Major Inclusion Criteria:

1. Age 18-80 years old
2. Histologically confirmed diagnosis of DLBCL
3. Fresh tumour tissue for central pathology review and correlative studies must be provided. The only exception is the availability of tumour tissue acquired ≤3 years prior to screening for this protocol
4. Patients must have:
   • relapsed and/or refractory disease
   • at least one bidimensionally measurable disease site (transverse diameter of ≥1.5 cm and perpendicular diameter of ≥1.0 cm at baseline)
   • received at least one, but no more than two previous systemic regimens for the treatment of DLBCL and one therapy line must have included a CD20-targeted therapy
   • Eastern Cooperative Oncology Group 0 to 2
5. Patients not considered in the opinion of the investigator eligible, or patients unwilling to undergo intensive salvage therapy including ASCT
6. Patients must meet the following laboratory criteria at screening:
   • absolute neutrophil count ≥1.5 × 109/L
   • platelet count ≥90 × 109/L
   • total serum bilirubin ≤2.5 × ULN or ≤3 × ULN in cases of liver involvement
   • alanine transaminase, aspartate aminotransferase and alkaline phosphatase ≤3 × ULN or <5 × ULN in cases of liver involvement
   • serum creatinine clearance ≥60 mL/minute
7. Females of childbearing potential (FCBP) must:
   • not be pregnant
   • refrain from breastfeeding and donating blood or oocytes
   • agree to ongoing pregnancy testing
   • commit to continued abstinence from heterosexual intercourse, or agree to use and be able to comply with the use of double-barrier contraception
8. Males (if sexually active with a FCBP) must
   • use an effective barrier method of contraception
   • refrain from donating blood or sperm
9. 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.

Major Exclusion Criteria:

1. Patients who have:
   • Non Hodgkin Lymphoma other than classical histology DLBCL
   • primary refractory DLBCL or relapsed within period ≤3 months of prior CD20-targeted therapy
   • a history of "double/triple hit" DLBCL
2. Patients who have, within 14 days prior to Day 1 dosing:
   • not discontinued CD20-targeted therapy, chemotherapy, radiotherapy, investigational anticancer therapy or other lymphoma specific therapy
   • undergone major surgery or suffered from significant traumatic injury
   • received live vaccines.
   • required parenteral antimicrobial therapy for active, intercurrent infections
3. Patients who:
   • were previously treated with CD19-targeted therapy or IMiDs® (e.g. thalidomide, LEN)
   • have undergone ASCT within the period ≤ 3 months prior to signing the informed consent form.
   • have undergone previous allogenic stem cell transplantation
   • 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
   • concurrently use other anticancer or experimental treatments
4. Prior history of malignancies other than DLBCL, unless the patient has been free of the disease for ≥3 years prior to screening.
5. Patients with:
   • positive hepatitis B and/or C serology.
   • known seropositivity for or history of active viral infection with human immunodeficiency virus (HIV)
   • 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.