4-1BB is a member of the tumor necrosis factor (TNF) receptor family. Its alternative names are tumor necrosis factor receptor superfamily member 9 (TNFRSF9), CD137 and induced by lymphocyte activation (ILA). It is currently of interest to immunologists as a co-stimulatory immune checkpoint molecule.
4-1BB can be expressed by activated T cells, but to a larger extent on CD8 than on CD4 T cells. In addition, 4-1BB expression is found on dendritic cells, follicular dendritic cells, natural killer cells, granulocytes and cells of blood vessel walls at sites of inflammation.
The best characterized activity of 4-1BB is its costimulatory activity for activated T cells. Crosslinking of 4-1BB enhances T cell proliferation, IL-2 secretion, survival and cytolytic activity. Further, it can enhance immune activity to eliminate tumors in mice.
HT1080 is derived from human fibrosacoma biopsy. It is highly active in NF-kB signaling pathway which is necessary for immune responses. HT1080 cells overexpressed with 4-1BB are significantly increased in immune response indicated by elevated production of IL-8.