Immunogen sequence: KGCKDCCFGT FNDQKRGICR PWTNCSLDGK SVLVNGTKER DVVCGPSPAD LSPGASSVTP PAPAREPGHS PQII. CD137, also known as TNFRSF9 or 4-1BB, is an inducible costimulatory molecule expressed mainly on activated T cells. Its ligand, known as 4-1BBL, is ex