4-1BB (TNFRSF9/CD137) belongs to the TNFR superfamily.4-1BB is expressed by activated CD4 helper T cells, B cells natural killer cells natural killer T cells, dendritic cells, and activated endothelium.A majority of regulatory T cells (Tregs) also express 4-1BB, but it remains unclear whether agonistic antibody treatment exerts pro-or anti-suppressive effect on these cells.4-1BB enhances tumor rejection because it is upregulated on T cells following activation and its engagement increases T cell proliferation and pro-inflammatory cytokine production.
