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     Red: Control Antigen (100ng); Purple: Antigen (10ng); Green: Antigen (50ng); Blue: Antigen (100ng);    

  
  

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     Flow cytometric analysis of MCF-7 cells using CEBPB mouse mAb (blue) and negative control (red).    

  
  

TNFSF9. also known as CD137 ligand or 4-1BBL, is a member of the tumor necrosis factor superfamily (TNFSF) and plays a critical role in modulating immune responses. It is primarily expressed on antigen-presenting cells (e.g., dendritic cells, B cells) and binds to its receptor, 4-1BB (CD137), which is found on activated T cells, natural killer (NK) cells, and regulatory T cells (Tregs). The TNFSF9-CD137 interaction provides co-stimulatory signals that enhance T-cell survival, proliferation, and cytotoxic activity, making this pathway a key target for cancer immunotherapy and autoimmune disease research.

Antibodies targeting TNFSF9 or its receptor are designed to either agonize or antagonize this signaling axis. Agonistic anti-CD137 antibodies (e.g., urelumab, utomilumab) have been explored in clinical trials to boost anti-tumor immunity by amplifying T-cell activation, though challenges like systemic toxicity and variable efficacy remain. Conversely, TNFSF9-blocking antibodies may suppress overactive immune responses in autoimmune conditions. Structurally, TNFSF9 exists as a homotrimer, and its receptor-binding epitopes are critical for antibody design. Research continues to optimize specificity, affinity, and safety profiles of these antibodies, with bispecific formats and combination therapies (e.g., with checkpoint inhibitors) being actively investigated to enhance therapeutic outcomes.