PK,PD,Safety and Tolerability of Multiple Dose Regimens of MT-3724 With Gemcitabine and Oxaliplatin for the Treatment of Patients With Relapsed/Refractory Diffuse Large B Cell Non-Hodgkin's Lymphoma

This is a multi-center, open-label two-part study evaluating the safety and tolerability of MT-3724 in combination with GEMOX in relapsed or refractory B-cell Lymphoma patients. Part 1: (MT-3724 Dose Escalation) Define the maximum tolerated dose (MTD) of MT-3724 in combination with standard treatment of GEMOX Part 2: (MTD Expansion Cohort) Confirm the safety and tolerability of the MTD of MT-3724 from Part 1 in the MTD Expansion Cohort, where MT-3724 will be given at the MTD in combination with GEMOX. In addition, the PK, PD, immunogenicity and tumor response at the MTD of MT-3724 in combination with GEMOX will be more thoroughly evaluated in Part 2. In original protocol and amendment 2, participants will be administered intravenous (IV) MT-3724 over 1 hour on Days 1, 3, 5, 8, 10 and 12 in Cycles 1 and 2 (each 28-day cycle) and on Days 1, 8, 15, and 22 in Cycles 3 and 4 (each 28-day cycle). Participants will also be administered Gemcitabine 1000 milligrams per meter square (mg/m\^2) as 30-minute IV infusion and Oxaliplatin 100 mg/m\^2 as 2-hour IV infusion on Days 2 and 16 in Cycles 1, 2, 3 and 4 (each 28-day cycle). Per amendment 2, participants will be administered MT-3724 on Days 1, 3, 5, 8, 10, 12, 15, 22, 29, and 36 in Cycle 1 (42-day cycle). In Cycles 2, 3 and 4, MT-3724 will be administered weekly on Days 1, 8, 15, and 22 of each 28-day cycle. Gemcitabine and oxaliplatin will be administered on Days 16 and 30 of Cycle 1 and on Days 2 and 16 in Cycles 2, 3 and 4 (42-day cycle for Cycle 1 and 28-day cycle for Cycle 2, Cycle 3 and Cycle 4). Continued Treatment with MT-3724 in combination with GEMOX will continue for four cycles of until death, disease progression, unacceptable toxicity, withdrawal of consent or another reason for withdrawal. After four cycles, the participants who experience clinical benefit can continue MT-3724 treatment with additional cycles of 28 days each (either alone or in combination with GEMOX) if supported by the investigator's assessment of the benefit-risk ratio, after consultation with sponsor and Medical Monitor