Inclusion Criteria:

          -  Confirmed DLBCL per local histopathology assessment.

          -  Relapsed or refractory disease after having recieved 2 or more lines of systemic
             therapy, including anti-CD20 and anthracycline based chemotherapy, and either having
             progressed after (or relapsed after) ASCT, or being not candidates for or not
             consenting to ASCT.

          -  Measurable disease at time of enrollment

          -  ECOG performance status that is either 0 or 1 at screening.

        Exclusion Criteria:

          -  Patients with Richter's transformation, and Burkitt lymphoma, and primary DLBCL of
             CNS.

          -  Prior treatment with any prior anti-CD19/anti-CD3 therapy, or any other anti-CD19
             therapy.

          -  Patients with active CNS involvement are excluded, except if the CNS involvement has
             been effectively treated and provided that local treatment was >4 weeks before
             enrollment.

          -  Prior allogeneic HSCT.

          -  Unstable angina and/or myocardial infarction and/or coronary artery bypass graft
             (CABG), or stroke within 6 months prior to screening, and/or impaired cardiac function
             or clinically significant cardiac disease

          -  Patients with a history of prior treatment with anti-PD-1, anti-PD-L1, anti-PD-L2,
             anti-CTLA-4 antibodies, other immune checkpoint inhibitors.

          -  History of interstitial lung disease or (non-infectious) pneumonitis that required
             oral or intravenous steroids (other than COPD exacerbation) or current pneumonitis.

        Other protocol-defined inclusion/exclusion criteria may apply.