A Study to Evaluate the Safety and Efficacy of SCTB35 in Combination With Gemcitabine and Oxaliplatin in Patients With Relapsed or Refractory Diffuse Large B-Cell Lymphoma

• SCTB35 injection (Drug): SCTB35 will be subcutaneously administered at a dose as specified
• Rituxumab (Drug): Participants will receive IV rituxumab on Day 1 of each cycle for up to 8 cycles.
• Gemcitabine (Drug): Participants will receive IV gemcitabine administration for up to 8 cycles.
• Oxaliplatin (Drug): Participants will receive IV oxaliplatin administration for up to 8 cycles.

Primary outcomes

• Adverse Events [Up to approximately 3 years]: Treatment-emergent adverse events/serious adverse events/adverse events of special interest
• Progression free survival (PFS) [Up to approximately 3 years]: Defined as the time from the date of randomization to the date of first documentation of progression disease (PD) or the date of death from any cause, whichever occurs first.

Secondary outcomes

• Overall Survival (OS) [Up to approximately 3 years]: Overall survival is defined as the duration from the date of randomization to the date of the participant's death.
• Percentage of Participants Achieving Best Overall Response (BOR) [Up to approximately 3 years]: BOR is defined as Complete Response (CR) or Partial Response (PR), determined by Lugano criteria
• Percentage of Participants Achieving CR [Up to approximately 3 years]: Percentage of participants who achieve a CR determined per Lugano criteria.
• Duration of Response (DOR) [Up to approximately 3 years]: DOR is defined as the time from the first occurrence of response (CR or PR) to disease progression or death, whichever occurs first.
• Duration of Complete Response (DOCR) [Up to approximately 3 years]: DOCR is defined as the time from the first occurrence of CR to disease progression or death, whichever occurs first.
• Time to Response (TTR) [Up to approximately 3 years]: Time to response is defined for participants achieving a CR/PR as the time from starting therapy to first a CR/PR.
• Time to Complete Response (TTCR) [Up to approximately 3 years]: Time to complete response is defined for participants achieving a CR as the time from starting therapy to first a CR.
• Event-Free Survival (EFS) [Up to approximately 3 years]: EFS is defined as the duration from randomization to disease progression determined by Lugano criteria as assessed by the investigator, initiation of any non-protocol-specified new anti-lymphoma therapy for any reason, or death (whichever occurs first).
• Blood Concentrations of SCTB35 [Up to approximately 1 years]: The pharmacokinetics of SCTB35 will be analyzed based on the drug concentrations at respective timepoints in the blood samples (or blood derivative)
• Anti-drug Antibodies of SCTB35 [Up to approximately 3 years]: Blood samples (or blood derivative) will be screened for antibodies binding to SCTB35

Sex: All, ages: 18 Years to 80 Years

Inclusion Criteria:

* Age 18-80 years old
* Histologically confirmed diffuse large B-cell lymphoma according to WHO 2022 criteria
* Relapsed or refractory (R/R) disease following at least one prior systemic regimen that contained an anti-CD20 monoclonal antibody (mAb) in combination with chemotherapy
* Participants who have failed after one prior line of therapy are not candidates for high-dose chemotherapy followed by autologous stem cell transplant (ASCT)
* Presence of measurable or evaluable disease at baseline ECOG PS 0-2
* ECOG PS 0-2
* Adequate organ function and bone marrow function
* Expected survival ≥ 3 months

Exclusion Criteria:

* Prior treatment with antibodies targeting both CD20 and CD3
* Contraindication to rituximab, gemcitabine or oxaliplatin, or prior treatment with an anti-CD20 antibody in combination with the GemOx regimen
* Peripheral neuropathy assessed to be Grade >1 according to National Cancer Institute Common Terminology Criteria for Adverse Events (NCI CTCAE) v6.0 at enrollment
* Known central nervous system (CNS) involvement by lymphoma
* Known any major episode of active infection requiring treatment with systemic antibiotics within 2 weeks
* Treatment with chimeric antigen receptor T-cell (CAR-T) therapy within 100 days prior to first SCTB35 administration
* Autologous HSCT within 100 days prior to first SCTB35 administration, or any prior allogeneic HSCT or solid organ transplantation
* Major surgery within 4 weeks prior to first SCTB35 administration
* Chemotherapy and other non-investigational antineoplastic agents (except CD20 mAbs) within 4 weeks or 5 half-lives (whichever is shorter) prior to first SCTB35 administration
* Administration of a live, attenuated vaccine within 4 weeks before first study treatment administration or anticipation that such a live, attenuated vaccine will be required during the study