); Epstein-Barr virus (EBV) positive DLBCL of the elderly (EBV-positive DLBCL), Grade 3b Follicular Lymphoma, Composite lymphoma with a DLBCL component with a subsequent DLBCL relapse, according to the Revised European American Lymphoma/World Health Organization (REAL/WHO) classification. Additionally, patients with the evidence of histological transformation to DLBCL from an earlier diagnosis of low grade lymphoma (i.e., an indolent pathology such as follicular lymphoma, marginal zone lymphoma, chronic lymphocytic leukaemia) into DLBCL with a subsequent DLBCL relapse are also eligible. 3. Patients received at least one, but no more than three previous systemic regimens for the treatment of DLBCL and one therapy line must have included a CD20-targeted therapy. 4. Patients must meet the following laboratory criteria at screening. 5. Patients must use an effective barrier method of contraception. 6. In the opinion of the investigator the patients must be able and willing to receive adequate prophylaxis and/or therapy for thromboembolic events; be able to understand the reason for complying with the special conditions of the pregnancy prevention risk management plan and give written acknowledgement of this. Exclusion Criteria: 1. Patients who have other histological type of lymphoma，primary refractory DLBCL，a history of "double/triple hit" genetics. 2. Patients who have, within 14 days prior to Day 1 dosing: 1. not discontinued CD20-targeted therapy, chemotherapy, radiotherapy, investigational anticancer therapy or other lymphoma specific therapy. 2. undergone major surgery or suffered from significant traumatic injury. 3. received live vaccines. 4. required parenteral antimicrobial therapy for active, intercurrent infections. 3. Patients who: 1. were previously treated with CD19-targeted therapy or IMiDs® (e.g. thalidomide, LEN). 2. have undergone ASCT within the period ≤ 3 months prior to signing the informed consent form. 3. have undergone previous allogenic stem cell transplantation. 4. have a history of deep venous thrombosis/embolism and who are not willing/able to take venous thromboembolic event prophylaxis during the entire treatment period. 5. concurrently use other anticancer or experimental treatments. 4. Prior history of malignancies other than DLBCL. 5. Patients with: 1. positive hepatitis B and/or C serology. 2. known seropositivity for or history of active viral infection with human immunodeficiency virus (HIV). 3. CNS lymphoma involvement. 4. history or evidence of clinically significant cardiovascular, CNS and/or other systemic disease that would in the investigator's opinion preclude participation in the study or compromise the patient's ability to give informed consent. 5. history or evidence of severe hepatic impairment (total serum bilirubin \> 3 mg/dL).